Handbook of Biofuels Production
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Woodhead Publishing Series in Energy:Number 98Handbook of BiofuelsProductionProcesses and TechnologiesSecond EditionEdited byRafael Luque, Carol Sze Ki Lin,Karen Wilson and James Clark AMSTERDAM • BOSTON • CAMBRIDGE • HEIDELBERG LONDON • NEW YORK • OXFORD • PARIS • SAN DIEGO SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO Woodhead Publishing is an imprint of Elsevier
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ContentsList of contributors xiiiWoodhead Publishing Series in Energy xviiPart One Key issues and assessment of biofuels production 11 Introduction: an overview of biofuels and production technologies 3 C. Du, X. Zhao, D. Liu, C.S.K. Lin, K. Wilson, R. Luque, J. Clark 1.1 Introduction 3 1.2 Development of (bio)chemical conversion technologies 5 1.3 Development of biological conversion technologies 7 1.4 Thermochemical conversion technologies 7 1.5 Process integration and bioreﬁnery 8 1.6 Future trends 9 Acknowledgment 11 References 112 Multiple objectives policies for biofuels production: environmental, 13 socio-economic, and regulatory issues C. De Lucia 13 2.1 Introduction 13 2.2 Energy security and supply 18 2.3 Emission reductions, land use, and other environmental impacts 20 2.4 Food safety and development of rural areas 25 2.5 Biofuels support policies 30 2.6 Conclusions 33 References3 Life cycle sustainability assessment of biofuels 41 P.A. Fokaides, E. Christoforou 3.1 Introduction 41 3.2 Main challenges for biofuel sustainability 42 3.3 Life cycle sustainability assessment methodology 45 3.4 LCA considerations of biomass to biofuel conversion routes 50
vi Contents 3.5 Overview of major ﬁndings of selected LCA studies in biofuel 53 production 56 56 3.6 Conclusions References4 Biofuels: technology, economics, and policy issues 61 P. Morone, L. Cottoni 4.1 Introduction 61 4.2 Moving from fossil fuel to biofuels: insights from socio-technical transition theory 62 4.3 Assessing ﬁrst- and next-generation biofuels 64 4.4 Economic, environmental, and social issues 71 4.5 Policy actions and the regulatory framework 74 4.6 Conclusions 79 References 805 Feedstocks and challenges to biofuel development 85 I.L. García 5.1 Introduction 85 5.2 Edible vegetable raw materials for biodiesel production 87 5.3 Nonedible/low-cost raw materials for diesel engine biofuel production 96 5.4 Raw materials for bioethanol production 104 Acknowledgments 109 References 110Part Two Biofuels from chemical and biochemical 119 conversion processes and technologies 1216 Production of biodiesel via catalytic upgrading and reﬁning of sustainable oleagineous feedstocks 121 N.A. Tajuddin, A.F. Lee, K. Wilson 124 6.1 Introduction 132 6.2 General background to biodiesel 149 6.3 Recent robust technology in biodiesel catalysis 151 6.4 Concluding remarks 151 Acknowledgments References7 Biochemical catalytic production of biodiesel 165 C. Luna, D. Luna, J. Calero, F.M. Bautista, A.A. Romero, A. Posadillo, C. Verdugo-Escamilla 165 7.1 Introduction 167 7.2 Lipases
Contents vii7.3 Enzymatic production of biodiesel 1707.4 New tendencies in enzymatic production of biodiesel 1777.5 Biofuels similar to biodiesel produced using several acyl acceptors, 181 different to methanol 1897.6 Industrial biodiesel production using enzymes 1927.7 Conclusions 193 193 Acknowledgements References8 Production of fuels from microbial oil using oleaginous 201 microorganisms E. Tsouko, S. Papanikolaou, A.A. Koutinas 201 8.1 Introduction 8.2 Oleaginous yeasts and raw materials used for microbial 202 oil production 8.3 The biochemistry of lipid accumulation in the oleaginous 214 microorganisms 220 8.4 Microbial oil production in fed-batch cultures 221 8.5 Biodiesel production from microbial oil 8.6 Techno-economic evaluation of biodiesel production 224 from microbial oil 224 8.7 Perspective of biofuel production from microbial oil 225 References9 Biochemical production of bioalcohols 237 M. Melikoglu, V. Singh, S.-Y. Leu, C. Webb, C.S.K. Lin 9.1 Introduction 237 9.2 Types of biomass for bioalcohol production 238 9.3 Bioalcohols 243 9.4 New technologies for bioethanol production 246 Acknowledgments 252 References 25210 Production of biogas via anaerobic digestion 259 E. Uçkun Kiran, K. Stamatelatou, G. Antonopoulou, G. Lyberatos 259 10.1 Introduction 261 10.2 Factors affecting the anaerobic digestion process 263 10.3 Advantages and limitations 265 10.4 Reactor conﬁgurations 270 10.5 Methods for enhancing the efﬁciency of anaerobic digestion 277 10.6 Process modeling 282 10.7 Process monitoring and control
viii Contents 10.8 Biogas utilization 287 10.9 Existing biogas installations 288 10.10 Conclusions and future trends 290 References 29111 Biological and fermentative production of hydrogen 303 C. Ding, K.-L. Yang, J. He 11.1 Introduction 303 11.2 Fundamentals of biohydrogen production 305 11.3 Biological hydrogen production strategies 306 11.4 Enhancing hydrogen production through metabolic engineering 317 11.5 Hydrogen production by cell-free enzymatic systems 319 11.6 Comparison of biohydrogen production techniques 320 11.7 Conclusions and outlook 323 References 32412 Biological and fermentative conversion of syngas 335 C. Wu, X. Tu 12.1 Introduction 335 12.2 Fundamentals of syngas fermentation 336 12.3 Bacteria for syngas conversion 338 12.4 Effects of process parameters 338 12.5 Reactors for fermentative conversion of syngas 345 12.6 Product recovery 347 12.7 Examples of commercial and semicommercial processes 348 12.8 Conclusions for biological fermentation of syngas 351 References 35113 Chemical routes for the conversion of cellulosic platform molecules 359 into high-energy-density biofuels J.A. Melero, J. Iglesias, G. Morales, M. Paniagua 359 13.1 Introduction 360 13.2 Oxygenated fuels via 5-HMF: furanic compounds 13.3 Levulinic acid as platform molecule to oxygenated fuels: 363 alkyl levulinates and valeric biofuels 367 13.4 Oxygenated fuels via furfural: furan derivatives 371 13.5 Blending effect of oxygenated biofuels with conventional fuels 13.6 Catalytic conversion of g-valerolactone to liquid 374 hydrocarbon fuels 13.7 Furan derivatives as platform molecules for liquid 375 hydrocarbon fuels 378 13.8 Sugars to hydrocarbon fuels: aqueous phase reforming process 381 13.9 Final remarks and future outlook 381 Acknowledgments 382 References
Contents ixPart Three Biofuels from thermal and thermo-chemical 389 conversion processes and technologies 39114 Catalytic fast pyrolysis for improved liquid quality S.W. Banks, A.V. Bridgwater 391 14.1 Introduction 392 14.2 Pyrolysis background 398 14.3 Catalytic pyrolysis 405 14.4 Catalytic pyrolysis: catalysts used 414 14.5 Catalytic pyrolysis: reactor setup 417 14.6 Conclusion and future opportunities 419 Acknowledgments 419 References 43115 Production of bio-syngas and bio-hydrogen via gasiﬁcation J.M. Bermudez, B. Fidalgo 431 15.1 Introduction 435 15.2 Biomass feedstock for gasiﬁcation 442 15.3 Biomass gasiﬁcation process 452 15.4 Gasiﬁcation technology 15.5 Syngas technology: composition, conditioning and 464 upgrading to valuable products 476 15.6 Current status in commercial gasiﬁcation of biomass 484 15.7 Challenges and opportunities 486 References 49516 Production of bioalcohols via gasiﬁcation J.M.N. van Kasteren 495 16.1 Introduction 497 16.2 Gasiﬁcation routes for alcohol production 16.3 Technical and economical analysis of the oxidative 500 coupling of methane process 506 16.4 Conclusions and future perspectives 506 Acknowledgments 506 References 50917 Production of biofuels via hydrothermal conversion P. Biller, A.B. Ross 509 17.1 Introduction 510 17.2 Process chemistry 517 17.3 Process layout 521 17.4 Feedstock considerations 524 17.5 Product distribution and properties 535 17.6 Development of technology and current research
x Contents 17.7 Lifecycle and techno-economic assessment 539 17.8 Conclusions 541 542 References18 Production of biofuels via FischereTropsch synthesis: 549 biomass-to-liquids A. Lappas, E. Heracleous 549 18.1 Introduction 552 18.2 Biomass-to-liquids process steps and technologies 577 18.3 Biomass-to-liquids ﬁnal fuel products 581 18.4 Environmental and economic considerations of the BTL process 583 18.5 Commercial status of the biomass-to-liquids processes 587 18.6 Future prospects and challenges 587 References19 Production of biofuels via bio-oil upgrading and reﬁning 595 D.C. Elliott 19.1 Introduction 595 19.2 Upgrading of biomass liquefaction products 598 19.3 Liquid fuel products from biomass through direct liquefaction and hydroprocessing 606 19.4 Conclusions 609 References 610Part Four Integrated production and application 615 of biofuels 61720 Biofuel production from food wastes S. Li, X. Yang 617 20.1 Introduction 618 20.2 Characteristics of food waste 621 20.3 Common food waste managements 623 20.4 Biofuels production 644 20.5 Conclusions and future trends 645 List of abbreviations 646 Acknowledgments 646 References21 Biochar in thermal and thermochemical bioreﬁneriesdproduction 655 of biochar as a coproduct O. Masek 655 21.1 Introduction 658 21.2 Biochar as a coproduct in biofuels and bioenergy production 663 21.3 Biochar from bioreﬁnery residues 665 References
Contents xi22 Algae for biofuels: an emerging feedstock 673 Z. Sun, J. Liu, Z.-G. Zhou 22.1 Introduction 673 22.2 Microalgal biomass and oil 674 22.3 Oil biosynthesis in microalgae 678 22.4 Mass cultivation 683 22.5 Biomass harvesting and dewatering 688 22.6 Oil extraction and transesteriﬁcation 690 22.7 Conclusions and future directions 693 Acknowledgments 694 References 69423 Utilization of biofuels in diesel engines 699 T. Le Anh, I.K. Reksowardojo, K. Wattanavichien 23.1 Introduction 699 23.2 Utilization of vegetable pure plant oil and crude oil in diesel engines 700 23.3 Utilization of biodiesel-based palm oil, jatropha oil, coconut oil, and kapok nut oil in diesel engines 718 23.4 Utilization of biodiesel B5-based cat-ﬁsh fat in diesel engines 721 23.5 The concept of using biofuel on engines (prime mover) 728 23.6 Conclusion and remarks 729 References 730Index 735
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List of contributorsG. Antonopoulou National Technical University of Athens, Athens, GreeceS.W. Banks Aston University, Birmingham, United KingdomF.M. Bautista University of Cordoba, Cordoba, SpainJ.M. Bermudez Department of Chemical Engineering, Imperial College, London,United KingdomP. Biller University of Leeds, Leeds, Yorkshire, United Kingdom; Aarhus University,Aarhus, DenmarkA.V. Bridgwater Aston University, Birmingham, United KingdomJ. Calero University of Cordoba, Cordoba, SpainE. Christoforou School of Engineering and Applied Sciences, Frederick University,Nicosia, CyprusJ. Clark University of York, York, United KingdomL. Cottoni Unitelma-Sapienza, Universita degli Studi di Roma, Roma, ItalyC. De Lucia University of Foggia, Foggia, ItalyC. Ding National University of Singapore, Singapore; Helmholtz Centre forEnvironmental Research e UFZ, Leipzig, GermanyC. Du University of Huddersﬁeld, West Yorkshire, United KingdomD.C. Elliott Paciﬁc Northwest National Laboratory, Richland, WA, United StatesB. Fidalgo Centre for Bioenergy & Resource Management, Cranﬁeld University,Bedford, United KingdomP.A. Fokaides School of Engineering and Applied Sciences, Frederick University,Nicosia, CyprusI.L. García University Cordoba Ediﬁcio Leonardo da Vinci, Campus de Rabanales,Cordoba, SpainJ. He National University of Singapore, Singapore
xiv List of contributorsE. Heracleous Centre for Research and Technology Hellas, Thessaloniki, Greece;International Hellenic University, Thessaloniki, GreeceJ. Iglesias Universidad Rey Juan Carlos, Mostoles, Madrid, SpainA.A. Koutinas Agricultural University of Athens, Athens, GreeceA. Lappas Centre for Research and Technology Hellas, Thessaloniki, GreeceT. Le Anh Hanoi University of Science and Technology, Hanoi, VietnamA.F. Lee Aston University, Birmingham, United KingdomS.-Y. Leu The Hong Kong Polytechnic University, Hong Kong, ChinaS. Li South China University of Technology, Guangzhou, ChinaC.S.K. Lin City University of Hong Kong, Hong Kong, ChinaD. Liu Tsinghua University, Beijing, ChinaJ. Liu Peking University, Beijing, ChinaC. Luna University of Cordoba, Cordoba, SpainD. Luna Seneca Green Catalyst S.L., Cordoba, SpainR. Luque University of Cordoba, Cordoba, SpainG. Lyberatos National Technical University of Athens, Athens, GreeceO. Masek University of Edinburgh, UK Biochar Research Centre, Edinburgh,United KingdomJ.A. Melero Universidad Rey Juan Carlos, Mostoles, Madrid, SpainM. Melikoglu Gebze Technical University, Kocaeli, TurkeyG. Morales Universidad Rey Juan Carlos, Mostoles, Madrid, SpainP. Morone Unitelma-Sapienza, Universita degli Studi di Roma, Roma, ItalyM. Paniagua Universidad Rey Juan Carlos, Mostoles, Madrid, SpainS. Papanikolaou Agricultural University of Athens, Athens, GreeceA. Posadillo Seneca Green Catalyst S.L., Cordoba, SpainI.K. Reksowardojo Institut Teknologi Bandung, Bandung, IndonesiaA.A. Romero University of Cordoba, Cordoba, SpainA.B. Ross University of Leeds, Leeds, Yorkshire, United KingdomV. Singh University of Illinois at Urbana-Champaign, Urbana, IL, United StatesK. Stamatelatou National Technical University of Athens, Athens, GreeceZ. Sun Shanghai Ocean University, Shanghai, China
List of contributors xvN.A. Tajuddin Aston University, Birmingham, United KingdomE. Tsouko Agricultural University of Athens, Athens, GreeceX. Tu University of Liverpool, United KingdomE. Uçkun Kiran National Technical University of Athens, Athens, GreeceJ.M.N. van Kasteren CAH Vilentum University of Applied Sciences, Dronten,The NetherlandsC. Verdugo-Escamilla Universidad de Granada, Granada, SpainK. Wattanavichien Chulalongkorn University, Bangkok, ThailandC. Webb The University of Manchester, Manchester, United KingdomK. Wilson Aston University, Birmingham, United KingdomC. Wu University of Hull, United KingdomK.-L. Yang National University of Singapore, SingaporeX. Yang South China University of Technology, Guangzhou, China; CityUniversity of Hong Kong, Kowloon, Hong KongX. Zhao Tsinghua University, Beijing, ChinaZ.-G. Zhou Shanghai Ocean University, Shanghai, China
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Woodhead Publishing Series in Energy 1 Generating power at high efﬁciency: Combined cycle technology for sustainable energy production Eric Jeffs 2 Advanced separation techniques for nuclear fuel reprocessing and radioactive waste treatment Edited by Kenneth L. Nash and Gregg J. Lumetta 3 Bioalcohol production: Biochemical conversion of lignocellulosic biomass Edited by Keith W. Waldron 4 Understanding and mitigating ageing in nuclear power plants: Materials and operational aspects of plant life management (PLiM) Edited by Philip G. Tipping 5 Advanced power plant materials, design and technology Edited by Dermot Roddy 6 Stand-alone and hybrid wind energy systems: Technology, energy storage and applications Edited by John K. Kaldellis 7 Biodiesel science and technology: From soil to oil Jan C. J. Bart, Natale Palmeri and Stefano Cavallaro 8 Developments and innovation in carbon dioxide (CO2) capture and storage technology Volume 1: Carbon dioxide (CO2) capture, transport and industrial applications Edited by M. Mercedes Maroto-Valer 9 Geological repository systems for safe disposal of spent nuclear fuels and radioactive waste Edited by Joonhong Ahn and Michael J. Apted 10 Wind energy systems: Optimising design and construction for safe and reliable operation Edited by John D. Sørensen and Jens N. Sørensen 11 Solid oxide fuel cell technology: Principles, performance and operations Kevin Huang and John Bannister Goodenough 12 Handbook of advanced radioactive waste conditioning technologies Edited by Michael I. Ojovan 13 Membranes for clean and renewable power applications Edited by Annarosa Gugliuzza and Angelo Basile 14 Materials for energy efﬁciency and thermal comfort in buildings Edited by Matthew R. Hall 15 Handbook of biofuels production: Processes and technologies Edited by Rafael Luque, Juan Campelo and James Clark
xviii Woodhead Publishing Series in Energy 16 Developments and innovation in carbon dioxide (CO2) capture and storage technology Volume 2: Carbon dioxide (CO2) storage and utilisation Edited by M. Mercedes Maroto-Valer 17 Oxy-fuel combustion for power generation and carbon dioxide (CO2) capture Edited by Ligang Zheng 18 Small and micro combined heat and power (CHP) systems: Advanced design, performance, materials and applications Edited by Robert Beith 19 Advances in clean hydrocarbon fuel processing: Science and technology Edited by M. Rashid Khan 20 Modern gas turbine systems: High efﬁciency, low emission, fuel ﬂexible power generation Edited by Peter Jansohn 21 Concentrating solar power technology: Principles, developments and applications Edited by Keith Lovegrove and Wes Stein 22 Nuclear corrosion science and engineering Edited by Damien Féron 23 Power plant life management and performance improvement Edited by John E. Oakey 24 Electrical drives for direct drive renewable energy systems Edited by Markus Mueller and Henk Polinder 25 Advanced membrane science and technology for sustainable energy and environ- mental applications Edited by Angelo Basile and Suzana Pereira Nunes 26 Irradiation embrittlement of reactor pressure vessels (RPVs) in nuclear power plants Edited by Naoki Soneda 27 High temperature superconductors (HTS) for energy applications Edited by Ziad Melhem 28 Infrastructure and methodologies for the justiﬁcation of nuclear power programmes Edited by Agustín Alonso 29 Waste to energy conversion technology Edited by Naomi B. Klinghoffer and Marco J. Castaldi 30 Polymer electrolyte membrane and direct methanol fuel cell technology Volume 1: Fundamentals and performance of low temperature fuel cells Edited by Christoph Hartnig and Christina Roth 31 Polymer electrolyte membrane and direct methanol fuel cell technology Volume 2: In situ characterization techniques for low temperature fuel cells Edited by Christoph Hartnig and Christina Roth 32 Combined cycle systems for near-zero emission power generation Edited by Ashok D. Rao 33 Modern earth buildings: Materials, engineering, construction and applications Edited by Matthew R. Hall, Rick Lindsay and Meror Krayenhoff 34 Metropolitan sustainability: Understanding and improving the urban environment Edited by Frank Zeman 35 Functional materials for sustainable energy applications Edited by John A. Kilner, Stephen J. Skinner, Stuart J. C. Irvine and Peter P. Edwards 36 Nuclear decommissioning: Planning, execution and international experience Edited by Michele Laraia
Woodhead Publishing Series in Energy xix37 Nuclear fuel cycle science and engineering Edited by Ian Crossland38 Electricity transmission, distribution and storage systems Edited by Ziad Melhem39 Advances in biodiesel production: Processes and technologies Edited by Rafael Luque and Juan A. Melero40 Biomass combustion science, technology and engineering Edited by Lasse Rosendahl41 Ultra-supercritical coal power plants: Materials, technologies and optimisation Edited by Dongke Zhang42 Radionuclide behaviour in the natural environment: Science, implications and lessons for the nuclear industry Edited by Christophe Poinssot and Horst Geckeis43 Calcium and chemical looping technology for power generation and carbon dioxide (CO2) capture: Solid oxygen- and CO2-carriers Paul Fennell and E. J. Anthony44 Materials’ ageing and degradation in light water reactors: Mechanisms, and management Edited by K. L. Murty45 Structural alloys for power plants: Operational challenges and high-temperature materials Edited by Amir Shirzadi and Susan Jackson46 Biolubricants: Science and technology Jan C. J. Bart, Emanuele Gucciardi and Stefano Cavallaro47 Advances in wind turbine blade design and materials Edited by Povl Brøndsted and Rogier P. L. Nijssen48 Radioactive waste management and contaminated site clean-up: Processes, technologies and international experience Edited by William E. Lee, Michael I. Ojovan, Carol M. Jantzen49 Probabilistic safety assessment for optimum nuclear power plant life management (PLiM): Theory and application of reliability analysis methods for major power plant components Gennadij V. Arkadov, Alexander F. Getman and Andrei N. Rodionov50 The coal handbook: Towards cleaner production Volume 1: Coal production Edited by Dave Osborne51 The coal handbook: Towards cleaner production Volume 2: Coal utilisation Edited by Dave Osborne52 The biogas handbook: Science, production and applications Edited by Arthur Wellinger, Jerry Murphy and David Baxter53 Advances in bioreﬁneries: Biomass and waste supply chain exploitation Edited by Keith Waldron54 Geological storage of carbon dioxide (CO2): Geoscience, technologies, environmental aspects and legal frameworks Edited by Jon Gluyas and Simon Mathias55 Handbook of membrane reactors Volume 1: Fundamental materials science, design and optimisation Edited by Angelo Basile
xx Woodhead Publishing Series in Energy 56 Handbook of membrane reactors Volume 2: Reactor types and industrial applications Edited by Angelo Basile 57 Alternative fuels and advanced vehicle technologies for improved environmental performance: Towards zero carbon transportation Edited by Richard Folkson 58 Handbook of microalgal bioprocess engineering Christopher Lan and Bei Wang 59 Fluidized bed technologies for near-zero emission combustion and gasiﬁcation Edited by Fabrizio Scala 60 Managing nuclear projects: A comprehensive management resource Edited by Jas Devgun 61 Handbook of Process Integration (PI): Minimisation of energy and water use, waste and emissions Edited by Jirí J. Klemes 62 Coal power plant materials and life assessment Edited by Ahmed Shibli 63 Advances in hydrogen production, storage and distribution Edited by Ahmed Basile and Adolfo Iulianelli 64 Handbook of small modular nuclear reactors Edited by Mario D. Carelli and Dan T. Ingersoll 65 Superconductors in the power grid: Materials and applications Edited by Christopher Rey 66 Advances in thermal energy storage systems: Methods and applications Edited by Luisa F. Cabeza 67 Advances in batteries for medium and large-scale energy storage Edited by Chris Menictas, Maria Skyllas-Kazacos and Tuti Mariana Lim 68 Palladium membrane technology for hydrogen production, carbon capture and other applications Edited by Aggelos Doukelis, Kyriakos Panopoulos, Antonios Koumanakos and Emmanouil Kakaras 69 Gasiﬁcation for synthetic fuel production: Fundamentals, processes and applications Edited by Rafael Luque and James G. Speight 70 Renewable heating and cooling: Technologies and applications Edited by Gerhard Stryi-Hipp 71 Environmental remediation and restoration of contaminated nuclear and NORM sites Edited by Leo van Velzen 72 Eco-friendly innovation in electricity networks Edited by Jean-Luc Bessede 73 The 2011 Fukushima nuclear power plant accident: How and why it happened Yotaro Hatamura, Seiji Abe, Masao Fuchigami and Naoto Kasahara. Translated by Kenji Iino 74 Lignocellulose bioreﬁnery engineering: Principles and applications Hongzhang Chen 75 Advances in membrane technologies for water treatment: Materials, processes and applications Edited by Angelo Basile, Alfredo Cassano and Navin Rastogi
Woodhead Publishing Series in Energy xxi76 Membrane reactors for energy applications and basic chemical production Edited by Angelo Basile, Luisa Di Paola, Faisal Hai and Vincenzo Piemonte77 Pervaporation, vapour permeation and membrane distillation: Principles and applications Edited by Angelo Basile, Alberto Figoli and Mohamed Khayet78 Safe and secure transport and storage of radioactive materials Edited by Ken Sorenson79 Reprocessing and recycling of spent nuclear fuel Edited by Robin Taylor80 Advances in battery technologies for electric vehicles Edited by Bruno Scrosati, J€urgen Garche and Werner Tillmetz81 Rechargeable lithium batteries: From fundamentals to applications Edited by Alejandro A. Franco82 Calcium and chemical looping technology for power generation and carbon dioxide (CO2) capture Edited by Paul Fennell and Ben Anthony83 Compendium of hydrogen energy Volume 1: Hydrogen production and puriﬁcation Edited by Velu Subramani, Angelo Basile and T. Nejat Veziroglu84 Compendium of hydrogen energy Volume 2: Hydrogen storage, transmission, transportation and infrastructure Edited by Ram Gupta, Angelo Basile and T. Nejat Veziroglu85 Compendium of hydrogen energy Volume 3: Hydrogen energy conversion Edited by Frano Barbir, Angelo Basile and T. Nejat Veziroglu86 Compendium of hydrogen energy Volume 4: Hydrogen use, safety and the hydrogen economy Edited by Michael Ball, Angelo Basile and T. Nejat Veziroglu87 Advanced district heating and cooling (DHC) systems Edited by Robin Wiltshire88 Microbial electrochemical and fuel cells: Fundamentals and applications Edited by Keith Scott and Eileen Hao Yu89 Renewable heating and cooling: Technologies and applications Edited by Gerhard Stryi-Hipp90 Small modular reactors: Nuclear power fad or future? Edited by Daniel T. Ingersoll91 Fuel ﬂexible energy generation: Solid, liquid and gaseous fuels Edited by John Oakey92 Offshore wind farms: Technologies, design and operation Edited by Chong Ng & Li Ran93 Uranium for nuclear power: Resources, mining and transformation to fuel Edited by Ian Hore-Lacy94 Biomass supply chains for bioenergy and bioreﬁning Edited by Jens Bo Holm-Nielsen and Ehiaze Augustine Ehimen95 Sustainable energy from salinity gradients Edited by Andrea Cipollina and Giorgio Micale96 Membrane technologies for bioreﬁning Edited by Alberto Figoli, Alfredo Cassano and Angelo Basile97 Geothermal power generation: Developments and innovation Edited by Ronald DiPippo
xxii Woodhead Publishing Series in Energy 98 Handbook of biofuels production: Processes and technologies (Second Edition) Edited by Rafael Luque, Carol Sze Ki Lin, Karen Wilson and James Clark 99 Magnetic fusion energy: From experiments to power plants Edited by George H. Neilson100 Advances in ground-source heat pump systems Edited by Simon Rees101 Absorption-based post-combustion capture of carbon dioxide Edited by Paul Feron102 Advances in solar heating and cooling systems Edited by Ruzhu Wang and Tianshu Ge
Part OneKey issues and assessmentof biofuels production
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Introduction: an overview 1of biofuels and productiontechnologiesC. Du 1, X. Zhao 2, D. Liu 2, C.S.K. Lin 3, K. Wilson 4, R. Luque 5, J. Clark 61University of Huddersﬁeld, West Yorkshire, United Kingdom; 2Tsinghua University, Beijing,China; 3City University of Hong Kong, Hong Kong, China; 4Aston University, Birmingham,United Kingdom; 5University of Cordoba, Cordoba, Spain; 6University of York, York,United Kingdom1.1 IntroductionThe increasing demand of renewable energy and the growing concern of global warm-ing are still considered to be key challenges for the society worldwide. The sustainabledevelopment of the energy industry needs a continuous supply of renewable, sustain-able energy. In 2013, over 90 million barrels of crude oil were consumed globally eachday (US Energy Information Administration, 2014). Along with economic and popu-lation growth, the demand of energy will surge as well. Currently, 80% global energyconsumption came from fossil resources, namely crude oil, natural gas, and coal.These fossil fuels are generated from organic materials that synthesized on Earth mil-lions of years ago, and are unable to be regenerated within a short period, eg, it takesover hundreds of years for regeneration. Although the recent booming of shale gas re-leases the tension of the fossil fuel shortage and drags down the fossil fuel price, theﬁnite nature of fossil fuel does not change. Based on the current daily fossil-usage data,the fossil regeneration rate (even the fossil discovery rate) will never match the con-sumption rate. A decade ago, some scientists warned that the fossil fuel would runout in 40 years. Our fossil fuel reserves might last for 40 or 100 years, dependingupon the conditions that are put on our fossil fuel use (Dunlap, 2015). Optimistseven consider that with the increasing fossil exploration, the fossil fuel would lastlonger than our current estimation. However, even if fossil fuel could last 300 years,this is just a short spell in human history. The exploration of new, renewable energyresources cannot wait until the depletion of fossil fuel. On the other hand, the appeal of the reduction of greenhouse gas (GHG) emis-sion has been the hottest topic in every recent United Nations Climate Change Con-ference. In 1997, the Kyoto Protocol was signed by most of the industrializedcountries with the aim of reducing the global GHG emission. After the Kyoto Pro-tocol’s ﬁrst commitment period expired on 2012, 37 countries, including 28 mem-bers of the European Union, agreed to a second commitment period of GHGHandbook of Biofuels Production, 2e. http://dx.doi.org/10.1016/B978-0-08-100455-5.00001-1Copyright © 2016 Elsevier Ltd. All rights reserved.
4 Handbook of Biofuels Productionemission reduction in Doha. Although the two largest GHG emission countries didnot participate in the Kyoto Protocol, they both set their own CO2 emission targets(UNFCCC, 2015). According to the latest report of the Intergovernmental Panel onClimate Change (IPCC, 2014), the GHG concentration in the atmosphere couldreach from 750 to 1300-ppm CO2 equivalents. As a consequence, the globalaverage surface temperature could increase by 3.7e4.8C. If we would like to con-trol the temperature change within 3C in 2100 compared to that of preindustriallevels, the GHG concentration in the atmosphere should be controlled to lowerthan 650-ppm CO2 equivalents. This means a change of GHG emission should atleast not exceed 24% of the 2010 emission level (IPCC, 2014). Since 78% ofGHG emissions in recent decades came from fossil fuel combustion and industrialprocesses, the development of a low-carbon economic system to replace the fossilfuelebased system is urgent. Along with several other renewable technologies, biofuel has made and willcontinuously make a signiﬁcant contribution to meet targets on the usage ofrenewable energy resources and the reduction of GHG emission. Besides theabove-mentioned major reasons, the advantages of development and application ofbiofuels also include: improving national energy security, utilizing existing transpor-tation system, utilizing existing fuel distribution system, and facilitating ruraldevelopment. Currently, in the ﬁrst generation of bioethanol, food crops such as corn, sugar cane,and wheat are used for the production of energy. These are starch- or sucrose-rich feed-stocks that are readily fermented by microorganisms. However, these crops are alsoused for food and feed production, resulting in competition. At present, commercialproduction of the ﬁrst-generation biomass utilizes readily-available sugars from thesefood plants for the fermentation process of biofuel production. However, the second generation of bioethanol uses lignocellulosic raw materials asthe main substrate, which has a more complex composition as compared to the ﬁrst-generation feedstocks. Lignocellulosic feedstocks are high in cellulose, hemicellulose,and lignin. Second-generation feedstocks avoid competition with food and feed prod-ucts. Examples are waste streams from food- or feed-crops such as wheat straw or cornstover, also municipal or industrial waste streams, or energy crops that grow on mar-ginal lands that are unsuitable for regular agriculture. To use the preferredsecond-generation feedstocks, further advances in technological development areneeded to unlock the more hidden sugars in the crop residues or woody plant materials.Signiﬁcant research efforts and investment have been spent to improve the technologyin order to enable the commercial use of the second-generation feedstocks. Different generations of biofuels also differ in other characteristics. While the foodpart of the food crops is made of easily digestible sugars, the sugars captured in ligno-cellulosic compositions of the second-generation feedstocks are more difﬁcult to uti-lize. So why do we want to use these more challenging second-generationfeedstocks? This is to reduce competition with food, arable land, and water. Using res-idues can help to avoid land-use changes, and energy crops can be genetically engi-neered to reduce water usage. It can also bring in extra income for farmers. In thefuture, water-based feedstocks such as algae may become as important as the
Introduction: an overview of biofuels and production technologies 5third-generation feedstocks. The third-generation feedstock is used for processeswhere CO2 is utilized as one of the substrates. A common example would be photo-synthetic algae that use sunlight and CO2 to produce useful organic molecules. Thesethird-generation systems would completely eliminate the need for agricultural land. This book aims to provide an overview of the latest progresses in various technol-ogies for biofuel production. The special emphasis has been focused on the advancedgeneration of biofuels, which produce biofuels from nonfood materials. We keep thesame the classiﬁcation method, dividing different technologies into three main sec-tions: chemical, biological, and thermochemical conversions. In the ﬁrst few introductory chapters, details on policies, socioeconomic, and envi-ronmental implications of the implementation of biofuels (chapter: Multiple objectivespolicies for biofuels production: environmental, socioeconomic and regulatoryissues), life-cycle assessment (LCA) (chapter: Life cycle sustainability assessmentof biofuels), techno-economic assessment (chapter: Techno-economic studies ofbiofuels), environmental concern (chapter: Multiple objectives policies for biofuelsproduction: environmental, socio-economic and regulatory issues), and the differentbiofuel feedstocks (chapter: Feedstocks and challenges to biofuel development) willbe presented. The rest of the book is aimed to give a detailed and balanced overviewon key technologies and processes for the production of various type of biofuels,including but not limited to, bioethanol, biodiesel, biohydrogen, biogas from anaerobicdigestion, biosyngas from gasiﬁcation, and bio-oil from pyrolysis.1.2 Development of (bio)chemical conversion technologiesThe utilization of “biofuels” in transportation has a long history. In 1900, the ParisExposition Universelle, a small version of the diesel engine, was shown, which runson peanut oil. Using vegetable oil in diesel engine began in the 1920s and continuedthrough the early 1940s. With the booming of oil industry, together with the shortcom-ings of directly using vegetable oil, eg, high viscosity, petroleum diesel has been pre-dominately used in the diesel engine. In the 1970s, the oil crisis sparked interests inbiofuels. Austria started biodiesel research in 1974, and in 1985, a pilot plant produc-ing 500 tons/year of biodiesel was built in Styria, Austria, using rapeseed oil as thestarting material. Fig. 1.1 shows the biodiesel production trend in Europe. Europeancountries had set its own policy to blend biodiesel to petroleum diesel. In the UnitedKingdom, around 3.4% of the total diesel used in 2014 was biodiesel. Biodiesel is a mixture of long-chain fatty acid methyl ester (FAME) that is pro-duced from biomaterials through transesteriﬁcation of triacylglycerol (TAG, ie, plantoil and animal fats) with methanol. In chemistry, the biodiesel synthesis could beexpressed by the reaction as shown in Fig. 1.2. In principle, any triacylglycerol couldbe used for biodiesel production. In fact, the ﬁrst generation of biodiesel was mainlyproduced from edible plant oil, such as soybean, rapeseed, and palm oil. The low priceof plant oil before 2008 and high diesel price in the European countries allowed
6 Handbook of Biofuels ProductionBiodiesel (M Ton) European biodiesel production 30 25 20 15 10 5 0 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 YearFigure 1.1 Biodiesel production trend in Europe in the period of 2003e2013. + Catalyst +Triglyceride Alcohol Methyl ester GlycerolFigure 1.2 The chemical equation of transesteriﬁcation reaction.enough proﬁt for the biodiesel production. For example, during 2004e2005, the rape-seed oil price was less than V600/ton, while the diesel price was V1.11/L. However, in2008, the plant oil price increased sharply, and the margin of biodiesel production fromplant oil was low. During the soaring of raw material cost, together with the concern offood shortage, production of biodiesel from nonedible oil, eg, waste cooking oil,grease, Jatropha oil, and microalgae attracted increasing interest. It was reported thatin the United Kingdom between April 2014 and 2015, over 50% of the biodiesel wouldbe derived from waste cooking oil (Biofuel statistics, UK government, 2014). In terms of biodiesel conversion processes, chemical conversion using alkali andacid-based catalysts is still the most favorite approach. Various investigations havebeen carried out to develop novel catalysts and/or novel processes for efﬁcient conver-sion of TAG to FAME. This part was reviewed in the chapter “Production of biodieselvia catalytic upgrading & reﬁning of sustainable oleageneous feedstocks.” The chapter“Biochemical catalytic production of biodiesel” introduced a promising alternativeway of biodiesel production via enzyme-catalyzed processes. Recently, microalgae
Introduction: an overview of biofuels and production technologies 7has been demonstrated to have the potential for biodiesel production. Signiﬁcant prog-ress has been made since the concept was ﬁrst introduced. The character of microalgaeoil showed its great potential of dominating biodiesel production. Since the publicationof the ﬁrst edition, further intensive investigation on this ﬁeld has been carried out.The advantages and limitations of microalgae oil production are discussed in thechapters “Production of fuels from microbial oil using oleaginous microorganisms”and “Utilization of biofuels in diesel engines.”1.3 Development of biological conversion technologiesA wide range of biofuels could be produced from fermentative and biological pro-cesses, with bioethanol that dominated the liquid biofuel production. The ﬁrst gener-ation of bioethanol production has already been fully developed, and its products havebeen utilized in many countries across continents. The second generation of bioethanolis still the center of bioethanol research, with only a few pilot plants and demonstrationplants on operation. However, Italy made a commitment of blending 0.6% advancedbiofuel by 2018, and 1% by 2022. Also, it built up the world’s ﬁrst second-generationof bioethanol plant “Beta Renewables” at Crescentino near Turin. This plant was ofﬁ-cially opened in October 2013, which was designed to produce 75 million liters of bio-ethanol per year. This will deﬁnitely boost the research and commercialization of thesecond generation of bioethanol. Besides bioethanol (chapter: Biochemical production of bioalcohols), anaerobicdigestion of organic waste materials for the biogas production progressed rapidlyworldwide in the past 5 years. For example, the annual biogas production in Chinaincreased dramatically from 10.5 billion m3 to 248 billion m3 from 2007 to 2010(Deng et al., 2014; Wellinger, 2011). The chapters “Production of biogas via anaerobicdigestion,” “Biological and fermentative production of hydrogen,” and “Biologicaland fermentative conversion of syngas” reviewed biogas, biohydrogen, and fermenta-tive conversion of syngas (synthesis gas), respectively.1.4 Thermochemical conversion technologiesDirect combustion of biomass is one of the ﬁrst types of energy that ancient peoplecould manage. Burning biomass for cooking, keeping warm, and safety have beenused by humans for thousands of years. Until now, biomass combustion still suppliesaround 11% of world energy. With the increasing incentive to utilize renewable mate-rials for fuels and chemicals generation, various thermochemical conversion ofbiomass technologies emerged. Biopyrolysis is a typical thermochemical process, which converts biomass intobiosyngas, bio-oil, and biochar at elevated temperature with limited supply of air(oxygen). Bio-oil is the target product of biopyrolysis. A wood chipederivedbio-oil normally has a density of around 1.2 kg/L with an energy density of around
8 Handbook of Biofuels Production18.0 MJ/kg, which is around 2e4 times higher than those of the wood chips. How-ever, the complex composition of the pyrolysis oil, the high water content, and thehigh acidity prevent wide applications of bio-oil. Various investigations have beencarried out with the hope of upgrading bio-oils into a replacement of fossil transpor-tation fuels, including optimizing operation conditions, pretreating biomass beforepyrolysis, introducing catalysts, designing novel reactors, and many others, asreviewed in the chapters “Catalytic fast pyrolysis for improved liquid quality,” “Pro-duction of biofuels via hydrothermal conversion,” and “Production of biofuels viabio-oil upgrading and reﬁning.” Further increase to the reaction temperature in the biopyrolysis process would leadthe thermochemical reactions to shift toward biosyngas production. Such a process isthen termed gasiﬁcation. The main components of biosyngas are CO and H2. The ratioof CO and H2 is depended on the type of substrate and gasiﬁcation conditions, eg,whether steam is used in the gasiﬁcation process. The resultant biosyngas could beburnt directly for energy generation, or to be used for the synthesis of biofuels viathe Fischer-Tropsch process or a newly-emerged gas fermentation process. These con-tents were reviewed in the chapters “Production of biosyngas and bio-hydrogen viagasiﬁcation,” “Production of bioalcohols via gasiﬁcation,” “Production of biofuelsvia Fischer-Tropsch synthesis: biomass-to-liquids,” and “Production of biofuels viabio-oil upgrading & reﬁning”. Besides these, the chapter “Chemical routes for the con-version of cellulosic platform molecules into high-energy density biofuels” discussedalternative approaches that could be used for the high-energy-density biofuels produc-tion via chemical conversion routes.1.5 Process integration and bioreﬁneryThe successful development of a biofuel production process, especially the secondgeneration of biofuel, required knowledge from biotechnology, engineering, chemis-try, plant science, and other relevant ﬁelds. Process integration is required to improvethe mass and energy ﬂow efﬁciency within a biofuel production process (Sadhukhanet al., 2014). Furthermore, production integration is also required, that is, to fully uti-lize the potential of the biomass raw materials and to generate a range of products. Thisconcept is designated as “Bioreﬁnery,” which is analogous to petroleum reﬁneries(Clark and Deswarte, 2008). These products include high-volume, low-value products,such as transportation fuels (eg, bioethanol, biodiesel), medium-volume, medium-value products, such as platform chemicals and materials (eg, succinic acid, lacticacid, polyhydroxybutyrate [PHB]), as well as low-volume, high-value products,such as pharmaceuticals (eg, arteannuin, antioxidants). Actually, the bioreﬁnery concept has already been applied in the ﬁrst generation ofbiofuels. Along with bioethanol production, Distiller’s Dried Grains with Solubles(DDGS) is generated. DDGS is sold as an animal feed, and is an important incomestream for a bioethanol company. Even more, companies consider themselves to beanimal feedeproducing or commodity foodeproducing companiesdthe biofuel
Introduction: an overview of biofuels and production technologies 9production is just to utilize the low nutritional parts of the biomass or the organic wasteto generate another product. Similarly, glycerol is the principle by-product of bio-diesel, which is produced from transesteriﬁcation of TAG with a glycerol to biodieselmass ratio of 1:10. At the earlier stage in a biodiesel business model, glycerol is nor-mally reﬁned to pure glycerol and is sold as an income stream. However, due to thesoaring of biodiesel production, the glycerol market was quickly saturated. As a conse-quence, the glycerol price dropped signiﬁcantly. Therefore, various research has beencarried out to convert glycerol, or crude glycerol into other value-added products, suchas 1,3-propanediol, succinic acid, PHB, and biogas via anaerobic digestion (Koutinaset al., 2014). Biofuel production actually plays a major role in the economics of bioreﬁneries. Thechapter “Biofuel production from food wastes” reviewed the topic of biofuel-driven bio-reﬁneries, and the chapters “Biochar in thermal and thermochemical bioreﬁneriesdproduction of biochar as a coproduct,” “Algae for biofuels: an emerging feedstock,”and “Utilization of biofuels in diesel engines” focused on the biofuels and othervalue-added production formation from the following interesting raw biomass: foodwaste, lignocellulose, and algae. Last but not least, engine tests are of utmost importanceto test the feasibility of biofuels implementation and are still on-going activities. Chapter“Utilization of biofuels in diesel engines” summarized some experimental results on theimplementation of biofuels in engine tests.1.6 Future trendsIn the past 5 years, the biofuel industry continuously grew with an average increase inannual biofuel production of 6.4% (BP, 2015 annual report). Currently, around 3% ofworld transportation fuel is provided by biofuel. According to a recent article pub-lished by the International Energy Agency, this ﬁgure could potentially grow up to27% in 2050 (IEA, 2011). In the past, most biofuel companies received government subsidies and tax reduc-tion. These policies stimulated the rapid growth of bioenergy industry. Nowadays,some governments have started to withdraw this kind of support to biofuel producers.On one hand, the proﬁt of biofuel production dropped signiﬁcantly, and some com-panies had to shut down or reduce their activities. On the other hand, this change en-ables only the highly efﬁcient, highly competitive technologies to survive, andtherefore increases the competitiveness of the whole biofuel industry in a nonprotec-tive energy market. The next 5e10 years will be a crucial period for the development of bioenergy tech-nologies. Most attention has been put in the industrialization progress of lignocellulosicbioethanol production. Various life-cycle assessments have demonstrated that utilizinglignocellulosic biomass for bioethanol fermentation would lead to a signiﬁcant reductionof GHG. Identiﬁcation of effective pretreatment methods, production of low-cost cellu-lolytic enzymes and enhanced fermentation yield and productivity using the hydrolysatefrom biomass into bioethanol are the most feasible ﬁelds to advance the technology.
10 Handbook of Biofuels Production Alternatively, lignocellulosic raw materials could be used for biofuel and biochem-ical production via thermochemical processes, such as fast pyrolysis, catalytic pyrolysis,and gasiﬁcation. Fast pyrolysis actually has been commercialized, and the main productis bio-oil that can be readily stored, transported, and used for the production of liquidfuels and various chemicals (Bridgwater, 2012). Bio-oils have been successfully testedas fuels in engines, turbines, and boilers, and upgraded to high-quality hydrocarbon fuels(Czernik and Bridgwater, 2004). However, upgrading of the bio-oils to a quality oftransport liquid fuel still faces several technical challenges due to the very complex com-positions, and the process is not currently economically feasible. Catalytic pyrolysis re-fers to the pyrolysis process of biomass using various catalysts with aims of eliminationand substitution of oxygen and oxygen-containing functionalities, in addition toincreasing the hydrogen to carbon ratio of the ﬁnal products (Dickerson and Soria,2013). However, robust and highly-selective catalysts have to be further developed,and the cost of the process has to be reduced for commercial application. Gasiﬁcationis one of the most promising technologies to produce gas fuels from lignocellulosicbiomass. It is a thermochemical partial-oxidation process converting carbonaceous sub-stances such as biomass into gas in the presence of a gasifying agent such as air, steam,oxygen, CO2, or a mixture of these. Syngas (synthesis gas) is the main product generatedby biomass gasiﬁcation, which consists mainly of H2, CO, CO2, N2, small particles ofchar, ashes, tars, and oils. However, in most markets, biomass gasiﬁcation has yet tobecome consolidated as a mature technology to compete with other methods of energyconversion (Ruiz et al., 2013). Utilizing various waste materials and by-products for biofuel and biochemical pro-duction not only reduced the burden of waste treatment but also provided an alternativeway to generate green fuels and chemicals. Such waste feedstocks include variousorganic wastewater and residues from food processing plants, pulp mills, sugar mills,ethanol or biodiesel plants, and other bioreﬁnery plants. The main components of thewaste materials including starch, sugars, glycerol, etc. could be used as carbon sourcesof various microorganisms for producing bioethanol, biochemicals, and biodiesel feed-stocks such as microbial lipids. Sugarcane molasses is a by-product of sugar process-ing, and has been successfully used for bioethanol production (Dasgupta et al., 2014).Organic efﬂuents from different plants could be well-converted to intracellular lipid byoleaginous microorganisms, which can be used as a feedstock for biodiesel production(Marjakangas et al., 2015; Sun et al., 2015). The by-product glycerol from biodieselproduction has many applications for producing chemicals and intermediates. A prom-ising way to utilize this glycerol is to produce 1,3-propanediol, a monomer for produc-ing polytrimethylene terephthalate (PTT). Actually, biological conversion of biodieselby-product glycerol to 1,3-propanediol has been successfully industrialized in China(Liu et al., 2010). However, the efﬁciency of conversion of various waste materialsto fuels and chemical needs yet to be enhanced. The impurities and inhibitors presentin the waste might exert inhibition to the enzymes and microorganisms during the bio-logical conversion. The economic feasibility of the processes still needs comprehen-sive evaluations. Marine biomass, including microalgae and macroalgae (seaweeds), would still beone of the centers of bioenergy research. The potential of microalgae for the biodiesel
Introduction: an overview of biofuels and production technologies 11production has been well-recognized. However, the high energy input in microalgaecultivation and microalgae processing limited its application in biofuel production.One of the most important challenges for autotrophic microalgae cultivation is thelow growth rate, biomass density, and oil content. Another challenge refers to thehigh energy consumption for oil extraction because most microalgae has rigid cellwall structure and it is usually energy-intensive to disrupt the wall and release the intra-cellular oils. Therefore, currently the production of algal oil is primarily conﬁned tohigh-value specialty oils with nutritional value such as polyunsaturated fatty acid,rather than commodity oils for biofuels (Hu et al., 2008). Modiﬁcation of the micro-algae by genetic engineering might improve the efﬁcacy of CO2 to oil conversionand increase biomass density. However, more work should be done to extract the intra-cellular oils in a lower cost and increase the economic competiveness of the microalgaeoil-based biofuel system. The signiﬁcant progress of the bioenergy industry encourages further explo-ration on low-carbon technologies for the production of advanced-generation bio-fuels (and biochemicals) from low-value waste biomass. Collective efforts fromvarious aspects surrounding bioenergy technologies, including politicians, econo-mists, environmentalists, scientists, and engineers, are needed to come up with al-ternatives, policies, and choices to advance the key technologies for a moresustainable future.AcknowledgmentC.S.K. Lin, R. Luque, and J. Clark gratefully acknowledge the contribution of the COST ActionTD1203-EUBis.ReferencesIEA (Ed.), 2011. Biofuels Can Provide up to 27% of World Transportation Fuel by 2050. IEA, Washington DC, USA. https://www.iea.org/newsroomandevents/pressreleases/2011/april/ biofuels-can-provide-up-to-27-of-world-transportation-fuel-by-2050-iea-report-.html.Bridgwater, A.V., 2012. Review of fast pyrolysis of biomass and product upgrading. Biomass and Bioenergy 38, 68.Biofuel Statistics: Year 7 (Renewable transport fuel obligation statistics: year 7, report 1 data tables), UK government, https://www.gov.uk/government/statistics/biofuel-statistics-year- 7-2014-to-2015-report-1 (published 06.11.14., last accessed 06.03.16).BP Strategic Report, 2015. http://www.bp.com/content/dam/bp/pdf/investors/bp-strategic- report-2015.pdf (last accessed 06.03.16.).Clark, J.H., Deswarte, F.E.I., 2008. The bioreﬁnery concept e an integrated approach. In: Clark, J.H., Deswarte, F.E.I. (Eds.), Introduction to Chemicals from Biomass. Wiley, Chichester, West Sussex.Czernik, S., Bridgwater, A.V., 2004. Overview of applications of biomass fast pyrolysis oil. Energy and Fuels 18, 590.
12 Handbook of Biofuels ProductionDasgupta, D., Ghosh, P., Ghosh, D., Suman, S., Khan, R., Agrawal, D., et al., 2014. Ethanol fermentation from molasses at high temperature by thermotolerant yeast Kluyveromyces sp. IIPE453 and energy assessment for recovery. Bioprocess and Biosystems Engineering 37, 2019.Deng, Y., Xu, J., Liu, Y., Mancl, K., 2014. Biogas as a sustainable energy source in China: regional development strategy application and decision making. Renewable and Sustain- able Energy Reviews 35, 294.Dickerson, T., Soria, J., 2013. Catalytic fast pyrolysis: a review. Energies 6, 514.Dunlap, R.A., 2015. Sustainable Energy, SI ed. Cengage Learning, Stamford, Connecticut, USA.EIA, 2014. Petroleum statistics. In: U.S. Energy Information Administration, pp. Oil: Crude and Petroleum Products Explained. http://www.eia.gov/energyexplained/index.cfm?page¼oil_ home#tab3.Hu, Q., Sommerfeld, M., Jarvis, E., Ghirardi, M., Posewitz, M., Seibert, M., et al., 2008. Microalgal triacylglycerols as feedstocks for biofuel production: perspectives and advances. The Plant Journal 54, 621.IPCC, 2014. Summary for policymakers. In: Field, C.B., Barros, V.R., Dokken, D.J., Mach, K.J., Mastrandrea, M.D., Bilir, T.E., et al. (Eds.), Climate Change 2014: Impacts, Adaptation, and Vulnerability Part A: Global and Sectoral Aspects Fifth Assessment Report of the Intergovernmental Panel on Climate Change Ed. IPCC, Cambridge, UK and New York, USA, p. 1.Koutinas, A.A., Vlysidis, A., Pleissner, D., Kopsahelis, N., Lopez Garcia, I., Kookos, I.K., et al., 2014. Valorization of industrial waste and by-product streams via fermentation for the production of chemicals and biopolymers. Chemical Society Reviews 43, 2587.Liu, H., Xu, Y., Zheng, Z., Liu, D., 2010. 1,3-Propanediol and its copolymers: research, development and industrialization. Biotechnology Journal 5, 1137.Marjakangas, J.M., Lakaniemi, A.-M., Koskinen, P.E.P., Chang, J.-S., Puhakka, J.A., 2015. Lipid production by eukaryotic microorganisms isolated from palm oil mill efﬂuent. Biochemical Engineering Journal 99, 48.Ruiz, J.A., Juarez, M.C., Morales, M.P., Mun~oz, P., Mendívil, M.A., 2013. Biomass gasiﬁcation for electricity generation: review of current technology barriers. Renewable and Sustain- able Energy Reviews 18, 174.Sun, Q., Li, A., Li, M., Hou, B., Shi, W., 2015. Advantageous production of biodiesel from activated sludge fed with glucose-based wastewater. Acta Scientiae Circumstantiae 35, 819.Sadhukhan, J., Ng, K.S., Hernandez, E.M., 2014. Bioreﬁneries and Chemical Processes: Design, Integration and Sustainability Analysis, ﬁrst ed. John Wiley & Sons, Malaysia.UNFCCC (Ed.), 2015. Doha Amendment to the Kyoto Protocol. Doha.Wellinger, A., 2011. Biogas: Simply the Best. European Biogas Association, Brussels, Belgium.
Multiple objectives policies 2for biofuels production:environmental, socio-economic,and regulatory issuesC. De LuciaUniversity of Foggia, Foggia, Italy2.1 IntroductionSince their introduction in the supply chain, biofuels contributed to the reductionof carbon emissions (Bergthorson and Thomson, 2015; Su et al., 2015). It is thisevidence, together with advances in technological progress for renewables use andrecent development of renewable energy policies, which suggests that governmentsadopt new practices to enhance the agricultural sector. A renovated agriculturalsystem was launched for biofuels feedstock production. This, in turn, served as astimulus for countries facing current unbalances for imported energy commoditiesto search for new energy supply and security initiatives. Additionally, current biofuelfeedstock production and future bioenergy and bioreﬁnery practices are instrumentalin the enhancement of rural development and the creation of further policy tools inthe biofuels industry, as well as the agricultural sector. This picture is nonethelesswithout drawbacks. The positive and negative synergies occurring across a multitudeof biofuels objectives should be carefully addressed. The aim of this chapter is toillustrate and discuss main objectives of biofuels policies viewed under multidirec-tional effects on economy, energy, and environment. The chapter is organized as fol-lows: Section 2.2 illustrates biofuels and bioenergy seen as energy security andsupply; Section 2.3 discusses environmental and land-use issues linked to biofuelspractices; Section 2.4 emphasizes the risk for food safety and the need for using mar-ginal areas for biofuels activities; Section 2.5 describes current biofuels policy sup-port and delineates future scenarios for climate change mitigation; ﬁnally, Section2.6 concludes the chapter.2.2 Energy security and supplyIn the current post-2008 global economic crises, the implementation of energy securityand supply policies should be seen as a short-/medium-term goal worldwide. Rich andindustrialized countries driving their economies on fossil fuels, oil products, andHandbook of Biofuels Production, 2e. http://dx.doi.org/10.1016/B978-0-08-100455-5.00002-3Copyright © 2016 Elsevier Ltd. All rights reserved.
14 Handbook of Biofuels Productionderivates are experiencing a shortage of ﬁnite resources with a consequential high riskof depletion and exhaustion. In addition, intensiﬁcation of trade in oil commoditiescreates trade unbalances in countries that are strongly dependent by energy-importedcommodities. The International Renewable Energy Agency (IRENA at www.irena.org), foundedin 2009, has put into practice the idea of combining the efforts of many governmentsaround the world to cooperate on renewable energy policies, ﬁnancing, and technolo-gies. Nowadays, the Agency counts 143 members plus 29 countries in accession. Themain mission of the IRENA is to create cooperation and synergies at a global scale toenhance technology and strengthen innovation by means of knowledge-sharing initia-tives, enabling policies advances across countries and at all level of governance, aswell as contributing to the common goal of energy safety and supply achieved withthe use of renewable energies. The ﬁrst study worldwide dealing with renewable energies is REmap 2030(www.irena.org/remap), which is a plan aiming at doubling the use of renewableenergies at a global level by 2030. The study addresses bioenergy issues in 26countries that are representative of three-quarters of actual energy demand. Themain ﬁnding of this study is that these countries would reach and surpass the targetsof global renewable energy share by 30% by 2030, given the present available tech-nology. This target can also be achieved by considering investments in renewableenergies in the key energy intensity sectors such as buildings, transport, industry,and electricity. Furthermore, the transition to this new economy using 30% ofrenewable energies and taking into account socio-economic beneﬁts can be attainedat minor additional costs. Finally, the global roadmap will enable countries toreduce CO2 emissions by 8.6 Gt by 2030 and contribute defense against climatechange (IRENA, 2014). In a number of countries regulation is currently being adopted or under scrutiny tofavor energy supply and safety. The following description will focus on the EuropeanUnion, United States, Brazil, and China.2.2.1 European UnionIn the European Union, a new set of energy regulations are changing current andfuture scenarios of energy use and supply. The Commission Directive 2009/28/ECon the “Promotion of the use of energy from renewable sources” abolishes the pre-vious Biofuels Directive (Commission Directive 2003/30/EC) and the CommissionDirective 2001/77/EC on electricity from renewables. The new legislation bodyput in place an exclusive framework for renewable energy production within MemberStates. In particular, the Directive sets reference values of energy from renewablescomputed from estimates of gross ﬁnal demand by 2020. These reference valuescorrespond to the achievement of the European Union “20e20e20” strategy, whichis a fundamental, voluntary policy adopted in March 2007 by the European Commis-sion to further attain the goals of the Kyoto Protocol. The 20e20e20 policy estab-lishes by 2020 to reach a target of 20% reduction of Greenhouse Gases (GHGs) byusing 20% renewables. Given this ambitious scenario, Member States are committed
82 Handbook of Biofuels ProductionNonhebel, S., 2014. Global food supply and the impacts of increased use of biofuels. Energy 37 (1), 115e121, 01.2012.OECD/IEA, 2008. Climate Policy and Carbon Leakage. Impacts of the European Emissions Trading Scheme on Aluminium (IEA Information paper).OECD/IEA, 2011. World Energy Outlook 2011. International Energy Agency, Paris.OECD/ITF, 2010. Reducing transport greenhouse gas emissions: trends & data 2010. In: Background Paper for the 2010 International Transport Forum, on 26e28 May in Leipzig, Germany, on Transport and Innovation: Unleashing the Potential.Oliveira, P., Almeida, E., 2015. Determinants of fuel price control in Brazil and price policy options. In: 5th Latin American Energy Economics Meeting, 2015.Palmer, J.R., 2015. How do policy entrepreneurs inﬂuence policy change? Framing and boundary work in EU transport bio fuels policy. Environmental Politics 24 (2).Phillips, S., Aden, A., Jechura, J., Dayton, D., Eggeman, T., 2007. Thermochemical Ethanol via Indirect Gasiﬁcation and Mixed Alcohol Synthesis of Lignocellulosic Biomass. National Renewable Energy Laboratory, Golden, Colorado. Technical Report NREL/TP- 510-41168.Prugh, T., 2014. Vital Signs Online Trend. Worldwatch Institute.Raven, R.P.J.M., van den Bosch, S., Weterings, R., 2010. Transitions and strategic niche management. Towards a competence kit for practitioners. International Journal of Tech- nology Management on Social Innovation 51 (1), 57e74.Richmond-Bryant, J., Meng, Q.Y., Davis, A., Cohen, J., Lu, S.E., Svendsgaard, D., Brown, J.S., Tuttle, L., Hubbard, H., Rice, J., Kirrane, E., Vinikoor-Imler, L.C., Kotchmar, D., Hines, E.P., Ross, M., 2014. The inﬂuence of declining air lead levels on blood lead-air lead slope factors in children. Environmental Health Perspectives 1, 1e27.Rip, A., 1992. A quasi-evolutionary model of technological development and a cognitive approach to technology policy. Rivista de Studi Epistemologici e Sociali Sulla Scienza e la Tecnologia 2, 69e103.Rothaermel, F.T., 2001. Incumbent’s advantage through exploiting complementary assets via interﬁrm cooperation. Strategic Management Journal 22, 687e699.Safarzynska, K., van den Bergh, J.C.J.M., 2010. Evolutionary modelling in economics: a survey of methods and building blocks. Journal of Evolutionary Economics 20 (3), 329e373.Sainz, M.B., 2011. Commercial cellulosic ethanol: the role of plant-expressed enzymes. Bio Fuels 237e264.Schot, J., Geels, F.W., 2008. Strategic niche management and sustainable innovation journeys: theory, ﬁndings, research agenda, and policy. Technology Analysis & Strategic Manage- ment 20, 537e554.Silva Lora, E.E., Escobar Palacio, J.C., Rocha, M.H., Grillo Reno, M.L., Venturini, O.J., del Olmo, O.A., 2011. Issues to consider, existing tools and constraints in biofuels sustain- ability assessments. Energy 36, 2097e2110.Sims, R.E.H., Mabee, W., Saddler, J.N., Taylor, M., 2010. An overview of second generation biofuel technologies. Bioresources Technology 101, 1570e1580.Sinn, H.W., 2008. Public policies against global warming: a supply side approach. International Tax and Public Finance 15, 360e394.Smith, A., Stirling, A., Berkhout, F., 2005. The governance of sustainable socio-technical transitions. Research Policy 34, 1491e1510.Steinbuks, J., Hertel, T.W., 2016. Confronting the food-energy-environment trilemma: global land use in the long run. Environmental and Resource Economics 63, 545e570.Timilsina, G.R., Mevel, S., Shrestha, A., 2011. Oil price, biofuels and food supply. Energy Policy 39 (12), 8098e8105.
Biofuels: technology, economics, and policy issues 83United Nations, 2014. The World Population Situation in 2014-A Concise Report. Department of Economic and Social Affairs Population Division, New York, United Nations. ST/ESA/ SER.A/354.Unruh, G.C., 2000. Understanding carbon lock in. Energy Policy 28, 817e830.Wiesenthal, T., Leduc, G., Schwarz, H.-G., Haegeman, K., 2009. R&D Investment in the Pri- ority Technologies of the European Strategic Energy Technology Plan. JRC Reference Report. EUR 23944.Wilson, D., Dragusanu, R., 2008. The Expanding Middle: The Exploding World Middle Class and Falling Global Inequality. Global Economics Paper No: 170, GS Global Economic Website, Economic Research from Goldman 360 at https://360.gs.com.York, R., 2006. Ecological paradoxes: William Stanley Jevons and the paperless ofﬁce. Human Ecology Review 13 (2), 143e147.
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Feedstocks and challenges 5to biofuel developmentI.L. GarcíaUniversity Cordoba Ediﬁcio Leonardo da Vinci, Campus de Rabanales, Cordoba, Spain5.1 IntroductionRenewable energy share of global ﬁnal energy consumption was around 19% in 2011,from which only 0.8% corresponded to biofuels (UNCTAD, 2015), not enough tomeet the sustainability criteria in accordance with 2020 Kyoto Protocol obligations.Global biofuel production increased by approximately 7.4% in 2014: 6.0% corre-sponding to ethanol production (second consecutive year of growth, concentratedon North America, South and Central America, and Asia Paciﬁc) whereas biodieselproduction increased by 10.3% (BP, 2014). A decrease in cereals, oilseeds, vegetableoil, and crude oil prices in 2014 has contributed to lower biofuel prices and therefore togrowing demand (Nations, 2015). Nevertheless, over the next decade, ethanol and bio-diesel use are expected to grow at a lower rate, with the level of production dependenton governmental policies in major producing countries (UNCTAD, 2015). Around the world, 64 countries have implemented targets or mandates related to theuse of biofuels: EU-27, 13 countries in the Americas, 12 in Asia-Paciﬁc, 11 in Africaand the Indian Ocean, and 2 from non-EU countries in Europe (Ukraine and Norway)(Lane, 2014). Besides the EU-27, with its Renewable Energy Directive (RED) thatspeciﬁed a 10% renewable content by 2020 (scaled back in recent times to5e7.5%), the major blending mandates that will drive global demand are those setin the US, China, and Brazil (15e25% by 2020e22). Present governmental policies may be reinforced in the 196 countries that submittedthe last Conference of the Parties held in Paris (November 30, 2015, to December 11,2015) that recognizes the urgent and potentially irreversible threat to human societiesand the planet that climate change represents. In this way, parties are encouraged totake actions in order to promote their obligations on human rights, the rights of devel-opment and health, the protection of indigenous people, local communities and chil-dren, as well as gender equality and intergenerational equity, among other humanuniversal rights (United Nations, 2015). The most relevant intended contribution ofthe Parties Conference relates to a reduction in aggregate greenhouse gas emissionsto preindustrial levels (40 Gt), holding the increase on global average temperatureto below 2C in 2030. In accordance with the adoptions of the Paris agreement, challenges to biofuel devel-opment in the 21st century must take into account the environmental sustainability of thewhole industrial processes (from cradle to grave) leading to biofuel production, in whichdeforestation and forest degradation play a key role, mostly in developing countries.Handbook of Biofuels Production, 2e. http://dx.doi.org/10.1016/B978-0-08-100455-5.00005-9Copyright © 2016 Elsevier Ltd. All rights reserved.
86 Handbook of Biofuels Production Calculation of greenhouse gas emissions (GHG) savings for biofuels are not easybecause they depend strongly on the production process, raw materials origin, andthe need for transportation, among other factors. The USDA Foreign Agricultural Ser-vice reports calculated values for different raw materials, selected production and sup-ply routes, in the EU Biofuels Annual 2014, based on life cycle assessment (LCA).The results, presented in Table 5.1, do not include net carbon emissions from indirectland-use change (Flach et al., 2014). There are several voluntary certiﬁcation systems such as the International Sustain-ability and Carbon Certiﬁcation (ISCC), the Round Table of Sustainable Biofuels EURED (RSB EU RED), or the Brazilian bioethanol veriﬁcation program (Greenenergy),among others, to ensure that biofuels meet certain sustainability criteria (Flach et al.,2014). Different generations of biofuels that coexist at the moment are classiﬁed not onlyin accordance with the raw materials employed, but also the sustainability of the con-version technologies involved in their production processes (Naik et al., 2010). First-generation biofuels are made using conventional chemical technology toconvert mainly oilseeds and grains into biodiesel and bioalcohol, respectively. Inmany cases, the same feedstocks can be used for animal or human feeding purposes,thus suffering criticism from organizations that point at biofuels as the leading factorfor food price rises and even deforestation including in the Amazon or Indonesia. Second-generation biofuels are based on nonfood crops (ie, Miscanthus) andbiomass residues (from crops and forests), thus providing an alternative that is sociallyacceptable. However, conversion technologies to produce biohydrogen, Bio-DME,FischereTropsch diesel, etc. are still under development. The overall efﬁciency andTable 5.1 Greenhouse gas emissions savings for different rawmaterials/processing methodsRaw material/process SavingsRapeseed biodiesel 38%Soybean biodiesel 31%Sunﬂower biodiesel 51%Palm oil biodiesel/unknown process 19%Palm oil biodiesel/process with methane capture at oil mill 56%Corn ethanol/locally produced and using natural gas as process fuel 49%Sugar beet ethanol 52%Sugarcane ethanol 71%Waste vegetable or animal oil biodiesel 83%Adapted from Flach, B., Bendz, K., Lieberz, S., 2014. EU Biofuels Annual 2014. U.F.A. Service. The Hage,USDA Foreign Agricultural Service.
Feedstocks and challenges to biofuel development 87land-water use of biofuel production represent a great concern; thus agricultural sys-tems (with different agronomic practices and biophysical factors) vary in terms of en-ergy inputs and outputs (van Duren et al., 2015). To serve as an example, A. Voinovet al. examined the potential of road verges (already polluted and disturbed areas) inthe Netherlands for biomass production, using geographical information systems(GIS), with very promising results (Voinov et al., 2015). There is also an emerging third-generation biofuel produced from algae and even anincipient fourth generation based on the conversion of biodiesel into gasoline or onthe recycling of carbon dioxide back into gasoline. Some companies claim that theycan produce economically sound petroleum from microorganisms with the ability to efﬁ-ciently convert renewable feedstocks into hydrocarbon-based fuels (Du et al., 2008).5.2 Edible vegetable raw materials for biodiesel productionMost relevant attributes for oily crops used in the production of biodiesel are oil yield(kg/ha), related to economic proﬁtability and land use; and fatty acid composition, thatrelates to engine performance, noise, and pollution emissions and the physical proper-ties of biodiesel (Redel-Macias et al., 2012, 2013, 2014; Pinzi et al., 2013). Global production of major vegetable oils for 2014/15 was 176.23 million metrictons, including coconut, cottonseed, olive, palm, palm kernel, peanut, rapeseed, soy-bean, and sunﬂower seed oil (Agriculture, 2015). Table 5.2 depicts the productionof major oilseeds and vegetable oils worldwide in 2014/15. The agricultural outlookfor 2015e20, published by the Food and Agricultural Organization of the UnitedNations (FAO) (Nations, 2015), reports that production of vegetable oil will suffer aremarkable restrain during the next decade in countries producing high-oil-yieldingcrops (eg, sunﬂower, rapeseed), due to limited growth in biodiesel production. Never-theless, increasing demand for protein meal worldwide will result in an expansion ofoilseed areas that traditionally produce soybeans for their high protein meal content.For the same period of time, use of edible oils for biodiesel production is projectedto account for more than 33% of the expected growth in edible oil use, which impliesan increase in water requirements (and therefore less water availability), more landsdedicated to intensive agriculture (with the consequent increase in GHG emissions)and higher biomass prices (Ahmia et al., 2014). Recent life cycle assessment (LCA) studies, to assess the environmental impactand use of resources during the life cycle of biodiesel, reveal that there are lessGHG emissions in second-generation biodiesel when compared with the ﬁrst gener-ation (Chatterjee et al., 2015). Therefore, research on edible oil biodiesel productionis mostly focused on cost competitiveness and sustainability of the process through:• Search for heterogeneous-based inorganic/organic catalysts (low cost and eco-friendly, thus they can be obtained from natural sources or industrial wastes) that have shown a highly effective low-cost catalytic performance, while eliminating waste from the environment (Veljkovic et al., 2015). Investigation is mainly focused on the search for new renewable
88 Handbook of Biofuels ProductionTable 5.2 Major oilseeds, vegetable protein meals andvegetable oil production worldwide in 2014/15(million metric tons)Production Oilseed Protein meals Vegetable oilCottonseed 44.34 15.48 5.13Olive 2.40Palm d d 61.44Palm kernel 7.20Copra/coconut d d 3.34Peanut 16.29 8.62 5.52Rapeseed 5.43 1.79 27.11Soybean 39.41 6.75 48.99Sunﬂower seed 72.12 40.23 15.10Total 319.00 207.20 176.23 39.98 15.87 536.56 295.95 Reproduced from Agriculture, U.S.D.O., 2015. Oilseeds: World Markets and Trade. F.A. Service, United States Department of Agriculture, p. 37. materials to produce low-cost catalysts, upgrade of their performance in environments with the presence of water and CO2, reduction of its dosage and recovering.• Use of auxiliary energies, such as microwave heating and low/high-frequency ultrasounds in order to accelerate the reaction, diminishes alcohol and catalyst dosage and increase the pro- duction yield of transesteriﬁcation.• Technoeconomic and environmental evaluation of the production processes in different sce- narios: environmental and economic inﬂuence of land size, use of fertilizers, plant capacity (large or farm scale), use of hybrid cultivars, life-cycle assessment of processes and adapta- tion to every region (Barontini et al., 2015).• Valorization of all by-products from the oil industry in a bioreﬁnery concept. The valoriza- tion of glycerol and cakes in fermentative processes for the production of biofuels, bio- plastics, and value-added chemicals serves as an example (Koutinas et al., 2014). Most frequent edible vegetable raw materials to produce biodiesel are presented inthis section.5.2.1 Rapeseed/canola seedRapeseed (Brassica napus) is widely cultivated throughout the world for the produc-tion of animal feed, cooking vegetable oil, and as a biodiesel. The seeds contain about40% oil, and after oil extraction, a rapeseed cake with 38e43% protein remains. Itbelongs to the Brassicaceae family. Rapeseed is one of the most important oilseeds in the world, ranking second inrespect to production after soybean (Division, 2014). Back in 2005, the European
Feedstocks and challenges to biofuel development 89Table 5.3 Global bioethanol production and raw materialsby country in 2014Country Share Production (%) (mill. US gallons)a Raw materialsUnited States 58 14,300 Corn and sorghymbBrazil 25 6190 SugarcanecEurope 6 1445 Sugar beet, corn, wheat, rye, and barleydChina 3 635 Corn, wheat, tapioca, cassava, sweetCanada 2 510 sorghum stalks, and corncobe 1 310Thailand 1 160 Corn and wheatb 1 155 Sugarcane, molasses, cassava, and ricefArgentina 3 865 Grain, molasses, and juiceg Sugarcane, molasses, and grainshIndia 100 24,570 VariousRest of the world Corn, sugarcane, molasses, cassava, rice sorghum, sugar beet, wheat, rye, andTotal barley productionaAssociation (2015).bBalat and Balat (2009).cBarros (2015).dFlach et al. (2014).eJi (2015).fPrasertsri (2015).gJoseph (2015).hAradhey (2015).Union (EU) was the world leading biodiesel producer and third in biofuel production;60% from the total of 10.2 billion liters of biodiesel produced worldwide in 2007 wasproduced in the EU. Rapeseed, cultivated in most European countries, accounted formore than half of the European production of biodiesel with a share of 79% of allEU biodiesel feedstock crops in 2008 (van Duren et al., 2015). Rapeseed-based biodiesel production has been widely studied in terms of optimizationand kinetics of alkali catalyzed transesteriﬁcation reaction (Luque et al., 2011). Recently,production of solid base catalysts, such as Ca/Zr mixed oxide catalysts (Liu et al., 2015),CaO-based catalysts or 4-sulfophenyl activated carbon-based solid acid catalyst, has beenreported with a performance similar to commercial heterogeneous catalyst Amberlyst-15(Malins et al., 2015). Present researches are also focusing on the use of supercriticalethanol and methanol as reagents to avoid drawbacks due to the use of homogeneous cat-alysts (Farobie and Matsumura, 2015a,b). Technoeconomic and performance studies onthe use of supercritical methanol concluded that lower direct costs and environmental im-pacts are achieved at highest biodiesel yields, where oil consumption per unit of biodiesel
90 Handbook of Biofuels Productionproduced is the lowest, despite a signiﬁcant increase in the reaction temperature (Tomicet al., 2015). The inclusion of auxiliary energies, such as microwave heating (Azcan andDanisman, 2008), or ultrasound (Saez-Bastante et al., 2014a,b) to improve biodiesel con-version rate has also been studied. The consequences of use and production of rapeseed-based biodiesel, such as performance in diesel engines and combustion kinetics, bothexperimental and simulated numerically (Alviso et al., 2015), LCA related to cultivationconditions (Queiros et al., 2015), or the degradation of sealing materials in aviation(Dubovsky et al., 2015) have been of major concern recently. Canola, the name of which derives from Canadian oil with low erucic acid, is arapeseed cultivar (Brassica napus L. and B. campestris L.), with a content of 40%oil and a high yield of oil per acre (127e160 gallons/acre) (Pahl, 2008). The mainuse of the oilseeds is human consumption, due to the lower level of erucic acidcompared to traditional rapeseed oils. It is also used to produce livestock feed dueto reduced levels of the toxin glucosinolates in the cake. Canola-based biodiesel gels at a lower temperature than the one produced fromother feedstocks make it a more suitable fuel for colder regions, with a “cloud point”of 1C and a “pour point” of À9C (Peterson et al., 1997). The Canola Council of Can-ada published in 2010 an LCA study on canola biodiesel that shows a crop with a goodenergy balance and a lower GHG emissions proﬁle when cultivated in Canada ratherthan in Europe. These effects are due to differences in the agronomic process: lowannual precipitation (less N2O emissions), alkaline soils (no pH adjustment required),use of ammonium-type fertilizers (with lower emissions than nitrate ones), and conser-vation tillage practices, among other factors (Inc., 2010). Recent studies have shown a good performance and possibility of controlling trans-esteriﬁcation reaction when heterogeneous catalysts based on functionalized CaOnanoparticles (Degirmenbasi et al., 2015), or honeycomb monolithic catalysts, formu-lated by impregnation with various metals such as ZnO, Na2O, MgO, and CaO (Kwonet al., 2015), are used for canola biodiesel production. Enzymatic catalysis using Alca-ligenes sp. lipase revealed the potential of biological and environmentally friendly cat-alysts to replace conventional homogeneous processes, even though they still presentsome inhibitory effects of methanol (Soler et al., 2016). Experiments under supercrit-ical conditions have also been performed for canola biodiesel production. Farobie et al.(2015) proposed a spiral reactor, as effective as a conventional one, with the advantageof a better performance in terms of heat recovery, using supercritical ethanol and su-percritical t-butyl methyl ether (MTBE) (Farobie and Matsumura, 2015a,b). Finally, biolubricants based on canola biodiesel have the potential to substitutepetroleum-based automotive lubricants; thus they present low cloud and pour pointproperties, good friction and antiwear properties, low phase transition temperature,and low viscosity (Sharma et al., 2015).5.2.2 Sunﬂower seedSunﬂower (Helianthus annuus L.), a member of the Compositea family, is an impor-tant oilseed crop worldwide, yielding approximately 45e50% oil with the qualitydepending on the region (Pereyra-Irujo et al., 2009). Sunﬂower oilseed and oil
Feedstocks and challenges to biofuel development 91production worldwide for 2014 and 2015 were 39.98 million metric tons (MMT) and15.10 MMT, respectively, with an estimation of 39.65 and 15.13 MMT, respectively,for 2015 and 2016, located in Ukraine, followed by Russia, EU, and Argentina, ac-cording to the Foreign Agricultural Service of the United States Department of Agri-culture (Agriculture, 2015). Recent studies of sunﬂower-based biodiesel production are focused on the sustain-ability of the production process (reduction of water and energy inputs, and catalystreuse) as well as on the simpliﬁcation of the operation process. Solid catalysts based on CaO are highly basic, require mild reaction conditions for ahigh biodiesel yield, have low or no cost, and can be produced easily from biobasedmaterials or wastes. In this sense, Kostic et al. reported the production of sunﬂowerfatty acid methyl esters (FAME) using a CaO-rich palm kernel shell biochar catalyst,obtained from a gasiﬁer for electricity production, demonstrating the potential of low-cost basic catalysts in transesteriﬁcation reactions (Kostic et al., 2016). Severe calcina-tion of eggshells provides a uniform CaCO3/CaO-based catalyst suitable for sunﬂowertransesteriﬁcation that loses activity in the presence of atmospheric air but can berecovered by methanol washing (Reyero et al., 2015). Calcium diglyceroxide(CaDG) catalyst, synthesized by mechanochemical treatment of lime-based CaOand glycerol, was reported to acts as an emulsiﬁer and therefore to increase the inter-facial area between oil and methanol in sunﬂower FAME production (Lukic et al.,2016). Miladinovic et al. also demonstrated a good performance of quicklime bits-based CaO catalyst on a packed-bed reactor for the continuous production ofsunﬂower-based FAME (Miladinovic et al., 2015). New trends in the ﬁeld of biodiesel production are oriented toward the use of ethanolinstead of methanol, due to its higher oil-dissolving power, lower toxicity and biode-gradability (Anastopoulos et al., 2013). Fatty acid ethyl esters (FAEEs) also presentseveral beneﬁts, in comparison with FAME, such as higher values for heat contentand cetane number, lower cloud and pour points, lower smoke density, lower nitrogenoxide and carbon monoxide emissions, and completely biorenewable origin. Heteroge-neously catalyzed ethanolysis of sunﬂower oil was studied by several authors usingdifferent catalysts such as CaO (Avramovic et al., 2015), calcium zincate (MiguelRubio-Caballero et al., 2013), or calcium ethoxide Ca(OCH2CH3)2 (Anastopouloset al., 2013) for basic transesteriﬁcation, as well as zirconium sulfate supported onMCM-41 silica as acid ethanolysis catalyst (Jimenez-Morales et al., 2011). Despite research on heterogeneous catalysts having taken place for the last three de-cades, to date several disadvantages make them less cost competitive and not as envi-ronmentally friendly as traditionally used homogeneous catalysts. As an example, theexcellence of CaO-based catalysts are numerous and well proven, but they still remaindistant from the industry due to their low resistance to water and CO2, low attritionendurance, and solubility in biodiesel and alcoholic phases, which results in ion con-centrations exceeding the limits imposed by the European Norm EN14214 (Micicet al., 2015). Auxiliary energies, like low-frequency ultrasonication using ethanol (Georgogianniet al., 2008), and methanol in combination with FTIR (Fourier transform infrared)method to monitor the reaction (Reyman et al., 2014), have been proposed to enhance
92 Handbook of Biofuels Productionthe reaction yield in transesteriﬁcation reactions for sunﬂower-based biodiesel produc-tion. Ultrasound technologies have also been researched to reduce methanol excessand enzyme dosage during biodiesel production, using immobilized lipases (eg, fromThermomyces lanuginosus), resulting in a cleaner process (Subhedar et al., 2015), andfor online monitoring of the transesteriﬁcation reaction means low-power ultrasoundand pulse/echo techniques (Figueiredo et al., 2015). Microwave-assisted transesteriﬁca-tion has been extensively used with basic and acid heterogeneous catalysts demon-strating that those based on calcium oxide (CaO) and potassium carbonate, pure orsupported by alumina, were the most efﬁcient when using sunﬂower as raw material(Dall’Oglio et al., 2014). The combination of microwaves and enzymatic catalyst forthe production of FAME (Narowska et al., 2015) and FAEE (Queiroz et al., 2015) usingCandida antarctica-based enzymes was reported to be faster and to provide higheryields than using conventionally heated reactors.5.2.3 Palm treeElaeis guineensis is an edible oleaginous plant, known as African oil palm or macaw-fat. This tree produces three different edible oils: palm oil extracted from the pulp ofthe palm fruit, coconut oil and palm kernel oil extracted from the kernels of the coconut(copra), and oil palm (Reeves et al., 1979). Palm oil can also be obtained from theAmerican oil palms Elaeis oleifera and Attalea maripa, but only hybrids between thesespecies are planted commercially; thus they present higher disease resistance andlower unsaturated fatty acid proﬁles in the oil. Due to high productivity of palm oil trees, palm oil production has increased in thelast 20 years being to date the most important oil worldwide (61.44 MMT in 2014/15),with production located mainly in low-lying, wet, tropical regions, such as Indonesia(35.0 MMT), Malaysia (21.0 MMT), and Thailand (2.2 MMT) (Agriculture, 2015).Unfortunately, rainforest also occurs in these areas, and therefore about 3.5 millionhectares of forest in Indonesia, Malaysia, and Papua New Guinea were replaced bypalm tree intensive cultivars in the last two decades, which implied the release of largeamounts of CO2 (when peat soils are cleared and drained), and loss of clean waters andfertile soils (Nature, 2010). A good representation of a growing demanding shift to sus-tainable palm oil production is the 18% of global palm oil production that was certiﬁedas sustainable by the non-for-proﬁt association Roundtable on Sustainable Palm Oil(RSPO) in 2014. Sustainability criteria required to obtain this certiﬁcation are: landused may not contain signiﬁcant biodiversity, wildlife habitat or other environmentalvalues, and exploitation should meet certain environmental, social and economicstandards (Oil, 2015). Palm oil is extensively used for cooking, cosmetics, and biofuel production usinghomogeneous catalysts (Darnoko and Cheryan, 2000; Crabbe et al., 2001). Themain research ﬁeld on biodiesel production from palm oil is focused on basic andacidic heterogeneous catalysis, searching for renewable bio-based materials such asincomplete carbonized glucose and starch (Lokman et al., 2016) for supercritical trans-esteriﬁcation. Inorganic catalysts based on nickel (Ni/HZSM-5) (Chen et al., 2016) ormixed oxide catalysts based on CaO-CeO2 (Wong et al., 2015), among others, have
Feedstocks and challenges to biofuel development 93also been tested, showing good results but also some active phase leaching and poreinactivation by ﬁlling. Due to thermal and oxidation instability of FAME produced meaning transesteriﬁ-cation, other methods such as catalytic cracking and hydrodeoxygenation of oils, toproduce fuels or blending components, are the objective of the study. Even though cat-alytic cracking is not hydrogen-consuming, it exhibits some drawbacks such as lowselectivity, side reactions of cyclization, and formation of aromatics. Wang et al. pro-posed a hydrogenation process for palm oil using a Ni-Mo-W/g-Al2O3-ZSM-5 cata-lyst, yielding a biodiesel that almost conformed to the European EN-590 standardnorm (Wang et al., 2015). Concerning energy saving in the industrial process, a continuous process for theproduction of palm-oil-based biodiesel in a microwave reactor was demonstrated tobe less time- and energy-consuming than traditional methods, while providing a99.4% yield on biodiesel in accordance with EN/ASTM standards (Choedkiatsakulet al., 2015). Simultaneous ultrasoundemicrowave irradiation for a transesteriﬁcationprocess with methanol resulted in a completed conversion within 2.2 min, yielding a97.53% of FAME reducing temperature to 58.4C. Low-cost palm stearin, the solid fraction of palm oil, produced by partial crystal-lization under temperature-controlled conditions, is normally used for food applica-tions but it causes manufacturing problems because of its low plasticity properties inedible fat end-products due to a high saturation degree in the fatty acids proﬁle:1e2% C14:0, 47e74% C16:0, and 4e6% C18:0. Theam et al. proposed the produc-tion of stearin-based biodiesel meaning heterogeneous metal doped calcium methox-ide based catalyst, with promising FAME yield results, even though betterconditioning of catalyst is necessary to improve its durability and performance(Theam et al., 2015). Good performance of palm oil biodiesel and its blends in diesel engines was alreadyreported and can be consulted in the previous edition of this book (Luque et al., 2011).5.2.4 Soybean seedSoybean (Glycine max) oil, used as an edible oil and transportation fuel, is the secondmost produced oil in the world, accounting for 48.99 MMT in 2014/15. China, theUnited States, and Argentina are the largest soybean oil producers accounting for13.4, 9.7, and 7.7 MMT, respectively. China also presents the greatest domestic con-sumption of soybean oil (14.1 MMT), followed by the United States (8.61 MMT) andBrazil (6.3 MMT) (Agriculture, 2015). Soybean oil-based biodiesel has been produced via homogeneous catalyst in thepresence of methanol for more than 20 years but its fatty acid composition needs tobe genetically modiﬁed in order to produce a biodiesel viable for colder regions(Luque et al., 2011). In recent years, research have been conducted with heterogeneous catalysts mainlybased on calcium, such as CaFeAl mixed oxide (Lu et al., 2015), magnetic nanopar-ticle MgFe2O4@CaO (Liu et al., 2016) or Ca-Mg-Al hydrotalcites (Xu et al., 2015)with good stability and recyclability properties.
94 Handbook of Biofuels Production Use of heterogeneous and homogeneous catalysts reinforced by auxiliary energieslike microwaves (Li et al., 2013; Muley and Boldor, 2013; Ye et al., 2014) or ultra-sound (Yu et al., 2010) generated interesting results concerning catalyst reuse aswell as time and energy savings. Soapstock acid oil, a concentrated by-product of the soybean oil reﬁning processbased on fatty acid salts, was proposed by Soares et al. as a raw material for the pro-duction of biodiesel via acid heterogeneous catalysts using ethanol. The esteriﬁcationreaction was conducted in a packed-bed bioreactor containing a lipase-rich fermentedsolid (sugarcane bagasse and sunﬂower seed meal fermented by Burkholderia cepacia)with a conﬁguration that avoided inhibition of the catalyst by the presence of ethanol(Soares et al., 2015). Combustion and emission characteristic tests on soybean oil biodiesel have beenperformed to assess the health effects associated with soybean-based biodiesel emis-sions. A program at the US Environmental Protection Agency (EPA) showed recentlythat particulate mass (PM) emissions were 30% lower with B100 combustion,compared to B0 (pure petroleum-derived diesel). Moreover, the latest results werealso richer in CO, while being slightly lower in NO and organic acids than B100(Mutlu et al., 2015). Different engine conﬁgurations and working pressures, oxygen concentration andlow-temperature combustion models have been extensively studied in order to reduceoxides of nitrogen and unburned hydrocarbons, as well as to improve the combustionefﬁciency of soybean-based biodiesel (Narayanan and Jacobs, 2015). Different rangesof intake pressure and oxygen concentration in a compression-ignition engine were re-ported by Kim et al. to have inﬂuence on thermal efﬁciency and CO emissions, but noton NOx ones (Kim et al., 2014). Soot formation in biodiesel combustion represents amajor concern for researchers. Xiao et al. studied the inﬂuence of temperature and ox-ygen concentration over soot appearance and concentration ﬁnding an opposite trendon soot creation behavior for different temperature ﬂames: soot formation was delayedat lower ﬂame temperatures (800 K) and decreased when lowering oxygen concentra-tions, while under higher temperatures (1000 K), soot mass increased while decreasingoxygen concentrations (Xiao et al., 2014). New geometries for engines, such aschamfered-bowl pistons were also proved to reduce soot, and provide a wider fuel dis-tribution and enhanced combustion under low-temperature conditions (Kim et al.,2015). Enhancement of fuel properties and emission levels were the main targets whenstudying blends of soybean-based biodiesel with n-butyl ether, that promotes the atom-ization of biodiesel (Guan et al., 2015), canola-oil-based biodiesel (Lee et al., 2014),alumina nanoparticles, ethanol and isopropanol (Shaaﬁ and Velraj, 2015), or ﬁeld-cress and meadow oils (Moser, 2016).5.2.5 Peanut seedPeanut (Arachis hypogaea L.), an annual crop widely cultivated in warm climates,was traditionally grown in the Mediterranean region, but nowadays China is the largest
Feedstocks and challenges to biofuel development 95world producer of this crop accounting for 16.5 and 2.7 MMT of peanut seeds and oil,respectively, in 2014/15 (Agriculture, 2015). Global production in 2014/15 was 5.52MMT for peanut oil and 39.41 MMT for peanut seeds. Most peanuts grown around the world are used for oil production, peanut butter,confections, and snack products (Yu et al., 2007). Even though Rudolf Diesel ranthe diesel engine for the ﬁrst time in 1900 using pure peanut oil (Luque et al.,2011), its biodiesel is not of major importance among researchers, most probablydue to its bad cold-ﬂow properties. Studies about peanut oil-based biodiesel havebeen focused on the reduction of long-chain saturated acid concentration, usingdifferent methods such as winterization (Perez et al., 2010), addition of antioxidantsto prevent oleate and linoleate ester oxidation (Pinto et al., 2015), or reduction ofthe production costs using in-ﬁeld shelling equipment (Butts et al., 2009) and hetero-geneous bio-based catalysts (Shah and Gupta, 2008).5.2.6 Cotton seedCotton is the common name for Gossypium spp., a tropical and subtropical plant fromthe Malvaceae family. In 2014/15, 44.34 MMT of cotton oilseeds were producedworldwide, generating 15.48 and 5.13 MMT of cottonseed meal (mainly for ruminantfeeding) and oil, respectively, located mainly in China, India, United States, andAustralia (Agriculture, 2015). Cotton ﬁber grows around the seeds and is used to make natural ﬁber-cloth (Dorado,2008), while the seeds contain only approximately 16.5% of oil (Bailey, 1984) which isused mainly for the production of cooking oil, margarine and nowadays, after a deodor-ization process, it is also used in oil dressings and mayonnaises. The same as other vegetable oils, production of cottonseed-based biodiesel hasbeen conducted under inorganic heterogeneous catalysts, such as ethanolysis withCaO-Mg/Al2O3, (Mahdavi and Monajemi, 2014) or in situ extraction and biodieselproduction with magnetic S2O8/ZrO2-TiO2-Fe3O4 and methyl acetate (Wu et al.,2014). Pseudomonas ﬂuorescences (Karuppasamy et al., 2013) and Rhizopus oryzae(Athalye et al., 2013) lipases were also studied as biocatalysts for FAME productionwith cottonseed oil. Most interesting investigations in this ﬁeld include different approaches to the bio-reﬁnery concept involving cottonseed. To serve as an example, Zhu et al. proposed theproduction of biodiesel, sterols, gossypol, and rafﬁnose and nontoxic cottonseed mealin an integrated bioreﬁnery, by a two-phase extraction process, using supercriticalmethanol (Zhu et al., 2014). Simultaneous production of alpha-tocopherol (a naturalantioxidant) and FAME was also presented as a viable bioreﬁnery concept (Zhuet al., 2012). Cottonseed methyl esters were tested in a four-stroke locomotive diesel resulting ina 0.7% loss of thermal efﬁciency, 32% reduction of particulate matter emissions, in-crease of NOx emissions as a function of several combustion parameters (eg, O/C ratioor injection timing) and a brake speciﬁc fuel consumption (BSFC) 13.4% higher thanpure petrodiesel (Gautam and Agarwal, 2013).
96 Handbook of Biofuels Production5.3 Nonedible/low-cost raw materials for diesel engine biofuel productionAs mentioned before, the use of edible vegetable oils for the production of biofuelscreates competition in food markets and increases commodity prices, affecting thefood chain. The main target of the scientiﬁc community should be the use of nonedible,low-cost, low-input, and sustainable raw materials for biofuel production. In this senseselection of indigenous vegetable oils may be a source of alternative fuels dependenton each climate region. Dorado and Pinzi already studied Aclepias syriaca seed, a milkweed native fromNortheast and North Central United States, Moringa oleifera seed and Terminalia cat-appa, as the most suitable low-cost vegetable raw material for biodiesel production, inthe ﬁrst edition of this book (Luque et al., 2011). Oleaginous crops like Bahapilu,castor, cuphea, Jatropha curcas, karanja seed, linseed, mahua, nagchampa, neem, rub-ber seed, tonka bean; low-cost edible oils like cardoon, Ethiopian mustard, Gold-of-pleasure, tigernut; and potential oil-bearing crops and trees like allanblackia, bitteralmond, chaulmoogra, papaya, sal, tung and ucuuba have already been revised andan extensive revision can be found in a previous work (Dorado, 2008). Transesteriﬁed biodiesel presents some drawbacks, such as high corrosion prob-lems, oxidation instability, methane toxicity, high viscosity, and high cost comparedto conventional diesel (Muthukumaran et al., 2015). Therefore, alternative methodsof fuel production from vegetable oils will also be discussed in this section.5.3.1 Green canola seedGreen seed canola oil is a low-quality and cheap green oil, rich in chlorophyll.Compared to green seed canola oil, pure canola oil is a crystal yellow color withlow chlorophyll content and is produced from canola seeds with low green seed con-tent (Luque et al., 2011). This high chlorophyll content in the oil prevents it fromedible purposes as it promotes oxidative degradation that inhibits hydrogenation toproduce margarine and generates bad odors. These circumstances make green canolaseed a good candidate for biodiesel production with no competition on food markets. Its higher content of linoleic and linolenic acids, compared to pure canola oil, pro-vides green seed canola biodiesel (GSCB) with a lower cloud point and good fuel qual-ity parameters, but its oxidation stability is lower than required by the internationalstandards and needs to be improved to be considered a viable diesel fuel alternative(Kulkarni et al., 2006). In this sense, Issariyakul and Dalai demonstrated that biodieselproduced via homogeneous KOH-catalyst, applying a montmorillonite K10 blanchpretreatment to remove pigments from green seed canola oil, shows better oxidativestability (Issariyakul and Dalai, 2010). Baroi and Dalai discovered a solid acid catalyst(12-tungstophosphoric acid) for simultaneous esteriﬁcation and transesteriﬁcation ofgreen seed canola oil, able to adsorb chlorophyll from the feedstock, improving bio-diesel quality (Baroi and Dalai, 2013). Production of GSCB by homogeneous and heterogeneous acid catalysis has beenevaluated in terms of sustainability including process economics, process safety,
Feedstocks and challenges to biofuel development 97environmental impact, and process energy efﬁciency. The most interesting conclusionof this study was that whenever feedstock price is under $0.35/kg, both catalysts con-ﬁgurations are economically proﬁtable, but the heterogeneous acid catalyzed process issafer, creates less environmental impact, and is more energy-efﬁcient, and thereforemore sustainable (Baroi and Dalai, 2015).5.3.2 Callophyllum inophyllum L.Calophyllum inophyllum L. (C.I.), also known as Alexandrian-laurel, Indian-Laurel,balltree, or beach-touringa, among other common names, is an evergreen tree nativeto east Africa, southern coastal India to Malasia and Australia (System, 2012). It isa good candidate for green energy production due to its high oil content (up to33.46% under optimal oil extraction conditions) (Fadhlullah et al., 2015), high fruitproduction rate, simple cultivation, and adaptation to different climate conditions(Jahirul et al., 2014). The fatty acids proﬁle of C. inophyllum, shown in Table 5.4, is mostly rich in unsatu-rated oleic (C18:1) and linoleic (C18:2) acids. Due to its high content of free fatty acids(FFA), and therefore high viscosity, that has removed it from biodiesel production formany years, it was selected by Muthukumaran et al. for the production of biofuel througha cracking process, using as catalyst inexpensive ﬂy ash, improving fuel viscosity andcaloriﬁc value when compared to the transesteriﬁcation process (Muthukumaran et al.,2015). Blends of cracked end-product were tested in a diesel engine showing that B25had comparable emissions and brake thermal efﬁciency to diesel, and that modiﬁcationson diesel engine must be accomplished to get better performance with pure biofuel. C.I. fruit shell was also used for the production of pyrolytic oil by Alagu et al. byboth thermal and catalytic (zeolite, kaolin, and Al2O3) pyrolysis processes, demon-strating that zeolite catalyzed pyrolysis generates a biofuel with improved caloriﬁcvalue and acidity (Alagu et al., 2015). C.I.-based trimethylpropane ester was also eval-uated as a biodegradable lubricant in substitution of commercial lubricant and parafﬁnmineral oil with encouraging results (Habibullah et al., 2015a,b). Recently, Atabani and Cesar reported the feasibility of C.I. as raw material forsecond-generation biodiesel production, considering its chemical properties, fattyacid composition, production technologies, and engine performance (Atabani andCesar, 2014). Most researchers complete a minimum of two steps in the productionprocess of CIBD (pre-esteriﬁcation/transesteriﬁcation) in order to avoid soap forma-tion in the presence of FFA (Jahirul et al., 2014). Other authors also propose a previousdegumming step (Ong et al., 2014). Long-chain unsaturated fatty acids esters con-tained in C.I.-based biodiesel are highly prone to oxidation. Synthetic antioxidant py-rogallol added at 500 ppm (Fattah et al., 2014a,b) and 2-tert-butylbenzene-1,4-diol(TBHQ) at 2000 ppm concentration (Fattah et al., 2014a,b) are good candidates todelay this degeneration stage. Bio-based heterogeneous catalysts, such as renewable cellulose/starch-derivedcatalysts (Ayodele and Dawodu, 2014a,b) or immobilized Rhizopus oryzae cells(Arumugam and Ponnusami, 2014), have been reported as good candidates to improvethe efﬁciency and sustainability of this nascent biofuel.
Table 5.4 Fatty acid methyl esters composition of nonedibleRaw material C12:0 C14:0 C16:0 C16:1 C18:0 C18: wt.% wt.% wt.% wt.% wt.% wt.%Azadirachta d 2 13 d 24 62 indica d d 14.8e18.5 d 6.0e9.0 36e5 d 0.2 4.5e5.7 d 3.9e5.2 11.8eCalophyllum inophyllumCroton megalocarpusMoringa d 0.1 13.8 1.1 4.7 72.1 oleifera d 3e10 30e7 d d 8e22Annona
vegetable oils for biodiesel production :1 C18:2 C18:3 C20:0 Others References% wt.% wt.% wt.% wt.% SathyaSelvabala 10 3.2 d et al. (2010)53 16e29 d 2.5e3.5 Muthukumaran et al. (2015)e13.9 70.5e71.6 3.7e6.9 d 1.9 Kivevele et al. 2.5 0.9 3.8 0.9 (2011a) and70 8e49 1e3 1 d Kivevele and Huan (2015) Kivevele and Huan (2015) Egydio and dos Santos (2011) and Reyes-Trejo et al. (2014)
Feedstocks and challenges to biofuel development 99 Engine tests carried out in recent years demonstrate good properties of this second-generation biodiesel as a lubricant in blends with traditional diesel (Habibullah et al.,2015a,b) that may be enhanced with addition (5e10%) of the oxygenated cold start-ing additive n-butanol (Imtenan et al., 2015), or gas to fuel (GTL, synthesized bymethane reforming, FischereTropsch synthesis or hydrocracking processes) in ablending mix containing 50% diesel, 30% CIBD, and 20% GTL (Sajjad et al.,2015). Comparative tests determined that the combustion duration of CIBD is higherthan diesel, while the ignition delay period is shorter (Nayak et al., 2015). It is alsoproved that CO and HC emissions are reduced in blends with diesel, while NOx con-centration in exhaust gas is increasing with higher concentrations of CIBD in blends(Rahman et al., 2013).5.3.3 AnnonaAnnona is a large genus from the Annonaceae family, containing approximately 166species of trees and shrubs, some of them producing edible sweet fruits used for nour-ishment (commercialized as fresh fruit or frozen pulp among others) or medicinal pur-poses (Egydio and dos Santos, 2011). Its seeds, a waste from the industrial process,contain high amounts of oil, yielding approximately 20e42% (w/w) depending onthe species. In some species, this oil contains neurotoxins that prevent it from havingedible purposes. Several authors have explored the potential of Annona oil for second-generationbiodiesel (AOBD) production as its low acid value and fatty acid proﬁle (rich in oleicand palmitic acids) bestows excellent properties on AOBD, meeting the internationalstandards ASTM D6751 (Reyes-Trejo et al., 2014) and EN14214 (Branco et al., 2010).Characterization of several Annona species showed different yields and fatty acid pro-ﬁles as Table 5.5 depicts. The greatest differences have been found for palmitic acid(C16:0), oleic acid (C18:1), and linoleic acid (C18:2), therefore affecting biodieselproperties from different Annona species. Engine tests with Annona methyl esters (AME) aim to ﬁnd optimal engine designparameters (eg, injection pressure and timing, compression ratio) regarding gas emis-sions, BTE, or speciﬁc fuel consumption (SFC), among other performance qualityparameters. A B20 blend with diesel has been found to be optimal with no drawbacksor modiﬁcations on engine performance (Ramalingam et al., 2014; Senthil andSilambarasan, 2015a,b). Moreover NOx emissions in AOBD, as well as CO, smokeand HC, may be considerably reduced, compared to neat diesel, by addition of anti-oxidant L-ascorbic acid (200 ppm) to AME (Senthil and Silambarasan, 2015a,b). A bioreﬁnery approach using Annona cherimolla Mill. seeds was presented byBranco et al. including valorization of the residual lignocellulosic fraction that re-mains after oil extraction. Hemicelluloses were removed from the solid fractionby autohydrolysis, generating nondigestible oligosaccharides liable to industrial pro-cessing for food, pharmacy or cosmetic applications. The remaining solids presentedhigh enzymatic digestibility and were rich in cellulose, representing a good rawmaterial for further valorization routes (eg, bioethanol production) (Branco et al.,2015).
Table 5.5 Total lipids yield (g/kg) and fatty acid proﬁles Fatty acidsSpecies Yield 16:0 18:0 20:0 SataA. crassiﬂora 345.8 8 6 1 15A. coriacea 447.0 13 4 d 17A. montana 212.5 16 3 d 19A. cherimola 203.4e421.6 13e22 7e10 1 21e31A. diversifolia 210 16 5 d 22aTotal saturated (Sat) and unsaturated (Uns) fatty acid composition.
(%) of several Annona species 100 Handbook of Biofuels Production18:1 18:2 18:3 D 20:1 Unsa References50 34 1 85 Egydio and51 30 2 8330 49 2 81 dos Santos45e51 15e33 1e3 69e79 (2011)70 8 78.39 d Reyes-Trejo et al. (2014)
Feedstocks and challenges to biofuel development 1015.3.4 Croton megalocarpusCommonly known as croton, this ﬂowering plant belongs to the Euphorbiaceae familyand grows wild in tropical and template areas. Megalocarpus represents one of thenumerous species of croton revealed as a proﬁtable substitute for Jatropha in biodieselproduction, as well as a solution for desertiﬁcation in Africa, due to lower water re-quirements and high oil productivity (Milich, 2009). Endemic in east Africa, its nutsproduce 40e45% (w/w) of a nonedible oil rich in free fatty acids (Aliyu et al.,2010) traditionally used for medicinal purposes. It has been proposed for biodiesel production in a one-step esteriﬁcation processusing heterogeneous acid Si-based catalyst (Kafuku et al., 2010), with better resultsthan a noncatalytic supercritical methanol process, that still needs to achieve higherconversion yields and high temperature stability (Kafuku et al., 2011). One-step homo-geneous transesteriﬁcation process (using KOH) was also studied, yielding a maximumof 89.6% FAME, with good cold ﬂow and lubrication properties, but low oxidationstability compared to ASTM D6751 and EN14214 norms (Kafuku and Mbarawa,2010; Kivevele and Mbarawa, 2010). Addition of antioxidants seems necessary to pre-vent oxidation of linoleic methyl esters (70% approx.). Synthetic antioxidants such aspyrogallol (PY), propyl gallate (PG), butylated hydroxianisole (Kivevele et al., 2011b),and several transition metals (Fe, Ni, Mn, Co, and Cu) were studied, demonstrating bestperformances for PY and Cu, respectively (Kivevele and Huan, 2015). The effects of antioxidant addition on engine performance, exhaust emissions andcombustion parameters were also tested showing no effect on combustion characteris-tics, low effect on exhaust emissions, and lower brake speciﬁc fuel consumption(BSFC) when oxidants PY and PG were added (Kivevele et al., 2011a). Blends ofCroton megalocarpus oil, butanol, and diesel were also tested for engine performanceand gas emissions, obtaining higher BSEC, comparable heat release rate, and lowerCO2 and smoke emissions compared to pure diesel (Lujaji et al., 2011). A 6.5-KWeelectricity generator prototype, running also on pure Croton megalocarpuis oil, wasconstructed aiming to solve electricity supply problems in subSaharan Africa, withpromising results (Wu et al., 2013).5.3.5 Azadirachta indicaNeem oil is extracted from fruits and seeds of Azadirachta indica, a tree from theMeliaceae family native to India and the Indian subcontinent. It is highly drought-resistant, and not sensitive to water quality, tolerating temperatures above 35C butnot below 4C. More than 2000 years ago, neem products were already used for me-dicinal purposes due to its antifungal, antidiabetic, antiviral, antibacterial, anthel-mintic, contraceptive, and sedative properties (Biswas et al., 2002). Nowadays, itssprouts and ﬂowers are still used in several bitter dishes in Southeast Asia; it representsa good alternative to synthetic pesticides and is very valuable in the cosmetics industry. Cold press extraction is the traditional way to obtain this nonedible oil. The need for ahigh-yield, high-quality and fast neem oil extraction process was the motivation of Ndeet al. to investigate the use of alternative energies (eg, microwaves), demonstrating a
102 Handbook of Biofuels Productiongood capacity for high oil volume extraction without signiﬁcant effects on acid numberand fatty acid proﬁle of the ﬁnal product (Nde et al., 2015). Fatty acid proﬁle of neem oil(see Table 5.4) reveals a high FFA content (approx. 24.4 mg KOH/g oil). Biodiesel pro-duction implies therefore a two-stage process to avoid undesirable soap formation,which is difﬁcult in biodiesel puriﬁcation (Betiku et al., 2014). SathyaSelvabala et al.proposed a homogeneous pre-esteriﬁcation process using a phosphoric-acid-basedcatalyst, reducing its FFA content to 1.8 mg KOH/g oil (SathyaSelvabala et al.,2010). Mathematical prediction models for the ultrasonicated production of biodieselfrom neem oil were studied by Prakash and Priya, demonstrating the boundaries of arti-ﬁcial neural networks (ANNs) on the prediction of process performance (Maran andPriya, 2015).5.3.6 Waste oilsValorization of waste oils implies both removal of a contaminant from the environ-ment and taking advantage of the energy that they contain, reducing biofuel productioncosts; thus 80% of this cost relies on raw material purchase (Yadav et al., 2015). The author and colleagues have already written a revision on the valorization pro-cesses for waste cooking or frying oils (WFO) (Pinzi et al., 2014). Nevertheless, theydeserve a special mention in this section due to its high quantity (15 million tons peryear), easy availability and low-cost transformation methods (Lopresto et al., 2015).The conversion of all available WFO into biodiesel would cover the world demandfor biofuels, increasing production sustainability, eliminating a harmful waste fromthe environment and overcoming the competition with food markets. The main challenges for the valorization of this waste are: optimization of theprocess design, selection of low-cost/high-efﬁciency pretreatments, and use of high-yielding, low-cost, reusable biocatalysts. Heterogeneous biocatalytic transesteriﬁca-tion of WFO within the bioreﬁnery concept was proposed recently by Tan et al.with promising results for waste ostrich- and chicken-eggshell CaO-based catalysts(Tan et al., 2015). As with other raw materials, WFO have also been proposed forenzymatic transesteriﬁcation. To serve as an example, Lopresto et al. used Pseudo-monas cepacia immobilized lipases and ethanol, added in three steps (because oflipase inhibition), for the production of WFO ethyl esters. Laboratory tests demon-strated a good performance of this biocatalyst and reﬂected the need for further inves-tigation on catalyst deactivation effects (Lopresto et al., 2015). Singh and Patelproposed the use of mono lacunary phosphotungstate, anchored to MCM-41 (a recy-clable catalyst) for low-cost WFO biodiesel production (Singh and Patel, 2015). Supercritical ethanol was used together with ionic liquid [HMim][HSO4] catalyst,yielding 97.6% biofuel in only 45 min, and the catalyst was not affected by high pres-sures, temperatures, or the presence of water, which implies a sustainable alternativefor WFO valorization (Caldas et al., 2016). Moreover, laboratory experiments have demonstrated that the use of ultrasoundenhances the production of WFO biodiesel when using heterogeneous catalysts suchas calcium diglyceroxide (Gupta et al., 2015) or sulfonated carbon (Maneechakret al., 2015), among others.
Feedstocks and challenges to biofuel development 103 Engine tests have been performed lately to assess the differences between methyland ethyl esters of WFO and its blends with diesel (Sanli et al., 2015), as well as blendswith butanol containing water (5%) and diesel (Tsai et al., 2015) with interestingresults. Deoxygenation of WFO for the production of biofuel and chemicals via catalyticcracking (FCC-ECAT enhanced with ZSM-5) generated a gasoline similar to that ob-tained for vacuum gas oil cracking, without formation of organic oxygenates such asphenolics, esters, or carboxylic acids (Lovas et al., 2015). Kinetic models for thermalcracking (fast pyrolysis) of WFO to produce hydrocarbons are able to describe the re-action pathways of different cracking products, and to group them based on the num-ber of carbon atoms in the hydrocarbon chain: WFO (>18C), heavy bio-oil(C12eC18), light bio-oil (C4eC11), and bio-gas (<C4) (Meier et al., 2015). Waste soybean and palm oils (by-product of the puriﬁcation process of palm oil)were proposed for a single-step process to generate jet-fuel (aviation is responsibleof 12% of CO2 emissions). Results showed a degree of oxygen removal of 95%,without using hydrogen, which are promising results for the sustainability of aviationtransportation (Choi et al., 2015). The ﬁsh processing industry discharges approximately 45% of total captures inthe form of heads, skin, viscera, etc. containing 1.4e40.1% (w/w) of oil (Zutaet al., 2003). Only omega-3 rich oils, produced in large quantities, are valuable foredible purposes, the rest may be valorized as raw material for biofuels. Propertiesof bio-oils derived from ﬁsh processing are very similar to petroleum-based fuelsand depend on the extraction system. Adeoti and Hawboldt compared modiﬁed ﬁsh-meal, CO2 supercritical extraction and soxhlet extraction methods for oil quality prop-erties and extraction yield. The results showed that supercritical-CO2 methodextracted 91% of total oil, containing lower quantities of FFA, and therefore demon-strating better fuel properties and the possibility of using it as a heating oil to meet in-ternal energy demand (Adeoti and Hawboldt, 2015). Leftovers of the salmon industrywere studied to develop a kinetic model for the production of methyl esters in a two-step process including homogeneous pre-esteriﬁcation (Serrano et al., 2015). The re-sults corroborate that cold ﬂow properties and oxygen stability of this kind of oils canlimit its use as diesel-engine fuels, and also oil price affects the viability of this sus-tainable valorization process. Waste-transformer oil (WTO) is a petroleum-based mineral oil, the disposal ofwhich causes severe environmental problems. Its valorization was studied by Yadavet al. among others, for the production of diesel-like fuels via catalytic cracking (Yadavet al., 2015) and transesteriﬁcation reaction (Yadav and Saravanan, 2015). This oil pre-sents high viscosity that prevents its direct use in diesel engines, and was treated in atwo-step process with sulfuric acid followed by a transesteriﬁcation reaction in thepresence of alkali catalyst and alcohol. The hydrocarbon fuel obtained was not richin methyl esters as expected, but in cyclo-hexenol and oxabicyclo-heptane, and there-fore engine modiﬁcations are required for its use. On the other hand, catalyticallycracked WTO was found adequate for use in diesel engines according to ASTM stan-dards. Blends of this hydrocarbon fuel with diesel improved greatly its BTE andPHRR, reducing emissions of HC, CO, and smoke with an increase in NOx emissions.
104 Handbook of Biofuels Production Synthetic single-use plastic waste is normally placed in landﬁll areas (40% of globalproduction), incinerated (150 million tons/year) which implies dangerous emissions ofhydrogen cyanide, or disposed of to the sea (García, 2012). Its recycling process isvery tedious and time-consuming. Moreover, the presence of additives such as pig-ments, coatings, or ﬁllers limits the use of the ﬁnal recycled material. Waste plasticoil (PO) can be obtained by pyrolysis and used in diesel engines mixed withpetroleum-derived diesel. Nevertheless, the performance of PO25, PO50, and PO75blends has shown that combustion characteristics are gravely affected and thereforethis route should not be considered as a valorization solution for waste plastics (Kaimaland Vijayabalan, 2015). Other synthetic waste oils such as waste lubrication oil or tire pyrolysis oil, as wellas bio-based municipal waste, olive mill, or kapok waste oils, have also been proposedfor biofuel production (Yadav et al., 2015).5.3.7 Other sources of low-cost, renewable oil for biofuel productionAnimal fats (mainly lard, tallow, and chicken), insects, soapstocks, or microorgan-isms for oil production (eg, microbial oil from yeast, microalgae, molds, bacteria,and cyanobacteria) were compared as cheap sources of biomass for renewable bio-fuel production by the author and her coworkers in 2014 and can be consulted (Pinziet al., 2014). Biodiesel production from microbial oil, food waste, or algae, amongothers, as well as challenging techniques for sustainable processing, is covered laterin this book.5.4 Raw materials for bioethanol productionWorldwide bioethanol (ethyl alcohol, CH2CH2OH) production was 24,570 milliongallons (equivalent to 93,008 million liters) in 2014. As presented in Table 5.3, theUnited States leads global production with 58% of total share, followed by Braziland Europe (25% and 6%, respectively) (Association, 2015). Bioethanol, a liquid oxygenated biofuel, is not only an alternative source of energy,but also an additive that increases fuel oxygen percentage, reducing CO and aromaticemissions, as well as a valuable platform chemical used for ethylene and ethylene-glycol production that is used in turn for the production of polyethylene andpolyethylene-terephthalate (Koutinas et al., 2014). Fermentation of several carbon sources, such as lignocellulosic materials, sucrose-containing feedstocks and starchy crops, using different microorganisms generatesthis bioalcohol. A description of natural and genetically modiﬁed microorganismsemployed in the fermentation process (eg, Saccharomycer cerevisiae, Zyomonasmobilis, E. coli), metabolic pathways, inhibitors, separation methods as well as thedevelopment of new strains and processes for the valorization of C5 and C6 sugarsfor bioethanol production were already reported by the authors in a previous study(Koutinas et al., 2014).
Feedstocks and challenges to biofuel development 1055.4.1 Most frequent raw materials for bioethanol productionIn the ﬁrst edition of this handbook (chapter: Biofuels: technology, economics, andpolicy issues), Pinzi and Dorado went through the most frequent raw materials forethanol production (Luque et al., 2011). Their work included a review on sucrose-containing feedstocks, such as sugarcane, sugar beet, and Sorghum bicolor; starchymaterials, covering Zea mays, Triticum spp. (wheat), and Manihot esculenta; as wellas lignocellulosic biomass comprising rice straw, Panicum virgatum (switchgrass),Miscanthus giganteus, Pennisetum purpureum (elephant grass), and Heliantus tuber-osus (also known as Jerusalem artichoke). The aim of this section is to deﬁne the state of the art for bioethanol productionworldwide based on the raw materials employed and the sustainability of the industry;thus description and challenges in processing, industrial methods, metabolic pathways,genetically engineering strains, etc., have been already extensively covered by differentauthors (Luque et al., 2011; Koutinas et al., 2014).126.96.36.199 Raw materials employed by countryAs depicted in Table 5.3, the United States was responsible for 58% of global ethanolproduction in 2014. The bioethanol industry represents a main driving force for ruraldevelopment, creating stable jobs annually all over the world: in only the US, 198ethanol factories were operative in 2014, supporting 83,949 direct jobs (in agricultureand renewable fuel industries) and 295,265 indirect and induced jobs (Association,2015). Approximately 98% of US bioethanol is based on corn (Zea Mays), a raw starchymaterial produced in high quantities in that country (14,216 MkT in 2014). Total do-mestic use of corn in US was 11,883 MkT in the same year. From that amount, 5208MkT of corn were used for ethanol production, 5315 MkT for feed and residual usepurposes, while the rest was transformed into high-fructose corn syrup, sugars (glucoseand dextrose), starch, alcohol for beverages and manufacturing, seeds, cereals, andother products (Service, 2015). Controversy around the competition of fuel and food markets for raw materials con-tinues to date, even though less than 3% of global grain supply was used in the bioethanolindustry in 2015, and the global food price index shrank for ﬁve consecutive years whileethanol production expanded to record numbers. Producers associations defend, based onthe analysis of the US Department of Agriculture, that for every dollar spent on food, only17 cents pay for the raw material; the rest corresponds to processing, transportation,labor, packaging and advertising, among other costs (Association, 2015). Nevertheless,the “food versus fuel” controversy is not the only indicator for the sustainability of thebioethanol industrial sector; thus it may also fulﬁll social, economic, and environmentalsustainability criteria. Sadeghinezhad et al. investigated the environmental impact andsustainability of ethanol as a biofuel worldwide regarding: direct and indirect changeof arable land use, clean water requirements, destruction of vital soil resources due tointensive agriculture, life cycle assessment, carbon footprint, air quality, preservationof forests and indigenous communities, etc. (Sadeghinezhad et al., 2014).
106 Handbook of Biofuels Production The bioethanol industry in the US processes corn and wheat through wet and drymilling schemes, generating value-added co-products that contribute to the overallproﬁtability of this industry. In 2014, 60% of corn distiller grains were dried type,27% wet and 13% were obtained by a modiﬁed wet process (Association, 2015).Corn wet milling process co-products are oil, corn gluten, meal, and corn glutenfeed, while dry milling generates distillers dried grains with solubles (DDGS), consist-ing mainly of ﬁbers, lipids, vitamins, minerals, and protein. It is easy to understand thatthese by-products are used effectively for the production of bioplastics, platform chem-icals, biofuels, animal feed, and other valuable end products (Koutinas et al., 2014). Asan example, 2.5 billion pounds of corn distillers oil (CDO) were produced in US bio-ethanol plants in 2014 that may be converted into biodiesel. Moreover, distillers grainsof the US are exported worldwide (11.3 MMT in 2014) for beef cattle (43%), dairycattle (30%), swine (16%), and poultry (10%) feed, mainly to China, western Asia,Turkey, Mexico, and Canada (Association, 2015). Sweet sorghum has become a new alternative raw material for bioethanol produc-tion in the US, due to its low water requirements, adaptability to different soils, nitro-gen- and radiation-use efﬁciency, genetic diversity, and potential for the production offood, feed, and biofuels. It contains both fermentable free sugars and lignocellulosicbiomass, susceptible to produce biofuel (Platform, 2015). Brazil is the second largest producer of ethanol worldwide since the 1970s,supporting its production and use though blend obligations, and several governmentalprograms such as the regional producer subsidy, tax incentives for ethanol-ﬂex fuelvehicles, and for ethanol fuel, credit lines and the ethanol import tariff (Barros,2015). The Brazilian government has had no control over the volume of ethanol pro-duced in Brazil since 1990; however it inﬂuences the market through the ethanol-usemandate (1977), with a minimum blend obligation of 18% established in 2011.Recently, an increase in ethanol blend to 25e27% was authorized by the governmentunder the ethanol industry pressure that accounts for 360 bioethanol reﬁneries with anestimated capacity of 38 billion liters of ethanol a year. Sugarcane is the only raw material employed for bioethanol production in Brazil,accounting for 322.2 million metric tons of this raw material destined to the productionof 29 billion liters of ethanol in 2015, 77.2% of the total installed capacity (Barros,2015). Sugarcane bagasse, a lignocellulosic by-product of the Brazilian bioethanol indus-try, may be valorized for the production of ethanol from the cellulose fraction, whilehemicelluloses and lignin, currently used as fuels for the generation of steam and elec-tricity, might be used for the production of value-added chemicals through fermenta-tive processes, increasing proﬁtability within a bioreﬁnery concept (Koutinas et al.,2014). Although sugarcane bioethanol is considered as a ﬁrst-generation biofuel, itshigh sustainability (related to high energy balance and high GHG savings) and lowimpact on food markets, together with the possibility of using it as an energy crop,make a difference with other ﬁrst-generation biofuels (Platform, 2015). Europe has 70 bioethanol plants that produced 5900 million liters of bioethanol in2014, generating 3200 MT of DDG and 165 MT of corn oil as by-products. The mainraw material for European bioethanol is sugar beet (11,434 MT), followed by corn(5775 MT), wheat (3060 MT), rye (780 MT), and barley (610 MT) (Flach et al., 2014).
Feedstocks and challenges to biofuel development 107 Sugar beet presents low-water, low-quality soil requirements, and less fertilizer thanother sugar crops. Residues from sugar beet-based ethanol production, pulp andbagasse, may be used for the production of cellulosic ethanol. A European demonstra-tion plant in Fresno County (California, US) operates with whole beet as feedstock,delivering 75 million liters of bioethanol per year, accounting for a 71% saving inCO2 emissions (Platform, 2015). China faced the end of its 12th 5-year energy plan in 2015, harboring ambitiousexpansion targets on the biofuel energy ﬁeld. Representing a major bioethanol pro-ducer globally, it faces an uncertain future due to recent governmental limitationson grain-based biofuel production and reduced possibilities to switch to alternativefeedstocks. Total installed bioethanol capacity in China is 3.21 MMT, based mainlyon corn and wheat, but also using tapioca, cassava, sweet sorghum stalks, and corncob (Ji, 2015). Six provinces adopted E10 blend mandates with an ethanol price ﬁxedby the government in 91% of the cases. Even though, average blending ratio in thecountry is 2.1% and therefore implementing E10 standards in other provinces is funda-mental for the expansion of the bioethanol industry in China. Canada presented a bioethanol capacity of 1800 million liters in 2014, with 15 oper-ative reﬁneries operating at 95%, under production incentives administrated by theFederal Department of Natural Resources. Canadian bioethanol industry, based oncorn and wheat, produced 1.1 MMT of DDGs, 6.5 MMT of WDG (wet dry grains),and 6000 metric tons of corn oil that could be valorized for second-generation biofuelproduction. This fact represents a major concern for older small factories, with weakco-product production lines, that need to compete with low-cost US ethanol. As anexample, the 25-million-liter-capacity wheat-based plant settled in Saskatchewan(from the American company Bioenergy Crop) shut down in 2015 with low possibil-ities of reopening (Dessureault, 2015). Provincial mandates and low gas prices (that inﬂuence low ethanol prices) haveincreased demand for fuel ethanol in Canada, exceeding domestic supply. Therefore,Canada imports 20% of the bioethanol consumed from US. Thailand, one of the major ethanol producers worldwide, accounts for 1070 millionliters per year (2014), basing its production on sugarcane molasses (70%), cassava, andrice, with 21 operative plants in 2015. The Alternative Energy Development Plan(2012e21), from the Thailand government, targets the use of 9 million liters of ethanolper day, and the increased consumption up to 3.5 million liters per day in 2015 reﬂectsa good performance. Also, E20 and E85 gasohol consumption has increased, due toprice incentives mainly, and subsidies from the State Oil Fund have made ethanolblends (E20 and E40) cheaper than E10 octane 95 gasoline. Moreover, ﬂexi fuel ve-hicles also present government reduced taxes and subsidies for acquisition. Meetingconsumption targets in Thailand implies an increase in feedstocks supply. Thereforeincreasing sugarcane yield and shift from rice to sugarcane cultivars in some unpro-ductive areas is contemplated in the Agricultural Restructuring Program of the Gov-ernment (Prasertsri, 2015). Argentina is predicted to reach a record ethanol production in 2016 (900 millionliters) half based on the sugar industry and the other half on the grain industry. Themain raw materials for Argentine bioethanol are grain, molasses, and from sugarcane.Predicted consumption is only domestic with no export is projected, with a current
108 Handbook of Biofuels Productionconsumption mandate of 10%. Low sugar market prices along with blending obliga-tions, makes sugarcane ethanol more proﬁtable than sugar production, and thereforesugar mill companies are aiming to produce more sugarcane-based bioethanol in thefuture. On the other hand, grain-based ethanol production, located in the center ofthe country, and therefore far from ports and trade areas, bears additional costs thatlower its proﬁtability. The main grain used in Argentina is corn, even though facilitiescould also use sorghum, but its price, due to export trade to China, has increasedrecently. All grain plants except one beneﬁt from DDGS domestic sells to feed mills,feed additive companies and dairies, increasing plant proﬁtability (Joseph, 2015). Finally, Indian bioethanol domestic production is predicted to remain stable at 2.2billion liters, produced in 115 reﬁneries, thanks to stable sugarcane supply. With agrowing economy, long-awaited government measures, such as ﬁxing price mecha-nisms for nonfood-based bioethanol (apart from molasses) or duty exemptions, willhopefully repair the sugar mill producer economy and propel bioethanol productionin this Asian country (Aradhey, 2015).5.4.2 Challenges for sustainable bioethanol productionResearch on new processes and new strains for the valorization of C5 and C6 ligno-cellulosic sugars is the main goal for researchers all over the world. As mentionedin the previous section, current ethanol production plants may beneﬁt from the integra-tion of a lignocellulosic residue valorization process (eg, cereal straws or sugarcanebagasse) for the production of biofuels and chemicals. In 2014, two of the most important bioethanol companies worldwide, the Andalu-sian Abengoa BioEnergy (Spain) and the American POET-DSM, opened commercial-scale cellulosic bioethanol facilities for the ﬁrst time in the United States (Association,2015). Mendota Bioenergy LLC operates also in the Wissington sugar factory(California, US), using local sugar beet including lignocellulosic residues for the pro-duction of ethanol. Research and development companies such as the Spanish Alkol Biotech, theBrazilian Granbio, or the American Arcadia Biosciences Inc. focus on the develop-ment of hybrid energy crops (eg, energy cane) with high yields, to use sugar beetfor the production of cellulosic ethanol, as well as on nitrogen-use efﬁciency to reduceconsumable inputs. Sweet sorghum bioreﬁneries are also a target for the industry with the implementa-tion in 2013 of a 20 million gallons per year (MMGY) bioethanol facility in Florida,US, and the launch of “high-biomass-sorghum” strains from the biotech companiesNexSteppe and Ceres, to be used in US, Brazil, and Europe (Platform, 2015). The Chinese government is also aware of the sustainability problem related toChinese biofuels, targeting the production of 300 million tons of cellulosic andnongrain-based ethanol by 2020. Even though, considering present challenges inraw material transport and slow progress on cellulose valorization processes, alongwith the impossibility of private companies to receive government incentives andsubsidies, most experts assume the production of only 10 million tons by the datetarget (Ji, 2015).
Feedstocks and challenges to biofuel development 109 The Thai Roong Ruang Group recently opened a second production line using canebagasse in its already-existing molasses-based ethanol plant. The project for second-generation biofuel production is still in the experimental stage, producing only10,000 L/day, due to high production costs compared to ﬁrst-generation ethanolfrom cassava roots and molasses. Low petroleum prices will negatively affect the sur-vival of this revolutionary project in Thailand (Prasertsri, 2015). Moreover, lignocellulosic biomass is a source of energy beyond the bioethanol in-dustry. For example, the wood-processing industry is an enormous market that gen-erates approximately 131,388,000 m3 of wood residues every year. Koutinas et al.evaluated the potential of wood-based waste, along with pulp and paper mills resi-dues and food industry waste streams, for the production of sustainable biofuelsand chemicals (Koutinas et al., 2014). Valorization of lignocellulosic raw materialsfor the production of biofuels is described later in this book and can be consulted inchapter “Algae for biofuels: an emerging feedstock.” As an example for the industrial application of waste valorization, the enterpriseEnerkem opened in Canada a 5-million-liter-capacity demonstration bioethanol andbiochemical plant in 2012 based on wood. The same company ﬁnished in 2015 theconstruction of a larger plant (30 million liter) in Edmonton, Alberta, for the produc-tion of lignocellulosic ethanol from municipal solid waste. Despite this, production isnowadays focused on methanol, carbon dioxide, and other chemicals that presenthigher revenues than ethanol due to their lower market prices (Dessureault, 2015).Future plants for the production of cellulosic ethanol from nonrecyclable wasteshave also been announced in Quebec, while other Canadian cities will produced cleanbio-based heat and power through gasiﬁcation, pyrolytic bio-oil, etc. Indian biofuel public and private industries also concentrate their efforts on the pro-duction of advanced biofuels from lignocellulosic materials from wood and forestwaste as well as agricultural waste (eg, corn cob, bagasse, stalk, and forage crops).This industry still has some years ahead to demonstrate its capacity to get over the tech-nological challenges presented and to prove large-scale economic viability. Sugarbagasse, an adaptable, carbon-neutral, abundant vegetable raw material in India,may be used for the production of heat and power; thus nowadays it is already usedas a fuel in sugar mills, rice mills, textiles, etc. Its utilization would promote ruraldevelopment with great social beneﬁts. Power generation in India relies also on otherbiomass materials, such as bagasse, rice husk, straw, cotton stalk, coconut shells, soyhusk, de-oiled cakes, coffee waste, jute wastes, peanut shells, or sawdust. The avail-ability of biomass in India, from both agricultural and forestry-wasteland residues,is estimated at 915 million metric tons, which implies great valorization possibilitiesfor a developing country (Aradhey, 2015).AcknowledgmentsThe author thanks the editors for their consideration in including her in this exciting project, andto the Elsevier Editorial Project Manager Mr. Alex White for his patience and empathy. Finally,the author sincerely thank Prof. Dr. Ma Pilar Dorado for her generous help and advice.
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178 Handbook of Biofuels Productionstudied for many years, and various carriers have been used. However, only a fewtypes of carrier and immobilization processes have been commercialized. Nevertheless, these commercialized ILs are still too expensive to be used for bio-diesel production. Some newly developed immobilization technologies by using mag-netic and nano-particles have been reported, but they are still far away from industrialapplication. One of the solutions to the high cost of lipase for biodiesel production is toincrease its life time in transesteriﬁcation. At this point, reaction media, operationparameters, as well as reactor development should be considered. For example, thestability of ILs in conventional aqueous system is usually poor due to the leachingof enzyme from carriers and the inhibitive effects from methanol and glycerol(Du et al., 2008). Reactor design is important for the scale-up of IL-catalyzed production of biodiesel,but the development of high-efﬁciency reactor for IL-catalyzed production of biodieselgoes slowly. Commonly used reactors are stirred tank reactor (STR), packed-bedreactor (PBR), or a combination of both. However, further improvement is still neededfor intensifying mass transfer with minimizing mechanic shearing force to avoiddamaging carriers and enzymes. Downstream processing is crucial to obtain biodieselproduct that meets corresponding quality standards. Simulation is usually used toobtain mass and energy balance data and process optimization. Enzymatic catalysis for biodiesel production is relatively a new research ﬁeld.However, it is attracting a lot of focus from scientiﬁc community and biodiesel indus-try. In recent past, novel techniques have been developed to improve the sustainabilityand economical viability of the enzyme catalysis. These techniques mainly deal withreducing the price of enzymes as well as with improving the efﬁciency of transester-iﬁcation conversion. In this respect, Table 7.2 shows various novel techniques andrecent trends in enzymatic biodiesel synthesis and their advantages and challenges.7.4.1 Novel immobilization techniquesNovel immobilization techniques are being developed to enhance the performance ofimmobilized lipase, solvent tolerance, reusability, stability, and to make the separationprocess easier. Protein-coated microcrystals (PCMC), cross-linked protein coated mi-crocrystals (CL-PCMC), magnetic particle carriers, and electro-spun nanoﬁbers are themain novel techniques for immobilization of lipases, which have been studied inbiodiesel production. Enzymes, after being immobilized on magnetic particles, havethe advantage of an easier separation, as well as that they become immobilized lipasesthat can be concentrated at speciﬁc places in a reactor by applying external magneticﬁelds (Dussan et al., 2010).7.4.2 Use of lipases from different sources in combinationLipases from different sources have shown different substrate speciﬁcity and catalyticactivity. Lipases with narrow speciﬁcity are not suitable for biodiesel production. Theperformance of regiospeciﬁc lipases can possibly improve when used with nonspeciﬁclipases in combination. Also, some lipases show more hydrolytic activity while others
Biochemical catalytic production of biodiesel 179Table 7.2 Various novel techniques and recent trends in enzymaticbiodiesel synthesis and their advantages and challengesNovel techniques Advantage ChallengesUse of lipases from different Wide substrate speciﬁcity, Preparation of enzyme sources in combination enhanced yields, reduced cocktail or genetic reaction time engineering is tediousIonic liquids as solvent process Improved stability,Enzyme-catalyzed selectivity, and activity of Expensive technique transesteriﬁcation under enzyme supercritical CO2 medium Expensive technique, Improves diffusion and requires sophisticatedEnzyme-catalyzed reaction rate, salvation instrumentation transesteriﬁcation for low ability can be engineered, cost and high free-fatty- can be used in extraction Meticulous collection and acid feedstocks of lipids as well, easy logistics issues separation from productsSolvent-free process Mass transfer limitations in Reduces the feedstock cost, reactionIn-situ transesteriﬁcation of waste management by microalgae biodiesel production Cost-effective only when the biomass has high Cost-effective, percentage of lipids environmentally friendly, safe Reduces solvent use, less energy consumptionshow more synthetic activity. Such lipases when used in combination enhanced theyield as well as reduced the times of reaction (Li et al., 2010; Tongboriboon et al.,2010). A wide range of feedstocks is used for biodiesel production, which is comprisedof triglycerides, FFA, and regioisomers of mono- and diglycerides. The combinationof lipases with distinct speciﬁcity and catalytic efﬁciency, when used for transesteriﬁ-cation of such feedstocks, has shown an improved performance (Rodrigues et al.,2011). However, the preparation of such enzyme cocktails, or the development of amicro-organism expressing different lipases, via genetic engineering route, could bea very tedious process.7.4.3 Ionic liquids as solvent in enzyme-catalyzed transesteriﬁcationThe use of volatile, toxic, ﬂammable solvents is neither safe nor environmentally-convenient. Novel solvents like ionic liquids are considered as green solvents because
180 Handbook of Biofuels Productionof their nonﬂammability, low vapor pressure, and high thermal stability. Ionic liquidsare composed of anions and cations, which can be altered to design a suitable solventin terms of their melting point, viscosity, density, hydrophobicity, and polarity (de losRios et al., 2011; Zhao et al., 2013). Enzymes show higher stability, selectivity, andimproved activity in ionic liquids at room temperature. Thus, ionic liquids currentlyare gaining interest in enzyme-catalyzed transesteriﬁcation. Hydrophobic ionic liquids have shown higher yields than hydrophilic ones. At pre-sent, ionic liquids are expensive, although they can be recovered and reused (Ha et al.,2007). Consequently, more simple recovery techniques and cheaper ionic liquids haveto be investigated to understand that ionic liquid-assisted biodiesel synthesis could beeconomically feasible.7.4.4 Enzyme-catalyzed transesteriﬁcation under supercritical CO2 mediumTo avoid the mass transfer limitations, organic solvents are being used extensively inenzyme-catalyzed biodiesel synthesis. As most of these organic solvents are toxic,volatile and ﬂammable use of supercritical ﬂuids as the reaction medium has gainedglobal interest. Enzyme catalysis can be carried out in supercritical CO2 (SC-CO2)because of its moderate critical temperature and pressure, 31.1C and 7.38 Mpa,respectively (Rathore and Madras, 2007). Supercritical CO2 as the reaction mediumin lipase-catalyzed reactions offers the advantage of easy separation by reducing thepressure; also, its salvation ability can be altered by controlling temperature and pres-sure. Also, supercritical CO2 has been simultaneously utilized for the extraction oflipids, as well as for the solvent where the transesteriﬁcation process is developed.This at some extent lowers the cost attributed to the reaction process in supercriticalconditions (Taher et al., 2011).7.4.5 Statistical approaches for optimization of reactionLipase-catalyzed biodiesel production is inﬂuenced by number of factors such as tem-perature, methanol to oil molar ratio, enzyme concentration, water content, ﬂow rate,in case of continuous process, and so on. Thus, optimization of these parameters be-comes crucial to obtain maximum yields. Statistical methods such as response surfacemethodology (RSM) have been widely used for the optimization of lipase-catalyzedbiodiesel production (Verdugo et al., 2011; Luna et al., 2014b). Statistical methodsgive the advantage of studying a great number of parameters in fewer experimentalsetups. These methods also give a better understanding of interactions of the parame-ters as well as extent of on their inﬂuence on the reaction.7.4.6 Enzyme-catalyzed transesteriﬁcation for low-cost and high free-fatty-acid feedstocksFeedstock contributes for a major portion of biodiesel production cost. Currently,edible oils are mostly used as feedstock for biodiesel production. Edible and nonedible
Biochemical catalytic production of biodiesel 181oil crops, however, compete with food crops for arable land, which leads to foodsecurity concern. A large amount of water and fertilizers are used to grow these oilcrops, which increases the cost of biodiesel production and carbon debt. Therefore,the use of low cost of waste cooking oil and animal-derived fats are gaining interestto be used as feedstocks. Besides, the use of waste cooking oil gets a dual purpose:the biofuel production and the waste management. The used cooking oil provides acheap source of feedstock; however, for its availability at large-scale production ofbiodiesel, it is necessary get a very meticulous collection and logistics of this feedstockfrom sources like restaurants and food processing. Besides, because of waste cookingoil oxidation, it exhibits a high free-fatty-acid content (Chen et al., 2009). Many nonedible oils, microalgal oils (Chisti, 2007; Mutanda et al., 2011a,b) such asthe waste cooking oils, are known to have high free-fatty-acid and/or moisture con-tents. Both parameters, high FFA and high moisture contents of feedstocks, hamperthe biodiesel yield when it is applied the chemical catalysis, while lipase has showngood tolerance toward these factors (Hama and Kondo, 2013). Thus, despite thehigh cost of enzymes, their application in converting low-quality feedstocks canimprove the economic balance in the overall biodiesel production process. The animal-derived products are usually by-products of slaughter houses andmeat-processing industries. Higher caloriﬁc values and cetane numbers are the mainattractive features of biodiesel derived from animal fats.7.5 Biofuels similar to biodiesel produced using several acyl acceptors, different to methanolTo avoid the associated problems with the generation of glycerol in the conventionalprocess, a series of alternative methods are currently considered to get higher atomefﬁciency. In this respect, currently the production is studied in only one reaction,of new biofuels that integrate the glycerol as a derivative product, miscible with thefatty acid methyl or ethyl esters (FAME or FAEE) obtained in the same transesteriﬁ-cation process. This is possible by using some acyl acceptors (basically some esters),instead of the alcohol usually employed in the conventional process. In this way, inthe interesteriﬁcation process, the corresponding glycerol ester is obtained togetherthe FAME (or FAEE). The mix of reaction products is constituted by lipophilic com-pounds completely miscible with fossil fuels, so that in that reaction is obtained a newbiofuel avoiding the presence of free glycerol, which is a dangerous compound forengines, and substituted by a derivative that operates like a fuel. Thus, this methodology avoids the separation of glycerol before its transformation,simplifying the process (Borges and Diaz, 2012; Mota et al., 2010). These biodieselproduction methods not only prevent the generation of waste, but also increase theyields of the process, always higher than normal 12 wt%, by incorporating somederivatives of glycerol into the reaction products as well as all the reactants used.In this way, the highest atom efﬁciency, practically 100 wt%, is obtained, becauseevery atom of reactive practically is incorporated in the reaction product. Novel
182 Handbook of Biofuels Productionmethodologies to prepare esters from lipids using different acyl acceptors whichdirectly afford alternative co-products are currently under development (Adamczaket al., 2009; Vasudevan and Briggs, 2008; Ganesan et al., 2009). The interesteriﬁcation processes can be performed with the same catalysts appliedin transesteriﬁcation processes (eg, homogeneous or heterogeneous, acid or basic cat-alysts, lipases, supercritical conditions). Although at present most of these processes,when applied to the biofuels production, are carried out using different lipases(Adamczak et al., 2009; Borges and Diaz, 2012). Instead of using methanol, thelipase-catalyzed synthesis of fatty acid alkyl esters can also be performed usingalternative alcohol donors. In this respect, methyl (or ethyl) acetate as well as dimethyl(or diethyl) carbonate can be used. These mixtures, including glycerol derivativemolecules, have relevant physical properties to be employed as novel biofuels. Insome cases, even the unused reactants are capable of being directly used as biofuels.7.5.1 Biodiesel produced together to glycerol triacetate in the same transesteriﬁcation process of oils and fatsMixtures of fatty acids methyl esters (FAME) and glycerol triacetate (triacetin) areproducts of the interesteriﬁcation reaction of triglycerides with methyl acetate in thepresence of strong acid catalysts (Fig. 7.7). All of these products generated from theabove process could be used as components of a patented novel biofuel, whichstrongly improves economy of the biofuel production (Calero et al., 2015). Such amixture, named Gliperol, has claimed that it exhibits fuel characteristics comparablewith traditional biodiesel fuel (Kijenski et al., 2007). This is composed of a mixtureof three molecules of FAME and one molecule of triacetin, and it can be obtained afterthe interesteriﬁcation of one mol of triglycerides (TG) with 3 mol of methyl acetate, byusing an enzymatic catalyst. A molar ratio oil/methyl acetate in the range 1:3 to 1:9,and temperatures in the range 40e200C are usually applied. Most studies describedin these processes apply lipases as catalysts, in solvent free systems (Demirbas, 2008;Usai et al., 2010), ionic liquids (Ruzich and Bassi, 2010), supercritical conditions(Saka and Isayama, 2009; Tan et al., 2010a), or ultrasound assisted interesteriﬁcation(Maddikeri et al., 2013). O OO O ORO CH3 O O CH3 OR CH3 Catalyst O O CH3 + 3 R OCH3 + 3 CH3 O OR OO Triglyceride Methyl acetate Glycerol triacetate Fatty acid methyl Ester (triacetin) (FAME)Figure 7.7 Gliperols is a novel biofuel proprietary by the Research Institute of IndustrialChemistry Varsow (Poland), formed by a mixture of 3 mol of FAME and 1 mol of triacetin,and obtained by interesteriﬁcation of triglycerides with methylacetate under strong acidicconditions (Calero et al., 2015).
Biochemical catalytic production of biodiesel 183 Despite the greener character of ethyl acetate, this acyl acceptor is less studied thanmethyl acetate (Adamczak et al., 2009; Jeong and Park, 2010; Modi et al., 2007; Kimet al., 2007), although results described indicate similar behavior to methyl acetate inthe interesteriﬁcation with lipases. However, in this case, the corresponding FAEE(instead of FAME) with triacetin are obtained. With respect to the inﬂuence of triacetin on engine performance, there are a highnumber of studies because this molecule is considered as a good solution for theupgrading of residual glycerol obtained in the conventional synthesis of biodiesel(Rahmat et al., 2010; Melero et al., 2010). It is noted that triacetin is an antiknockingadditive when it is used along with the biodiesel in DI-diesel engine, improving theperformance and reducing tail pipe emissions (Casas et al., 2010). In this respect, itcan be concluded that the interesteriﬁcation of triglycerides with methyl or ethylacetate may be an adequate methodology to obtain conventional biodiesel (FAMEor FAEE), also including some amount of a well-recognized additive such astriacetin.7.5.2 Biodiesel produced together to fatty acid glycerol carbonate esters in the same transesteriﬁcation process of oils and fatsTo this purpose, dimethyl carbonate (DMC) can be used as a transesteriﬁcation reagentfor making esters from lipids, which directly achieves alternative soluble co-productsin the biodiesel solutions. The reaction is rather attractive, as DMC is reputed to be theprototype of green reagents due to its health and environmental inertness (Li et al.,2005). Therefore, a fuel produced using DMC and vegetable oils or animal fats asraw materials must be considered as an alternative fuel fully derived from renewableresources. Thus, DMC operates as an alternative acyl acceptor, which is neutral, cheap,and nontoxic. The reaction between triglycerides and DMC produces a mixture of FAME and cy-clic fatty acid glycerol carbonate esters (FAGCs), which constitutes a novel biodiesel-like material, named DMC-BioD (Fabbri et al., 2007) in the corresponding patent. Theinteresteriﬁcation reaction of triglycerides with DMC can generate a mixture ofFAME, FAGCs molecules, and also glycerol carbonate (GC), as it is indicated inFig. 7.8, (Calero et al., 2015). These mixtures, including glycerol derivative molecules,have relevant physical properties to be employed as a new patented biofuel where theatom efﬁciency is also improved, as the total number of atoms involved in the reactionis part of the ﬁnal mixture. DMC is reputed to be a prototype of green reagents for its health and environmentalinertness (Li et al., 2005), and avoided the co-production of glycerol. The main differ-ence between DMC-BioD and biodiesel produced from vegetable oil and methanol(MeOH-biodiesel) is the presence of fatty acid glycerol carbonate monoesters(FAGCs) in addition to FAMEs. In this respect, details regarding the compositionof DMC-BioD, as well as physical and rheological properties relevant for its use asa fuel, also have been studied to some extent. (Calero et al., 2015).
184 Handbook of Biofuels Production O O RO O O Fatty acid glycerol carbonate (FAGC) O O DMCRO OR O CH3 Catayst O +O 2 R OCH3+ O O O + R OCH3 OR O CH3 H3C O O (FAME) O OTriglyceride Dimethyl carbonate Fatty acid methyl Ester Glycerol dicarbonate (GDC) (DMC) (FAME) H2O CH2 O O + CH3 OH + CO2 HC O CH2 OH Glycerol carbonate (GC)Figure 7.8 DMC-BioDs is a new biodiesel-like biofuel proprietary by Polimeri Europa (Italy),obtained by reacting oils with DMC under alkaline conditions, which avoids the co-productionof glycerol by obtaining a mixture of 2 mol of FAME and 1 mol of FAGC. This latter can bedecomposed, in this way generating GDC and GC in a variable extension (Calero et al., 2015). In summary, with respect to beneﬁts and drawbacks of DMC as an alternative re-agent for carrying out interesteriﬁcation of oil and fats to produce biofuel from renew-able resources and alternative co-products (GC and glycerol dicarbonate (GDC)), itshould be mentioned that DMC is a less toxic chemical than methanol that can becurrently manufactured by environmentally safe industrial methods, from CO2 andrenewable resources. Besides, GC and its derivatives are characterized by low toxicity,and the remaining nonreacted DMC does not need to be separated from the reactionproducts, because it is an effective additive for diesel engines, due to its high oxygencontent (Rounce et al., 2010). Here we have that the fabrication process is very simpli-ﬁed with respect to the conventional biodiesel obtained from methanol.7.5.3 Biodiesel produced together to monoacylglycerol in the same transesteriﬁcation process of oils and fatsIn this respect, a protocol was recently developed for the preparation of a new kind ofbiodiesel that integrates glycerol into their composition via 1,3-regiospeciﬁc enzy-matic transesteriﬁcation of sunﬂower oil using free (Caballero et al., 2009; Verdugoet al., 2010) and immobilized (Luna et al., 2012, 2013) pig pancreatic lipase (PPL). Thus, the already patented Ecodiesel-100 (Luna et al., 2014c), is a mixture of twoparts of FAEE and one part of MG that integrates the glycerol as a soluble derivative
Biochemical catalytic production of biodiesel 185 O O O OH ORO RO OR + 2R OCH2CH3 Lipase OH + 2CH3CH2OH OR O Ethanol Monoglyceride Fatty acid ethylEsterTriglyceride (FAEE)Figure 7.9 Ecodiesel-100 is a biofuel obtained by enzymatic technology patented by theUniversity of Cordoba (UCO) incorporating glycerin, as it is formed of 2 mol of ethyl esters offatty acids (FAEE) and 1 mol of monoglyceride (MG).product (MG) in the diesel fuel, but unlike these methods, no speciﬁc reagent (such asDMC or methyl acetate) more expensive than ethanol is used. The procedure takesadvantage of the 1,3 selective nature of lipases, which allows it to “detain” the processin the second step of the alcoholysis, there by obtaining a mixture of 2 mol of FAEEand one of MG, as products shown in Fig. 7.9. This strategy is based on obtaining anincomplete alcoholysis by application of 1,3-selective lipases, so that the glycerolremains in the form of monoglyceride, which avoids the production of glycerol asby-product, reducing the environmental impact of the process. Ecodiesel exhibits similar physicochemical properties to those of conventional bio-diesel. Last, but not least, monoacylglycerides (MG) were proven to enhance lubricityof biodiesel as it was demonstrated by recent studies (Wadumesthrige et al., 2009;Xu et al., 2010; Haseeb et al., 2010). Besides, ethanol does not spent in the enzymaticprocess remain in the reaction mixture in such a way that after the reaction the prod-ucts blend obtained can be directly used as a fuel. In this respect, some studies(Cheenkachorn and Fungtammasan, 2009; Jaganjac et al., 2012) have proven thatblends of diesel fuel and ethanol with biodiesel led to a slight decrease in maximumpower output, with respect to regular diesel. Besides, no signiﬁcant difference in theemissions of CO2, CO, and NOx between regular diesel and biodiesel, ethanol anddiesel blends was observed. However, the use of these blends resulted in a reductionof particulate matter. Consequently, such blends can be used in a diesel enginewithout any modiﬁcation, taking into account the limited changes obtained respectto the use of pure diesel. Thus, the Ecodiesel expression is currently ascribed towhich ever blend of fatty acid alkyl ester is with the ethanol, alone or with anyproportion of diesel fuel (Pang et al., 2008). The Ecodiesel production with different lipases and several biocatalytic systems, aswell as the main reaction parameters, have been studied, and the obtained results aresummarized in Table 7.3. Table 7.4 shows a summary sheet of the pros and cons of different existing meth-odologies for obtaining biofuels by integrating glycerol as a derivative. This enablesthem to work as combustible, together with FAME or FAEE, thus avoiding the pres-ence of free glycerin. In this respect, the production process of biodiesel-like biofuels by interesteriﬁca-tion of vegetable oils with methyl acetate or methyl carbonate, used as acyl acceptors,
Table 7.3 Different enzymatic systems studied for the bioBiocatalyst (Lipase) Form of use AnoPPL (commercial pig pancreatic lipase) Oil/EtOH Free 1:2.6Lipopan (Thermomyces lanuginosus) Physical adsortion 1:10.3MML (Rhizomucor miehei) Covalent Inmob1 1:4Lipozyme RM IM (Rhizomucor miehei) Covalent Inmob2 1:4Biolipase-R (Rhizopus oryzae) Free 1:3.5 Free 1:6 Commercial immobilized 1:6 Free 1:6 Physical adsortion 1:6 Covalent Inmob1 1:6 Covalent Inmob2 1:6
ocatalytic production of Ecodiesel 186 Handbook of Biofuels Production Crucial reaction parametersova OVATH T 8C Biocatalyst weight (g) Reuses References 45 0.01 0 Verdugo et al. (2010) 45 0.5/0.01 11 Caballero et al. (2009) 40 0.5/0.01 40 Luna et al. (2013) 40 0.5/0.01 25 20 0.02 0 Verdugo et al. (2011) 30 0.015 0e 40 0.04 12 Calero et al. (2014) 20 0.02 0 Luna et al. (2014b) 30 0.5/0.01 9 Luna et al. (2014a) 30 0.5/0.01 - 30 0.5/0.01 9
Biocatalyst (Lipase) OriginCommercial Wild strains CALB Candida Phylipases N435© antarctica ads Standard G. Terribacillus CoEnzymatic strain Oil environment G. Bacillus Fre extracts Animal fat Fre C. antarctica environment Fre CALB (CECT)
Crucial Reaction parameters Biochemical catalytic production of biodiesel ANOVA OVAT Form Oil/ T Biocatalyst weight Reuses EtOH (8C) (g) 0 Free 1:6 30 0.02 10 16ysical MS 1:6 0.05 10sortion 3030 1:6 30 0.1 10 1:6 30 0.5 PMO 1:6 30 0.5 10 30 0.5ommercial immobilizedeeeeee 1:6 30 0.5 187
Table 7.4 Schematic comparison of the main characteristirenewable liquid fuels from vegetable oilsType Biodiesel EN 14214 GliperolName BiodieselReactive Methanol or ethanol Methyl acetateCatalyst NaOH or KOH Acid, basic or liProducts 3 FAME or 3 FAEE Glycerol triacetaBy-products Glycerol 3 FAMESeparation process Complex No waste Not needed and cleaning MediumInvestment facilities Free fatty acids are LowFree fatty acids and/or Free fatty acids transformed to soaps water in the starting oil Low transformed tCatalyst cost High. Alkaline and saline HighEnvironmental impact Low efﬂuents are generated. Wastewater treatment is needed
ics of the different technologies available to produce 188 Handbook of Biofuels Production ipases Biodiesel-like biofuels Ecodiesel ate þ DMC-Biod Ethanol Lipases are Methyl carbonate Monoglycerides þ 2 FAEEto biofuel Basic or lipases Fatty acid glycerol No waste Carbonate þ 2 FAME Not needed No waste Not needed Low Low Free fatty acids are Free fatty acids are transformed to biofuel transformed to biofuel High High Low Low
Biochemical catalytic production of biodiesel 189Vegetable Catalyst Filtering Finished oils 60ºC biodiesel-like + Neutralization biofuels Interesterification ACYL acceptor (methylacetate or dimethylcarbonate)Figure 7.10 Production process of biodiesel-like biofuels by interesteriﬁcation of vegetable oilswith methyl acetate or methyl carbonate, used as acyl acceptors.Vegetable oils Lipase+ Room FinishedEthanol temperature biodiesel-like Filtering biofuels 1,3 selective ethanolysisFigure 7.11 Production process of biodiesel-like biofuels by selective ethanolysis of vegetableoils using lipases as biocatalyst.is clearly more simple than the conventional biodiesel production, as is shown inFig. 7.10, regardless of the use of chemical catalysis or enzymes. However, biofuelsobtained by selective ethanolysis of vegetable oils using lipases as biocatalyst areeven simpler, as shown in Figs. 7.10 and 188.8.131.52 Industrial biodiesel production using enzymesMost of the IL-catalyzed biodiesel productions in lab scale are batch reactions per-formed in stirred ﬂasks, but for a larger-scale operation, the reactor must be speciallydesigned. Several types of reactors have been studied for industrial biodiesel produc-tion, such as stirred tank reactor (STR) (Keng et al., 2008), packed-bed reactor (PBR)(Halim et al., 2009), ﬂuidized bed reactor (FBR) (Ricca et al., 2009) and bubblecolumn reactor (BCR) (Hilterhaus et al., 2008). However, only a few of these reactorsare actually suitable for the industrial enzymatic production of biodiesel.
190 Handbook of Biofuels Production In order to reduce operational costs, enzymatic biodiesel must be produced incontinuously operated plants. Several possible solutions obtained in laboratory scalecould be CSTRs, PBRs, ﬂuid beds, expanding bed, recirculation, or membrane reac-tors (Zhao et al., 2015). PBRs are very applicable for continuous biodiesel production,but the main disadvantage is that the resulted glycerol remains at the bottom of thereactor, so that this glycerol could be deposited on the surface of the support immobi-lized lipase, thus decreasing the catalytic efﬁciency. Thus, the glycerol must be contin-uously eliminated in a timely manner during the enzymatic reaction process. Severalstudies reported the successful application of PBRs for enzymatic biodiesel productionusing different setups: a single PBR used with stepwise addition of methanol (Zhaoet al., 2015), a single recirculating PBR (Mireille Alloue et al., 2008), three PBRsin series with intermediate glycerol removal and methanol addition (Zhao et al.,2012), and nine PBRs in series with a hydrocyclone set after PBR to separate glycerol(Cheirsilp et al., 2008). Although many processes have been developed for immobilization of lipases in labscale, only a few techniques have been successfully commercialized. In this respect,the major drawback for the technical transfer is the high cost of lipase immobilizationsteps. This explain that, the market price of Novozyms 435, one of the most usual sup-ported lipase systems, reaches to $1000/kg (Zhao et al., 2015). The immobilizationprocess should be enough efﬁcient for recovering proteins as much as possible, butstill retaining their enzymatic activities. Besides, the ILs obtained should have highstability to avoid enzyme leaching or activity loss. The ﬁrst industrial plant for enzymatic production of biodiesel was built in China in2006, with a capacity of 20,000 tons/year. Tert-butanol was selected as the reactionmedium, and immobilized lipases like Lipozymes TL IM and Novozyms 435 wereboth used in this plant as enzymatic catalysts (Zhao et al., 2015). Technoeeconomic evaluation is vitally important to estimate the production costand to determine the costliest units for further optimization. Economic evaluationusually consists of several steps: the development of process ﬂow sheets, timecharts, equipment lists followed by estimations of equipment cost, and plant andmanufacturing cost (Alves et al., 2013). The economic feasibility of enzymatic production of biodiesel depends on a seriesof factors. These factors mainly include (1) the raw material costs such as the prices ofoil feedstock, alcohol and enzyme; (2) the process parameters, such as oil-to-biodieselconversion ratio, retention time for transesteriﬁcation, biodiesel recovery yield, lipaselife time, and solvent loss (if used); (3) process design regarding water recycle and heatintegration; and (IV) by-product credit. It has been found that lipase cost contributes agreat part of the total production cost. The extensively used IL, Novozym 435, has a high price per kilogram, indicatingthat a very high productivity is required for the process to be cost-effective (Nielsenand Rancke-Madsen, 2011). Therefore, the reusability of ILs is important to reducebiodiesel production cost. As shown in Fig. 7.12, the reuse time of IL has a signiﬁcantinﬂuence on enzyme cost for IL-catalyzed production of biodiesel. It can be estimatedthat to make the enzyme cost less than 0.1 $/kg of biodiesel, the IL should be reused
Biochemical catalytic production of biodiesel 19135 Lipase cost: 1500 $/kg30 Lipase cost: 1000 $/kg Lipase cost: 750 $/kg 35 Lipase cost: 250 $/kg25 Lipase cost: 100 $/kg 30Lipase cost ($/kg biodiesel) Lipase cost ($/kg biodiesel) 2520 20 1515 10 510 0 0 3 6 9 12 15 Reuse time 5 0 0 20 40 60 80 100 Reuse timeFigure 7.12 Effect of IL reused time on the estimated lipase cost under different enzymeprices. IL loading: 2% based on raw oil feedstock; oil-to-biodiesel conversion: 95% (Zhaoet al., 2015).for more than 320, 210, 160, 50, and 20 batches without loss of enzyme activitywhen lipase price are 1500, 1000, 750, 200, and 100 USD/kg, respectively. Technoeeconomic and life cycle analyses are very important for giving directionsto this technology for its successful commercial-scale implementation. However, thereare very few studies available on this topic. Also, it becomes imperative to comparealternative technology with the conventional technique. Jegannathan et al. (2011)investigated the economics of biodiesel production process using alkali catalyst,free, and immobilized enzyme catalysts. A production capacity of 103 tons and batchprocess were considered for the study. The lowest biodiesel production cost was foundto be 1166.67 USD/ton for alkali catalyst. Among the biocatalyst, immobilizedenzyme has shown a lower biodiesel production cost of 2414.63 USD/ton comparedto free enzyme (7821.37 USD/ton). The conventional alkali catalyst price was muchlower than the enzyme catalysts. Among biocatalyst, immobilized enzyme showed alower price because of its reuse potential. Life-cycle analysis study by Harding et al. (2008), compared the chemical catalysisand enzyme catalysis for biodiesel production. Study showed that the biological routehas an advantage over the chemical route in terms of simpliﬁed puriﬁcation processand energy savings. Life cycle analysis also showed that the biocatalytic route ismore environmentally friendly. Global warming, acidiﬁcation, and photochemicaloxidation in the case of enzyme catalysis were reduced by 5%. Reduction in freshwater aquatic toxicity was approximately 12%, while reduction in marine aquatictoxicity and human toxicity were almost 10%. Reduction in terrestrial ecotoxicity
192 Handbook of Biofuels Productionwas over 40%; this was mainly due to avoiding the neutralization step, which requiresacids. Authors suggested these results are mainly due to lower steam requirement forenzymatic process. Even though the cost of the enzyme catalysis is higher it providesenvironmental beneﬁts over the conventional process. With the last novel strategies,enzyme price can be cut down by improving its catalytic performance and stability.Both technoeeconomic and life cycle analysis suggest the promising potential ofenzyme catalysis for biodiesel production at commercial-scale production plants.7.7 ConclusionsNumerous lipases have been applied for biodiesel production, with a large variety oftriglyceride substrates and acyl acceptors. They have been successfully used for theconversion of waste fats and oils, eliminating the main issue of traditional alkalinetransesteriﬁcation. However, some precaution must be taken when using methanolin order to avoid lipase inhibition. The results obtained have proved that high produc-tivity, involving yield and numbers of reuse, as well as low reaction time, can beachieved when using enzymes. Further improvements can make industrial enzymaticbiodiesel production a viable option for the future. Lipase-catalyzed production of biodiesel has attracted great attention recently, dueto the merits such as mild reaction conditions, environmental friendliness, and wideadaptability for feedstocks. Immobilization of lipase facilitates enzyme recoveryand increases the stability of the enzyme. This technique shows great potential forindustrial-scale production of biodiesel. Various approaches have been developedfor lipase immobilization, mainly including physical adsorption, ionic bonding, cova-lent bonding, entrapment, and cross-linking. Nevertheless, only a few of these tech-niques seem to be economically feasible. Each immobilization technique has itsown advantage and disadvantage, and lipase immobilization is usually performed bya combination of two or more of these approaches. Most of the commercial ILs areprepared by adsorption of free lipase on polymeric materials, because this this processis simple and the carrier is relatively easy to obtain at a cheap cost. However, the sta-bility of ILs still should be enhanced, especially to strengthen the interaction betweenlipase and carriers to prevent the enzyme leaching. On the other hand, the cost of the lipase continues to be the main obstacle forexploiting its potential. Lipase reuse is therefore essential. This can be achieved byusing immobilized lipases. The industrial usage of immobilized lipases requiresdifferent qualities and characteristics of the biocatalyst depending on the speciﬁc appli-cation. Therefore, a continued effort within immobilization technology is necessary toprovide solutions for each application. Several operation parameters have been found that affect the biodiesel yield and sta-bility of ILs. These parameters mainly include acyl acceptor types and concentration,water content, enzyme loading, alcohol to oil ratio, temperature, and reaction media.Parameter optimization is important to obtain high biodiesel yield and maximize thereuse of the enzyme. However, the optimum condition is greatly dependent on oilfeedstock and the IL that is employed.
Biochemical catalytic production of biodiesel 193 Technoeeconomic evaluation is important for IL-catalyzed production of bio-diesel. Lipase cost contributes a signiﬁcant part of the total production cost. Thisexpenditure can be decreased by reducing the lipase loading (increasing lipase speciﬁcactivity) or increasing the reusability of IL. However, to further reduce productioncost, the whole process optimization with consideration of water and heat integrationsshould be performed. In summary, it is mandatory that the following issues suggested be considered toimprove the economic competiveness of IL-catalyzed production of biodiesel in thenear future:1. Increase the stability of ILs during transesteriﬁcation: This can be done by preventing lipase from leaching off the carriers and denaturing to loss activity caused by the accumulation of alcohol and/or glycerol or shearing force of stirring.2. Process integration and optimization should be further investigated. Since the total produc- tion cost is dependent on the whole process, the process integration with consideration of wa- ter and heat recycle should be conducted. Optimization of the whole process should be done with the production cost as the ﬁnal objective function.3. The development and maturation of new technologies to avoid glycerol generation as by- product. In this way, biofuels produced is applicable to diesel engines in a similar way that biodiesel, but without generating unwieldy waste glycerin, avoiding in this way any cleaning process with an additional high cost in water and energy.4. Obtain more economical enzyme preparations.AcknowledgementsGrants from the Spanish Ministry of Economy and Competitiveness, Project ENE 2011e27017and ENE2015-70210-R, FEDER funds and Junta de Andalucía FQM 0191, PO8-RMN-03515and P11-TEP-7723 are gratefully acknowledged by the authors.ReferencesAdamczak, M., Bornscheuer, U.T., Bednarski, W., 2009. The application of biotechnological methods for the synthesis of biodiesel. European Journal of Lipid Science and Technology 111, 800e813.Aguieiras, E.C.G., Souza, S.L., Langone, M.A.P., 2013. Study of immobilized lipase Lipozyme RM IM in esteriﬁcation reactions for biodiesel synthesis. Quimica Nova 36, 646e650.Alves, M.J., Nascimento, S.M., Pereira, I.G., Martins, M.I., Cardoso, V.L., Reis, M., 2013. Biodiesel puriﬁcation using micro and ultraﬁltration membranes. Renewable Energy 58, 15e20.Atabani, A.E., Silitonga, A.S., Badruddin, I.A., Mahlia, T.M.I., Masjuki, H.H., Mekhilef, S., 2012. A comprehensive review on biodiesel as an alternative energy resource and its characteristics. Renewable & Sustainable Energy Reviews 16, 2070e2093.Borges, M.E., Diaz, L., 2012. Recent developments on heterogeneous catalysts for biodiesel production by oil esteriﬁcation and transesteriﬁcation reactions: a review. Renewable & Sustainable Energy Reviews 16, 2839e2849.
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Production of fuels from microbial 8oil using oleaginousmicroorganismsE. Tsouko, S. Papanikolaou, A.A. KoutinasAgricultural University of Athens, Athens, Greece8.1 IntroductionBioethanol (mainly from sucrose and starchy crops) and biodiesel production (viatransesteriﬁcation of triglycerides) are the main ﬁrst-generation biofuels that arecurrently produced on industrial scale. Biodiesel is produced by transesteriﬁcationof triacylglycerols with short-chain alcohols (mainly methanol or ethanol) to producemonoalkyl esters, namely fatty acid methyl esters (FAMEs) and fatty acid ethyl esters(FAEEs). The worldwide production of biodiesel is mainly dependent on the utiliza-tion of waste oils, animal fats, and oilseeds such as rapeseed, sunﬂower, and soybeans.The recent food crisis has shown that research should focus on the development ofsecond-generation biofuels generated from lignocellulosic raw materials and industrialwaste streams (eg, food industry wastes). In the past few years, research has focused on the development of biodiesel produc-tion from single cell oil (SCO) that can be produced via fermentation using variousoleaginous microorganisms (ie, microorganisms that are able to accumulate lipidsintracellularly at more than 20% of the total cellular dry weight). The proposed strategymay provide a more eco-efﬁcient and sustainable option as compared to ﬁrst-generation biofuels and second-generation bioethanol production routes utilizinglignocellulosic biomass. Potential advantages include:• The raw materials that will be used for the production of SCO-derived biodiesel do not compete with food production. In this way, cultivation of land for food production as well as industrial food processes could coincide with biodiesel production by utilizing residues and agro-industrial wastes.• Microbial oil could be produced from various carbon sources (eg, glucose, lactose, xylose, sucrose, glycerol) using natural microorganisms contrary to bioethanol production where natural microorganisms that are traditionally used in industrial processes utilize mainly glucose and sucrose.• Bioethanol separation is an energy-intensive technology with signiﬁcant capital investment requirements, while separation of intracellularly accumulated SCO is likely to be achieved at signiﬁcantly lower capital cost and energy requirements.• Biodiesel production from oilseeds and waste oils will never provide adequate quantities of biodiesel to sustain the worldwide demand. In addition, the production cost of oilseeds is approximately 70e80% of the total biodiesel production cost. Biodiesel production fromHandbook of Biofuels Production, 2e. http://dx.doi.org/10.1016/B978-0-08-100455-5.00008-4Copyright © 2016 Elsevier Ltd. All rights reserved.
202 Handbook of Biofuels Production SCO will depend on the utilization of low-value waste streams or residues and therefore will offer a sustainable option for biofuel production.• Transesteriﬁcation of SCO results in the production of crude glycerine that could be used as a platform intermediate for the production of biofuels, chemicals, and biodegradable plastics (Koutinas et al., 2007b; Aggelis, 2009).8.2 Oleaginous yeasts and raw materials used for microbial oil productionThere are many microalgae, yeasts (eg, Candida, Cryptococcus, Lipomyces, Rhodo-torula, Rhodosporidium, Trichosporon), fungi (eg, Mortierella, Cunninghamella),and bacteria (eg, Rhodococcus, Mycobacterium) that can accumulate intracellularlyhigh amounts of SCO that has similar fatty acid composition to vegetable oils(Meng et al., 2009; Papanikolaou and Aggelis, 2011). Microorganisms can be charac-terized as oleaginous in the case that they can accumulate SCO to more than 20% oftheir total cellular dry weight (Ratledge, 1991). SCO could be used either for value-added applications (eg, food additives) or commodity uses (eg, biodiesel production).The ﬁrst attempts to use SCOs in industrial-scale operations mostly referred to the uti-lization of these fatty materials as substitutes of rarely found lipids of the Plant or An-imal Kingdom (eg, microbial replacements of lipids containing g-linolenic acid likeborage oil or substitutes of exotic fats like cocoa-butter) (Papanikolaou and Aggelis,2010; Bellou et al., 2012). The industrial application of SCO for fuel production isdependent on the development of a fermentation process that provides high carbonsource to SCO conversion yields, high productivities, high lipid content in cellularbiomass, and high SCO concentrations. The previous criteria constitute a useful toolso as to select the appropriate microorganisms that will facilitate the industrial imple-mentation of biodiesel production from SCO. For instance, microalgae that are culti-vated both autotrophically via photosynthesis and CO2 ﬁxation as well asheterotrophically utilizing various organic carbon sources in order to accumulate intra-cellular lipids cannot compete with oleaginous yeasts and fungi because their cultiva-tion requires a large area and long fermentation duration (Koutinas et al., 2014).Furthermore, although bacteria may achieve high growth rates and are genetically trac-table due to their less-complex genome, the majority of bacterial strains accumulate arelatively low amount of SCO (up to 40% of total cellular dry weight) (Meng et al.,2009). Some yeast strains (eg, Rhodosporidium sp., Rhodotorula sp., Lipomycessp.) may biosynthesize intracellularly around 70% (w/w) of SCO (Guerzoni et al.,1985; Li et al., 2007; Angerbauer et al., 2008; Meng et al., 2009; Leiva-Candiaet al., 2015). Table 8.1 shows that mainly yeasts and some fungi may offer appropriatecell factories for the production of SCO although the former are superior in terms ofgrowth rates, yields, and productivities. Table 8.1 demonstrates that cell densities upto 185 g/L with a lipid content up to 67.5% (w/w) have been achieved (Yamauchiet al., 1983; Pan et al., 1986; Ykema et al., 1988; Meesters et al., 1996; Li et al.,2007). In many cases, SCO has similar fatty acid composition as in the case of
Table 8.1 SCO production from various microorganisms, cMicroorganism Cultivation mode Carbon sourceYeast speciesYarrowia lipolytica Single-stage continuous GlucoseYarrowia lipolytica Crude glycerolYarrowia lipolytica Single-stage continuous StearinCandida sp. 107 GlucoseCandida curvata Shake ﬂask Glucose Single-stage continuous SucroseApiotrichum Single-stage continuous Lactose curvatum Single-stage continuous Xylose Single-stage continuous EthanolApiotrichum Single-stage continuous Glucose curvatum Single-stage continuous Whey BatchCryptococcus Glycerol curvatus Batch Recycling Continuous Partial recycling Fed-batch
carbon sources, and cultivation modesTotal MO Productivity References Production of fuels from microbial oil using oleaginous microorganismsdry content (g/L/h)weight (%,(g/L) w/w)9.2 25 0.08 Aggelis and Komaitis 203 (1999)8.1 43 0.11 Papanikolaou and Aggelis15.2 52 N.A. (2002)18.1 37.1 0.413.5 29 0.16 Papanikolaou et al. (2007b)16 28 0.18 Gill et al. (1977)18 31 0.22 Evans and Ratledge (1983)15 37 0.2711.5 35 0.2 Hassan et al. (1993)14.5 45.6 N.A. Ykema et al. (1988)21.6 36 0.119 Meesters et al. (1996)85 35 0.372 Continued20 36 0.38291.4 33 0.995118 25 0.59
Table 8.1 ContinuedMicroorganism Cultivation mode Carbon sourceLipomyces starkeyi Shake ﬂaskLipomyces starkeyi Shake ﬂask Glucose and Xylose Glucose and SewageLipomyces starkeyi Fed-batchTrichosporon Shake ﬂask sludge Glucose fermentans Glucose SucroseTrichosporon Shake ﬂask Xylose fermentans Lactose FructoseRhodosporidium Fed-batch Molasses toruloides Mannose Continuous GalactoseRhodotorula gracilis Shake ﬂask Cellobiose GlucoseRhodotorula glutinis Glucose Monosodium glutamate wastewater
Total MO Productivity References 204 Handbook of Biofuels Productiondry content (g/L/h) Zhao et al. (2008)weight (%, N.A. Angerbauer et al. (2008)(g/L) w/w) N.A. Yamauchi et al. (1983) Zhu et al. (2008)20.5 61.5 0.599.4 68 N.A. Huang et al. (2009) N.A.153 54 N.A. Li et al. (2007)24.1 56.6 N.A. Choi et al. (1982)19.5 62.6 N.A. Xue et al. (2008)17.1 57.8 N.A.16.9 49.6 N.A.21.5 40.7 N.A.36.4 35.3 N.A.22.7 50.4 0.5423.6 5915.8 65.6 0.096106.5 67.5 N.A.9.60 49.825 20
Rhodotorula glutinis Fed-batch Glucose Batch fermentor Crude glycerolRhodotorula glutinis Fed-batch Crude glycerol Batch in fermenter Pure glycerolRhodotorula glutinis 5-L fermentor Crude glycerolRhodosporidium toruloides 26-L fed-batch Crude glycerol bioreactorRhodosporidium Pure glycerol toruloides Batch fermenter Crude glycerolPichia kudriavzevii Fed-batch Crude glycerolRhodosporidium Fed-batch bioreactor toruloides Crude glycerol Fed-batch bioreactorRhodosporidium Crude glycerol toruloides Fed-batch bioreactor Crude glycerolRhodosporidium Fed-batch bioreactor toruloides Glucose þ VFAs 7-L fed-batch bioreactor Flour based industrialCryptococcus Fed-batch bioreactor curvatus waste streamsCandida freyschussiiRhodosporidium toruloidesYarrowia lipolyticaLipomyces starkeyi
185 40 0.88 Pan et al. (1986) Production of fuels from microbial oil using oleaginous microorganisms14.8 36.5 N.A. Yen et al. (2012)13.77 60.70 0.116 Saenge et al. (2011a,b)18.8 58.7 N.A. Xu et al. (2012) Xu et al. (2012)26.7 69 N.A. Sankh et al. (2013) Kiran et al. (2013)32.1 23 0.05 Kiran et al. (2013) Leiva-Candia et al. (2015)43 45.8 0.164 Leiva-Candia et al. (2015) Raimondi et al. (2014)31.1 41.7 0.108 Yang et al. (2014) Fontanille et al. (2012)37.4 51.3 0.17 Tsakona et al. (2014)34.6 52.9 0.11 Continued82 34.15 0.2824.9 45 N.A.41.02 40.22 0.33109.8 57.8 0.4 205
Table 8.1 ContinuedMicroorganism Cultivation mode Carbon sourceLipomyces starkeyi Shake ﬂask Glucose þLipomyces starkeyi Shake ﬂask monosodium 5-L fermenter glutamateRhodotorula glutinis 300-L fermenter wastewaterRhodotorula glutinis Glucose þ ﬁshmealFungal species Shake ﬂask wastewaterCunninghamella Shake ﬂask Starch wastewater Starch wastewater echinulata Shake ﬂaskCunninghamella Shake ﬂask Glucose echinulata Shake ﬂask Starch Commercial-scale batch PectinMortierella Glucose isabellina bioreactor StarchMortierella Pectin isabellina Tarioca starch GlucoseMucor sp. RRL001Mortierella ramanniana
Total MO Productivity References 206 Handbook of Biofuels Productiondry content (g/L/h) Liu et al. (2012)weight (%,(g/L) w/w) 0.014.6 24.717.6 15.3 0.01 Huang et al. (2011) Xue et al. (2010)60 30 0.3 Xue et al. (2010)40 35 0.35-0.47 Fakas et al. (2009a)15 46 N.A. Papanikolaou et al. (2007a)13.5 28 N.A. Fakas et al. (2009a)4.1 10 N.A. Papanikolaou et al. (2007a)27 44.6 N.A. Ahmed et al. (2006)10.4 36 N.A. Hiruta et al. (1996)8.4 24 N.A.28 17.8 N.A.62 46.1 N.A.
Production of fuels from microbial oil using oleaginous microorganisms 207vegetable oils used for biodiesel production. SCO is mainly composed of triacylgry-cerols with a fatty acid composition rich in C16 and C18, namely palmitic (16:0),palmitoleic (C16:1), stearic (18:0), oleic (18:1), and linoleic (18:2) acids (Meesterset al., 1996; Ratledge and Wynn, 2002; Li et al., 2007; Meng et al., 2009). TheSCO produced by Cryptococcus curvatus has similar composition to palm oil(Davies, 1988). The SCO produced by Yarrowia lipolytica contains stearic, oleic,linoleic, and palmitic acid (Papanikolaou et al., 2002a). The SCO accumulationproﬁle produced by Lipomyces starkeyi is 33% palmitic and 55% oleic acid(Li et al., 2008). There is a remarkable plethora of (pure or raw agro-industrial) substrates that can beused by oleaginous microorganisms for microbial growth and accumulation of micro-bial lipids (Table 8.1). Production of SCO implicates utilization of pure sugars as sub-strates (eg, analytical glucose, lactose) (Moreton, 1985; Moreton and Clode, 1985;Aggelis et al., 1996; Papanikolaou et al., 2004a,b; Li et al., 2007; Zhao et al., 2008;Fakas et al., 2009a), sugar-based renewable materials or sugar-enriched wastes (Ykemaet al., 1989, 1990; Davies et al., 1990; Papanikolaou et al., 2007a; Fakas et al., 2006,2007, 2008a,b, 2009a), molasses (Chatzifragkou et al., 2010), vegetable oils (Batiet al., 1984; Koritala et al., 1987; Aggelis and Sourdis, 1997), crude industrial hydro-phobic materials (eg, industrial free-fatty acids, waste fats, crude ﬁsh oils, soap-stocks)(Guo et al., 1999; Guo and Ota, 2000; Papanikolaou et al., 2001, 2002a, 2007b;Papanikolaou and Aggelis, 2003a,b), pure fatty acids (Mlickova et al., 2004a,b), orbiodiesel by-products (Meesters et al., 1996; Papanikolaou and Aggelis, 2002;Mantzouridou et al., 2008; Andre et al., 2009; Makri et al., 2010; Chatzifragkouet al., 2011; Kiran et al., 2013; Tchakouteu et al., 2015). This indicates that it is feasibleto utilize various natural resources for the production of SCO, providing the opportunityto develop processes producing SCO-derived biodiesel either integrated in existingfood industries or as individual production plants (eg, in agricultural areas so as toutilize various lignocellulosic feedstocks). Bioreﬁneries should depend entirely on crude biological entities for the formula-tion of fermentation media that will contain all the necessary nutrients for microbialgrowth and SCO accumulation. In order to implement this principle, protein-richindustrial waste streams should be used for the production of fermentation mediaenriched in organic sources of nitrogen (eg, amino acids, peptides), phosphorus,minerals, vitamins, and trace elements. Such nutrient supplements for fermentationprocesses could be produced from oilseed residues generated after oil extraction inﬁrst-generation biodiesel production plants (eg, protein-rich rapeseed or sunﬂowercakes), meat-and-bone meal, sewage sludge, protamylase (residual stream enrichedin amino acids and peptides that is generated during the industrial production ofstarch from potatoes), corn steep liquor, and residual yeast from potable or fuelethanol production plants. Protein and other nutrients are also contained togetherwith carbon sources in various food waste streams (eg, waste bread, whey). There-fore, in many cases, a single waste stream from the food industry could be sufﬁcientfor the production of nutrient-complete fermentation media for SCO production(Tsakona et al., 2014). It should be stressed that organic N-sources may enhancelipid accumulation (even two or three times higher than the amount of lipids
Production of biogas via anaerobic digestion 273hydrolysis and AD process. However, a large amount of ozone is generally requiredfor ozonation, which makes this method quite expensive. Although thermal/thermochemical pretreatments might promote better results insolubility and methane yield, the energy required for the pretreatment process shouldbe taken into account before including them in the AD system. Ariunbaatar et al.(2014) demonstrated that the enhanced methane production could cover the energyrequired for thermal pretreatment. However, Liu et al. (2008) reported that therewas no energy surplus when the energy consumed during the pretreatment processwas taken into account.10.5.1.4 Biological pretreatmentsBiological pretreatments using enzymes may improve the solubility of the biomasswithout producing any inhibitory compounds. Commercial enzymes including amy-lases, proteases, and lipases have been reported to improve the hydrolysis of FW, whilethe pretreatments using cellulolytic and hemicellulolytic enzymes intensiﬁed thebiogas production from lignocellulosic agricultural residues (Moon and Song, 2011;Parawira, 2012). The pretreatment of complex biomasses with multiple commercialenzymes appeared to be more efﬁcient than that with a single commercial enzyme(Kim et al., 2006; Moon and Song, 2011). However, it should be realized that commer-cial enzymes are costly and generally available in single-type form. In order to makethe enzymatic hydrolysis more cost-effective, enzymes can be produced on-site from acheap feedstock. In the study of Uçkun Kiran et al. (2015), a fungal mash rich in glu-coamylase and protease was produced from cake waste and was applied directly forenzymatic hydrolysis of mixed FW. The enzymatic pretreatment using this fungalmash was shown to be more efﬁcient than commercial enzymes. The biomethane yieldand production rate from FW pretreated with the fungal mash were found to be, respec-tively, 2.3 and 3.5 times higher than without pretreatment, indicating that direct use ofthe fungal mash without any puriﬁcation is a promising option for FW treatment. Biological pretreatments by the addition of microorganisms have also been found toimprove biogas production from cattle manure and agricultural residues (Angelidakiand Ahring, 2000; Chen et al., 2010; Zhong et al., 2011). The bacteria and fungi basi-cally degrade lignin and hemicellulose and increase the accessibility of cellulose in anenvironmentally friendly way. However, the main drawback of microbial pretreatmentis the long incubation time, which hinders its applicability in large scale. Furthermore,it should also be noted that most of these lignocellulolytic microorganisms can utilizecellulose beside hemicellulose, which negatively affects the ﬁnal biogas yield. Anotherbiological pretreatment method is ensiling, which is particularly applied for energycrops. It is applied using starter cultures or enzymes to convert soluble sugars toorganic acids such as lactic and acetic acids in order to inhibit the growth of undesir-able microorganisms during the storage (Weiland, 2010). As explained above, pretreatments might improve the solubility and AD of FWwhen they are applied under optimized conditions. However, most of the pretreatmentstudies have been conducted in lab- or pilot-scale so far. In order to have a more
274 Handbook of Biofuels Productionrealistic idea about their effectiveness and feasibility, these processes should be eval-uated in an integrated system considering the capital costs and applicability.10.5.2 Anaerobic codigestionAD has great potential for energy recovery from and stabilization of the wastebiomass (Zhang et al., 2014). However, AD of single substrates in long-term opera-tions presents some negative aspects linked to the substrate characteristics, ie, theimbalance of the nutrients in the system. For example, sewage sludge has low organicsolid content, which leads to low methane production. Animal manures have highnitrogen concentrations that may inhibit the methanogens. FW has high concentra-tions of sodium and has low buffering capacity. Agro-industrial wastes are seasonalbiomass and are lacking in nitrogen. Slaughterhouse wastes contain high concentra-tions of long-chain fatty acids and nitrogen, which inhibit the AD. Anaerobiccodigestion of feedstocks is a promising option to overcome the drawbacks of mono-digestion and to improve a plant’s economic feasibility. Therefore, currently there is adramatic increase in codigestion research, particularly using sludge/manure withagro-industrial residues, organic fraction of municipal solid waste (OFMSW), algaeand fats, oils, and greases (FOG). The effects of anaerobic codigestion of differentbiomass are summarized in Table 10.1. Traditionally, anaerobic codigestion betweensewage sludge and OFMSW has been applied in many codigestion plants. However,nowadays most of the research interest is on anaerobic codigestion of sewage sludgewith OFMSW and FOG, because both of these substrates can be obtained at the samewastewater treatment plant (Mata-Alvarez et al., 2014). Sewage sludge has high water content, providing a low methane yield probably dueto its low VS/TS ratio and high ammonia content (Dai et al., 2013). However, codiges-tion of sludge with easily degradable high carbon content biomass improves themethane yield. OFMSW and sewage sludge mixture show a complementary andsynergistic effect in AD (Kim et al., 2011). OFMSW balances the lack of carbonsource in sludge, while sludge provides ammonia and dilutes the harmful and exces-sive sodium, which inhibits the growth of anaerobic microorganisms in FW. FOGoriginated from wastewater treatment plants and industrial processes is also success-fully used together with the sludge due to its high methane potential. On the otherhand, the presence of sludge will moderate the high LCFA concentration, whichmay cause failure of AD (Zonta et al., 2013). The process parameters such as composition of the substrates and their mixing ratioare very important for the performance of the codigestion process. The ratio ofsubstrates is generally optimized based on C/N ratio, still, as mentioned in Section10.2, other parameters such as macro- and micronutrients, pH and free ammoniaand inhibitory compounds should be considered (Dai et al., 2013; Koch et al., 2015;Zhang et al., 2011). Hence, before the codigestion applications, it is better to conductlab-scale experiments to detect the presence of inhibitory compounds/dosages andoptimize the mixing ratio and substrate loading rates to prevent any inhibition andimprove the effectiveness of AD.
Table 10.1 Co-digestion of various feedstocks for improvFeedstock Action of codigestion InDS and FW Enhance system stability LeDS and FW Improve methane yield LeSS and OFMSW Afford high organic loading rate HiSS and FW Improve methane yield and production rate HiSS and OFMSW Allow higher organic loadings TrSS and FOG Improve methane yield and production rate HiWW and FW Improve biogas productivity and process Tr stabilityWW and FW HiCM and FW Improve methane yield and TOC utilization Hi Improve methane yield and system stabilityCM and FW Improve biogas production Hi
ving performance of AD References Production of biogas via anaerobic digestion Dai et al. (2013) nﬂuencing factor Carucci et al. (2005) ess inhibition from sodium Kim et al. (2011) ess inhibition from lipids and Koch et al. (2015) potassium Parry and Evans (2012) igh buffering capacity from Noutsopoulos et al. (2013) ammonia Zhang et al. (2011) igh BMP potential race elements supplement Wang et al. (2013) igh BMP potential, less inhibition Zhang et al. (2013) from LCFA Maran~on et al. (2012) race elements supplement Continued igh buffering capacity igh buffering capacity and trace elements supplement igh buffering capacity from ammonia 275
Table 10.1 ContinuedFeedstock Action of codigestion In NuCM and FW Improve methane yield NuCM and OFMSW Increase energy returns and reduce GHG HiOFMSW and livestock emission waste Improve methane yield and VS reduction Hi LiCM, FW, and FOG Improve methane yield TrCM, FW, and FOG Improve methane yieldCM, OFMSW, and card Allow higher organic loadings and gave a Le Hi packaging more stable processFW and yard waste Improve methane yieldFW and distiller’s grains Increase biogas productionFW and green waste Improve VS reduction C/SS, Sewage sludge; DS, dewatered sludge; OFMSW, organic fraction of municipal solid waste; CMRevised from Zhang, C., Su, H., Baeyens, J., Tan, T., 2014. Reviewing the anaerobic digestion of f
nﬂuencing factor References 276 Handbook of Biofuels Production utrient balance El-Mashad and Zhang (2010) utrient balance Banks et al. (2011b)igh buffering capacity Kim and Oh (2011)igh buffering capacity Neves et al. (2009b)ipid supplement Neves et al. (2009a)race elements supplement Zhang et al. (2012)ess VFA accumulation Brown and Li (2013) Wang et al. (2012)igh buffering capacity from ammonia Kumar et al. (2010)/N ratioM, cattle manure; WW, wastewater; FOG, fats, oils and grease. food waste for biogas production. Renewable & Sustainable Energy Reviews 38, 383e392.
Production of biogas via anaerobic digestion 277 Acclimation is another possible approach to overcome the inhibition and preventthe lag phase during codigestion. Carucci et al. (2005) reported that AD of FW wasinhibited due to the high potassium (55 g/kg dry FW) and lipid content (13%) ofthe FW when unacclimated inoculum was used. After a long acclimation period, theAD of a mixture of FW and sludge (60% and 40%, respectively) provided signiﬁcantlyhigher methane yield (53%). Thermophilic AD usually provides a faster metabolic rate and higher system perfor-mance than mesophilic AD (Zhang et al., 2014). However, Kim et al. (2011) reportedthat a temperature-phased anaerobic sequencing batch reactor provides faster meta-bolism at high organic loading rates compared to two-stage mesophilic systems. Thismight be due to the enhanced stability of thermophilic methanogens and alleviated alka-linity by improved protein degradation. In long-term operations, they obtained44.2e76.5% VS removal from the codigestion of sewage sludge and FW while produc-ing 0.2 m3 CH4/kg VSadded at organic loading rate of 6.1 g VS/L/d with short HRT(7 days) through the synergy of sequencing-batch operation, codigestion, andtemperature-phasing. In another study, the codigestion of cattle manure with cheesewhey in a two-stage system provided a 40% higher methane yield than a one-stagesystem (Bertin et al., 2013). The biomethane yield can be increased signiﬁcantly by codigestion of organicwastes (Parry and Evans, 2012). However, the transportation of waste inﬂuencesthis effect negatively. In order to achieve a sustainable waste treatment strategy, thetransportation of the wastes should be minimized.10.6 Process modelingMathematical models have been developed to improve understanding of the complexdynamics of the AD process and to predict the response of the anaerobic systems tochanges in operating conditions (hydraulic retention time, organic load, temperature,etc.). Models are tools for process design, control strategies, diagnosis or predictionof system performance under conditions of increasing or decreasing load and variationof feeding characteristics. There are many types of anaerobic models ranging from steady-state models to sin-gle-, double-, or multistep dynamic models. Steady-state models can be applied in sys-tems where the ﬂuctuations in the feed characteristics and organic loading rate areminimized. This basis of static design modeling has been employed in several text-books (Tchobanoglous and Burton, 1991). In most cases, however, the model shouldprovide information about the dynamics of the system toward changes in the input ofthe system. Dynamic models can be utilized successfully in control schemes or forsimulation purposes. Depending on the purpose, the model should be simple enough,including only the basic steps for describing the dynamics of the core process (control)or more complex, including as many steps as possible making it widely applicable(simulation).
278 Handbook of Biofuels Production The typical steps usually included in an anaerobic digestion model are:• Hydrolysis of particulate matter: Although the mechanisms of the individual hydrolysis steps are known, the hydrolysis step is usually lumped as a single ﬁrst-order process (Pavlostathis and Giraldo-Gomez, 1991).• Acidogenesis of soluble organic matter: Modeling of sugar fermentation is challenging due to the variety of the possible fermentation products and the determination of the stoichiom- etry (subjected to the regulation mechanisms prevailing in the heterogeneous group of acidogens). The main pathways acknowledged to take place are toward formation of buty- rate, acetate, ethanol, and acetate, as well as propionate and acetate as end products (Batstone et al., 2002). Lactate has also been considered important to be included among the sugar fermentation products (Costello et al., 1991). In mixed fermentation processes, the mechanisms that regulate the composition of the fermentation product mixture have not been elucidated completely and as a result, modeling of this step has not yet been effec- tive (Costello et al., 1991; Ruzicka, 1996). This limitation has become critical due to the increasing interest concerning the production of biohydrogen produced along with the other sugar fermentation metabolic products. As far as the modeling of amino acid fermentation is concerned, the pathways based on Stickland reactions have been proposed (Ramsay and Pullammanappallil, 2001).• Acetogenesis and methanogenesis: Both steps have been extensively and successfully simu- lated. However, the incorporation of hydrogen, free ammonia, and pH effects on the kinetics of both steps can be further improved. Table 10.2 refers to various models developed before 2002, some of which were theprecursor of a generic model which was developed in 2002 by a group of scientistsexpert on AD modeling. They constructed the AD model (ADM1) to be a frame modelbasis for several applications in AD (Batstone et al., 2002). The model has been usedas a reference basis for many extensions made by several researchers afterward toutilize it in speciﬁc applications, such as the AD of brewery wastewater in a full-scale high-rate system (Ramsay and Pullammanappallil, 2005) or the start-up of amanure digester (Normak et al., 2015). The model is considered to be complicated(consisting of 29 processes; 19 biochemical and 10 physicochemical) and lacks stepssuch as sulfate reduction, acetate oxidation, homoacetogenesis, and solids precipita-tion. Extensions to include sulfate reduction have rarely been attempted because ofthe complicated biochemical reactions taking place and the antagonism between thesulfate reduction bacteria (SRB) and the methanogens. Moreover, the electron donorsfor sulfate reduction are not only hydrogen but also the volatile fatty acids as reportedby Barrera et al. (2015), who succeeded in simulating the anaerobic digestion of a highorganic strength and sulfate-rich wastewater. The model could predict the experi-mental results with medium (10e30%) to high (Æ10%) accuracy, and more impor-tantly, the model was able to predict the system limits when tested underoverloading conditions. Carbonate precipitation and acetogenesis of isovalerate havebeen considered in the modiﬁcations of ADM1 proposed by Batstone and Keller(2003) and Batstone et al. (2003), respectively. In the case of semidry and dry feed-stocks, Esposito et al. (2008) found that the effect of the surface of the particulatematter can be taken into account by modifying the disintegration constantincluded in the ADM1. Another important modiﬁcation involved the correlation of
Table 10.2 Steps involved in various models of anaerobicHydrolysis Acidogenesis AParticulate organics / soluble Soluble organics / VFAs organics (glucose)Particulate organics / amino acids, Glucose / butyrate, B sugars, fatty acids propionate, acetate H PParticulate organics (fats, Amino acids, sugars, fatty B carbohydrates, proteins) / acids / propionate, acetate soluble organics B Glucose / butyrate,Easily biodegradable propionate, acetate biomass / soluble organics Soluble organics / acetate Soluble organics (glucose) / VFAs (acetate) Soluble organics / VFAs Glucose / lactate, butyrate, propionate, acetate
c digestion developed before 2002 Production of biogas via anaerobic digestionAcetogenesis Methanogenesis ReferencesButyrate, VFAs Graef and Andrews propionate / acetate (acetate) / CH4, (1974) CO2 Hill and BarthH2, CO2 / acetate VFAs (1977)Propionate / acetate (acetate) / CH4Butyrate, Acetate / CH4 Hill (1982) H2, CO2 / CH4 propionate / acetate Acetate / CH4 Bryers (1985) H2, CO2 / CH4Butyrate, Acetate / CH4 Mosey (1983) propionate / acetate H2, CO2 / CH4 Pullammanappallil et al. (1991) Acetate / CH4 Kleinstreuer and Acetate / CH4 Poweigha (1982) Moletta et al. VFAs / CH4 Acetate / CH4 (1986) H2, CO2 / CH4 Smith et al. (1988) Costello et al. 279 (1991) Continued
Table 10.2 Continued Acidogenesis A B Hydrolysis Lactate / propionate, acetate Particulate carbohydrates / soluble Soluble P carbohydrates / butyrate, carbohydrates propionate, acetate P Particulate carbohydrates, proteins, Amino acids and B fats / amino acids, sugars, fatty sugars / propionate, acids acetate fatty acids / acetate Particulate carbohydrates, proteins / soluble carbohydrates Soluble carbohydrates, and proteins proteins and other organics / propionate, Particulate acetate organics / carbohydrates, proteins, fats / amino acids, Amino acids and sugars, fatty acids sugars / butyrate, propionate, acetateVFAs, Volatile fatty acids. Fatty acids / acetate
Acetogenesis Methanogenesis References 280 Handbook of Biofuels Production Acetate / CH4Butyrate, Angelidaki et al. propionate / acetate (1993)Propionate / acetate Acetate / CH4 Siegrist et al.Propionate / acetate H2, CO2 / CH4 (2002) Acetate / CH4 Gavala et al. (1996)Butyrate, Acetate / CH4 Batstone et al. propionate / acetate H2, CO2 / CH4 (2002)
Production of biogas via anaerobic digestion 281stoichiometry with thermodynamics to account for the shifts in the metabolic pathwaysduring AD (Rodriguez et al., 2006). Integration of activated sludge model 1 (ASM1) and ADM1 resulted in BenchmarkSimulation Model No 2 (BSM2) to simulate an integrated sewage treatment plantincluding a primary clariﬁer, an activated sludge system consisting of ﬁve compart-ments, a secondary clariﬁer, a gravitational thickener, an anaerobic digester, a dewa-tering unit, and a sludge storage tank (Jeppsson et al., 2007). Since ASM1 andADM1 are based on different substrates, the interface between these models wasvery crucial to be deﬁned properly. Moreover, several researchers prefer to use simpler models. The basis for simpli-fying a model is the “rate-limiting step” concept, that is, the slowest step in a sequenceof reactions that determines the overall rate of a multistep process. The two sloweststeps recognized in anaerobic systems are hydrolysis and acetoclastic methanogenesis(Pavlostathis and Gossett, 1988). When the feedstock contains particulate organicmatter (sludge, organic fraction of municipal solid wastes, solid residues, etc.), therate of hydrolysis usually determines the overall rate. In this case, the steps that followare usually considered to be at pseudo steady state and can be described by algebraicequations reducing the degree of complexity of the model. In the absence of particulatematter in the feedstock, acetoclastic methanogenesis is the rate-limiting step, consid-ering the preceding steps to be at a pseudo steady state. Models derived from massbalances as the ones described above can give a better insight of how the processevolves. On the other hand, models based on the black box concept may also be accu-rate provided that their main parameters are tuned on a constant basis (Premier et al.,1997). In a recent work by Lopez et al. (2015), a simple model (with ﬁrst-order kineticsof the methane production and a time delay transfer function) was validated over acontinuous experiment. These models are particularly useful for control purposesdue to their simplicity. The ADM1 type models consist of equations describing the biochemical and thephysicochemical parts. In the biochemical part of the model, the kinetic relationshipsexpressing the reaction rates are very important. There is a wide range of kinetics thatcan be applied in each step of the AD (Pavlostathis and Giraldo-Gomez, 1991), but themost common relationship is the Monod kinetics:r ¼ S S$X [10.1] km$KS þwhere r is the consumption rate of the substrate, km is the maximum speciﬁcconsumption rate constant, KS is the saturation constant, S is the concentration of thesubstrate, and X is the concentration of the microorganisms that consume the substrate. Eq. [10.1] can be extended to include any inhibition or regulation mechanisms ifrequired (Batstone, 2006):r ¼ S S$X$I1$I2$.$In [10.2] km$KS þ
282 Handbook of Biofuels Productionwhere I1, I2, ., In are functions expressing inhibition mechanisms can include classicnoncompetitive or competitive inhibition, or empirical formulas. Modiﬁcation ofMonod kinetics to account for all kinds of product, cell and substrate inhibition hasbeen extensively applied in biochemical engineering (Han and Levenspiel, 1988). The physicochemical part of the model is important to assess the gas transfer andcalculate the pH (if required in the biochemical part). The gas transfer can be modeledby applying the gaseliquid transfer theory for each gas. Equilibrium can also beassumed for those gases that are practically insoluble in water, such as hydrogenand methane. The total gas production rate can be calculated as the sum of individualgas production rates. Gas ﬂow can also be derived by setting a pressure differencebetween the headspace and the atmosphere (Batstone, 2006). The pH calculationrequires solving algebraic equations derived from the equilibrium of weak acids andbases as well as charge balance. Dissociation of acids and bases can also be consideredas dynamic processes evolving at a high rate. A modiﬁcation of the ADM1 tested in theframework of BSM2 involves the effect of the ionic strength on the predictions of themodel. The chemical activities (inﬂuenced by the ionic strength) are used instead ofmolar concentrations (Solon et al., 2015). The results of this work show that thiscorrection is necessary for cases of high ionic strength (>0.2 mol/L). Depending on the bioreactor design (homogeneous or heterogeneous system), sim-ple hydraulic or more complex models taking into account mass transfer phenomenacan be developed. Mass transfer is important in the case of “bioﬁlm” bioreactors wheremicroorganisms are attached to the surface of an inert material (anaerobic ﬁlters) orattached on each other (UASB). There are different degrees of complexity that canbe entailed in modeling bioﬁlm bioreactors. Several parts of the bioreactor can beconsidered to be homogeneous, as in UASB reactors modeled by Bolle et al.(1986), thus a nonhomogeneous system can be depicted by a combination of thehomogeneous systems connected. In a more complex model design, the layerscomposing the bioﬁlm in a ﬁlter or the granule in a UASB are taken into account,with each layer being formed by a speciﬁc group of microorganisms. Many UASBmodels assume that the granules are spherical and the relative concentration of theacidogens and methanogens remain constant in the granule. The density of the gran-ules is also assumed to remain constant. Saravanan and Sreekrishnan (2006) reviewthe various model approaches available for bioﬁlm reactors extensively.10.7 Process monitoring and controlProcess monitoring and control is very crucial to evaluate the biogas process, toidentify upcoming instabilities in AD before a failure, to have a successful start-upor re-start of a plant, and to secure or even improve the digestion performance. In orderto develop a control scheme the following steps should be considered:• Deﬁnition of the control objective: The objective could be as simple as the pH stabilization or more complicated involving stabilization and optimization of the bioreactor operation in terms of biogas production or chemical oxygen demand removal. Since optimization and
Production of biogas via anaerobic digestion 283 stabilization are conﬂicting objectives, the control law should be sophisticated enough to meet these targets in the best way.• Selection of the suitable measurements: The properties of a suitable measurement to be used in a control scheme are the ability to reﬂect the process state and its changes due to distur- bances (sensitivity), as well as the time response and the simplicity of the measurement method. The most common measurements in anaerobic digesters (Table 10.3) are: • pH: Monitoring pH is very important since it affects the microorganisms’ activity and can be correlated with changes in acids and bases as well as activity. However, it cannot be used to evaluate the state of the system since it is affected by the buffer capacity of the liquid (determined mostly by the bicarbonate, ammonia, and volatile fatty acids). • Alkalinity: It is distinguished in total and bicarbonate alkalinity. Total alkalinity is measured through titration to pH 3.7 and expresses the capacity of an anaerobic system to maintain the pH under acidiﬁcation (Powell and Archer, 1989). However, total alka- linity increases as the VFA concentration increases. Therefore, the bicarbonate alkalinity, measured through titration to 5.75, can reﬂect the effective buffer capacity of the system. Various methods have been developed for the online measurement of the bicarbonate alkalinity (Table 10.3). • Organic matter: Common parameters such as the total and volatile solids, chemical oxy- gen demand, total organic matter, and biochemical methane potential (preferable to bio- logical oxygen demand in the case of anaerobic systems) express the aggregate organic matter present in a digester and, correlated with the organic matter of the inﬂuent, give an accurate estimate of the organic matter removal. However, these are time-consuming, off- line measurements, except for the total organic carbon method which can be applied on- line in the case of anaerobic systems with low solid content (Table 10.3). • Biogas ﬂow: The biogas production rate, and especially the performance in methane, is the most commonly used measurement to detect the process stability. A reduction in the biogas production rate usually suggests that the volatile fatty acids have been accumu- lated as a result of overloading or the presence of a toxicant. However, any change in this parameter is caused by process instability and cannot be an early warning, that is, it is not sensitive enough. • Biogas composition: The principal gases in the headspace of an anaerobic digester are CO2 and CH4. When CO2 increases relatively in proportion to CH4, process imbalance has already evolved and, consequently, this index cannot be used as an early indicator. On the other hand, CO2 in the gas phase is inﬂuenced by changes in alkalinity and pH in the bioreactor, and as a result when pH control is applied in low buffered systems, changes in its value do not reﬂect process instability (Ryhiner et al., 1992). Hydrogen is another signiﬁcant intermediate compound, which regulates the performance of the acetogens, used for the detection of an upcoming imbalance (Molina et al., 2009). Measuring anions and cations produced or consumed as a result of the metabolic hydrogen in the headspace does not correspond to the actual concentration sensed by the microorganisms which are in the aqueous phase. Thus, the measurement of dissolved hydrogen is suggested as a more reliable index (Frigon and Guiot, 1995). Accumulation of hydrogen leads to VFA accumulation due to thermodynamic limitations of acetogen- esis. Its concentration should be kept lower than 40 nM (which corresponds to a partial pressure less than 6 Pa at 35C). Hydrogen sulﬁde and carbon monoxide can also be detected but they are not frequently used for process control. Although the above-mentioned parameters need to be monitored and adjusted, they cannot be used as early indicators of process imbalance because they will not provide information about the complex biochemical reactions that occur in the AD process.
284 Handbook of Biofuels ProductionTable 10.3 Major methods used for monitoring the anaerobicdigestion processParameter Method ReferencesAlkalinity Titration APHA (2005), Salonen Spectrophotometry et al. (2009), and MolinaTotal, volatile solids et al. (2009)Chemical oxygen Drying Bjornsson et al. (2001) demand Oxidation and spectrometryTotal organic carbon APHA (2005)Biochemical methane Infrared analyzer APHA (2005) potential BioassayBiogas ﬂow Ryhiner et al. (1993)Methane Volumetric displacement Manometric Owens and ChynowethHydrogen (1993) Gas chromatographyDissolved hydrogen Infrared analyzer Angelidaki et al. (1992); Treatment of biogas Walker et al. (2009)VFAs with lime Smith and St€ockle (2008) Chemical sensors Alzate-Gaviria et al. (2007) Mercury-mercuric oxide Liu et al. (2004) detector cell Rozzi and Remigi (2004) Nordberg et al. (2000) Exhaled hydrogen monitor Palladium metal oxide Mathiot et al. (1992), and Pauss et al. (1990) semiconductors Thermistor thermal Collins and Paskins (1987) Pauss et al. (1990) conductivity Bjo€rnsson et al. (2001) Amperometric probe Kuroda et al. (1991) Hydrogen/air fuel cell Pauss et al. (1990) Mass spectrometry Meyer and Heinzle (1998) Silicon or Teﬂon membrane Bj€ornsson et al. (2001) tubing to transfer dissolved Brondz (2002) hydrogen to gas phase Pind et al. (2003) Boe et al. (2008) Gas chromatography (ofﬂine) Molina et al. (2009) On-line sampling and gas Peck and Chynoweth chromatography (1992) Gas phase extraction Lomborg et al. (2009) at pH < 2 Indirectly via titration Fluorescence spectroscopy Near-infrared spectroscopy
Production of biogas via anaerobic digestion 285 It is crucial to monitor and control the early process indicators such as VFA concentration and biogas composition to have a comprehensive insight of the microbiological dynamics of the AD before a process imbalance happens.• Volatile fatty acids (VFAs): These are the most important intermediate compounds in anaerobic digestion since their accumulation leads to pH decrease, stressing the metha- nogens further. The increase in acetate concentration under overload conditions does not indicate necessarily process imbalance if the biogas production rate has also increased. In this case, the system may operate at a higher acetate concentration at a new steady state, without rejecting the possibility of process failure. However, propionate and butyrate accumulation denote signs of imbalance since it usually happens when the hydrogen concentration increases. Propionate is accumulated ﬁrst, since its conversion requires a six times lower concentration of hydrogen than butyrate (Ozturk, 1991). There- fore propionate has been suggested as a suitable indicator for process imbalance along with butyrate, the ratio of propionate to butyrate, and the iso forms of butyrate and valerate (Boe et al., 2008). Depending on the metabolic pathways prevailing in an anaerobic bioreactor, VFAs may be formed at various concentrations and there cannot be a rule of thumb for a “safe” level of VFAs securing stable operation. For example, Pullammanappallil et al. (2001) found that operation of a controlled, glucose-fed biore- actor in the presence of phenol remained stable at a high propionate concentration (2750 mg/L). Moreover, the inhibition of VFAs is pH-dependent and their inhibitory effect increases at pH values ranging from 6 to 7.5. VFA concentrations and biogas composition are generally analyzed ofﬂine by chro- matographic methods (gas chromatography (GC)) and Headspace GC in large-scale biogas plants and research laboratories, which require technically more complex analyt- ical systems and well-trained employees (Vanrolleghem and Lee, 2003). They can also be monitored spectroscopically, electrochemically and by some other (mass spectrometry and titration) methods (Madsen et al., 2011). However, most of these analyses require sample preparation (Holm-Nielsen et al., 2006). Taking representative samples from the digester is a difﬁcult task and leads to sampling errors due to the highly heterogeneous and viscous nature of the AD medium. Therefore, process parameters should be moni- tored online to prevent experimental/sampling errors and human interference. Moreover, it would be easier to detect the sudden changes and predict any possible problems on time by online monitoring. The main problems in online monitoring are sample preparation and fouling of the sensors, which make most of the analytical methods inapplicable for online detection (Falk, 2012). However, recent advances in process analytical technologies using, eg, spectroscopic and electrochemical measurement principles, provide online monitoring and deciphering of the complex bioconversion processes. Most of the online process monitoring systems measure the overall process signals which are related to the mixture of different parameters. With the help of the chemometric multivariate data analysis techniques, these promising online process monitoring systems bring the AD process monitoring and control to a more reliable and effective direction. At present, online methods have not been frequently utilized in biogas plants. Still, infrared and near-infrared spectroscopies were shown to be able to monitor VFA, COD, and TOC concentrations simultaneously in industrial and lab-scale digesters (Holm-Nielsen et al., 2008; Spanjers et al., 2006; Steyer et al., 2002). To achieve this, an ultraﬁltration unit is generally included to the system to provide clear liquid free of
286 Handbook of Biofuels Production particles. Besides the ultraﬁltration, gas bubbles also interfere with the reading in spec- troscopy, therefore it is recommended to use debubblers or macerators to obtain clear, particle- and bubble-free samples (Madsen et al., 2011). The online monitoring systems should be calibrated using the samples from the system in long-term operations. It is important to calibrate the spectrometer using the samples itself; the calibration with individual standards would not provide a feasible curve because the medium in the digester has complex chemical components. Besides sampling and calibration, multivar- iate data analysis (ie, chemometrics) is a critical factor to obtain proper readings by considering the chemical interferences in the reactor. This is done by delivering the full spectra obtained from one or more process analyzers to the data interpreter in order to be analyzed, correlated, and interpreted. Then, the prediction model is estimated by the use of external validation. Although such controlling systems seem complex at present, these technologies will be improved on and simpliﬁed in the near future. • Metabolic activity: The physicochemical parameters available for measurement respond to changes in the metabolic activity of the anaerobic microorganisms, but the correlation is not always direct. Since the success of a control scheme applied on anaerobic systems is based on directing the microbial activity to the desired performance, its assessment is very important. The microbial activity can be evaluated through measurement of the speciﬁc methanogenic activity, application of molecular techniques (for the qualitative and quantitative detection of speciﬁc microorganisms based on the DNA and RNA probing) and detection of changes in cellular components such as enzymes (NADH and coenzyme F420), ATP and phospholipid fatty acids (Fountoulakis et al., 2004; Montero et al., 2009; Nordberg et al., 2000). Moreover measurements of the activity of certain enzymes and application of microcalorimetry (heat released in an anaerobic ecosystem which can be correlated to the size of the microbial population, the metabolic state, and activity) have also been used for monitoring (Switzenbaum et al., 1990). Since most of the analytical procedures required for assessing the metabolic activity are elab- orate and time-consuming or require samples of low solid content, the utilization of these measurements is limited for online control, but can be used ofﬂine to give a better insight to the system status.• Manipulated variables: The manipulated variables are operating parameters through which the process state can be affected and lead to the satisfaction of the control objective according to the applied control law. The most common manipulated variable is the dilution rate, or equivalently, the hydraulic retention time (inverse of the dilution rate). The dilution rate should generally be lower than the maximum speciﬁc growth rate constant of the slowest-growing microorganism group to avoid wash out in a continuously stirred tank reactor. In such a type of bioreactor, the sludge (solids) retention time coincides with the hydraulic retention time. In order to increase the conversion rate, recirculation of the sludge is often applied to increase the biomass con- centration. In systems fed with waste of high solid content, the liquid efﬂuent stream is recir- culated to provide it with nutrients and microorganisms. In both cases, the hydraulic and sludge retention times are separated and can be manipulated independently. The extent of manipulation of the hydraulic retention time is restricted in practice given the waste storage capacity of the treatment plants (a few hours to a few days). The hydraulic retention time in thermophilic conditions can be as low as 4e6 days, while in mesophilic conditions it is 10e15 days, although higher values of the hydraulic retention time result in more stable operation (Pind et al., 2001).
Production of biogas via anaerobic digestion 287 The organic loading rate, inﬂuenced by the organic content of the waste at a given hydrau- lic retention time, is another manipulated parameter, but since the organic content of the waste does not vary, its use is rather restricted. In the case of more than one waste stream being commonly digested (codigestion), the composition of the waste mixture is another manipulated variable. In codigestion, wastes can be combined to make up for nutrient deﬁciencies, dilute the inhibitory compounds of waste stream, and enhance the process yield of low potential waste (Alatriste-Mondragon et al., 2006; Angelidaki and Ellegaard, 2003; Dareioti et al., 2009; Li et al., 2009; Nielsen and Angelidaki, 2008; Shanmugam and Horan, 2009). Other manipulated variables are the acid, base or bicarbonate addition rates to control the pH or alkalinity in the bioreactor or the feed (Pind et al., 2001). The pH and alkalinity control require the addition of chemicals, which raises the cost of the process. An alternative is to recycle the CO2 produced in order to increase the alkalinity, but this is not effective in the case that the bioreactor pH is lower than 6.5 (Romli et al., 1994).• The control law: This is the information ﬂow structure through which the manipulated vari- ables are handled based on the measurements. The complexity of the control law is deter- mined by the diversity of the control objective. As a result, the controller can be simple (oneoff, proportional, proportional-integrated differential), more complicated adaptive model-based, empirical (expert systems), fuzzy or neural network-based. Detailed references on the various control systems applied on anaerobic digesters can be found in Boe (2006) and Pind et al. (2003).10.8 Biogas utilizationBiogas is mainly composed of methane and carbon dioxide, but also contains smallamounts of hydrogen sulﬁde, ammonia, and traces of hydrogen, nitrogen, carbon mon-oxide, saturated or halogenated carbohydrates, and oxygen. Biogas is usually saturatedwith water vapor and may also contain particles and siloxanes. The energy content isdetermined by the methane content (1 kWh per m3 of biogas with 10% of methane). The biogas can be used in as many applications as the natural gas (heating, com-bined heat and power systems, fuel cells). There may be different speciﬁcations forbiogas to be used in different applications, especially when biogas is to be used in sta-tionary appliances or to be fed to a pipeline grid. The biogas needs puriﬁcation toimprove its quality in most cases. Hydrogen sulﬁde and its oxidation products arethe major “contaminants” of the biogas (corrosive) and corrosion starts when the con-centration of H2S is above 50 ppm (Gosh, 2007). Hydrogen sulﬁde reacts with most metals. Conditions of high pressure and temper-ature (prevailing during storage or usage of biogas) favor the reactivity of this contam-inant. Sulfur dioxide also lowers the dew point of the stack gas. There are biologicalmethods for hydrogen sulﬁde removal that can be applied in the anaerobic digester aswell as other physicochemical methods applicable after biogas has been collected. Thebiological methods include the supply of a small amount of air to activate the sulﬁdeoxidizing microorganisms (Thiobacillus) grown in a microaerophilic environment onCO2 (autotrophic). The hydrogen sulﬁde is converted to elemental sulfur but also tosulfate. A combination of biological ﬁlter (containing sulﬁde oxidizing microorgan-isms) and a water scrubbing step can be used alternatively. Physicochemical methodsinclude the use of iron-containing compounds (iron chloride, iron oxide), activated
288 Handbook of Biofuels ProductionTable 10.4 Requirements to remove gaseous compounds depends onbiogas utilization (Wellinger and Lindberg, 2000)Application H2S CO2 H2OGas heater (boiler) <1000 ppm No NoKitchen stove Yes No NoCombined heat and power device <1000 ppm No NoVehicle fuel Yes Recommended YesNatural gas grid Yes Recommended YesYes, Removal is required; No, removal is not required.carbon, water scrubbing, dimethylether of polyethylene glycol (or selexol) scrubbingand NaOH scrubbing. Iron chloride can be supplied into the digester which forms ironsulﬁde (insoluble) and is applied when hydrogen sulﬁde is produced at highconcentrations. Humidity should also be removed because the presence of water favors the forma-tion of sulfur oxidation products. Water is condensed and frozen under high pressureduring biogas storage. Siloxanes can spoil pumps and heat exchangers because theyare converted to silicon oxides during the combustion and accumulate on equipmentsurfaces and reduce heat transfer and equipment lifespan. Adsorption using activatedcarbon and membrane separation techniques is used to remove siloxanes. Polydime-thylsiloxane (PDMS) has been investigated as a membrane material to eliminatesiloxanes and other traces of volatile compounds (Ajhar et al., 2012). Carbon dioxide must also be removed if the biogas has to meet natural gas speci-ﬁcations. Especially if biogas is to be used as a vehicle fuel, its methane content shouldbe enriched until it becomes higher than 90% (Harasimowicz et al., 2007). Suitablemethods for carbon dioxide removal include water absorption, polyethylene glycolabsorption (the carbon dioxide is better dissolved in selexol), carbon molecular sieves(a series of carbon columns is used to save energy required for pressure application),and membrane separation (with gas phase in both sides of the membranedhighpressure or with a liquid phase in one side for absorption of the carbon dioxide whilediffusing through the membranedlow pressure). Halogenated compounds (present inlandﬁll biogas) and oxygen (due to air entrance when landﬁll biogas is collected) mustbe removed too. The requirements for removal of these constituents are reported inTable 10.4 depending on the biogas usage.10.9 Existing biogas installationsThere are biogas plants worldwide with different degrees of technical developments.There are thousands of biogas plants in Europe and North America which processagricultural byproducts, while there are millions of small-scale digesters in China
Production of biogas via anaerobic digestion 289and India. Europe has advanced biogas plants in operation, and Germany is the leader,particularly, in biogas production from agricultural residues and sewage sludge. In2012, there were 8960 biowaste digesters (mainly farm-based; 171 industrial-scale)in European Union, which convert agricultural, industrial, and municipal wastes tobiogas (Guo et al., 2015). In the National Renewable Energy Action plan, anticipatedbiogas production in the European Union is 28 billion m3 natural gas equivalents.According to this plan, the electricity production from biogas would increase from25.2 TWh in 2009 to 63.3 TWh in 2020 (with the highest contribution (23.4 TWh)from Germany), while the production of recovered heat will rise from 0.6 to 5 Mtoe(Wellinger, 2011). Moreover, the consumption of natural gas as vehicle fuel willreach to 10e15 billion m3 by 2020 (5% of the market share in the transport sector)(Kovacs, 2013). Unlike Europe, experience with AD in North America is still limited. AD in NorthAmerica only began in late 1970s to control the odor in farms (Lusk, 1998). Recently,the anaerobic digesters for manure stabilization and energy production has improveda great deal. The number of operating farm-biogas plants increased from 25 in 2000 to176 in 2011. Biogas from farm digesters provided sufﬁcient heat to the farms andgenerated 541 million kWh of electricity in 2011 (Costa and Voell, 2012). In addition,594 US municipal solid waste disposal facilities and 1238 municipal wastewater treat-ment plants are collecting biogas from the sites, recovering 155 billion MJ of energyfor heat and electricity. This in turn reduced 99 million metric tons of greenhouse gasemissions, which is about 4% of the greenhouse gases produced by US (Kumar et al.,2015). In Canada, the Ontario government implemented a Renewable Energy StandardOffer Program in 2006, which provides farmers a higher rate for biogas-produced elec-tricity. According to this program, farmers are ﬁnancially assisted to reduce the costsof digester construction (Hilborn et al., 2007). On the other hand, AD is less promotedin Manitoba due to the well-established and cost-effective hydroelectricity industry inthat region (Wohlgemut, 2006). In Latin America, many biogas plants operate in the agricultural, industrial andmunicipal sectors. Biogas is mainly used for cooking, lighting, and as fuel for vehicles.Brazil had 25 biogas plants connected to the electricity grid in 2014 and the productionof electricity from biomass corresponded to 8.75% of the Brazilian electricity produc-tion (IEA-Members, 2015). In Mexico, farm-based digesters are widespread, gener-ating energy from cow manure (Kumar et al., 2015). In Africa, there are attempts by international organizations and foreign aid agenciesto promote biogas technology. Some digesters have been installed in some sub Saharancountries to convert feedstocks, such as slaughterhouse waste, municipal waste, indus-trial waste, and manure to biogas. Small-scale biogas plants have been established allover the continent but only a few of them are in use (Parawira, 2009). Insufﬁcientknow-how concerning anaerobic technology is claimed to be the main reason forinadequate operational potential of the installed plants. In some cases, the installationof the plant is of poor quality and lacking appropriate maintenance. In Asia (mostly China and India, but also Vietnam, Thailand, etc.) there are millionsof low-tech, hand-made plants consisting of underground, noninsulated digesters inoperation for decades. Manure and food residues are the main feedstocks used and
290 Handbook of Biofuels Productionthe biogas energy generated is used for cooking and lighting. In order to support thedevelopment of renewable energy sources, China enforces suitable legislation andtakes steps to promote the industrialization of the construction of biogas plants.In 2009, about 34,000 small-scale biogas plants and 22,900 medium- (MLBGPs,fermenter >50 m3) and 3717 large-scale biogas plants (fermenter > 300 m3) wereinstalled. The biogas project of China is forecast to increase to 10,000 livestock farmsand 6000 industrial plants by 2020 (Kumar et al., 2015). In Korea, there are 82 biogasplants, producing electricity (2578 GWh per year) particularly from landﬁlls andsewage sludge. There are 15 new biogas plants under construction to treat4764 tons of food waste and food waste leachate daily to produce 454 GWh biogasby 2017 (IEA-Members, 2015). In India, there were over three million family-sizedbiogas plants in 1999. The Indian Government provided ﬁnancial assistance in orderto build nearly four million family-sized biogas plants by the end of 2007 (Bond andTempleton, 2011). Nowadays, there is a trend toward using bigger and more sophis-ticated digesters with improved biogas productivity and digester cleansing conve-nience (Kumar et al., 2015). The ministry of nonconventional energy resourcesimplements a program (national biogas and manure management program) forproviding ﬁnancial, training and technical support for the construction and mainte-nance of biogas plants. Similar initiatives have been taken in Nepal and Vietnam(Van Nes, 2006). In Australia, electricity generation from biogas has been increased from 1605 GWhto 3234 GWh from 2000 to 2007 (UN-Statistics-Division, 2010). Wastes from foodprocessing plants, livestock manure, and human sewage are the primary feedstocksfor biogas production. Most of the installed capacity is at sewage treatment plants,which are considered highly cost-effective. The future of biogas as a competitive biofuel relies on the economic feasibility ofthe anaerobic technology. The income sources of a biogas plant are the energy and fer-tilizer sales as well as the tipping fees for receiving off-farm waste. Remuneration orsubsidies from the government is an extra income. If the cost of energy production istoo high, biogas can be burned to eliminate odors and greenhouse gas emissions, butthis is not a viable option. The biogas production cost is distinguished into the capital(or investment) and operational expenses for the installation of the plant and its main-tenance, respectively. Capital costs are determined mainly by the plant size and thetechnology selected. The prices of components (feeders, stirrers, CHP, etc.), construc-tion materials (concrete, steel) and also process monitoring equipment affect theinvestment cost. The operational costs include maintenance of the biogas plant, laborcosts, insurance, and other utilities. Laaber et al. (2007) estimated that the capital costsvary between 3000 and 5000 V/kW electricity for the AD of energy crops.10.10 Conclusions and future trendsAD is a well-established, reliable and successful technology implemented worldwide.In the past, anaerobic systems required high capital costs and elaborate expertise tooperate and maintain with low process efﬁciencies. However, in the last decade, the
Production of biogas via anaerobic digestion 291deployment of successful operating systems has increased the technical reliability ofanaerobic digesters, reducing the requirements for maintenance and special operativeskills. Moreover, many national and regional programs have been designed to cost-share in the development of anaerobic systems and promote the energy policiesexpanding the renewable energy markets. The EU policy has set a goal of supplying20% of European energy demands from renewable energy sources by 2020. The majorsources for conversion to gaseous, liquid and solid biofuels will be from farming andforestry. At least 25% of the total bioenergy may come from biogas produced from wetorganic materials such as animal manure, crop silages, wet organic food, and feedresidues, etc. There is also a growing interest in the AD of the organic fraction ofthe municipal solid waste in an attempt to reduce the materials ﬂow to landﬁlls. Apartfrom the biogas production beneﬁts, AD offers opportunities for enhanced recycling oforganics and nutrients. Codigestion of organically derived municipal waste withsewage sludge, manure, and a range of food processing and other industrial organicwastes is also promising, as it may result in producing more nutrient-balanced fertil-izers. A signiﬁcant category of lignocellulosic feedstock (primarily crops residues)has also been considered to be exploited through AD schemes. There are severalpretreatment methods developed that would allow the enhancement of the rate-limiting hydrolysis for the solubilization of the particulate substrates. Practices promoting the biogas technology may also include dissemination ofknow-how to all countries worldwide, as well as further research and developmenton: (1) small-scale systems (to go from the economy of scale to the economy ofnumbers); (2) process optimization through efﬁcient process control that would strikea balance between the often conﬂicting targets of biogas maximization and waste sta-bilization; (3) pretreatment for enhancing the process performance; (4) post-treatment(for further valorization of all byproducts and reduction of the transportation costs);(5) molecular and microbiological level that would give a better insight to the process;(6) reduction of capital and management costs; and (7) more effective elimination ofodors to minimize negative social impacts.ReferencesAhn, Y.H., 2006. Sustainable nitrogen elimination biotechnologies: a review. Process Biochemistry 41, 1709e1721.Ajhar, M., Bannwarth, S., Stollenwerk, K., Spalding, G., Y€uce, S., Wessling, M., Melin, T., 2012. Siloxane removal using silicone-rubber membranes. Separation and Puriﬁcation Technology 89, 234e244.Alatriste-Mondragon, F., Samar, P., Cox, H.H.J., Ahring, B.K., Iranpour, R., 2006. Anaerobic codigestion of municipal, farm, and industrial organic wastes: a survey of recent literature. Water Environment Research 78, 607e636.Alzate-Gaviria, L.M., Sebastian, P.J., Perez-Hernandez, A., Eapen, D., 2007. Comparison of two anaerobic systems for hydrogen production from the organic fraction of municipal solid waste and synthetic wastewater. International Journal of Hydrogen Energy 32, 3141e3146.
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Biological and fermentative 11production of hydrogenC. Ding 1,2, K.-L. Yang 1, J. He 11National University of Singapore, Singapore; 2Helmholtz Centre for EnvironmentalResearch e UFZ, Leipzig, Germany11.1 Introduction11.1.1 Hydrogen is a suitable alternative sustainable energyHydrogen, the most abundant element in the universe, is widely considered as an idealenergy carrier due to its multiple advantages. Hydrogen gas has a high energy density(lower heating value of 120.1 MJ/kg), which is three times higher than gasoline(Table 11.1). Unlike fossil fuels, there is no greenhouse gas produced from combustionof hydrogen and water vapor is its only combustion product. Therefore, hydrogen isespecially attractive due to the need for global carbon emission reduction. Moreover,when hydrogen is “burned” in vehicles through hydrogen fuel cells, the efﬁciency(usually in the range of 35e50%) is much higher than traditional hydrocarbon fuels(Ghenciu, 2002). Currently hydrogen storage is problematic because it is so light that even high-pressure cylinders cannot meet the capacity requirement for vehicles. Cryogenic sys-tems also suffer from the drawback of considerable energy input for condensation.However, there have been recent advances in hydrogen storage by chemical means.The most promising storage systems are metal hydrides (Schlapbach and Zuttel,2001) as well as metal organic frameworks (Langmi et al., 2014). Some of the mate-rials tested have shown the potential to meet the targets set by the US Department ofEnergy (DOE) for on-board hydrogen storage (Table 11.2). It should be noted that mass production of hydrogen will facilitate release ofhydrogen into the atmosphere and might have certain environmental impacts, eg,ozone depletion (Tromp et al., 2003). The potential hydrogen release from on-boardhydrogen storage can be as high as 2 million tons annually, assuming a hydrogenloss rate of 0.05 g/h/kg H2 stored (Table 11.2), vehicle number of 1 billion worldwide,and 5 kg H2 per vehicle. Considering hydrogen production and transportation, the totalamount of hydrogen release can be much higher.11.1.2 Advantages of biological production of hydrogen over physical/chemical methodsHydrogen can be produced by multiple ways including thermal processes, electrolysisof water, and biological production. Nowadays most hydrogen for industrial usage isHandbook of Biofuels Production, 2e. http://dx.doi.org/10.1016/B978-0-08-100455-5.00011-4Copyright © 2016 Elsevier Ltd. All rights reserved.
304 Handbook of Biofuels ProductionTable 11.1 Energy densities of common energy storage materials(Vendruscolo, 2014)Fuel type Energy CE LHV Density (MJ/kg) (kg C/kg) (MJ/kg) (g/cm3)Biodiesel 37 0.5 e w0.88Coal (anthracite) 15e19 0.5 33.3 w0.865Diesel 42.8 0.9 43.0 w0.832Ethanol 21 0.5 27.0 0.789Gasoline 42e45 0.84 42.5 w0.745Hydrogen gas 122 0 120.1 0.0000804 (30C)Natural gas 33e50 0.46 38.1 0.0007e0.0009CE, carbon emission; LHV, lower heating value.Table 11.2 Summary of US DOE technical system targets foron-board hydrogen storage for light-duty fuel cell vehicles(US DOE, 2012)Storage parameter Unit 2020 UltimateSystem gravimetric capacity wt.% 5.5 7.5System volumetric capacity g/L 40 70Fuel cost $/GGE at 2e4 2e4Min/max delivery temperature pump À40/85 À40/85Operational cycle life (1/4 tank to full) C 1500 1500Min/max delivery pressure from storage Cycles 5/12 3/12 bar (abs) system 3.3 2.5System ﬁll time (5 kg) min 0.05 0.05Loss of usable H2 (g/h)/kg H2 storedstill produced by steam reforming (Norskov and Christensen, 2006). As reported in2009, the worldwide production of hydrogen exceeds 1 billion m3/day, of which48% is produced from natural gas, 30% from oil, 18% from coal, and the remaining4% by water electrolysis (Venkata Mohan and Pandey, 2013).
Chemical routes for the conversion of cellulosic platform molecules 36913.4.2 Esters and ethers from furfuryl alcoholIntrinsic energy of FA can also be upgraded by means of etheriﬁcation with short-chain alcohols, transformation of alkyl-furfuryl ethers into alkyl levulinates and ester-iﬁcation with short alkyl carboxylic acids. In the following, we will discuss the mostrelevant processes. Etheriﬁcation of furfuryl alcohol is performed in the presence of strong acid cata-lysts in an alcoholic medium. In this transformation, it is important to control the re-action time and conditions. Severe reaction conditions (increasing of catalyst acidityand temperature) leads to heavy byproducts production coming from condensation re-actions of furfuryl alcohol. Likewise, although alkyl levulinates can be easily obtainedby direct esteriﬁcation of levulinic acid with the corresponding alkyl alcohol in thepresence of an acid catalyst (see Section 13.3.1), they can be advantageously preparedfrom furfuryl alcohol, without the need for isolating levulinic acid. The reaction mech-anism involves the quickly etheriﬁcation of furfuryl alcohol into the alkyl-furfurylether followed by a slowly transformation into alkyl levulinate. It is important totake into account that the transformation also involves the formation of byproductssuch as humins and ethers (dialkyl ethers from the alcohol used as reaction media).Lange et al. (2009) reported a decrease in catalytic activity in the following order:H2SO4 > macroreticular resins > gel resins > zeolites, ﬁnding that the two major fac-tors that settle the activity of catalysts are the acid strength of active sites and theiraccessibility. Another approach is the esteriﬁcation of furfuryl alcohol in the presence of carbox-ylic acids. Particularly, a process that can be considered a promising route is the directproduction of furfuryl acetate in a one-step hydrogenation-esteriﬁcation of furfuralwith acetic acid. Under moderate reaction conditions, a bifunctional catalytic systemcomposed of an acid functionality for esteriﬁcation reaction and a hydrogenating func-tionality (5% Pd/Al2 (SiO3)3 and 5% Pd/Al-SBA-15) has been proposed with goodselectivity to the desired products (Yu et al., 2011a,b).13.4.3 g-Valerolactone from furfuralDirect synthesis of GVL from furfural involves hydrogenation steps and acid-driventransformations. However, for large-scale production of GVL, catalytic systems thatmaximize yield without the use of precious metals, high H2 pressure and excessivenumber of unit operations are highly required. Catalytic transfer hydrogenation offersan alternative to molecular hydrogen. In this sense, Bui et al. (2013) have reported anintegrated catalytic process for the efﬁcient production of GVL from furfural in a one-pot process using a combination of Lewis and Br€onsted catalysts. Furfural was ﬁrstlyconverted into furfuryl alcohol through a transfer hydrogenation reaction promoted bya Lewis acid catalyst (Zr-Beta zeolite) and using 2-butanol as the hydrogen donor.Next, a Bro€nsted acid catalyst (Al-MFI zeolite) converted furfuryl alcohol into amixture of levulinic acid and butyl levulinate through hydrolytic ring-opening reac-tions. Finally, both levulinic acid and butyl levulinate underwent a second transfer-hydrogenation step to produce GVL with a yield close to 80% (see Fig. 13.3). Note
OH OH H+ HO R2 H+ O H H2O R1 O OH R OHHO R1 OHO H O O R2HO H O H OH Xylose Furfural Furfuryl alcohol Furfuryl a etherFigure 13.3 Cascade reaction for the production of GVL from xylose by the
H+ O HO R2 H3C O O 370 Handbook of Biofuels Production R O R1 O O CH3 R1 R2 R O Gamma-valerolactonealcohol Alkyl levulinates (GVL) rse combination of Lewis and Bro€nsted acid catalyst.
Chemical routes for the conversion of cellulosic platform molecules 371that a multifunctional catalyst which enables promotion of both type of reactions is achallenge for the future.13.5 Blending effect of oxygenated biofuels with conventional fuelsOxygenated fuels from lignocellulosic biomass can be used as blend components ingasoline, diesel, and biodiesel. In this section, we will discuss the works describedin the literature dealing with the blending effect of these advanced oxygenated biofuelswith conventional fuels (see Table 13.1). Christensen et al. (2011a) blended some oxygenate compounds derived from ligno-cellulosic biomass (MF, DMF, MTHF, ML, EL, BL, and MV) with three different gas-oline blend-stocks at levels up to 3.7 wt.% oxygen. Chemical and physical propertiesof the blends were compared to the requirements of ASTM speciﬁcation D4814 forspark-ignited engine fuels to determine their utility as gasoline extenders. With theexception of MF, all other oxygenates reduced vapor pressure. This may indicate aneconomic and environmental beneﬁt by eliminating the need to remove light-end com-ponents to meet maximum vapor pressure limits set to reduce evaporative emissions.The density and viscosity of blends with some of the oxygenates increased, althoughthe impact that these changes will have on vehicle fuel delivery systems is unclear. BLwas found to raise distillation temperatures (distillation end point exceeded 225C,thus failing the speciﬁcation) which may cause excessive combustion chamber de-posits and lube oil dilution. Distillation parameters for the other oxygenated com-pounds were within the speciﬁcation limits. All oxygenates tested except MTHFincreased octane rating. However, oxygenates other than MF and DMF did not havea sufﬁcient blending octane number to raise the antiknock index (AKI) (AKI ¼[RON þ MON]/2) above the 87 minimum requirement. ML is fully miscible with wa-ter and can separate from gasoline under cold temperatures. Concluding, MF and DMFappear to have good potential because of their favorable properties, MV and EL mayalso have potential as gasoline blend-stocks, while MTHF appears to have less poten-tial because of its low octane number and high water solubility. DMF is considered superior to ethanol in several important ways: it has an energycontent of 31.5 MJ/L, similar to that of regular gasoline (31.7 MJ/L) and 40% greaterthan that of ethanol (23 MJ/L); DMF (bp 92e94C) is less volatile than ethanol (bp78)C); it blends more easily with petroleum; and, contrary to ethanol, it is immisciblewith water, so it does not absorb water from the atmosphere. Rothamer and Jennings(2012) blended DMF with gasoline at volume concentrations of 5, 10, and 15%. Theknocking propensity of these mixtures was compared to the performance of E10 andgasoline. The results indicated that for direct-injection operation, ethanol is potentiallymore effective at reducing engine knock than DMF at the same blend percentage.However, due to the attractive energy density and much lower water solubility ofDMF, it is a potentially competitive blending additive. Moreover, analysis of combus-tion emissions showed that DMF mixtures gave the lowest total carbonyl emissions
372 Handbook of Biofuels ProductionTable 13.1 Oxygenated biofuels from biomass reported inliterature blended with conventional fuelsBiofuel Chemical structure Oxygen Blended with (wt%) GLN DSL BDSL2-Methylfuran (MF) O CH3 19.5 X2-Methyl-tetrahydrofuran O CH3 18.6 X (MTHF) 36.9 X 33.3 X XXMethyl levulinate (ML) O O 27.9 XXEthyl levulinate (EL) CH3 32.0 XButyl levulinate (BL) CH3g-Valerolactone (GVL) O O O CH3 CH3 O O O CH3 CH3 O H3C O O2,5-Dimethylfuran H3C O CH3 16.6 X (DMF) H3C 27.5 X O 24.6 XMethyl valerate (MV) H3C CH3 24.6 O XEthyl valerate (EV) O XEthyl tetrahydrofurfuryl O CH3 ether (ETE) O O CH3Furfuryl ethyl ether (FEE) O O CH3 25.45-Methoxy-methyl O 34.3 X furfural (MMF) O X O X5-Ethoxymethyl furfural O O 31.1 (EMF) O CH35-Buthoxymethyl furfural O 26.4 O(BMF) O CH3GLN, gasoline; DSL, diesel; BDSL, biodiesel.
Chemical routes for the conversion of cellulosic platform molecules 373and, more signiﬁcantly, the lowest emissions of the more harmful formaldehyde andacetaldehyde among the four oxygenated fuels (n-butanol, ethanol, methanol, andDMF) and gasoline (Daniel el at., 2012). Horvath et al. (2008) compared the blended properties of 10 v/v % mixtures of GVLor ethanol with 95 octane gasoline. All the data for GVL were similar to those obtainedwith ethanol, but its lower vapor pressure leads to improved performance. DerivedGVL oxygenates such as “valeric esters” have also shown even better propertiesthan GVL as gasoline extenders (Lange et al., 2010). The EV blends (10% and 20%v/v in gasoline) showed a favorable increase in octane number (RON and MON)without deterioration of properties such as corrosion and gum formation. EV blendingincreased the gasoline density and reduced its volatility and lowered its content of ar-omatics, oleﬁns, and sulfur. Moreover, the presence of EV in gasoline showed nomeasurable impact on engine wear, oil degradation, vehicle durability, engine de-posits, or regulated tailpipe emissions (EURO 4 and 5 speciﬁcations). The mixtureswere stable over the 4-month period of the test and had no negative impact on thefuel storage and dispensing equipment (tanks, pipes, pumps, and ﬁlters). Levulinate esters of ethanol (EL) and higher-molecular-weight alcohols (BL) havebeen shown as potential diesel-blending components (Christensen et al., 2011b). Bothesters improved the lubricity and conductivity of the diesel fuel. Nevertheless, the lowcetane number of both esters and poor solubility in diesel fuel at low temperatureslimits partially their commercial application as diesel blend components. EL hasalso been explored as a blend component for biodiesel (Joshi et al., 2011). The mix-tures of EL with biodiesel (2.5, 5, 10 and 20% v/v in biodiesel) showed better coldproperties with a gradual decrease of cloud, pour and ﬁlter plugging points upon addi-tion of EL. Recently, BL has been examined for blending with jet aviation kerosene(Chuck and Donnelly, 2014). Although the miscibility of BL in kerosene is good incomparison with EL, this oxygenated fuel showed the worst performance of the fuelsunder investigation. The performance of furan derivatives (FEE and ETE) in diesel engines has alsobeen assessed (de Jong et al., 2012). Smoke and particulates, as well as sulfur content,decreased signiﬁcantly with increasing ETE blending concentrations. Fuel consump-tion increases with increasing ETE amount, but is completely in line with the calcu-lated lower energy content of ETE. The CO, CO2, NO2 exhaust percentages, andTHC content appeared to be independent of ETE concentrations. NOX only shows aslight increase at higher blending percentages (>10%). Hydrogenated furanics(ETE) gave slightly better engine performance than nonhydrogenated ones (FEE). 5-HMF ethers such as MMF, EMF, and BMF are also interesting blending com-pounds for fuels (Gruter and de Jong, 2009). EMF is the main representative of the5-alkoxymethyl furfural ethers family and it is considered to be an excellent additivefor diesel. It has a high energy density of 31.3 MJ/L, which is similar to regular gas-oline (31.7 MJ/L), nearly as good as diesel (34.9 MJ/L) and signiﬁcantly higher thanethanol (23 MJ/L). With favorable blending properties, EMF has been used mixedwith commercial diesel in engine tests, leading to promising results with a signiﬁcantreduction in soot (ﬁne particulates), and a reduction in the SOx emissions. AlthoughMMF and EMF are useful as fuel additives, these ethers show at high concentrations
374 Handbook of Biofuels Productionphase separation problems. In contrast, di-ethers coming from the hydrogenation inalcohol medium of EMF and MMF are miscible with commercial diesel in all blendratios. Moreover, the ring hydrogenated products of these di-ethers have been shownto be good candidates for aviation fuel formulation (Gruter and de Jong, 2009).13.6 Catalytic conversion of g-valerolactone to liquid hydrocarbon fuelsg-Valerolactone (GVL) is a starting point (raw material) in numerous transformations.One of these processes is the production of biomass-derived hydrocarbons, with thesame properties as regular fuels obtained from conventional feedstock/procedures(Fig. 13.4). The transformation of GVL into hydrocarbons can be achieved in multiple ways,for instance, by its transformation into valeric acid (pentanoic acid) through the hydro-genolysis of the lactone cycle, as previously discussed in Section 13.3.2 (Pham et al.,2011; Du et al., 2012). From this point, once the valeric acid is produced, the mostobvious and direct way to obtain hydrocarbons is the direct hydrogenation of valericacid. However, this alternative would involve high hydrogen consumption and theﬁnal product (pentene) would not fulﬁll the requirements of conventional transporta-tion fuels, such as the boiling point. As an alternative to this option, the construction oflarger carbon chains, followed by a hydrogenation step, is preferred. In this way, theﬁnal products show carbon chains in the range of those shown by regular fuels, leadingto similar physicochemical properties in the so-obtained hydrocarbons. Carbon chainenlargement has been reported to be easily obtained from valeric acid through a keto-nization route, yielding 5-nonanone as a ﬁnal product, both in presence of CeO2/ZrO2 C9 route O Ring opening/ KetonizationGVL hydrogenation OH O O –CO2, H2O Valeric acid O H2 5-nonanone–CO2 C4 route Dehydration OH Dehydration hydrogenation Isomerization oligomerization Oligomerization hydrogenation hydrogenation hydrogenation C9 alkanes Branched C18 alkanesC12 alkanes C9 alkanesFigure 13.4 Conversion of GVL into hydrocarbons.
Chemical routes for the conversion of cellulosic platform molecules 375(Serrano-Ruiz et al., 2010a; Martin-Alonso et al., 2010; Zaytseva et al., 2013) and Pd/Al2O3 catalysts (Serrano-Ruiz et al., 2010b; Pham et al., 2011), although in the lattercase, larger contact times are required. The resultant 5-nonanone can be easily sepa-rated from water because of immiscibility, which leads to an important energy savingas compared to other alternatives. 5-Nonanone can be later hydrogenated to the corre-sponding alcohol and submitted to hydrogenation/dehydration to provide C9 hydrocar-bons, which can ﬁnally be isomerizated to achieve the required properties for thedesired fuel. A different alternative for the transformation of GVL into hydrocarbons is the directdecarboxylation of this platform molecule (Bond et al., 2010a,b) to produce a mixtureof butenes (mostly 1-butene), which can be fed as starting raw-material to conventionalalkylation units, such as the UOP Butamer process, to produce large hydrocarbonfuels. This option is quite interesting, because of the low requirements of the decarbox-ylation step, both in terms of reactantsdthe use of hydrogen, unlike hydrogenolysis, isnot requireddas well as in term of technologyddecarboxylation of GVL can beachieved in presence of mild-acid catalysts such as SiO2-Al2O3 gels operating above250C (Bond et al., 2011). In addition, the ﬁnal products, the mixture of butenes can beprocessed in already-present alkylation units in standard reﬁnery units. In this way, theproduction of regular hydrocarbon fuels can be easily achieved, by combination ofthe use of biomass-derived feedstock and conventional reﬁnery units. This procedurehas been calculated to provide proﬁts for selling prices for the ﬁnal butene oligomers inthe range 4.40e4.92 $/gallon (Sen et al., 2012a,b). Although the transformation of GVL into hydrocarbons has been mainly reportedthrough the reaction pathways involving valeric acid and butenes formation, there isstill another one, recently reported, that, due to its simplicity, shows enormous poten-tial to be carried out at an industrial scale. This is the catalytic pyrolysis of GVL toyield aromatic hydrocarbons (Zhao et al., 2012). In this case, several heterogeneousacid catalysts were tested, including different zeolites and mesostructured materials.Catalytic assays revealed a very high catalytic activity and selectivity toward aromatichydrocarbon in the case of the HZSM-5 zeolite (Si/Al ¼ 25), which provided morethan 55% of carbon yield, being fully recyclable for several consecutive catalytic as-says. This work opens a new possibility for the inclusion of biomass-derived feedstockin conventional oil reﬁnery units, a highly desirable alternative in the substitution offossil fuels by renewable energy sources such as lignocellulosic biomass.13.7 Furan derivatives as platform molecules for liquid hydrocarbon fuelsFuran platform molecules (5-HMF and furfural) can be efﬁcient converted to liquidalkanes with a high number of carbons, which can be used as gasoline, diesel, andjet fuels, by means of CeC coupling reactions whereas oxygen is removed by dehy-dration, hydrogenation, and hydrogenolysis reactions (see Fig. 13.5). These kinds ofprocesses will be discussed in this section.
HO O OH HO H OH OHDehydration H2O 2 ∙ H2 HO HMTFAHO O H O Hydrogenation O Aldol 5-HMF condensation O HMTHFA Aldol Ocondensation 3 ∙ H2 H2HO HO O O Hydrogenation O OH Deh hydro OH OH HMF AldolcondensationHO OH 5 ∙ H2 HO OO O OH O OH HydrogenationFigure 13.5 Pathways to convert 5-HMF into alkanes.Reprinted with permission of Walter de Gruyter (Ed.), Bioreﬁnery: From Bio
HO H2 H2O 376 Handbook of Biofuels ProductionHO O O OH Dehydration/ n=8 OH hydrogenation C12 alkaneHydrogenation H2 OHO HO OH O O H2O n=5 C9 alkanehydration/ ogenation OH H2 H2O O Dehydration/ n = 11 hydrogenation C15 alkaneOH OH OHomass to Chemicals and Fuels.
Chemical routes for the conversion of cellulosic platform molecules 37713.7.1 5-HMF upgrading via CeC coupling reactionsIn order to obtain diesel fuels of high quality, West et al. (2008) proposed a processinvolving the aldol condensation of 5-HMF with acetone in a biphasic reactor systemcatalyzed by aqueous NaOH, followed by hydrogenation/dehydration/ring opening inthe presence of a bifunctional catalyst such as Pd/Al2O3 and Pt/NbPO5 producing amixture of linear C9 and C15 alkanes with a yield of 73%. Similar protocol was fol-lowed by Chatterjee et al. (2010) but using Pd/Al-MCM-41 catalyst for the secondstep in supercritical carbon dioxide, achieving a 99% selectivity of C9 linear alkanes.In an attempt to coupling aqueous phase aldol-condensation of 5-HMF with acetoneand hydrogenation/dehydration reactions, a bifunctional base-metal catalyst basedon Pd supported over different mixed oxides (MgO, ZrO2, CaO, and Al2O3) hasbeen reported. For instance, using Pd/MgO-ZrO2 in that process produce C12 alkanesfrom 5-HMF (Faba et al., 2011). Recently, Liu and Chen (2014) have developed an integrated catalytic process forthe conversion of 5-HMF into alkane fuels. The integrated catalytic process involvesthree different steps: (1) 5-HMF production from fructose and glucose; (2) self-coupling of 5-HMF catalyzed by n-heterocyclic carbine (NHC) to yield furoin interme-diates; and (3) linear alkanes production by hydrodeoxygenation using metal-acidtandem as catalysts system consisting of Pd/C þ La(OTf)3 þ acetic acid. Alkaneswere produced in 78% yield with a 64% selectivity to n-C12H184.108.40.206 Furfural upgrading via CeC coupling reactionsSimilar to 5-HMF, furfural can also undergo aldol-condensation with externalcarbonyl-containing molecules using base or acid catalyst. Further hydrogenation ofaldol products can produce high-quality longer-chain alkanes. Opposite to 5-HMF, high yields of single and double condensation products areachieved in the aldol-condensation of furfural with acetone in the presence of anaqueous phase with NaOH catalyst. Mixed oxides with different basic strength havealso been used for this reaction, getting more activity with those catalysts with higherconcentration of strength basic sites, ie, Mg-Zr > Mg-Al > Ca-Zr (Faba et al., 2012).Moreover, the basic site distribution can be improved supporting the Mg-Zr mixedoxide on mesoporous carbons which leads to a higher interaction of the reactantswith the carbon surface achieving 96% conversion of furfural with 88% selectivityfor C13 and C8 adducts (Faba et al., 2013). More interesting is the sequential strategy developed by the Dumesic group. Similarto 5-HMF, the production of C10 alkanes is carried out by a cascade reaction aldol-condensation of furfural with acetone followed by hydrogenation/dehydration usinga bifunctional catalyst Pd/MgO-ZrO2 with high overall carbon yield (>80%) (Barretet al., 2006). Another sequential process of two consecutive steps to obtain a mixtureof long-chain alkanes with excellent properties as a diesel fuel (cetane number andﬂow properties at low temperature) was recently reported by Corma et al. (2012)named the “Sylvan process.” The ﬁrst step consists of a hydroxyalkylation/alkylationof three molecules of 2-methylfuran (sylvan) or hydroxylation of sylvan with
378 Handbook of Biofuels Productionaldehydes or ketones catalyzed by organic and inorganic acids to yield oxygenated in-termediate molecules (butanal is considered to be the most promising molecularlinker). In the second step, a complete hydrodeoxygenation of the previous productscatalyzed by platinum metal supported on nonacidic materials leads to the desiredmixture of alkanes within the diesel range namely 6-alkylundecane. More recently, different solid acid catalysts were studied for the alkylation of MFwith mesityl oxide (Li et al., 2014b). Among the investigated candidates, Naﬁon-212resin exhibited the highest catalytic efﬁciency, which can be explained by its higheracid strength. For the second step of hydrodeoxygenation, NieMo2C/SiO2 exhibitedan evident advantage at the cost and the selectivity to diesel range alkanes (77%yield).13.8 Sugars to hydrocarbon fuels: aqueous phase reforming processHydrodeoxygenation reactions are an effective alternative for the removal of the oxygenatoms of selected biomass-derived compounds in order to obtain biofuels (Furimsky,2013; Chaudhari et al., 2013; Nakagawa et al., 2015). However, this alternative is quiteexpensive for several reasons: the consumption of hydrogen and the usually harsh reac-tion conditions, in terms of hydrogen pressure and temperature conditions, needed todrive the desired chemical transformations. The development of highly efﬁcient, selec-tive heterogeneous catalysts enables the promotion of these transformations to partiallyovercome these latter drawbacks (De et al., 2015). In contrast, the consumption ofhydrogen is still a concern, because of the high cost associated with the productionand puriﬁcation of this chemical. Hydrogen is conventionally obtained from a process starting from fossil fuelsdtypically by methane steam reforming. However, during the last decade great effortshave been applied to develop alternative hydrogen production techniques to the con-ventional ones or in the adjustment of the already-existing methods to the use of alter-native feedstock. An interesting alternative in this last sense is the use of biomass asfeedstock for hydrogen production (Kalinci et al., 2009; Balat and Kirtay, 2010;Tanksale et al., 2010; Uddin and Daud, 2014), closing the cycle in the use of renewablematerials for the production of both the structural carbon chains of the ﬁnal pursuedchemicals and the required hydrogen used for the removal of oxygen. The production of both hydrogen and alkanes can be achieved using the same pro-cedure in a single step, aqueous phase reforming (APR) of biomass-derived oxygen-ated hydrocarbons coming from renewable biomass sources (Davda et al., 2005).APR takes advantage of the ability of several noble metal-based catalysts with hydro-genating activity, including Pd, Pt, Ru, Rh, or Ir, and their mixtures (Huber andDumesic, 2006; Shabaker and Dumesic, 2004; Tanksale et al., 2007), to favor the wa-ter gas shift reaction (WGS), starting from oxygenated hydrocarbons, under aqueousphase conditions to yield H2 þ CO or H2 þ CO2 gas mixtures, depending on the sub-strate and the reaction conditions.
Chemical routes for the conversion of cellulosic platform molecules 379 The reactions taking place in APR processes include hydrolysis, dehydration,reforming, aldol-condensation, and hydrogenolysis transformations (Benson et al.,2013), starting from polysaccharides and involving a whole collection of oxygenatedreaction intermediates. These intermediates react in contact with the surface of theaforementioned catalystsdbased on metals with hydrogenating/dehydrogenatingcapability, yielding CO. Subsequent transformation of CO into CO2 through theWGS reaction leads to the formation of hydrogen, as the main hydrogen productionpathway. Depending on the starting oxygenated hydrocarbon, the reaction mechanismis more or less complicated, but, in any case, these can be summarized as CeC andCeO bonds cleavage reactions, dehydration, hydrogenation, and dehydrogenation re-actions. In this way, the transformation of oxygenated hydrocarbons by APR allowsobtaining of multiple possible products, ranging from hydrogen to alkanes(Fig. 13.6). Depending on the objective of the APR transformation, this can be used H2O H2 C–C CO cleavage H2O H2 H2 H2O CO2 C–O cleavageOH OH H2 H2O H2 H2O CHCH CH2 Alkanes CH C–O Alcohols C–O cleavage cleavage OH H2O H2 H2O H2 Dehydration H2 Dehydration hydrogenation hydrogenation O C H2 H2O CH2 Aldehydes / ketones H2O H2 H2 OH CO2 C O CH2 Dehydrogenation Acids DecarboxylationFigure 13.6 APR reaction mechanism.Reprinted with permission of the Royal Society of Chemistry. Energy Environmental Science2012, 5, 7393e7420.
380 Handbook of Biofuels Productioneither for the production of hydrogen (ﬁrst stage) or looking for maximizing the pro-duction of larger alkanes (if reaction is allowed to proceed further). This can beachieved by tuning the catalytic activity of the hydrogenation/dehydrogenation cata-lyst, promoting or depressing the different reaction pathways, thus favoring hydrogenor alkane production. This knowledge, the ability to tune the catalytic selectivity of the heterogeneous cat-alysts which play the crucial role in the transformation of biomass-derived water-soluble oxygenated chemicals into hydrogen/alkanes, is the basis of the BioFormingProcess (Virent Energy Systems) (Dumesic and RomaneLeshkov, 2009, Fig. 13.7).The process consists of two different reaction stages in which, starting from sugarsor lignocellulosic biomass hydrolysates, hydrogen is produced in the ﬁrst step.Together with H2, several low-molecular-weight oxygenated compounds, includingStarches Soluble sugars Lignocellulose Biomass fractionation & pretreatment Polysaccharides Lignin C5&C6 sugars furans, phenolics Process heating acidsHydrogenolysis Sugar Aqueous phaseC2–C6alcohols oxygenates reforming HydrogenationHydrogen Hydrogen C1–C4 alkanes Dehydration Base catalyzed Gasoline condensation Alkene Keroseneoligomerization HDO jet fuel Alkene ZSM-5 Diesel saturationFigure 13.7 Virent’s bio-forming process.Reprinted with permission of the Royal Society of Chemistry. Energy Environmental Science2012, 5, 7393e7420.
Chemical routes for the conversion of cellulosic platform molecules 381alcohols, acids, ketones, and aldehydes are also produced. These are the basis for theproduction of larger alkanes since, in the second reaction step, the oxygenated chem-icals can be transformed, through multiple reaction pathways (condensation, hydro-deoxygenation, dehydration, oligomerization, etc.) into regular fuels, includingdiesel, gasoline, or kerosene, which can economically compete with petroleum fuelsat crude oils prices greater than 60 $ per barrel (Blommel et al., 2008).13.9 Final remarks and future outlookCommercial processes for the conversion of biomass to biofuels are now basedmainly on the production of bioethanol (from sugar cane and corn, and recentlysome commercial plants processing lignocellulose feedstock have been set up) andbiodiesel by processing of triglycerides molecules. In this chapter, the conversionof lignocellulose toward liquid biofuels has been demonstrated through the formationof several platform molecules (5-HMF, levulinic acid, and furfural). But, unfortu-nately, these kind of processes are still far from being commercial large scaleoperations. We have seen that in most cases the catalytic processes involve a large number ofreaction steps. An integrated development of catalytic cascade processes and adaptedseparation steps will be necessary for the future. Likewise, the design ofmultifunctional catalysts than can perform cascade-type reactions in less reaction stepsand avoiding intermediate product separation and puriﬁcation will facilitateimplementation of sustainable lignocellulose-based production processes. Likewise,heterogeneous catalysts must have an outstanding role to substitute homogeneous min-eral acids and bases. On the other hand, a great number of the approaches reported inthis chapter need a high amount of hydrogen in order to remove the oxygen and yieldhigh-energy-density biofuels which will have a great impact on the ﬁnal cost. Hope-fully, the transformation of carbohydrates to hydrogen using APR processes mightbe a good alternative to the current fossil-based hydrogen sources and supplyingrenewable hydrogen. Hence, much catalysis and engineering research are still neededto achieve the potential of these platform molecules for biofuel production. Other aspects to have in mind are the improvement of feedstock sustainability andavailability, and acceleration of the market deployment of the most promisingadvanced biofuels. Of course, commercial deployment of such fuels will requiresigniﬁcant effort in the areas of registration, speciﬁcation, and legislation.AcknowledgmentsFinancial support from the Spanish Ministry of Economy and Competitiveness through the proj-ect CTQ- 2014e52907-R and Regional Government of Madrid through the project S2013/MAE-2882 RESTOENE-2 are kindly acknowledged.
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Part ThreeBiofuels from thermal andthermo-chemical conversionprocesses and technologies
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Catalytic fast pyrolysis 14for improved liquid qualityS.W. Banks, A.V. BridgwaterAston University, Birmingham, United Kingdom14.1 IntroductionRenewable energy sources from biomass or waste materials are becoming more impor-tant when considering the reduction of the environmental concerns from fossil fuelsfrom carbon dioxide emissions. It has been widely accepted that climate change isoccurring due to the combustion of fossil fuels resulting in the accumulation of green-house gases in the atmosphere (Haines et al., 2006). Known global oil, gas, and coalreserves are steadily increasing due to exploration and improved extraction technolo-gies without any immediate depletion threat in sight (Abas et al., 2015); however thesefossil fuels are ﬁnite resources, so energy security has become a major world issue.Heat and power production and transportation are major uses of fossil fuels and willbe greatly affected as the fossil fuels become more scarce and more expensive. Renew-able and alternative energy sources are keys to the solution of a twin problem, energyand climate change, but require a high initial investment. Alternative sources of energy such as wind, solar, and nuclear are not able toreplace fossil fuels in current petrochemicals requirements. Large-scale industrialchange would be required to replace current large-scale chemical technologies basedon fossil fuel processing that supplies ﬁne chemicals, fertilizer, polymers, etc. Aneffective alternative for the generation of petroleum-like products from renewable orwaste material sources is required to meet the essential requirements of the currentchemical and petroleum economies. Fast pyrolysis is one of the means of producingpetroleum-like products and higher-value chemicals from renewable or waste materialsources. As fast pyrolysis technologies improve and the quest for suitable alternativeand renewable energy sources continues, pyrolysis has the potential to play a biggerrole in reducing the reliance on fossil fuels. Generally there are two methods thatcan be used to improve the ﬁnal quality of the bio-oil produced from pyrolysis. Theﬁrst option is to improve the quality of the source biomass prior to processing. Thiscan be achieved by using feedstocks that have the required composition, such asthrough careful growing and harvesting or by using genetically modiﬁed sources ofbiomass (Strauss et al., 2001). Alternatively the feed material can be pretreated priorto pyrolysis (Banks et al., 2014; Bergman and Kiel, 2005; Jenkins et al., 1996;Mani et al., 2004) such as by washing. The second option is to upgrade the ﬁnal prod-uct (Pattiya et al., 2006); this can be achieved by introducing a catalyst into the fastpyrolysis reaction system to improve the quality of the bio-oil vapors (Bridgwater,1996). Upgrading bio-oil to a conventional transport fuel requires full deoxygenation,Handbook of Biofuels Production, 2e. http://dx.doi.org/10.1016/B978-0-08-100455-5.00014-XCopyright © 2016 Elsevier Ltd. All rights reserved.
392 Handbook of Biofuels Productionwhich can be accomplished by two main routes: catalytic vapor upgrading and hydro-treating. This review will focus on catalytic pyrolysis vapor upgrading.14.2 Pyrolysis backgroundPyrolysis is a thermochemical conversion technique where organic material is decom-posed at elevated temperatures in the absence of oxygen. The term pyrolysis is derivedfrom the Greek elements pyro “ﬁre” and lysis “separating.” Pyrolysis of organic ma-terial always produces three products; liquid, noncondensable gas, and a solid char res-idue (Bridgwater, 2012a,b). The proportions are determined by the technology andtimeetemperature envelope, and are detailed below. Renewable energy sourcesfrom organic material are of growing importance when considering trying to reducethe environmental concerns from fossil fuels and pyrolysis is one of several possiblestrategies to develop a renewable energy source. Current fast pyrolysis research and industrial use focuses on lignocellulosic mate-rials (Bu et al., 2012; Shra’ah and Ahmad, 2014; Choi et al., 2012; Liu et al., 2014) andresidues and waste materials (Fonts et al., 2012; Azargohar et al., 2014; Muhammadet al., 2015a,b; Ridout et al., 2015; Zwetsloot et al., 2015; Zhang et al., 2015) as arenewable energy source for heat and power and as a potential biofuel source or forproduction of higher-value chemicals. This is to avoid the conﬂict of edible crops be-ing used to produce biofuel (Hunger, 2008; Graham-Rowe, 2011; Valentine et al.,2012; Mekonnen et al., 2015) such as ﬁrst-generation bioethanol and biodiesel.Bioethanol is currently the most common biofuel worldwide (particularly Brazil)(Chen and Saghaian, 2015) and is currently mostly produced by the fermentation ofsugars derived from edible crops such as wheat, corn, and sugarcane, although anew waste gasiﬁcation and alcohol synthesis plant has recently started up in Edmon-ton, Canada (Chornet et al., 2013; Lavoie et al., 2013). Increasing attention is beingpaid to second-generation ethanol to avoid the use of food crops. Lignocellulosic material includes wood from forestry, forest residues, short rotationcoppice, and lignocellulosic energy crops such as energy grasses. Residues and wastematerials include agricultural residues, municipal solid waste (MSW), municipal plas-tic waste (MPW), sewage sludge, waste food, and vegetable residues.14.2.1 PyrolysisPyrolysis converts organic materials by heating in the absence of oxygen to produce anumber of products; bio-oil, char, and noncondensable gas (Bridgwater, 2012a,b).There are a number of types of pyrolysis, with the main two being slow pyrolysisand fast pyrolysis. Details on each pyrolysis residence time, heating rate, operatingtemperature range, and product spectrum are given in Table 14.1 (Bridgwater andBridge, 1991). Bio-oil refers to the volatile components from fast pyrolysis aftercondensation and much current research aims to upgrade this bio-oil into a moreacceptable heat and power resource and also biofuels and chemicals. Upgrading is
Catalytic fast pyrolysis for improved liquid quality 393Table 14.1 Modes of pyrolysisPyrolysis Hot vapor Solid Heating Operating Liquid Solid chartype residence residence temperature time time rate (8C) (oC/s)Slow 5e30 s 200e 0.10e1 350e500 30e50% 30e50 wt.%Fast 1e2 s 20000 s 2 phases: 60e70% aqueous, 30e40% organic 2e10 s 10e200 450e550 50e75 wt.% 10e20 wt.% Usually This is usually single phase burned in the process for heatmostly based on catalytic processing supplemented by feed modiﬁcation and processimprovement (Banks et al., 2014; Jenkins et al., 1996; Raveendran et al., 1995; Tanand Wang, 2009; Harmsen et al., 2010). The types of biomass, especially ash content, heating rates, and hot vapor residencetimes, have a major effect on the product composition (Jahirul et al., 2012). The typicalproduct composition for fast pyrolysis of clean dry wood is 75 wt.% liquid, 12 wt.%char (usually consumed in the process for heat), and 13 wt.% gas, compared to slowpyrolysis which is 30 wt.% liquid, 35 wt.% char, and 35 wt.% gas (Bridgwater,2012a,b).14.2.2 Fast pyrolysisThe homogeneity and much higher yield of liquid from fast pyrolysis mean that this isthe preferred technique for liquid products (bio-oil). There are a number of essentialfeatures of a fast pyrolysis process:1. Small particle sizes to minimize heating time and maximize heating rate;2. Low feed water content of less than 10 wt.% to minimize water in the liquid product;3. Very high heating rates to minimize reaction times;4. Carefully controlled pyrolysis reaction temperatures of typically 475e525C to maximize bio-oil yields;5. Short hot vapor residence times of typically less than 2 s to minimize secondary reactions such as cracking;6. Rapid removal of char to minimize secondary catalytic cracking of vapors on the active char;7. Rapid cooling of vapors and aerosols to form bio-oil to minimize further cracking reactions which lead to increased yields of water, gas, char, and tar. The hot vapor residence time is deﬁned as the time feed material spends passingthrough the pyrolysis chamber heated zone and associated hot pipework and cyclones
394 Handbook of Biofuels Productionprior to any condensation processes (Moo-Young, 2013). The heating rate is deﬁned asthe time taken for the feed material to reach the pyrolysis reaction temperature (Lédé,2010); the feed material maximum temperature may be less than the pyrolysis reactiontemperature as it is not always possible to reach equilibrium. In addition, very small particle sizes of typically less than 5 mm are required toachieve the necessary high heating rates as biomass has low thermal conductivity;and the feed material needs to be dried to less than 10 wt.% moisture to control theliquid product water content as all feed water reports to the liquid bio-oil.14.2.3 Distribution of fast pyrolysis products from certain biomass componentsThere are no standard decomposition processes for biomass components: cellulose,hemicellulose, and lignin. The varying proportions of cellulose, hemicellulose, andlignin in biomass inﬂuence the fast pyrolysis product distribution. The thermal decom-position of cellulose has been studied extensively as it is the major component of woodand has a less complex structure compared to hemicellulose and lignin. Fast pyrolysisconditions (biomass particle size, pyrolysis temperature, and hot vapor residence time)have an effect on fast pyrolysis products, as well as biomass component composition,poor thermal conductivity of biomass, high reactivity of volatiles, and the catalyticeffect of char and alkali metals contained in ash (Nowakowski and Jones, 2008;Nowakowski et al., 2007; Nik-Azar et al., 1997; Patwardhan et al., 2010). Fig. 14.1shows the general distribution of fast pyrolysis products from speciﬁc biomasscomponents. Cellulose and hemicellulose primary decomposition components arecondensable vapors (bio-oil) and gas. Lignin’s primary decomposition componentsare bio-oil, solid (char), and noncondensable gases. Also found in biomass are extrac- Cellulose WaterHemicellulos Organic Lignin liquid Non- condensable gasExtractives CharAsh AshFigure 14.1 Distribution of fast pyrolysis products from certain biomass components.
Catalytic fast pyrolysis for improved liquid quality 395tives which contribute to bio-oil and noncondensable gas yields and mineral content(such as alkali metals) are entrained in char. The fast pyrolysis decomposition of cellulose starts at temperatures as low as150C. Pyrolysis of cellulose below 300C results in the formation of carboxyl,carbonyl, and hydro peroxide groups, elimination of water and production of carbonmonoxide and carbon dioxide as well as char residue (Evans and Milne, 1987). There-fore low pyrolysis temperatures will produce low yields of organic liquid yields. Fastpyrolysis of cellulose, above 300C, results in liquid yields up to 80 wt.%. Celluloseinitially decomposes to form activated cellulose (Bradbury et al., 1979). Activated cel-lulose has two parallel reaction pathways, depolymerization and fragmentation (ringscission). The main products from each reaction pathway are rather different as ringscission produces hydroxyacetaldehyde, linear carbonyls, linear alcohols, esters, andother related products (Bradbury et al., 1979; Zhu and Lu, 2010; Lin et al., 2009)and depolymerization produces monomeric anhydrosugars, furans, cyclopentanones,and pyrans and other related products (Bradbury et al., 1979; Zhu and Lu, 2010;Lin et al., 2009). Each reaction pathway is independent and is inﬂuenced by pyrolysistemperature and residence time (Bradbury et al., 1979). The primary hemicellulose components are xylan and glucomannans, which whenpyrolyzed form varying yields of char and depolymerization products (Zhu and Lu,2010). Pyrolysis of xylan produces higher char yields compared to cellulose and nottypical depolymerization products such as levoglucosan (Zhu and Lu, 2010). Pyrolysisof glucomannan produces similar pyrolytic products to cellulose (Zhu and Lu, 2010).Glucomannans pyrolysis is similar to cellulose as the glycosidic bonds are cleaved tofrom stable monomeric anhydrosugars (Shen et al., 2010). Xylan follows an alternativepyrolytic dehydration pathway which results in an increased char formation (Shenet al., 2010). Lignin is the most thermally stable component of biomass. Fast pyrolysis of ligninproduces high char yields and low liquid yields compared to both cellulose and hemi-cellulose. The liquid product has three speciﬁc groups, large molecular oligomerswhich account for the majority of the liquid product (Garcia-Perez et al., 2008). Theother two groups are monomeric phenolic compounds and light compounds such asacetic acid (Garcia-Perez et al., 2008; Oasmaa et al., 2003). Due to the complexityof its structure, there are no general pathways which can be proposed. From previousexperiments it can be found that the pyrolysis products from lignin can be split intoeight different groups: light volatiles, catechols, vanillins, guaicols, propyl guaicols,phenols, aromatic hydrocarbons, and others (Hosoya et al., 2007; Nowakowskiet al., 2010; Yang et al., 2007). Distribution of pyrolysis products and speciﬁc compounds produced (particularlyin the liquid fraction) can be greatly affected by the introduction of a catalyst to thepyrolysis reaction system. Catalytic pyrolysis, the main subject of this chapter, isnot so different to standard pyrolysis but has a signiﬁcant effect on pyrolysis productsby enhancing potential biofuel or higher-value chemical production. Catalytic pyroly-sis is covered in depth below.
396 Handbook of Biofuels Production14.2.4 Fast pyrolysis products220.127.116.11 Liquid bio-oilBio-oil is relatively viscous, acidic, and relatively unstable and contains a high level ofoxygen due to the oxygenated compounds (Czernik and Bridgwater, 2004). Advancesin current fast pyrolysis techniques are aimed at producing a bio-oil of improved qual-ity so that it can replace or supplement current fossil fuel usage in heat and power ap-plications. Fast pyrolysis liquids are nonmiscible with hydrocarbons (Bridgwater andPeacocke, 2000). High water content in the product of above 40 wt.% can result inphase separation (Oasmaa and Czernik, 1999). This phase separation is irreversible un-less large quantities of a miscible chemical such as ethanol are added. Table 14.2shows the typical properties of wood pyrolysis bio-oil. The composition of bio-oil is dependent on feed material composition and origin,pyrolysis temperature, residence time, heating rates, collection system, and storageconditions (Huber et al., 2006). The chemical composition of bio-oil is very complex,and in general is composed of water, organics, and a small amount of ash. Theorganic components consist mainly of alcohols, furans, phenols, aldehydes, andorganic acids (Garcia-Perez et al., 2007). Bio-oil is a homogeneous mixture of anaqueous phase and a nonaqueous phase compounds. The aqueous phase consistsof low-molecular-weight oxygenated organic compounds (Williams and Nugranad,2000). The nonaqueous phase consists of high-molecular-weight oxygenates, aro-matics, and polycyclic aromatic hydrocarbons (Williams and Nugranad, 2000).Table 14.2 Some typical properties of bio-oilPhysical property Bio-oilMoisture content, wt.% 15e30pH 2.5Speciﬁc gravity 1.2Elemental composition, wt.%C 54e58H 5.5e7.0N 0e0.2O 35e40Ash 0e0.2HHV, MJ/kg 16e19Viscosity (at 50C), cP 40e100Solids, wt.% 0.2e1Distillation residue, wt.% Up to 50
Catalytic fast pyrolysis for improved liquid quality 397Bio-oil has a low hydrogen/carbon ratio which is a limiting factor on hydrocarbonyield; methanol can be added to the pyrolysis process as a hydrogen donor (Horneet al., 1995). Due to the number of compounds and complexity of bio-oil, it hasbeen difﬁcult to fully characterize. Gas chromatography (GC) analysis has beenused to identify compounds within bio-oil but is limited due to a large fraction ofthe oil comprising of lignin and carbohydrate oligomers, which are not volatileenough to be detected by GC analysis (Mohan et al., 2006). A single-phase bio-oil has a water content of approximately 15e30 wt.% (Czernikand Bridgwater, 2004) but the water content of the aqueous phase of a phase-separatedbio-oil can be as high as 80 wt.%. ASTM has recently deﬁned several grades of bio-oilas well as the conditions necessary for its formation and production (ASTM D7544-12,2012). The water is derived from feed material moisture, reaction water produced dur-ing pyrolysis, reaction water from secondary cracking, and bio-oil storage. The pres-ence of water has both a positive and negative effect on bio-oil characteristics: waterlowers the heating value but reduces the viscosity and helps to stabilize the bio-oil.Bio-oil can separate into two phases as water content increases (Oasmaa and Czernik,1999). A tar-like product with a high viscosity forms a bottom layer comprising ofhigh-molecular-weight lignin products (Oasmaa and Czernik, 1999); while an aqueousphase of low viscosity forms a top layer comprising mainly of products from thedecomposition of cellulose and hemicellulose (Oasmaa and Czernik, 1999). The oxygen content of bio-oil is usually 35e40 wt.% (Czernik and Bridgwater,2004), and is contained in oxygenated organic compounds making up bio-oil. Thehigh oxygen content results in a lower energy density when compared to conventionalfuel by up to 50% (Zhang et al., 2007). Bio-oil contains large amounts of organic acids,such as acetic and formic acids, which leads to an acidic liquid with a typical pH valueof 2e3 (Zhang et al., 2007). Due to the acidity of bio-oil it is corrosive, which requiresspeciﬁc construction materials being used for storage vessels (Laird et al., 2009; Aubinand Roy, 1990) or subsequent upgrading processes. Bio-oil viscosity can vary greatlydepending on feed material, pyrolysis parameters, content of light compounds, temper-ature, and storage time. Sipil€a et al. (1998) found that viscosity was reduced in bio-oilwith higher water contents and less water-insoluble components. When bio-oil isstored it goes through an aging process which leads to an increase in viscosity (Oasmaaand Czernik, 1999) from condensation reactions taking place within the bio-oil. Themajority of ash contained in biomass is concentrated in char, but small amounts ofﬁne char can be entrained in bio-oil. Alkali metals within the ash are problematic,which can lead to cracking reactions within the bio-oil.18.104.22.168 Solid charFast pyrolysis char is a byproduct of pyrolysis which is high in carbon, contains lowamounts of hydrogen and almost all of the ash which was present in the feed material(Brewer et al., 2009; Chun et al., 2004; Westerhof, 2011; Jeffery et al., 2011). The py-rolysis char can be separated from the other products where it can be used for otherapplications such as Biochar or more usually in all current fast pyrolysis demonstrationand commercial processes, it is burned to provide process heat in a secondary
398 Handbook of Biofuels Productioncombustion reactor (Yanik et al., 2007; Tsai et al., 2007). If separated, the char can beadded to soil to improve upon its characteristics as a soil amendment (Biochar) (Jefferyet al., 2011; Lehmann et al., 2006; Laird, 2008). This is potentially an interesting appli-cation due to the carbon sequestration beneﬁt that biochar can have (Laird, 2008;Lehmann et al., 2006). It has been claimed that it can also be used as a replacementfor coke (Lovel et al., 2007; Goyal et al., 2008), an advanced adsorbent (Goyalet al., 2008; Mohan et al., 2011; MacDonald and Quinn, 1996; Raveendran andGanesh, 1998; Mohan et al., 2014), or a catalyst for speciﬁc processes/reactions (Goyalet al., 2008; Zabaniotou and Stavropoulos, 2003).22.214.171.124 GasesFast pyrolysis gas (noncondensable gas) mostly consists of carbon dioxide, carbonmonoxide, and methane. Research by Yanik et al. (2007) pyrolyzed three agriculturalwastes and found that carbon oxides made up 84e90 v/v% of the fast pyrolysis prod-uct gas, with methane accounting for 6e8 v/v%, hydrogen and C2eC4 were found inminor amounts. The composition varied very little between all three agricultural wasteproduct gases. As pyrolysis gas contains the basic components of syngas (carbon mon-oxide, carbon dioxide, and hydrogen), it could be utilized as an energy source but othertechnologies are more competitive (gasiﬁcation) for syngas production (McKendry,2002; Patra and Sheth, 2015). In some pyrolysis systems, the pyrolysis gas can beused for ﬂuidization (Ringer et al., 2006); this results in the pyrolysis product gasbecoming diluted with the ﬂuidizing gas. By using the pyrolysis gas as part of the ﬂuid-izing stream can increase the hydrogen/carbon ratio within the pyrolysis reactor systemtherefore increasing hydrocarbon content in the bio-oil.14.3 Catalytic pyrolysis14.3.1 Catalytic upgradingCatalytic upgrading offers the possibility of upgrading bio-oil to a product with morefavorable properties (Bridgwater, 2012a,b). Fast pyrolysis produces bio-oil by rapidlyheating biomass up to a controlled temperature of between 400 and 600C (Scott et al.,1988). Bridgwater and Peacocke (2000) reported that fast pyrolysis producesmaximum yields at processing temperatures around 500C. The feed material isusually speciﬁed as less than 10 wt.% water content (Jahirul et al., 2012) as all feedwater ends up in the hydrophilic bio-oil as well as the water of reactions (Demirbas,2004). The essential features of fast pyrolysis for producing liquids are very high heat-ing (Fred and Peter, 1977) and heat transfer rates (Bridgwater and Bridge, 1991)which require a feed of an appropriate particle size which is usually less than 3 mm(Papadikis et al., 2010; Wang et al., 2005; Di Blasi, 2002). The pyrolysis temperatureshould be carefully controlled as reported above. The vapor phase temperature has tobe carefully monitored and controlled to at least 425C to minimize tar condensationleading to blockages and not above 460C to minimize thermal cracking reactions.
Catalytic fast pyrolysis for improved liquid quality 399Fast pyrolysis has a short hot vapor residence time typically less than 1 s (Bridgwateret al., 1999). The residence time has to be kept as short as possible to prevent second-ary reactions taking place which will convert the condensable fast pyrolysis vaporsinto permanent gases, water vapor, and char (Liden et al., 1988; Scott et al., 1999).Typical liquid yields are around 75% from clean wood (Bridgwater et al., 1999). Catalytic pyrolysis is usually carried out to improve one or more of the less desir-able properties of bio-oil. There are many such attributes that are summarized inTable 14.3. Usually only one or two of these properties can be successfully addressed in anupgrading process, so attention is best focused on properties that inhibit use in com-mon applications such as acidity and/or which offer the most valuable productssuch a biofuels.Table 14.3 Characteristics of bio-oilCharacteristic Cause EffectsAcidity or low pH Organic acids from biopolymer Corrosion of vessels andAging degradation pipeworkAlkali metals Continuation of secondary Slow increase in viscosity from reactions including secondary reactions such asChar polymerization condensation, potential phase separationChlorine The majority of all alkali metalsColor report to char so not a big Catalyst poisoning, depositionContamination of problem, high ash feed, of solids in combustion, incomplete solids separation erosion and corrosion, slag feed formation, damage to turbinesDistillability is poor Incomplete char separation in process Aging of oil Sedimentation Contaminants in biomass feed Filter blockage Cracking of biopolymers and Catalyst blockage Engine injector blockage char Alkali metal poisoning Poor harvesting practice Catalyst poisoning in upgrading Reactive mixture of degradation products Discoloration of some products such as resins Contaminants, notably soil, act as catalysts and can increase particulate carry over Bio-oil cannot be distilleddmaximum 50% typically. Liquid begins to react at below 100C and substantially decomposes above 100C Continued
400 Handbook of Biofuels ProductionTable 14.3 ContinuedCharacteristic Cause EffectsHigh viscosity Biomass has low H:C ratio Gives high-pressure drop increasing equipment cost,Low H:C ratio Phenolics and aromatics high pumping cost, poorMaterials atomization Highly oxygenated nature of incompatibility bio-oil Upgrading to hydrocarbons isMiscibility with more difﬁcult Contaminants in biomass feed hydrocarbons is High-nitrogen feed such as Destruction of seals and gaskets very low proteins in wastesNitrogen Biomass composition Will not mix with any hydrocarbons so integrationOxygen content is High feed water, high ash in into a reﬁnery is more very high feed, poor char separation difﬁcultPhase separation or Aldehydes and other volatile Unpleasant smell, catalyst inhomogeneity organics, many from poisoning in upgrading, NOx hemicellulose in combustionSmell or odor See also char, particulates from Poor stability, nonmiscibilitySolids reactor such as sand, with hydrocarbons particulates from feedStructure contamination Phase separation, partial phase separation, layering; poorSulfur The unique structure is caused mixing, inconsistency inTemperature by the rapid depolymerization handling, storage and and rapid quenching of the processing sensitivity vapors and aerosols While not toxic, the smell is Contaminants in biomass feed often objectionable Incomplete reactions Sedimentation, erosion and corrosion, blockage Susceptibility to aging such as viscosity increase and phase separation Catalyst poisoning in upgrading Irreversible decomposition of liquid into two phases above 100C, irreversible viscosity increase above 60C, potential phase separation above 60C
Catalytic fast pyrolysis for improved liquid quality 401Table 14.3 ContinuedCharacteristic Cause EffectsToxicity Biopolymer degradation Human toxicity is positive butViscosity products small, eco-toxicity isWater content negligible Chemical composition of bio-oil Fairly high and variable with Pyrolysis reactions, feed water time Greater temperature inﬂuence than hydrocarbons Complex effect on viscosity and stability: increased water lowers heating value, density, stability, and increase pH, affects catalysts14.3.2 Catalytic pyrolysis: improved pyrolysis oil generation or production of higher-value chemicalsThe conversion of lignocellulosic materials and waste materials into bio-oil using py-rolysis technology is one of the most promising technologies to convert solid feed-stocks into liquid products. However, substituting bio-oil for conventional liquidfossil fuels is problematic due to high viscosity, high oxygen content, and thermalinstability. Therefore catalysts are being utilized in the pyrolysis reaction system to up-grade pyrolysis vapor to obtain a bio-oil product with decreased oxygen and polymer-ization precursor content to improve its heating value and thermal stability. Catalyticpyrolysis has many advantages over other conversion processes (Carlson et al., 2011).These are:1. Converting biomass into hydrocarbons and higher-value chemicals in a single step with one reactor (other pyrolysis reaction systems can be used which have more than one step and reactor);2. Increased yields of ﬁve major petrochemicals (benzene, toluene, xylene, ethylene, and propylene);3. The pyrolysis reactions take place in an inert atmosphere without high-pressure hydrogen;4. Pyrolysis vapors are directly upgraded without bio-oil condensation and vaporizing processes;5. Operated with short residence times (<10 s) to minimize secondary reactions;6. Inexpensive catalysts can be used;7. A broad range of feedstocks can be used, from lignocellulosic materials to waste materials;8. Feedstocks may require simple pretreatment processing. Added costs are incurred when catalysts are introduced to the pyrolysis system. Dueto this increased operation cost catalysts have to be developed to show good
466 Handbook of Biofuels Productionto be lower than the ash melting point (around 1000C) in order to avoid ash sinteringand slagging (Navarro et al., 2007; Ni et al., 2006; Huber et al., 2006).15.5.2 Cleaning technologiesDue to the presence of the contaminants previously described, syngas must be condi-tioned prior to its use. Cold and hot conditioning routes can be followed (Fig. 15.12)(Huber et al., 2006; Hamelinck and Faaij, 2002; Tijmensen et al., 2002). The cold routeis the most extended at industrial level, since the hot route has not been completelydeveloped (Hamelinck and Faaij, 2002). However, the hot route presents better overallenergy efﬁciency when the syngas is to be used downstream at high temperature.For this reason intense efforts are being made to implement the hot route treatments(Xu et al., 2010; Hamelinck et al., 2004).126.96.36.199 TarsThe removal of tars is one of the biggest challenges of biomass gasiﬁcation (Navarroet al., 2007; Huber et al., 2006; Hannula, 2009; Devi et al., 2002; Zwart, 2009). Its costcan knock down a whole project (Balat and Kirtay, 2010). Primary and secondaryapproaches can be used to deal with the problem. Primary measures are taken inthe gasiﬁer: improvement of gasiﬁer design, optimization of operation conditions,and use of additives (Navarro et al., 2007; Ni et al., 2006; Devi et al., 2002). Cold route Gas Bag filter COS cooling EPS hydrolysisRaw syngas Tar Cyclones Tars Scrubber Scrubber ashes oil NaOH cracker Tars ashes Tars H2S Tars HCl Use of syngas Traces H2S HCl NH3Hot routeRaw syngas Granular beds H2S/HCl NH3 Use of syngas Tar candle filters adsorption decomposition cracker Tars H2S NH3 ashes HCl TarsFigure 15.12 Routes for removal of contaminants from syngas (Huber et al., 2006; Hamelinckand Faaij, 2002; Milne et al., 1998; Zwart, 2009).
Production of bio-syngas and bio-hydrogen via gasiﬁcation 467Secondary measures are taken after the gasiﬁcation process. In this section onlythe second approach will be described. Tar removal starts with tars cracking in both hot and cold routes, since it is donebefore cooling down the gas stream due to the high temperatures needed (Hamelinckand Faaij, 2002). In the cold route, gas is cooled down and the remaining tars areremoved by wet scrubbing (in water or oils), ﬁltering, cyclones, or electrostatic precip-itators (Hannula, 2009; Basu, 2010a,b; Han and Kim, 2008; Zwart, 2009). Alkalimetals and particulates are also removed in wet scrubbers along with tars. These tech-nologies are simple and cheap, although the ﬁnal production tar-laden products needfurther treatment (Hannula, 2009; Han and Kim, 2008). Hot tars can be removed by thermal or catalytic cracking (Huber et al., 2006; Deviet al., 2002; Abu El-Rub et al., 2004). Thermal cracking comprises very high temper-atures, even higher than gasiﬁcation, leading to energy penalties (Huber et al., 2006).Moreover, it gives rise to soot production, which can be a technical problem down-stream (Huber et al., 2006). For these reasons catalytic cracking is the preferredprocess (Huber et al., 2006). Catalytic cracking consists of the reaction of the tars with steam (steam reforming,Reaction [xv]), CO2 (dry reforming, Reaction [xvi]), O2 (partial oxidation, Reaction[xvii]), or H2 (hydrocracking, Reaction [xviii]) (Huber et al., 2006).CnHm þ nH2O/ðm=2 þ nÞH2 þ nCO [xv]CnHm þ nCO2/m=2 H2 þ 2nCO [xvi]CnHm þ n=2O2/m=2H2 þ nCO [xvii]CnHm þ ð4n À mÞ=2H2/nCH4 [xviii] These reactions affect the H2/CO/CO2 ratio, which will determine the ﬁnal use ofthe syngas (Huber et al., 2006). Similarly to catalytic gasiﬁcation, natural mineralsand synthetic catalysts can also be used (Huber et al., 2006; Abu El-Rub et al.,2004; Zwart, 2009). Natural minerals include low-price dolomite, olivine, limonite,and clays that work at temperatures from 700 to 1000C and contact times from0.007 to 7 s (Turner et al., 2008; Huber et al., 2006; Xu et al., 2010; Yung et al.,2009; Abu El-Rub et al., 2004). From the synthetic catalysts, noble metal-based catalysts are the best, especiallyfrom the coking resistance point of view (Holladay et al., 2009; Han and Kim,2008; Yung et al., 2009). However, as in the oil and gas industry for naphta cracking,their high price makes Ni the most common catalyst for tar cracking (Huber et al.,2006; Holladay et al., 2009; Han and Kim, 2008; Yung et al., 2009). Ni-based catalystsnormally work at temperatures in the range of 600e900C and contact times around0.01e3 s (Huber et al., 2006). Other metals that can be used are Co or Fe (Huber et al.,2006; Yung et al., 2009). Regarding the supports, alumina is normally used forNi-based catalysts due to its high surface area and good mechanical properties (Huberet al., 2006; Yung et al., 2009). In addition, it provides acid sites, which promote
468 Handbook of Biofuels Productioncracking. However, supports like SiO2, ZrO2, activated carbons, zeolites, or naturalminerals have also been used (Han and Kim, 2008; Xu et al., 2010; Yung et al.,2009; Abu El-Rub et al., 2004). Deactivation of the catalysts is a great issue in the catalytic cracking of tars. It can becaused by carbon deposition (due to the high C/H ratio of the tars) or poisoning by sul-fur, chloride, and alkali (Huber et al., 2006; Yung et al., 2009; Trimm, 1999). Differentstrategies have been developed in the design of the catalyst to avoid this problem(Huber et al., 2006; Yung et al., 2009; Abu El-Rub et al., 2004; Xie et al., 2010;Nikolla et al., 2006; Laosiripojana et al., 2014):1. Use of bimetallic catalysts: a second metal (Sn, Co, Rh, Cu) can give rise to different struc- tures like alloys, more resistant to carbon deposition (by decreasing solubility and diffusion of carbon atoms in metal particles) and sulfur poisoning (by sacriﬁcing the second metal which is more easily sulﬁded, whereas the main metal can maintain its activity).2. Use of promoters: basic oxides (Na2O, K2O, MgO, CaO, ZrO, La2O3) are able to reduce car- bon deposition due to their ability to adsorb CO2 that can gasify the carbon deposits. La2O3 can form carbon-resistant spinels with Ni and alumina. Ce2O3 has also been shown as a very promising promoter since its high oxygen storage capacity helps gasifying the carbon deposits and its redox capacity increases resistance to sulfur poisoning. The catalysts can be regenerated by oxidizing agents (O2, air, H2O) that can removecoke and sulfur from the catalyst surface (Huber et al., 2006; Argyle and Bartholomew,2015). However, repeated regeneration cycles lead to irreversible deactivation due tosintering, phase transformations, or loss of active metal particles (Huber et al., 2006;Argyle and Bartholomew, 2015).188.8.131.52 SulfurIn the cold route, H2S is removed by scrubbing the syngas using amines (normallymethyl diethanol amine, MDEA). Methanol or liquid solutions of NaOH and physicalsorbents like polyethylene glycol are also widely used (Hannula, 2009; Liu et al.,2009; Higman and van der Burgt, 2008; Zwart, 2009). This technology, althoughwell established, presents some disadvantages like the need for large scrubbers or dif-ﬁculties handling and disposing of amines and byproducts (Ma et al., 2009). After thescrubber, a metal oxide bed guard (Zn, Cu, or Fe at low temperatures, 300e500C, andCa or Mn at higher temperatures) and/or activated carbon ﬁlters can be included tokeep the sulfur concentration below 0.1 ppm (Van der Drift and Boerrigter, 2006;Hamelinck and Faaij, 2002; Torres et al., 2007; Higman and van der Burgt, 2008;Zwart, 2009). In the hot route, H2S is absorbed on different oxides (Zn, Fe, Co, orMn) guard beds (Liu et al., 2009; Torres et al., 2007).184.108.40.206 HClHCl is commonly removed in the cold route by wet scrubbing using basic solutions(normally NaOH in water), or absorption in CaO, MgO, Na carbonates (Na2CO3,NaHCO3), or activated carbons (Basu, 2010a,b; Xu et al., 2010; McKendry, 2002;Tijmensen et al., 2002; Boerrigter et al., 2003; Zwart, 2009). Normally H2S is removed
Production of bio-syngas and bio-hydrogen via gasiﬁcation 469at the same time, giving rise to stable salts like NaCl, NaHS, or Na2S. CO2 can also beremoved by these basic solutions, but the kinetics of absorption of HCl and H2S arefaster, so these gases can selectively be separated while almost no CO2 is removed(Zwart, 2009). In the hot route, guard beds or in-stream sorbents can be used(Hamelinck et al., 2004). As for H2S, ZnO guard beds and activated carbon ﬁltersare needed to achieve the desired degree of removal (Van der Drift and Boerrigter,2006; Boerrigter et al., 2003).220.127.116.11 AmmoniaIn the hot conditioning route, ammonia can be removed from syngas by means of cat-alytic decomposition (Reaction [xix]) or selective oxidation (Reaction [xx]) (Xu et al.,2010; Torres et al., 2007; Zwart, 2009; Dou et al., 2002). In catalytic decomposition,some components of the syngas (CO, CO, or H2) can compete with NH3 for theadsorption in the active sites of the catalyst (Xu et al., 2010; Simell et al., 1997).The catalysts used are similar to those used in the tar catalytic cracking: Ni-based, no-ble metals (mainly Ru), Fe-based, and natural oxides (limonite or dolomite) (Xu et al.,2010; Torres et al., 2007; Zwart, 2009; Dou et al., 2002).2NH343H2 þ N2 DH ¼ þ46 kJ=mol [xix]4NH3 þ 3O242N2 þ 6H2O DH ¼ À1358 kJ=mol [xx] In the cold route ammonia is removed by scrubbing with water or acid aqueous so-lutions (normally H2SO4), or activated coal beds (Basu, 2010a,b; Tijmensen et al.,2002; Boerrigter et al., 2003; Zwart, 2009; Dou et al., 2002). At the end of the process,ZnO guard beds and activated carbon ﬁlters remove the last traces of NH3 (Van derDrift and Boerrigter, 2006; Boerrigter et al., 2003).18.104.22.168 AshesPretreatment of the biomass, such as fractionation and leaching, has been employedwith the aim of minimizing ash production. Leaching seems to be the best option, sinceit can remove the inorganic fraction of biomass and improve the quality of the remain-ing ash (Navarro et al., 2007; Ni et al., 2006; Arvelakis and Koukios, 2002). However,even using pretreatments, some particles will be present in the syngas and need to beremoved. In cold conditioning, cyclones, bag ﬁlters, scrubbers, or electrostatic precip-itators can be used; whereas granular beds and ceramic candle ﬁlters are the preferredtechnologies applied in hot conditioning (Huber et al., 2006; Hamelinck and Faaij,2002; Han and Kim, 2008; McKendry, 2002; Boerrigter et al., 2003; Zwart, 2009).15.5.3 Upgrading technologies: from syngas to hydrogen, biofuels, and high-value chemicalsAlthough H2 is the most demanded product that can be obtained from syngas,there is a wide range of syngas-derived products, as illustrated in Fig. 15.13
470 Handbook of Biofuels Production Syngas (H2 + CO)Ammonia synthesis Methanol synthesis NH3 CH3OHOxo-synthesis Steam reforming Methanation CnHm + n H2O → (n+m/2) H2 + n CO CH4 Aldehydes AlcoholsIsosynthesis H2 production Fermentation Fischer–Tropsch Isobutene H2 H2 Alkanes Isobutane CH4 Ethanol acetateFigure 15.13 Production routes of the different products usually are obtained from syngas.(Navarro et al., 2007; IEA, 2006a,b; Wender, 1996; Van der Drift and Boerrigter,2006; Huber et al., 2006; Higman and van der Burgt, 2008). The ﬁnal use of the syngas produced will affect the type of gasiﬁcation chosen.Thus, air gasiﬁcation leads to syngas diluted in high amounts of nitrogen that isonly attractive if the ﬁnal use of syngas is the production of ammonia (Hamelinckand Faaij, 2002; Bridgwater, 2003). Otherwise, steam or oxygen gasiﬁcation ismore suitable, since N2 will not act as a diluent in subsequent processes and down-stream equipment size will be smaller (Hamelinck and Faaij, 2002; Bridgwater,2003). In addition, light hydrocarbons can still be present, representing an importantpart of the heating value of the syngas. These hydrocarbons are converted to H2and CO by means of steam reforming (Reaction [xxi]) (Huber et al., 2006; Quaaket al., 1999).CH4 þ H2O/3H2 þ CO DH ¼ þ206 kJ=mol [xxi]22.214.171.124 Production of H2In the case of hydrogen production, H2:CO ratio needs to be shifted to the maximumvalue possible, with water gas shift being the most widespread option (Hamelinck andFaaij, 2002). However, the production of sponge iron is an alternative that has gained
Production of bio-syngas and bio-hydrogen via gasiﬁcation 471interest. Once hydrogen content has been maximized, it is separated from the syngasby means of pressure swing adsorption or membranes.Water gas shift reactionThe WGS reaction (Reaction [i]) is a well-established process for the production ofH2 from syngas (Navarro et al., 2007; Hannula, 2009; Higman and van der Burgt,2008). This technology has been extensively used in reﬁneries. The process involvesthe reaction of CO with steam to produce CO2 and H2 (Huber et al., 2006; Holladayet al., 2009). Thermodynamically this reaction is favored at low temperatures.However, to achieve high reaction rates and conversions, two stages are normallyneeded (Navarro et al., 2007; Huber et al., 2006; Hannula, 2009):1. Firstly, a high-temperature reactor (350e500C) using a Fe oxide-based catalyst (Fe2O3/ Cr2O3), where CO concentration is reduced to levels around 2e3%.2. Secondly, a low-temperature reactor (200C) where a Cu-based catalyst is used (CueZnO/Al2O3). This second reactor can reduce CO concentration to values lower than 0.1%. The use of these catalysts presents some drawbacks such as slow kinetics or thepyrophoric nature of the CueZnO/Al2O3, which can hinder the application in smalldevices like fuel cells attached to small-scale gasiﬁers. Different alternatives to theconventional catalysts have been proposed, including Co-V binary oxides and noblemetals supported in CeO2 for low-temperature WGS, and CoeMo and NieMo sul-ﬁdes for high-temperature WGS (Navarro et al., 2007; Huber et al., 2006; GonzalezCastan~o et al., 2014; Reina et al., 2014, 2015).Sponge ironDirect reduction iron or sponge iron is an old method for producing hydrogen (Milneet al., 2006; Pe~na et al., 2010; Biljetina and Tarman, 1981) that was replaced by moreefﬁcient and economic processes. Recently, the interest in sponge iron as a hydrogenproduction process has grown again, although the technology still has some majortechnical and economic challenges to overcome (Milne et al., 2006; Pe~na et al.,2010; Sime et al., 2003). The main reasons for this renaissance are the simplicity ofthe process and the high purity of the H2 produced (Navarro et al., 2007). The conceptis based in a cyclic process. Firstly, Fe oxides are reduced to metallic iron and/or Fe(II)oxide with the syngas (Reactions [xxii] and [xxiii]). The metallic iron is then oxidizedto iron oxide using steam (Reaction [xxiv]) (Milne et al., 2006; Pe~na et al., 2010).After oxidation, H2 is recovered and the Fe2O3 is recycled to the initial step (Simeet al., 2003).Fe3O4 þ 4CO/3Fe þ 4CO2 DH ¼ þ88 kJ=mol [xxii]Fe2O3 þ H2/2FeO þ H2O DH ¼ þ48 kJ=mol [xxiii]3Fe þ 4H2O/Fe3O4 þ 4H2 DH ¼ À252 kJ=mol [xxiv]
472 Handbook of Biofuels ProductionSeparationThe ﬁnal step for hydrogen production is its separation from the syngas with the aim ofobtaining a product with the required purity. The main techniques for this operationare pressure swing adsorption (PSA) and membrane separation (Huber et al., 2006;Balat and Kirtay, 2010; Hannula, 2009; Higman and van der Burgt, 2008; Spathand Dayton, 2003). The leading technology to efﬁciently separate H2 from syngas is PSA (Bermudezet al., 2013; Yang et al., 1997; Ahn et al., 1999). PSA is a cheap, low-energy and efﬁ-cient technology for gas separation, based on the different adsorption behavior of themolecules present in the syngas. Adsorption of gases like CO, CO2, CH4, and othercontaminants is stronger than H2 adsorption, which leads to high-purity hydrogen.Carbonaceous materials, alumina oxides, or zeolites are the most commonly usedadsorbents in PSA (Yang et al., 1997; Wiessner, 1988; Schr€oter, 1993). A promising alternative to the widely used PSA is membranes (polymer, metallic,or ceramic) (Hannula, 2009; Bermudez et al., 2013). Membrane gas separation is a par-tial pressure-driven process in which a gas mixture is forced to pass across the surfaceof a membrane through which some components selectively permeate (Hamelinck andFaaij, 2002; Hannula, 2009). Membrane gas separation entails several advantages likeeasy operation, low CAPEX-OPEX, and low-energy requirements (Han and Kim,2008). In addition, ceramic membranes can work at high temperatures, so they canbe implemented in the hot conditioning process (Hamelinck and Faaij, 2002).126.96.36.199 AmmoniaAmmonia is an important chemical used in several industrial processes like the pro-duction of fertilizers, disinfectants, or nitric acid. It is produced by a catalytic reactionbetween N2 and H2 (Reaction [xxv]) (Ni et al., 2007; Barreto et al., 2003; Stahlet al., 2004):N2 þ 3H2/2NH3 DH ¼ À46 kJ=mol [xxv] The production process is the HabereBosch method based on the use of anFe-based catalyst working at high pressures (100e200 bar) and temperatures higherthan 450C (Basu, 2010a,b; Higman and van der Burgt, 2008; Spath and Dayton,2003). High pressures are needed for thermodynamic reasons, since the conversionper pass is extremely low and the equilibrium needs to be shifted toward the products.In the case of temperature, a trade-off occurs between equilibrium and reaction rate(Spath and Dayton, 2003). Thermodynamics establish that lower temperatures favorthe direct reaction, while kinetics are reduced. Even under optimum conditions andwith good catalysts, the conversion per pass is about 15% and the unreacted gas needsto be recirculated (Stahl et al., 2004).188.8.131.52 Methanol productionMethanol is one of the most important chemicals in industry due to its high versatilityand several applications (Wender, 1996; Bermudez et al., 2013; Olah et al., 2011).
Production of bio-syngas and bio-hydrogen via gasiﬁcation 473Methanol can be used as an H2 carrier, fuel, or platform chemical for the production ofa wide range of chemicals (oleﬁns, dimethyl ether, acetic acid, formaldehyde) (Huberet al., 2006; Spath and Dayton, 2003; Olah et al., 2011). Its synthesis is carried out attemperatures in the range of 220e300C and pressures about 50e100 bar using a cata-lyst of CueZnO supported on alumina (Wender, 1996; Olah et al., 2011). Methanolsynthesis takes place through two different reactions (Reaction [xxvi] and [xxvii])(Wender, 1996; Olah et al., 2011; Tjatjopoulos and Vasalos, 1998):CO þ 2H2/CH3OH DH ¼ À91 kJ=mol [xxvi]CO2 þ 3H2/CH3OH þ H2O DH ¼ À41 kJ=mol [xxvii] As both CO and CO2 react with hydrogen in the process, the ratio between thesegases should be optimized according to the R parameter (Eq. [15.1]), which shouldbe in the range of 2.03e2.05 (Wender, 1996; Olah et al., 2011; Tjatjopoulos andVasalos, 1998; Bermudez et al., 2013):R ¼ ðH2 À CO2Þ=ðCO þ CO2Þ [15.1] Normally, the conversion per pass is quite low, so recycling is needed (Wender,1996; Olah et al., 2011; Bermudez et al., 2013). One of the main challenges for thisprocess is the efﬁcient removal of the heat generated in the methanol synthesis reactor,which is usually a ﬁxed-bed reactor. The integration of these reactors with other pro-cess streams can play a key role in the global efﬁciency of the process (Hamelinck andFaaij, 2002; Bermudez et al., 2013; Olah et al., 2011). As an alternative to the ﬁxed-bed reactor, the liquid phase methanol (LPMEOH)synthesis was developed (Wender, 1996; Hamelinck and Faaij, 2002). In LPMEOH,syngas dissolves in the liquid phase and diffuses until the reactants reach the catalyst,where they react to produce MeOH. An example of this technology is the slurry bubblecolumn reactor developed by Air Products and Chemicals Inc., which can reachconversions higher than 50% (Air Products, 1998, 2015).184.108.40.206 Production of liquid fuels: FischereTropschFischereTropsch (FT) is a technology that transforms syngas into high-quality liquidfuels (alkanes free from S or other contaminants) that followed a similar developmentto gasiﬁcation. It was mainly developed by Germany during the Second World Warand SASOL in South Africa after that. It is a very mature technology currently usedby leading companies like SASOL from coal gasiﬁcationederived syngas or Shellfrom natural gasederived syngas (Wender, 1996; Luque et al., 2012; Higman andvan der Burgt, 2008; Dry, 2002; Khodakov et al., 2007). Currently, FT can be carried out using two different options: high temperature inﬂuidized bed reactors (300e350C, for gasoline production) and low temperaturein slurry bed reactors (200e240C, for wax production) (Wender, 1996; Tijmensenet al., 2002; Luque et al., 2012; Dry, 2002; Khodakov et al., 2007).
474 Handbook of Biofuels Production Only metals from group VIII (Ni, Fe, Co, and Ru) present good catalytic propertiesfor FT synthesis; among them Ru and Ni have been discarded due to the excessiveprice and the high production of CH4 respectively (Wender, 1996; Dry, 2002;Khodakov et al., 2007; Iglesia, 1997). Thus, only Fe- and Co-based catalysts areused in FT synthesis (Luque et al., 2012; Dry, 2002; Tavakoli et al., 2008). Fepresents the advantage of low cost and that yields high oleﬁnic content in the productdistribution. However, it is also active for the WGS reaction what decreases the yieldof the overall process (Huber et al., 2006; Tijmensen et al., 2002; Boerrigteret al., 2003; Dry, 2002). Co is more expensive but has higher stability, higheractivity, and lower yield of oxygenated products. However, it is only used in low-temperature FT because at high temperature it gives rise to high production ofCH4 (Luque et al., 2012; Dry, 2002; Tavakoli et al., 2008). Several reactions (Reactions [xxviii], [xxix], and [xxx]) take place in FT synthesis togive rise to parafﬁns, oleﬁns, and alcohols (as byproducts) (Wender, 1996). As a resultof FT process, a range of straight chain alkanes from C1 to C50 are obtained regardlessof operating conditions (Wender, 1996; Huber et al., 2006; Basu, 2010a,b; Dry, 2002;Iglesia, 1997). The product distribution is governed by the AndersoneSchulzeFlory(ASF) polymerization model, which predicts the selectivity of the different productson the basis of a chain growth probability parameter (Fig. 15.14(a)) (Huber et al.,2006; Tijmensen et al., 2002; Luque et al., 2012; Dry, 2002; Iglesia, 1997; Tavakoliet al., 2008; Martínez and Lopez, 2005). Based on this product distribution, it is notpossible to selectively synthesize diesel or gasoline without obtaining byproducts(light hydrocarbons or waxes) (Huber et al., 2006). Nevertheless, the catalyst designcan inﬂuence the selectivity, maximizing different target products (gasoline, kerosene,diesel, fuel oil, waxes) (Fig. 15.14(b)) (Huber et al., 2006; Tijmensen et al., 2002;Luque et al., 2012; Dry, 2002; Iglesia, 1997; Martínez and Lopez, 2005).(a)Weight fractionCH4 C20+ (b) Base Hydrocarbon distribution (%C) 1.00 C2–C4 C5–C11 80 FeZ15 0.90 C11–C20 FeZ25 0.80 60 FeZ40 0.70 FeZ140 0.60 40 0.50 FeZN50 0.40 20 0.30 0.20 0.2 0.4 0.6 0.8 1 0 C2–C4 C5–C12 C13+ 0.10 Probability of chain growth C1 0.00 0Figure 15.14 (a) Product distribution of the FischereTropsch synthesis predicted byAndersoneSchulzeFlory (ASF) polymerization model. (b) Product distribution obtained inthe FischereTropsch synthesis with different catalysts.Reprinted with permission from Huber, G.W., Iborra, S., Corma, A., 2006. Synthesis oftransportation fuels from biomass: chemistry, catalysts, and engineering. Chemical Reviews 106(9), 4044e4098. Copyright (2006) American Chemical Society; Reprinted from Martínez, A.,Lopez, C., 2005. The inﬂuence of ZSM-5 zeolite composition and crystal size on the in situconversion of FischereTropsch products over hybrid catalysts. Applied Catalysis A: General294 (2), 251e259 with permission from Elsevier.
Production of bio-syngas and bio-hydrogen via gasiﬁcation 475Paraffins ð2n þ 1ÞH2 þ nCO/CnH2nþ2 þ nH2O [xxviii]Olefins 2nH2 þ nCO/CnH2n þ nH2O [xxix]Alcohols 2nH2 þ nCO/CnH2nþ1OH þ ðn À 1ÞH2O [xxx] FT technology has been proven with syngas from biomass gasiﬁcation in a demon-stration plant in the Netherlands. The plant included a ﬂuidized bed gasiﬁer followedby wet gas cleaning and conditioning, WGS and FT synthesis to produce waxes thatwere then cracked to obtain a high-quality sulfur-free diesel fuel (Wender, 1996;Huber et al., 2006).220.127.116.11 Production of synthetic natural gas: methanationUnder the adequate conditions, H2 and CO can be used for the production of CH4(Reaction [xxxi]) (Wender, 1996; Kopyscinski et al., 2010). The process, uses a Nicatalyst (although other transition metals can be used) and works at temperatures inthe range of 700e1000C (Wender, 1996; Kopyscinski et al., 2010).CO þ 3H2/CH4 þ H2O DH ¼ À206 kJ=mol [xxxi] Initially, this process was used for removing CO traces from H2-rich streams inammonia production plants (Kopyscinski et al., 2010). However, nowadays it isconsidered as an interesting alternative for producing substitute natural gas (SNG),since it is free from contaminants like H2S and its production from biomass has aneutral carbon footprint (Kopyscinski et al., 2010).18.104.22.168 Production of iso-C4: isosynthesisIsosynthesis is part of the FT process, but involving the conversion of syngas to isobu-tane and isobutene (Wender, 1996; Spath and Dayton, 2003). Other differencescompared to conventional FT synthesis are the catalyst used (ThO2- or ZrO2-based cat-alysts), the extreme operating conditions (450C and 150e1000 bar) and that the pro-cess does not follow the ASF polymerization model (Wender, 1996; Huber et al.,2006). It was developed during the Second World War, since iso-C4 are raw materialsfor the synthesis of high-octane gasoline. However, the development of catalysts forthe production of high-octane gasoline from petroleum stopped its commercial use(Wender, 1996; Huber et al., 2006).22.214.171.124 Production of alcohols and aldehydes: oxosynthesisOxosynthesis (or hydroformylation) is a reaction between syngas and oleﬁns to giverise to aldehydes or alcohols (Wender, 1996; Spath and Dayton, 2003). This processis the fourth largest use of syngas and involves the production of chemicals of highimportance (eg, butanol, propanol, or isobutanol) (Wender, 1996; Huber et al.,2006; Higman and van der Burgt, 2008). Firstly, the oleﬁn is hydroformylated to
476 Handbook of Biofuels Productiongive rise to an aldehyde with one carbon more than the original oleﬁn (Reaction[xxxii]). Then, the aldehyde is hydrogenated to give rise to the alcohol (Reaction[xxxiii]) (Wender, 1996):R À CH2 ¼ CH2 þ CO þ H2/R À CH2 À CH2 À COH [xxxii]R À CH2 À CH2 À COH þ H2/R À CH2 À CH2 À CH2OH [xxxiii] The reaction is highly exothermic and takes place in the presence of a homogeneouscatalyst that is a soluble complex of Co or Ru (Wender, 1996; Huber et al., 2006).126.96.36.199 Syngas fermentationSome bacteria have the ability of metabolizing syngas to give rise to a wide variety ofvaluable products, depending on the bacteria and the fermentation conditions (seeTable 15.5) (Huber et al., 2006; Beneroso et al., 2015a,b; Munasinghe and Khanal,2011). These bacterial systems present a great potential for integration in bioreﬁningschemes. They present the important advantage of being almost unaffected by theH2/CO ratio or the presence of CO2. However the production rates are low and furtherdevelopment is needed (Huber et al., 2006).15.6 Current status in commercial gasiﬁcation of biomassFig. 15.15 shows the number of commercial, demonstration, and pilot biomass gasiﬁ-cation plants which are currently in operation worldwide (updated data from ThermalGasiﬁcation Facilities DatabasedIEA Task 33 (IEA, a)). Most of the existingcommercial plants on biomass gasiﬁcation are dedicated to the production of poweror combined heat and power (CHP) and are located in Europe. On the contrary, nearlyall the facilities currently producing biofuels from biomass gasiﬁcation at a commer-cial level are located in US and Canada. American Process, Enerkem Corporation,Range Fuels, CORE BioFuel, and Abengoa operate facilities which produce ethanolfrom woody biomass and MSW. In the case of demonstration and pilot plants, the ratioof facilities producing biofuels to those producing CHP increases signiﬁcantly, withmore facilities dedicated to the production of biofuels from high-quality syngas.This trend shows the increasing interest of research and development in the synthesisof biofuels and chemicals from biomass gasiﬁcation. Similar to the commercial plants,all the demonstration and pilot facilities operating in US and Canada are producingbiofuels. The balance between projects dedicated to CHP and biofuels in Europe isin line with the strategy of the region for maintaining its leadership on the developmentof state-of-the-art technology for CHP generation, and the increasing investment onR&D for the production of second-generation biofuels via gasiﬁcation of lignocellu-lose biomass.
Production of bio-syngas and bio-hydrogen via gasiﬁcation 477Table 15.5 Examples of the products that can be obtained by meansof syngas fermentation and bacteria responsible of the process(Munasinghe and Khanal, 2011, 2010; Younesi et al., 2005,2008; Henstra et al., 2007; Beneroso et al., 2015)Product BacteriaAcetate Acetobacterium woodii Archaeoglobus fulgidusButanol Butyribacterium methylotrophicumButyrate Clostridium autoethanogenumEthanol Clostridium carboxidivoransFormate Clostridium ljungdahliiHydrogen Desulfotomaculum kuznetsovii Desulfotomaculum thermobenzoicum subsp. Thermosyntrophicum Eubacterium limosum Methanosarcina acetivorans strain C2A Moorella thermoacetica Moorella thermoautotrophica Oxobacter pfennigii Peptostreptococcus productusv Butyribacterium methylotrophicum Clostridium carboxidivorans Butyribacterium methylotrophicum Clostridium carboxidivorans Oxobacter pfennigii Butyribacterium methylotrophicum Clostridium autoethanogenum Clostridium carboxidivorans Clostridium ljungdahlii Archaeoglobus fulgidus Methanosarcina acetivorans strain C2A Archaeoglobus fulgidus Carboxydothermus hydrogenoformans Carboxydibrachium paciﬁcus Carboxydocella sporoproducens Carboxydocella thermoautotrophica Citrobacter sp. Y19 Desulfotomaculum carboxydivorans Moorella strain AMP Rhodopseudomonas palustris P4 Rhodospirillum rubrum Rubrivivax gelatinosus Thermincola carboxydiphila Continued
478 Handbook of Biofuels ProductionTable 15.5 Continued Bacteria Product Thermococcus strain AM4 Thermolithobacter carboxydivorans Methane Thermosinus carboxydivorans Methanobacterium formicum Polyhydroxyalkanoates Methanobacterium thermoautotrophicum Methanosarcina acetivorans strain C2A Methanosarcina barkeri Methanothermobacter thermoautotrophicus Rhodospirillum rubrum Rhodospirillum rubrumNumber of operating plants 45 40 35 Demonstration Pilot 30 Scale 25 20 15 10 5 0 Commercial CHP (US, Canada) Biofuels (US, Canada) CHP (Europe) Biofuels (Europe)Figure 15.15 Commercial, demonstration and pilot biomass gasiﬁcation facilities.Data from IEA. Task 33. Thermal Gasiﬁcation of Biomass. International Energy Agency. The number of biomass-to-liquid facilities at all scales rises signiﬁcantly whenincluding plants under construction and projected (IEA; World GasiﬁcationDatabase, 2015). A summary of the main facilities including raw material, main prod-uct, and status is shown in Table 15.6. One of the best-known biomass gasiﬁcation technologies is probably the ChorenCarbo-V Process developed by Choren Industries and currently owned by Linde En-gineering Dresden. The Carbo-V process consists of three stages: carbonization atmoderate temperature, oxidation of evolved volatiles to generate hot gasiﬁcationagent, and entrained gasiﬁcation of char obtained from the ﬁrst step. Other companies
Table 15.6 Commercial, demonstration, and pilot biomasCompany Type Country Raw materialEnerkem Commercial Canada Lignocellulosics, MCORE BioFuel Commercial CanadaDiamond Green Commercial US Waste woodAltAir Commercial US Animal fat, used cAbengoa Commercial US otherREG Synthetic Fuels Commercial US Lignocellulosics, cAmerican Process Commercial US LignocellulosicsRange Fuels Commercial US Animal fat, used cBioMCN Commercial Netherlands other CommercialFulcrum US Lignocellulosics, w BioEnergy’s Commercial biomass Sierra Biofuels Plant Lignocellulosics, w wood waste froClean Fuels harvesting oper Technology Inc. Biodiesel and oleo others MSW US Various
ss gasiﬁcation facilities Production of bio-syngas and bio-hydrogen via gasiﬁcation Product Status OperationalMSW Ethanol Operationalcooking oil, Gasoline type fuel Operational Diesel Operationalcamelina Diesel, jet fuel Operationalcooking oil, Ethanol Operational Diesel Operationalwoody Ethanol Operational wood and Ethanol, methanolom timber Methanol Operationalrations Under ochemicals, commissioning Ethanol, power Under construction FT-liquids, fuel gas Continued 479
Table 15.6 ContinuedCompany Type Country Raw material US Lignocellulosics, cDuPont Commercial US US switchgrassEmerald Biofuels Commercial US Waste fats and oil USClean Fuels Commercial Sweden Various Technology Inc. Commercial Sweden Commercial Sweden LignocellulosicsAce Ethanol Commercial Netherlands (Sweetwater) Commercial Canada Woody biomass USRed Rock Biofuels Canada Lignocellulosics, b LLC Lignocellulosics, wRottneros AB biomass Lignocellulosics, wRottneros AB biomassV€armlandsMethanol Commercial Lignocellulosics, w AB Commercial biomassBioMCN WasteEnerkem and Commercial Lignocellulosics, w GreenField Commercial biomassCool Planet Lignocellulosics, bTembec Chemical Demonstration Group
corn stover, Product Status 480 Handbook of Biofuels Productionls, other Ethanol Under Dieselblack liquour FT-liquids, fuel gas constructionwoody Ethanol Underwoody FT-liquidswoody Methanol construction Methanol Underwoody Methanolblack liquor Methanol construction Ethanol Under Gasoline type fuel Ethanol construction Under construction Planned Planned Planned Planned Planned Announced Operational
Enerkem Demonstration Canada Lignocellulosics, w Demonstration US clean wood, sawWest Biofuels Demonstration US Demonstration US Clean wood, wastEdeniq & Logos Demonstration US wood, other bio Tech Demonstration Denmark Demonstration Sweden Lignocellulosics, cAmerican Process Demonstration Sweden baggasseCoskata Demonstration France Demonstration Netherlands LignocellulosicsBTN Bionic Fuel Demonstration UK Lignocellulosics, w Technologies AG Demonstration US natural gasGoeteborg Energi Pilot US Lignocellulosics, sE.ON Gasiﬁcation Lignocellulosics, w Development AB biomassThyssenKrupp Uhde Lignocellulosics, wECN biomassSolena/British Various Airways LignocellulosicsSynGest Inc. WasteZeaChem Lignocellulosics, c energy crops, a wood Lignocellulosics, p wood, chips
waste wood, FT-liquids, fuel gas Operational Production of bio-syngas and bio-hydrogen via gasiﬁcationw mill residues FT-liquids te wood, clean Ethanol Operationalomass Ethanol Ethanol Operational corn stover, Diesel, FT-liquids SNG Operational wood chips, SNG Operational straw pellets Diesel, kerosene woody SNG Operational woody Jet fuel Ammonia Operational corn cobs,and waste Ethanol, mixed alcohols, Under various chemicals construction poplar, sugar, Planned Planned 481 Planned Planned Operational Continued
Table 15.6 ContinuedCompany Type Country Raw material USRange Fuels Pilot Lignocellulosics, G US hardwoods, andIowa State Pilot beetle kill pine University US Pilot US Lignocellulosics, gCoskata Pilot US oilseeds, vegetaGTI Gas Technology Pilot US glycerin Pilot US Institute Pilot LignocellulosicsUniversity of ToledoDuPont Lignocellulosics, p wood chipsSouthern Research Institute Waste wood Lignocellulosics, c switchgrass Lignocellulosics, c MSW, coal/bioINEOS New Planet Pilot US Vegetal waste, MS Bioenergy Pilot US Algae, othersAlgenol Pilot Canada Lignocellulosics, MEnerkem chips, treated w petroleum coke plastics and wh
Georgia pine, Product Status 482 Handbook of Biofuels Production d Colorado Mixed alcohols Operational grains, able oils, Ethanol, FT-liquids, biodiesel, Operational pyrolysis oils pellets, Operational Ethanol Operational corn stover, Clean syngas Operational cellulosics, Operationalomass, syngas Diesel Operational Ethanol SW, others Operational FT-liquids; mixed alcohols; Operational MSW, wood industrial sugars; mixed Operationalwood, sludge, fossil/lignocellulosice, spent feedstocks for powerheat straw production Ethanol, power Ethanol Ethanol, methanol, SNG
Vienna University of Pilot Austria Lignocellulosics Technology Pilot France Forestry and agricAirLiquid Pilot Germany Lignocellulosics, sCutec Pilot Germany dried silage, org LignocellulosicsKarlsruhe Institute of Pilot Netherlands Technology (KIT) Pilot Sweden Waste wood Pilot Turkey Lignocellulosics, bECN Biomass and biom Pilot TurkeyLTU Green Fuels blendsTU€ BI_TAK MRC e Pilot US Biomass and biom Energy Institute blendsTU€ BI_TAK MRC e Lignocellulosics Energy InstituteResearch Triangle InstituteData from IEA. Task 33. Thermal Gasiﬁcation of Biomass. International Energy Agency; Worldgasiﬁcation/world-database/.
cultural waste FT-liquids Operational Production of bio-syngas and bio-hydrogen via gasiﬁcation straw, wood, ganic residues Diesel, kerosene Operational FT-liquids Operational black liquourmass coal Diesel, gasoline type fuel Operationalmass coal SNG Operational DME Operational FT-liquids Operational SNG Operational FT-liquids, mixed alcohols Plannedd Gasiﬁcation Database. June 2015; Available from: http://www.gasiﬁcation.org/what-is- 483
484 Handbook of Biofuels Productionfocused on the development of entrained ﬂow gasiﬁcation technology for biofuelsproduction are Pearson, FZK/KIT, and Mitsubishi Heavy Industries. In the case ofbubbling ﬂudized bed biomass gasiﬁers, Enerkem Technologies has long expertisewith the ﬁrst demonstration facilities of the BioSyn process for CHP generation builtin the 1970s. Foster Wheeler, Andritz Carbona, Energy Products of Idaho LP (nowOutotec), and ThyssenKrupp Uhde are also important technology developers ofﬂudized bed (BFB and CFB) gasiﬁers. Andritz Carbona is also involved in the devel-opment of gas conditioning for downstream FT synthesis of liquid hydrocarbons. In the case of new gasiﬁcation technologies, Westinghouse Plasma Corp. providescommercial plasma gasiﬁers, which are to be used in the plant that Coskata is buildingin Pennsylvania (US) to produce ethanol or the Air Products’ plant to be built in theUK. InEnTec develops and provides the Plasma Enhanced Melter (PEM) gasiﬁertechnology for waste to liquid projects. There are yet other examples of commercial innovative gasiﬁcation technologies.Rentech-ClearFuels has developed a high efﬁciency hydrothermal reformer (HEHTR)which converts cellulosic feedstocks into hydrogen and syngas. On the other hand,Bionic’s Fuel Technologies has developed microwave-assisted gasiﬁcation technol-ogy combined with catalyst development for the production of biofuels viabio-syngas.15.7 Challenges and opportunitiesBiomass gasiﬁcation is the most effective technology for the conversion of solidbiomass into hydrogen, biofuels, and high-value chemicals through the productionof bio-syngas. However, it is not a mature technology and the majority of the commer-cial facilities which are in operation worldwide are dedicated to heat and power gen-eration. Technical challenges need to be addressed in order to ensure cost-effectiveproduction of high-quality bio-syngas to meet the demand for downstream conversioninto hydrogen and other high-value products. One of the challenges is related to biomass feedstock selection, consistency, avail-ability, and logistics. Biomass resources are scattered and long-distance transportationis expensive and nonsustainable due to the low energy density of the feedstock. Newsolutions are being investigated such as selection of biomass which yields largeramount of syngas and H2, pretreatment processes to increase biomass energy density,use of waste as feedstock, and distributed technology. There is also a lack of large-scale performance indicators. Signiﬁcant efforts arebeing made on process intensiﬁcation and improvement of gasiﬁer design in orderto allow cost-effective production of syngas and hydrogen. However, more pilotand demonstration projects are required in order to validate and demonstrate the tech-nology at industrially relevant environments, and to compete with well-establishedprocesses at a commercial level, including biomass combustion. Cogasiﬁcation ofbiomass in large integrated gasiﬁcation combined cycles (IGCC) is a short- and
Production of bio-syngas and bio-hydrogen via gasiﬁcation 485mid-term alternative until mature biomass gasiﬁcation technology is available.This process would reduce the need for dedicated biomass logistics and technologies,while giving improved biomass economies of scale. A signiﬁcant number of challenges are related to the improvement of clean-uptechnologies to obtain a syngas stream with the quality required by downstreamconversion processes. The development of more efﬁcient tar removal techniques,both in cold and in hot conditioning routes, will improve the economics of biomassgasiﬁcation. In addition, further progress is necessary to implement the hot condition-ing route for avoiding energy penalties when biomass gasiﬁcation is coupled withsteam reforming both at large scale (for production of bio-hydrogen or other chemi-cals) and small scale (for application in fuel cells). Engineering aspects like pressuredrop or mechanical properties of catalysts of the hot conditioning reactors have beenoverlooked, since most of the studies have been performed at lab-scale and mainlyfocused on catalytic performance. Studies on the hot gas conditioning technologiesat pilot and demonstration scales are needed. Although lab-scale results areencouraging, the conditions will differ after scaling up and its viability needsto be demonstrated at a higher scale. Nontechnical challenges also have an important inﬂuence on the development ofgasiﬁcation technology. Although the economic and environmental reasons are majordrivers for the continuous advance in the development of the technology, politics andgovernmental decisions are required for achieving deployment of biomass gasiﬁcation,as well as other renewable energies (Huber et al., 2006; Balat and Kirtay, 2010; Jahirulet al., 2012; Higman and Van der Burgt, 2011; Bridgwater, 2003; Faaij, 2006). Thishas been recognized in the World Energy Outlook, where the International EnergyAgency states that government policies can inﬂuence the pace at which these energiescan substitute fossil fuels (IEA, 2013). Lately some governments and policymakers seem to have realized this need andhave started taking decisions in this way (Van der Drift and Boerrigter, 2006; Balatand Kirtay, 2010; Faaij, 2006; The President’s, 2015; SET, 2015). Two interestingexamples of these change of behavior are the Climate Action Plan in the US andthe European Strategic Energy Technology Plan of the European Union (ThePresident’s, 2015; SET, 2015). Focusing on the EU plan, one of the objectives is toachieve 14% of the European energy mix by 2020 from cost-competitive and sustain-able bioenergy, what is expected to create more than 200,000 jobs. With this in mind,9 billions V are going to be invested by the EU in the coming years in bioenergy pro-jects (SET, 2015). In this sense, gasiﬁcation will play a key role in the development ofa cost-competitive bioenergy sector, due to its highest degree of development and bestpositioning to be implemented shortly. Projects like BioSNG (http://www.bio-sng.com) and BioProGreSs (http://bioprogress.se/) are good examples of the importantbet of the EU in gasiﬁcation as a key technology in the future energy plans. Addressing technical and nontechnical challenges is required now in order todevelop mature gasiﬁcation technology, which will allow the deployment of syngasplatform bioreﬁning and production of sustainable hydrogen, biofuels, and chemicalsfrom biomass to be a reality.
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494 Handbook of Biofuels ProductionYounesi, H., Najafpour, G., Mohamed, A.R., 2005. Ethanol and acetate production from syn- thesis gas via fermentation processes using anaerobic bacterium, Clostridium ljungdahlii. Biochemical Engineering Journal 27 (2), 110e119.Zhang, L., Xu, C., Champagne, P., 2010. Overview of recent advances in thermo-chemical conversion of biomass. Energy Conversion and Management 51 (5), 969e982.Zainal, Z.A., et al., 2001. Prediction of performance of a downdraft gasiﬁer using equilibrium modeling for different biomass materials. Energy Conversion and Management 42 (12), 1499e1515.Zwart, R.W.R., 2009. Gas Cleaning Downstream Biomass Gasiﬁcation. Task 33-Thermal Gasiﬁcation of Biomass. International Energy Agency.
Production of bioalcohols via 16gasiﬁcationJ.M.N. van KasterenCAH Vilentum University of Applied Sciences, Dronten, The Netherlands16.1 IntroductionThe production of alcohols via gasiﬁcation is a very well-established process formethanol production. Methanol is produced from natural gas in very large quantities(global demand around 63 million tons in 2012). The world production capacity isover 100 million tons.1 In fact, most of the methanol produced nowadays is basedon the catalytical conversion of synthesis gas (Ullmann, 2012). The synthesis gasis produced from fossil fuels, the largest part being natural gas. Although methanolcan be readily made from synthesis gas, other sources than fossil fuels have beenstudied and are being used nowadays. By using biomass-based resources for synthe-sis gas production so-called biomethanol can be produced. In Sweden, there is a (pi-lot) plant which uses black liquor2 as a resource for synthesis gas production and thenconverts synthesis gas to methanol/dimethyl ether (DME).3 In the Netherlands(waste) glycerin is used as a feedstock for producing methanol from synthesis gasby a company called BioMCN.4 They claim to be the ﬁrst in the world to produceand sell industrial quantities of high-quality biomethanol. Research in the methanolworld is being focused not only on making synthesis gas from renewable feedstocksbut also on producing methanol via hydrogen (from electrolysis of water) and CO2(from ﬂue gases).5 For the higher alcohols the gasiﬁcation routes are not so common. Ethanol being thesecond largest alcohol produced is mainly produced via fermentation of sugars and fora smaller part via direct hydrolysis of ethylene. The latest development comprises therealization of a pilot synthesis gas to ethanol plant via fermentation by Ineos Bio.6Ineos Bio is further optimizing the world’s ﬁrst synthesis gas fermentation plant toethanol in their facility in Vero Beach, Florida. If it is successful, this technology1 http://www.redorbit.com/news/science/1113093940/world-methanol-production-to-exceed-1077-mln- tonnes-according-to/.2 Black liquor is the waste product from the kraft process when digesting pulpwood into paper pulp removing lignin, hemicelluloses, and other extractives from the wood to free the cellulose ﬁbers. https://en. wikipedia.org/wiki/Black_liquor.3 http://www.ieatask33.org/app/webroot/ﬁles/ﬁle/2014/WS2/Gebart.pdf.4 http://www.biomcn.eu/.5 http://www.biomcn.eu/our-vision/.6 http://www.ineos.com/de/businesses/ineos-bio/technology/.Handbook of Biofuels Production, 2e. http://dx.doi.org/10.1016/B978-0-08-100455-5.00016-3Copyright © 2016 Elsevier Ltd. All rights reserved.
Production of biofuels via FischereTropsch synthesis: biomass-to-liquids 559 After the gas cleaning train, the biomass-derived syngas has to be conditioned inorder to adjust the H2/CO ratio to that required for the FT reactor. Typical conditioningincludes steam reforming of methane and light hydrocarbons to CO and H2 over anickel catalyst, following by a water gas shift reactor. Finally, as the concentrationof inert gases must be kept below 15 vol% (Boerrigter et al., 2004), CO2 is removedwith amine treating. The puriﬁed and conditioned synthesis gas is then compressed tothe required pressure and is fed to the FT reactor.18.2.2 Synthesis of biofuels via FischereTropsch188.8.131.52 FischereTropsch catalystsThe main requirement for a good FischereTropsch catalyst is high hydrogenationactivity in order to catalyze the hydrogenation of CO to higher hydrocarbons. Theonly metals with sufﬁciently high hydrogenation activity to warrant application inFT synthesis are four transition metals from the VIII group of the periodic table:Fe, Co, Ni, and Ru. Although Ru exhibits the highest hydrogenation activity, itsextremely high price and low availability render it unsuitable for large-scale applica-tions such as the FT process. Nickel, on the other hand, is essentially a methanationcatalyst, its application leading to the undesired production of large amounts ofmethane. Therefore, Fe and Co are the only industrially relevant catalysts that arecurrently commercially used in FT. The choice of catalyst depends primarily onthe FT operating mode. Fe-based catalysts are suitable for the high-temperatureFischereTropsch (HTFT) operating mode that takes places in the 300e350C tem-perature range and is used for the production of gasoline and linear low-molecular-mass oleﬁns. Both Fe- and Co- catalysts can be used for the low-temperatureFischereTropsch (LTFT) that operates in the 200e240C range and produceshigh-molecular-mass linear waxes (Dry, 2002). Moreover, the choice of metal alsodepends on the feedstock used for the FT synthesis. As Fe, unlike Co, catalyzesthe water gas shift (WGS) reaction, it is usually used for hydrogen-poor synthesisgas, most especially that from coal (w0.7H2/CO molar ratio), to increase via theWGS reaction the hydrogen content of syngas to the optimum 2H2/CO ratio of theFT reaction (Rao et al., 1992). Cobalt is therefore the catalyst of choice for GTL pro-cesses, using natural gas as feedstock. Whether the catalysts are Fe or Co, FischereTropsch catalysts are notorious for their sensitivity toward sulfur and their permanentpoisoning by sulfur compounds. As aforementioned, syngas requirements for FTsynthesis ask for S content below 0.05 ppm (Dry, 1990). An extensive amount of research has been performed on several aspects of the Feand Co catalysts, including fundamental, basic and applied research. These effortsinclude investigation of the effect of promoters, supports, additives, pretreatments,preparation, and generally all chemical and physical properties of the materials inorder to increase catalyst activity, enhance selectivity to the desired products, inhibitformation of unwanted products, especially methane, and improve resistance to sulfurpoisoning. A summary of improved modiﬁed Fe and Co catalysts employed in industryfor the FT process is presented in Table 18.3 (Bartholomew, 1990).
560 Handbook of Biofuels ProductionTable 18.3 Catalytic systems used in industry for productionof premium products by FTSPremium Catalysts Reactors ProcessesproductC2eC4 oleﬁns Fe/K, Fe/Mn, Fe/Mn/Ce Slurry, ﬂuid-bed Synthol, Koelbel, Fe/K/S, Ru/TiO2, RheinpreusseneGasoline Fluid-bedDiesel fuel Fe2O3Cx Fixed-bed KoppersWaxes Fe/C, Mo/C Slurry/ﬁxed-bed DowLPG Fused Fe/K Synthol Co/ThO2/Al2O3/Silicalite, Fixed-bed (low T) Gulf-Badger Fe/K/ZSM-5, co/ZSM-5, Slurry-bed(low T) Mobil one-stage Ru/ZSM-5 Fe/Cu/K and ZSM-5 Slurry-bed(low T) Mobil two-stage Fe/K, Ru/V/TiO2 Fixed-bed (low T) Sasol-Arge, Gulf- Co/Zr, Ti or Cr/Al2O3 Badger Co/Zr/TiO2 Sasol-two stage Co-Ru/Al2O3 Shell-middle distillate Fe/K, Fe/Cu/K Eisenlohr/Gaensslen Co/Zr, Ti or Cr/Al2O3 Mobil (ﬁrst stage) Shell-middle distillate Co/R/Al2O3, Prom. Fe/Ru (ﬁrst stage)Reproduced from Bartholomew, C.H., 1990. Recent technological developments in FischereTropsch catalysis. CatalysisLetters 7, 303e316.Iron catalystsIron-based catalysts are used in both LTFT and HTFT process mode. Precipitated ironcatalysts, used in ﬁxed-bed or slurry reactors for the production of waxes, are preparedby precipitation and have a high surface area. A silica support is commonly used withadded alumina to prevent sintering. HTFT catalysts for ﬂuidized bed applications mustbe more resistant to attrition. Fused iron catalysts, prepared by fusion, satisfy thisrequirement (Olah and Molnar, 2003). For both types of iron-based catalysts, the ba-sicity of the surface is of vital importance. The probability of chain growth increaseswith alkali promotion in the order Li, Na, K, and Rb (Dry, 2002), as alkalis tend toincrease the strength of CO chemisorption and enhance its decomposition to C andO atoms. Due to the high price o Rb, K is used in practice as a promoter for iron cat-alysts. Copper is also typically added to enhance the reduction of iron oxide to metalliciron during the catalyst pretreatment step (Adesina, 1996). Under steady state FT con-ditions, the Fe catalyst consists of a mixture of iron carbides and reoxidized Fe3O4phase, active for the WGS reaction (Adesina, 1996; Davis, 2003).
Production of biofuels via FischereTropsch synthesis: biomass-to-liquids 561Cobalt catalystsCobalt-based catalysts are especially interesting from the commercial point of viewdue to their rather high activity and selectivity with respect to linear hydrocarbons.Furthermore, they exhibit higher stability, smaller negative effect of water on conver-sion, and higher resistance to attrition in slurry bubble column reactors (Khodakov,2009). Co-catalysts are only used for the LTFT process, as at higher temperaturesexcess methane is produced (Dry, 2002). As the cost of cobalt is higher than that ofFe, it is desirable to increase the surface metal exposure and therefore Co-based cata-lysts are mostly supported on high surface area stable supports, such as Al2O3, TiO2, orSiO2 (Oukaci et al., 1999). Zeolites have also been studied as supports (Bessell, 1995).According to a review by Iglesia (1997), the use of supporteprecursor pairs with in-termediate interaction strengths and the slow and controlled reduction of impregnatedprecursors appears to be the most promising route to the synthesis of supported Co cat-alysts with high Co concentrations and modest dispersions (0.10e0.15). SiO2 isconsidered the ideal support for Co FT catalysts, as its high surface area favors highCo dispersion at high Co loadings while its surface chemistry enables high reductionof Co3þ or Co2þ to Co0 (Dalai and Davis, 2008). The latter is especially important asmetal Co is the active phase for FT and cobalt oxide is reduced at >300C, temperaturehigher than the LTFT, implying that prereduction of the catalyst should take placeprior to loading the reactor with consequent increase of cost and complexity. Promo-tion with small amounts of noble metals, eg, Pt, Ru, or Re, also enhances the reductionprocess (Iglesia et al., 1993). Although in general cobalt catalysts are less inﬂuencedby the presence of promoters than iron-based ones, the presence of noble metals isclaimed to increase activity and selectivity to C5 þ products via enhancement of thehydrogenolysis of the carbonaceous deposits and thus the cleaning of the catalyticsurface (Iglesia et al., 1993).Suitable catalysts for the BTL-FT processAs discussed in the previous paragraphs, Fe and Co are the industrially relevant cata-lysts that are currently commercially used in FT, with the choice of catalyst dependingprimarily on the target product (waxes versus gasoline and oleﬁns) and the feedstock(syngas H2/CO ratio). Cobalt is the catalyst of choice for GTL processes, using naturalgas as feedstock and a H2/CO syngas molar ratio of 2, while Fe is used for CTL pro-cesses with a low hydrogen content syngas. Few studies have investigated in depth thetype of catalysts suitable for the BTL-FT process, starting from biomass feedstock(Escalona et al., 2009; van Steen and Clayes, 2008; Lapidus et al., 1994; Jun et al.,2004). It is of crucial importance to explore the differences between GTL and CTLon the one hand and BTL on the other, in order to successfully implement the FT re-action in the BTL process. Both conﬁgurations currently investigated for the BTL pro-cess (full conversion and once through FT, see Section 18.2) require high overall andper pass CO-conversion and high C5þ-selectivity. As cobalt is more active than iron,cobalt has been so far used as the catalyst of choice for economic and exergetic eval-uations of the BTL process. However, as analyzed in an excellent recent review by vanSteen and Clayes (2008), it is debatable whether this is truly the optimal choice of
562 Handbook of Biofuels Productioncatalyst for the BTL process. Van Steen argues that although Fe-catalysts can operatewith a lower hydrogen content syngas such as that from biomass gasiﬁcation, a watergas shift reactor after gasiﬁcation might be required for both cobalt and iron catalysts inorder to obtain good productivity. Since cobalt yields higher productivity at high con-version levels, it seems to be the catalyst of choice for BTL synthesis of linear heavierHCs if clean syngas is available. However, given that biomass syngas contains severalpoisons for FT catalysts, such as sulfur-, chloride-, and nitrogen-containing com-pounds, and keeping in view the fact that Fe-catalysts are reported to be more resistantto sulfur (van Steen and Clayes, 2008) and ammonia poisoning (Koizumi et al., 2004),the ﬁnancial risk of operating the FT reactor with an iron-based catalyst seems to belower. In real operation, deviations from design conditions are inevitable and contam-ination of the syngas entering the FT reactor is possible. In such cases, iron catalystswould be less severely affected than cobalt ones. Even in the case that the catalystshould be replaced, the much lower cost of iron compared to cobalt offers obvious eco-nomic advantages. Wrapping up, both cobalt and iron catalysts should be considered as options forthe FT reactor in the BTL process. A number of scenarios for the BTL processshould be developed with both type of catalysts, while the overall process designshould be coupled with catalyst developments in both cases in order to clearlyprove the superiority of the one catalyst system over the other for commercialapplications.184.108.40.206 Reactors and process conditionsSeveral good reviews have been published in the last decade analyzing the fundamen-tals and comparing different reactors for the FischereTropsch synthesis (Dry, 1996,2002; Geerlings et al., 1999; Guettel and Turek, 2009; Sie and Krishna, 1999). Theheterogeneously catalyzed FT reaction is highly exothermic, with the heat releasedper reacted carbon atom averaging at about 146 kJ (Anderson, 1956), about an orderof magnitude higher than heat release in processes typically applied in the oil industry(Sie and Krishna, 1999). Due to this extremely high exothermicity, the rapid removalof heat is one of the major considerations in the design of FT reactors that have to beable to quickly abstract the heat from the catalyst particles in order to avoid catalystoverheating and catalyst deactivation and at the same time maintain good temperaturecontrol. Moreover, the reaction usually takes place in a three-phase system, gas (CO,H2, steam, and gaseous HCs), liquid HCs and solid catalysts, thus imposing great de-mands on the effectiveness of interfacial mass transfer in the reactor (Sie and Krishna,1999). Last but not least, the FT process is a capital-intensive process and, therefore,for both economic and logistic reasons, it is only economically favorable on a verylarge scale. Easy reactor scale-up is therefore a third important requirement whenconsidering a reactor type for the FT process. Three main reactor types, discussedin the following paragraphs, have been commercialized or are thought promising forindustrial applications: multitubular ﬁxed-bed reactors, gas/solid ﬂuidized-bed reac-tors and three-phase slurry reactors.
Production of biofuels via FischereTropsch synthesis: biomass-to-liquids 563Fixed-bed reactorsIn a multitubular ﬁxed-bed reactor, the catalyst particles are packed into narrowtubes, grouped in bundles and enclosed in an outer shell (see Fig. 18.5). The tubebundles are immersed in water, which abstracts the heat and converts to high-pressure steam. The use of narrow tubes, high syngas velocities, and large catalystparticles ensures rapid heat exchange and minimizes exothermic temperature rise(Dry, 1996). The increased particle size of the catalyst is also necessary in order toavoid large pressure drops (Sie and Krishna, 1999), a problem encountered withSteam collector Gas inlet Steam heater Steam outlet Feed water inlet Inner shellTube bundle Gas outlet Wax outletFigure 18.5 Multitubular ﬁxed-bed reactor for FT synthesis.From Dry M.E., 2002. The FischereTropsch process: 1950e2000. Catalysis Today 71,227e241.
564 Handbook of Biofuels Productionthis reactor type. Still, catalytic particles with a large diameter reduce the effective-ness of the material and reduce the overall reaction rate due to intraparticle diffusionlimitation. Overall, the ﬁxed-bed reactor choice is easy to operate and scale up. They can beused over a wide temperature range and the liquid/catalyst separation can be performedeasily and at low costs, rendering this reactor type suitable for LTFT (low-temperatureFischereTropsch). Moreover, in the case of syngas contamination with H2S, the H2Sis absorbed by the top catalyst layer and does not affect the rest of the bed, thus noserious loss of activity occurs (Dry, 1996). On the down side, ﬁxed-bed reactors areexpensive to construct and the high gas velocities required translate to high gascompression costs for the recycled gas feed. Moreover, it is maintenance- and labor-intensive and has a long downtime due to the costly and time-consuming process ofperiodical catalyst replacement (Tijmensen et al., 2002). Recent advances in this type of reactor are the multitubular ﬁxed-bed reactorsapplied in the Shell Middle Distillate Synthesis (SMDS) process for the conversionof syngas from methane in a heavy, waxy FT product (Eilers et al., 1990; Sie et al.,1991). Shell operates such reactors in its GTL plants in Bintulu and Ras Laffan andmany improvements and advancements were realized in the process of scaling upthe reactors for the Pearl plant. The Pearl GTL plant in Qatar has 24 multitubularﬁxed-bed reactors, with diameter of around 7 m and weight of 1200 tonnes a piece.They each contain 29,000 tubes full of Shell’s cobalt synthesis catalyst, which speedsup the chemical reaction (de Klerk et al., 2013). Their capacity is orders of magnitudehigher than previous ﬁxed-bed reactors developed by Lurgi and Ruhrchemie and isattained due to the specially developed Shell catalyst formulation and reactor design(Geerlings et al., 1999; Sie and Krishna, 1999).Fluidized-bed reactorsFluidized-bed reactors are theoretically an excellent reactor type choice for highlyexothermic reactions, such as the FT reaction. Fluidized-bed reactors offer a muchhigher efﬁciency in heat exchange, compared to ﬁxed beds, and better temperaturecontrol, due to the turbulent gas ﬂow and rapid circulation. At the same time, thehigh gas velocities do not cause any pressure drop issues and smaller catalyst parti-cles can be employed. This translates to high cost reduction, due to smaller requiredheat exchange area, lower gas compression costs and easier construction. Moreover,ﬂuidized beds permit online catalyst removal, thus no downtime for catalyst changeis necessary as opposed to the ﬁxed-bed reactor (Dry, 1996). However, the ﬂuidized-bed reactor is only suitable for HTFT (high-temperature FischereTropsch), as it canonly operate with two phases, solid and gas; if not, liquid and heavy componentsdeposit on the catalyst, leading to solid agglomeration and loss of the ﬂuid phase(Davis, 2002). This means that ﬂuidized-bed reactors cannot be used for maximizedproduction of products heavier than gasoline/naphtha (Steynberg et al., 2004).Moreover, according to Geerlings et al. (1999), ﬂuidized-bed reactors are more suit-able for coal conversion, as opposed to the ﬁxed-bed and slurry reactors which oper-ate well in natural gas conversion processes.
Production of biofuels via FischereTropsch synthesis: biomass-to-liquids 565 (a) (b) Product gases Cyclones Out Fluidized bed Hopper Boiler feed waterCatalyst SteamStandpipeSlide valve Gas distributor Total feedGas inFigure 18.6 Fluidized bed reactors for FT synthesis.From Dry M.E., 2002. The FischereTropsch process: 1950e2000. Catalysis Today 71,227e241. Some disadvantages of the ﬂuidized beds are the complexity in operability, difﬁcultseparation of the ﬁne catalyst particles from the exhaust gas (imposing signiﬁcant cap-ital costs for cyclones and oil scrubbers) and erosion problem due to the high linearvelocities (Dry, 1996). Moreover, H2S contamination of the synthesis gas feed meanscomplete deactivation. Currently two types of ﬂuidized-bed reactors have been developed and used mainlyby Sasol: the circulating ﬂuidized bed (CFB) and the ﬁxed ﬂuidized bed (FFB). In theCFB reactor the ﬁne catalyst particles are entrained by a high-velocity gas streamthrough a riser reactor. The catalyst is separated from the efﬂuent by cyclones andis returned to the reactor inlet. Due to ﬂuidization problems observed in the CFBreactor, Sasol developed the FFB version, which operates in the bubbling regimeand is internally cooled by cooling tubes, as shown in Fig. 18.6(b) (Sie and Krishna,1999). The main advantages of the FFB reactor versus the CFB type are the lower con-struction costs, increased capacity per reactor, less energy required for gas circulation,less catalyst attrition, and easier operation and maintenance (Dry, 2002; Sie andKrishna, 1999).Slurry reactorsSlurry bubble reactors are a version of the ﬂuidized-bed reactors, however in athree-phase system the catalyst is suspended in a liquid through which the feedgas is bubbled as shown in Fig. 18.7. It is therefore employed for LTFT withhigh-molecular-weight liquid waxes as the main product, which naturally servesas the liquid phase of the reactor (Dry, 1996). Slurry reactors share many of theadvantages of the ﬂuidized-bed reactors, such as good isothermal operation dueto excellent heat transfer both within the slurry as well to the cooling system, nointraparticle diffusion limitations as the catalyst particles are small, lower pressure
566 Handbook of Biofuels Production ProductsSteam Slurry bed Boiler feed water Wax Gas distributor Syngas inFigure 18.7 Slurry reactor for FT synthesis.From Dry M.E., 2002. The FischereTropsch process: 1950e2000. Catalysis Today 71,227e241.drop thus lower compression costs, and of course easier catalyst replacement(Geerlings et al., 1999; Tijmensen et al., 2002; Dry, 1996). The main disadvantageof slurry reactors is the difﬁcult catalyst/wax separation. The removal of wax, butnot catalyst, is a critical aspect of bubble column reactor operation. Sasol, which isthe main company operating slurry bubble reactors, uses wax/slurry separationconsidered to be proprietary information, paying special attention to the productionof the catalyst and its physical characteristics as well as to the separation processes(Davis, 2002). The different reactor types discussed above for the FischereTropsch synthesisreaction all seem to have limitations and advantages. Therefore, there is no univer-sal optimum FT reactor; the choice rather depends on the target product and theprocess conditions. According to different modeling studies in the literature (Iglesiaet al., 1991; de Swart et al., 1997), slurry reactors are more suitable for the FT syn-thesis and result in up to 60% lower capital costs. Shell on the other hand operatesmultitubular ﬁxed-bed reactors and claims that the superior performance of theShell catalyst invalidates most of the slurry reactor advantages, rendering theﬁxed-bed technology competitive with the current slurry technology (Geerlingset al., 1999). Therefore, FT reaction selection should be based on process condi-tions and products, aiming at achieving optimized reactor/catalyst combination,based on the physicochemical characteristics and activity performance of eachtype of catalyst.
Production of biofuels via FischereTropsch synthesis: biomass-to-liquids 56718.2.3 Upgrading of biomass-to-liquids productsSummarizing the above, there are at present two catalyst systems available forlarge-scale commercials plants (cobalt-based and iron-based) and two operatingmodes of the FischereTropsch processdlow and high temperature. The iron cata-lyst produces gaseous and gasoline range products when operated in the high-temperature range, usually in ﬂuid catalyst bed reactors. In the low-temperaturerange, both iron and cobalt catalysts produce a large amount of high boiling,waxy products and straight-run diesel and naphtha. The wax is then upgraded tolower boiling range products and normally distilled to yield highly parafﬁnic,zero sulfur and zero aromatic middle distillate diesel fuels, with naphtha as acoproduct. Typical carbon number distribution of HTFT and LTFT products isgiven in Table 18.4 (de Klerk, 2008). As the focus of the BTL process so far has been to maximize the production of pre-mium BTL-FT fuels, we will focus in this section on the technologies for upgradingthe FT waxes originating from the LTFT process mode to FT diesel and gasoline byhydrocracking and catalytic cracking respectively. The upgrading of the FT naphthacoproduct to gasoline will also be discussed.Table 18.4 The carbon number distribution of high-temperatureFischereTropsch (HTFT) and low-temperature FischereTropsch(LTFT) products, excluding C1eC2 hydrocarbonsDescription HTFT (Synthol) LTFT (Arge)Carbon number distribution (mass %)C3eC4, LPG 30 10 19C5eC10, naphtha 40 22 46C11eC22, distillate 16 3C22 and heavier 6 Major product >10%Aqueous products 8 <1% 5e15%Compound classes None Major by-productParafﬁns >10%Oleﬁns Major productAromatics 5e10%Oxygenates 5e15%S- and N-species NoneWater Major by-productReproduced from de Klerk A., 2008. Hydroprocessing peculiarities of FischereTropsch syncrude. Catalysis Today 130,439e445.
568 Handbook of Biofuels Production220.127.116.11 Hydrocracking of BTL wax to dieselAlthough different options have been proposed for the post-treatment and upgrading ofthe FT waxes (Dupain et al., 2005; de Klerk, 2007; Dancuart et al., 2003), it is gener-ally accepted that hydrocracking is the most effective route to maximize the middledistillate yield and it is the currently applied option. Given the small number of com-mercial FT plants, little technology has been developed speciﬁcally for the reﬁning ofthe FT wax products. In most commercial sites, standard crude oil reﬁning approacheshave been used without taking into account the speciﬁc characteristics of the FT waxproduct compared to conventional reﬁnery streams, such as extra low aromatics con-tent (<1 wt%) and virtually zero sulfur (<5 ppm) (see Table 18.4). Conventional hydrocracking takes places over a bifunctional catalyst with acid sitesto provide isomerization/cracking function and metal sites with hydrogenationedehydrogenation function. Platinum, palladium, or bimetallic systems (ie, NiMo,NiW, and CoMo in the sulﬁded form) supported on oxidic supports (eg, silica-aluminas and zeolites) are the most commonly used catalysts, operating at high pres-sures, typically over 10 MPa, and temperatures above 350C. In recent years, considerable research has been ongoing to investigate the effect ofthe operating conditions, both experimentally (Calemma et al., 2005, 2010; Rossettiet al., 2009; Rosyadi et al., 2011) and computationally (Pellegrini et al., 2004;Fernandes and Teles, 2007), and the catalytic material on the yield and quality ofthe FT-wax hydrocracking products. Concerning the operating conditions, it wasfound that wax hydrocracking requires milder pressure and temperature, as the paraf-ﬁnic nature of the wax implies higher availability of hydrogen in the unit (littlehydrogen consuming aromatics) and thus suppressed coke formation (de Klerk,2008). FT-wax hydrocracking to middle distillates is favored at pressures rangingfrom 3e5 MPa and temperatures between 250e300C (Calemma et al., 2010) andyields a product containing light parafﬁns up to C24, as presented in a product samplechromatograph obtained from FT-wax hydrocracking experiments performed inCPERI (Fig. 18.8). At these conditions, middle distillate yield (C10eC22) reaches upto 80e85 wt% at intermediate conversion levels (w60 wt%) (Calemma et al.,2010). At higher conversions, a small reduction in the middle distillate yield can beobserved, indicating an increase of consecutive hydrocracking reactions leading tolighter products. Still the consecutive reactions are limited, allowing the reaction tobe carried out at high conversions without lowering signiﬁcantly the middle distillateselectivity (Calemma et al., 2010). Extensive work has also been conducted by our group as part of the EU-fundedIP RENEW project which explored technology routes for the production of BTLfuels (Lappas et al., 2004). More speciﬁcally, the operating conditions (temperature,pressure, H2/oil ratio) were investigated in experiments with different commercialhydrocracking catalysts in a specially designed hydroprocessing pilot plant unit.The main conclusions were that with all catalysts hydrocracking temperature ap-pears to play the most important role and inﬂuences signiﬁcantly the product yields,as shown in Fig. 18.9. It was shown that the yields of naphtha and kerosene inthe product increase as the temperature increases and so does the conversion.
Production of biofuels via FischereTropsch synthesis: biomass-to-liquids 569 ADC1 B, 1 GC signal (REN2004A\BM000780.D) 40 minNorm. 5.160 16.3535800 C95600 C12 C20 33.30354005200 10.708 22.0145000 C24480046004400 5 10 15 20 25 30 35Figure 18.8 Chromatograph sample of hydrocracked BTL-FT wax. 70% Catalyst A 60% 50%Overall yield 40% 30% 20% 10% 0% –10ºC –5ºC Base +5ºC +10ºC +15ºC –15ºC Temperature Naphtha Kerosene DieselFigure 18.9 Effect of temperature on product yields in the hydrocracking of BTL-FT wax.However, the diesel yield is maximized at a certain temperature and then decreasesas a result of higher conversions achieved at higher temperatures (RENEW, 2008).Moreover, it was shown that the yield of gasoline and diesel in the product de-creases as the H2/oil ratio decreases and so does the conversion. The diesel
570 Handbook of Biofuels Productionselectivity is also slightly decreased as a result of the decreasing yield and conver-sion. Studies by Calemma et al. (2010) showed additionally that the composition ofFT diesel, speciﬁcally the ratio of iso- and n-parafﬁns, is also inﬂuenced by theoperating parameters. The nature of the catalyst also affects signiﬁcantly the product quality and yield.Experiments performed in CPERI with three different commercial hydrocrackingcatalysts showed measurable differences in diesel selectivity at isoconversion as afunction of the catalytic material (Fig. 18.10) (RENEW, 2008). Catalysts loadedwith a noble metal (particularly Pt) were reported to show better performances in termsof selectivity for hydroisomerization and products distribution in comparison withnon-noble metal-based catalyst (Archibal et al., 1960; Gibson et al., 1960). Calemmaet al. (2001) reported high diesel selectivities obtained over a Pt/SiO2-Al2O3 catalystduring the hydroprocessing of FT waxes and attributed the observed results to themild Br€onsted acidity, high surface area, and pore size distribution of the support.Similar conclusions were also reached in a recent collaborative work between ourgroup in CERTH and the University of Alicante in Spain (Iliopoulou et al., 2015).The work aimed at investigating the effect of acidity and mesoporosity in low loading(0.1 wt%) Pt/based catalysts supported on conventional microporous ZSM-5 zeolite ormicro/mesoporous ZSM-5 prepared by controlled desilication/acid extraction, BETAzeolite and a commercial, amorphous, mesoporous silica/alumina support on the hy-drocracking/hydroisomerization of FT waxes using n-hexadecane as the model 70 80% conversion 60 50Selectivity, % 40 30 20 10 0 Naphtha Kerosene Diesel Fractions Catalyst A Catalyst B Catalyst CFigure 18.10 Product selectivity at isoconversion for different catalytic materials in thehydrocracking of BTL-FT wax.
Production of biofuels via FischereTropsch synthesis: biomass-to-liquids 571compound. Hydroisomerization experiments performed at 30 bar, 275C and WHSV4 hÀ1 demonstrated that the activity of the catalysts reduces in the following orderPt/BETA > Pt/ZSM-5 > Pt/ZSM-5 (meso) >> Pt/ASA. However, all zeolites ledmainly to the production of a high amount of light gases and C5eC10 cracking prod-ucts. This behavior was attributed to a combination of the acidic and textural propertiesof the zeolitic supports. Although the microporous/mesoporous ZSM-5 and BETAsupports had a lower number of Br€onsted acid sites than microporous ZSM-5 andwere thus expected to have lower cracking activity, the opposite was observed.The increased mesoporosity and the much larger pore size of the two ﬁrst zeolitesseems to enhance the accessibility of hexadecane to the acid sites, leading toincreased conversion and cracking reactions. It is interesting to note however thatthe ratio of iso/normal alkanes in the cracked products was much higher for thePt/BETA catalyst. This could also be attributed to the mesoporosity of BETA whichallows more space for skeletal rearrangement. The deposition of Pt on an amorphoussupport such as silica-alumina with negligible Br€onsted and high Lewis acidity led toa catalyst with much lower activity than its zeolitic counterparts, but with very highselectivity toward iso-hexadecane, which was the only liquid product formed in thecase of Pt/ASA. Concerning the type of active metal, Zhang et al. (2001) showed that Pt performs bet-ter than Ni and Pd supported on tungstated zirconia for the hydroisomerization of themodel compound n-hexadecane. The use of hybrid catalysts based on Pt/WO3/ZrO2with addition of sulfated zirconia, tungstated zirconia, or mordenite zeolites was studiedby Zhou et al. (2003). According to the authors, hybrid catalysts based on Pt/WO3/ZrO2provide a promising way to obtain higher activity and selectivity for transportation fuelsfrom FT products. Given the high cost of noble metals, hydroprocessing of FT waxeshas also been studied over nickel catalysts (de Haan et al., 2007). De Haan et al.(2007) demonstrated the beneﬁt of using non-sulﬁded nickel catalysts. In conventionalhydroprocessing units, catalysts are sulfated to avoid poisoning by the sulfur species incrude oil. However in the case of the sulfur-free FT waxes, use of a sulﬁded catalystimplies the continuous addition of sulfur-containing compounds to avoid catalyst deac-tivation (de Klerk, 2008). Other advantages of developing a non-sulﬁded catalyst for thehydrocracking of FT waxes are a simpliﬁed, less costly and environmentally friendlyprocess (no H2S in the tail gas) (de Haan et al., 2007). Nickel supported on a commercialsilicated alumina yielded results which compare favorably with those of a commercialsulﬁded NiMo catalyst, with diesel selectivities of 73e77% at a conversion of w52%(de Haan et al., 2007).18.104.22.168 Fluid catalytic cracking of BTL wax to gasolineAlthough hydrocracking yields an appealing spectrum for the production of diesel, it isnot an attractive option for gasoline. The relatively low extent of branching achieved inhydrocracking yields a product in the gasoline range with a low octane number. Inaddition, hydrocracking is considered an expensive process due to the high-pressureoperation and high hydrogen consumption. The ﬂuidized catalytic cracking (FCC) pro-cess has been investigated as an interesting option for the cracking of FT waxes aimed
572 Handbook of Biofuels Productionat the production of FT gasoline (Dupain et al., 2005, 2006; Lappas et al., 2007;Lappas, 2007; Triantafyllidis et al., 2007; Lappas and Vasalos, 2006). The FCC process is the most important reﬁnery process mainly for the productionof gasoline from heavy petroleum fractions, such as atmospheric and vacuum gas oil(VGO). In the FCC unit, the long hydrocarbons are cracked in the 480e540C tem-perature range over zeolite catalysts to smaller n- and i-parafﬁns, n- and i-oleﬁns,and aromatics. Conventional FCC feedstocks are relatively aromatic, with a high sulfurand nitrogen content, in contrast to FT waxes that are highly parafﬁnic with extra-lowaromatics content (<1 wt%) and virtually zero sulfur (<5 ppm) (see Table 18.4). Thedevelopment therefore of new catalyst formulations, as well as optimization of theoverall process parameters, are both very critical to optimize the yield and qualityof FCC products from FT waxes. Lappas et al. (2007) compared the crackability of conventional VGO feed and FTwax provided by CHOREN over a typical reﬁnery FCC E-cat. As can be seen inFig. 18.11, the FT wax is much more crackable than VGO due to the highly parafﬁnicmolecules of wax compared to VGO that contains a signiﬁcant amount of aromatics.In fact, the cracking rate of the wax molecules was calculated about 4.2 times fasterthan that of the VGO molecules. Moreover, coke formation was much less comparedto VGO, again due to the parafﬁnic nature of the feed and the absence of aromaticcompounds or coke precursors even at high conversion levels. Very high conver-sions, over 80 wt%, can be achieved with conventional FCC catalysts at very lowcatalyst/oil ratios and low temperatures. In Table 18.5, a comparison between thetwo feeds regarding the product distribution at 70 wt% conversion is given. The tableshows that gasoline (C5-221C) yield is about the same with both feeds. Gasolinefrom VGO has as expected higher octane number; however the RON number ofthe wax gasoline is still acceptable. The RON of the wax gasoline was almost con-stant and independent of the conversion due exactly to the low aromaticity of thisgasoline (Lappas et al., 2004). Dupain et al. (2006) also observed that the crackingof wax to gasoline is a primary reaction with a gasoline selectivity that is independent% wt conversion 100 VGO 90 Wax 80 70 60 50 3.6 0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 Cat to oil ratioFigure 18.11 Comparison of wax and VGO FCC crackability using E-cat.
Production of biofuels via FischereTropsch synthesis: biomass-to-liquids 573Table 18.5 Comparison of product yields (wt% on feed) at70 wt% conversion from the processing of vacuum gas oil andBTL-FT wax via FCC Total TotalC/O Gasoline Coke Dry C3 C4 LCO RON MONWax-1 0.9 45.6 0.1 0.35 8.1 16.1 21.3 88.5 77.5VGO 3.05 46.3 4.3 3.00 5.75 9.85 18.4 94.4 83.3of conversion level or temperature. Despite the lower RON number, gasoline fromthe cracking of FT waxes in an FCC unit is very promising due to the low contentof aromatics in the product and the extremely low sulfur and nitrogen concentrations,leading to the production of very clean gasoline. Moreover, it was found that thediesel-range LCO product produced from the catalytic cracking of FT waxes is betterthan that produced from the cracking of conventional FCC feedstocks. The degreeof branching in the diesel product is lower than that of the gasoline, improvingmarginally the cetane number but acting very beneﬁcially for the diesel cloud pointand pour point, in addition to the very low sulfur and nitrogen content (Dupain et al.,2006). The addition of ZSM-5 additive to a conventional E-cat was found to enhance thecracking rate of FT waxes, enhancing the cracking of gasoline-range oleﬁns to gas-range oleﬁns and especially propene and butene (Dupain et al., 2006). This was attrib-uted to the diffusions of the initially formed smaller oleﬁns in the ZSM-5 pores. Theoleﬁns are not able to leave the ZSM-5 pores rapidly enough and they are thus easilyactivated and overcracked to gas-range oleﬁns (Dupain et al., 2006). Use of pureZSM-5 resulted in an octane-enhancing effect of the produced gasoline due to theenhanced formation of oleﬁns and aromatics. Triantafyllidis et al. (2007) investigatedthe potential utilization of various microporous (zeolites H-Y and H-ZSM-5) andmesoporous (amorphous silica-alumina and Al-MCM-41) aluminosilicates as cata-lysts or active matrices in the cracking of FischereTropsch waxes toward the produc-tion of liquid fuels. Focus was placed on the effect of porous and acidic characteristicsof the materials on product yields and properties. According to the authors, the type ofcatalyst plays a signiﬁcant role in the product selectivities. The percent conversion ofwax, the product yields (gasoline and LPG), and the research octane number (RON)of the produced gasoline are shown in Fig. 18.12 for different investigated micropo-rous and mesoporous catalysts. The behavior is typical for the two zeolitic catalystswhen used in ﬂuidized catalytic cracking (FCC) of petroleum fractions, where H-Yzeolite is being utilized as the main active-cracking component of the catalyst andZSM-5 is being used as an additive in small amounts leading to lower gasoline andhigher LPG yields, and usually to higher RON. Similar trends are observed inFig. 18.12 for the cracking of F-T waxes. One of the main reaction pathways thatZSM-5 catalyzes with higher rates than H-Y is the cracking of parafﬁns, thus makingit very active in the conversion of waxy feedstocks in agreement with the results of
574 Handbook of Biofuels Production100 (1) ASA+H-Yst (2) ASA+H-ZSM-5 80 (3) H-ZSM-5 (3%cryst.) (4) Al-MCM-41 6040200 Gasoline LPG RON ConversionFigure 18.12 Conversion, product yields (gasoline and LPG) and RON of produced gasoline inthe FCC of BTL-FT wax on different microporous and mesoporous catalysts.Dupain et al. (2006). The 3%-crystalline H-ZSM-5 sample, not diluted with amor-phous silica-alumina (ASA), showed high conversion activity (79 wt%), very closeto that of the diluted catalyst of the crystalline H-ZSM-5. It can thus be suggestedthat the acid sites present in this sample are much more active for the conversionof wax compared to those of Al-MCM-41 and ASA, although the very-low crystal-linity H-ZSM-5 sample consists mainly of XRD amorphous aluminosilicate phase.Fig. 18.13 shows the yields (wt% on feed) of various gasoline components. Thedata in Fig. 18.13 can also be used for a qualitative comparison of catalyst perfor-mance with regard to their selectivity toward speciﬁc gasoline components, especiallyin the case of H-Y- and H-ZSM-5-based catalysts, which showed similar percent con-version of wax (Fig. 18.12). The H-Y-st. catalyst presented a signiﬁcant selectivity25 (1) ASA+H-Yst (2) ASA+H-ZSM-520 (3) H-ZSM-5 (3%cryst.) (4) Al-MCM-41151050 Olefins Naphthenes Aromatics Branched paraffinsFigure 18.13 Yields (%wt on feed) of gasoline components in the FCC of BTL-FT wax ondifferent microporous and mesoporous catalysts.
Production of biofuels via FischereTropsch synthesis: biomass-to-liquids 575toward the production of branched parafﬁns (22 wt% on feed) compared to muchlower yields with the rest of the catalysts (3.5e4 wt%). The increased formation ofbranched parafﬁns in gasoline is considered as a major target toward the productionof environmentally friendly fuels in accordance with EU regulations. Oleﬁns werealso higher with the H-Y-st. catalyst (15 wt% on feed) compared to the rest catalysts(w12 wt%), while naphthenes were 1e2 wt% for all the catalysts. As far as aromaticsare concerned, the H-ZSM-5 catalyst led to higher yields compared to the rest of thecatalysts. The high RON values of gasoline with the H-ZSM-5 catalyst (w92, seeFig. 18.12) were mainly attributed to the high aromatics content; while in the caseof H-U-st. catalyst the high RON (w87) was mainly attributed to the relativelyhigh C5eC7 oleﬁn and iso-alkane yields. The 3%-crystalline H-ZSM-5 sampleshowed similar trends with the fully crystalline H-ZSM-5 with regard to the yieldsof gasoline components, except for the case of aromatics, which are signiﬁcantlylower with the former sample. Interestingly, the RON of the gasoline producedfrom the 3%-crystalline H-ZSM-5 sample remained considerably high (81). The yieldof aromatics with the Al-MCM-41 sample was very low but cannot be compared withthose of the rest of the catalysts due to the relatively low percentage conversion ofwax with the mesoporous catalytic material. In general, research has shown that the cracking of highly parafﬁnic FT waxesunder FCC conditions can yield an interesting spectrum of renewable fuels, bothin the gasoline and diesel range, by adapting the process parameters and catalystformulations. Optimization of catalyst acidic and porosity properties as well as ofprocess parameters is necessary in order to visualize a potential commercializationof the FCC-based upgrading of F-T waxes.22.214.171.124 Upgrading of BTL naphtha to gasolineNaphtha is produced as a byproduct of the BTL-FT process, both straight-run from theFT reactor and as a coproduct of the upgrading of the FT wax to middle distillates.BTL naphtha has low octane number and cannot be used as a gasoline blendingcomponent. The two dominant processes that have been considered for upgradingFT naphtha to high-octane gasoline are isomerization and reforming. Given thatstraight-run FT naphtha contains oleﬁns and oxygenates that are not compatiblewith commercial reforming or isomerization technologies, a hydrotreating step is ﬁrstrequired to convert oleﬁns and oxygenates in the naphtha to parafﬁns (Gregor andFullerton, 1989). According to a techno-economic study by Kreutz et al. (2008), theoptimum BTL-FT plant conﬁguration in order to maximize the yield of premium dieseland gasoline fuels is to isomerize a portion of the naphtha in order to convert normalparafﬁns to isoparafﬁns and boost its octane value and catalytically reform the otherfraction to provide some aromatic content to (and further boost the octane value of)the ﬁnal gasoline blendstock. In a similar study by Takeshita and Yamaji (2008), itwas found that the upgrading of highly parafﬁnic FT-naphtha into FT-gasoline canhave a major inﬂuence on the overall process economics. In the frame of the European project RENEW, BtL-naphtha was also identiﬁed tohave suitable properties for use in future power trains like homogeneous charge
576 Handbook of Biofuels Productioncompression ignition engines. It was however found that further upgrading of thenaphtha fraction is needed for optimized engine performance, targeted toward mildreduction of its cetane number via isomerization (RENEW, 2008). Through its partic-ipation in the EU projects RENEW and OPTFUEL, our group in CERTH establishedhydroisomerization as a viable upgrading option for BtL-naphtha on both laboratory(Heracleous et al., 2013; Iliopoulou et al., 2014) and pilot scales (Iliopoulou et al.,2012). Investigation of the effect of the zeolitic support (mordenite, ZSM-5, andbeta zeolite) on the isomerization performance of a series of low-loading (0.1 wt%)Pt catalysts showed that the use of ZSM-5 leads to the synthesis of the most activematerial with satisfactory selectivity to isoparafﬁns. The superior performance ofPt/ZSM-5 was attributed to its high Bro€nsted acidity and the formation of homoge-neously dispersed, cubic-shaped and highly crystalline Pt particles on the zeolite sur-face, as shown in the TEM image in Fig. 18.14 (Iliopoulou et al., 2014). In an effort tofurther increase selectivity to large isoparafﬁns, we prepared and tested a low-loadingPt catalyst supported on a hierarchical ZSM-5 support. Introduction of mesoporositywas achieved by treating the support with alkaline and acidic solutions (Heracleouset al., 2013). Fig. 18.15 shows selectivity to C4eC8 isoparafﬁns at 40% conversionin the hydroisomerization of surrogate naphthadsimulating the composition ofBTL-naphthadat 30 bar and temperature range 240e300C. A clear increase ini-C8 species at the expense of i-C5 and i-C6 is apparent for both the alkaline- andacid-treated Pt catalysts, showing clearly that the introduction of mesopores in the (a) (b)Figure 18.14 (a) TEM image depicting the dispersion of the Pt particles on the ZSM-5 plateletsand (b) typical HRTEM image of a single crystalline Pt particle, oriented along its [1 1 0] zoneaxis.From Iliopoulou, E.F., Heracleous, E., Delimitis, A., Lappas, A.A., 2014. Producing highquality biofuels: Pt-based hydroisomerization catalysts evaluated using BtL-naphtha surrogates.Applied Catalysis B 145, 177e186.
Production of biofuels via FischereTropsch synthesis: biomass-to-liquids 577 80Sel at 40% conv,% Pt/H-ZSM-5 70 Pt/alk-ZSM-5 60 Pt/acid-ZSM-5 50 40 30 20 10 0 i-C4 i-C5 i-C6 i-C7 i-C8Figure 18.15 Selectivity to C4eC8 isoparafﬁns at 40% total n-parafﬁn conversion overmicroporous/mesoporous Pt/ZSM-5 catalysts (reaction conditions: P ¼ 30 bar;WHSV ¼ 2 hÀ1).From Heracleous, E., Iliopoulou, E.F., Lappas, A.A., 2013. Microporous/mesoporous Pt/ZSM-5catalysts for hydroisomerization of BTL-naphtha. Industrial and Engineering ChemistryResearch 52, 14567e14573.ZSM-5 structure improves selectivity, possibly due to the improved diffusivity withinthe zeolite pores and the reduced residence time of the intermediates within the porechannels. As discussed above, the upgrading of the BTL naphtha byproduct into gasoline/HCCI fuel can greatly improve the economics of the overall BTL-FT process. How-ever, this option has yet to be considered in commercial operations. Kreutz et al.(2008) argue that it is still uncertain whether the additional gasoline blending stockvalue can justify the great capital and operational costs that these upgrading unitsimpose on the BTL-FT process.18.3 Biomass-to-liquids ﬁnal fuel productsAs analyzed in detail in the previous section, the BTL-FT process (as any XTL pro-cess) can yield a different range of products, ranging from chemicals and gasoline-range hydrocarbons to middle distillate-range alkanes, based on the FischereTropschsynthesis reaction operating conditions, choice of catalyst and reactor type. TheBTL-FT process has been however mainly studied so far with the aim of maximizingthe production of diesel-range products due to two main reasons: (1) the decisive shiftof the EU toward a diesel economy and (2) the increasing EU diesel deﬁcit in terms ofreﬁning capacity (European Biodiesel Board, 2008). International Energy Agency(IEA) ﬁgures presented in Fig. 18.16 clearly show the upward trend of the diesel de-mand in the EU compared to the downward trend of gasoline consumption. In addi-tion, EU car registration ﬁgures show that the majority of new cars purchased are
578 Handbook of Biofuels Production 350,000 300,000 Diesel Gasoline250,000200,000Kilotonnes 22000010150,000 222222000000000000765432 22000089100,00050000 0 199019911992 19931994 19951996199719981999Figure 18.16 Evolution of diesel and gasoline demand in EU 27.Reproduced from Eurostat.diesel cars (70% of new cars in France, Italy, and Belgium are diesel cars) (ACEA,2008). In this context, interest in the BTL-FT process lies in the production of renew-able, high-quality middle-distillate fuels via the LTFT synthesis reaction to diesel,naphtha, and FT waxes and subsequent upgrading of the FT waxes to premium diesel.With such BTL-FT conﬁguration, BTL naphtha is produced both as straight-runand as coproduct of the FT wax upgrading. We will therefore focus on the propertiesand combustion characteristics of the two main BTL-FT ﬁnal fuel products: diesel andnaphtha.18.3.1 Biomass-to-liquids dieselBTL diesel is a renewable fuel of excellent quality, compared to both fossil-deriveddiesel and ﬁrst-generation biodiesel produced via the transesteriﬁcation of vegetableoils. BTL synthetic fuel consists mainly of linear parafﬁnic hydrocarbons with almostzero aromatics and sulfur compounds. The physical properties of BTL diesel presentedin Table 18.6 (Rantanen et al., 2005) demonstrate its very high cetane number that canreach up to 75, much higher than conventional diesel. The big advantage of BTL dieselis that it is directly usable today in the transportation sector and furthermore it may besuitable for future fuel cell vehicles via on-board reforming since it is free of sulfur.
Production of biofuels via FischereTropsch synthesis: biomass-to-liquids 579Table 18.6 Typical properties of different bio- and fossil-origindiesel product streamsFuel properties Biodiesel-FAME BTL-diesel Fossil diesel (EN 590/2005)Density @ 15C (kg/m3) 885 770e785 835Viscosity @ 40C (mm2/s) 4.5 3.2e4.5 3.5Cetane number 51 73e81 53Distillation 10 vol% (oC) 340 260 200Distillation 90 vol% (oC) 355 325e330 350Lower heating Value (MJ/kg) 38 43 43Lower heating Value (MJ/I) 34 34 36Polyaromatics (wt%) 0 0 8Oxygen (%wt) 11 0 0Sulfur (pmw) <10 <10 <10Adapted from Rantanen L., Linnaila R., Aakko P., Harju T., 2005. NExBTL - Biodiesel Fuel of the Second Generation,SAE paper 2005-01-3771.It is fully blendable with conventional diesel and compatible with current diesel en-gines and with common materials used in the tank system and the engine components.This constitutes a great plus, as the fuel can be used today using the current distributionand retail infrastructure. Due to its bio-origin, BTL diesel has much lower CO2 emissions than fossil-derivedfuels. Moreover, it shows considerably improved emission behavior. BTL diesel fuelshave been tested by Volkswagen AG and DaimlerChrysler AG in modern, state-of-the-art passenger cars, as part of the EU-funded IP RENEW project which explored tech-nology routes for the production of BTL fuels (RENEW, 2008). The vehicles wereequipped with different types of exhaust gas after-treatment systems: oxidationcatalytic converters (oxycats), which reduce CO and HC emissions and are the mostcommon technique in the existing ﬂeet and additional particulate ﬁlters (DPF), theafter-treatment technology of future diesel passenger cars. The reduction of the differentemissions with the BTL diesel compared to conventional diesel is tabulated inTable 18.7. Great emission reductions were achieved with no special adaptation ofthe engine. The BTL diesel causes a signiﬁcant reduction of CO and HC emissions,a medium reduction of particulate emissions and only a slight reduction of NOx emis-sions. The next lines of the table present emission reductions with different after-treatment technologies and optimization of the engine operation with special software.It can be generally seen that a further reduction of particulates or a signiﬁcant reductionof NOx can be realized. In general, the BTL diesel manages to reduce not only CO2, butalso the emissions of most air pollutants. What is also important is that the BTL fuel
580 Handbook of Biofuels ProductionTable 18.7 Emission reduction factors for BTL-FT diesel fueland different emission reduction technologies (negative valuesindicate a reduction of emission)Technology NOx PM CO HCState of the art, no adaptation À6% À30% À90% À60%State of the art, oxycat, PM opt. À7% À44% À95% À73%State of the art, oxycat, NOx opt. À35% À12% À95% À73%State of the art, oxycat, DPF À29% À94% À92% À79%Future dedicated BtL, oxycat þ DPF À72% À95% À59% À16%Adapted from RENEW, 2008. Renewable Fuels for Advanced Powertrains: Final Report, SYNCOM, Ganderkesee.exhibited at least the same fuel consumption as conventional fuels when compared onan energetic base (RENEW, 2008). With adapted engines the improved combustionprocess could also lead to better efﬁciency and thus reduced fuel consumption.18.3.2 Biomass-to-liquids naphthaBeside the diesel main product, naphtha, a gasoline fraction of less value is producedas a byproduct. Straight-run FT-naphtha has low octane, is oleﬁnic, and has high levelsof oxygenates (Gregor and Fullerton, 1989). The chemical composition of two naphthastreams produced via a low-temperature (LTFT) and high-temperature FischereTropsch (HTFT) process is tabulated in Table 18.8. Currently, the BTL-FT syntheticnaphtha is rather sold as a low-cost chemical feedstock and cannot be used as a fuel.Untreated naphtha can also be used as an energy source for the production of heat andpower or can be alternatively reformed on-site to synthesis gas and fed to the FTreactor to increase the process yield (Bienert, 2007). In the frame of the EU-fundedNICE (New Integrated Combustion System for Future Passenger Car Engines) project,Renault/Regienov and Volkswagen tested naphtha fuels in experimental HCCI (homo-geneous charge compression ignition) engines and found signiﬁcant improvementscompared to standard diesel fuel (RENEW, 2008). In this context, although BTLnaphtha is not a suitable fuel for conventional engines, it may be advantageous forfuture power-trains like HCCI and CCS (combined combustion system) being evenmore efﬁcient and having less emissions. It should however be mentioned that the re-quirements for these future engines are not clear for the time being. Even though the light FT-byproduct naphtha is not for application as fuel in its pre-sent form and in conventional gasoline engines, it could be upgraded by an additionalisomerization or reforming unit to boost its octane number and fulﬁll the above, as dis-cussed in Section 126.96.36.199. It should be noted that the production of ﬁnished gasolineblendstock is not yet considered because of the added cost and energy expendituresassociated with upgrading naphtha to gasoline with the current technology.
Production of biofuels via FischereTropsch synthesis: biomass-to-liquids 581Table 18.8 Typical composition of straight-run naphtha fromLTFT and HTFTProduct, wt% Low-temperature High-temperature FischereTropsch (LTFT) FischereTropsch (HTFT)Normal parafﬁns 57.0 7.7Branched Parafﬁns 3.0 6.3Oleﬁns 32.0 65.0Aromatics 0.0 7.0Alcohols 7.0 6.0Ketones 0.6 6.0Acids 0.4 2.0 100.0 100.0Adapted from Gregor J.H., Fullerton H.E., 1989. FischereTropsch naphtha upgrading. In: Proceedings of the DOE IndirectLiquefaction Contractors Review Meeting, November 14e15, Pittsburgh.18.4 Environmental and economic considerations of the BTL processThe incentives that drive progress in the area of biofuels are primarily environmentaland BTL-FT fuels, as biomass-derived fuels, offer considerable reductions in fossil en-ergy use and exhibit reduced greenhouse gas emissions compared to their fossil-basedcounterparts. This is due to the renewable nature of the biomass feedstock and theCO2-neutral cycle, ie, CO2 emitted during fuel combustion equals the amount ofCO2 adsorbed for the cultivation of the biomass feedstock. Besides their obvious envi-ronmental beneﬁts, there are also various parameters that should also be considered forthe environmental beneﬁts of biofuels, such as energy consumption for the productionof biofuels, transportation requirements of biomass feedstock and ﬁnal product, etc. Itis thus essential to assess the potential of alternative fuels using a lifecycle analysis(LCA) approach, considering the full lifecycle of biofuels from biomass cultivationthrough production and distribution to the end users. Several LCA or otherwise knownWell-to-Wheel (WtW) studies have been published examining the lifecycle environ-ment of BTL-FT diesel (CONCAWEeEUCAReJRC, 2008; van Vliet et al., 2009;Williams et al., 2009; Henrich et al., 2009; General Motors Europe, 2002; Fleminget al., 2006; Baitz et al., 2004). An LCA study investigating the environmental perfor-mance of BTL-FT diesel produced via the CHOREN-Shell technology and comparedto fossil diesel showed the clear environmental beneﬁts of BTL-FT in different envi-ronmental impact categories (Baitz et al., 2004). More speciﬁcally, reductions in theorder of 61e91% in GHG emissions, 89e94% in smog formation, 3e29% in eutro-phication potential, and 5e42% in acidiﬁcation potential can be achieved with the
582 Handbook of Biofuels Productionreplacement of fossil diesel with BTL-FT diesel. Moreover, in the JRC-EuCar-CONCAWE Well-to-Wheels study (CONCAWEeEUCAReJRC, 2008) where thelifecycle energy and greenhouse gas (GHG) balance is examined for a wide numberof different fuel routes (including coal-, oil-, gas-, and biomass-based fuels), BTL-FTdiesel appears to have one of the highest potentials for reducing the emissions ofGHG gases as shown in Fig. 18.17. The BTL-FT fuels therefore are a very attractive renewable fuel option. Still, thereare a number of drawbacks and technological challenges/limitations that need to beaddressed to maximize the beneﬁts of BTL-FT fuels and allow their large-scalecommercialization and use. One of the main issues is the large capital costs ofBTL-FT conversion and the subsequent high price of BTL-FT fuels compared to theirfossil counterparts. According to a study by Tijmensen et al. (2002), short-term pro-duction costs of BTL-FT fuels are estimated at 14 US$/GJ, compared to current dieselcosts of around 5 US$/GJ, a number that also agrees with the estimations of Hamelincket al. (2004). Investment costs represent 50% of this cost, while the biomass feedstockaccounts for 40% of the production cost. Technological advancements could reducecosts in the long-term future to w9 US$/GJ. The number is still higher than that ofdiesel, but taking into account the uncertainties in oil prices and assumptions in thedifferent studies, the long-term economics perspectives of BTL-FT fuels are notconsidered unattractive. In a more recent techno-economical study by PNNL (Zhuet al., 2011) the minimum selling price of BTL diesel was estimated around4.5 US$/gal compared to 3.13 US$/gal for conventional diesel. Roughly 40% of thiscost was attributed to the feedstock price, 20% to depreciation of the capital costand 20% to operating expenses. According to the study, the economics of the processcan be improved by recycling the off-gas from the FischereTropsch reactor to the tarreformer. This would signiﬁcantly increase the FT diesel yields, although it would WTW fossil energy MJ/100km300 WTW GHG emissions g CO2eq/km250200150100500 Gasoline EtOH EtOH EtOH, EtOH, Diesel RME Syn sugar farmed DICI diesel PISI wheat NG wheat NG cane wood farmed (Brazil) wood boiler GT + CHPFigure 18.17 LCA performance in fossil energy use and GHG emissions of different biofuels.From CONCAWEeEUCAReJRC, 2008. Well-to-wheels Analysis of Future Automotive Fuelsand Powertrains in the European Context, Well-to-wheels report, Version 2c. Joint study byCONCAWE, EUCAR and the Joint Research Centre of the European Commission.
Production of biofuels via FischereTropsch synthesis: biomass-to-liquids 583increase costs as the size of the syngas compressor and the FT area would be bigger.However, the signiﬁcant increase in ﬁnal product yield offsets the disadvantages, thuscausing an overall reduction in cost. Because of the complex technology applied for the production of the BTL-FTfuels, production can only be economical in large-scale facilities. A reasonableBTL plant capacity is >1 Mt/year biofuel, similar to the existing commerciallyoperated CTL and GTL plants (Henrich et al., 2009). Such large-scale projectsentail the uncertainty of adequate biomass resources to procure enough feedstockto feed plants of such scale. This implies great logistical hurdles and large transpor-tation costs. Several biomass pretreatment options have been investigated to over-come this issue. The two most promising are torrefaction and fast biomasspyrolysis. Torrefaction is a mild thermal treatment in which CO2 and H2O areevaded and the material is made brittle and very easy to mill. The process is suit-able for a wide range of biomass materials and has a high energy efﬁciency of up to97%. The torreﬁed material can be handled and fed to the gasiﬁer within existingcoal infrastructure (Bergman et al., 2005). Fast pyrolysis of biomass is a process inwhich biomass is thermally decomposed to bio-oil, gases, and char in an inert at-mosphere using high heating rates and short residence times at temperatures of450e550C (Bridgewater et al., 1999; Antonakou et al., 2006). In both cases,biomass volume is reduced and energy density is increased, therefore decreasingthe high transport costs.18.5 Commercial status of the biomass-to-liquids processesWithin a few years, we have witnessed large steps toward the commercialization of theBTL-FT process. There are several companies active in technology development andcommercialization of individual steps in the BTL-FT process sequence. A number ofcompanies have large-scale biomass gasiﬁcation technologies including ConocoPhillips, Siemens, VTT, TPS, CHOREN, Lurgi, Shell, GE, Kellogg Brown and Root,Prenﬂo, Advantica BGL, Noell, Winkler, and KRW (E4tech, 2008). Additionally, thereare companies focusing on the production of fuels from syngas, such as Sasol, Shell, JFEHoldings in Japan (slurry bed FT reactor producing DME), Fuel Frontiers Inc. (ethanolfrom syngas), and Syntroleum (focus so far on CTL and GTL) (E4tech, 2008). Very few companies however are active in the whole BTL process chain. Theworld’s ﬁrst commercial BTL plant was inaugurated in 2008 in Frieberg, Saxony(Germany), utilizing the Choren Carbo-V Process for converting biomass to syngas(see Section 188.8.131.52). Choren, a German-based technology company, partneredwith Shell, Volkswagen, and Daimler to construct the ﬁrst commercial BTL plant inthe world based on the Carbo-V gasiﬁcation process and the Shell SMDS (Shell Mid-dle Distillate Synthesis) FischereTropsch process. Choren had been operating a betademonstration plant in Freiberg, Germany, since 2005, with a capacity of 45 MW ther-mal and 15,000 tons of BTL fuel per year and started constructing the ﬁrst commercial
584 Handbook of Biofuels ProductionBTL plant in Schwedt, Germany, with a capacity of 640 MW thermal and 200,000tons of BTL fuel per year using these technologies, with fuel production scheduledto start in 2012 (Rudloff, 2005). Unfortunately, as the manufacturing costs and thetechnology appeared to be uncontrollable, Shell opted out in 2009, followed by VWand Daimler (Luque et al., 2012), and insolvency was announced in 2011 (Reuters,2011). In 2012, Linde announced that they acquired the Carbo-V® Technology andall related patents and trademarks and planned to offer the gasiﬁcation technologyas licensor (Linde, 2012). Several BTL demonstration projects are currently ongoing, mainly in Europe.The European Union funded in 2010 through NER 300, one of the world’s largestfunding programs for innovative low-carbon energy demonstration projects, twolarge-scale BTL projects with a total of w260MV (EU, 2012). The ﬁrst projectwas Finland Bioenergy Ajos BTL which aimed at constructing a biofuel-to-liquidplant in Ajos, northern Finland, to produce biodiesel and bionaphta in the BalticSea area for sale to a market primarily of diesel and petrol retailers. The plant wasplanned to use 950,000 tonnes/year (t/y) of woody feedstock and 31,000 t/y of talloil to deliver an annual output of 115,000 t/y of biofuel (EU, 2012). The projectwas launched by Vapo Oy and Mets€aliitto in 2007. Mets€aliitto withdrew from theproject in 2012. In February 2014, Vapo Oy published a press release accordingto which they made the decision to freeze the project planning for the plant inAjos in Kemi. According to the company’s press release: “The ﬁnal, decisive blowto the project was that the EU’s climate and energy strategy published in Januarydid not agree on new binding limits for the share of the renewable component intrafﬁc fuels after 2020. In this situation it is not possible to conclude long term com-mitments, which would have created the ﬁnancial preconditions for Vapo’s biodieselproject.” (Vapo Oy, 2014). The second BTL project that was awarded fundingthrough NER300 was the UPM Stracel BTL in France. The project consisted ofbuilding a second-generation biomass-to-liquid plant in Strasbourg, using about 1million tonnes of woody biomass to deliver an annual output of 105,000 tonnes ofbiofuel. The plant was designed to be integrated into the paper and pulp productionline of an existing paper mill, enabling exchanges of energy and products. Unfortu-nately, the project followed the fate of the Ajos BTL project as it was announced in27 February, 2014 that the project would freeze due to uncertainty in the regulatoryoutlook for advanced biofuels (NER300, 2014). Neste Oil and Stora Enso also operated a BtL demonstration plant at Stora Enso’sVarkaus Mill in Finland with an output of 656 t/y from a 12-MW gasiﬁer. Althoughthe plan was to develop a commercial production plant in partnership with FosterWheeler and VTT with a projected output capacity of 100,000 t/y and a potentiallaunch date of 2016, in August 2012 the companies announced that they would notprogress with the construction of the plant (European Biofuels Technology Platform,2015). A more successful example is the BioTfueL project, launched in 2010, with the aimto develop a production chain for second-generation diesel and kerosene-type biofuels.The project was undertaken by IFP Energies nouvelles, CEA, Axens, Soﬁprotéol,
Production of biofuels via FischereTropsch synthesis: biomass-to-liquids 585Total, and Uhde ThyssenKrupp Industrial Solutions, with a total budget of 112.7MV.The process chain is expected to be launched in the market by 2020 and will involvedrying and crushing of biomass, torrefaction at Soﬁprotéol’s site in Venette, France,and gasiﬁcation, syngas puriﬁcation and FischereTropsch conversion at Total’s sitein Dunkirk, France. The project will use Uhde’s proprietary PRENFLOTM™ gasiﬁ-cation process with direct quench (PDQ) the Gasel™ process developed jointly byIFP Energies nouvelles, ENI, and Axens for the FishereTropsch synthesis process.According to a recent press release by IFP (2014), the project is about to sign the en-gineering, procurement, and construction contracts and the two demonstration plantsare expected to become operational by the end of 2016. Also in France, CEA (theFrench Alternative Energies and Atomic Energy Commission) announced the con-struction of a pilot BTL plant in Bure Saudron producing diesel, kerosene, and naphthafrom forestry and agricultural residues (G€uell et al., 2012). The Karlsruhe bioliq® process has also been operating successfully on pilotscale in KIT in Germany since 2005. The plant consists of a 2-MW(th) (0.5 t/h),pilot-scale fast pyrolysis of lignocellulosic materials and biosyncrude preparation,bioslurry PEF gasiﬁcation up to 80 bar in a 5-MW(th) pilot gasiﬁer with a mem-brane screen, high-temperature, high-pressure raw syngas cleaning and condition-ing, H2/CO ratio adjustment, and CO2 separation and conversion of a c.700 N m3 synthesis sidestream to gasoline (Dahmen et al., 2012). Also in Germany,the Forschungszentrum Karlsruhe GmbH in partnership with LURGI GmbH is con-structing a pilot plant for production of BTL fuels. The pilot plant is due to open in2016 (G€uell et al., 2012). A demonstration plant in Europe exhibiting impressive robustness is also the GRE(G€ussing Renewable Energy) multifuel gasiﬁcation plant, located in Gu€ssing,Austria. The gasiﬁcation technology employed in the Gu€ssing plant has beendescribed in detail in Section 18.2.1 describing the different technologies for biomassgasiﬁcation to synthesis gas, which is the ﬁrst step of the BTL process. The plant con-sists of an 8-MW circulating ﬂuidized-bed steam-blown gasiﬁer producing heat andpower (4.5 MWth, 2 MWel) with a gas engine and a total efﬁciency of 80%. It is theworld’s ﬁrst functioning fast internally circulating ﬂuidized bed (FICFB) gasiﬁcationplant. The technology was developed by GRE together with German engineeringconsultancy Consulectra (RWTU€ V group) and the scientiﬁc support by the ViennaUniversity of Technology. What is impressive is the fact that the plant has been oper-ating for the last 12-plus years with over 80,000 h of operations until today. Due tothe use of steam as a gasiﬁcation agent, the produced synthesis gas has low nitrogencontent and suitable H2/CO ratio for downstream synthesis reactions. It also enablesthe different syngas applications to be realized at smaller scale (10e100 MW fuel)(Rauch, 2014). Exactly due to the favorable properties of the produced gas, the planthas served as a demonstration site for the further conversion of synthesis gas torenewable synthetic natural gas (BioSNG) and renewable liquid hydrocarbon fuelsvia the FT process. The FischereTropsch pilot plant has been in operation since2005 producing 5e10 kg/day of FT raw product (Rauch, 2014). In order for the syn-gas to meet the FT-reactor requirements, a multistep cleaning step has been added,
586 Handbook of Biofuels Productionconsisting of a biodiesel scrubber used to dry the gas, a sodium aluminate ﬁxed bed toseparate chlorine, hydration of organic sulfur compounds over a hydrodesulfurizationcatalyst, and H2S separation with ZnO. The FischereTropsch reaction takes place in aslurry reactor at 20e22 bar pressure and temperature of 230C, able to convert about7 N m3/h of synthesis gas to hydrocarbons over a Co-Ru catalyst (Ripfel-Nitscheet al., 2007). Although Europe seems to be leading the race in the development of BTL technol-ogy, successful demonstration projects are also currently ongoing in the USA. A majordevelopment for the BTL process in the USA is the construction of the Sierra BioFuelsfacility by Fulcrum Bioenergy. The Sierra BioFuels Plant will include a feedstockprocessing facility and a bioreﬁnery that will convert approximately 147,000 tons ofmunicipal solid waste (MSW) into more than 10 million gallons of jet fuel or dieselannually. According to the company, Fulcrum has entered into 20-year MSWfeedstock agreements with waste service partners for the delivery of the feedstockand construction of the plant is expected to begin in late 2015. In May 2015, Fulcrumawarded a ﬁxed-price engineering, procurement, and construction contract to Abengoathat will be responsible for constructing the Sierra Bioreﬁnery (Fulcrum Bioenergy,2015). In June 2015 United Airlines, one of the largest air carriers in the US,announced a $30-million equity investment in Fulcrum and entered an agreement tojointly develop up to ﬁve other projects located near its hubs. According to the pressrelease (United Airlines, 2015), the production potential of these sites would be up to700 million liters of aviation fuel per year. Moreover, the two companies signed a longterm agreement according to which United Airlines will purchase 350 million liters ofsustainable aviation fuel a year for a minimum of 10 years at a cost that is competitivewith conventional jet fuel. One other prominent BTL plant in the US is the Velocys plant in Oregon. Velocys isthe company that developed microchannel FischereTropsch reactors that use superac-tive cobalt catalysts, offering increased yields and stability compared with conventionalsystems and resulting in a high productivity per unit volume. According to the company“Conventional FT plants are only economically viable at production capacities of30,000 bpd or higher. Velocys’ microchannel FT technology is commercially viableat production capacities of as low as 1500 bpd, making it an idea choice for smallerscale GTL and BTL” (Velocys, 2015). As discussed in the previous section, the BTLprocess, due to its great complexity, can only be economical in large-scale facilities,something that entails great uncertainty of adequate biomass resources and great logis-tical hurdles and transportation costs. Using an intensiﬁed FT technology, such as theone developed by Velocys, can overcome this barrier. Red Rock Biofuels, a customerof Velocys, was awarded a $70 million grant to construct a biomass-to-liquids (BTL)plant incorporating Velocys technology to convert about w170,000 tons per year offorestry and sawmill waste into approximately 1100 barrels per day of military aviationjet fuels (Velocys, 2014). Construction of the plant was scheduled to begin in the sum-mer of 2015. According to recent reports, in July 2015 Red Rock announced an agree-ment to supply FedEx Express with 100,000 tons per year of bio jet fuel from 2017and signed agreement also with Southwest Airlines (European Biofuels TechnologyPlatform, 2015).
Production of biofuels via FischereTropsch synthesis: biomass-to-liquids 58718.6 Future prospects and challengesThe production of sustainable second-generation biofuels via the BTL-FT process rep-resents one of the most, if not the most, promising options for large-scale replacement offossil fuels in the world fuels market. The most important advantages of the BTL processhave been mentioned throughout this chapter and can be brieﬂy summarized as follows:(1) the BTL process is very versatile concerning both feedstock and products; it can pro-duce hydrocarbons of different lengths from any carbon-containing feedstock, such ascoal, natural gas, and biomass, including any lignocellulosic material such as woodand forest residues, agricultural residues, byproducts and bagasse, lignocellulosic feed-stock from processing residues (paper slurry, black liquor, etc.); (2) BTL-FT fuels arehigh-quality products, free of sulfur, nitrogen, aromatics, and other contaminants typi-cally found in fossil fuels; (3) BTL-FT fuels are largely compatible with current vehiclesand fully blendable with conventional fuels and can thus be handled by existing fuelinfrastructure. Intensive research efforts in the ﬁeld, from both academia and industry,have signiﬁcantly advanced progress and have brought the BTL process one step beforecommercialization. Of course there are still limitations, technological challenges, andplenty of room for further optimization. One of the main issues is the large capital costs of BTL-FT conversion and the sub-sequent high price of BTL-FT fuels compared to their fossil counterparts. Technologicaladvancements to improve the energy efﬁciency of the process and reduce the capital costdue to technological learning and scaling are necessary to bring down the costs. The cur-rent overall efﬁciency of the BTL plants is relatively low, ranging between 40 and 45%on an HHV basis (Hamelinck et al., 2004). Further progress has to be made to developand improve technologies of biomass feedstock pretreatment, gasiﬁcation, syngas puri-ﬁcation, and oxygen production required by the gasiﬁcation step in a more economicalway to achieve better energy integration and carbon balance. In particular, developmentwill need to examine more closely the choice of gasiﬁcation technology (eg, entrainedﬂow versus ﬂuidized bed) and its design to account for biomass feeding and syngas qual-ity requirements, the gas cooling and cleaning technologies to reliably meet the stringentdownstream catalytic process requirements while reducing losses in thermal efﬁciencyand the design of downstream processes and optimization of outputs based on consider-ations of process efﬁciency and product values, including catalyst development to pro-duce the required products. For the latter, it is crucial to couple catalyst developmentwith the speciﬁcs of syngas derived from biomass for the advancement of an integratedhighly efﬁcient and selective BTL process.ReferencesACEA, 2008. EU Economic Report. February 2008 (Brussels).Adesina, A.A., 1996. Hydrocarbon synthesis via FischereTropsch reaction: travails and tri- umphs. Applied Catalysis A 138, 345e367.Anderson, R.B., 1956. Chapters 1e3. In: Emmett, P.H. (Ed.), Catalysis, vol. IV. Reinhold, New York.
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Biochar in thermal and 21thermochemicalbioreﬁneriesdproduction ofbiochar as a coproductO. MasekUniversity of Edinburgh, UK Biochar Research Centre, Edinburgh, United Kingdom21.1 IntroductionBiochar is a solid carbonaceous material produced as a coproduct of thermochemicalconversion (pyrolysis, gasiﬁcation, or hydrothermal carbonization) of biomass. It ispurposefully produced for application to soil or other storage media with the intentionto serve as a carbon sink and/or soil conditioner. Therefore its properties need to bedesigned to match this purpose. Depending on the feedstock and production condi-tions, the carbon content of biochar and its stability (resistance to decomposition)can be varied, together with other parameters, such as physical (porosity, strength, den-sity, etc.) and chemical (composition, active surface groups, etc.) properties. Theresulting set of properties determines the suitability of any particular biochar fordifferent applications. The concept of biochar as a method for carbon sequestration is fairly new, despitenumerous historical examples of widespread use of carbonized biomass in agriculturalpractices around the globe as a soil amendment medium (Ogawa and Okimori, 2010;Young, 1804). The concept relies on diverting a portion of carbon away from theglobal carbon cycle (60 Gt of carbon per year) into a much slower cycle, or a carbonsink in the form of stable carbon. Due to the scale of the carbon cycle, diverting even asmall fraction into a stable form can contribute considerably to offset anthropogenicemissions of greenhouse gases (GHGs) (7 Gt of carbon per year). As a result, wide-spread deployment of biochar can slow down increases in atmospheric GHG concen-trations and eventually lead to their reduction, once stabilization of emissions fromfossil fuels is achieved. In the context of biofuels and bioenergy, biochar can help to achieve their improvedenvironmental performance and move these technologies along a carbon intensity axisfrom close to carbon neutral to carbon negative. Therefore, there are several possiblemotivations for integrating biochar as a concept into biofuels, bioreﬁnery, andbioenergy concepts; climate change mitigation, agricultural productivity, and wastemanagement. Often more than one of these would apply in any given scenario, asimportant synergies can be achieved.Handbook of Biofuels Production, 2e. http://dx.doi.org/10.1016/B978-0-08-100455-5.00021-7Copyright © 2016 Elsevier Ltd. All rights reserved.
656 Handbook of Biofuels Production21.1.1 Biochar for climate change mitigationTurning organic matter into biochar, with organic carbon stabilized in a recalcitrantcarbonized matrix, diverts carbon from a relatively rapid biological cycle, with averageturnaround time of at most a few decades (Prentice et al., 2001), into a slow carboncycle, with turnaround time in the order of centuries to millennia (Kuhlbusch,1998). This use and function of biochar depends critically on its environmental stabil-ity, ie, recalcitrance to decomposition and release of carbon back into the atmosphere.Besides high stability, a second condition must also be met for biochar to play a validrole in carbon sequestration. As the actual removal of carbon from the atmosphere isthe result of photosynthesis, which converts atmospheric CO2 into organic carboncompounds in plant matter that can be used as feedstock for biochar production, itis necessary that new biomass is grown at least at the same rate at which it is beingturned into biochar. The stability of biochar is a complex topic, and its detailed discussion is beyond thescope of this chapter. It is an area of intensive ongoing research (Cross and Sohi, 2013;Lehmann et al., 2009; Naisse et al., 2013; Spokas, 2010), owing to its importance. Themain issues arise because of the long timescales involved, and the difﬁculty of reliableexperimental determination of biochar carbon resistance to decomposition on suchlong timescales. This is further complicated by the sensitivity of stability to environ-mental conditions, reﬂecting different climatic and geographic regions. Although,determination of absolute biochar carbon stability is still not possible, differentapproaches to assessment of relative stability have been proposed. Among these, prox-imate analysis (ASTM D1762-84(2013)), O:C or H:C molar ratios (Enders et al., 2012;Spokas, 2010), chemical oxidation (Cross and Sohi, 2013), and thermal oxidation(Harvey et al., 2012) are among those most commonly used. Analyses using thesemethods show strong dependence of biochar stability on production conditions andfeedstock. However, the carbon sequestration potential, calculated as the product ofbiochar carbon stability and its yield, appears to be much less sensitive to productionconditions (Crombie et al., 2013; Masek et al., 2011; Zhao et al., 2013). In addition to this direct way of carbon sequestration, evidence suggests that biocharcan also have an indirect effect on GHG emissions from agricultural activities. This isdue to its potential to reduce the need for primary inputs (water, fertilizer, etc.) andassociated energy consumption, as well as reduced emissions of CH4 and N2O fromcultivated soils (Karhua et al., 2011; Yanai et al., 2007).21.1.2 Biochar for soil conditioningThere is growing evidence that the addition of biochar to agricultural soils, at leastunder certain circumstances (ie, where it helps to address existing constraints), leadsto improved crop yield and therefore enhanced productivity (Sohi et al., 2010;Spokas et al., 2012; Verheijen et al., 2009, 2010). There are a number of potentialreasons for this beneﬁcial effect and these can be categorized as physical (change insoil texture, bulk density, water-holding capacity, etc.) or chemical (change of soilpH, addition of nutrients from leachable ash, promotion of microbial activity, etc.)
Biochar in thermal and thermochemical bioreﬁneries 657(Atkinson et al., 2010). Often more important than direct addition of macronutrientsto soil in the form of P and N is its ability to alter their availability to plants(Gundale and DeLuca, 2006a,b). Some of these effects are likely to be only short-term while others are likely to be longer-lasting (over a number of years). Currentresearch suggests that addition of biochar can bring the biggest beneﬁts to poor soilsby inﬂuencing carbon content and water-holding capacity (Shackley and Sohi,2010).21.1.3 Biochar for waste managementAs biochar can be produced from nearly any organic matter, it can, with certaincaveats, also be produced from wastes and nonvirgin biomass. In fact, pyrolysishas been used extensively for waste management, as it can signiﬁcantly reduce thevolume and weight of waste material. As a result, signiﬁcant experience existswith associated material handling and processing (Heermann et al., 2002), and theindustry has accumulated a great deal of knowledge and experience with pyrolysistechnology. However, production of biochar from waste requires a cautious approach to avoidrisks associated with potential biochar contamination. This is despite the fact thatpyrolysis destroys many potential pathogens and contaminants found in wastes thatwould otherwise usually pose a challenge to their application to soil (Bicudo andGoyal, 2003; Westrell et al., 2004). There are two main types of contamination(inorganic and organic) and associated sources. The ﬁrst potential source is the feed-stock itself. Most heavy metals contained in the feed would be retained in the biocharafter pyrolysis, and therefore feedstock with a high content of heavy metals yieldscontaminated biochar. In addition, the relative concentrations of heavy metals in bio-char are higher than in the feedstock, due to the loss of volatile matter. The secondsource is the pyrolysis (or other thermochemical conversion) process, which cancontaminate biochar with organic compounds, such as polycyclic aromatic hydrocar-bons (PAHs), furans, dioxins, and other potentially toxic compounds (Buss et al.,2015b; Buss and Masek, 2014; Hale et al., 2012). While in reality the content of heavymetals in biochar can only be controlled by choice of feedstock, the content of organiccontaminants can be successfully minimized by suitable design and operation of theconversion process (Buss et al., 2015a), or by additional post-treatment of contami-nated biochar (Kołtowski and Oleszczuk, 2015). In many cases, pyrolysis and biochar can be an attractive solution to waste manage-ment of organic residues, as it diverts organic material from disposal routes such aslandﬁll or incineration. Conversion (upcycling) of such waste materials into a usefulproduct offers several beneﬁts, as material for agricultural applications as well as amethod for carbon sequestration. At the same time, diverting the organic materialfrom landﬁll and stabilizing it in the form of biochar prevents a release of methane(a potent GHG) that would otherwise occur during its decomposition. Besides management of wastes, pyrolysis can also be used to manage coproducts ofdifferent processes, producing further useful products. Application of this concept tobioreﬁneries will be discussed in Section 21.3.
658 Handbook of Biofuels Production21.2 Biochar as a coproduct in biofuels and bioenergy productionMost thermochemical conversion technologies used for production of biofuels andbiochemicals yield solid residues as a byproduct. Depending on the technology, thisresidue contains more or less carbon, and can therefore be considered biochar in itsown right, or a biochar precursor. The key relevant technologies, fast pyrolysis, gasi-ﬁcation, and hydrothermal carbonization are discussed individually in the followingsections. The properties of biochar produced as a coproduct of biofuel and biochemical pro-duction depend greatly on the feedstock and conversion technology selected. As theprimary objective of these processes is not the production of biochar, it is unlikelythat the process conditions would be set up to yield biochar with properties tunedfor speciﬁc applications, so-called “bespoke” or “engineered” biochar. Althoughthis may reduce the perceived value of these biochars, it does not necessarily precludetheir use. Based on understanding of interactions between biochar properties andrequirements of different applications, such as soil amendment, environmentalmanagement, carbon sequestration, it is possible to match biochar from different pro-duction units to a suitable application. In addition, in some cases further modiﬁcation/upgrading of biochar can be justiﬁed to improve its properties, and increase its value.21.2.1 Fast pyrolysisFast pyrolysis is a thermochemical conversion process capable of producing liquidbiofuels (bio-oil) (Balat et al., 2009; Bridgwater, 2000, 2012; Czernik and Bridgwater,2004) from a range of lignocellulosic feedstock. Typical fast pyrolysis conditions arecharacterized by: moderate pyrolysis treatment temperatures (400e600C), rapid heat-ing rates of biomass particles (>100C/min), combined with short residence times ofthe biomass particles and pyrolysis vapors (0.5e2 s) at high temperatures (Demirbas,2004). Combination of medium pyrolysis temperature with short vapor residence timeensures high yield of good-quality pyrolysis liquids (up to 70e75 wt%, expressed ondry biomass feedstock basis), while keeping the char and gas yields to a minimum, 12and 13 wt%, respectively (Bridgwater, 2012; Nachenius et al., 2013). To achieve thehigh heating rate needed, the process requires intensive heat transfer from heat sourceto biomass particle. For this reason, small particle sizes (1e2 mm) are required, due tolow thermal conductivity of biomass. As a result, considerable physical pretreatmentof biomass is necessary before fast pyrolysis. A key distinguishing feature of fast pyrolysis technology is the need to keep thevapor residence time in hot zone to the minimum (below a few seconds), to achievegood bio-oil quality. This can be achieved by ensuring rapid quenching or coolingof the vapors. In this way, unwanted secondary vapor phase decomposition reactions,which would give rise to additional char and noncondensable gases, at the expense ofbio-oil yield, are avoided. In this respect, fast pyrolysis differs from slow pyrolysis,where the latter process aims at achieving a maximum yield of char (up to 35 wt%)
Biochar in thermal and thermochemical bioreﬁneries 659by employing long particle and vapor residence times and slower heating rates(Bridgwater and Peacocke, 2000; Brown et al., 2015; Lu et al., 2009). Different types of fast pyrolysis reactors have been proposed, developed, and scaledup to pilot or even commercial scale level (Bridgwater, 2000; Venderbosch and Prins,2010) over several decades of development, each with its strengths and weaknesses.However, due to their scalability, well-understood design, process control, and favor-able parameters, such as feedstock ﬂexibility, high heat and mass-transfer rates, pos-sibility of use of catalysts, ﬂuidized beds have become the preferred technology forindustrial bio-oil production (Ringer et al., 2006; Venderbosch and Prins, 2010). Ina ﬂuidized bed, a preheated solid material (heat carrier, often sand or catalyst) is sus-pended in a stream of hot, inert gas, although mechanical ﬂuidization is also possible.The resulting vigorous motion of biomass and bed-material particles ensures optimalmixing behavior and high heat and mass-transfer rates. Downstream of the pyrolysisreactor, cyclones separate the vapors from the char/heat carrier, followed by collectionof bio-oil using electrostatic precipitators or spray condensers. For detailed discussionof fast pyrolysis and upgrading of bio-oil to biofuels, see chapters “catalyticfast pyrolysis for improved liquid quality” and “Production of biofuels via bio-oilupgrading & reﬁning.” In terms of biochar production, fast pyrolysis yields only approximately 12e15%of char, and therefore it is not the most suitable technology for dedicated biochar pro-duction. However, the solid residues resulting from bio-oil production can still be usedas biochar if they possess the right properties. One potential disadvantage of fastpyrolysis biochar is the physical size of char particles (very ﬁne powder), which makesits handling and ﬁeld application challenging (Husk and Major, 2010). This can, how-ever, be overcame by pelleting or granulation of biochar to obtain biochar in a moresuitable physical form. In addition, it is also important to note that the primary decom-position of biomass during fast pyrolysis is an endothermic process (Venderbosch andPrins, 2010) and thus (in commercial-scale units) the required process heat is usuallyobtained by complete or partial combustion of the noncondensable gases or char.Therefore, to allow for valorization of fast pyrolysis biochar, other low-value sourcesof heat would need to be utilized. Given the speciﬁcs of the fast pyrolysis process in terms of feedstock requirementsand process conditions, ie, fast heating and short residence time in reactor, it can beexpected to yield biochar with a different set of properties compared to other conver-sion processes, such as slow pyrolysis or gasiﬁcation. The short residence time canlead to incomplete charring of the biomass particle, as observed by Bruun et al.(2011, 2012). This in turn leads to lower environmental stability of biochar, and there-fore lower carbon sequestration potential. This is the case even when the biomass con-version during pyrolysis is apparently complete, as reported in Brewer et al. (2009).These authors observed lower stability of fast pyrolysis biochar, assessed based onﬁxed carbon content and aromaticity, compared to slow pyrolysis and gasiﬁcation bio-char produced from the same feedstock. Besides stability, reﬂecting chemical composition, the physical properties of fastpyrolysis biochar also differ from those of slow pyrolysis biochar. Research by Bruunet al. (2012) showed somewhat higher surface area of fast pyrolysis biochar, and its
660 Handbook of Biofuels Productionhigher pH, which will affect the effect of such biochar on soil. The ﬁne powder natureof fast pyrolysis biochar may also make it more susceptible to microbial attack, due tolarger surface:volume ratio (Zimmerman, 2010), resulting in higher carbon turnover.On the other hand, ﬁne biochar particles are also likely to beneﬁt from physicalprotection against degradation by interactions with minerals or by encapsulation(Brodowski et al., 2006). In terms of integration with biofuel production, utilization of fast pyrolysis biocharinstead of its combustion for process heat has been shown to positively affect the life-cycle GHG emissions of biofuel production (Zaimes et al., 2015), and offer a poten-tially attractive option for carbon sequestration and transportation fuel production(Brown et al., 2011).21.2.2 GasiﬁcationGasiﬁcation is a thermochemical conversion process in which solid carbonaceousmaterials are converted into product gas, containing H2, CO, CH4, CO2, etc. This isachieved by reacting the solid fuel with steam, CO2, O2, or air at relatively high tem-peratures (McKendry, 2002) in an atmosphere with a low concentration of oxygen.The main product of gasiﬁcation is a ﬂammable gas (product gas), that can be usedas a feedstock for production of liquid fuels and/or chemicals, or as fuel for power gen-eration (using combustion engines, gas turbines, or fuel cells). With carbon conversionlevels in most large-scale commercial biomass gasiﬁcation systems in the order of94e99%, there is only a relatively small yield of coproducts (char/ash and tar). Formore detailed discussion of gasiﬁcation technology for biofuel production see chapters“Production of bio-syngas and bio-hydrogen via gasiﬁcation,” “Production of bio-alcohols via gasiﬁcation,” and “Production of biofuels via Fischer-Tropsch synthesis:biomass-to-liquids.” In gasiﬁcation units with high carbon conversion efﬁciency the solid residue, ie,gasiﬁcation ash/char, contains only a small amount of carbon, and is therefore less suit-able for use as biochar compared to biochar from pyrolysis, at least from the carbonsequestration point of view (Leiva et al., 2007). One possible exception could beﬂy-ash from ﬂuidized bed gasiﬁcation, as its carbon content can be up to 70% (Pelset al., 2005). However, in this case, close attention would need to be paid to contam-inant content in this material, as harmful organic and inorganic contaminants can bepresent in high concentrations. At the other end of the scale, small and medium-size gasiﬁcation units, suitable fordistributed biomass utilization, do not generally achieve such high carbon conversionefﬁciencies, and therefore more carbon is retained “lost” in the solid residue. However,instead of this being a disadvantage, it can present an opportunity for valorization ofthe solid residue, rather than dealing with its disposal. In addition, sequestering of theunconverted carbon in this way can improve the carbon balance of the gasiﬁcation pro-cess in terms of GHG emission (Shackley et al., 2012a). It has been shown in a number of studies that gasiﬁcation char can have positiveeffects on soil and plants (Deal et al., 2012), and could therefore be beneﬁcially usedin agricultural, horticultural, and environmental applications. Muter et al. (2014)
Biochar in thermal and thermochemical bioreﬁneries 661carried out glasshouse plant tests, using biochar obtained from a large-scale(500 MWth) wood gasiﬁer, mixed with peat-sand substrate. The results showed a sig-niﬁcant increase in substrate pH with addition of biochar, and stimulation effect on thebiometric indices of the aboveground plant part and roots. Deal et al. (2012) showedthat gasiﬁcation biochar can be a suitable amendment for acidic soils, due to its positiveeffect on soil pH, as a result of high ash content. In this work improved plant (maize)growth (plant height, stem volume, leaf area, and cut dry weight) was reported whengasiﬁcation char produced from eucalyptus and maize cobs was added to soil. Onthe other hand, Rogovska et al. (2012) reported inhibition of corn seedling growthwhen treated with water extract of high-temperature (750e850C) gasiﬁcation charsproduced from switchgrass and corn ﬁber. The presence of inhibiting compounds,such as polycyclic aromatic hydrocarbons (PAHs) in these extracts was suspected asa potential cause of the observed inhibition effect. Besides PAHs, other potential com-pounds could be responsible for the effect (Buss et al., 2015b; Buss and Masek, 2014). One concern with gasiﬁcation biochar is the potential for a high concentration oforganic and inorganic contaminants. The concentration of inorganic contaminants,such as heavy metals, in biochar is mainly dictated by their concentrations in the start-ing feedstock, although attrition of steel parts (mainly stainless steel) of equipment canalso contribute (Buss et al., 2015a). Therefore this parameter can be well controlled bysuitable feedstock selection. It is important to note that due to the high burnout oforganic matter during gasiﬁcation, the concentrations of inorganic matter increasedramatically. However, the typically high concentration of metals and minerals in gasi-ﬁcation char itself does not present a problem, as long as potential contaminants arepresented in stable form, preventing their leaching. In fact, in some cases, high mineralcontent can be a source of nutrients, as shown for example by Kuligowski et al. (2010),Mozaffari et al. (2002), and M€uller-Sto€ver et al. (2012). The situation is more complicated when it comes to organic contaminants, as thesecan be either introduced with the feedstock, or produced during the gasiﬁcation pro-cess. Concerns about the use of gasiﬁcation char in agricultural, horticultural, or envi-ronmental applications include the presence of PAHs (Buss et al., 2015b; Kloss et al.,2012) and tars. The extent to which such organic contaminants are present in the result-ing char varies a lot with feedstock and process. PAH concentrations ranging from lessthan one to above 100 mg/kg (Hansen et al., 2015; Shackley et al., 2012b; Wiedneret al., 2013) were reported. For comparison, guideline values for priority 16 USEPA PAHs content for biochar are 12 mg/kg (4 mg/kg for premium grade) accordingto European Biochar Certiﬁcate guidelines (“‘European Biochar Certiﬁcate e Guide-lines for a Sustainable Production of Biochar.’ European Biochar Foundation (EBC),”2015) and 20 mg/kg according to International Biochar Initiative (“IBI. Standardizedproduce deﬁnition and product testing guidelines for biochar that is used in soil,”2013) guidelines. The reasons for such a large variation in PAH concentrations arethe different potential mechanisms of contamination. These include: PAH formationwithin and outwith biochar particles, PAH release and potential PAH depositiononto biochar particles. Depending on the conditions and environment surrounding bio-char particles during their stay in the gasiﬁcation chamber and in separators, where bio-char is separated from syngas, different mechanisms will be enhanced and suppressed.
662 Handbook of Biofuels ProductionIn addition, in some systems, water is used to cool down biochar discharged from thegasiﬁcation chamber, and this water is often recycled and used in tar scrubbers, thuscontaminating biochar (Shackley et al., 2012b). Therefore, if gasiﬁcation biochar isto be used for soil application, the production system needs to be set up to minimizethe risk of contamination.21.2.3 Hydrothermal carbonizationHydrothermal carbonization (HTC) is a thermal treatment process that can achieve avery high conversion of biomass carbon into solid carbonaceous residue. During theHTC process, organic substances are treated in an aqueous environment at tempera-tures between 150 and 350C, under autogenous pressure, to form condensed carbo-naceous solid product, also called hydrochar or HTC solid, and a liquid stream richin organic compounds. Laboratory tests have shown that carbon retention may be ashigh as 80% in the solid residues (Sevilla and Fuertes, 2009), which gives the processexcellent emission characteristics. The HTC process releases about one-third of theenergy content of the feedstock (Titirici et al., 2007), with the rest remaining in thesolid product. As no external source of energy and no feedstock dewatering and dryingis required, this energy can be used, for example, for generating steam and power, forheating the process and for drying the produced hydrochar. These characteristics andthe fact that wet starting material is not only acceptable, but required, make the HTCprocess potentially very suitable for processing of various organic residues with highmoisture content. Besides converting wet biomass into hydrochar, the HTC process is also capable ofcoproducing chemicals, which include phenolic compounds, 2,5-HMF, and aldehydes(acetic, lactic, propenoic, levulinic, and formic acids) that can potentially be used inbioreﬁneries (Axelsson et al., 2012; Hoekman et al., 2012; Oladeji et al., 2015). Theformation and concentration of these chemicals can be controlled by adjusting theHTC process conditions (Libra et al., 2011; Xiao et al., 2012), such as temperature,pressure, and residence time. Therefore the HTC process could be a useful part of bio-logical and thermochemical bioreﬁneries, processing wet residues, and coproducingchemicals and hydrochar. It has been reported that unlike biochar, with highly aromatized carbon structure,hydrochar is mostly composed of aliphatic hydrocarbons (Fuertes et al., 2010;Schimmelpfennig and Glaser, 2011; Wiedner et al., 2013). This means that the envi-ronmental stability of hydrochar is considerably lower (Abel et al., 2013; Sun et al.,2014) than that of biochar with a higher degree of carbonization and higher aroma-ticity. The high content of labile/easily degradable carbon results in different effectsof application of hydrochar to soil, compared to biochar. For example, hydrochargreatly affects composition of soil microorganisms, and causes a dramatic bacterialand archaeal community shift (Andert and Mumme, 2015). Besides this, the presenceof phenolic and organic acid compounds on hydrochar surface, which cause negativeplant and microbial response, makes effective direct use of hydrochar in environmentaland agricultural applications complicated (Bargmann et al., 2013; Titirici et al., 2012),although this does not have to always be the case (Wiedner et al., 2013). However, it
Biochar in thermal and thermochemical bioreﬁneries 663appears that these unfavorable properties, from the perspective of soil application, canbe ameliorated by post-treatment of hydrochar. Biological post-treatment, such ascomposting of hydrochar with other organic materials can reduce its toxicity (Buschet al., 2013). Other biological treatments, such as anaerobic digestion could also reducehydrochar toxicity and make it suitable for soil application. Another alternative tothese biological post-treatment routes is thermal post-treatment, such as pyrolysis.The advantage of pyrolysis of hydrochar is not only the fact that it removes toxic com-pounds, making hydrochar suitable for soil application, but also the fact that it stabi-lizes it, due to development of aromatic carbon structures (Zhu et al., 2015). Thesechanges during thermal post-treatment also lead to structural changes of hydrochar,developing its porosity and increasing ash content, thus further increasing itssuitability for soil application.21.3 Biochar from bioreﬁnery residuesBesides production of biochar as an intended or unintended coproduct during conver-sion of biomass to biofuels and chemicals in thermochemical bioreﬁneries, biochem-ical bioreﬁneries also provide opportunities for production of biochar as a standaloneprocess, valorizing residues resulting from biological treatments. Various residues canbe left behind after enzymatic, microbial, and other treatments in bioreﬁneries, mainlyconstituting recalcitrant fractions high in lignin and mineral matter. Both of thesestreams can be used in biochar production, as discussed below. For dedicated production of biochar from bioreﬁnery residues, such as lignin, slowpyrolysis provides a viable choice, due to its ﬂexibility in terms of feedstock, its tech-nical maturity, and level of control. Slow pyrolysis is in many aspects the opposite offast pyrolysis. It is characterized by slow heating and relatively long residence times ofbiomass in the reactor, in the order of tens of minutes or even several hours. Due to therelatively slow heating, the feedstock particle size requirements are not as tight as forfast pyrolysis, and depending on the technology used feedstock in form ranging fromsmall chips to cord wood can be successfully used. As a result of these markedlydifferent production conditions in slow pyrolysis, the product distribution and proper-ties are very different from those in fast pyrolysis (see Table 16.1). The yield of biocharin slow pyrolysis is considerably higher and subsequently the yields of liquid andgaseous products are lower. Due to its high biochar yield, slow pyrolysis is a very suitable technology for bio-char production. Unlike other more recent biomass conversion technologies, eg, fastpyrolysis, hydrothermal carbonization (HTC), and to some extent gasiﬁcation, slowpyrolysis has been used extensively for production of charcoal and chemicals for thou-sands of years (Domac et al., 2008) and could therefore be considered well understood.Although this may be true for charcoal production processes, there are many uncer-tainties and unknowns when it comes to production of speciﬁed/bespoke biochar.The key challenges are related to production of biochar with desirable propertiesand stability, as an integral part of systems for coproduction of biochar, energy,
664 Handbook of Biofuels Productionand/or chemicals. Historically, charcoal production was focused on converting a rela-tively limited range of feedstock, mostly woody biomass, to fuel-grade charcoal,which did not require a high degree of speciﬁcation, ie, relatively simple quality con-trol could be used. On the other hand, to make biochar a useful material for agricultureor for other speciﬁc purposes such as cleaning-up waste water requires detailed under-standing of the relationship between feedstock properties, conversion process param-eters, and the end use of the resulting biochar. Perhaps the only comparably demandinghistoric application for charred biomass was in the production of gun powder, wherespeciﬁc properties of char were required, to ensure good product quality, however thiswas typically achieved by use of a limited range of carefully selected feedstock. Tosome extent, activated carbon industry may also be a useful analogue. Therefore,future research and development needs to focus on production of biochar with prop-erties speciﬁcally suited for its application, whether carbon storage, soil amendment,etc., in a way that is environmentally sustainable and economically viable. Two examples of modern slow pyrolysis systems are the rotary drum and screwpyrolyzer. Rotary drum pyrolyzers move feedstock through an externally heated hor-izontal (or slightly inclined) cylindrical reactor by rotation of the reactor or by action ofpaddles moving inside a stationary cylindrical shell. Both of these technologies canachieve long residence times in the order of tens of minutes and good control of prod-uct quality and distribution (Klose and Wiest, 1999). In addition, rotary drum pyro-lyzers can operate at a wide range of scales up to tens of thousands tons per yearcapacity. Screw pyrolyzers use a rotating auger to move material through a tubularreactor that can be heated either externally or internally by introduction of heat carriermaterial such as sand or metal balls. Screw pyrolyzers also offer good control of thepyrolysis process and are well suited for small to medium-scale applications, butunlike rotary drum pyrolyzers are not suitable for large-scale applications. In both cases, ie, the rotary drum and screw pyrolyzer, the heat needed to drive theconversion process is most often provided by combustion of the gaseous and liquidbyproducts of the pyrolysis process. The heat thus released can then be directed todifferent parts of the pyrolyzer to achieve the desired operating conditions. Any excessheat can be used in external applications (eg, heating, feedstock drying). In some cases,part of the gaseous and liquid stream can be used for combined heat and power (CHP)generation, where the gases are burned in a combustion engine driving a generator andthe heat contained in the ﬂue gases is used for heating applications. On the other hand,in certain cases, the heat released by combustion of byproducts is not sufﬁcient to drivethe pyrolysis process (particularly where feedstock with high moisture content is used)and additional fuel needs to be provided. Due to the wide range of processing conditions (temperature and residence time)available and feedstock options (woody biomass, agricultural biomass, and diverseorganic residues) that can be processed in slow pyrolysis units, the yield and propertiesof biochar can vary widely. This provides an opportunity to optimize the production toyield biochar with properties matching its application. In their research Ronsse et al.(2013) and Zhao et al. (2013) showed that certain biochar properties are primarilyaffected by processing conditions (eg, surface area, pH, carbon sequestration poten-tial), while others are mainly feedstock-dependent (eg, content of total organic carbon,
Biochar in thermal and thermochemical bioreﬁneries 665ash, and ﬁxed carbon). Based on such information and knowledge, it is possible todesign biochar (Crombie et al., 2014; Novak et al., 2009) to address speciﬁc require-ments, whether it is soil improvement, carbon sequestration, or environmental func-tions. A thorough review of different biochars and their uses is beyond the scope ofthis chapter, more information can be found in the relevant reviews (Qian et al.,2015; Spokas et al., 2012; Verheijen et al., 2009; Xu et al., 2012). In addition to biochar as the main product (in terms of yield), the slow pyrolysisprocess also yields gases and liquids. The pyrolysis gases are of relatively low heatingvalue (2e12 MJ/kg), and generally contain less than one-quarter of the energy con-tained in all coproducts (Crombie and Masek, 2015). Pyrolysis gases therefore havea low value for external applications, but can be used as a source of heat for the pyrol-ysis process itself or potentially for feedstock drying. In terms of energy content,pyrolysis liquids, without water separation, have also a low heating value (HHV of5e9 MJ/kg), and contain approximately 20% of energy in the coproducts (Crombieand Masek, 2015). The heating value is low mainly due to the high water content,which also causes the liquids to separate into several phases. This issue can be at leastpartially overcome by fractional condensation of the pyrolysis vapors, to obtainwater and organic fractions separately (Tumbalam Gooty et al., 2014; Westerhofet al., 2011). Although the energetic content of pyrolysis liquids is relatively low, due to the lowcaloriﬁc value (CV) and low yield of water-free fraction, the composition makes it apotentially interesting source of chemicals in the bioreﬁnery context. The type andconcentration of chemicals that can be obtained from pyrolysis liquid depends mainlyon the feedstock composition. A number of key value-added chemicals have beenidentiﬁed in recent studies (Bozell et al., 2007; Werpy and Petersen, 2004). Forexample, furfural and levoglucosan can be obtained from hemicellulose and cellulosefractions of biomass, while BTX chemicals and phenols can be obtained from lignin.One obstacle in the commercialization of production of these chemicals from pyrolysisliquids has been their complex nature, and also the relatively low concentration of mostof these chemicals, typically below 1%. To overcome this, the so-called staged pyrol-ysis (De Wild et al., 2009) in combination with fractional condensation (TumbalamGooty et al., 2014; Westerhof et al., 2011) can be used to increase the content of thesechemicals in resulting liquids, and make their recovery more proﬁtable.ReferencesAbel, S., Peters, A., Trinks, S., Schonsky, H., Facklam, M., Wessolek, G., 2013. Impact of biochar and hydrochar addition on water retention and water repellency of sandy soil. Geoderma 202e203, 183e191. http://dx.doi.org/10.1016/j.geoderma.2013.03.003.Andert, J., Mumme, J., 2015. Impact of pyrolysis and hydrothermal biochar on gas-emitting activity of soil microorganisms and bacterial and archaeal community composition. Applied Soil Ecology 96, 225e239. http://dx.doi.org/10.1016/j.apsoil.2015.08.019.Atkinson, C.J., Fitzgerald, J.D., Hipps, N.A., 2010. Potential mechanisms for achieving agricultural beneﬁts from biochar application to temperate soils: a review. Plant and Soil 337 (1e2), 1e18. http://dx.doi.org/10.1007/s11104-010-0464-5.
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Algae for biofuels: an emerging22feedstockZ. Sun a,1, J. Liu a,2, Z.-G. Zhou11Shanghai Ocean University, Shanghai, China; 2Peking University, Beijing, China22.1 IntroductionTo date, fossil fuels including coal, petroleum, and natural gas still serve as the mainenergy sources; the growing consumption of fossil fuels, however, has led to signiﬁ-cant environmental problems. Furthermore, fossil fuels are recognized to be unsustain-able due to their depleting supplies. Hence there is an urgent need to explore clean andrenewable energies, such as biofuels. Compared with traditional fuels, biofuels arecarbon-neutral, contribute to less emission of gaseous pollutants, and are consideredenvironmentally beneﬁcial (Hu et al., 2008). Currently, the commercial production of biodiesel is mainly from plant oil, which isfar below the demand of transport fuels, because huge amounts of arable land arerequired for the cultivation of oil plants. Taking the United States as an example, ifoil palm, a high-yielding oil crop, is used for biofuel production, 24% of the total na-tional cropland would have to be devoted to meet only 50% of the transport fuel needs(Chisti, 2007; Mata et al., 2010). The requirement for huge amounts of arable land andthe resultant conﬂicts between food and oil make biofuels from plant oil unrealistic tocompletely replace the petroleum-derived fuels in the foreseeable future. In this regard,microalgae, which are believed to possess various advantages over other candidates,have been envisioned as an emerging feedstock for biofuels. Microalgae, also knownas microphytes, refer to algae in microscopic size ranging from a few micrometers to afew hundreds of micrometers. The research on algal oil for biodiesel production can betraced back to as early as 1970s, and the main superiorities of microalgae include (1)high oil contents, with some species exceeding 60e70% of the dry weight of biomass,much higher than oil crops; (2) rapid growth rates, much faster than higher plants,whilst the entire growth cycle can be completed within a few days; and (3) a betteradaptability to distinctly different environmental conditions from water to land andeven in unusual locations such as snow and desert soil, which causes no competitionwith food for arable lands. Much less land is needed if using microalgae as biodieselfeedstock. According to Chisti (2007), only 2.5% of the existing US cropping areawould be sufﬁcient for producing algal biomass to satisfy 50% of the transport fuelneeds, which accounts for 0.7% of soybean. These unique properties, in combinationwith the CO2 capture and recycling capacities, make microalgae a promising cella These authors equally contributed to this work.Handbook of Biofuels Production, 2e. http://dx.doi.org/10.1016/B978-0-08-100455-5.00022-9Copyright © 2016 Elsevier Ltd. All rights reserved.
Doubling time (h)674 Handbook of Biofuels ProductionChloroBcoturcycoucomclicttuosrsalpe.factory for biofuel production. The key properties of microalgae-derived biofuels, eg,energy density, viscosity, ﬂash point, cold ﬁlter plugging point, and acid value, havebeen proved to comply with the speciﬁcations established by the American Society forTesting and Materials (Xu et al., 2006). In this chapter, an overview of the currentresearch progress of microalgal biofuels is presented; obstacles and future researchtrends are also discussed.22.2 Microalgal biomass and oil22.2.1 BiomassCurrently it is estimated that over 50,000 microalgal species exist in nature. Theyrepresent a diverse group of prokaryotic (eg, cyanobacteria) or eukaryotic photo-synthetic microorganisms, either in unicellular or multicellular form (Grahamet al., 2009). Microalgae are sunlight-driven cell factories, converting CO2 tobiomass through photosynthesis. Compared with land plants, they exhibit higherphotosynthetic efﬁciency and grow much faster, completing an entire growth cyclewithin a few days (Chisti, 2007). As indicated in Fig. 22.1, under speciﬁc cultureconditions, the fastest-growing species Chlorocuccum littorale has a doubling timeas short as 8 h (Ota et al., 2009). Microalgal biomass can reach as high as 10 g/L depending on algal species andculture conditions. In terms of biomass productivity (biomass density divided byculture time), Chlorella sp. was reported to achieve 0.93 g/L/day (Li et al., 140 120 100 80 60 40 20 0 Chlorella protothecCoChidhloCelorsherlelolalrleasllpvaHu.CzalgoehafmoirnirNsaigcteiyoeoscnctosihscislcomSuriiscsneoponrllueevdoieaasblimsuSnucdseAanopnebhsdlaieqnTsuoemutthrsuaessceeslpmmC. iiysccrsloopst.ecollapNiccitrazIysspoctchichiaarylsaiesvgIissaoNlbcaahnnrynaCsoRircsyhhpsolotpdhr.oeomcposodisninaisumspc. ohniiFigure 22.1 Growth rates of selected microalgal species. The greater the doubling time, thelower the growth rate. Error bars represent the highest and lowest values reported.
Algae for biofuels: an emerging feedstock 6752011a), but most microalgae lie between 0.1 and 0.3 g/L/day. In addition, there aresome reports using glucose or other organic carbon sources for heterotrophic and/ormixotrophic growth of microalgae, where much higher biomass density and produc-tivity can be achieved. For example, the heterotrophic Chlorella could accumulatebiomass up to 100 g/L with an average volume productivity of 13 g/L/day (Yanet al., 2011).22.2.2 Oil content and productivityHigh oil content is a key desirable characteristic of a microalgal strain for biodieselproduction. Generally, microalgae synthesize a relatively low level of oil underfavorable growth conditions, but the oil content can signiﬁcantly increase understress conditions such as nitrogen deﬁciency. Green microalgae produce muchhigher amounts of oil than other algae (Fig. 22.2). Among the studies reviewedhere, the green alga Scenedesmus sp. accumulates the highest oil content (73% ofdry weight), which was achieved under nutrient starvation for 11 days (Matsunagaet al., 2009). Oil productivity is another important indicator. Fig. 22.3 summarizes the oil pro-ductivities of selected green microalgae and other algae. Green microalgae have anaverage oil productivity of 72 mg/L/day, which is much higher than that of otheralgae (w30 mg/L/day). According to Fig. 22.3A, Pseudochlorococcum sp. (Liet al., 2011b) has the highest lipid productivity of 290 mg/L/day among the greenmicroalgal strains under photoautotrophic batch cultivation conditions, followed byParietochloris incisa (153 mg/L/day, Solovchenko et al., 2010), Neochloris oleoa-bundans (133 mg/L/day, Li et al., 2008), Scenedesmus rubescens (133 mg/L/day,Lin and Lin, 2011), Scenedesmus obliquus (131 mg/L/day, Mandal and Mallick,2011) and Chlorella sp. (110 mg/L/day, Hsieh and Wu, 2009). In some cases, oil pro-ductivity can be enhanced by using continuous cultivation mode (red column inFig. 22.3). There are some species showing very low oil productivities, for example,Chlorella saccharophila and Dunaliella tertiolecta (Fig. 22.3A). This is because in-dustrial wastewater was used to cultivate these algae, making them grow extremelyslowly (Chinnasamy et al., 2010). It is also worth noting that some studies employheterotrophy to grow microalgae in fermentor without light supply for lipid produc-tion, where sugars (eg, glucose) are added as the organic carbon source. Generally,microalgae grown under heterotrophic conditions give much higher lipid productiv-ities than those under photoautotrophic conditions (Miao and Wu, 2006; Liu et al.,2010, 2011).22.2.3 Fatty acid compositionThe characteristics of fatty acids of biodiesel feedstock are of great importance becausethey determine, to a great extent, the key properties of biodiesel. Properties like viscos-ity, cold ﬂow, and oxidative stability depend heavily on the composition and structureof fatty acyl esters (Knothe, 2005). Fatty acids are either in saturated or unsaturatedform, of which the unsaturated fatty acids may vary in the number and position of
Figure 22.2 Oil contents of green (A) and other (B) microalgae under nitrogen-replete PAThpIhsaNChaoSCPeaaylSCMcPaoynolrnhCkihslyndnooreNnresappheadnytuoliahetIhaeocscrorhsScCnoetyoehittsdoRoheSsoypntycrctiouhcclcrilonihkceooEdzuhParcsheeoPPNceeluochrimryolaIrmurcSdoleyaplamssldhaiiysoetivNatpmisprnepvuosvNolznsitntstlooacsiirsloeaaollibcsismscijoolriissrruoicciatcvhuvnhutaclooszvvpoepcmiroaoaimrgdeoildnspsacuacailasyrconlrnaaomsicgchrusrelntouscrccasuavyattellnoiietilnaibe6utaneasuoaaeasiptsnrraprnhtesan9ttlalihrliteulsuauusnississdssaipeevncs0nnncumpppmtmmppapipiei.rraia3saassaisss..ii.i.... (b) 70 CDShPicNlHcCaSesteCmaycShneCoehoelTeMcuCyCBochmlcPnDdeCeddTorhhohilheeceanotooraeuhlltlrCloedorClorsrSeromcattCnBllayioaoorrlermhreDTdhrlschaaiecooeahocorcsslTteleeeopluoestuolcotullnopimlilorsseelDtnorreannrlaosrmccarycsliomoaCrotlealuacliachucloceiresmuzqtsaccsicdyasshcluoslnuucoleomiououcolrseeeisulmtsataosssaerlforhtarchetclellsisupeoilciilmnbiprcadsiospcepvrasnmlbeletclkmtgubuueiururrbusclihitielumuilooaissuinrnltmsnnlmoolcleeiaaaogassivapsltsidcqidaiiiecchlnracrnddiaullhisaasdsusiuhiasiuscesssendnoceernipppplntupptdulmliapilinaaaiaerasasaises..i..sis..ai.s 676 and -deﬁcient conditions. Error bars represent the highest and lowest values reported. Lipid content is deﬁned as percentage of dry weight. Nitrogen-replete, nitrogen is stoichiometrically 60 (a) 80 balanced where no evidence of nitrogen reduction or depletion in the medium is observed; 50 nitrogen-deﬁcient, nitrogen is completely removed from medium or reduced below 40 70 stoichiometric concentrations for microalgal growth, either by changing the medium or 30 60 maintaining a batch culture until nitrogen in the medium is severely depleted. Data are based 20 50on studies during the past 5 years. 10 40 30 0 20 10 0 Oil content (% dry weight) Oil content (% dry weight) Nitrogen replete Handbook of Biofuels Production Nitrogen deficient Nitrogen replete Nitrogen deficient
Figure 22.3 Reported or calculated maximum oil productivity of green (A) and other APTphhhNaaaePaMlSCPanonoCkhsloodeNnresahntapuNohIlaieaoesochRrceinSteoodtttsyohchozyntccuikrcleorslonoiohhuEePsaPdeccIdecrrrmmlsliarhaeeosyylupomhNooivipvurtspsimsmlacocstooalaliisbsreoossrhnsirovcocitocuvccovsreenicgfaiosmyardcoa.pdrmauaoalcsruroscpsiunlrsoeascloiulatnibistuaetausaunnneptrasashlsttlsalterilssipuaunnisuceanpeplnuppl.mtmpaaamreaa.r.ass..i.i (b) 160 (a) 350 Algae for biofuels: an emerging feedstock(B) microalgae under autotrophic conditions. Data are based on studies during the past 5 years. 140 300 120 250 100 80 60 40 20 0 Oil productivity (mg L–1 day–1) ChSNlaPcSeOmeCsconSueheycMeruCcClBdnDhCoodedioehoPhlcrcuheonoemCdlrtloaonlsorCrBeaScloeCicyhlromrarshadcohcrisecoelhTenletloeemtiououoliclsletrealnllrosnoarlsyalsCoraolauetsiimorlecoruccaccehsqzomsachydercmccuololuoaesotloslroeulhuaescolfuarbeictircissnalpopcrirntebdulcosvctmiimhruukssgisbluernuobuolaismomipaiurnimscdlpliselsiargiineolscaiqdaidhnslanuascscurseuuesntipssnuonpiprtlipmnpsdauaiasii.pasri..ss.asi.as. Oil productivity (mg L–1 day–1) 0 50 100 150 200 Batch Batch Continuous Continuous 677
678 Handbook of Biofuels Productiondouble bonds on the acyl chain. The synthesized fatty acids in algae are commonly inmedium length, ranging from 16 to 18 carbons. There are some exceptions producinglong-chain polyunsaturated fatty acids as the main components, for example, the greenmicroalga Parietochloris incise produces C20:4 as the major fatty acid that accountsfor about 59% of total fatty acids (Khozin-Goldberg et al., 2002), and the dinoﬂagellateCrypthecodinium cohnii accumulates C22:6 of around 50% of total fatty acids (Coutoet al., 2010). In general, saturated fatty esters possess high cetane number and betteroxidative stability, whilst unsaturated, especially polyunsaturated fatty esters havesuperior low-temperature properties (Knothe, 2008). In this context, modiﬁcation offatty esters, for example enhancing the proportion of oleic acid (C18:1) ester, is consid-ered to be a feasible approach toward providing a compromise solution between oxida-tive stability and low-temperature properties and therefore promotes the quality ofbiodiesel (Knothe, 2009). Thus, microalgae with a high percentage of C18:1 arepreferred for biodiesel production. The fatty acid proﬁle of various Chlorella speciesis shown in Table 22.1. These data are obtained under speciﬁc conditions, and mayvary greatly when parameters such as temperature, pH, light intensity, and nitrogenconcentration are changed. The major fatty acids in Chlorella are C16:0, C18:1,C18:2, and C18:3.22.3 Oil biosynthesis in microalgaeUnlike land plants in which individual classes of lipids may be synthesized and local-ized in a speciﬁc cell, tissue, or organ, microalgae produce distinct lipids, includingphospholipids, glycolipids, and neutral lipids in a single cell. Neutral lipids, especiallytriacylglycerols (TAGs) are considered superior to others for biodiesel production, asthey are devoid of phosphate and have higher fatty acids content. The synthesizedTAGs are commonly deposited in lipid bodies located in cytoplasm of microalgal cells(Rabbani et al., 1998; Damiani et al., 2010). The current understanding of TAGbiosynthesis in microalgae is mainly deduced from the well-characterized pathwaysof fungi and land plants.22.3.1 Fatty acid biosynthesisSimilar to land plants, microalgae synthesize fatty acids in the chloroplast using a sin-gle set of enzymes. As shown in Fig. 22.4, the ﬁrst step is to generate malonyl-CoAfrom acetyl-CoA in the presence of acetyl-CoA carboxylase (ACCase). ACCase is arate-limiting enzyme and represents a key controlling point of carbon ﬂux for fattyacid biosynthesis. The ﬁrst characterized microalgal ACCase is from the diatom Cyclo-tella cryptica (Roessler and Ohlrogge, 1993). The malonyl group of malonyl-CoA istransferred to a protein cofactor on the acyl carrier protein (ACP), leading to the for-mation of malonyl-ACP that is involved in subsequent condensation and elongationreactions. The ﬁrst condensation reaction is catalyzed by 3-ketoayl ACP synthaseIII (KAS III), giving rise to a four-carbon product. KAS I and KAS II catalyze the
Table 22.1 Fatty acid proﬁle of various Chlorella speciesMicroalgae C16:0 C16:1 C16:2 C16:3 C16:4 C17:0 C18:0 C1 14.3 1.0 e e e 0.32 2.7 71Chlorella protothecoidesChlorella 12.7 e e e e 0.5 4.3 66 protothecoides 22.62 1.97 7.38 1.94 0.22 e 2.09 35Chlorella 24 2.1 e e e e 1.3 24 zoﬁngiensis 25.4 3.1 10.7 4.1 e e 1.4 12 26 e e e e e e 4Chlorella vulgarisChlorella sorokinianaChlorella ellipsoidea
18:1 C18:2 C18:3 C18:4 C18:5 C20:0 Cultural References1.6 9.7 e e e e condition Cheng et al.6.8 15.1 e e e e Heterotrophic (2009) (Utilizing5.68 18.46 7.75 0.49 e e Jerusalem Gao et al. (2010)4.8 47.8 e e e e artichoke)2.4 34.4 7.1 e e e Heterotrophic Liu et al. (2011) 40 23 e e e (Utilizing sweet sorghum juice) Yoo et al. (2010) Autotrophic Chen and Johns Autotrophic (1991) Heterotrophic Abou-Shanab Autotrophic et al. (2011)
680 Handbook of Biofuels ProductionAcetyl-CoA C16:0-ACP C18:0-ACPACCase HCO3– Acyl-ACPMalonyl-CoA ENRMAT Trans- Malonyl-ACP enoyl-ACPAcetyl-CoA HD KAS III/I/II 3-hydroxyacyl- ACP 3-ketoacyl- ACP KARFigure 22.4 A simpliﬁed illustration of saturated fatty acid biosynthesis in microalgalchloroplast. ACCase, Acetyl-CoA carboxylase; ACP, acyl carrier protein; CoA, coenzyme A;ENR, enoyl-ACP reductase; HD, 3-hydroxyacyl-ACP dehydratase; KAR, 3-ketoacyl-ACPreductase; KAS, 3-ketoacyl-ACP synthase; MAT, malonyl-CoA:ACP transacylase.subsequent condensations and ﬁnally the saturated C16:0- and C18:0-ACP are pro-duced. The initial product of each condensation reaction is a b-ketoacyl-ACP, whichrequires three additional reactions of reduction, dehydration, and reduction to form in-dividual acyl-ACP. In recent years, the de novo synthesis of saturated fatty acids hasbeen reconstructed and the related enzymes have been identiﬁed in several oleaginousmicroalgae, including Dunaliella tertiolecta (Rismani-Yazdi et al., 2011), Nanno-chloropsis gaditana (Radakovits et al., 2012), and Nannochloropsis oceanica (Vieleret al., 2012). To obtain unsaturated fatty acids, double bonds are added to the acyl chains bydesaturases. Stearoyl-ACP desaturase (SAD) is a well-characterized soluble enzyme,which is localized in chloroplast stroma and catalyzes the insertion of a cis doublebond at the ninth position of C18:0-ACP to form C18:1-ACP. A detailed characteriza-tion of SAD from Chlorella zoﬁngiensis has been reported (Liu et al., 2012a). The het-erologously expressed Chlorella SAD successfully catalyzed the desaturation of C18:0 to C18:1. In addition, it was also able to convert C16:0 to C16:1, although the con-version efﬁciency was much lower compared with the conversion of C18:0eC18:1,which suggested the substrate preference on C18:0. Some microalgae also producelong-chain polyunsaturated fatty acids (C20eC22) that are derived from the furtherelongation and/or desaturation of C18, eg, C20:5 (eicosapentaenoic acid, EPA) byNannanochloropsis (Vieler et al., 2012) and C22:6 (docosahexaenoic acid, DHA)by Isochrysis (Liu et al., 2013). The ﬁnal fatty acid composition of individual micro-algae is determined by the activities of enzymes that use these acyl-ACPs as substratesat the termination phase of fatty acid biosynthesis.
Algae for biofuels: an emerging feedstock 68122.3.2 TAG biosynthesisThe fatty acids act as the precursors for the synthesis of cellular membranes and neutralstorage lipids like TAGs. Among multiple TAG synthesis pathways, the acyl-CoA-dependent Kennedy pathway is a well-characterized one. As shown in Fig. 22.5,acyl-CoAs initially react with the hydroxyl groups in glycerol-3-phosphate to formphosphatidic acid via lysophosphatidic acid. These two steps are catalyzed by glyc-erol-3-phospate acyltransferase (GPAT) and lysophosphatidic acid acyltransferase(LPAAT), respectively. Both GPAT and LPAAT have been identiﬁed in microalgae,but the number of gene homologs differs depending on species. For example,C. reinhardtii harbors only a plastidic LPAAT (Merchant et al., 2012) whilst Nanno-chloropsis oceanica has six additional extraplastidic ones (Vieler et al., 2012). Phosphatidic acids undergo dephosphorylation to produce diacylglycerols (DAGs)with the presence of phosphatidate phosphatase (PAP). DAGs subsequently accept athird acyl from CoA to give rise to TAGs. This ﬁnal step is catalyzed by an enzymeuniquely involved in TAG synthesis, namely diacylglycerol acyltransferase (DGAT).Among various enzymes involved in the TAG biosynthesis, DGAT is considered asthe primary one in all organisms studied so far (Chen and Smith, 2012). Currently thereAcyl-CoA Glycerol-3-phosphate GPATLysophosphatidic acid LPAATPhosphatidic acid PAP Diacylglycerol PhospholipidsDGAT GlycolipidsDiacylglycerol PDAT/GDAT? DGTA/PDAT? Lysophospholipids Triacylglycerol LysoglycolipidsFigure 22.5 Proposed TAG biosynthesis in microalgae. Dashed arrows denote reactions inwhich the enzymes are not shown. GPAT, glycerol-3-phosphate acyltransferase; LPAAT,lysophosphatidic acid acyltransferase; PAP, phosphatidic acid phosphatase; DGAT,diacylglycerol acyltransferase; PDAT, phospholipid:diacylglycerol acyltransferase; DGTA,diacylglycerol transferase; GDAT, glycolipid:diacylglycerol acyltransferase.
682 Handbook of Biofuels Productionare three families of DGATs identiﬁed in nature: DGAT1 and -2 are the main enzymesresponsible for TAG formation in plants, whereas DGAT3 has only been reported inpeanuts (Saha et al., 2006), whose exact function remains unclear. Although bothDGAT1 and -2 are known as the primary enzymes for de novo TAG biosynthesis,they share no similarities in amino acid sequence and differ in their biochemical, cellularand physiological functions (Yen et al., 2008). In contrast to DGAT1 that is structurallyrelated to sterol: acyl-CoA acyltransferase, DGAT2 has more homology with monoa-cylglycerolacyl transferases (MGATs) and acyl-CoA wax-alcohol acyltransferases.So far there are very few studies on DGATs in microalgae in spite of the availabilityof increasing full genomic sequences of microalgae. For example, PtDGAT1 fromthe diatom Phaeodactylum tricornutum is the only algal DGAT1 that has been biochem-ically characterized (Guiheneuf et al., 2011). Our research group is currently undertak-ing research to identify and characterize genes encoding DGAT from the green algaMyrmecia incisa (Chen et al., 2015). In addition to the Kennedy pathway, an alternative pathway which is independentof acyl-CoA may also be found in microalgae for TAG biosynthesis (Dahlqvist et al.,2000). This pathway is mediated by a phospholipid: DAG acyltransferase (PDAT) thattransfers a fatty acyl moiety from a phospholipid to DAGs to form TAGs. According toYoon et al. (2012), PDAT may act as a multifunctional enzyme, possessing both acyl-transferase and acylhydrolase activities with a broad substrate speciﬁcity. It wassuggested that the contribution of PDAT to TAG synthesis in Chlamydomonas wasprominent under the favorable growth conditions rather than stress conditions. Thisindicates that PDAT is essential for membrane lipid turnover with the concomitantsynthesis of TAG and may collaborate with DGATs for survival of algal cells understress.22.3.3 Lipid bodies in microalgaeTAGs, a minor portion of polar lipids and proteins compose the lipid bodies (LBs).Typically, LBs are thought to be formed at endoplasmic reticulum (ER), which hasbeen well characterized in yeasts and land plants. In microalgae, LBs are alsocommonly found in cytosol. Fig. 22.6 shows the ﬂuorescence-dyed LBs of certainmicroalgae. In addition to cytosolic LBs, microalgae also accumulate LBs in plastid(Fan et al., 2011; Goodson et al., 2011). A deep study of microscopic visualizationof LBs in Chlamydomonas classiﬁed three types of LBs, namely a-cyto-LBs,b-cyto-LBs, and cp-LBs (Goodson et al., 2011). a-Cyto-LBs are produced in cytosol under nonstress conditions with the sizeranging from 250e1000 nm. They serve as the “seeds” for b-cyto-LBs, the largerbodies formed in stressed cells. ER-derived LBs are assembled from TAGs catalyzedby DGATs localized at ER, whilst chloroplast-derived LBs are from TAGs by PDATor even DGAT. Although all the currently identiﬁed Chlamydomonas DGATs lackplastid targeting sequences based on prediction programs, they may reach the outerenvelope where DAGs and fatty acids are available. The employment of in situ immu-nolocalization or fusion reporter gene (eg, green ﬂuorescent protein) may have thepossibility to address the localization of DGATs.
Algae for biofuels: an emerging feedstock 683 Isochrysis galbana Nannochloropsis oceanica Chlorella vulgaris Chlorococcum sp. Chlamydomonas reinhardtiiFigure 22.6 Microscopic observation of bodipy-stained lipid bodies in selected microalgae.Left panel, bright ﬁeld; right panel, green ﬂuorescence ﬁeld. Green ﬂuorescence indicates lipidbodies. cp-LBs are bodies present in chloroplast, which have only been found in chloroplastof Chlamydomonas starchless mutant (Fan et al., 2011; Goodson et al., 2011). Thismay be attributed to the fact that blocking starch biosynthesis diverts carbon ﬂuxand/or ATP/NADPH to cp-LB production. However, it is not clear whether it alsohappens in other starch-producing microalgae such as Chlorella.22.4 Mass cultivationThe outdoor mass cultivation of microalgae started in the late 1940s with almostconcurrent launch in the United States, Germany, and Japan. From then on, the
684 Handbook of Biofuels Productionmass culture of algae becomes one of the hottest topics in algal biotechnology andmany culture systems have been developed for commercial applications. Generally,these culture systems can be simply classiﬁed into open and closed systems, and themicroalgal cultures are grown autotrophically, heterotrophically, or mixotrophically.22.4.1 Open pond systemsOpen ponds can be grouped into natural systems (eg, lakes and lagoons), artiﬁcialponds, or containers. They resemble mostly closely the nature of microalgae, and serveas the oldest and simplest systems for algal production (Shen et al., 2009). Thecommonly used forms include raceway ponds, circular ponds, and tanks, of whichraceway ponds have received the most attention. The raceway pond system wasinitially used to culture Spirulina for commercial production and is now also employedfor mass culture of many other microalgal strains. A typical open pond is made frompoured concrete, or just simply dug into the earth and lined with a plastic liner to pre-vent the ground from soaking up the liquid. A closed loop and oval-shaped recircula-tion channels are equipped in open pond systems, where algal cells and nutrients aremixed by a paddle wheel. An open pond usually is shallow (0.25e0.4 m deep) becauseoptical absorption and self-shading by the algal cells limits light penetration throughthe algal broth (Chisti, 2007). Usually a relatively low cell density is achieved using the raceway pond system(<1 g dry weight/L). Czech researchers developed an inclined thin-layer cascade sys-tem, which is able to sustain much higher cell density (Masojidek et al., 2011). In thissystem, the turbulent ﬂow of Chlorella cultures on inclined channels is created bygravity; a pump is applied to return the cultures from the bottom to the top of the chan-nels. The system is characterized by the highly turbulent ﬂow, thin layer of suspension(less than 1 cm), and high ratio of exposed surface area to total volume, and thus canachieve dramatically higher volumetric yield (up to 40 g/L) than open ponds (Douchaand Livansky, 2009). However, the overall areal productivity obtained from thissystem is around 20e25 g/m2/day (Doucha and Livansky, 2009), similar to that ofopen ponds (20 g/m2/day, Richmond et al., 1990).22.4.2 Closed photobioreactorsClosed photo bioreactors (PBRs) usually refer to those closed systems in which allgrowth elements are introduced into the reactor and controlled according to therequirements. There are various categories of PBRs, including tubular reactors(horizontal and vertical), ﬂat panel reactors, vertical column reactors, bubble columnreactors, air life reactors, and immobilized reactors. They are made of transparentmaterials with a large surface area-to-volume ratio so that they can efﬁciently getthe illumination when exposed to sunlight (Ugwu et al., 2008). Artiﬁcial light canalso be used to grow microalgae. However, due to the cost, it is preferably used forthe production of high-value-added ingredients instead of algal oils. Tubular PBRsare widely used for mass cultivation of microalgae. The tubes have very narrow diam-eters (no more than 0.1 m) so that the sunlight penetration is maximized. For ﬂat-plate
Algae for biofuels: an emerging feedstock 685PBRs, light path is an important factor to inﬂuence the biomass productivity. Liu et al.(2013) conducted the outdoor culture of Isochrysis galbana using the ﬂat-plate PBRswith light paths from 1.9 to 7.6 cm. Results showed that the longer the light path, thehigher the areal biomass productivity, suggesting that the highest photosynthetic efﬁ-ciency occurred in the longest light path PBRs. On the other hand, from a volumetricproductivity standpoint, a reverse relationship was evident, with the shorter light pathof PBRs resulting in greater volumetric biomass productivity. Generally, the overallbiomass productivity of closed PBRs is higher than that of open ponds; however,different algal species may favor distinct culture systems to achieve maximized celldensity, biomass productivity, and oil productivity. Comparison between differentlarge-scale culture systems is illustrated in Table 22.2. In some cases, the hybrid cul-ture system, such as the PBR-pond system can be used. In such systems, microalgaeare ﬁrstly cultured in PBRs for rapid growth and oil accumulation, and then serve asthe seed to inoculate in raceway ponds for biomass production.22.4.3 Heterotrophic and mixotrophic cultivationFor those microalgal species that can survive in complete darkness, heterotrophic culti-vation is available, which uses organic carbon substances as the sole carbon and en-ergy source. Sugars, hydrolyzed carbohydrates, acetate, and glycerol have beendemonstrated to be effective carbon sources (Liu et al., 2010, 2012b; De la Hoz Siegleret al., 2011). Compared with autotrophy, heterotrophy provides substantial advantagesincluding high biomass yield and productivity, elimination of light requirement, easeof control for monoculture, and low-cost for harvesting the biomass (Chen, 1996).Mass culture of heterotrophic Chlorella in fermentors has achieved commercial suc-cess in Japan, with an annual production of around 1100 tons biomass (Lin, 2005).It has been reported that the heterotrophic Chlorella could achieve up to 100 g/Lwith an average volume productivity of 13 g/L/day (Yan et al., 2011). Nevertheless,considering the high cost of organic carbon sources, fermentation of algae may beeconomically viable only for high-value products but not for the low-cost, large-volume commodity products like biofuels. Many microalgal species are able to grow well under mixotrophic conditions utiliz-ing both CO2 and organic carbons in the presence of light. Commonly, microalgaegrow better under mixotrophic conditions than under autotrophic conditions. To boostthe biomass production, in some cases, the organic carbons are added into the openponds and PBRs to achieve mixtrophic production of biomass. However, the microal-gal cultures in open ponds supplemented with organic carbons, especially sugars, aresusceptible to bacterial contamination. In this context, step-wise feeding could be abetter solution. The mixotrophic monoculture is relatively easier to maintain inPBRs than in open ponds. Lee et al. (1996) reported a successful maintaining of Chlor-ella monoculture mixotrophically grown in a 10-L outdoor tubular PBR in the pres-ence of sugars. Nevertheless, the monoculture failed when scaled up to 300 L,which indicated the critical challenge of microbial contamination in mixotrophicmicroalgal culture at scale.