Introduction to BIOFUELS David M. Mousdale CRC Press Taylor & Francis Group Boca Raton London New York CRC Press is an imprint of the Taylor & Francis Croup, an informa business
Contents Preface Acknowledgments The Author Units and Conversion Factors xv xxi xxiii xxv Ethanol as the Leading "First-Generation" Biofuel 1 1.1 Introduction 1 1.2 Historical Development of Ethanol as a Fuel from Neolithic Times to the Twentieth Century 1 1.3 Oil Supply and Oil Price in the Twentieth Century: Necessity and Alternative Fuel Programs 6 1.4 Case Study 1: Brazil and Sugarcane Ethanol 10 1.5 Case Study 2: Starch-Based Ethanol in the United States 18 1.6 Thermodynamic and Environmental Aspects of Ethanol as a Biofuel 31 1.6.1 Net Energy Balance 31 1.6.2 Effects on Emissions of Greenhouse Gases and Other Pollutants 37 1.7 Summary 41 References 41 Cellulosic Ethanol as a "Second-Generation" Biofuel 45 2.1 Introduction 45 2.2 Bioethanol and Cellulosic Ethanol: The Rise of Biomass-Based Biofuels 45 2.3 Structural and Industrial Chemistry of Cellulosic Biomass 46 2.3.1 Cellulose, Hemicelluloses, and Lignin 46 2.3.2 Lignocellulose as a Biochemical Resource 51 2.3.3 Pretreatment of Lignocellulosic Materials 53 2.3.3.1 Physical and Chemical Pretreatment of Lignocellulosic Biomass 53 2.3.3.2 Acid Hydrolysis of Pretreated Lignocellulosic Biomass 59 2.4 Cellulases: Biochemistry, Molecular Biology, and Biotechnology 61 2.4.1 Enzymology of Cellulose Degradation by Cellulases 61 2.4.2 Cellulases in Lignocellulosic Feedstock Processing 65 vii
viii Contents 2.4.3 Molecular Biology and Biotechnology of Cellulase Production 68 2.4.3.1 Physiological Regulation of Cellulase Production 68 2.4.3.2 Regulatory Genes Involved in Cellulase Production 69 2.4.3.3 New-Generation Cellulases 70 2.4.3.4 Novel Molecular Features of Cellulases 74 2.4.3.5 Immobilized Cellulases 75 2.5 Hemicellulases: New Horizons in Energy Biotechnology 75 2.5.1 A Multiplicity of Hemicellulases 75 2.5.2 Hemicellulases in the Processing of Lignocellulosic Biomass 78 2.5.3 Molecular Biology of Hemicellulases 79 2.5.4 Multifunctional Hemicellulases? 79 2.6 Lignin-Degrading Enzymes as Aids to Saccharification 80 2.7 Commercial Choices of Cellulosic Feedstocks for Ethanol Production 81 2.8 Biotechnology and Platform Technologies for Cellulosic Ethanol 82 2.9 Summary 83 References 83 Chapter 3 Microbiology of Cellulosic Ethanol Production I: Yeasts 91 3.1 Introduction 91 3.2 Traditional Ethanologenic Yeasts 91 3.2.1 Conventional Yeasts 92 3.2.2 Nonconventional Yeasts 99 3.3 Metabolic Engineering of Yeasts for Cellulosic Ethanol 100 3.3.1 Increased Pentose Utilization by Ethanologenic Yeasts by Genetic Manipulation with Yeast Genes for Xylose Metabolism via Xylitol 100 3.3.2 Increased Pentose Utilization by Ethanologenic Yeasts by Genetic Manipulation with Genes for Xylose Isomerization 106 3.3.3 Engineering Arabinose Utilization by Ethanologenic Yeasts 107 3.3.4 Comparison of Industrial and Laboratory Yeast Strains for Ethanol Production 109 3.3.5 Improved Ethanol Production by Naturally Pentose-Utilizing Yeasts 115 3.4 Toward the Perfect Yeast Ethanologen? 116 3.4.1 "Omic" Analyses of Yeast Metabolism during Ethanol Production 117 3.4.2 Stress Responses in Yeast Ethanologens 120
Contents ix 3.5 Summary 121 References 122 Chapter 4 Microbiology of Cellulosic Ethanol Production II: Bacteria 131 4.1 Introduction 131 4.2 Assembling Gene Arrays in Bacteria for Ethanol Production 131 4.2.1 Metabolic Routes in Bacteria for Sugar Metabolism and Ethanol Formation 132 4.2.2 Genetic and Metabolic Engineering of Bacteria for Cellulosic Ethanol Production 135 4.2.2.1 Recombinant Escherichia coli: Lineages and Metabolic Capabilities 135 4.2.2.2 Engineering Zymomonas mobilis for Xylose and Arabinose Metabolism 143 4.2.2.3 Development of Klebsiella Strains for Ethanol Production 146 4.2.2.4 Other Bacterial Species 148 4.3 Thermophilic Species and Cellulosome Bioproduction Technologies 149 4.4 "Designer" Cells and Synthetic Organisms 150 4.5 Summary 151 References 152 Chapter 5 Biochemical Engineering of Cellulosic Ethanol 159 5.1 Introduction 159 5.2 Case Study: The logen Corporation Process with Wheat Straw 159 5.3 Biomass Substrate Pretreatment Strategies 162 5.3.1 Wheat Straw 163 5.3.2 Switchgrass 165 5.3.3 Corn Stover 166 5.3.4 Softwoods 170 5.3.5 Sugarcane Bagasse 173 5.3.6 Other Large-Scale Agricultural and Forestry Biomass Feedstocks 174 5.4 Fermentation Media and the Very High Gravity Concept... 175 5.4.1 Fermentation Media for Ethanol Production 176 5.4.2 High-Concentration Media Developed for Alcohol Fermentations 177 5.5 Fermentor Design and Novel Fermentor Technologies 182 5.5.1 Continuous Fermentations for Ethanol Production 182 5.5.2 Fed-Batch Fermentations 187
X Contents 5.5.3 Immobilized Yeast and Bacterial Cell Production Designs 189 5.5.4 Contamination Events and Buildup in Fuel Ethanol Plants 192 5.6 Simultaneous Saccharification and Fermentation and Consolidated Bioprocessing 192 5.7 Downstream Processing and By-Products 196 5.7.1 Ethanol Recovery from Fermented Broths 196 5.7.2 Continuous Ethanol Recovery from Fermentors 198 5.7.3 Solid By-Products from Ethanol Fermentations 199 5.8 Summary 202 References 203 Chapter 6 The Economics of Fuel Ethanol 217 6.1 Introduction 217 6.2 Market Forces and Incentives 217 6.2.1 1'he Impact of Oil Prices on the Future of Biofuels after 1980 217 6.2.2 Production Price, Taxation, and Incentives in the Market Economy 218 6.3 Cost Models for Fuel Ethanol Production 221 6.3.1 Early Benchmarking Studies of Corn and Lignocellulosic Ethanol in the United States 222 6.3.1.1 Corn-Derived Ethanol in 1978 222 6.3.1.2 Wheat-Straw-Derived Ethanol in 1978 224 6.3.1.3 Fuel Ethanol from Sugarcane Molasses... 226 6.3.1.4 Farm-Scale Ethanol Production 226 6.3.2 Corn Ethanol in the 1980s: Rising Industrial Ethanol Prices and the Development of the Incentive Culture 228 6.3.3 Western Europe in the Mid-1980s: Assessments of Biofuels Programs Made at a Time of Falling Real Oil Prices 231 6.3.4 Brazilian Sugarcane Ethanol in 1985: After the First Decade of the PROÄLCOOL Program to Substitute for Imported Oil 234 6.3.5 Economics of U.S. Corn and Biomass Ethanol Economics in the Mid-1990s 234 6.3.6 Case Study: The View from Sweden 236 6.3.7 Subsequent Assessments of Lignocellulosic Ethanol in Europe and the United States 240 6.3.7.1 Complete Process Cost Models 240 6.3.7.2 Reviews of "Gray" Literature Estimates and Economic Analyses 243
Contents 6.4 Pilot Plant and Industrial Extrapolations for Cellulosic Ethanol 245 6.4.1 Near-Future Projections for Cellulosic Ethanol Production Costs 245 6.4.2 Short- to Medium-Term Technical Process Improvements and Their Anticipated Economic Impacts 246 6.4.3 Bioprocess Economics: A Chinese Perspective 250 6.5 Governmental and Macroeconomic Factors 253 6.5.1 Mandatory Biofuels Targets 253 6.5.2 Impact of Fuel Economy on Ethanol Demand for Gasoline Blends 257 6.5.3 Biofuels Pricing in the Era of Carbon Taxation 258 6.6 Summary 259 References 260 Chapter 7 Advanced Biofuels: The Widening Portfolio of Alternatives to Ethanol 265 7.1 Introduction 265 7.2 Biobutanol and ABE 265 7.3 Bacterial Production of C3-C7 Alcohols and Related Compounds 268 7.4 Glycerol 271 7.5 The MixAlco Process 272 7.6 Biohydrogen 273 7.6.1 The Hydrogen Economy and Fuel Cell Technologies 273 7.6.2 Bioproduction of Gases: Methane and H 2 as Products of Anaerobic Digestion 276 7.6.2.1 Heterotrophic Microbes Producing H 2 by Hydrogenase Activity 277 7.6.2.2 Nitrogen-Fixing Microorganisms 280 7.6.2.3 Development of "Dark" H 2 Production Systems 281 7.6.3 Production of H 2 by Photosynthetic Organisms 284 7.7 Microbial Fuel Cells: Eliminating the Middlemen of Energy Carriers 291 7.8 Summary 293 References 293 Chemically Produced Biofuels 301 8.1 Introduction 301 8.2 Biodiesel: Chemistry and Production Processes 301 8.2.1 Vegetable Oils and Chemically Processed Biofuels 301
xii Contents 8.2.2 Biodiesel Composition and Production Processes... 303 8.2.3 Biodiesel Economics 308 8.2.4 Energetics of Biodiesel Production and Effects on Greenhouse Gas Emissions 311 8.2.5 Case Study 1: Hydrogenated Plant Oils and "Green Diesel" 315 8.2.6 Case Study 2: Enzymes for Biodiesel Production... 316 8.3 Fischer-Tropsch Diesel: Chemical Biomass-Liquid Fuel Transformations 318 8.3.1 The Renascence of an Old Chemistry for Biomass-Based Fuels? 318 8.3.2 Economics and Environmental Impacts of FT Diesel 320 8.4 Biodiesel from Microalgae and Microbes 322 8.4.1 Marine and Aquatic Biotechnology 322 8.4.2 Microdiesel 325 8.5 Chemical Conversions of Glycerol Produced by Fermentation 326 8.6 Chemical Routes for the Production of Monooxygenated C6 Liquid Fuels from Biomass Carbohydrates 327 8.7 Biomethanol and Biodimethylether 328 8.8 Chemistry and the Emergence of the Hydrogen Economy 330 8.9 Summary 333 References 334 Chapter 9 Sustainability of Biofuels Production 341 9.1 Introduction 341 9.2 Delivering Biomass Feedstocks for Cellulosic Ethanol Production: The Logistics of a New Industry 341 9.2.1 Upstream Factors: Biomass Collection and Delivery 344 9.2.2 Limitations Imposed by Land Availability and Land Use 346 9.3 Sustainable Development and Biomass Production 354 9.3.1 Definitions, Semantics, and Analysis 354 9.3.2 Case Study: Sustainability of Brazilian Sugarcane Ethanol 360 9.3.3 Future Horizons for Cane Sugar Ethanol 365 9.4 Bioenergy Crops and Genetically Manipulated Plants 367 9.4.1 Engineering Resistance Traits for Biotic and Abiotic Stresses 368 9.4.2 Bioengineering Increased Crop Yield 369
Contents xiii 9.4.3 Optimizing Traits for Energy Crops Intended forbiofuel Production 371 9.4.4 Genetic Engineering of Dual-Use Food Plants and Dedicated Energy Crops 374 9.5 Summary 376 References 377 Chapter 10 Biofuels as Products of Integrated Bioprocesses (Biorefineries) 383 10.1 Introduction 383 10.2 The Biorefinery Concept 383 10.3 Biorefinery Entry Routes 386 10.3.1 Fermentation of Biomass-Derived Substrates 387 10.3.2 Biomass Gasification 390 10.4 Biorefinery Pivotal Products 392 10.4.1 Case Study 1: Succinic Acid 395 10.4.2 Case Study 2: Xylitol and Rare Sugars as Fine Chemicals 400 10.4.3 Case Study 3: Glycerol 403 10.5 Central Substrates and Biorefinery Flexibility 405 10.6 When Will the Biobased Economy Be Possible and When Will It Be Unavoidable? 407 10.7 Summary 413 References 413 Index 421 4