Aqueous Pretreatment of Plant Biomass for Biological and Chemical Conversion to Fuels and Chemicals Wiley Series in Renewable Resource Series

Plant biomass is attracting increasing attention as a sustainable resource for large-scale production of renewable fuels and chemicals. However, in order to successfully compete with petroleum, it is vital that biomass conversion processes are designed to minimize costs and maximize yields. Advances in pretreatment technology are critical in order to develop high-yielding, cost-competitive routes to renewable fuels and chemicals.

Aqueous Pretreatment of Plant Biomass for Biological and Chemical Conversion to Fuels and Chemicals presents a comprehensive overview of the currently available aqueous pretreatment technologies for cellulosic biomass, highlighting the fundamental chemistry and biology of each method, key attributes and limitations, and opportunities for future advances.

Topics covered include:

? The importance of biomass conversion to fuels
? The role of pretreatment in biological and chemical conversion of biomass
? Composition and structure of biomass, and recalcitrance to conversion
? Fundamentals of biomass pretreatment at low, neutral and high pH
? Ionic liquid and organosolv pretreatments to fractionate biomass
? Comparative data for application of leading pretreatments and effect of enzyme formulations
? Physical and chemical features of pretreated biomass
? Economics of pretreatment for biological processing
? Methods of analysis and enzymatic conversion of biomass streams
? Experimental  pretreatment systems from multiwell plates to pilot plant operations 

This comprehensive reference book provides an authoritative source of information on the pretreatment of cellulosic biomass to aid those experienced in the field to access the most current information on the topic.  It will also be invaluable to those entering the growing field of biomass conversion.

List of Contributors xvii

Foreword xxi

Series Preface xxiii

Preface xxv

Acknowledgements xxvii

1 Introduction 1
Charles E. Wyman

1.1 Cellulosic Biomass: What and Why? 2

1.2 Aqueous Processing of Cellulosic Biomass into Organic Fuels and Chemicals 3

1.3 Attributes for Successful Pretreatment 5

1.4 Pretreatment Options 7

1.5 Possible Blind Spots in the Historic Pretreatment Paradigm 8

1.6 Other Distinguishing Features of Pretreatment Technologies 9

1.7 Book Approach 9

1.8 Overview of Book Chapters 10

Acknowledgements 10

References 11

2 Cellulosic Biofuels: Importance, Recalcitrance, and Pretreatment 17
Lee Lynd and Mark Laser

2.1 Our Place in History 17

2.2 The Need for Energy from Biomass 17

2.3 The Importance of Cellulosic Biomass 18

2.4 Potential Barriers 18

2.5 Biological and Thermochemical Approaches to the Recalcitrance Barrier 19

2.6 Pretreatment 20

Acknowledgements 21

References 21

3 Plant Cell Walls: Basics of Structure, Chemistry, Accessibility and the Influence on Conversion 23
Brian H. Davison, Jerry Parks, Mark F. Davis and Bryon S. Donohoe

3.1 Introduction 23

3.2 Biomass Diversity Leads to Variability in Cell-wall Structure and Composition 24

3.3 Processing Options for Accessing the Energy in the Lignocellulosic Matrix 26

3.4 Plant Tissue and Cell Types Respond Differently to Biomass Conversion 28

3.5 The Basics of Plant Cell-wall Structure 29

3.6 Cell-wall Surfaces and Multilamellar Architecture 30

3.7 Cell-wall Ultrastructure and Nanoporosity 31

3.8 Computer Simulation in Understanding Biomass Recalcitrance 32

3.8.1 What Can We Learn from Molecular Simulation? 32

3.8.2 Simulations of Lignin 33

3.8.3 Simulations of Cellulose 34

3.8.4 Simulation of Lignocellulosic Biomass 35

3.8.5 Outlook for Biomass Simulations 35

3.9 Summary 35

Acknowledgements 36

References 36

4 Biological Conversion of Plants to Fuels and Chemicals and the Effects of Inhibitors 39
Eduardo Ximenes, Youngmi Kim and Michael R. Ladisch

4.1 Introduction 39

4.2 Overview of Biological Conversion 40

4.3 Enzyme and Ethanol Fermentation Inhibitors Released during Pretreatment and/or Enzyme Hydrolysis 42

4.3.1 Enzyme Inhibitors Derived from Plant Cell-wall Constituents (Lignin, Soluble Phenolics, and Hemicellulose) 43

4.3.2 Effect of Furfurals and Acetic Acid as Inhibitors of Ethanol Fermentations 48

4.4 Hydrolysis of Pentose Sugar Oligomers Using Solid-acid Catalysts 50

4.4.1 Application of Solid-acid Catalysts for Hydrolysis of Sugar Oligomers Derived from Lignocelluloses 50

4.4.2 Factors Affecting Efficiency of Solid-acid-catalyzed Hydrolysis 51

4.5 Conclusions 56

Acknowledgements 57

References 57

5 Catalytic Strategies for Converting Lignocellulosic Carbohydrates to Fuels and Chemicals 61
Jesse Q. Bond, David Martin Alonso and James A. Dumesic

5.1 Introduction 61

5.2 Biomass Conversion Strategies 62

5.3 Criteria for Fuels and Chemicals 64

5.3.1 General Considerations in the Production of Fuels and Fuel Additives 64

5.3.2 Consideration for Specialty Chemicals 66

5.4 Primary Feedstocks and Platforms 66

5.4.1 Cellulose 66

5.4.2 Hemicellulose 67

5.5 Sugar Conversion and Key Intermediates 68

5.5.1 Sugar Oxidation 69

5.5.2 Sugar Reduction (Polyol Production) 70

5.5.3 Sugar Dehydration (Furan Production) 77

5.6 Conclusions 91

Acknowledgements 92

References 92

6 Fundamentals of Biomass Pretreatment at Low pH 103
Heather L. Trajano and Charles E. Wyman

6.1 Introduction 103

6.2 Effects of Low pH on Biomass Solids 104

6.2.1 Cellulose 104

6.2.2 Hemicellulose 105

6.2.3 Lignin 106

6.2.4 Ash 107

6.2.5 Ultrastructure 107

6.2.6 Summary of Effects of Low pH on Biomass Solids 108

6.3 Pretreatment in Support of Biological Conversion 108

6.3.1 Hydrolysis of Cellulose to Fermentable Glucose 108

6.3.2 Pretreatment for Improved Enzymatic Digestibility 109

6.3.3 Pretreatment for Improved Enzymatic Digestibility and Hemicellulose Sugar Recovery 110

6.4 Low-pH Hydrolysis of Cellulose and Hemicellulose 114

6.4.1 Furfural 114

6.4.2 Levulinic Acid 115

6.4.3 Drop-in Hydrocarbons 115

6.5 Models of Low-pH Biomass Reactions 116

6.5.1 Cellulose Hydrolysis 117

6.5.2 Hemicellulose Hydrolysis 118

6.5.3 Summary of Kinetic Models 120

6.6 Conclusions 122

Acknowledgements 123

References 123

7 Fundamentals of Aqueous Pretreatment of Biomass 129
Nathan S. Mosier

7.1 Introduction 129

7.2 Self-ionization of Water Catalyzes Plant Cell-wall Depolymerization 130

7.3 Products from the Hydrolysis of the Plant Cell Wall Contribute to Further Depolymerization 131

7.4 Mechanisms of Aqueous Pretreatment 131

7.4.1 Hemicellulose 131

7.4.2 Lignin 134

7.4.3 Cellulose 136

7.5 Impact of Aqueous Pretreatment on Cellulose Digestibility 137

7.6 Practical Applications of Liquid Hot Water Pretreatment 138

7.7 Conclusions 140

References 140

8 Fundamentals of Biomass Pretreatment at High pH 145
Rocıo Sierra Ramirez, Mark Holtzapple and Natalia Piamonte

8.1 Introduction 145

8.2 Chemical Effects of Alkaline Pretreatments on Biomass Composition 146

8.2.1 Non-oxidative Delignification 147

8.2.2 Non-oxidative Sugar Degradation 148

8.2.3 Oxidative Delignification 150

8.2.4 Oxidative Sugar Degradation 151

8.3 Ammonia Pretreatments 153

8.4 Sodium Hydroxide Pretreatments 155

8.5 Alkaline Wet Oxidation 155

8.6 Lime Pretreatment 158

8.7 Pretreatment Severity 161

8.8 Pretreatment Selectivity 161

8.9 Concluding Remarks 163

References 163

9 Primer on Ammonia Fiber Expansion Pretreatment 169
S.P.S. Chundawat, B. Bals, T. Campbell, L. Sousa, D. Gao, M. Jin, P. Eranki, R. Garlock, F. Teymouri, V. Balan and B.E. Dale

9.1 Historical Perspective of Ammonia-based Pretreatments 169

9.2 Overview of AFEX and its Physicochemical Impacts 170

9.3 Enzymatic and Microbial Activity on AFEX-treated Biomass 175

9.3.1 Impact of AFEX Pretreatment on Cellulase Binding to Biomass 175

9.3.2 Enzymatic Digestibility of AFEX-treated Biomass 176

9.3.3 Microbial Fermentability of AFEX-treated Biomass 178

9.4 Transgenic Plants and AFEX Pretreatment 183

9.5 Recent Research Developments on AFEX Strategies and Reactor Configurations 185

9.5.1 Non-extractive AFEX Systems 185

9.5.2 Extractive AFEX Systems 186

9.5.3 Fluidized Gaseous AFEX Systems 186

9.6 Perspectives on AFEX Commercialization 186

9.6.1 AFEX Pretreatment Commercialization in Cellulosic Biorefineries 186

9.6.2 Novel Value-added Products from AFEX-related Processes 190

9.6.3 AFEX-centric Regional Biomass Processing Depot 192

9.7 Environmental and Life-cycle Analyses for AFEX-centric Processes 193

9.8 Conclusions 194

Acknowledgements 195

References 195

10 Fundamentals of Biomass Pretreatment by Fractionation 201
Poulomi Sannigrahi and Arthur J. Ragauskas

10.1 Introduction 201

10.2 Organosolv Pretreatment 202

10.2.1 Organosolv Pulping 202

10.2.2 Overview of Organosolv Pretreatment 202

10.2.3 Solvents and Catalysts for Organosolv Pretreatment 203

10.2.4 Fractionation of Biomass during Organosolv Pretreatment 209

10.3 Nature of Organosolv Lignin and Chemistry of Organosolv Delignification 210

10.3.1 Composition and Structure of Organosolv Lignin 210

10.3.2 Mechanisms of Organosolv Delignification 213

10.3.3 Commercial Applications of Organosolv Lignin 214

10.4 Structural and Compositional Characteristics of Cellulose 214

10.5 Co-products of Biomass Fractionation by Organosolv Pretreatment 216

10.5.1 Hemicellulose 216

10.5.2 Furfural 217

10.5.3 Hydroxymethylfurfural (HMF) 218

10.5.4 Levulinic Acid 218

10.5.5 Acetic Acid 219

10.6 Conclusions and Recommendations 219

Acknowledgements 219

References 219

11 Ionic Liquid Pretreatment: Mechanism, Performance, and Challenges 223
Seema Singh and Blake A. Simmons

11.1 Introduction 223

11.2 Ionic Liquid Pretreatment: Mechanism 225

11.2.1 IL Polarity and Kamlet–Taft Parameters 226

11.2.2 Interactions between ILs and Cellulose 226

11.2.3 Interactions between ILs and Lignin 227

11.3 Ionic Liquid Biomass Pretreatment: Enzymatic Route 228

11.3.1 Grasses 228

11.3.2 Agricultural Residues 230

11.3.3 Woody Biomass 230

11.4 Ionic Liquid Pretreatment: Catalytic Route 231

11.4.1 Acid-catalyzed Hydrolysis 232

11.4.2 Metal-catalyzed Hydrolysis 232

11.5 Factors Impacting Scalability and Cost of Ionic Liquid Pretreatment 233

11.6 Concluding Remarks 234

Acknowledgements 234

References 234

12 Comparative Performance of Leading Pretreatment Technologies for Biological Conversion of Corn Stover, Poplar Wood, and Switchgrass to Sugars 239
Charles E. Wyman, Bruce E. Dale, Venkatesh Balan, Richard T. Elander, Mark T. Holtzapple, Rocıo Sierra Ramirez, Michael R. Ladisch, Nathan Mosier, Y.Y. Lee, Rajesh Gupta, Steven R. Thomas, Bonnie R. Hames, Ryan Warner and Rajeev Kumar

12.1 Introduction 240

12.2 Materials and Methods 242

12.2.1 Feedstocks 242

12.2.2 Enzymes 243

12.2.3 CAFI Pretreatments 243

12.2.4 Material Balances 244

12.2.5 Free Sugars and Extraction 244

12.3 Yields of Xylose and Glucose from Pretreatment and Enzymatic Hydrolysis 245

12.3.1 Yields from Corn Stover 245

12.3.2 Yields from Standard Poplar 247

12.3.3 Yields from Dacotah Switchgrass 248

12.4 Impact of Changes in Biomass Sources 249

12.5 Compositions of Solids Following CAFI Pretreatments 251

12.5.1 Composition of Pretreated Corn Stover Solids 252

12.5.2 Composition of Pretreated Switchgrass Solids 252

12.5.3 Composition of Pretreated Poplar Solids 253

12.5.4 Overall Trends in Composition of Pretreated Biomass Solids and Impact on Enzymatic Hydrolysis 253

12.6 Pretreatment Conditions to Maximize Total Glucose Plus Xylose Yields 254

12.7 Implications of the CAFI Results 255

12.8 Closing Thoughts 256

Acknowledgements 257

References 258

13 Effects of Enzyme Formulation and Loadings on Conversion of Biomass Pretreated by Leading Technologies 261
Rajesh Gupta and Y.Y. Lee

13.1 Introduction 261

13.2 Synergism among Cellulolytic Enzymes 262

13.3 Hemicellulose Structure and Hemicellulolytic Enzymes 263

13.4 Substrate Characteristics and Enzymatic Hydrolysis 264

13.5 Xylanase Supplementation for Different Pretreated Biomass and Effect of b-Xylosidase 265

13.6 Effect of b-Glucosidase Supplementation 269

13.7 Effect of Pectinase Addition 269

13.8 Effect of Feruloyl Esterase and Acetyl Xylan Esterase Addition 270

13.9 Effect of a-L-arabinofuranosidase and Mannanase Addition 270

13.10 Use of Lignin-degrading Enzymes (LDE) 271

13.11 Effect of Inactive Components on Biomass Hydrolysis 271

13.12 Adsorption and Accessibility of Enzyme with Different Cellulosic Substrates 271

13.13 Tuning Enzyme Formulations to the Feedstock 272

13.14 Summary 273

References 274

14 Physical and Chemical Features of Pretreated Biomass that Influence Macro-/Micro-accessibility and Biological Processing 281
Rajeev Kumar and Charles E. Wyman

14.1 Introduction 281

14.2 Definitions of Macro-/Micro-accessibility and Effectiveness 283

14.3 Features Influencing Macro-accessibility and their Impacts on Enzyme Effectiveness 284

14.3.1 Lignin 284

14.3.2 Hemicellulose 286

14.4 Features Influencing Micro-accessibility and their Impact on Enzymes Effectiveness 289

14.4.1 Cellulose Crystallinity (Structure) 289

14.4.2 Cellulose Chain Length/Reducing Ends 291

14.5 Concluding Remarks 293

Acknowledgements 296

References 296

15 Economics of Pretreatment for Biological Processing 311
Ling Tao, Andy Aden and Richard T. Elander

15.1 Introduction 311

15.2 Importance of Pretreatment 311

15.3 History of Pretreatment Economic Analysis 313

15.4 Methodologies for Economic Assessment 314

15.5 Overview of Pretreatment Technologies 315

15.5.1 Acidic Pretreatments 315

15.5.2 Alkaline Pretreatments 315

15.5.3 Solvent-based Pretreatments 316

15.6 Comparative Pretreatment Economics 316

15.6.1 Modeling Basis and Assumptions for Comparative CAFI Analysis 317

15.6.2 CAFI Project Comparative Data 320

15.6.3 Reactor Design and Costing Data 320

15.6.4 Comparison of Sugar and Ethanol Yields 324

15.6.5 Comparison of Pretreatment Capital Costs 325

15.6.6 Comparison of MESP 326

15.7 Impact of Key Variables on Pretreatment Economics 327

15.7.1 Yield 327

15.7.2 Conversion to Oligomers/Monomers (Shift of Burden between Enzymes and Pretreatment) 328

15.7.3 Biomass Loading/Concentration 328

15.7.4 Chemical Loading/Recovery/Metallurgy 329

15.7.5 Reaction Conditions: Pressure, Temperature, Residence Time 330

15.7.6 Reactor Orientation: Horizontal/Vertical 330

15.7.7 Batch versus Continuous Processing 330

15.8 Future Needs for Evaluation of Pretreatment Economics 331

15.9 Conclusions 332

Acknowledgements 332

References 332

16 Progress in the Summative Analysis of Biomass Feedstocks for Biofuels Production 335
F.A. Agblevor and J. Pereira

16.1 Introduction 335

16.2 Preparation of Biomass Feedstocks for Analysis 337

16.3 Determination of Non-structural Components of Biomass Feedstocks 338

16.3.1 Moisture Content of Biomass Feedstocks 338

16.3.2 Determination of Ash in Biomass 338

16.3.3 Protein Content of Biomass 338

16.3.4 Extractives Content of Biomass 339

16.4 Quantitative Determination of Lignin Content of Biomass 340

16.5 Quantitative Analysis of Sugars in Lignocellulosic Biomass 342

16.5.1 Holocellulose Content of Plant Cell Walls 342

16.5.2 Monoethanolamine Method for Cellulose Determination 343

16.6 Chemical Hydrolysis of Biomass Polysaccharides 343

16.6.1 Mineral Acid Hydrolysis 343

16.6.2 Trifluoroacetic Acid (TFA) 344

16.6.3 Methanolysis 344

16.7 Analysis of Monosaccharides 345

16.7.1 Colorimetric Analysis of Biomass Monosaccharides 345

16.7.2 Gas Chromatographic Sugar Analysis 345

16.8 Gas Chromatography-Mass Spectrometry (GC/MS) 347

16.9 High-performance Liquid Chromatographic Sugar Analysis 347

16.10 NMR Analysis of Biomass Sugars 349

16.11 Conclusions 349

References 349

17 High-throughput NIR Analysis of Biomass Pretreatment Streams 355
Bonnie R. Hames

17.1 Introduction 355

17.2 Rapid Analysis Essentials 356

17.2.1 Rapid Spectroscopic Techniques 357

17.2.2 Calibration and Validation Samples 358

17.2.3 Quality Calibration Data for Each Calibration Sample 359

17.2.4 Multivariate Analysis to Resolve Complex Sample Spectra 362

17.2.5 Validation of New Methods 364

17.2.6 Standard Reference Materials and Protocols for Ongoing QA/QC 364

17.3 Summary 366

References 367

18 Plant Biomass Characterization: Application of Solution- and Solid-state NMR Spectroscopy 369
Yunqiao Pu, Bassem Hallac and Arthur J. Ragauskas

18.1 Introduction 369

18.2 Plant Biomass Constituents 370

18.3 Solution-state NMR Characterization of Lignin 371

18.3.1 Lignin Sample Preparation 372

18.3.2 1 H NMR Spectroscopy 372

18.3.3 13 c NMR Spectroscopy 372

18.3.4 HSQC Correlation Spectroscopy 375

18.3.5 31 P NMR Spectroscopy 377

18.4 Solid-state NMR Characterization of Plant Cellulose 381

18.4.1 CP/MAS 13 C NMR Analysis of Cellulose 381

18.4.2 Cellulose Crystallinity 383

18.4.3 Cellulose Ultrastructure 385

18.5 Future Perspectives 387

Acknowledgements 387

References 387

19 Xylooligosaccharides Production, Quantification, and Characterization in Context of Lignocellulosic Biomass Pretreatment 391
Qing Qing, Hongjia Li, Rajeev Kumar and Charles E. Wyman

19.1 Introduction 391

19.1.1 Definition of Oligosaccharides 391

19.1.2 Types of Oligosaccharides Released during Lignocellulosic Biomass Pretreatment 392

19.1.3 The Importance of Measuring Xylooligosaccharides 392

19.2 Xylooligosaccharides Production 394

19.2.1 Thermochemical Production of XOs 394

19.2.2 Production of XOs by Enzymatic Hydrolysis 396

19.3 Xylooligosaccharides Separation and Purification 397

19.3.1 Solvent Extraction 397

19.3.2 Adsorption by Surface Active Materials 397

19.3.3 Chromatographic Separation Techniques 398

19.3.4 Membrane Separation 399

19.3.5 Centrifugal Partition Chromatography 401

19.4 Characterization and Quantification of Xylooligosaccharides 402

19.4.1 Measuring Xylooligosaccharides by Quantification of Reducing Ends 402

19.4.2 Characterizing Xylooligosaccharides Composition 402

19.4.3 Direct Characterization of Different DP Xylooligosaccharides 403

19.4.4 Determining Detailed Structures of Oligosaccharides by MS and NMR 408

19.5 Concluding Remarks 408

Acknowledgements 409

References 410

20 Experimental Pretreatment Systems from Laboratory to Pilot Scale 417
Richard T. Elander

20.1 Introduction 417

20.2 Laboratory-scale Pretreatment Equipment 421

20.2.1 Heating and Cooling Capability 421

20.2.2 Contacting of Biomass Particles with Water and/or Pretreatment Chemicals 421

20.2.3 Mass and Heat Transfer 422

20.2.4 Proper Materials of Construction 423

20.2.5 Instrumentation and Control Systems 424

20.2.6 Translating to Pilot-scale Pretreatment Systems 424

20.3 Pilot-scale Batch Pretreatment Equipment 424

20.4 Pilot-scale Continuous Pretreatment Equipment 427

20.4.1 Feedstock Handling and Size Reduction 427

20.4.2 Pretreatment Chemical and Water Addition 429

20.4.3 Pressurized Continuous Pretreatment Feeder Equipment 432

20.4.4 Pretreatment Reactor Throughput and Residence Time Control 436

20.4.5 Reactor Discharge Devices 438

20.4.6 Blow-down Vessel and Flash Vapor Recovery 438

20.5 Continuous Pilot-scale Pretreatment Reactor Systems 439

20.5.1 Historical Development of Pilot-scale Reactor Systems 439

20.5.2 NREL Gravity-flow Reactor Systems 441

20.6 Summary 445

Acknowledgements 446

References 447

21 Experimental Enzymatic Hydrolysis Systems 451
Todd Lloyd and Chaogang Liu

21.1 Introduction 451

21.2 Cellulases 452

21.2.1 Endoglucanase 452

21.2.2 Cellobiohydrolase 453

21.2.3 b-glucosidase 453

21.3 Hemicellulases 453

21.4 Kinetics of Enzymatic Hydrolysis 454

21.4.1 Empirical Models 455

21.4.2 Michaelis–Menten-based Models 455

21.4.3 Adsorption in Cellulose Hydrolysis Models 456

21.4.4 Rate Limitations and Decreasing Rates with Increasing Conversion 457

21.4.5 Summary of Enzyme Reaction Kinetics 459

21.5 Experimental Hydrolysis Systems 460

21.5.1 Laboratory Protocols 460

21.5.2 Considerations for Scale-up of Hydrolysis Processes 463

21.6 Conclusion 465

References 465

22 High-throughput Pretreatment and Hydrolysis Systems for Screening Biomass Species in Aqueous Pretreatment of Plant Biomass 471
Jaclyn DeMartini and Charles E. Wyman

22.1 Introduction: The Need for High-throughput Technologies 471

22.2 Previous High-throughput Systems and Application to Pretreatment and Enzymatic Hydrolysis 472

22.3 Current HTPH Systems 473

22.4 Key Steps in HTPH Systems 478

22.4.1 Material Preparation 478

22.4.2 Material Distribution 479

22.4.3 Pretreatment and Enzymatic Hydrolysis 480

22.4.4 Sample Analysis 481

22.5 HTPH Philosophy, Difficulties, and Limitations 482

22.6 Examples of Research Enabled by HTPH Systems 484

22.7 Future Applications 485

22.8 Conclusions and Recommendations 485

References 486

23 Laboratory Pretreatment Systems to Understand Biomass Deconstruction 489
Bin Yang and Melvin Tucker

23.1 Introduction 489

23.2 Laboratory-scale Batch Reactors 491

23.2.1 Sealed Glass Reactors 491

23.2.2 Tubular Reactors 492

23.2.3 Mixed Reactors 495

23.2.4 Zipperclave 496

23.2.5 Microwave Reactors 497

23.2.6 Steam Reactors 499

23.3 Laboratory-scale Continuous Pretreatment Reactors 501

23.4 Deconstruction of Biomass with Bench-Scale Pretreatment Systems 503

23.5 Heat and Mass Transfer 505

23.5.1 Mass Transfer 506

23.5.2 Direct and Indirect Heating 506

23.6 Biomass Handling and Comminuting 508

23.7 Construction Materials 508

23.7.1 Overall Considerations 508

23.7.2 Materials of Construction 509

23.8 Criteria of Reactor Selection and Applications 510

23.8.1 Effect of High/Low Solids Concentration on Reactor Choices 510

23.8.2 Role of Heat-up and Cool-down Rates in Laboratory Reactor Selection 510

23.8.3 Effect of Mixing and Catalyst Impregnation on Reactor Design 510

23.8.4 High Temperatures and Short Residence Times Result in High Yields 511

23.8.5 Pretreatment Severity: Tradeoffs of Time and Temperature 511

23.8.6 Minimizing Construction and Operating Costs 512

23.9 Summary 513

Acknowledgements 514

References 514

Index 523

Professor Charles Wyman has devoted most of his career to leading advancement of technology for biological conversion of cellulosic biomass to ethanol and other products that will reduce our excessive dependence on petroleum. A substantial portion of this research is directed at advancing technologies for the most expensive and critical unit operations: pretreatment and cellulose and hemicellulose hydrolysis. Professor Wyman is Chair in Environmental Engineering at the Center for Environmental Research and Technology and Professor in Chemical and Environmental Engineering at the University of California at Riverside.