Bioenergy

Principles and Applications

Yebo Li, Samir Kumar Khanal

• Publisher: Wiley-Blackwell
• Year: 2016
• Print ISBN: 9781118568316
• eBook ISBN: 9781118568378
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Biology
• Index: Biological Sciences

BIOENERGY:
PRINCIPLES AND APPLICATIONS

BIOENERGY: PRINCIPLES AND APPLICATIONS

With growing concerns over climate change and energy insecurity coupled with dwindling reserves of fossil energy resources, there is a growing search for alternative, renewable energy resources. Energy derived from renewable bioresources such as biomass (energy crops, agri- and forest residues, algae, and biowastes) has received significant attention in recent years. With the growing interest in bioenergy, there has been increasing demand for a broad-ranging, introductory textbook that provides an essential overview of this very subject to students in the field. Bioenergy: Principles and Applications offers an invaluable introduction to both fundamental and applied aspects of bioenergy feedstocks and their processing, as well as lifecycle and techno-economic analyses, and policies as applied to bioenergy.

Bioenergy: Principles and Applications provides readers with foundational information on first-, second-, and third-generation bioenergy, ranging from plant structure, carbohydrate chemistry, mass and energy balance, thermodynamics, and reaction kinetics to feedstock production, logistics, conversion technologies, biorefinery, lifecycle and techno-economic analyses, and government policies. This textbook gives students and professionals an incomparable overview of the rapidly growing field of bioenergy.

Bioenergy: Principles and Applications will be an essential resource for students, engineers, researchers, and industry personnel interested in, and working in, the bioenergy field.

SECTION III
Biological Conversion Technologies

CHAPTER 12
Pretreatment of Lignocellulosic Feedstocks

Chang Geun Yoo and Xuejun Pan

---

What is included in this chapter?

This chapter covers various pretreatment methods for lignocellulosic feedstocks. Discussion of common pretreatment methods, the mechanism, representative conditions, effects on plant cell wall structure and composition, enzymatic digestibility of pretreated substrates, formation of fermentation inhibitors, and co‐products potential are covered. Pertinent examples and calculations are also included.

---

12.1 Introduction

Lignocellulosic feedstocks are the most abundant renewable resource on Earth, with an availability of approximately 200 billion dry metric tons per year (Zhang et al., 2007). Examples of lignocellulosic feedstocks include crop residues, such as corn stover, wheat and rice straws, and other crop stalks; forest residues, such as forest thinnings and sawmill residues; and energy crops, such as switchgrass, miscanthus, sweet sorghum, energy cane, Napier grass, and fast‐growing trees (e.g., poplar, eucalyptus, and willow). Compared to starch‐rich feedstocks, these bioresources are cost competitive and do not directly compete with food and feed. Lignocellulosic feedstocks have thus been considered the most promising and sustainable resources for bioenergy, chemicals, and other value‐added products.

Chemically, lignocellulosic biomass is composed of three major components (cellulose, hemicellulose, and lignin) and minor substances (e.g., extractives and ash). These components coexist in the cell wall of plants. In general, lignocellulosic biomass contains approximately 35–45% cellulose, 25–35% hemicellulose, and 15–30% lignin, depending on plant species, age, and tissue type (Figure 12.1). Cellulose is a linear polymer of glucose linked together by β‐1,4 glycosidic bonds; hemicellulose is a group of branched co‐polymers of multiple sugars (e.g., xylose, mannose, arabinose, galactose, glucose, and uronic acids); and lignin is a three‐dimensional aromatic polymer of phenylpropane units (coniferyl, sinapyl, and p‐coumaryl alcohols), cross‐linked primarily through ether and carbon–carbon bonds (Figure 12.2).

Fig. 12.1 Chemical composition of lignocellulosic biomass.

Fig. 12.2 Structural organization of the plant cell wall.

Source: Rubin, 2008. Reproduced with permission of Nature Publishing Group.

Current bioconversion of lignocellulosic feedstocks to liquid fuels and chemicals is primarily based on a carbohydrate (or sugar) platform, also known as a biochemical platform. Specifically, the sugar (primarily glucose) is first extracted from lignocellulosic biomass by either enzymatic or chemical (acidic) hydrolysis of cellulose, and then fermented into target products such as ethanol, butanol, propanediol, succinic acid, and lactic acid. Therefore, the hydrolysis of cellulose to glucose (saccharification) is considered to be the most critical and important step of the bioconversion process. However, because of the physical and chemical recalcitrance of the biomass to cellulose hydrolytic enzymes (cellulases), effective saccharification of lignocellulosic feedstock continues to be a technical challenge.

12.2 What Does Pretreatment Do?

In the cell wall, cellulose is surrounded by hemicellulose and lignin, so the cellulose is not readily accessible to enzymes or cellulases (Figure 12.2). In addition to acting as a physical barrier, lignin is a natural inhibitor of biodegradation of cell wall components, thus contributing to the self‐defense system of plants against attacks by insects, bacteria, and fungi. Minor components of the cell wall, such as extractives, also retard the enzymatic hydrolysis of cellulose. The tough and rigid structure and poor permeability of plant cell walls form another barrier to cellulases. Also, the particle size (surfa...

Table of contents

• Cover
• Title Page
• Table of Contents
• List of Contributors
• Preface
• Acknowledgments
• About the Companion Website
• SECTION I: Bioenergy Fundamentals
• SECTION II: Bioenergy Feedstocks
• SECTION III: Biological Conversion Technologies
• SECTION IV: Thermal Conversion Technologies
• SECTION V: Biobased Refinery
• SECTION VI: Bioenergy System Analysis
• Index
• End User License Agreement