Pre-treatment Methods of Lignocellulosic Biomass for Biofuel Production

Shyamal Roy

• Publisher: CRC Press
• Year: 2021
• Print ISBN: 9781032066929
• eBook ISBN: 9781000481549
• Topic: Biological Sciences
• Subtopic: Energy
• Index: Biological Sciences

Bioconversion of lignocellulosic biomass to biofuel is materially obstructed by the compositional and chemical complexity of biomaterials, resulting in a challenge in using these as raw materials for the biofuel production process. This book explains various lignocellulosic biomass pre-treatment methods with emphasis on concepts, practicability, mechanisms of action, and advantages and disadvantages and potential for industrial applications. It also highlights the main challenges and suggests possible ways to make these pre-treatment technologies feasible for the biofuel industry.

Features

• Presents different pre-treatment technologies available for lignocellulosic biomass in a concise manner.
• Covers use of different pre-treatment methods in laboratory to industrial scales.
• Includes combined pre-treatment and deep eutectic solvents methods.
• Discusses problems related to industrial adaptation and corresponding economics of different techniques.
• Explores significant fuels and chemicals derived from lignocellulosic biomass.

This book is aimed at graduate students and researchers working on biomass conversion, characterization, cellulose, hemicellulose, lignin, microbial enzymes, fermentation technology, and industrial biotechnology.

1

Introduction

DOI: 10.1201/9781003203414-1

1.1 Introduction

The development of sustainable energy systems based on renewable lignocellulosic biomass feed stocks is now a global endeavor. The shifting of the crude oil-based refinery to biomass-based biorefinery has enticed compelling scientific interest which focuses on the development of cellulosic ethanol as an alternative transportation fuel to fossil fuels. It is needless to say that of late biofuel has drawn attention as a renewable energy resource that may help cope with rising fuel prices, address environmental concerns associated with greenhouse gas emissions, and create new earnings and employment opportunities for the people in rural places around the globe. Release of CO₂ increases through the combustion of fossil fuel, and it is a major concern of global warming. The United States having only 4.5% of the world’s population utilizes 25% of global energy consumption and responsible for 25% of global CO₂ emissions.¹ Therefore, conversion of plentiful lignocellulosic biomass to biofuel as transportation fuels will be a feasible alternative for boosting energy security and abating greenhouse gas emissions.^2,3 Unlike fossil fuels that originate from plants that grew millions of years ago, lignocellulosic biofuels are synthesized from plants grown today. Lignocellulosic biofuel has the great potential to reduce greenhouse gas emissions by 85%.⁴ Lignocellulosic biomasses such as forest products (hardwood and softwood), dedicated crops (switch grass, salix) and agricultural residues (wheat straw, sugarcane bagasse, corn stover, etc.) are sustainable energy resources.^5,6 Lignin, cellulose, hemicellulose and pectin contribute ca. 90% of the dry weight of most plant biomasses.¹ The lignin acts as a protective wall that resists plant cell destruction by bacteria and fungi for conversion to fuel. It is essential to break down the hemicellulose and cellulose into their respective monomers (sugars) for producing fuel from lignocellulosic biomass.⁷ Some physicochemical, structural, and compositional features resist the digestibility of cellulose existing in lignocellulosic biomass. Pretreatment of lignocellulosic biomass is essential for exposing the cellulose in the plant fibers prior to conversion of lignocellulosic biomass to biofuel using the digestion technique. Various pretreatment methods are used such as chemical, biological, steam explosion, ammonia fiber explosion, and extractive ammonia for modification of the structure of lignocellulosic materials in order to augment the accessibility of the cellulose towards enzyme during hydrolysis.⁸ The pretreatment process is used to disintegrate the lignin structure and deconstruct the cellulose structure so that the cellulose hydrolysis rate increases with favoring the higher accessibility of enzymes or acids.^{9, 10, 11, 12, 13} Pretreatment is a salient technique for biofuel production from lignocellulosic biomass and our effort to survey the recent advances in pretreatment methods for the economic design of the sustainable biofuel production process.

1.2 Structure of Lignocellulosic Biomass

In general, the lignocellulosic biomass consists of lignin, hemicelluloses, cellulose, polyoses, and trace amounts of pectin, protein, extractives (soluble nonstructural materials such as nonstructural sugars, nitrogenous material, chlorophyll, and waxes), and ash.¹⁴ Biomass cell wall consists of lignin, hemicelluloses, and cellulose. The structural segment of plant cell walls consists of polysaccharides. The key factor of economic bio refining is untwisting the complex polymeric structures. Cellulose microfibrils made of a crystalline structure of thousands of strands and thousands of sugar molecules form each strand. These microfibrils are enveloped in hemicelluloses and lignin, which prevents the cellulose from microbial attack (as shown in Figure 1.1). Hemicelluloses are relatively easy to break down using pretreatment process. It also disrupts the hemicelluloses or lignin enveloped around the cellulose, which results in the accessibility...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• List of Figure
• List of Tables
• Author
• 1 Introduction
• 2 Physical Pretreatments
• 3 Physicochemical Pretreatments
• 4 Chemical Pretreatments
• 5 Biological Pretreatment
• 6 Combined Pretreatment
• 7 Problems of the Industrial Adaptation
• 8 Economics of Different Pretreatment Technologies
• 9 Environmental Concerns
• 10 Conclusions and Recommendations
• References
• Index