Pretreatment of Lignocellulosic Biomass Using Green Ionic Liquids

Abstract

Bioenergy is a critical part of renewable energy solution to today’s energy crisis that threatens world economic growth. Corn ethanol has been growing rapidly in the past few years. Policy-makers and researchers alike are becoming aware that corn ethanol has some serious drawbacks. It adversely impacts food prices and is harsh on soil fertility. Lignocellulosic ethanol on the other hand uses abundant lignocellulosic biomass. Various types of lignocellulosic biomass are agricultural wastes or can be grown as energy crops on poor lands that are otherwise vacant. However, lignocellulosic biomass is notoriously recalcitrant by nature’s design. Enzyme hydrolysis yield for glucose from lignocellulosic is very low without proper pretreatment. Quite a few pretreatment methods have been reported in the literature. For mobile and on-farm biomass processing, a pretreatment method that uses no chemicals or green chemicals without the need for waste treatment is preferred. In recent years, research on using ionic liquids as green solvents for pretreatment of lignocellulosic biomass has exploded. Hundreds of papers have been published in the literature in the past few years alone. Some ionic liquids such as [Amim]Cl and [C2mim]OAc have been proven highly effective in the dissolution of cellulose, lignin, and hemicellulose in different types of lignocellulosic biomass including corn stover, switchgrass, rice straw, and various hard and softwoods. This simple pretreatment method has been proven highly effective for improving sugar yields in the enzyme hydrolysis of the recovered biomass after pretreatment. Various methods have been developed for ionic liquid recycling after pretreatment. Although costly, ionic liquids hold great potential for green pretreatment of biomass as the technology improves. This chapter investigated the mechanisms and various parameters in ionic liquid pretreatment of various types of lignocellulosic biomass.