CELLULOSIC ETHANOL PRODUCTION THROUGH BIOCONVERSION OF LIGNOCELLULOSIC BIOMASS
Authors: Yi Zheng
Abstract: Cellulosic ethanol has been taken as a promising alternative energy source for the nonrenewable fossil fuel. Cellulose is one of the three primary polymers of lignocellulosic biomass cell wall. It is the most abundant biomaterial on earth. Each cellulose molecule is a linear polymer of thousands of glucose residues. Cellulose can be hydrolytically broken down into glucose either enzymatically by cellulolytic enzymes or chemically by sulfuric or other acids. The produced glucose can be fermented into ethanol. However, structural and compositional features of lignocellulosic biomass such as lignin/hemicellulose shield and crystallinity of cellulose present challenges to efficient hydrolysis of cellulose. Employment of enzymes for the hydrolysis of the lignocellulose is considered the prospectively most viable strategy to offer advantages over other chemical conversion routes of higher yields, minimal byproduct formation, low energy requirements, mild operating conditions, and environmentally friendly processing. It has long-term potential for cost reductions compared to other more established routes such as concentrated acid and two-stage dilute acid hydrolysis, even though the enzymatic route has the highest current costs. Considerable research efforts have been made to improve the bioconversion efficiency of cellulose into ethanol, mainly focusing on three major steps of biomass pretreatment, enzymatic hydrolysis, and fermentation. This chaper reviews the development of biochemical conversion of biomass materials into cellulosic ethanol, including previous achievements, current status, and future work.