Fuel Ethanol from Lignocellulosic Biomass

Abstract Cellulosic ethanol has been identified as a promising biofuel for transportation because it is produced from abundant and renewable lignocellulosic biomass such as crop residues, forest residues, and dedicated energy crops; it does not compete with food source such as starch, sucrose, and lipids; it reduces fossil fuel use and thereby lowering greenhouse gas emission; it improves energy security and independence; and it promotes rural economy. Biological production of cellulosic ethanol consists of five major operations, namely, biomass production and process, biomass pretreatment, enzymatic saccharification of polysaccharides (cellulose and hemicellulose), fermentation of sugars to ethanol, and concentration and purification of ethanol. Existing technologies for these operations are briefly summarized and reviewed in this article, including structure, composition, and recalcitrance of lignocellulose; biomass logistics for harvest, handling, transport, and storage; available pretreatment methods and their features; cellulase and substrate features affecting enzymatic hydrolysis of lignocellulose; fermentation of hexoses and pentoses to ethanol; ethanol distillation and dehydration; and lignin and hemicellulose as potential co‐products. Challenges and future directions of cellulosic ethanol production were addressed as well. Commercialization of cellulosic ethanol still faces technical, engineering, and economical challenges. Aggressive research and development are still needed to reduce the cost and improve the efficiency of cellulosic ethanol production.