Lignocellulosic Bioethanol Production: Perspectives and Challenges

Biofuels produced from different lignocellulosic materials have the potential to be a valuable substitute for gasoline. Many physicochemical structural and compositional factors hinder the hydrolysis of cellulose present in biomass to sugars and other organic compounds that can later be converted to fuels. Different pretreatment techniques can change the physical and chemical structure of the lignocellulosic biomass and improve their hydrolysis rates. Many methods have been shown to result in high sugar yields, above 90% of the theoretical yield. Advances in pretreatment and biological-processing steps clearly provide the greatest opportunity to reduce bioethanol costs, and much more emphasis is needed in these areas. For pretreatment, improved process configurations are needed that reduce chemical costs for hemicellulose hydrolysis and subsequent conditioning for biological processing. In addition, energy requirements for biomass milling and heating must be reduced, and less corrosive environments are desired to reduce the cost of vessels.  Future biotechnology-based developments in processing technology will likely include: Improved cellulase and hemicellulase production economics via microbe or plant-based production systems; improved fermentation strains that efficiently utilize both hemicellulose and cellulosic sugars; consolidated bioprocessing microbes which combine the ability to break down cellulosic materials with the ability to efficiently ferment sugars to ethanol.