Prospects of Cellulosic Ethanol from Sugarcane Bagasse

AGRICULTURAL residues such as grain straws and corn stover are abundant, readily available biomass feedstocks for the production of next generation biofuels, with collection and transport costs being a major component of their cost. Sugarcane bagasse is thus an especially attractive biomass feedstock in that it is an agricultural residue already present in large quantities at sugar and ethanol mills. The efficient conversion of bagasse lignocellulose to fermentable sugars is the major techno-economic challenge to the commercially viable production of ethanol from this feedstock. Bagasse is first pretreated by a combination of high temperatures and pressures in the presence of chemicals, to facilitate subsequent enzymatic hydrolysis to break down the cellulose and hemicellulose to fermentable sugars. The sheer volume (an estimated 15–25 kg/t bagasse) and costs of the enzymes required for hydrolysis make the process economically unfeasible using current fermentation-based enzyme production technologies. The expression of enzymes in crop plants represents a promising approach to reduce the costs of enzyme production, and is an area in which Syngenta has strong intellectual property and advanced proprietary technologies. Syngenta’s corn amylase, currently undergoing regulatory approval in the United States, features a thermostable α-amylase expressed in the grain for dry grind ethanol production applications, the first of a series of Syngenta traits designed for the biofuels industry. To enable the in planta production of cell wall-degrading hydrolases for commercial next generation biofuels production requires an integrated approach within an overall engineering process model, incorporating upstream pre-treatment and downstream fermentation methodologies in addition to enzyme expression, extraction, storage and hydrolysis technologies. Progress in the development of this suite of technologies for the conversion of bagasse lignocellulose to fermentable sugars will be described.