Cost competitive second-generation ethanol production from hemicellulose in a Brazilian sugarcane biorefinery

Producing second-generation ethanol from the five carbon (C5) sugars in bagasse and cane trash could increase ethanol yield at first-generation sugarcane biorefineries in Brazil. Co-fermenting C5 sugars with cane juice and molasses in the first-generation fermenters is a potentially attractive process configuration enabled by recent biotechnology advances. To assess the feasibility of this cofermentation, batch fermentations of molasses supplemented with xylose, the primary C5 sugar in hemicellulose, were conducted at lab scale using a yeast strain, M3799, engineered to ferment xylose. At cell loadings consistent with Brazilian fuel ethanol fermentation, M3799 was able to convert 17.8 g/L of xylose sugar along with sugars typically found in molasses to produce 71.5 g/L of ethanol in 8 h. Based on this capability, a process that produces a C5-enriched cane juice by integrating a steam pre-treatment reactor with the existing cane mill is investigated. Process modeling analysis of several integrated pre-treatment configurations predicts that sugar recovery on cane can be increased by 11% to 20% compared to traditional milling. This additional sugar can be fermented by C5 yeast in the first-generation fermentation to produce up to 37% more ethanol without effecting sugar coproduction. Due to close integration with the first-generation host plant, these projects achieve a minimum ethanol selling price (MESP) of $0.17/L to $0.29/L at a 10% return, which is lower than the reported MESP for other second-generation projects and is cost competitive with first-generation ethanol and gasoline. This translates to capital payback (EBITA/Capex) in two to four years. (c) 2016 The Authors. Biofuels, Bioproducts, and Biorefining published by Society of Chemical Industry and John Wiley & Sons, Ltd.