(731b) Comparison of Ethanol Yields from Fermentation of Hydrolysates Produced By CO-Solvent Enhanced Lignocellulosic Fractionation (CELF) and Dilute Acid Pretreatments of Switchgrass

For decades, numerous environmental, economic, and strategic concerns have motivated research into sustainable, domestic sources of fuels to replace those derived from petroleum. Lignocellulosic biomass represents the most abundant renewable resource and provides the only known route to sustainably produce liquid fuels on a large scale and low cost. Due to its complex and recalcitrant structure, raw biomass hinders biological conversion of polysaccharides, thus necessitating pretreatment to deconstruct the plant with high yields through making cellulose and hemicellulose more accessible to enzymes for release of fermentable sugars. Several pretreatment methods, including hydrothermal and dilute acid approaches, have been developed to improve enzyme accessibility, but each is limited in their ability to remove lignin, a key contributor to biomass recalcitrance, and require expensive enzyme loadings to achieve high yields. Recently, we developed a novel pretreatment called Co-solvent Enhanced Lignocellulosic Fractionation (CELF) that applies aqueous tetrahydrofuran (THF) with dilute sulfuric acid to remove a large portion of the lignin, simultaneously achieve high yields of five carbon sugars from hemicellulose during pretreatment, and subsequently hydrolyze most of the glucan at very low enzyme loadings. In this study, we applied CELF to switchgrass to determine optimum pretreatment conditions for maximum sugar release in the combined operations of pretreatment and enzymatic hydrolysis at low solids loadings and compared the results to those for DA pretreatment performed at conditions that realized maximum sugar yields from pretreatment coupled with enzymatic hydrolysis. For each pretreatment, we then established ethanol yields from fermentation of the hydrolysates produced at the optimum conditions, the degree to which fermentation was inhibited by dissolved compounds, and the effectiveness of various conditioning strategies in reducing inhibition.