13-24: Separate hydrolysis and fermentation of Extractive-AFEX (E-AFEXTM) pretreated corn stover at high solid loadings

Extractive-AFEX (E-AFEX^TM) is a novel alkaline pretreatment method developed at GLBRC/MSU based on the existing AFEX^TM process. E-AFEX^TM pretreatment is capable of converting cellulose I to cellulose III, while simultaneously extracting lignin from the biomass. These pretreatment features further improve enzymatic digestibility and microbial fermentability of E-AFEX^TM pretreated biomass compared to conventional AFEX^TM. In this study we study the impact of this new pretreatment method on the enzymatic digestibility and fermentability of lignocellulose at high solids loading. For this study, corn stover was subjected to two different E-AFEX^TM conditions that varied in the type of solvent system applied; (1) ammonia alone, and (2) ethanol/ammonia mixture. An optimized enzyme mixture was developed for each pretreated biomass hydrolyzed at high solids loading using various commercial enzymes (i.e, Cellic enzymes from Novozymes and Multifect enzymes from Genencor).  Each substrate was hydrolyzed with the optimal enzyme mixture at high solid loadings (16-24% solids) with varying protein loadings (7.5-30 mg/g glucan). The fermentability of the hydrolyzate to ethanol was assessed with Saccharomyces cerevisiae 424A strain. The optimal conditions that maximize ethanol productivity for each substrate were determined by regression over a set of statistically defined experimental data points. A detailed material balance for each substrate was analyzed around the pretreatment, enzymatic hydrolysis and fermentation processes based on the protocols established by previous CAFI studies.