High titer ethanol production from corn stover pretreated solids prepared by novel co-solvent enhanced lignocellulosic fractionation (CELF) pretreatment

Our recently developed co-solvent enhanced lignocellulosic fractionation (CELF) pretreatment employs an acidic aqueous tetrahydrofuran (THF) solution to realize nearly theoretical hemicellulose sugar removal and recovery and up to 90% delignification. It is particularly noteworthy that the glucan-rich solids resulting from CELF were nearly completely digested by fungal cellulase loadings of only 5 mg/g-glucan. However, these results were for conventional batch fermentations at 4% glucan concentrations, while greater than 5% ethanol titers in the broth are desirable to reduce downstream distillation costs. Thus, this study employed simultaneous saccharification and fermentation (SSF) to corn stover pretreated with the CELF technology at low to high solids loadings and low and moderate enzyme loadings of 2 to 15 mg/g glucan to identify key operating parameters to achieve high yields at industrially relevant solids and enzyme loadings. Initial experiments showed high ethanol titers were possible with excellent yields within 5 days (58 g/l, 90% yield) at an enzyme loading of 15 mg/g-glucan and 11.5% glucan solids, and results for lower enzyme loadings will be presented to better understand how lignin removal by CELF impacts SSF performance at high solids concentrations. In addition, a pre-hydrolysis strategy was applied to determine if improved mixing at high solids loadings could further enhance performance. Because inconsistent results have been reported on the benefits of pre-hydrolysis, it was also applied to solids from dilute acid pretreatment of corn stover to determine how pre-hydrolysis impacts performance for readily digested CELF pretreated solids vs. more recalcitrant solids from dilute acid pretreatment.