(290c) Increasing Cellulose Accessibility Is More Important Than Lignin Removal: A Comparison of Cellulose Solvent-Based Lignocellulose Fractionation and Soaking in Aqueous Ammonia

Efficient sugar release from lignocellulosic biomass continues to be one of the most important considerations for reducing the cost of cellulosic biofuel production. While many pretreatments attempt to improve the enzymatic digestibility of biomass by removing lignin or hemicellulose, this study shows that improving the surface area accessible to the enzymes is a more important factor for high sugar yields. Here we compare the pretreatment of switchgrass by two methods, Cellulose solvent- and Organic Solvent-based Lignocellulose Fractionation (COSLIF) and Soaking in Aqueous Ammonia (SAA), to demonstrate this principle. COSLIF was conducted for 45 min at 50°C with 85% phosphoric acid, and SAA was conducted at an elevated temperature using 15% aqueous ammonia. Following pretreatment, enzymatic hydrolysis was conducted at two enzyme loadings: 15 FPUs cellulase and 10 units of β-glucosidase per gram of glucan, and 3 FPUs of cellulase and 10 units β-glucosidase per gram of glucan. Hydrolysis experiments were repeated in the presence of 10g/L BSA, used to block competitive lignin adsorption of cellulase. Switchgrass pretreated by both methods was also examined by scanning electron microscope (SEM), quantitative determination of the cellulose accessibility to cellulase (CAC), and crystallinity as determined by nuclear magnetic resonance (NMR). The results show that despite the effective removal of lignin and hemicellulose by SAA, COSLIF results in higher digestibility, especially at low enzyme loadings, due to the dramatically increased substrate surface area caused by the COSLIF pretreatment.