Tuesday, April 30, 2013
Exhibit Hall
Fractionation of carbohydrates and lignin is a potential route to improving carbohydrate digestibility via lower enzyme loadings and a means to separate lignin for downstream upgrading to fuels and chemicals. Several organosolv fractionation processes have been developed to remove lignin from biomass including the NREL Clean Fractionation (CF) process, which utilizes water, ethanol, and MIBK in a 50/34/16 wt% mixture with concentrations of sulfuric acid ranging from 0.025 to 0.1 wt% in a temperature range from 120 to 160°C. Here, we demonstrate that CF is a potentially viable process to produce insoluble cellulose with reduced lignin content, solubilized hemicellulose species, and solubilized lignin into the organic phase from corn stover. Mass balance closure of the three components after CF process increased both with increasing acid loading and increasing temperature, as previously reported on switchgrass. The CF lignin fractions were examined with gel permeation chromatography, FT-IR spectroscopy, and NMR spectroscopy, which overall indicate a decrease of both the molecular weight distribution and ether substructures in the CF lignins as severity is increased. To understand the effect of lignin removal on enzymatic digestibility, enzymatic hydrolysis was performed on the residual solid fraction with Novozymes CTec2. The CF corn stover containing the least amount of lignin was considerably more digestible than dilute-acid pretreated corn stover with CTec2 at the same enzyme and solids loadings. This in turn suggests that with further optimization and refinement, CF may offer significant cost savings in the enzymatic hydrolysis step to produce sugars from cellulose.