Novel Biomass Pretreatment Using Alkaline Organic Solvents: A Green Approach for Biomass Fractionation and 2,3-Butanediol Production

Valorization of each component of lignocellulosic biomass is critical for sustainability of biorefinery industries. Current biorefineries are confined to ethanol-centric processes and focus only on the carbohydrate-derived sugar using energy-intensive pretreatment methods, leading to deteriorated lignin quality for high-value applications. Organosolv fractionation is an effective method to improve hydrolysis efficiency of cellulose and extract a good quality lignin stream; however, hemicelluloses recovery is challenging if an acid catalyst is used. An alkali catalyst in the organosolv process, therefore, could be a promising alternative approach. We evaluated various organic solvents (glycerol, 2,3-butanediol, dimethyl sulfoxide, ethanol, butanol, isopropanol, acetonitrile, and water) for pretreatment of different biomass feedstocks, including corn stover (grass), poplar (hardwood), and Douglas fir (softwood) using sodium hydroxide as a catalyst. Results showed that an ethanol and isopropanol mixture led to 18 % more sugar released per gram of biomass than the control (conventional aqueous alkali pretreatment) for corn stover; a mixture of ethanol, butanol, and water was the next most effective solvent. For pretreatment of poplar biomass, glycerol and 2,3-butanediol were the most efficient solvents; glycerol pretreatment offers further process improvement opportunities. The organic solvents used in this experiment were not effective for Douglas fir. The quality of released sugars was statistically equal to that of synthetic sugars for 2,3-butanediol fermentation using Klebsiella oxytoca. This study opened up a promising route for high value application for all biomass components. Further research is needed to characterize the extracted lignin for quality evaluation.