(51a) Production of Sugars, Lignin and Lignin Monomers from Biomass Using Gamma-Valerolactone As a Solvent
Widespread production of biomass-derived fuels and chemicals requires cost-effective processes for breaking down cellulose, hemicellulose and lignin into their constituent monomers. Soluble carbohydrates can be produced at high yields (70 to 90%) from corn stover, hardwood and softwood in a solvent mixture of gamma-valerolactone (GVL), water, and dilute acid (0.05 wt% H2SO4). When used as a solvent, GVL promotes thermocatalytic saccharification of biomass by complete solubilization of the biomass, including the lignin fraction, and can be produced at high-yields from biomass itself (about 60% yield from cellulose). Rates of acid-catalyzed reactions in GVL appear to be linked to the increased catalytic activity of the proton due to solvent effects.
The carbohydrates can be recovered and concentrated (up to 127 g/L) in an aqueous solution by addition of CO2 to form a CO2-expanded GVL phase no longer miscible with water. This strategy is well suited for catalytic upgrading to furans or fermentative upgrading to ethanol at high titers and near theoretical yield. In parallel, the solubilized lignin stream can be recovered at high yields (>70% of the original lignin) by precipitation in water. Analysis of the isolated lignin by NMR demonstrated that its chemical properties remained remarkably similar to native lignin or enzymatically-isolated lignin despite the high temperatures and acid used during processing. Because of this, we show that this stream can be converted catalytically converted to lignin monomers at similar yields to those obtained from unprocessed biomass.