Biocompatible Choline-Based Deep Eutectic Solvents Enable One-Pot Production of Cellulosic Ethanol

Abstract

Previous configurations of biomass conversion technologies based on the use of ionic liquids (ILs) suffer from problems such as high operating costs and large amounts of water used. There have been recent efforts toward process intensification and integration to realize a one-pot approach for biofuel production using certain ILs, but these typically still require pH adjustment and/or dilution after pretreatment and before saccharification and fermentation. Deep eutectic solvents (DESs) were investigated as an alternative to ILs to address these challenges, and the results obtained suggest that certain DESs are compatible with hydrolytic enzymes and common biofuel producing microorganisms such as Saccharomyces cerevisiae. Among the DESs investigated, choline chloride/glycerol (Ch12) achieved the highest rates of lignin extraction and pretreatment efficiency in terms of sugar yields (>80%) after enzymatic hydrolysis. Most importantly, the DES-Ch12-based "one-pot" biomass conversion process does not require any pH adjustment before commencing with saccharification and fermentation. Degradation compounds generated from polysaccharides (e.g., furfural) and lignin (e.g., ferulic acid) during biomass conversion were characterized and evaluated for their potential inhibitory effect on yeast growth and biofuel production. We conclude that this DES can be used to achieve biofuel (e.g., ethanol) production with a theoretical yield of 77.5% based on the initial glucan present in the biomass in a consolidated one-pot process configuration, redefining biomass conversion using DESs.