Feedstock-agnostic reductive catalytic fractionation in alcohol and alcohol–water mixtures

Abstract

Many biomass conversion technologies focus primarily on tailor-made processing conditions for a single feedstock, in contrast to developing a practical operational window for effective processing of a broad variety of lignocellulosic biomass substrates available year-round. Here, we demonstrate the feedstock flexibility of reductive catalytic fractionation (RCF), performed in both batch and flow-through (FT) modes, to effectively process a range of biomass types (hardwoods, softwoods, and herbaceous monocots), regardless of their macromolecular composition and morphological structure differences. Both batch and FT-RCF performed with pure methanol as a solvent allow delignification (or lignin oil yield) values and lignin monomer yields greater than 65 wt% and 25 wt%, respectively, and high retention of carbohydrates (>90%) from herbaceous monocots (corn stover and switchgrass) and hardwood (poplar) biomass substrates, despite the inherent differences between woody and herbaceous biomass feedstocks. FT-RCF of pine (softwood) exhibited lower lignin extraction efficiency (<40%), but the high content of lignin in pine enabled a similar lignin oil yield on a biomass basis relative to other feedstocks. FT-RCF was subsequently tested by adding water as a co-solvent (i.e., 50 : 50 w/w methanol/water), and delignification values increased to greater than 78% regardless of the feedstock. Together with the comparable delignification values, similar lignin oil and carbohydrate yields, as well as lignin oil properties, were observed across the tested feedstocks, suggesting that RCF with an alcohol/water mixture can effectively and consistently handle a wide range of lignocellulosic biomasses, including hardwoods, softwood, and herbaceous biomasses.