Catalytic transfer hydrogenolysis of ionic liquid processed biorefinery lignin to phenolic compounds

Abstract

Lignocellulosic biomass has the potential to play a significant role in the global bioeconomy for the production of renewable fuels and chemicals. It has been estimated that there are roughly a billion tons of lignocellulose available annually in the United States alone. Valorization of residual lignin streams generated from lignocellulosic biorefineries is key for economic viability and sustainability. In this work, catalytic transfer hydrogenolysis using isopropyl alcohol (IPA) as a hydrogen-donor solvent was employed at 300 °C to valorize lignin-enriched residues obtained from an ionic liquid (IL) conversion process. This process results in high liquid yields (65.5 wt%) with a significant amount of monomers present (27 wt%) and low char formation. Compositional analysis of the process streams indicates that alkyl-substituted phenols are the main products. Lignin depolymerization was enhanced at longer reaction times and in the presence of Ru/C, producing more, low molecular weight products with a greater extent of alkylation on the aromatic rings. This work suggests that residual lignin fractions from IL-based lignocellulosic conversion technologies can be depolymerized to value-added products and low molecular weight platform chemicals for the renewable fuels and chemicals sector.