Double Salt Ionic Liquids for Lignin Hydrolysis: One Cation for Catalyst and Solvent Anions

Abstract

Hydrolysis of lignin, the only direct renewable source of aromatics, is a promising strategy to obtain industrially important aromatic compounds owing to the nature of the bonds that dominate the lignin structure. In this study, we developed an imidazolium cation-based double salt ionic liquid (DSIL) for lignin hydrolysis with hydrogen sulfate as catalyst and diethyl phosphate as reaction media, and investigated the hydrolytic cleavage as a function of different reaction conditions and recyclability of catalytic system. Under mild conditions, value-added aromatics such as 2-methoxy phenol, 2,6-dimethoxy phenol, vanillin, and 4-hydroxy-3,5-dimethoxy benzaldehyde were obtained. Although yields are currently low, this study revealed that 1-ethyl-3-methylimidazolium hydrogen sulfate is an effective catalyst for lignin hydrolysis and the DSIL strategy could be promising for biomass utilization.