Ethanol/1,4-dioxane/formic acid as synergistic solvents for the conversion of lignin into high-value added phenolic monomers

In this study, a mixture solvent of ethanol/1,4-dioxane/formic acid (FA) is firstly reported to efficaciously depolymerize industrial lignin to produce high-value added phenolic monomers, in which 1,4-dioxane acts as lignin solvent, ethanol acts as solvent, reactant and in situ hydrogen donor, and FA acts as acid catalyst and in situ hydrogen donor. The effects of solvent composition and reaction conditions on the lignin conversion and product yields were explored, resulting in a low residue yield of 6.57% and a high phenolic monomers yield of 22.4% at 300 °C for 2 h when Kraft lignin was depolymerized in the mixture solvent of ethanol/1,4-dioxane/FA (10:10:2, v/v). Moreover, possible reaction mechanism on lignin depolymerization in the mixture solvent was illustrated, suggesting a favorable synergistic effect among the three components of the mixture solvent. In addition, the satisfactory applicability of the mixture solvent was approved through the feedstock adaptability and recyclability experiments.