Investigation into the effect of solvents on lignin hydrogenation for the production of phenolic compounds

Abstract

Solvents play a critical role in the lignin hydrogenation process. However, elucidating the role of solvents in lignin hydrogenation solely through experimental methods presents considerable challenges. The present report integrates experimental results, quantum chemical calculations, and molecular dynamics simulations to study the effect of solvents on the hydrogenation of lignin on Ru/C to produce phenolic compounds. Solvents not only disperse the substrate and promote the mass transfer process in the hydrogenation reaction, but also significantly affect the hydrogenation reaction rate of lignin. We show that the hydrogenation reaction rates of lignin in different solvents differ by an order of magnitude (isopropanol > methanol > water > γ-valerolactone > tetrahydrofuran). By innovatively combining quantum chemical calculations with experimental results, it was reported for the first time that solvent affects the free energy barrier by regulating the properties of the transition state (C–O bond strength), thereby affecting the lignin hydrogenolysis reaction rate. Based on molecular dynamics simulations, this study investigated the interaction between lignin and various solvent molecules. The research results confirmed that solvent molecules regulate the solvent shell on the surface of lignin, thereby influencing the mechanism of the hydrogenation reaction process.