Catalytic hydrogenation of levulinic acid in ionic liquid mixtures using hydrogen gas in high-pressure CO2

Abstract

Hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) in ionic liquid (IL) mixtures with hydrogen gas in high-pressure CO2 was studied to demonstrate tuning of product selectivity. Ethyl- or butyl- imidazolium-based cation with Cl, acetate [OAc], diethylphosphate, bis(trifluoro-methanesulfonyl)imide or tetrafluoroborate anion IL mixtures were used as the reaction phase with Pd/C, Pd/Al2O3 or Ru/Al2O3 commercial catalysts. Experiments were performed with batch reactors using (1 to 5) MPa partial pressure H2 at nominal pressures of 8 MPa at 110 °C. GVL selectivities as high as 88% at 50% conversion were obtained in [EMIM]Cl-[EMIM][OAc] using 3 MPa partial pressure H2 in presence of CO2 at 4 h reaction time. Specific interactions of LA with Cl anion IL and CO2 with [OAc] anion IL are key to the reaction mechanism. Reaction systems containing Cl anion - [OAc] anion IL mixtures with H2 gas and CO2 have wide application to hydrogenation of biomass-related compounds.