Kinetic and thermodynamic studies of HMF-ester synthesis using Brønsted–Lewis acidic ionic liquid catalyst

Abstract

The valorization of 2nd generation biomass-derived 5-HMF into HMF-ester following the esterification reaction is a promising and appealing route for the production of renewable platform chemicals. Herein, we report the thermodynamics and kinetics of the HMF-ester products synthesized using bifunctional IL [SMIM][FeCl₄] catalyst. The effects of the various reaction parameters such as reaction temperature and time were studied and optimized for maximum 5-HMF conversion into HMF-levulinate in a batch autoclave. Bifunctional IL [SMIM][FeCl₄] catalyst gave 97% 5-HMF conversion with a maximum 78% yield of HMF-levulinate within 5 h reaction time at 378 K. The thermodynamic properties such as critical temperature (T_c), critical volume V_c, critical pressure (P_c), Gibbs free energy of formation (ΔG⁰_f), enthalpy of formation (ΔH⁰_f), and heat capacity (C_p) for the HMF-ester products (HMF-levulinate, HMF-propionate, HMF-lactate, HMF-formate, and HMF-acetate) were estimated following the group contribution methods (GCMs). To elucidate the kinetics for the synthesis of HMF-levulinate, a series of the reaction runs were performed in a batch reactor in the temperature range of 348–393 K. Based on the results obtained by the experimental study, a reaction kinetic model for this HMF-levulinate synthesis reaction was formulated and the activation energy for the first order reaction was found to be 32.78 kJ mol⁻¹.