Kinetic and thermodynamic studies of oil palm mesocarp fiber cellulose conversion to levulinic acid and upgrading to ethyl levulinate via indium trichloride-ionic liquids

Abstract

This study investigated the kinetic and thermodynamic studies of oil palm mesocarp fiber cellulose conversion to levulinic acid and upgrading to ethyl levulinate via an eco-friendly Bronsted-Lewis acidic ionic liquid, that is, indium trichloride-1-methylimidazolium hydrogen sulfate (InCl3-[HMIM][HSO4]). The conversion reactions, i.e. cellulose depolymerisation to levulinic acid, and the subsequent upgrading esterification to ethyl levulinate, were conducted at a temperature range of 135–175 °C and 65–105 °C, respectively. Pseudo-homogeneous kinetic models were adapted to evaluate the best reaction order. The results indicate that both reactions followed the pseudo-homogeneous first-order kinetic models. Relative low activation energies of 56.5 kJ mol−1 and 28.1 kJ mol−1 were obtained for the cellulose depolymerisation, and the subsequent upgrading esterification, respectively, implying a higher energy and catalytic efficiency system. The first-order rate constants were calculated to analyse the thermodynamic activation parameters. The Gibbs free energy of activation for the cellulose depolymerisation, and the subsequent upgrading esterification were +115.5 kJ mol−1 and +90.3 kJ mol−1 respectively, which were relatively lower than the previous works that used various type of catalysts. These kinetic and thermodynamic parameters provide insights to the oil palm mesocarp fiber cellulose conversion to levulinic acid and ethyl levulinate via the proposed eco-friendly ionic liquids.