Insights into the Synthesis of Ethyl Levulinate under Microwave and Nonmicrowave Heating Conditions

The effects of microwave and nonmicrowave heating methods on the synthesis of ethyl levulinate (EL) from levulinic acid (LA) have been investigated in the present study. The levulinic acid esterification experiments were performed in the presence of silicotungstic acid catalyst and ethanol in a microwave and nonmicrowave instant heating reactor. An experimental fit of experimental data in a kinetic model suggested that LA esterification follows a pseudo-first-order reaction mechanism. Consequently, activation barriers were calculated (44-45 kJ/mol) and a negligible difference was found for LA esterification reaction performed in both the reactors. Nevertheless, slightly higher LA conversions were measured under microwave irradiations as compared to experiments performed in a nonmicrowave instant heating reactor. Thus, series of experiments were performed to study the (i) nonthermal and (ii) thermal effects of microwave heating irradiations. Eventually, it was found that the enhanced LA conversion in microwave reactor could be due improved heat transfer into the reaction mixture owing to direct heating by microwaves, as compared to conventional conductive and convective heat transfer in the instant heating reactor. In addition, experiments performed under different operating conditions such as at varying stirring speed, varying sample volume, and different catalyst concentration and reactant concentration indicated the absence of nonthermal microwave effects.