Intensification of enzymatic synthesis of propylene glycol monolaurate from 1,2-propanediol and lauric acid under microwave irradiation: kinetics of forward and reverse reactions

Abstract

Several organic syntheses have been carried out very effectively using microwave irradiation. In the current studies, immobilized lipases were used for the esterification of lauric acid with 1,2-propanediol under conventional heating and microwave irradiation. These esters are commercially valuable. Various commercially available lipases, such as Novozym 435, Lipozyme RM IM, Lipozyme TL IM and Lipase PS-C were screened among which Novozym 435 was found to be the best catalyst. Optimization of reaction conditions included speed of agitation, catalyst loading, mole ratio of reactants and effect of temperature under the microwave irradiation as well as conventional heating. A kinetic model was developed for both forward and backward reactions. A synergistic effect microwave irradiation on reaction rate and specificity of lipases was observed in comparison with the conventional heating. The initial rate and progress curve data were used to arrive at a suitable model and various parameters were estimated for both forward as well as reversible reaction at 30 °C. The forward reaction follows ping-pong bi-bi mechanism for the reactants 1,2-propanediol and lauric acid with inhibition by 1,2-propanediol whereas the reverse reaction also follows the same mechanism for the reactants propylene glycol monolaurate and water with inhibition by water. This model was used to stimulate the rate data, which were in excellent agreement with experimental values.