Kinetic, thermodynamic, optimization and reusability studies for the enzymatic synthesis of a saturated wax ester

Abstract

Cetyl decanoate was synthesized by esterification reaction catalyzed by immobilized lipase from Thermomyces lanuginosus (TLL) via physical adsorption on poly-(styrene-divinylbenzene) resin (PSty–DVB). The effect of relevant factors on the ester synthesis was evaluated. In this study, a second-order reversible reaction kinetic model was proposed in order to estimate apparent kinetic constants and good agreement with experimental data was observed (0.9430≤R2≤0.9938). The reaction was found to be a spontaneous and endothermic process. The biocatalyst prepared with initial protein loading of 115mg/g of support (immobilized protein concentration of 108.7±3.1mg/g) yielded the highest initial reaction rate (113.5mM/min of reaction), then selected for subsequent tests. The reaction in heptane medium required a slight excess of cetyl alcohol (molar ratio acid:alcohol of 1:1.25) and 7.5% m/m of biocatalyst to attain a maximum conversion of 92.5% for 30min of reaction. In a solvent-free system, maximum conversion of 85.4% was observed for 50min of reaction conducted in an equimolar ratio acid:alcohol and 10% m/m of biocatalyst. The productivity for the reaction performed in heptane medium was higher than in a solvent-free system – 68.5 and 56.4mM/ming of biocatalyst, respectively. The prepared biocatalyst was more active than commercial biocatalysts such as IMMTLL–T2–150 and Lipozyme TL–IM that exhibited maximum conversion around 92% for 45 and 75min of reaction, respectively. The biocatalyst could be reused at least eight times without significant decrease of its activity.