Enzymatic esterification of ethanol and oleic acid — a kinetic study

Abstract

The formation of ethyl oleate from ethanol and oleic acid using a free or immobilised Rhizomucor miehei lipase as catalyst was evaluated in a biphasic system. Based on a 2(3) factorial design previously developed [1], it was possible to study the reaction kinetics. The data obtained indicated that the reaction follows a Michaelis–Menten kinetics and it is described by the ternary complex mechanism. Based on the proposed model, the kinetic constants to the esterification reaction, without considering substrate inhibition, were determined. The kinetic results showed that the free lipase had the same affinity for both substrates (Km(Et)=1.79 M, Km(Ol)=1.80 M) while the lipase in its immobilised form had higher affinity for oleic acid (Km,app(Et)=1.20 M, Km,app(Ol)=1.16×10−8 M). It was also verified that the specificity was higher in the immobilised lipase system (Ks,app(Et)=2.90 mmol h−1 mg−1 M−1) than in the free one (Ks(Et)=0.637 mmol h−1mg−1 M−1). Diffusional effects were detected for low ethanol and oleic acid concentrations, when using the enzyme in its immobilised form, and related to the effectiveness factor. The integrated Michaelis–Menten equation coupled to the kinetic constants obtained, accord well with experimental results.