ACTIVITY-BASED KINETIC MODELLING OF LIPASE CATALYSED SYNTHESIS OF PEROCTANOIC ACID

Abstract

Carboxylic peroxy acids are organic oxidants of relevance in the cosmetic, food, and agrochemical industries. However, they are traditionally used as intermediaries in a process known as Prileschajew epoxidation and synthesized using sulfuric acid as a catalyst, promoting undesirable reactions on the final epoxides. Therefore, the study of selective catalysts such as enzymes is a topic of interest. In this work, peroctanoic acid synthesis was carried out using n-hexane as the solvent and an immobilized Candida Antarctica Lipase B commercial preparation as the catalyst. On the other hand, the oxidant, hydrogen peroxide was supplied as an aqueous solution, comprising the disperse phase of the reacting system. The reaction progression was quantified by iodometric and cerimetric titration of the peroctanoic acid concentration in the hexane phase. Four different initial amounts of octanoic acid were tested (0.74, 1.57, 10, and 20 millimoles). Substrate inhibition by octanoic acid was observed having at 1.57 millimoles the maximum initial reaction rate. The experimental data were fitted to a ping-pong bi-bi enzymatic kinetic model to estimate the initial reaction rate. Since this system constituted a liquid-liquid (organic-aqueous) two-phase system, the model was evaluated employing the thermodynamic activities of all species involved, assuming phase equilibria with time. The activities of all species were estimated using UNIFAC. As a result, the model was able to reproduce the trend of the initial rate with the change of the initial amount of octanoic acid.