Petroleum based phthalate plasticizers encounter enormous claims to prohibit their production due to their harmful health impacts when they are mixed with plastics. That is why efforts are being done to find safer natural alternatives. We have investigated the reaction kinetics of the esterification epoxidation of oleic acid and 2-ethylhexanol in the presence of hydrogen peroxide catalyzed using Candida antarctica lipase (Novozym 435, Novozymes, Kobenhavn, Denmark). The product of this reaction is epoxidized 2-ethylhexyl oleate, a non-phthalate green plasticizer. The kinetic model for this reaction follows a multi-substrate PingPong Bi-Bi mechanism with competitive inhibition by the alcohol. The reaction's kinetic parameters were found to be 0.76 M, 0.37 M, 0.08 M, and 37.20 mM/min for Michalis-Menten constant for oleic acid (Kmo), Michalis-Menten constant for alcohol (Kma), alcohol inhibition constant (Kia), and maximum reaction velocity (Vmax), respectively. Then the Gibbs function analysis of the transition state based on the Arrhenius and Eyring equations was carried out. The internal diffusional limitations were found to be negligible as the effectiveness factor took the value of almost unity. While the external mass transfer resistance had no effect on the reaction due to operating at relatively high agitation speed and high temperature. This investigation confirms that this reaction was only kinetically controlled.
Keywords: Gibbs function; Novozym 435; Ping-Pong Bi-Bi model; esterification-epoxidation; plasticizer.