Lipase-catalysed synthesis of n-octyl oleate : a kinetic study
Laudani, Chiara Giulia ...
The n-octyl oleate is a very useful organic compound that finds widespread uses in cosmetic, plastic and pharmaceutical industries. The synthesis of n-octyl oleate by esterification reaction of oleic ...acid with n-octanol was performed by using lipase from Rhizomucor Miehei (Lipozyme IM), immobilised on a macroporous anion exchange resin, as catalyst. Experiments were carried out in a stirred batch reactor equipped with adequate control systems. Influence of operating variables was studied. Various reaction parameters including acid and/or alcohol concentration, enzyme concentration, temperature, stirring rate, water content and reaction time affecting the synthesis of n-octyl oleate were investigated. The present work focuses on the screening and optimisation of various reaction conditions such as temperature and biocatalyst concentration. A kinetic study of oleic acid esterification with 1-octanol has been in a range of 20-120 °C of temperatureand 0.2 g-1.7 g of initial catalyst concentration, at atmospheric pressure in solvent-free system. An equimolar solution of oleic acid (63 mmol) and 1-octanol (63 mmol) was used as reaction mixture. The direct esterification of oleic acid and 1-octanol was performed with magnetic stirring of 500 rpm. Modulating the enzyme amount significant changes in the ester contents was not observed, but important changes are in the initial reaction rates. An optimum temperature of 50 °C for maximum activity was observed and good activities were still observed at higher temperatures up to 70 °C. At temperatures higher than 70 °C thermal deactivation of the enzyme occurred. The optimal conditions for esterification reaction were obtained with enzyme concentration of 1.5 g at 50 °C. Under these conditions, the esterification percentage was 88.5 % after 5 hours of incubation time. Evolution of concentration of the species involved was determined. The ester content was quantified by calculating the residual fatty acid content in the reaction mixture. Reaction kinetics was described in terms of the Michaelis-Menten mechanism. According to the mechanism maximum reaction rate, Michaelis-Menten constant were determined. Kinetic constants, as well as activation and deactivation enthalpy, Gibbćs free energy and entropy values, were determined for the model proposed for the esterification reaction within the experimental range studied.
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