Kinetic study of methyl oleate epoxidation under phase transfer catalysis by heat flow measurement

The epoxidation of vegetable oils is an environmentally friendly process that allows the synthesis of platform molecules for many industrial applications. The diphasic nature of the reaction results in limitations due to mass transfer. Phase transfer catalysis is used as an alternative solution to improve the kinetics of methyl oleate epoxidation. This epoxidation was investigated by using quaternary ammonium salts, hydrated sodium tungstate and phosphoric acid. The chemical kinetics are monitored by measurements of the thermal flow in the RC1-RTCal calorimetric reactor. The effects of the molar ratios of the co-catalysts Na₂WO₄/H₂O₂ and H₃PO₄/H₂O₂, the nature and the concentration of the phase transfer agent and the temperature of the process on the chemical kinetics have been investigated. Five transfer agents, Aliquat336, MTOAB, CTAC, CTAB and BDHAC, were tested. The reaction kinetics is faster in the following order: Aliquat336 > CTAC > BDHAC. The reaction time is reduced to less than two hours compared to a conventional epoxidation using percarboxylic acids where the average reaction time is ten hours. The kinetic parameters estimation method is based on the comparison of the experimental thermal power profiles with the calculated ones by means of a simplified model. A pseudo-homogeneous model based on the main epoxidation reaction and that of catalyst regeneration is proposed. The activation energy obtained for the epoxidation reaction is 40.5 kJ mol⁻¹. The safety parameters ∆T_ad, the maximum temperature of synthesis reaction and T_D24 were determined.