Optimization of epoxidation of ricinoleic acid methyl ester by hydrogen peroxide and phase-transfer catalyst using response surface methodology

Abstract

The epoxidation of ricinoleic acid methyl ester (RAME) has been investigated using an environmentally friendly oxidant (i.e., hydrogen peroxide) and a phase-transfer catalyst ([π-C₅H₅N(CH₂)₁₅CH₃]₃[PW₄O₁₆]) in dichloroethane. The response surface methodology (RSM), based on the Box–Behnken design was used to assess individual and interactive effects of the process variables and to optimize the epoxidation reaction condition. The coefficient of determination (R²=0.9544) obtained from analysis of the variance confirmed the suitability of the fitted model. The RSM analysis results indicated that the molar ratio of H₂O₂ to C=C bonds and the reaction temperature are the most significant (P < 0.01) factors affecting the conversion of RAME epoxide. In addition, the interaction between the H₂O₂/C=C molar ratio and the catalyst dosage also has significant effect (P < 0.05) on the conversion of RAME epoxide. The optimum reaction conditions for the epoxidation of RAME were H₂O₂ : C=C molar ratio of 1.93:1, catalyst dosage of 3.11wt% (substrate:catalyst molar ratio = 207), reaction temperature of 52 °C and reaction time of 75 min, under which a conversion of 94.52% could be achieved. The epoxidation of RAME by hydrogen peroxide and the [π-C₅H₅N(CH₂)₁₅CH₃]₃[PW₄O₁₆] phase-transfer catalyst followed pseudo-first order kinetics with an activation energy (E_a) of approximately 21.6 kJ/mol. The reaction process is a mass-transfer control process.

Practical applications: RSM was found to be a useful technique for optimizing epoxidation of RAME. The high conversion of the epoxidation of RAME indicates that [π-C₅H₅N(CH₂)₁₅CH₃]₃[PW₄O₁₆] is a very efficient phase-transfer catalyst for the epoxidation of RAME under the mild conditions mentioned above. The epoxidized RAME have the potential to be used as biolubricants, surfactants, biobased polymers, and surface-active compounds for high-value cosmetic.

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