Response Surface Methodology for Optimization of Epoxidized Trimethylolpropane Ester Synthesis from Palm Oil

Abstract

To improve the oxidative stability of the palm oil-based biolubricant, the fatty acid double bonds in palm oil-based trimethylolpropane ester (TMP ester) was converted into an oxirane ring via an in-situ epoxidation method. The epoxidized TMP ester was produced from a reaction between TMP ester and peracetic acid which was prepared in-situ by reacting glacial acetic acid with hydrogen peroxide in the presence of concentrated sulphuric acid. The response surface methodology was applied using a central composite design technique to optimize the conditions of the epoxidation reaction to produce the epoxidized TMP ester. The effects of four independent variables namely concentration of acetic acid (0-2 mol), concentration of hydrogen peroxide (1.5-9.5 mol), temperature of reaction (30-110°C) and reaction time (0.5-26.5 h) on the three dependent variables; percentage of oxirane oxygen, iodine value, and hydroxyl value were studied. A second-order polynomial multiple regression model was employed to predict the three dependent variables under optimum conditions of 0.59 mol of glacial acetic acid, 7.5 mol of hydrogen peroxide concentration, at temperature of 50°C and reaction times of 7 h. The optimum values of percentage of oxirane oxygen, iodine value, and hydroxyl value were 4.01%, 1.94%, and 0.43% respectively. The analysis of variance yielded a high coefficient of determination value of 0.9395-0.9880, hence indicating the fitness of the second-order regression model to the experimental data.