Kinetic Study of Methanolysis of Jatropha Curcas-Waste Food Oil Mixture

Abstract

Methanolysis of a Jatropha curcas-waste food oil mixture that contained 1 wt% of free fatty acids was carried out in the presence of a KOH catalyst in a batch reactor at various methanol-to-oil molar ratios; the reaction temperature was varied from 25 to 60°C; the catalyst concentration was varied from 0.5 to 2.0 wt% of oil; the mixing speed was fixed at 900 rpm and the reaction time was 2 h. Samples were collected during the reaction time and analyzed by gas chromatography (GC) to determine the weight percentages of the reaction constituents on glycerol-free basis. The experiments revealed that the reaction conditions (mixing level, reaction temperature, catalyst concentration, and methanol-to-oil molar ratio) have a significant effect on the hydroxide catalyzed methanolysis reaction of the Jatropha curcas-waste food oil mixture. The conversion rate of the oil mixture and the methyl ester production rate increased with the mixing speed, reaction temperature, catalyst concentration and methanol-to-oil molar ratio. A second-order kinetic model with the reaction rate constants obtained in the experiment provided a satisfactory mechanism for the methanolysis reactions. The kinetic model was able to describe the experimental data, and the average relative average difference (RAD) was 4.7%. The simulation and experiments also indicated that although the methanolysis reaction consisted of three stepwise and reversible reactions, the forward reactions were the most important. Activation energy analysis showed that the methanolysis reactions of the Jatropha curcas-waste food oil mixture were sensitive to reaction temperature changes.