Soybean Oil Transesterification Reactions in the Presence of Mussel Shell: Pseudo-First Order Kinetics

Calcium oxide is one of the appropriate catalysts for biodiesel production. In this study, cheap and compatible with environment catalyst has been used. Mussel shell of Persian Gulf coast is one of the sources of calcium carbonate that is converted to calcium oxide at calcination temperature up to 950°C. Transesterification reaction was carried out at optimum condition of our previous study (calcination temperature of 1050°C, methanol to oil ratio of 24:1 and catalyst to oil ratio of to 12 wt.%) in a 250mL two-necked flask. In this study, the effects of stirrer speed (250 and 350rpm), the reaction temperature (328.15, 333.15, and 338.15K) and reaction time (1, 3, 5, 7 and 8h) on the methyl ester conversion were investigated. The methyl ester conversion, in stirrer speed of 250rpm, reaction temperatures of 328.15 and 333.15K and reaction times of less than 5h is too low. But at the reaction temperature of 338.15K (near to methanol boiling point), the mixing is increased slightly and the reaction occurs at a higher rate and the methyl ester conversion is increased. These results indicate that diffusion has a significant role in the methyl ester conversion rate in the heterogeneously catalyzed reaction. In stirrer speed of 350rpm, the diffusion problem has been solved somewhat and the reaction in the catalyst surface is the controller of the overall reaction rate. In this stirrer speed (350rpm) the methyl ester conversion versus time in all temperature shows pseudo-first-order kinetics. Firstly, the rate was determined at the various temperatures and then the activation energy for the transesterification reaction of soybean oil with methanol was obtained in the presence of mussel shell as the catalyst. Results demonstrate the high precision of the pseudo-first-order kinetics model regard to methyl esters concentration.