Comparison in Catalytic Activities of Sulfated Cobalt-Tin and Sulfated Aluminium-Tin Mixed Oxides for Esterification of Free Fatty Acids to Produce Methyl Esters

In this study, sulfated tin oxide was modified with cobalt oxide and aluminium oxide resulting in sulfated cobalt-tin (SO42-/Co2O3-SnO2) and sulfated aluminium-tin (SO42-/Al2O3-SnO2) mixed oxide catalysts, respectively. Their catalytic activities for esterification of free fatty acids (FFA) in crude palm oil were investigated. Cobalt-tin and aluminium-tin mixed oxides were prepared by co-precipitation method. The mixed oxides were further impregnated with sulfate ions by immersing in sulfuric acid solution, dried and calcined at 450-500 °C. The properties of SO42-/Co2O3-SnO2 and SO42-/Al2O3-SnO2 samples were determined by nitrogen adsorption, X-ray diffraction and potentiometric titration. The activities of SO42-/Co2O3-SnO2 and SO42-/Al2O3-SnO2 catalysts were tested in a stirred-tank reactor equipped with a reflux condenser. Esterification between crude palm oil containing 10-10.2 wt% of FFA and methanol was carried out at various reaction times. The comparison in the catalytic activities of SO42-/Co2O3-SnO2 and SO42-/Al2O3-SnO2 was made. The results showed that the SO42-/Al2O3-SnO2 had higher catalytic activity than SO42-/Co2O3-SnO2 in esterification of FFA to produce methyl esters.