Comparison in Catalytic Activities of Sulfated Zirconia and Sulfated Tin Oxide for Converting Free Fatty Acids in Crude Palm Oil to Their Methyl Esters

For the first time, the catalytic activities of sulfated zirconia and sulfated tin oxide have been directly compared for esterification of free fatty acids (FFA) in crude palm oil to produce fatty acid methyl esters (FAME). Both sulfated zirconia and sulfated tin oxide catalysts were prepared by hydroxide precipitation, followed with impregnation using sulfuric acid as the source of sulfate. The concentrations of sulfuric acid were varied. The sulfated zirconia and sulfated tin oxide catalysts were characterized by XRD, nitrogen adsorption, elemental analysis, FTIR and potentiometric titration. Esterification of FFA in crude palm oil was carried out in a stirred-tank reactor equipped with a reflux condenser. The influences of the amount of methanol and catalysts were investigated. The results have revealed that both sulfated zirconia and sulfated tin oxide well catalyze the esterification of FFA to produce FAME. Sulfated tin oxide is, on average, 2 times more active than sulfated zirconia. Increasing the concentration of sulfuric acid used in the preparation of both catalysts results in higher sulfur contents and greater acidities of the catalysts. As a result, the conversions of FFA increase. Moreover, the conversions of FFA have been found to increase with the amounts of methanol and catalysts up to certain values and then level off.