Abstract

In this study, sulfated tin oxide was modified with cobalt oxide and aluminium oxide resulting in sulfated cobalt-tin (SO<inf>4</inf>^2-/Co<inf>2</inf>O<inf>3</inf>-SnO<inf>2</inf>) and sulfated aluminium-tin (SO<inf>4</inf>^2-/Al<inf>2</inf>O<inf>3</inf>-SnO<inf>2</inf>) 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 SO<inf>4</inf>^2-/Co<inf>2</inf>O<inf>3</inf>-SnO<inf>2</inf> and SO<inf>4</inf>^2-/Al<inf>2</inf>O<inf>3</inf>-SnO<inf>2</inf> samples were determined by nitrogen adsorption, X-ray diffraction and potentiometric titration. The activities of SO<inf>4</inf>^2-/Co<inf>2</inf>O<inf>3</inf>-SnO<inf>2</inf> and SO<inf>4</inf>^2-/Al<inf>2</inf>O<inf>3</inf>-SnO<inf>2</inf> 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 SO<inf>4</inf>^2-/Co<inf>2</inf>O<inf>3</inf>-SnO<inf>2</inf> and SO<inf>4</inf>^2-/Al<inf>2</inf>O<inf>3</inf>-SnO<inf>2</inf> was made. The results showed that the SO<inf>4</inf>^2-/Al<inf>2</inf>O<inf>3</inf>-SnO<inf>2</inf> had higher catalytic activity than SO<inf>4</inf>^2-/Co<inf>2</inf>O<inf>3</inf>-SnO<inf>2</inf> in esterification of FFA to produce methyl esters.