Abstract

In this study, sulfated tin oxide was modified with cobalt oxide resulting in sulfated cobalt-tin mixed oxide (SO<inf>4</inf>^2-/Co<inf>2</inf>O<inf>3</inf>-SnO<inf>2</inf>). For the first time, the catalytic activity of SO<inf>4</inf>^2-/Co<inf>2</inf>O<inf>3</inf>-SnO<inf>2</inf> for the esterification reaction of free fatty acids (FFA) in crude palm oil to produce methyl esters has been investigated. The effects of amount of Co and calcination temperature were studied. The properties of SO<inf>4</inf>^2-/Co<inf>2</inf>O<inf>3</inf>-SnO<inf>2</inf> were determined with N<inf>2</inf> adsorption, X-ray diffraction and X-ray fluorescence analysis, Fourier transform infrared spectroscopy, thermogravimetric analysis and potentiometric titration. The esterification was carried out in a stirred-tank reactor equipped with a reflux condenser. The reaction conditions (methanol/oil ratio, catalyst size, catalyst loading and reaction time) were optimized. The results confirm that SO<inf>4</inf>^2-/Co<inf>2</inf>O<inf>3</inf>-SnO<inf>2</inf> is a promising catalyst in the production of methyl esters from FFA in crude palm oil. The addition of Co improved the reusability of sulfated tin oxide.