Tin compounds as Lewis acid catalysts for esterification and transesterification of acid vegetable oils

Several catalysts based on tin compounds (tin(II) acetate, tin(II) chloride, tin(II) 2-ethylhexanoate and tin(II) stearate) have been tested in transesterification and esterification reaction in order to treat acid vegetable oils. All of them, except tin(II) stearate, showed good catalytic activity in transesterification reaching a methyl ester content higher than 96.5 wt. % in 24 h. When catalysts were tested in the simultaneous trans- and esterification of acid oil, the formation of water deactivated the catalyst tin(II) 2-ethylhexanoate. Best results were obtained with tin(II) acetate (methyl ester content, 96.6 wt. % at 150 °C and 3 h). Finally, the reusability of tin(II) acetate was studied, because it could be recovered from the reaction by filtration.