Esterification of fatty acids to biodiesel over polymers with sulfonic acid groups

Abstract

The esterification of palmitic acid with methanol was studied using poly(vinyl alcohol) cross-linked with sulfosuccinic acid (SSA) and polystyrene cross-linked with divinylbenzene with sulfonic acid groups, as catalysts, at 60 ºC. It was observed that the PVAmatrixes with sulfonic acid groups were more active than the polystyrene ones. With the most active polymeric matrix (PVA_SSA40), an almost 90% equilibrium conversion was achieved after 2 h. Further, the optimisation of reaction parameters, such as, catalyst loading, molar ratio alcohol to fatty acid and type of alcohol was carried out with PVA_SSA40 catalyst. Catalytic stability of the PVA_SSA40 was evaluated by performing consecutive batch runs with the same catalyst sample. After the second batch, a stabilisation of the catalytic activity was observed. The PVA_SSA40 was also used as catalyst in the esterification of oleic and stearic acid with methanol,having been obtained an equilibrium conversion of almost 80%. In order to become the biodiesel totally biogenerated, the esterification of palmitic acid was carried out with ethanol, at 60 ºC and 80 ºC. It was observed that the reaction rate is slower when the reaction is carried out with methanol, at 60 ºC. In a posterior catalytic experiment at 60 ºC, PVA_SSA40 showed catalytic activity to obtain biodiesel from animal fats (lard), in the presence of methanol.