Biodiesel production using 4-dodecylbenzenesulfonic acid as catalyst

Abstract

The synthesis of biodiesel from triglycerides and methanol using 4-dodecylbenzenesulfonic acid as catalyst was studied. The use of acid catalysts in the production of biodiesel has the advantage that in addition to accelerating the transesterification of triglycerides, they also catalyze the esterification of free fatty acids and, moreover, they do not form soaps or emulsions. Regarding the 4-dodecylbenzenesulfonic acid catalyst used in this work, it has a further advantage in that it has a hydrophobic moiety in its molecular structure, which permits a much higher transesterification rate than that of other acid catalysts and, hence, conversions higher than 95% can be attained under mild reaction conditions in less than 3h.From the results of a first set of experiments, an empirical model was calculated that related the values of conversion, at 3h of reaction, and the values of the influencing factors quantitatively. From this model, it was found that the effects of temperature and the catalyst/oil molar ratio meant that the higher the values of any of these factors, the higher the conversions obtained. Conversely, methanol proved to be an obstacle at low conversions because it slowed down the reaction. However, under high temperature and/or high proportions of catalyst, (i.e., for conversions >80%), higher proportions of methanol also favored higher conversions.A second set of experiments was also carried out at 80 and 90°C and from the joint analysis of the results of all experiments performed in this work (first and second sets) it was observed that the transesterification kinetics reflected a first-order reaction, with an activation energy of 66.3kJ/mol. At 90°C it was possible to obtain conversions higher than 98% in less than 2h.