Kinetics of ethylic esterification of lauric acid on acid activated montmorillonite (STx1-b) as catalyst

Abstract

This work reports a kinetic study of catalyzed esterification of lauric acid with anhydrous ethanol related to biodiesel production. The catalyst consists of a clay mineral (montmorillonite STx1-b) prepared according to procedure previously described in literature. The acid activation was confirmed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Operating parameters: temperature (T=140 and 180°C), molar ratio ethanol to lauric acid (MR=6:1 and 12:1) and catalyst loading (CAT=2 and 10wt%, in relation to the fatty acid mass) were evaluated as a preliminary study to the kinetics. Temperature is clearly the factor that most contributes to higher conversions of fatty acid, however, its effect was less pronounced with the use of the catalyst. Moreover, reaction kinetic experiments were performed at different conditions (T=140, 160 and 180°C; MR=3:1, 6:1 and 9:1, CAT=0, 10 and 20wt%) as well as kinetics modeling are presented. The Eley–Rideal mechanism with surface reaction between adsorbed ethanol and lauric acid in the bulk as the limiting step was proposed to represent the catalyzed reactions, in which the global reaction rate was expressed as the sum of non-catalyzed (thermal conversion) and catalyzed reactions. From the results presented, it can be seen that the catalyst montmorillonite STx1-b was able to lead the system to high conversions in shorter time when compared to the non-catalyzed reaction.