Kinetics for the biodiesel production from lauric acid over Keggin heteropolyacid loaded in silica framework

Abstract

Kinetic models were developed to describe the esterification reaction of lauric acid and ethanol over heterogeneous catalysts, which is a reaction of special interest in the biodiesel production. Vanadium Keggin heteropolyacid was included on a silica framework by sol–gel procedure, using different loadings. The synthesized materials were characterized by FT-IR, XRD, SEM, nitrogen adsorption/desorption isotherms, and potentiometric titration, and tested as solid catalysts in the esterification of lauric acid. Best performance was achieved with SiO2@20PMoV, which was used in the esterification of others fatty acid and alcohols. The reuse was successfully tested in five consecutive runs. Kinetic data using SiO2@20PMoV were obtained at different temperatures (48–78°C), fatty acid:alcohol molar ratios (4mmol of lauric acid and 2.5, 5, 10 and 15mL of ethanol), and catalyst amounts (12.5, 25 and 50mg). The best heterogeneous models were LH3 (surface reaction as rate-limiting step) and ER3 (desorption of ethyl laurate as rate-limiting step when the adsorbed reactant is lauric acid). The activation energies were 56.1kJmol−1 and 64.8kJmol−1, and the reaction rate constants at 78°C were 0.2791molg−1h−1 and 0.0768molg−1h−1 for LH3 and ER3, respectively.