Kinetic study of the esterification of t-cinnamic acid over Preyssler structure acid

Abstract

A kinetic study, based on Langmuir-Hinshelwood-Hougen-Watson (LHHW) and Eley-Rideal (ER) approaches, was developed to describe the esterification reaction of trans-cinnamic acid and n-butanol over heterogeneous catalysts. It is a reaction of special interest for many applications in different areas such as food conservation, pesticides, and pharmacology. Preyssler heteropolyacid was anchored on a silica framework by the sol-gel method with different loadings, which was characterized using common techniques. The best performance was achieved with SIPWMo with 20% of loading (SIPWMo20), being tested in the catalytic esterification reaction of trans-cinnamic acid with several alcohols such as methanol, ethanol, n-propanol, and benzyl alcohol. The reusability tests showed that heteropolyacid can be successfully used in three consecutive cycles. Kinetic data using SIPWMo20 were obtained at temperatures between 90 and 120 °C, amount of butanol between 8 and 64 mL (for 4 mmol of trans-cinnamic acid), and catalyst concentrations between 0.4 and 0.5 mmol%. The best heterogeneous model was LH3, which was deduced from the assumption of the surface reaction as the rate-limiting step and adsorption of both reactants. The activation energy and the pre-exponential factor were 50.9 kJ mol−1 and 6.12 × 107 mol g−1 h−1, respectively. A plausible reaction mechanism was proposed for the esterification reaction over the SIPWMo20 catalyst, which is consistent with the kinetic results.