Methyl Oleate Synthesis by TiO2 Photocatalytic Esterification of Oleic Acid: Optimisation by Response Surface Quadratic Methodology, Reaction Kinetics and Thermodynamics

摘要

Methyl oleate, an example of a FAME (fatty acid methyl ester), was produced by oleic acid (OA) photoesterification with TiO2 and UVA light. Different parameters were evaluated and optimised: catalyst pretreatment, temperature (25–65 °C), catalyst loading (1–30% w/w_(OA)) and oleic acid : alcohol molar ratio (1 :3–1: 55). Response surface quadratic methodology obtained by central composite rotational design (RSM-CCRD) was used to evaluate the main operational conditions of the photoesterification process. A high conversion of 98% (±0.8) at 55°C, 20% TiO2 (w/w_(OA)), and 1(OA) : 55(methanol) molar ratio was achieved. The photoesterification mechanism is furthermore proposed. The Langmuir-Hinshelwood kinetic model considered the forward and backward reaction as first-order fits with the best accuracy (R~2 of 0.997). The thermodynamic results (ΔG_(338.15K)= - 20.75 kJ/mol, ΔH=13.75 kJ/mol, and ΔS=0.47 kJ/mol.K) indicate that the operating conditions are important, both to supply the energy requirement of the reaction, but also to increase the miscibility of the reactants.