Kinetics of free fatty acids esterification with methanol in the production of biodiesel fuel

Abstract

The aim of this study was the determination of optimal conditions of free fatty acid esterification by methanol using acid catalyst, and the calculation of the kinetic parameters of this process. It was found that the reaction rate depends on the amount of the catalyst and the acidity of the reaction mixture. The reaction rate changes also depending on the reaction duration, especially during the first 15 min. Establishing the above mentioned parameters proved the effect of the agents on the reaction rate. Such dependence is characteristic to many heterogeneous processes. The data suggest that having excluded diffusion, the reaction order is about 1. Within the limits of the experimental conditions (free fatty acids 0.162 mol//L-1.948 mol/L, temperature 20–60 °C, constant mixing speed –850 min-1, 1% of catalyst (H₂SO₄)) the apparent energy of activation E_t is ≈ 13.3 kJ/mol, while pre-exponent A = 1.27. These parameters allow the assumption that diffusion restrictions are characteristic to the entire range of the concentrations and the reaction duration studied.