Determination of methanolysis rate constants for low and high fatty acid oils using heterogeneous surface reaction kinetic models

Abstract

Catalytic methanolysis of soybean oil with Amberlyst A26-OH basic ion-exchange resin was studied in the presence and absence of free fatty acids. Catalytic methanolysis of soybean oil is a key step in the biodiesel production process. The use of the heterogeneous Amberlyst A26-OH basic resin to catalyze this conversion is of interest due to the resin’s ability to be recovered, regenerated, and reused. This current research modeled methanolysis on the surface of the heterogeneous catalyst using both the Eley–Rideal and Langmuir–Hinshelwood–Hougen–Watson reaction kinetic models. For all experiments, soybean oil (with and without 5 % oleic acid incorporated) was reacted with methanol at a molar ratio of 1:10 soybean oil to methanol in the presence of Amberlyst A26-OH (added at 20 % by weight of oil). The reaction was carried out over multiple investigations in a batch reactor where the reactants were mixed at 550 rpm and held at 50 °C and atmospheric pressure. The resulting data demonstrated that the Eley–Rideal reaction mechanism offered the best description of the surface interactions occurring on the resin. Based upon Eley–Rideal model fitting, the mean (± standard deviation) methanolysis rate constant (the rate at which methanol was consumed during the reaction) was determined to be 7.48 × 10⁻⁴ (±4.05 × 10⁻⁵) h⁻¹ with free fatty acid absent and 1.94 (± 1.25 × 10⁻¹) h⁻¹ with free fatty acid present.