Kinetics of esterification of propanoic acid with methanol over a fibrous polymer-supported sulphonic acid catalyst

Esterification kinetics of propanoic acid with methanol in the presence of a fibrous polymer-supported sulphonic acid catalyst as well as a conventional resin catalyst was studied. Kinetic experiments were carried out in a laboratory-scale batch reactor operating isothermally at 55, 60 and 63°C and with different initial molar ratios of propanoic acid and methanol (1:1, 2:3 and 3:2). The fibre catalyst was active and stable in all the experiments. A reference experiment with the conventional catalyst, Amberlyst 15 was carried out at 60°C, with the initial molar ratio 1:1. The reaction rate was higher with the fibre catalyst than with the Amberlyst 15. The apparent second-order rate constant for the fibre catalyst was 1.82×10^-3 dm⁹/(mol² g min) at 60°C with the initial molar ratio 1:1 and 7.03×10^-4 dm⁹/(mol² g min) for the conventional catalyst under comparable conditions. The fibre catalyst was re-used in four experiments to explore its durability. After four successive experiments, the catalyst activity and capacity remained on the initial level, indicating good stability. A new kinetic model comprising the adsorptive interaction of propanoic acid and water with the sulphonic acid groups on the catalyst surface was developed and tested with the experimental data. The new rate equation gave a good fit to the data and was able to describe the behaviour of the system at various initial molar ratios of propanoic acid and methanol.