Effect of water on sulfuric acid catalyzed esterification

This paper reports on an investigation into the impact of water on liquid-phase sulfuric acid catalyzed esterification of acetic acid with methanol at 60 °C. In order to diminish the effect of water on the catalysis as a result of the reverse reaction, initial reaction kinetics were measured using a low concentration of sulfuric acid (1 × 10−3 M) and different initial water concentrations. It was found that the catalytic activity of sulfuric acid was strongly inhibited by water. The catalysts lost up to 90% activity as the amount of water present increased. The order of water effect on reaction rate was determined to be −0.83. The deactivating effect of water also manifested itself by changes in the activation energy and the pre-exponential kinetic factor. The decreased activity of the catalytic protons is suggested to be caused by preferential solvation of them by water over methanol. A proposed model successfully predicts esterification rate as reaction progresses. The results indicate that, as esterification progresses and byproduct water is produced, deactivation of the sulfuric acid catalyst occurs. Autocatalysis, however, was found to be hardly impacted by the presence of water, probably due to compensation effects of water on the catalytic activity of acetic acid, a weak acid.

Graphical abstractThe catalytic activity of sulfuric acid was found to be strongly inhibited by water for liquid-phase esterification of acetic acid with methanol. The decreased activity is suggested to be caused by preferential solvation of the catalytic protons by water. A proposed model successfully predicts esterification rate as reaction progresses.Dependence of the catalyzed rate constant, kc, on water concentration at T = 60 °C. The dotted line represents the fitted power law reaction model. Figure optionsDownload full-size imageDownload as PowerPoint slide