Working-state morphologies of ion exchange catalysts and their influence on reaction kinetics

The esterification of fatty acids is an important pretreatment step in the production of biodiesel from low-cost raw materials. It was thus used as a model reaction in a study of the influence of concentration variations of the polar component (methanol) in a reaction mixture on the morphology and functioning of ion exchange catalysts. For a gel-type ion exchange catalyst, a decrease in the methanol concentration proved to have unambiguously negative effects, as it induced de-swelling of the polymer matrix and diminished the accessibility of the active centers. For macroreticular ion exchange catalysts, on the other hand, the drop in methanol concentration had a positive influence on the efficiency of the catalytic action mechanism of the acidic centers. This was due to the existence of some swelling-independent porosity, causing a shift from a general to a specific catalysis-like mechanism.

Changes of the morphology of ion exchanger catalysts in response to variations of the reaction environment composition may influence both the accessibility of the catalytically active centers and mechanism of their action.Figure optionsDownload high-quality image (110 K)Download as PowerPoint slideResearch highlights▶ Ion exchangers are effective catalysts of fatty acid esterification. ▶ Their activity depends on alcohol concentration in the reaction mixture. ▶ Lowering of alcohol concentration inhibits activity of the gel-type catalysts. ▶ In macroreticular types it promotes access of fatty acid molecules to the acidic centers.