Novel Ion-Exchange Catalysts for Reactions Involving Lipophilic Reagents: Perspectives in the Reaction of Esterifications of Fatty Acids with Methanol

Abstract

New catalysts for the esterification of fatty acids with methanol have been obtained from a gel type polystyrene-divinylbenzene resin (2 % cross-linked). To this purpose the starting resin was first acylated with either acetyl, butyrroyl or capryloyl groups and then sulfonated with concentrated sulfuric acid. The acylation degree ranged from 51 to 82 % and the ion exchange capacity ranged from 2.87 to 4.16 mmol/g. These catalysts were tested in the esterification of stearic acid with methanol (solution in edible oil: 5 % for the acid, 5 or 20 % for the alcohol) in a continuous glass reactor at 85 °C. At high relatively methanol concentration the catalytic activity is mainly correlated to the degree of swelling of the catalysts and the best one was the non-acylated benchmark (hence the most hydrophilic) material. At low methanol concentration the swelling is smaller and practically the same for all the catalysts. In spite of this their activity does not level down to the same value. Under these conditions the capryloyl functionalized catalysts, the most lipophilic ones, by far outperform the benchmark catalyst and in general the activity increases with the increasing lipophilic character of the catalyst. This is likely caused by the enhanced adsorption of the fatty acid close to the acidic active site, assisted by the lipophilic acyl groups.