Effect of polymer matrices of gels bearing a sulfo group on their catalytic properties for acetalization of glycerol to solketal and esterification of oleic acid to ethyl oleate

Abstract

A novel type of copolymer gel bearing the sulfo group was developed as a heterogeneous acid catalyst for the solvent free acetalization of glycerol with acetone to form a desirable solketal, as well as the solvent free esterification of oleic acid with ethanol to form ethyl oleate as a biodiesel fuel. The copolymer gels were synthesized by the copolymerization of a primary monomer (ethoxy diethyleneglycol acrylate (EDGA), N-isopropylacrylamide (NIPA), etc.) with 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS). The copolymer gels, such as EDGA-co-AMPS gel and NIPA-co-AMPS gel, successfully catalyzed both reactions with a higher reaction rate than those of AMPS gel and the conventional sulfonic ion exchange resin (Amberlyst). According to Le Chatelier's principle, if a gel catalyst absorbs reactants well, and expels or poorly absorbs products, the apparent rate of the reaction occurring within the gel is enhanced. This hypothesis was examined by analyzing the solution absorptions of these gels and their reaction rates, including Eley–Rideal kinetic analysis.