Hypercrosslinked Polymer Supported Sulfonic Acids For Esterification of Carboxylic Acids

This work focused on the catalytic performance of hypercrosslinked sulfonic acid for esterification of carboxylic acids. The commercially available hyercrosslinked poly(styrene-divinylbenzine)sulfonic acids, Purolite D5081 and D5082 were found to be active than macroporous Amberlyst 35 for esterification of long-chained carboxylic acid with ethanol. The high activities have been attributed to the high accessibility of the acid sites in the catalysts. However, a relationship between the deactivation od D5081 and D5082 and acid site leaching was observed, and the acid sites were found to leach out only in polar liquids. Further investigation revealed that the leachable acid sites are mainly sulphuric acid trapped in the polymer. Based on these findings, a series of solid sulfonic acids on the hypercrosslinked poly (St-DVB)MN 200 were prepared, with the trapped sulphuric acid thoroughly removed. The surface areas and porosities were measured, and the structures were characterised by solid-state NMR. The home-made catalysts were used for catalysing esterification of acetic acid with ethanol, and the catalyst that showed no site leaching was used for kinetic modelling of the reaction. It was shown that the Eley-Rideal(single site) model best fits acetic acid esterification catalysed by the chosen hypercrosslinked sulfonic acid. The home-made catalyst which was highly active and reusable in esterification of pure oleic acid was tested in esterification of oleic acid esterification blended with rapeseed oil in biodiesel synthesis. The catalytic synthesis was compared with that of macroporous Amberlyst 35 and gel-type C100X4. The effect of reaction parameters on the reaction kinetics was evaluated for the oil-blended esterification over the hypercrosslinked sulfonic acid catalysis, and the reaction conditions were optimised. Finally, the reusability of the hypercrosslinked sulfonic acid was studied. This home-made hypercrosslinked catalyst in this reaction suffered from deactivation which is due to pore blocking and the loss of functional acid groups. The latter is caused by both sulfonic acid leaching and cation exchange with metal ions in the acidic oil.