Transesterification of triacetin with methanol on various solid acid catalysts: A role of catalyst properties

Abstract

Present studies concentrated on a comparison of catalytic performance of number of solid acid catalysts, namely Amberlyst-15, Nafion-SAC-13, polyaniline-sulfate, silver and cesium salts of H 3PW 12O 40 in transesterifiaction of triglycerides with methanol. Reaction was studied for triacetin, the short triglyceride and for castor oil consisting of vegetable fatty acid esters under mild reaction conditions (atmospheric pressure, 50 °C). The catalysts were characterized by measuring textural (specific surface area, porosity, pore diameter) and acid (concentration and the strength of acid centers) properties. The affinity of catalyst to highly hydrophobic triglyceride reactant relative to that toward rather hydrophilic glycerol was also evaluated from the measurements of contact angles for droplets of triacetin, castor oil and glycerol on the surface of pressed tablet of catalyst. This affinity of catalysts was also evaluated from the drop of catalyst activity induced by glycerol added to the reaction mixture or by pre-treatment of catalyst with triacetin. Cs 2HPW 12O 40 salt was the most active catalyst, but it deactivated in the transesterification. The highest strength of acid sites and high affinity to glycerol was determined for this Cs salt. Thus, affinity of studied catalysts toward glycerol and the strength of acid sites seem to be decisive factors for their activity and in particular for deactivation due to polar reagents adsorption. Greater affinity toward glycerol and higher strength of acid sites, deactivation of catalysts would be easier.