Solventless esterification of glycerol with p-methoxycinnamic acid catalyzed by a novel sulfonic acid mesoporous solid: Reaction kinetics

As a way to valorise glycerol, the main by-product of biodiesel, this study is focused on the production of esters of p-methoxycinnamic acid and glycerol. These esters can replace hazardous octylmethoxycinnamate in the cosmetic industry, which is thought to act as an endocrine disruptor and can interfere with thyroid function. Several sulfonated mesoporous catalysts, with and without endcapping, were easily synthetized using several alcohols as porogens. These catalysts were characterized for structure and surface area, chemical composition and acidity, and tested under solventless conditions for the esterification of glycerol with p-methoxycinnamic acid. Their activity was similar to that of p-toluenesulfonic acid. The best catalysts for the reaction under study was the end-capped mesoporous solid prepared in isopropanol. Finally, the selected catalyst was tested in 9 runs conducted at 150–170 °C and at molar ratios glycerol:p-methoxycinnamic acid ranging from 3:1 to 9:1. The kinetic model that better fits to the experimental data comprises two esterification reactions in-series and a first-order catalyst deactivation. The activation energies were 87.33 ± 5.67 kJ mol−1 for the average esterification to the monoglycerides, 69.17 ± 9.84 kJ mol−1 in average for the reactions yielding the diglycerides, and 104.00 ± 15.30 kJ mol−1 for the catalyst deactivation.