Mineral acid-activated sugarcane bagasse ash as solid acid catalyst for the liquid phase esterification of acetic acid with n-amyl, benzyl, and n-butyl alcohols

Abstract

Liquid phase esterification of carboxylic acids with alcohols is an important organic synthesis process in the petrochemical and fine chemical industries. These reactions required mineral acid catalysts, which are corrosive and difficult to be separated from the reaction mixture. Therefore, the use of solid acid catalysts is economically viable, reusable, and environmentally amicable. In this study, sugarcane bagasse ash (SCBA) was impregnated with 1–10 wt% of sulfuric acid (H2SO4) or perchloric acid (HClO4) for the liquid-phase esterification of acetic acid with n-amyl, benzyl, and n-butyl alcohols under various reaction conditions. The catalysts were characterized using X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier-transform infrared (FTIR), N2 sorption, and scanning electron microscopy (SEM). Their acidities were measured through the dehydration of isopropyl alcohol and pyridine adsorption FTIR. The effects of the acid activation of SCBA on its texture properties (such as surface area and the nature of the surface functional groups), acidity, and catalytic activity were studied in detail. FTIR of the pre-saturated catalysts with pyridine reflected the presence of Brønsted and Lewis acid sites. The concentrations of the acid sites were improved by increasing the percentages of acid loading. All the catalysts showed high catalytic activity with 100% selectivity to ester formation. The catalyst pretreated with H2SO4 showed the higher ester yields compared to that of treated with HClO4. The optimum reaction conditions were a reaction time of 2 h, an alcohol-to-acid molar ratio of 1:3, and catalyst loading of 0.5 g. The highest yields of n-amyl acetate, benzyl acetate, and n-butyl acetate of 98, 90.8, and 70.5%, respectively, were achieved over the SCBA pretreated with 10 wt% H2SO4 catalyst. The high catalytic performance of this catalyst is due to the high surface acidity generated by the inductive effect of the SO bond.