The role of acidity in fatty acid esterification with heterogeneous silica catalysts impregnated with Zr and sulfates

The esterification reaction of oleic acid using heterogeneous catalysts can be a promising alternative for the production of biodiesel. This study proposed to obtain biodiesel from the esterification of oleic acid with the Zr-SBA-15 and SO 4 2− /Zr-SBA-15 catalysts obtained by inserting Zr and subsequent sulphation of SBA-15 synthesized by the hydrothermal method. Zr-SBA-15 and SO 4 2− /Zr-SBA-15 catalysts were initially synthesized by the wet impregnation method, followed by the sulphation process. The characterization of the catalysts was performed by: X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, nitrogen adsorption/desorption, scanning electron microscopy, energy-dispersive X-ray spectroscopy and acidity test, with the aim of identifying the structure, composition and verification of the presence of acidic sites. The characterization results indicated that SBA-15 preserved the ordered hexagonal structure, after the incorporation of Zr, with the presence of nanoparticles of this metal dispersed on the surface and inside the microporous and mesoporous channels of the Zr-SBA-15 catalyst. After sulphation, the amount of acid sites increased and the ordered structure was maintained. For the Zr-SBA-15 and SO 4 2− /Zr-SBA-15 catalysts, there was the formation of tetragonal and monoclinic structures of ZrO 2 . The catalytic activity was evaluated by the esterification reaction of oleic acid via the methyl route. Biodiesel obtained with SO 4 2− /Zr-SBA-15 presented physico-chemical properties within the standards specified by ANP Resolution N° 798/2019 and a better yield of 80.7%. SBA-15 did not show catalytic activity for the oleic acid esterification reaction under the reaction conditions of this study.