Determination of the thermal stability of sulfonic groups in heterogeneous acid catalysts derived from residue of guarana amazon biomass

Heterogeneous acid catalysts derived from residues of the guarana ( Paullinia cupana ) industry were synthesized using the traditional method of carbonization/sulfonation and one-pot hydrothermal carbonization/sulfonation. These residues present physicochemical properties that are suitable for synthesis of solid acid catalysts. The sulfonated-based carbon catalysts were characterized by X-ray diffraction, thermogravimetry, infrared spectroscopy (FTIR), EDS-coupled scanning electron microscopy for elementary mapping, low-temperature N 2 sorption and Boehm titration. The catalytic activity was tested by reaction of esterification of oleic acid with methanol with catalyst loading of 5% by mass, molar ratio oleic acid/methanol 1:12 at 100 ºC for 1 h. The catalyst, produced via the traditional method, showed a yield of 93%, and the one-pot hydrothermal catalyst a yield of 96%. In the reuse tests, the hydrothermal sample was stable for four cycles, with a yield of 78%, and the traditional sample showed a sharp reduction in yields. The best activity of the one-pot hydrothermal catalyst was also tested in a free fatty acid (FFA) esterification reaction in cooking oil residues. The effects of reaction time, methanol to oil ratio, catalyst concentration and temperature on conversion were investigated. The results show maximum FFA conversion of 63% using 5% by mass catalyst, 2 h, molar ratio oil/methanol 1:12 and 75 °C. The use of this industrial waste for the production of catalysts can help to avoid accumulation of materials that are usually inadequately disposed of. In addition, its production is cheap, fast and simple and has excellent catalytic activity.