Avanços em catalisadores sólidos ácidos derivados de carbono na valorização de resíduos de biomassa

Abstract

Carbon materials are efficient precursors for the production of solid acid catalysts with the potential to replace homogeneous catalysts, such as sulfuric acid. After treatment, they can exhibit attractive physicochemical properties, such as thermal stability, electrical properties, acidic surface, high surface area, and satisfactory pore volume and distribution. They can also yield low-cost, sustainable, and efficient catalysts, much like the catalysts produced in this research. Thus, the aim of this work is to produce sustainable acid catalysts derived from biomass residues and apply them to the esterification reaction. Chapter 1 provides a brief review of carbon materials, as well as their applications. It covers the main methods of obtaining biochar and hydrochar, and the sulfuric acid functionalization employed in the research. Chapter 2 describes the production of sulfonated catalysts derived from guarana residues. Traditional carbonization/sulfonation and one-pot hydrothermal carbonization were used to synthesize them. They were characterized by X-ray diffraction (XRD), scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), N2 adsorption-desorption and Boehm titration. The one-pot sample CGH10* showed 96% conversion in the esterification with a 5% mass catalyst, oleic acid/methanol molar ratio of 1:12 at 100 °C for 1 hour. It remained stable up to the fourth cycle during reuse, at 78% conversion. It was also tested in the esterification reaction of free fatty acids (FFA) in waste cooking oil. A maximum FFA conversion of 63% was achieved using a 5% mass catalyst, 2 hours, an oil/methanol molar ratio of 1:12, and 75° C. Chapter 3 describes the production of sulfonated carbon sphere catalysts derived from acai berry residues, produced via hydrothermal carbonization with and without the use of citric acid as a catalyst. They were characterized by XRD, X-ray photoelectron spectroscopy (XPS), SEM-EDS, thermogravimetric-mass spectroscopy (TG-MS), FTIR, and Boehm titration. Catalytic activity was tested up to the fifth reuse, using a 5% mass catalyst, 1-hour reaction time at 100 °C, and an oleic acid/methanol molar ratio of 1:12. The CS.100-1 catalyst showed 91-88% conversion up to the fifth use. Reaction parameters were optimized, but there was no significant variation in oleic acid conversion (89-93%). The results indicate that catalytic activity is related to the sulfonic groups anchored on the catalyst's surface. The use of biomass residues prevents improper material disposal. Furthermore, these catalysts are rapidly produced, economically valuable, and simple, exhibiting excellent catalytic activity and recyclability.