Produção de hidrocarbonetos renovavéis a partir da pirólise termocatalítica de sebo bovino utilizando catalisadores mesoporosos de óxidos metálicos

Abstract

The need to study new energy sources has increased due to issues caused by the use of fossil fuels, such as acid rain, greenhouse effect, and global warming. This also impacts society, threatening the survival of humanity and long-term sustainability. A study was conducted on mesoporous MCM-41 catalysts with incorporated metallic oxides (Co/MCM-41, Mo/MCM-41, Ni/MCM-41, CoMo/MCM-41, NiMo/MCM-41 and NiCo/MCM-41) to produce renewable hydrocarbons from bovine tallow. The raw material was physicochemically characterized, and the synthesized catalysts had their structural, chemical, and morphological characteristics analyzed through X-ray Diffraction (XRD), X-ray Fluorescence (XRF), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS), confirming the formation and preservation of porous structures after the impregnation of metallic oxides. Activation energies with and without catalysts were determined according to isoconversional methods proposed by Ozawa-Flinn-Wall (OFW) and Kissinger Akahira Sunose (KAS), based on thermogravimetric analyses of bovine tallow and mixtures of bovine tallow with catalysts, with heating rates (β) of 10, 20, and 30 °C/min, and conversion rates (α) of 5, 10, 20, 30, 40, 50, 60, 70, 80, and 90%. The catalysts produced in this study, according to both methods, proved effective in reducing the activation energy (Ea) in the thermocatalytic degradation reaction of bovine tallow. The average Ea for the thermal degradation of bovine tallow was 188.1 and 186.2 kJ/mol by the OFW and KAS models, respectively. With the presence of catalysts, the average Ea found showed lower values, especially for reactions in the presence of Mo/MCM-41, with 147.8 (OFW) and 143.8 kJ/mol (KAS), representing an average reduction of approximately 21% of the raw material's Ea according to the OFW model and approximately 22% according to the KAS model. Both models used showed satisfactory results, with R2 above 0.95, confirming the reliability of the methods. These results were essential in obtaining parameters for thermocatalytic pyrolysis. The thermal pyrolysis reaction of bovine tallow produced a high percentage of hydrocarbons (31.76%). This percentage increased with the addition of catalysts to the reaction process, reaching about 75% with CoMo/MCM-41, 76% with Ni/MCM-41, and 85% with NiCo/MCM-41. As for the percentage of hydrocarbons formed in thermal pyrolysis, production was observed at 52.2% in the bio-kerosene range, 70.4% in the green diesel range, and 14.6% of hydrocarbons with chains above C24. While thermocatalytic pyrolysis favors deoxygenation through decarboxylation, producing an even higher percentage of hydrocarbons, especially in the green diesel range. The use of MCM-41 catalysts, Ni/MCM-41, Mo/MCM-41, Co/MCM-41, NiMo/MCM-41, CoMo/MCM-41, and NiCo/MCM-41 produced, respectively, 51.0%, 34.0%, 38.6%, 42.8%, 32.5%, 36.8%, and 40.0% in the bio-aviation kerosene range and 87.9%, 88.6%, 83.0%, 90.6%, 98.4%, 95.7%, and 93.3% in the green diesel range. Thus, the production of bio-oil from bovine tallow by catalytic pyrolysis proves to be a promising alternative, given the high production of hydrocarbons at the expense of oxygenated compounds, remaining an important raw material in biofuel production and in minimizing environmental impacts derived from its production, using catalysts impregnated with metallic oxides.