Material mesoporoso MCM-41 sintetizado a partir da biossílica extraída do cauxi da Amazônia como catalisador na produção de biodiesel

Abstract

The synthesis of mesoporous materials, such as MCM-41, due to its wide applications in areas like adsorbents, catalysts, and controlled drug release. Although MCM-41 is easily synthesized, exhibits high thermal stability, and possesses a large surface area with significant pore volume, its limitations, primarily related to low acidity, can be improved through the impregnation of heteropolyacids (HPA) or sulfated zirconia (SO_4^(2-)/ZrO_2). In the present study, MCM-41 samples were hydrothermally synthesized using a mixture of biogenic silica, NaOH, and cetyltrimethylammonium bromide (CTAB), with the silica derived from the spicules of the freshwater sponge (Metania kiliani). This alternative source, known as "cauxi," contains 90% silica. Catalysts were prepared by aqueous impregnation of commercial 12-tungstophosphoric acid (HPW) and synthesized sulfated zirconia (ZS) in different proportions (5, 10, 15, 20, and 30%) on the previously prepared MCM-41. The materials were extensively characterized using techniques such as XRF, XRD, FTIR, SEM, and N2 adsorption/desorption analysis (BET and BJH methods). Additionally, MCM-41 was characterized by TEM. The catalysts were tested in the esterification reaction of oleic acid with methanol. Analytical results indicated the complete removal of CTAB after the calcination of MCM-41. Infrared spectra confirmed the presence of characteristic molecular sieve groups, while XRD identified the phases present in the catalysts, including MCM-41 (hexagonal structure; P6mm), HPW (cubic), and a mixture of ZS phases (tetragonal and monoclinic). The diffraction patterns revealed broadened reflections, indicating the presence of amorphous phases due to the material mixture. BET analysis demonstrated the presence of mesopores with high surface area, especially in calcined MCM-41. A 2³ factorial experimental design was conducted to investigate the optimal parameters (time, molar ratio, and catalyst content) on the reactional and kinetic influence of the oleic acid conversion reaction into biodiesel. The 2³ factorial experimental design was conducted to investigate the best parameters (5-hour reaction time, 1:14 molar ratio, and 5% catalyst) influencing the reaction and kinetics of oleic acid conversion to biodiesel at a fixed temperature of 65 ºC. For the PCHPW30 catalyst, the biodiesel yield was 89% by titration and 82% by FTIR, respectively. On the other hand, for the PCZS30 catalyst, a yield of 61% was obtained by FTIR. Kinetic studies indicated that both catalysts exhibited pseudo-second-order profiles. In summary, the research demonstrated the successful synthesis of the hexagonal phase of MCM-41 and the feasibility of impregnation with 12-tungstophosphoric acid and sulfated zirconia for the studied catalysts. The study highlighted the significant influence of catalyst content on esterification reactions.