No abstract

Resumo Nas últimas décadas, pesquisas estão sendo desenvolvidas para obtenção de materiais eficientes e economicamente viáveis para aplicação em diversos setores da indústria. Os materiais mesoporosos da família MCM-41 estão entre os candidatos eficazes pela facilidade de síntese e estrutura que favorece uma gama de aplicações. O objetivo desse trabalho foi apresentar uma abordagem rítica das características e propriedades dos materiais mesoporosos do tipo MCM-41, enfocando nos aspectos estruturais. Além isso, foram discutidas as vantagens e desvantagens do uso de sílica comerciais e alternativas. As fontes de sílica comerciais analisadas foram sílica gel e TEOS; já as fontes de sílica alternativas foram cinza da casca de arroz, quartzo e pó de vidro. Os materiais analisados foram sintetizados pelo método hidrotérmico e caracterizados por DRX, FTIR, BET e TG. Os resultados apresentados comprovam a eficiência das fontes de sílica alternativas na síntese do MCM-41, pois os materiais apresentaram propriedades texturais dentro dos padrões exigidos. Dessa forma, eles estão aptos a serem testados na indústria em substituição aos MCM-41 sintetizados com fonte de sílica comercial.

No abstract

Biomass has attracted considerable attention as energy, economic, and environmental asset, as result of its abundance and range of properties. The use of mesoporous catalysts during fast pyrolysis has been a highly important route to improve efficiency as well adding value to biomass. The addition of titanium to molecular sieves increases the efficiency of the pyrolysis reaction by improving production and selectivity of products of interest. This study aims at analyzing the catalytic pyrolysis products of elephant grass using titanium catalysts prepared at different Si/Ti molar ratios, i.e., 25 and 50. The material was supported on MCM-41 for the catalytic pyrolysis of biomass. The biomass pyrolysis reactions were performed in a micropyrolyzer coupled to a GC/MS analyzer. The Ti-MCM-41 samples were characterized by XRD, BET-specific area, and UV-visible. The distribution of pyrolysis products depended on process parameters such as temperature and catalyst type. The highest yield for hydrocarbon production, such as styrene, benzene, methylbenzene, and naphthalene, was observed at 600 °C using Si/Ti equal to 50.

This work assessed the thermal degradation of surfactants, i.e., tetradecyltrimethylammonium bromide (TTMA ? -C 17 H 38 NBr), cetyltrimethylammonium bromide (CTMA ? -C 19 H 42 NBr) and trimethyloctadecylammonium bromide (DTMA ? -C 21 H 46 NBr), used to obtain MCM-41-type mesoporous materials using Flynn-Wall kinetic model. The cationic surfactants and their mixture at ratios of 1:1 and 1:1:1 resulting materials were labeled C hydrothermal method were characterized by physical, chemical and microstructural analyses such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy, thermogravimetric and nitrogen adsorption-desorption plots (BET). The mesoporous materials showed a well-defined hexagonal arrangement from the calcination process and significant structural differences. The kinetic model was used to determine the apparent activation energy for the removal of pure surfactant and associated with pores of the MCM-41-type molecular sieve. From the kinetic study results, a decrease in activation energy was observed when using the mixture of surfactants, especially C 17 C 19 . Combining these results with XRD and BET analyses, it was observed that C 17 C 19 showed the largest surface area and pore volume along with hexagonal arrangement. The mixture of cationic surfactants of hydrophobic chains of different sizes used in the preparation of MCM-41 reduced the activation energy and surfactant removal.