Atividade e estabilidade de catalisador à base de carbono sulfonado na reação de esterificação: influência da temperatura de pirólise no processo de funcionalização

Abstract

In the present study, the pyrolysis temperature on the activity and catalytic stability of sulfonated biochars, from the agroindustrial waste of murumuru kernel shell, was evaluated in the esterification reaction of oleic acid with methanol. In view of the investigation of factors related to catalytic functionalization and its impact on reuse processes, carbonaceous materials were synthesized by direct pyrolysis under different carbonization temperatures, at 450, 600 and 750 °C. The process of biochars functionalization was carried out by sulfonation with concentrated sulfuric acid at 200 °C and 4 h. The materials were characterized in terms of determining the density of sulfonic groups, Scanning Electron Microscopy (SEM), Energy Dispersion X-Ray Spectroscopy (EDS), Elemental Analysis (CNHS), Fourier Transform Infrared Spectroscopy (FT- IR), Raman Spectroscopy, Thermogravimetric Analysis (TG) and X-Ray Excited Photoelectron Spectroscopy (XPS). The influence of the variables temperature and reaction time on the catalytic performance and reuse capacity of the catalysts was also evaluated. The data obtained showed that the functionalization with sulfonic groups occurred directly in the carbon chain of the biochars, higher temperatures carbonization resulted in more stable polycondensed carbonaceous catalysts and a higher degree of structural order. The carbonized catalyst at 750 °C achieved the conversion of oleic acid in the esterification reactions of 98.37% and maintained in the third reaction cycle conversion of 89.30%. Such a catalyst also has the highest content of sulfur groups, even after reuse processes. The increase in temperature and time in the reaction medium was able to improve the reuse capacity of relatively low stability catalysts. Thus, these results show the impact of the pyrolysis temperature in obtaining catalysts with greater activity and catalytic stability in the esterification reactions, and in this way provide great support for the development of new heterogeneous sulfonated carbon-based catalysts, applied in the biodiesel production process. Furthermore, they corroborate the high potential for using the residual biomass of murumuru kernel shell in the development of a new material.