Avaliação do desempenho de catalisadores de cobalto na síntese de Fischer-Tropsch

Abstract

The purpose of this work is to study the efficiency of different cobalt-based catalysts for Fischer-Tropsch synthesis (SFT). For this purpose, two different catalysts were prepared. The first catalyst was a 20% percentage of cobalt supported on SBA-15 molecular sieve. The second catalyst was supported on MCM-41 molecular sieve, containing 20% active metal, cobalt, and 0.5% ruthenium, promoter of the reaction. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), physical adsorption of N2, dispersive energy X-ray fluorescence spectroscopy (FRX-ED), programmed temperature reduction (RTP) transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The characterization results revealed that the prepared materials had good mesopore structure and satisfactory surface area. X-ray diffraction showed that addition of cobalt and calcination did not modify the structure of the supports and that cobalt was in the form of cobalt oxide Co3O4. The impregnation of the metals in the carriers reduced the specific surface area and pore volume, however the structure of the molecular sieves (SBA-15 and MCM-41) was not altered. the presence of ruthenium in the Co/Ru/MCM-41 catalyst was not observed via XRD due to the small amount (0.5%) added. The catalytic test was performed on a sludge bed reactor and 5 pressure and temperature conditions were tested for two H2:CO ratios. For the Co/SBA-15 catalyst, temperatures ranged from 240-270 °C and pressures were in the range of 20-30 atm. H2:CO ratios of 1:1 and 2:1 were used. For all conditions tested, total conversion of CO to hydrocarbons was observed. The selectivity of C5+ hydrocarbons was higher at the lower H2: CO ratio (1.0) and when the temperature was kept at lower temperature (240 °C). The Co/Ru/MCM-41 catalyst was tested in only one H2:CO (1.0) ratio, with temperatures ranging from 200-270 °C and pressures of 20-30 atm. The catalyst activity was lower than Co/SBA-15. The main products of the synthesis were the hydrocarbons in the range of C2-4. The production of C5+ was favored at low temperature (200 °C) and low pressure (20 atm). The C10+ hydrocarbons had higher selectivity at lower pressure (20 atm) and higher temperature (270 °C).