Heavy gas oil hydrotreating over NiMo supported on alumina and alumina-silica

Presently, oil refining in Mexico has been focused into increased Maya heavy crude oil processing. This type of crude oil contains high levels of heavy hydrocarbons and poly-aromatic structure compounds containing metals (Ni + V), sulfur and nitrogen. On the other hand, the worldwide fuel specifications are now being considered that may require reducing the sulfur content for both gasoline and high-speed diesel fuels to less than 50-wt ppm by year 2005. Therefore, one alternative route is the Heavy FCC feeds pretreatment in order to improve the Fluid Catalytic Cracking catalyst performance increasing its life cycle and the quality of gasoline and diesel (without sulfur and low aromatic content). In this article the hydrotreating activity of heavy gas oil was studied over NiMo/Al₂O₃ and NiMo/Al₂O₃-SiO₂ at pilot plant level. These materials were characterized by scanning Electronic Microscopy; FTIR Pyridine thermodesorption, nitrogen physisorption and the elemental analysis. The nominal content of Mo was around 3.5 Mo atoms per square nanometer in both catalysts. It was found that the rate of Hydrodesulfurization (HDS) at 613K over NiMo/Al₂O₃-SiO₂ was higher than the observed for the NiMo/Al₂O₃ support (7.3E-2 > 5.4E-2 molS h^-1 g^-1), respectively. Furthermore, the rate of hydrodearomatization (HDA) for NiMo/Al₂O₃-SiO₂ showed better results than NiMo/Al₂O₃ at the same temperature range. Characterization data were correlated with the catalytic activity results. The activity of these catalysts showed significant differences when the alumina was modified by silica, where the apparent rate of conversion of sulfur and aromatic compounds were major for NiMo/ Al₂O₃-SiO₂ catalyst, as previously reported for other reactions.