Effect of Metal Loading in NiMo/Al2O3 Catalysts on Maya Vacuum Residue Hydrocracking

Hydrocracking catalysts with large porosity need to be developed to treat heavy oil feedstocks rich in large molecular weight components such as asphaltenes and withstand deactivation due to coke formation. In this work, catalysts were prepared by impregnation of varying NiMo loadings on a mesoporous Al2O3 support. The effect of metal loading on the hydrocracking of a vacuum residue at three temperatures (400, 425, and 450 °C) was studied in a batch microbomb reactor. Catalysts were reutilized in a second reaction with fresh feed to assess their activity following the initial period where results are dominated by a large carbon deposition. The textural properties and the coke content on the spent catalysts were evaluated after both reactions. It was found that the reaction temperature had an important effect on the conversion of the fraction with a boiling point above 450 °C, whereas metal loading had minimal impact. On the other hand, metal loading had a significant effect on hydro­de­asphalteni­za­tion (HDA); higher asphaltene conversions were obtained with higher metal loading. Reaction temperature had an influence on HDA, particularly for lower metal loadings, as catalysts with higher loadings showed significant activity at the lower temperatures studied. It was observed that coke deposits were mainly formed during the initial hour of reaction with little additional coke being formed in the reutilization of the catalysts. More deposits were obtained at lower reaction temperature, as coke precursors, polyaromatic hydrocarbons, polymerize into coke. No evidence of pore mouth plugging was observed, indicating that catalysts could accommodate coke while retaining most of their textural properties. Catalysts with higher metal loadings took longer to reach a stable amount of deposits, but they stabilized at an overall smaller coke deposition and retained significant HDA activity.