Kinetics of Promotional Effects of Oil-Soluble Dispersed Metal (Mo, Co, and Fe) Catalysts on Slurry Phase Hydrocracking of Vacuum Gas Oil

This study deals with the promotional effects of dispersed cocatalysts on hydrocracking of vacuum gas oil (VGO). The influence of oil-soluble molybdenum-, iron-, and cobalt-based materials is investigated with and without the presence of a commercial first-stage W-Ni/Al₂O₃-SiO₂ hydrocracking catalyst. The experiments are conducted in a batch autoclave reactor (at 8.5 MPa and 420°C). The dispersed metal catalysts enhanced the hydrogenation activity and reduced coke formation. Cobalt- and molybdenum-based cocatalysts show lower coke formation than the Fe cocatalyst. An addition of 500 ppm of Co or Mo cocatalyst decreased the amount of coke to 0.9 wt % from 2.5 wt % observed during the thermal cracking. The dispersed catalyst together with the supported catalyst shows similar decrease in coke formation and enhanced the yield of naphtha. A 5-lump kinetic model is developed based on the experimental data using dispersed and supported catalysts. The model incorporates coke formation and conversion of VGO to distillate, naphtha, and C1-C5 hydrocarbons. The VGO hydrocracking to distillate requires least activation energy (1.5 kcal/mol) as compared to the other competing reactions. On the basis of kinetic model results, it is concluded that VGO is most likely cracked to form distillate, followed by cracking of distillate, then distillate is cracked to form naphtha, and finally naphtha is cracked to gases.