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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.

Unconventional feedstocks, such as heavy vacuum residue (VR), have become potential candidates that could be positively exploited to meet the increasing demand of high-value transportation fuels, in view of the growing scarcity in other energy sources. However, such feeds contain extremely high-molecular-weight species, besides many impurities of heteroatom-containing organic compounds that lead to quick fouling, poisoning, and deactivation of catalysts. This causes a significant pressure decrease during the conventional hydrocracking in ebullated- or fixed-bed reactors. In contrast, slurry-phase hydrocracking has the ability to overcome these drawbacks through the enhancement of hydrogenation reactions in the presence of the dispersed catalysts. Slurry-phase processing is a resilient technology, which employs catalysts that are generally categorized as heterogeneous solid supported catalysts and homogeneously dispersed catalysts. The dispersed catalysts are classified into water or oil-soluble types and fine powders. Soluble dispersed catalysts show higher catalytic activity, compared to finely powdered catalysts, because of the in situ formation of infinitesimally minute active metal sites at high surface-area-to-volume ratios. Recent technologies and studies on heavy oil upgrading that implement the dispersed catalysts have been reviewed. Studies using a combination of two-phase catalysts have also been included.

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