Recent Advances in Heavy Oil Upgrading Using Dispersed Catalysts

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.