Review of Molybdenum Disulfide Research in Slurry Bed Heavy Oil Hydrogenation

With the growing demand for gasoline and diesel fuel and the shortage of conventional oil reserves, there has been extensive interest in upgrading technologies for unconventional feedstocks such as heavy oil. Slurry bed reactors with high tolerance to heavy oil have been extensively investigated. Among them, dispersive MoS₂ is favored for its excellent hydrogenation ability for heavy oil even under harsh reaction conditions such as high pressure and high temperature, its ability to effectively prevent damage to equipment from deposited coke, and its ability to meet the requirement of high catalyst dispersion for slurry bed reactors. This paper reviews the relationship between the structure and hydrogenation effectiveness of dispersive molybdenum disulfide, the hydrogenation mechanism, and the improvement of its hydrogenation performance by adding defects and compares the application of molybdenum disulfide in heavy oil hydrogenation, desulfurization, deoxygenation, and denitrification. It is found that the current research on dispersive molybdenum disulfide catalysts focuses mostly on the reduction of stacking layers and catalytic performance, and there is a lack of research on the lateral dimensions, microdomain regions, and defect sites of MoS₂ catalysts. The relationship between catalyst structure and hydrogenation effect also lags far behind the application of MoS₂ in the precipitation of hydrogen, etc. Oil-soluble and water-soluble MoS₂ catalysts eventually need to be converted to a solid sulfide state to have hydrogenation activity. The conversion history of soluble catalysts to solid-type catalysts and the key to their improved catalytic effectiveness remain unclear.

Molybdenum Carbide and Sulfide Nanoparticles as Selective Hydrotreating Catalysts for FCC Slurry Oil to Remove Olefins and Sulfur

As the two types of major impurities in FCC slurry oil (SLO), olefins and sulfur seriously deteriorate the preparation and quality of mesophase pitch or needle coke. The development of a hydrotreatment for SLO to remove olefins and sulfur selectively becomes imperative. This work presents the potentiality of dispersed Mo₂C and MoS₂ nanoparticles as selective hydrotreating catalysts of SLO. Mo₂C was synthesized by the carbonization of citric acid, ammonium molybdate and KCl mixtures while MoS₂ was prepared from the decomposition of precursors. These catalysts were characterized by XRD, HRTEM, XPS, BJH, BET, and applied to the hydrotreating of an SLO surrogate with defined components and real SLO. The conversion of olefins, dibenzothiophene and anthracene in the surrogate was detected by GC-MS. Elemental analysis, bromine number, diene value, ¹H-NMR and spot test were used to characterize the changes of the real SLO. The results show that hydrotreating the SLO surrogate with a very small amount of Mo-based nanoparticles could selectively remove olefins and sulfur without the overhydrogenation of polyaromatics. Mo₂C exhibited much better activity than MoS₂, with 95% of olefins and dibenzothiophene in the surrogate removed while only 15% anthracene was hydrogenated. The stability of the real SLO was significantly improved. Its structural parameters changed subtly, proving the aromatic macromolecules had been preserved.

Recycling the CoMo/Al2O3 catalyst for effectively hydro-upgrading shale oil with high sulfur content and viscosity

Hydrotreatment is an effective upgrading technology for removing contaminants and saturating double bonds. Still, few studies have reported the hydro-upgrading of shale oil, with unusually high sulfur (13200 ppm) content, using the CoMo/Al₂O₃ catalyst. Here we report an extensive study on the upgrading of shale oil by hydrotreatment in a stirred batch autoclave reactor (500 ml) for sulfur removal and viscosity reduction. From a preliminary optimization of the reaction factors, the best-operating conditions were 400 °C, an initial H₂-pressure of 5 MPa, and an agitation rate of 800 rpm, a catalyst-to-oil ratio of 0.1, and a reaction time of 1 h. We could achieve a sulfur removal efficiency of 87.1% and 88.2% viscosity reduction under the optimal conditions. After that, the spent CoMo/Al₂O₃ was repeatedly used for subsequent upgrading tests without any form of pre-treatment. The results showed an increase in the sulfur removal efficiency with an increase in the number of catalyst runs. Ultimately, 99.5–99.9% sulfur removal from the shale oil was achieved by recycling the spent material. Both the fresh and the spent CoMo/Al₂O₃ were characterized and analyzed to ascertain their transformation levels by XRD, TEM, TG, XPS, TPD and N₂ adsorption analysis. The increasing HDS efficiency is attributed to the continuing rise in the sulfidation degree of the catalyst in the sulfur-rich shale oil. The light fraction component in the liquid products (IBP–180 °C) was 30–37 vol% higher than in the fresh shale oil. The product oil can meet the sulfur content requirement of the national standard marine fuel (GB17411-2015/XG1-2018) of China.

The CoMo/Al₂O₃ catalyst was used to upgrade shale oil. Sulfur removal was increased on the spent catalyst. The transition of oxidic Mo-species into active phase MoS₂ was observed with recycling. The high sulfidation degree of the CoMo/Al₂O₃ suppressed deactivation by coking.