With the depletion of conventional oil, heavy oil plays a significant role in the world energy market. Due to a great deal of impurities in heavy oils, the production and refining of it requires more advanced technologies, such as more efficient catalysts for hydroprocessing. Molybdenum based catalysts have been widely used in the petroleum industry for hydrotreating of heavy oil fractions. They can be used as both supported and unsupported catalysts. Supported catalysts suffer severe deactivation in the traditional hydrotreating process, whereas unsupported molybdenum catalysts have higher catalytic activity with better metal dispersion, and can be recovered, recycled or discarded in the process. In this study, micro/nano size (maximum 500nm) unsupported molybdenum catalysts were synthesized from a water/oil emulsion. These catalysts were prepared in a continuous mode particularly designed for online application to hydroprocessing, or to in situ upgrading. This ultradispersed solid has the potential application for both in-situ &ex-situ upgrading of heavy oil.
The depletion of conventional crude oil reserves urges the development and production of heavy oil reserves. This is particularly important for Canada since there are extensive heavy oil reserves in Alberta. These heavy oils contain considerable amount of impurities, such as sulfur compounds, compared to conventional oils. These impurities pose a lot of challenges for hydroprocessing operations at refineries because they tend to deactivate and poison the catalysts used in hydroprocessing operations.
One of the important reactions involved in hydroprocessing is hydrodesulfurization (HDS). Transition metal sulfides exhibit excellent properties in terms of sulfur removal. Catalysts are mainly molybdenum or tungsten disulfide, promoted with cobalt or nickel .
Molybdenum catalysts can be used as supported and unsupported catalysts in hydrotreating processes. At present, most of commercial hydroconversion processes use supported molybdenum catalysts. Supported catalysts suffer deactivation due to the deposition of carbonaceous components on the surface of the catalyst when they are used in conventional fixed bed reactors .
Dispersed molybdenum catalysts have a number of advantages over supported ones. These catalysts are less prone to deactivation so they are more suitable for processing heavier feeds , their submicron sizes ensure high activities due to a large specific surface area and are sufficiently small to be readily dispersed in the residual oil .
The present study aims at obtaining submicron sized molybdenum catalysts ex-situ from water-in-oil emulsions in a continuous mode in controlled ways. There are so far no reports published on the ex-situ synthesis of molybdenum catalysts in a continuous mode with emulsion-mediated route. This process will be a cost-effective approach for in-line production of upgraded heavy oils in refineries.
All experimental runs are based on a two-level full factorial experimental design (Fusion Pro software, S-Matrix Corporation). The number and range of experimental variables are set according to our previous experience and the equipment limitations.
The synthesis of the molybdenum catalysts is performed in a continuous mode (Fig. 1). First 6ml of surfactant (Brij 30 from Aldrich) was put in 200g of vacuum gas oil (VGO, boiling point is from 250 to 600 °C).