Conventional hydroprocessing

Conventional hydroprocessing catalysts contmn oxidic active metal forms of Mo, W, Co and Ni, which are converted into their active sulfided forms by sulfiding in an hydroprocessing reactor (in-situ sulfiding). Since the sulfiding reactions are rather highly exothermic, careful... 

The information on carbon-supported catalysts has been dominated by cata-lytically active metals that are part of the conventional hydroprocessing catalysts, i.e. Co(Ni)Mo(W). In a sulfided form, the structure of the Co(Ni)-Mo(W)-S active phase in these catalysts should approach that of Type-II phase observed on the y-Al203-supported catalysts after a high-temperature sulfidation. " Apparently, there is a sufficient driving force for a direct interaction of carbon with either Mo or sulfur leading to the formation of the Mo-C(S) bonds. Then, in carbon-supported catalysts, the presence of another active phase, i.e. Co-Mo C(S), appears to be plausible. The formation of metal carbides may take place if the supply of sulfur to maintain the catalyst surface in a sulfided form becomes limited, particularly if such a state persists for an extended period. ... 

The kinetics and mechanism have been investigated using both model compounds, as well as petroleum feeds and biofeeds. In this regard, studies involving carbon and carbon-supported catalysts in parallel with conventional hydroprocessing catalysts are of a particular interest. Such studies provide a database required for elucidation of the effects of carbon support in comparison with traditionally used y-Al203 support. 

Liquid products contain sulfur and nitrogen and must be hydroprocessed to improve quality. Separate hydroprocessing units for upgrading the naphtha, kerosene, and gas oil fractions can be used to optimize the overall process. Refined gas oil or diesel fuel is aromatic in character and contains more cycloparaffins than conventional crude oil. The resulting fuel is low in cetane number, high in density, and typically has very good low-temperature handling properties. 

The electrical conductivity of ethanol is higher than hydroprocessed, conventional fuels. This theoretical safety advantage is of benefit and can help to prevent static buildup or discharge during transfer and loading of fuel. However, the high electrical conductivity can enhance galvanic and electrolytic corrosion of steel, especially in water-contaminated systems. 

The distinction in Table XX between hydrotreating and hydrocracking processes is frequently misleading when residuum hydroprocessing is being considered. Hydrotreating conventionally has been referred to processes... 

With these criteria in mind, various reactors have been designed to satisfy the needs of the hydroprocesses, including hydrodesulfurization (McEvoy, 1996). Thus, reactors may vary from as little as 4 ft. in diameter to as much as 20 ft. in diameter and have a wall thickness anywhere from 4.5 to 10 in. or so. These vessels may weigh from 150 tons to as much as 1000 tons. Obviously, before selecting a suitable reactor, shipping and handling requirements (in addition to the more conventional process economics) must be given serious consideration. 

Figure 19-39 shows examples of gas-liquid-solid fluidized-bed reactors. Figure 19-39a illustrates a conventional gas-liquid-solid fluidized bed reactor. Figure 19-39h shows an ebuUating bed reactor for the hydroprocessing of heavy crude oil. A stable fluidized bed is maintained by recirculation of the mixed fluid through the bed and a draft tube. Reactor temperatures may range from 350 to 600°C (662 to 1112°F) and 200 atm (2940 psi). An external pump sometimes is used instead of the built-in impeller shown. Such units were developed for the liquefaction of coal. 

The ex-situ presulfided hydroprocessing catalysts processed by Sulficat Process have been successfully used over 30,000 tons worldwide in petroleum refining industry since 1986. The main advantage over a conventional in-situ sulfiding is to allow a refinery a quick and efficient start-up without requiring addition of a sulfur compound. 

The hydrodeoxygenation plays a minor role in the case of the conventional feeds, whereas for the feeds derived from coal, oil shale, and, particularly from the biomass, its role can be rather crucial. This process also occurs during the hydroprocessing of petroleum fractions along with hydrodesulfurization, hydrodenitrogenation. 

The information on the activity of various carbons for hydroprocessing reactions involving model compounds is usually part of the more comprehensive studies involving carbon-supported catalysts. In such studies, the activity of carbon is only determined as a baseline for investigating catalytic effects of the addition of metals to carbon support. With respect to the catalytic activity of carbon alone, this makes the experimental results less conclusive. Moreover, the accuracy of the experimental data may be limited because of generally low conversions observed when carbons alone are used as catalysts. For the purpose of this review, the results from testing of carbon and conventional supports such as y-Al203 under identical conditions are of primary interest. 

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