Processes hydrodesulfurization

Thermal Cracking. In addition to the gases obtained by distillation of cmde petroleum, further highly volatile products result from the subsequent processing of naphtha and middle distillate to produce gasoline, as well as from hydrodesulfurization processes involving treatment of naphthas, distillates, and residual fuels (5,61), and from the coking or similar thermal treatment of vacuum gas oils and residual fuel oils (5). 

Sulfur, another inorganic petrochemical, is obtained by the oxidation of hydrogen sulfide 2H2S + O2 — 2H2 0 + 2S. Hydrogen sulfide is a constituent of natural gas and also of the majority of refinery gas streams, especially those off-gases from hydrodesulfurization processes. A majority of the sulfur is converted to sulfuric acid for the manufacture of fertilizers and other chemicals. Other uses for sulfur include the production of carbon disulfide, refined sulfur, and pulp and paper industry chemicals. 

Although desulfurization is not the goal of cat cracking operations, approximately 50% of sulfur in the feed is converted to HjS. in addition, the remaining sulfur compounds in the FCC products are lighter and can be desulfurized by low-pressure hydrodesulfurization processing. 

Today s society asks for technology that has a minimum impact on the environment. Ideally, chemical processes should be clean in that harmful byproducts or waste are avoided. Moreover, the products, e.g. fuels, should not generate environmental problems when they are used. The hydrogen fuel cell (Chapter 8) and the hydrodesulfurization process (Chapter 9) are good examples of such technologies where catalysts play an essential role. However, harmful emissions cannot always be avoided, e.g. in power generation and automotive traffic, and here catalytic clean-up technology helps to abate environmental pollution. This is the subject of this chapter. 

Kolodziej, R. J. Harrison, G. E., and Mckinley, D. H., Multi-step hydrodesulfurization process. Patent No. US5968347. 

Schematic showing the hydrodesulfurization process in refineries. (From Yamaguchi, N., Trans-Energy Research Associates, Seattle, WA. With permission.)...

These metals form chalcogenolate complexes in several oxidation states, and from the application-oriented point of view manganese compounds have been synthesized as models for hydrodesulfurization processes and rhenium and technetium derivatives as models for radiopharmaceuticals. 

Diesulforming A hydrodesulfurization process which used a molybdenum-containing catalyst. Developed by the Husky Oil Company and first operated in Wyoming in 1953. 

GO-flning [Gas-oil refining] A hydrodesulfurization process adapted for gas oil. The proprietary catalyst is regenerable. Developed by Esso Research Engineering Company and the Union Oil Company of California and jointly licensed by them. First commercialized at Wakayama, Japan, in 1968 by 1972, nine units had been built. 

Gulfining [Gulf refining] A hydrodesulfurization process adapted for heavy gas oils. Developed by the Gulf Research Development Company in the early 1950s. 

Hyperforming A hydrodesulfurization process in which the catalyst moves by gravity down the reactor and is returned to the top by a solids conveying technique known as hyperflow. Developed by the Union Oil Company of California in 1952 and first operated commercially in 1955. 

RDS Isomax [Residuum desulphurization] A hydrodesulfurization process for removing sulfur compounds from petroleum residues, while converting the residues to fuel oil. Developed by Chevron Research Company in the early 1970s. Ten units were operating in 1988. See also VGO Isomax, VRDS Isomax. 

RESID-fining [Residuum refining] A hydrodesulfurization process adapted for petroleum residues. Developed by Esso Research Engineering Company and licensed by them... 

Ultrafining Two hydrodesulfurization processes developed by Standard Oil of Indiana, one for petroleum residua and one for vacuum gas oil. 

Unifining A hydrodesulfurization process developed jointly by UOP and Union Oil Company of California. It is now incorporated in the UOP hydiotreating and UOP Unibon processes. 

VGO Isomax [Vacuum gas oil] A hydrodesulfurization process adapted for treating vacuum gas oil, a petroleum fraction. Developed by Chevron Research Company in the early 1970s. In 1972, five plants were in operation and six were under construction. See also RDS Isomax and VRDS Isomax. 

VRDS Isomax [Vacuum residua desulphurization] A hydrodesulfurization process adapted for processing the residues from the vacuum distillation of the least volatile fraction of petroleum. An extension of the RDS Isomax process, developed and piloted by Chevron Research Company in the early 1970s. In 1988, one unit was under construction and one was being engineered. 

This compound is notorious as a hard sulfide that cannot be removed from petroleum by current hydrodesulfurization processing. Oxidation by tert-butyl hydroperoxide occurs readily when 1 is used as the catalyst. After trying several combinations, this was the most effective 0.5 mmol of DMDBT, 1.75 mmol B OOH, and 0.05 mol% of 1 were placed in refluxing toluene (384 K). A quantitative yield of the dioxide was obtained in 2h. The oxidation product is insoluble in toluene and can readily be removed by filtration (42). 

Himmelblau, D.M. and Bickel, T.C. (1980) Optimal expansion of a hydrodesulfurization process. Computers el Chemical Engineering, 4, 101—112. 

Fig. 38. Comparison between the conventional single-stage hydrodesulfurization process and co-current/countercurrent reaction system (153).

Light oils are invariably hydroprocessed in gas-liquid-solid catalyst trickle-bed reactors (TBR). In these reactors, both the hydrogen and hydrocarbon streams flow down through one or more catalyst beds. A typical schematic diagram is shown in Figure 5.2—41 as an example of hydrodesulfurization process [60, 61]. 

Figure 5.2—41. Typical hydrodesulfurization process flow (after Meyers [60]).

One of the more important uses of molybdena catalysts is in hydrodesulfurization processes. In operation, the catalyst is usually presulfided with hydrogen sulfide/hydrogen or other suitable sulfiding agents. Even when presulfiding is not employed, the catalysts become... 

Nevertheless, it became evident that reforming processes instituted in many refineries were providing substantial quantities of by-product hydrogen, enough to tip the economic balance in favor of hydrodesulfurization processes. In fact, the need for such commercial operations has become more acute because of a shift in supply trends that has increased the amount of high-sulfur crude oils employed as refinery feedstocks. 

It appears that the high molecular weight species originally present in the feedstock (or formed during the process) are not sufficiently mobile (or are too strongly adsorbed by the catalyst) to be saturated by the hydrogenation components and, hence, continue to condense and eventually degrade to coke. These deposits deactivate the catalyst sites and eventually interfere with the hydrodesulfurization process. Thus, the deposition of coke and, hence, the rate of catalyst deactivation, is subject to variations in the asphaltene (and resins) content of the feedstock as well as the adsorptive properties of the catalyst for the heavier molecules. 

The data indicate the types of reactions that can occur during the hydrode-sulfurization reaction and include those reactions that will occur at the upper end of the temperature range of the hydrodesulfurization process whether it is a true hydrodesulfurization reaction or a cracking reaction. Even though some of the reactions given here may only be incidental, they must nevertheless be taken into account because of the complex nature of the feedstock. The several process variations (Chapter 9) which (in addition to the fact that the overall hydrodesulfurization process is exothermic (Table 4-2) also contribute to the complexity of the product mix. 

Thus, it has become possible to define certain general trends that occur in the hydrodesulfurization of petroleum feedstocks. One of the more noticeable facets of the hydrodesulfurization process is that the rate of reaction declines markedly with the molecular weight of the feedstock (Figure 4-6) (Scott and Bridge, 1971). For example, examination of the thiophene portion of a (narrowboiling) feedstock and the resulting desulfurized product provides excellent evidence that benzothiophenes are removed in preference to the dibenzothiophenes and other condensed thiophenes. The sulfur compounds in heavy oils and residua are presumed to react (preferentially) in a similar manner. 

Application of the second-order rate equation to the hydrodesulfurization process has been advocated because of its simplicity and use for extrapolating and interpolating hydrodesulfurization data over a wide variety of conditions. However, while the hydrodesulfurization process may appear to exhibit second-order kinetics at temperatures near 395°C (745°F), at other temperatures the data (assuming second-order kinetics) does not give a linear relationship (Figure 4-9) (Ozaki et ah, 1963). 

One marked effect of a hydrodesulfurization process is the buildup of hydrogen sulfide and the continued presence of this reaction product in the reactor reduces the rate of hydrodesulfurization. Thus, using the two first-order models, the effect of hydrogen sulfide on the process can be represented as ... 

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