Hydrodesulfurization feed

TABLE 23-16 Hydrodesulfurization Feed Rates of Gas and Liquid and Residence Times of the Mixture... 

Figure 8 Colour plot of the GCxGC separation of a hydrodesulfurization feed [36]. The different groups indicated are the major sulphur compounds. In between these groups are the groups that also contain a saturated (hydrocarbon) ring in the molecule.

In most applieations, the reaetion oeeurs between a dissolved gas and a liquid-phase reaetant in the presenee of a solid eatalyst. In some eases, the liquid is an inert medium and the reaetion takes plaee between the dissolved gases at the solid surfaee. These reaetors have many diverse applieations in eatalytie proeesses and are used extensively in the ehemieal industry. Triekle-bed reaetors have been developed by the petroleum industry for hydrodesulfurization, hydroeraeking, and hydrotreating of various petroleum fraetions of relatively high boiling point. Under reaetion eonditions, the hydroearbon feed is frequently a vapor-liquid mixture that reaets at liquid hourly spaee veloeities (LHSV in volume of fresh feed, as liquid/volume of bed, hr) in the... 

The feed to a catalytic reformer is normally a heavy naphtha fraction produced from atmospheric distillation units. Naphtha from other sources such as those produced from cracking and delayed coking may also be used. Before using naphtha as feed for a catalytic reforming unit, it must be hydrotreated to saturate the olefins and to hydrodesulfurize... 

In the two-stage operation, the feed is hydrodesulfurized in the first reactor with partial hydrocracking. Reactor effluent goes to a high-pressure separator to separate the hydrogen-rich gas, which is recycled and mixed with the fresh feed. The liquid portion from the separator is fractionated, and the bottoms of the fractionator are sent to the second stage reactor. 

Products from hydrodesulfurization of feeds with different sulfur levels ... 

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. 

J. Hydrodesulfurization unit effluent exchanger channel head and shell plate. (Hydrocarbon feed to unit and make-up hydrogen Bom ethylene unit)... 

Gulf HDS A process for hydrorefining and hydrocracking petroleum residues in order to make fuels and feeds for catalytic cracking. Developed by the Gulf Research Development Company. See also hydrodesulfurization. 

Trickle Hydrodesulfurization A process for removing sulfur-, nitrogen-, and heavy-metal-compounds from petroleum distillates before catalytic cracking. The preheated feed is hydrogenated, without a catalyst, in an adiabatic reactor at 315 to 430°C. Developed by Shell Development Company. As of 1978, 91 units had been installed. 

From a separation-process point of view, a fluid-fluid reaction is intended to enhance separation (e.g., preparation of feed for a subsequent process step, product purification, or effluent control for environmental protection). Examples include the use of ethanolamines for the removal of H2S and C02 (reactions (A) and (B) in Section 9.2), the removal of SO, by an aqueous stream of a hydroxide, and absorption of 02 by blood or desorption of C02 from blood. A solid catalyst may be involved as a third phase, as in hydrodesulfurization in a trickle-bed reactor. 

Catalysts used for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) of heavy oil fractions are largely based on alumina-supported molybdenum or tungsten to which cobalt or nickel is added as a promoter [11]. As the catalysts are active in the sulfided state, activation is carried out by treating the oxidic catalyst precursor in a mixture of H2S and H2 (or by exposing the catalyst to the sulfur-containing feed). The function of hydrogen is to prevent the decomposition of the relatively unstable H2S to elemental sulfur, which would otherwise accumulate on the surface of the... 

From the preceding discussion, it can be seen that the mathematical description of the chemical transformations involved in product formation can be extremely difficult. However, knowledge of the response of HDS reaction rates to different kinds of feed components and byproducts is extremely important for designing new processes that will allow refineries to meet the stringent standards of the future. The following text attempts to summarize the observations reported in the literature on the effects of inhibitors on the hydrodesulfurization rates of alkyl-substituted dibenzo-thiophenes. It is quite possible that many reports have been overlooked, and the present authors apologize for any oversights that may have occurred in this review. 

A number of refinery processes require the use of a fixed-bed catalyst These processes include catalytic reforming, hydrodesulfurization, hydrotreating, hydro-cracking, and others. These catalysts become inactive in six months to three years and are eventually replaced in the reactors with fresh catalyst during a unit shutdown. Many of these catalysts contain valuable metals which can be recovered economically. Some of these metals, such as platinum and palladium, represent the active catalytic component other metals such as nickel and vanadium are contaminants in the feed which are deposited on the catalyst during use. After valuable metals are recovered (a service usually performed by the outside companies), the residuals are expected to be disposed of as solid waste. 

The liquid hourly space velocity is the ratio of the hourly volume flow of liquid in, say, barrels to the catalyst volume in barrels, and the reciprocal of the liquid hourly space velocity gives the contact time. Since the catalyst volume for the process will be constant, the space velocity will vary directly with the feed rate. A decrease in the liquid hourly space velocity (or, alternatively, an increase in the contact time) will usually bring about an increase in the efficiency (or extent) of the hydrodesulfurization process (Figure 5-14) (Frost and Cottingham, 1971). In order to maintain a fixed rate of hydrodesulfurization when the feed rate is increased, it may be necessary to increase the temperature. 

Under the relatively mild processing conditions used for the hydrodesulfurization of these particular feedstocks, it is difficult to achieve complete vaporization of the feed. Process conditions may dictate that only part of the feedstock is actually in the vapor phase and that sufficient liquid phase is maintained in the catalyst bed to carry the larger molecular constituents of the feedstock through the bed. If the amount of liquid phase is insufficient for this purpose, molecular stagnation (leading to carbon deposition on the catalyst) will occur. 

Combined with hydrodesulfurization, the process is fully applicable to the feed preparation for fluid catalytic cracking and hydrocracking. The process is capable of using a variety of feedstocks including atmospheric and vacuum residues derived from various crude oils, oil sand, visbroken tar and so on. 

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