MXPA96006178A - Process for the refinement of raw materials of hydrocarbons on a sensitive catalyst alazu - Google Patents

Abstract

The present invention relates to a process for converting a hydrocarbon feedstock containing at least 20 ppb by weight of sulfur onto a sulfur sensitive catalyst, characterized in that it comprises: contacting the hydrocarbon feedstock with the catalyst sensitive to sulfur in a reaction zone, with the hydrocarbon feed and catalyst flowing in opposite directions through the reaction zone, so that the hydrocarbon feedstock containing at least 20 ppb in weight of sulfur Initially makes contact with the catalyst based catalyst which acts as a sorbent for the sulfur contained in the feed, removing the spent catalyst from the reaction zone, once it has passed through and has had contact with the hydrocarbon contaminated with sulfur fed and absorbs the sulfur thereof, and pass the spent catalyst removed to a regeneration zone

Description

PROCESS FOR THE REFINING OF RAW MATERIALS OF HYDROCARBONS ON A SULFUR SENSITIVE CATALYST BACKGROUND OF THE INVENTION The present invention relates to a multi-stage process for the refining of hydrocarbon raw materials boiling in the temperature range of gasoline. The process can be used to make hydrogen, high octane streams for the gasoline mixture and currents rich in benzene, toluene and / or xylene for petrochemical use. In particular, the present invention relates to a refining process wherein the Refining catalyst is highly sensitive to sulfur. The refining process encompasses a number of reactions such as dehydrocyclization, hydrodecyclization, isomerization, hydrogenation, dehydrogenation, catalytic hydrodisintegration, catalytic disintegration, etc. The desired result is the conversion of paraffins, naphthalenes and olefins to aromatics and hydrogen. Usually, the reaction is carried out by mixing a hydrotreated hydrocarbon feedstock with recycle hydrogen and passing the mixture over a refining catalyst at a temperature of 427-5600 ° C (800-1050 ° F) and a pressure of 0 - 42 Kg / cm2 (0 -600 pounds per square inch gauge). Highly active and selective refining catalysts have recently been developed which comprise a noble metal such as platinum on a zeolite support. These catalysts are particularly effective for the conversion of paraffins of 6 to 8 carbon atoms to compounds REF: 23496 aromatics such as benzene, toluene and xylenes, which can be recovered by extraction for subsequent use in the petrochemical industry. However, some of these zeolite catalysts, while highly selective, are rapidly inactivated by sulfur. The non-acidic Pt-zeolite L catalysts are a prime example of such sulfur-sensitive catalysts. Examples of Pt-K-zeolite-L catalysts are described in U.S. Patent Nos. 4,104,320 (Bernard et al.), 4,544,539 (Wortel) and 4,987,109 (Kao et al.). The Pt-Ba, K zeolite-L catalysts are described in U.S. Patent No. 4,517,306 (Buss et al.). It is disclosed in U.S. Patent No. 4,456,527 that such catalysts are capable of achieving satisfactory operation times only when the sulfur content of the feed is substantially reduced, e.g., preferably to less than 100 parts per billion by weight (ppbw) and more preferably less than 50 ppbw. The lower the sulfur content of the feed, the longer the duration of the run. The patent literature provides several methods that have been specifically identified as being suitable for regenerating a zeolite refining catalyst highly sensitive to sulfur that has been contaminated by sulfur. For example, see redirect 34,250 issued to Van Leirsburg et al. See also the description of European patent 316,727 which involves the pretreatment of Pt-zeolite-L catalysts deactivated at 500CC with a halogen compound, such as carbon tetrachloride and nitrogen. The continuous regeneration of the catalyst using the technology described, for example, in the report "Continuous reformer catalyst regeneration technology mproved" by Roger L. Peer, et al., Oil & Gas Journal. May 30, 1988, is also known. In the process, the catalyst is moved continuously through the regeneration process by gravity, while the gas streams flow radially easily through the catalytic bed. The objective is to provide the operation of the new catalyst in an essentially continuous manner, in order to give stable yields by this. Various other methods for regenerating the sulfur-contaminated catalysts are also known to those skilled in the art. The removal of sulfur from the hydrocarbon stream before contact with the sulfur-sensitive catalystHowever, it has received the main focus in maximizing refining results when such catalysts are used. For example, various ways to obtain raw feedstocks with an ultralow sulfur content are provided in the patent literature. U.S. Patent No. 4,456,527 describes a process wherein the ñaña feed is hydrogenated and then passed over a sulfur absorber supported on CuO at 149 ° C (300 ° F) to produce a feed containing less than 50 parts by billion in weight (ppbw) of sulfur. In U.S. Patent No. 4,925,549, the residual sulfur is separated from a hydrotreated feedstock by reacting the feedstock with hydrogen on a refining catalyst less sensitive to sulfur, to convert the residual sulfur compounds to sulfur hydrogen and absorb the hydrogen sulfide on a solid sulfur absorbent such as zinc oxide. In U.S. Patent No. 5,059,304, a similar process is described, except that the sulfur absorbent comprises a metal oxide of group IA or NA on a support. In U.S. Patent No. 5,211,837, a sulfur sorbent of manganese oxide is used. In U.S. Patent No. 5,106,484, a hydrotreated feedstock is passed over a solid nickel catalyst and then treated on a metal oxide under conditions which result in a substantially purified naphtha. The metal oxide is preferably manganese oxide and the treatment can be carried out in the presence of recycled hydrogen. While the sulfur removal techniques of the prior art are effective, they add to the complexity of the refining process. For example, the additional sulfur absorbent and the sulfur converter / sorbent reactors of the recycle gas are necessary, together with their associated catalysts and absorbent materials. In addition, recycle gas sulfur converter / sorbent reactors which normally operate under moderate refining conditions can catalyze side reactions that cause some loss of performance.

Therefore, any process involving a sulfur-sensitive catalyst which can reduce the need for complicated sulfur separation steps would be desirable. It is therefore an object of the present invention to provide a new refining process which involves a sulfur-sensitive catalyst and which is relatively simple in its process for the separation of sulfur and protection of the sulfur-sensitive catalyst used. Another object of the present invention is to provide an efficient and effective refining process which involves a sulfur-sensitive catalyst. These and other objects of the present invention will become apparent upon review of the following specification, the drawings and the claims appended thereto.

SUMMARY OF THE INVENTION In accordance with the above objectives, the present invention provides a process for catalytically refining a hydrocarbon feedstock containing at least 20 ppbw of sulfur, but in general not more than 500 ppbw of sulfur. The process comprises contacting the hydrocarbon feedstock and a sulfur-sensitive catalyst in a reaction zone, the hydrocarbon feed and the catalyst flowing in opposite directions through the reaction zone, such that the catalyst enters the reaction zone at the end from which the product stream separates. The contact is generally made in the presence of hydrogen. Once the catalyst is passed through the reaction zone, it is then passed to a regeneration zone for regeneration. Therefore, in this process, the hydrocarbon feed contaminated with sulfur is put in contact with the spent catalyst, this is the catalyst that is about to leave the reaction zone and be regenerated, which catalyst acts as an absorbent for the sulfur contained in the feed. Accordingly, the new or regenerated catalyst is always in contact with a relatively sulfur-free reaction stream. For the purposes of this invention, a refining catalyst is highly sensitive to sulfur if run times or operation in a fixed bed reactor with a substantially sulfur-free feed, that is, less than 200 ppbw of sulfur, are less twice as long as when the feed contains 100 ppbw of sulfur (the operation is done in the absence of a sulfur removal step.) Among other factors, the present invention is based on the discovery that sulfur deposition occurs in general on a relatively small portion of the catalytic bed when a refining process is carried out on a catalyst highly sensitive to sulfur. Thus, when a feed contains 20-500 ppbw of sulfur, the transfer of sulfur mass from the feed to the catalyst occurs in a narrow zone which changes through the catalyst as each catalyst increase becomes inactive. The catalytically active sites are essentially titrated by sulfur in the feed. Thus, the process of the present invention employs a smaller portion of the refining catalyst highly sensitive to sulfur itself as a refining catalyst and a sulfur removal agent, but uses only that portion of the catalyst which is already depleted and is ready to leave the reaction zone for regeneration. The result is a more efficient and effective refining process; among the advantages of which is that the need for a recycle sulfur converter / absorber of gas such as that described in U.S. Patent Nos. 4,925,549, 5,059,304, 5,211, 837 and 5,105,484 is eliminated. By this, the process of the present invention provides a simplified refining process and in some cases, improved yields of hydrogen and aromatics.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 of the drawings is a graphic representation of the heat loss of the reactor and increase in reactor exit temperature when the catalytic beds in a refinery plant of multiple reactors are quenched by sulfur. Figure 2 of the drawings schematically shows a refining process according to the present invention. The process involves a countercurrent flow reaction zone which allows the outgoing catalyst to act as a sulfur absorbent.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The feedstocks which are suitable for the process of this invention are generally hydrocarbon streams that boil substantially within the temperature range of the gasoline and contain at least 20 ppbw of sulfur, but of preference not more than 500 ppbw of sulfur. The process of the present invention is also quite useful for hydrocarbon streams containing at least 50 ppbw of sulfur, the amount of sulfur is preferably in the range of 50-200 ppbw. This would include streams that boil at a temperature within the range of 83-232 ° C (70-450 ° F), preferably 49 ° C to 204 ° C (120 to 400 ° F). For petrochemical applications, currents of 6, 6-7, 6-8 carbon atoms are preferred. Examples of suitable feedstocks include naphthas from the first distillation of petroleum refining or fractions thereof which have been hydrotreated to remove sulfur and other catalyst inactivators. Also suitable are synthetic naphthas or fractions of naphtha derived from other sources such as coal, natural gas liquids, mobile bed catalytic disintegrators and hydrodisintegrators. Usually, these will also require hydrotreating to bring their sulfur content to the desired range and eliminate other catalyst inactivators. Other pretreatment steps of the feed may include passing the feed as a liquid through a sulfur absorber containing, for example, nickel oxide or copper oxide on a support and drying the feed with the use of molecular sieves. . A sulfur absorbent can also be used as a precaution in case the hydrotreating system fails. The contact of the feed with the solid nickel, for example, before the refining reaction would protect against a major failure of the hydrotreating system. The refining reaction is carried out in a reaction zone through which the hydrocarbon feedstock and the catalyst flow in opposite directions, such that the catalyst is introduced at the end from which the stream of the product is separated. The reaction zone may consist of one or more reactors. In a preferred embodiment, the reaction zone comprises three to six reactors connected in series. More preferably, the various reactors are stacked, particularly when the catalyst moves down through the reactor train and the reactant gases move upward. The feed to the reaction zone generally comprises from 20 to 500 ppbw of sulfur. Sulfur is absorbed by contact with the catalyst traveling in the opposite direction. The result is that reagents leaving the first contact reactor with the series feed generally contain less than 20 ppbw of sulfur, more preferably less than 5 ppbw of sulfur and more preferably less than 1 ppbw of sulfur. The stream of the recovered product will therefore be substantially free of sulfur and will contain less than 20 ppbw of sulfur, more generally less than 5 ppbw of sulfur and more preferably less than 1 ppbw of sulfur.

Since the refining process is endothermic, the feed is reheated between the reactors. The reactor employed in this process can be any conventional type of moving bed reactor which can accommodate a continuous flow of the hydrocarbon feed and the catalyst. All reactors can be the same or different, radial flow reactors are preferred. However, in a preferred embodiment, all reactors are radial flow reactors, except the last reactor in the flow direction of the catalyst, which reactor employs the traditional countercurrent contact between the catalyst and the feedstock. In general, the refining reaction can be carried out with the use of any conventional refining conditions, but preferably it is carried out at temperatures ranging from 315 ° C to 593 ° C (600 to 1100 ° F) and more preferably at temperatures in the range of 427 ° to 565 ° C (800 to 1050 ° F). Reaction pressures may range from atmospheric pressure to 42 Kg / cm2 (600 pounds per square inch gauge), but are preferably from 2.8 to 7 Kg / cm2 (40 to 100 pounds per square inch gauge). The molar ratio of hydrogen to the hydrocarbon feed is usually between 0.5 and 10, the preferred range is 2.0 to 5.0. The space velocity per hour, by weight, of the hydrocarbon feed is 0.5 to 20 and more preferably 0.50 to 5.0, based on the catalyst in the reaction zone. Another important aspect of the present invention is that the reaction zone is equipped for the continuous regeneration of the catalyst. The catalyst can be regenerated according to any known continuous regeneration process for the sulfur sensitive catalysts. For example, in Reissue 34,250, issued to Van Leirsburg et al., Which is expressly incorporated by reference herein, the regeneration process comprises a carbon separation step, a platinum agglomeration step and sulfur separation and a stage of redistribution of platinum. In the description of European patent 316,727, which is expressly incorporated by reference herein, the deactivated L-Pt zeolite catalysts are pretreated at 500 ° C with a halogen compound such as carbon tetrachloride and nitrogen. Then oxygen is added to the mixture to remove carbon and finally, the catalyst is treated with a chlorofluorocarbon, oxygen and nitrogen compound. The continuous catalyst regeneration system as described in the report by Peer et al., Oil & amp;; Gas Journal. May 30, 1988, which is incorporated herein by reference, may also be used. Various other methods for regenerating the catalysts contaminated with sulfur are known to those skilled in the art. The use of a process which involves the separation of the sulfur and the redispersion of the platinum, however, is the most preferred for the regeneration of the catalyst. It is also part of the preferred embodiment that the dimensions of the reactor and the rate of catalyst circulation can be chosen in such a way that the catalyst is regenerated from once a day to once a month, regeneration every 5 to 14 days it is preferred. It is also preferred that the yield of the aromatic compounds and the profile of the sulfur concentration for the reaction zone remain constant. The refining catalysts used in the process of this invention are highly sensitive to sulfur. Such catalysts highly sensitive to sulfur are well known in the industry, for example, as described in U.S. Patent Nos. 4,456,527 and 4,925,549, the descriptions of which are expressly incorporated herein by reference. The sulfur sensitivity of a catalyst can be determined by carrying out two runs or refining operations in a fixed bed micro-reactor under identical conditions. The first run should be done with a hydrocarbon feedstock substantially free of sulfur containing less than 5 ppbw of sulfur, while the second run should be done with the same feed, but with thiophene added to the feed to raise its sulfur content at 100 ppbw. A substantially sulfur-free feed can be obtained by first hydrotreating the feed to bring its sulfur content to less than 100 ppbw and then using a sulfur converter / absorber, as described in U.S. Patent No. 5,059,304. The duration of the run can be defined by allowing either a fixed increase in temperature at constant yield of aromatics or a given drop in conversion at constant temperature. If the duration of the run in the presence of 100 ppbw of feed sulfur is less than half that obtained with the feed substantially free of sulfur, then the catalyst is said to be highly sensitive to sulfur. In order to provide a more quantitative measure of sulfur sensitivity, a test is defined herein which can be used to determine a Sulfur Sensitivity index or SSI. The test is carried out by comparing the durations of the runs obtained with a sulfur-free feed and the same feed with thiophene. The base feed is n-hexane which contains less than 20 ppbw of sulfur. In the sulfur-free case, a sulfur converter / absorber is used, whereas in the case of added sulfur, sufficient thiophene is added to raise the sulfur content to 100 ppbw. In each run, one gram of the catalyst is charged to a 0.476 cm (3/16") internal diameter tubular reactor.Sulfur-free reactors are used for each run.The catalyst is dried by heating to 260 ° C ( 500 ° F) at a rate of 27.8'C / min (50 ° F / min), while nitrogen is flowed through the reactor at 3.5 Kg / cm2 (50 pounds per square inch gauge) and a speed of 500 cc / minute The catalyst is reduced to 260 ° C (500 ° F) and 3.5 Kg / cm2 (50 pounds per square inch gauge), hydrogen flows at 500 cc minute, then the temperature is raised to 482 ° C ( 900 ° F) at a rate of 27.8 ° C / min (50 ° F / min) while continuing the flow of hydrogen, then the temperature is decreased to approximately 454 ° C (850 ° F) and started The reaction is carried out at a space velocity per hour, by weight of 5.0, 3.5 Kg / cm2 (50 pounds per square inch gauge) and a molar ratio of hydrogen. no to hydrocarbon feed of 5.0. The n-hexane-free container is filled with dry nitrogen to prevent contamination by water and oxygen and the hydrogen also dries, such that the reactor effluent contains less than 30 ppm of water. The reactor effluent is analyzed by gas chromatography at least once every hour and the reaction temperature is adjusted to maintain a 50% aromatic yield. Runs are terminated when the reaction temperature has increased 14 ° C (25 ° F) from the start of the extrapolated temperature. The Sulfur Sensitivity Index is then calculated by dividing the duration of the run obtained in the sulfur-free case by the duration of the run obtained in the case of added sulfur. In the process of this invention, it is preferred that the refining catalysts have an SSI of at least 2.0. It is especially preferred that your SSI exceed 5.0 and it is more preferable that the SSI exceed. A preferred form of the highly sulfur-sensitive catalyst consists of 0.05 to 5.0% by weight of noble metal on a zeolite support. The zeolite can be mixed with an inorganic oxide binder such as alumina or silica and formed into 0.635 cm (1/4") to 0.079 cm (1/32") diameter spherical or cylindrical catalyst pieces. The noble metals are preferably platinum or palladium, but some catalysts may also contain other noble metals as promoters, such as iridium and rhenium, which act to improve the selectivity or duration of the run. The catalyst may also comprise non-noble metals such as nickel, iron, cobalt, tin, manganese, zinc, chromium, etc. It is preferred that the zeolite support be substantially non-acidic. Zeolites having pore dimensions of greater than 6.5 A are especially preferred. Catalysts comprising a large pore zeolite with non-intersecting channels such as L and omega zeolites are especially sensitive to sulfur and more advantageous to the process of this invention. One way to determine if a catalyst is substantially non-acidic is to immerse 1.0 gram of the catalyst in 10 grams of distilled water and measure the pH of the supernatant liquid. A substantially non-acidic zeolite will have a pH of at least 8.0. Catalysts comprising platinum on the substantially non-acidic forms of zeolite L are especially preferred for the process of this invention. Such catalysts are described in U.S. Patent Nos. 4,104,539, 4,517,306, 4,544,539 and 4,456,527, the disclosure of which is expressly incorporated by reference herein. Accordingly, the present invention provides an efficient and effective method for separating sulfur during the refining of a hydrocarbon feedstock, while using a sulfur-sensitive catalyst. The process uses a portion of the catalyst for the purpose of separating the sulfur. The portion used is the spent catalyst about to leave the reaction zone. By using a flow of the hydrocarbon feed reaction stream and the catalyst in opposite directions, the sulfur contaminated feed always comes into contact with the spent catalyst and the new or regenerated catalyst always comes into contact with the purified feed. The catalyst that is contaminated with the sulfur immediately leaves the reaction zone and is passed on to regeneration. Accordingly, the catalyst in the reaction zone performs the double function of sulfur removal and selective refining, the catalyst about to leave the reaction zone removes the sulfur and begins the selective refining reaction. Accordingly, there is no need for an additional sulfur absorbent. The process of the present invention will be illustrated in greater detail by the following specific examples. It will be understood that these examples are given by way of illustration and are not intended to limit the description or the claims that follow. All percentages in the examples and anywhere in the specification, are by weight unless otherwise specified.

Example I A gas rich in sulfur products is injected into the hydrogen recycling system of a four-reactor refining plant employing a non-acidic Pt-zeolite L catalyst. The reactors were of a fixed bed type, of downward flow and were in series. The catalyst was protected by a sulfur absorber. Inevitably, the capacity of the absorber was exhausted and the hydrogen sulfide began to penetrate. There was then a sequential inactivation of the catalyst in each subsequent reactor. A loss of catalytic activity was indicated by a loss of heat from the reactor and an increase in reactor exit temperature as shown in figure 1. The second, third and fourth series reactors did not begin to experience a heat loss until the preceding reactor was completely deactivated. The plant was stopped just after the catalyst in the last reactor had been deactivated. The sulfur content of the catalyst samples after the incident ranged from 249 ppm in the first reactor to 149 ppm in the last reactor. These observations show that the sulfur adsorption of a Pt-zeolite L catalyst is very fast and occurs on a very narrow band of the catalyst. The data also shows that the sulfur adsorption was 100% effective until the sulfur loading on the catalyst exceeded 100 ppm.

Example II A sample of a catalyst containing 0.64% by weight of platinum on zeolite L extrusion products exchanged with barium was tested as described above to determine its Sulfur Sensitivity index. The SSI was determined to be 11. According to the process of the present invention, the above catalyst can be charged to a refining unit as shown in Figure 2. The refining unit can comprise a number of reactors in series , five stacked reactors 1 are shown in the figure. More or fewer reactors can be used in the series. The catalyst is charged via line 2 to the upper reactor of the refining unit, such that the catalyst passes down via gravity, through the various reactors of the refining unit. Preferably, in the lower reactor 10, the flow of the catalyst provides a conventional countercurrent contact with the hydrocarbon feedstock. The reactors remaining in the series are all radial flow reactors. A hydrocarbon feedstock, a naphtha of 6 to 7 carbon atoms which has been hydrotreated and passed through a sulfur absorber (comprising solid nickel) and a molecular sieve drier, is introduced via the line 3 to the bottom of the lower reactor, in such a way that the feed passes upwards through the refining unit. The sulfur content of the hydrocarbon feed at the introduction to the refining unit is 50 ppbw and its moisture content is less than 5 ppbw. The hydrogen is mixed with the hydrocarbon feedstock before introduction to the refining zone. The hydrogen is added to the feedstock via line 4. The mixture of the feedstock and hydrogen is generally passed through a feed / effluent exchanger and an oven before introduction to the unit. reformation, where the feed is heated to the reaction temperature. After start-up, the refining reaction is carried out at the reactor inlet temperatures at about 493-515 ° C (920-960 ° C). The average pressure of the reactor drops from 6.3 to 3.5 Kg / cm2 (90 to 50 pounds per square inch gauge). as you proceed through the series of reactors. The molar ratio of hydrogen to the naphtha feed entering the first reactor is generally about 5.0. The space speed per hour, by weight of the naphtha based on the total volume of the catalyst is 1.0. The feed stream proceeds through the reactor train. Between each reactor, the stream is removed and heated back to the inlet temperature of the reactor by means of the heaters 5. Once heated, the current is returned to the next reactor for continuous upward flow. The catalyst moves down through the series of reactors and exits the last reactor 10 via line 6. The catalyst leaving the refining unit has been contacted with the contaminated sulfur feed and the refining reaction begins while it also absorbs sulfur. The catalyst is then moved via line 6 to regenerator 7, which processes the catalyst in a continuous base. In a preferred embodiment, the regenerator comprises a series of radial flow zones of the gas. As the catalyst moves through the regeneration vessel 7 it is treated by a series of gas mixtures at high temperatures and high speed to remove the sulfur and carbon and to redisperse the platinum. Inevitably, the catalyst leaves the regenerator via line 8 and returns to the reactors via line 2. The rate of catalyst circulation is such that the average catalyst particle is regenerated once every 5 to 14 days. The feed / reagent stream leaves the last reactor in the series in the direction of flow of the feed stream via line 9 as effluent. This effluent can then be cooled by a feed / effluent exchanger and a compensation cooler. Then the cooled effluent is passed to a separator, from which a liquid product containing about 80% by weight of aromatic compounds is collected from the bottom. This liquid product can be further purified to collect a higher percentage of aromatics stream. A gaseous product is collected from the top of the system and is inevitably divided into streams of clean gas and recycled hydrogen. The recycled hydrogen is returned via line 4 at the beginning of the process. The clean gas is further purified to provide hydrogen for the refinery and to recover the additional aromatic compounds. While the invention has been described with the preferred embodiments, it will be understood that variations and modifications may be resorted to as will be apparent to those experienced in the art. technique. Such variations and modifications should be considered within the spirit and scope of the claims appended hereto. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following

Claims (23)

1. Claims 1. A process for the refining of a hydrocarbon feedstock containing at least 20 parts per billion by weight of sulfur on a sulfur sensitive catalyst, characterized in that it comprises: contacting the hydrocarbon feedstock with the catalyst sensitive to sulfur in a reaction zone, the hydrocarbon feed and the catalyst flow in opposite directions through the reaction zone; separating the catalyst from the reaction zone once it has been passed through it; and passing the separated catalyst to a regeneration zone.
2. 2. The process according to claim 1, characterized in that the flow of the catalyst through the reaction zone is continuous and the flow of the catalyst to and through the regeneration zone is continuous.
3. 3. The process according to claim 2, characterized in that the catalyst is recycled continuously to the reaction zone from the regeneration zone.
4. 4. The process according to claim 1, characterized in that the catalyst comprises a zeolite L.
5. 5. The process according to claim 4, characterized in that the catalyst further comprises platinum dispersed on the zeolite L.
6. 6. The process according to claim 1, characterized in that the reaction zone consists of 2 to 6 reactors in series.
7. 7. A process according to claim 1, characterized in that the hydrocarbon feed contains from 20 to 500 parts per billion by weight of sulfur.
8. 8. The process according to claim 1, characterized in that the hydrocarbon feed is passed through a sulfur absorber before being passed to the reaction zone.
9. 9. The process according to claim 8, characterized in that the sulfur absorbent comprises solid nickel.
10. 10. The process according to claim 6, characterized in that the reactors are stacked.
11. 11. The process according to claim 10, characterized in that the flow of the hydrocarbon feed through the reaction zone is upward and the flow of the catalyst through the reaction zone is downward.
12. 12. The process according to claim 6, characterized in that the last reactor in the flow direction of the catalyst employs the traditional countercurrent contact between the catalyst and the feedstock.
13. 13. The process according to claim 6, characterized in that at least one of the reactors is a radial reactor.
14. 14. The process according to claim 12, characterized in that the last of the reactors is a radial flow reactor.
15. 15. A process for the refining of a hydrocarbon feedstock containing at least 20 parts per billion by weight of sulfur on a sulfur sensitive catalyst comprising a zeolite L containing a metal of group VIII, characterized in that it comprises: in contact the hydrocarbon feed with the sulfur sensitive catalyst in a reaction zone, comprising from 2 to 6 reactors in series, the hydrocarbon feed and the catalyst flow in opposite directions on a continuous basis through the reaction zone; separating the catalyst from the reaction zone once it has been passed and passing the separated catalyst to a regeneration zone for regeneration on a continuous basis; and recycling the regenerated catalyst to the reaction zone.
16. 16. The process according to claim 15, characterized in that the reactors of the reaction zone are stacked.
17. 17. The process according to claim 15, characterized in that at least one of the reactors is a radial flow reactor.
18. 18. The process according to claim 15, characterized in that the hydrocarbon feedstock is passed through a sulfur absorbent before being passed to the reaction zone.
19. 19. The process according to claim 18, characterized in that the sulfur absorbent comprises solid nickel.
20. 20. The process according to claim 15, characterized in that the catalyst comprises a zeolite L containing platinum.
21. 21. The process according to claim 15, characterized in that the last reactor in the flow direction of the catalyst employs the traditional countercurrent contact between the catalyst and the feedstock stream.
22. 22. The process according to claim 15, characterized in that a stream of the refined hydrocarbon product is recovered from the reaction zone, which contains less than 5 parts per billion by weight of sulfur.
23. 23. The process according to claim 15, characterized in that a stream of the refined hydrocarbon product is recovered from the reactor zone, which contains less than 1 part per billion by weight of sulfur.