MXPA98007588A - Process for the simultaneous selective hydrogenation of diolephins and nitrile in reactormultip units - Google Patents

Abstract

A process for the simultaneous hydrogenation of diolefins and nitriles is simultaneously provided from a hydrocarbon feedstock, wherein the hydrogenation is carried out using a catalyst in one reactor while the partially deactivated catalyst is regenerated in another area of the reactant.

Description

PROCESS FOR SIMULTANEOUS SELECTIVE HYDROGENATION OF r-tr > T.tre-rT3 * g- V NITRILES IN MULTIPLE REACTOR UNITS l'b 'K ENTES DB IA INVENTION The invention relates to a process for the simultaneous selective hydrogenation of diolefins and nitriles using a plurality of reactors or reactor zones. Processes and catalysts are known in the art for hydrogenating unsaturated compounds in hydrocarbon feedstocks in liquid. U.S. Patent Nos. 4,152,351, 4,271.3: 3 and 4,734,540 each describe processes by which particular elements of a hydrocarbon feedstock are hydrogenated. It is particularly desirable to hydrogenate diolefin and nitrile contaminants which may be present in the hydrocarbon feedstocks. During the course of treatment of the hydrogenation raw materials of diolefins and nitriles, however, the catalysts used in the process are gradually depleted or deactivated. Conventionally, the catalyst must be extracted from the reaction bed or other apparatus used during the treatment so as to replace and / or regenerate the catalyst. This results in significant delays of. hydrogenation process.

The need remains for a method or process for regenerating an exhausted or partially depleted catalyst which reduces the delays of the hydrogenation process. Therefore, the main objective of the present invention is to provide a process for regenerating a hydrogenation catalyst. A further objective of the present invention is to provide a process for regenerating a hydrogenation catalyst in which the catalyst is regenerated in the hydrogenation reactor bed. A further object of the present invention is to provide a process for regenerating a hydrogenation catalyst in which the catalyst is regenerated to a substantial level with respect to the original activity. Another object of the present invention is to provide a process for treating a raw material including diolefin and nitrile reactions, wherein the catalyst is regenerated in the reaction bed when deactivated to a certain level. Yet another objective of the present invention is to provide a process for treating a raw material such as a FCC raw material in multiple reactor zones, wherein the catalyst in one zone is regenerated while another zone is used to treat the raw material. Other objects and advantages of the present invention will appear in the following.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the present invention, the above objects and advantages are easily obtained. According to the invention, a process for simultaneous selective hydrogenation of diolefins and nitriles is provided from a hydrocarbon feedstock, which process comprises the steps of: (a) providing a hydrocarbon feedstock having a diolefin content more than or equal to about 0.1% by weight and a nitrile content of greater than or equal to about 2 ppm; (b) providing at least a first and second reactor zone, each containing a catalyst comprising a support material that is selected from the group consisting of inorganic oxide-zeolite composite material, carbon and zeolite, and a metal phase catalytically active which is selected from the group consisting of partially reduced group IB metals and completely reduced group VIII metals, the metallic phase is present in an amount of more than or equal to about 0.03% by weight, the catalyst has an activity of hydrogenation of the initial diolefin and the catalyst in the second reactor has a reduced diolefin hydrogenation activity; (c) mixing the raw material with hydrogen to provide a reaction feedstock having a ratio of hydrogen to diolefins and nitriles of less than about 3 times a stoichiometric amount necessary to selectively hydrogenate diolefins and nitriles; (d) treating the reaction stock in the presence of the catalyst in the first reactor zone at a hydrogenation temperature and pressure until the catalyst in the first reactor zone has a reduced diolefin hydrogenation activity of not less than about 50. % of the initial diolefin hydrogenation activity; (e) flushing the catalyst in the second reactor zone with an inert gas so as to remove traces of hydrocarbon of the catalyst and in this way a F catalyst washed in the second reactor zone; (f) regenerating the washed catalyst in the reactor zone by the additional flow of the hydrogen-washed catalyst so that a regenerated catalyst is provided in the second zone of The reactor having a regenerated diolefin hydrogenation activity which is greater than the reduced hydrolenation activity of diolefin; (g) treating the reaction raw material in the presence of the catalyst in the second reactor zone at a hydrogenation temperature and pressure; until The catalyst has a reduced diolefin hydrogenation activity not less than about 50% of the initial hydrolenation activity of diolefin; (h) flushing the catalyst in the first reactor zone with an inert gas so as to remove traces of hydrocarbon from the catalyst and in this manner a washed catalyst is provided in the first reactor zone; (i) regenerating the washed catalyst in the first reactor zone by further flowing the hydrogen washed catalyst so that a regenerated catalyst is provided in the first reactor zone having a regenerated diolefin hydrogenation activity which is greater than the reduced hydrogenation activity of diolefin; and (j) repeating steps (d) to (i). Additionally, according to the invention, the process as set forth above is preferably carried out until the hydrogenation activity of spent diolefin is reduced to not less than about 50% of the additional diolefin hydrogenation activity, At the point where the stages of abundant washing and regeneration are carried out, and repeated as desired. Additionally according to the invention, the process includes regenerating the hydrogenation catalyst to a hydrogenation activity of at least about 90% of the initial "diolefin" hydrogenation activity of the catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS A detailed description of the preferred embodiments of the invention follows, with reference to the drawings, in which: Figure 1 shows a schematic illustration of a process according to the present invention; Figure 2 illustrates the conversion or activity of a catalyst with respect to time, and after regeneration according to the process of the present invention; Figure 3 illustrates the regeneration effect according to the invention after significant deactivation of the catalyst, according to the present invention; Figure 4 further illustrates the activity with respect to time of a regenerated catalyst according to the present invention, and uses only a regeneration of hydrogen, so as to demonstrate the advantages of the process of the present invention; and Figure 5 shows a schematic illustration of a process for simultaneous selective hydrogenation of diolefins and nitriles in multiple reactor units according to the present invention.

P SCPletton nTftT.T-z ft, The invention relates to a process for regenerating an exhausted hydrogenation catalyst, preferably in a hydrogenation reactor, so as to avoid the need for catalyst removal and / or replacement, and also with a process for simultaneous and selective hydrogenation of the catalyst. a raw material C4-C5 using multiple reactor zones and a process for regeneration. A preferred catalyst for simultaneous and selective hydrogenation of diolefins and nitriles present in a hydrocarbon feedstock comprises a support material preferably selected from the group consisting of an inorganic oxide-zeolite composite material, carbon and zeolite, with a catalytically active deposited phase on the support material which is preferably selected from the group consisting of partially reduced group IB metals and completely reduced group VIII metals, wherein the catalytically active metal phase is preferably present in an amount of greater than or equal to about 0.03% by weight. These and other catalysts, when used for the hydrogenation of diolefins and nitriles, are deactivated during use to the point where the catalyst must be discarded and / or regenerated. According to the present invention, there is provided a process for regenerating an exhausted or at least partially depleted or depleted hydrogenation catalyst. According to the invention, a hydrogenation catalyst used to treat a hydrocarbon feedstock having diolefins and nitriles, for example greater than or equal to about 0.1% olefin and greater than or equal to about 2 ppm nitrile, is monitored, particularly with respect to the activity of the catalyst towards the desired hydrogenation reactions. When the hydrogenation activity of diolefins of the catalyst reaches a particular level, preferably not less than about 50% of original activity, more preferably not less than about 70% of original activity, and most preferably not less than about 80 % of original activity, the hydrocarbon feed to the catalyst material is temporarily interrupted, and the deactivated catalyst is first treated by abundant washing with an inert gas so that it removes traces of hydrocarbon from the catalyst, and then with a reducing gas e? a regeneration step so as to provide a regenerated catalyst having a regenerated hydrogenation activity. In additional accordance with the present invention, the catalyst as set forth above can be provided in a plurality of reactors or reactor zones such as reactive adsorption units and the like, and the hydrogenation can be carried out with a first zone of reactor while the regeneration process of the present invention is carried out, preferably substantially simultaneously, in a second, different reactor zone. According to this embodiment of the invention, advantageously a reactor zone can be used to process raw material while another is regenerated, and vice versa, so that inactive periods of time are avoided during the regeneration process. According to the invention, the abundant washing treatment of the catalyst with inert gas is preferably carried out using an inert gas which is selected from the group consisting of nitrogen, helium, argon, methane, ethane, propane, hydrogen or other saturated hydrocarbon light and mixture thereof, preferably nitrogen, helium, argon and a light saturated hydrocarbon, and more preferably nitrogen. The abundant washing of the catalyst deactivated with inert gas according to the invention advantageously serves to remove hydrocarbon greases from catalyst and in this way provide a washed catalyst which can then be regenerated by abundant washing with hydrogen, according to the invention. It should be noted that this gas must be inert with respect to the catalyst. After washing with inert gas, according to the invention, the catalyst is subsequently thoroughly washed in an additional manner during a regeneration step with reducing gas such as hydrogen so that a large portion, preferably at least about 90%, of the original or initial catalyst activity. According to the process of the present invention, the steps of washing and regeneration using inert gas and reducing gas are preferably carried out in the hydrogenation reactor so that the catalyst to be regenerated does not need to be removed therefrom. Furthermore, and advantageously, the washing and regeneration steps of the present invention are carried out at temperature and pressures in the reactor which are similar to the hydrogenation reaction, so as to provide an additional interruption or rupture in the hydrogenation reaction. Referring now to Figure 1, the catalyst regeneration process of the present invention. The hydrogenation reaction is typically carried out in a reactor, generally referred to in the drawings as reference numeral 10. The hydrogenation catalyst ^ k is placed inside the reactor 10. During normal operation, the reaction raw material comprising the raw material that goes to be treated and a source of hydrogen that feed the reactor as schematically illustrated by arrow A. The reaction raw material is contacted with the hydrogenation catalyst in reactor 10 so as to provide a hydrogenated product leaving reactor 10, as shown by the arrow B.

When the activity of the hydrogenation catalyst inside the reactor 10 decreases to a desired or pre-specified level, the feed of the reaction raw material is stopped along the arrow A, and a flow of nitrogen is introduced into the reactor. As shown in the drawing, the nitrogen is preferably fed to the reactor 10 in a direction opposite to the flow of the raw material during the hydrogenation reactions. In the drawing of figure 1, and more typically, the reaction raw material is fed to the reactor 10 in a direction of upward flow. Therefore, preferably, the nitrogen is fed to the reactor 10 as illustrated schematically by the arrow C in a direction opposite to the flow with respect to the feed, specifically a downflow direction. The nitrogen is shown leaving the reactor 10 in arrow D. The nitrogen flow according to the invention is carried out in a manner that removes traces of hydrocarbons from the hydrogenation catalyst inside the reactor-10, thereby preparing the catalyst for a subsequent stage of regeneration according to the invention. Preferably, it is flushed with nitrogen through the reactor 10 at a speed of space and superficial velocity sufficient to remove such traces of hydrocarbons. According to a preferred embodiment of the invention, the nitrogen can preferably be fed to the reactor 10 at a space velocity between about 10 to about 1000 h "1, preferably at about 5500 h" 1, measured under pressure and temperature conditions. standard. The nitrogen is also preferably fed at a surface velocity of between about 50 to about 150 m / min measured under standard pressure and temperature conditions. The nitrogen flow is preferably carried out in the reactor at a temperature of less than about 300 ° C, preferably between about 150 ° C to about 300 ° C, and more preferably between about 200 ° C to about 290 ° C. . Once the traces of hydrocarbons have been sufficiently removed, the flow of nitrogen in the direction of arrows C and D is stopped, and a flow of hydrogen is introduced into the reactor 10, preferably in a direction opposite to the direction of the nitrogen. Therefore, as shown in Fig. 1, the hydrogen is preferably introduced in the direction illustrated schematically with the arrow E, and leaves the reactor 10 in an arrow direction F. The flow of hydrogen is preferably carried out under conditions of pressure and reactor temperature similar to that of the hydrogenation reaction. Preferably, the hydrogen flow is carried out at a pressure of 10.5-46 kg / cm2 (150-650 psi), preferably between about 14 to about 21 kg / cm2 (200-300 psi) at a temperature of between about 100 -300 ° C, and at a space speed of between approximately 20 h "1 to approximately 200 h" 1. Preferably, the hydrogen is passed through the reactor 10 so as to expose to the hydrogenation catalyst therein from about 5 to about 20 times the amount of hydrogen required to completely reduce the metal phase of the hydrogenation catalyst. According to the invention, this advantageously results in the regeneration of the hydrogenation catalyst within the reactor 10 at a regenerated hydrogenation activity of at least about 90% of the original activity. Upon completion of the catalyst regeneration, the flow of hydrogen in the direction of the arrows EF is stopped, and the reactor 10 is brought back into line by re-feeding the reaction raw material along the arrow A, so that obtains a raw material treated or treated in some other way at the reactor outlet, as shown in arrow B. As stated above, "the regeneration process is preferably carried out in the reactor at similar temperature conditions. and pressure to those of the hydrogenation process In this regard, a typical hydrogenation process can be carried out at temperatures between about 60 to about 160 ° C or higher, and pressures of between about 14 to about 28 kg / cm2 ( 200-400 psi.) Therefore, advantageously, the regeneration process can be started as soon as the feed to the reactor is stopped, without delays being required to adjust r the temperature or pressure in the reactor. According to the invention, it has been found that the inert gas of the nitrogen washing step according to the invention is critical to obtain the regeneration of the hydrogenation catalyst according to the invention. As also stated in the foregoing, it has been found that the flow of nitrogen and hydrogen is advantageous sequentially in opposite directions to one another so that improved regeneration of the hydrogenation catalyst is provided. In this regard, and as illustrated in Figure 1, the nitrogen flow in this manner can be carried out in a direction opposite to the normal feed, while the hydrogen is carried out in a direction parallel to the normal feed . Of course, the flow direction of nitrogen and hydrogen can be reversed, if desired, according to the invention. Now with reference to Figure 5, a process for the simultaneous selective hydrogenation of diolefins and nitriles according to the present invention is illustrated. As shown, a first reactor 20 and a second reactor 22 can be adequately provided and connected to a source 24 of raw material, a source 26 of hydrogen, a source 28 of inert gas.

In accordance with the present invention, each reactor or reactor zone 20, 22 is provided with catalyst according to the present invention as described above. According to the present invention, the flow from the raw material source 24 is preferably controlled so as to direct a mixture of hydrogen from raw material or reaction raw material to the reactor zone 20 for treatment in the presence of catalyst in accordance with the present invention, while the flow is also controlled through the reactor zone 22 so that it first flushes the catalyst in the reactor zone 22 with an inert gas, and then further washes or exposes the reactor zone 22 to a regenerating flow of hydrogen according to the regeneration process of the present invention. Thus, although the catalyst in the first reactor zone 20 is used to treat the reaction feedstock in accordance with the present invention, and therefore it is also gradually deactivated, the catalyst in the reactor zone 22 is regenerated as described. before, "advantageously, when the catalyst in the reactor zone 20 is deactivated to the point where it must be regenerated, the flow of the reaction raw material can be diverted to the reactor zone 22 and the regenerated catalyst contained therein. in the same, while the catalyst in the reactor zone 20 is regenerated through abundant washing with inert gas and then with hydrogen according to the present invention.

In figure 5, reactor zones 20, 22 connected to sources 24, 26, 28 of reaction raw material, hydrogen and inert gas are shown through a series of lines and valves adapted to control the flow so that they alternately direct the reaction of the raw material to one reactor zone while the other zone is regenerated. Figure 5 shows the valves in an open / closed position to provide flow of the reaction raw material to the reactor zone 20, and provide regeneration flow of hydrogen to the reactor zone 22. The operation according to the present invention can be carried out in this configuration until the reactor zone 22 is sufficiently regenerated, and the catalyst in the reactor zone 20 is deactivated to the point where it must be regenerated, at which time the reaction raw material is redirected to the reactor zone 22, and the inert gas followed by hydrogen is directed to the reactor zone 20. According to the process of the present invention, this sequence can be carried out alternately in a manner * that provides a substantially continuous hydrogenation without interruptions. Of course, Figure 5 provides an illustration of a configuration for carrying out the process, and numerous additional configurations as well as more reactors or reactor zones can be used.

The following examples illustrate the advantageous regeneration of a hydrogenation catalyst according to the invention.

EXAMPLE 1 500 cc of a nickel catalyst sample such as that described in US Pat. No. 5,523,271 is loaded into a packed reactor bed of a pilot plant unit. A raw material is provided which has a naphtha cut C5 having the composition as set forth in table 1 below.

Table 1 COMPOSITION,% IN WEIGHT C3 0 C4 2.92 C4 = 6.98 C5 38.25 C5 = 25.56 IC5 = 25.98 C6 + 0.40 CONTAMINANTS DIOLEPHINS,% IN WEIGHT 1.9 NITRILE, ppm IN WEIGHT ACETONITRILOS 0.24 PRQPIQNITRILQS 80.12 BASIC NITROGEN, ppm IN WEIGHT 1.40 TOTAL SULFUR, ppm IN WEIGHT 40 MERCAPTANES, ppm IN WEIGHT < 1 5 WATER, ppm ON WEIGHT 150 The raw material is mixed with hydrogen in a 2.8: 1 molar ratio and fed upstream to the reactor of the pilot plant. Afterwards, the hydrogenation as set forth in the North American patent No. ^ 5,663,446. After 115 hours of operation, the conversion or hydrogenation activity of diolefin has decreased by less than about 5% of the original initial total conversion. At this point, the naphtha fed to the reactor stops and starts a regeneration process according to the present invention. Initially nitrogen is passed through the The reactor is in a downward flow direction, opposite to the flow of the raw material. Nitrogen is flowed through the reactor at a space velocity measured under standard conditions of 450 h "1 and a surface velocity of 1500 cm / min, at room temperature for about 3 hours This nitrogen flow advantageously has the effect of separating hydrocarbons from the surface of the hydrogenation catalyst.

After flow, the flow of nitrogen is stopped and a flow of hydrogen is introduced into the reactor in a direction of upward flow at a space velocity of 50 h "1. The same hydrogen is fed through the reactor to a temperature of 200 ° C for 24 hours After this treatment, the regeneration process according to the present invention is completed and the bed is re-established for operating feed of a naphtha hydrogen reaction raw material for treatment. Hydrogenation shows excellent regeneration in activity, as shown in figure 2.

EXAMPLE 2 The catalyst of Example 1 is subjected to the same hydrogenation reaction conditions and raw material as described in Example 1, but the regeneration process is initiated when the hydrogenation catalyst illustrates a hydrogenation activity of diolefin of about 30% and a hydrogenation activity of nitrile which is almost completely deactivated, after 220 hours of operation.The catalyst deactivated in this way is regenerated according to the present invention as described in example 1. Figure 3 illustrates the excellent regeneration of the catalyst after such deactivation and extreme contamination exceeding 200 hours of operation.

EXAMPLE 3 The same catalyst as that established in example 1 is again subjected to the reaction of the raw material and hydrogenation as described in example 1. When the hydrogenation catalyst shows a deactivation similar to that of example 1, a hydrogen treatment was started without an abundant wash of initial nitrogen so that it removes naphtha and other hydrocarbons from the catalyst bed. Figure 4 illustrates the initial operation, regeneration number 1 according to example 2 and subsequent regeneration number 2 using only hydrogen as described above. As shown in the figure, regeneration using only hydrogen, without an initial release of nitrogen, does not regenerate the hydrogenation catalyst. Therefore, it is clear that the nitrogen washing step of the process of the present invention advantageously serves to provide excellent regeneration of a hydrogenation catalyst according to the invention. This invention may be constituted in other ways or may be carried out in other ways without departing from the spirit or essential characteristics thereof. Therefore, it is considered that the present modality in all its aspects is illustrative and not limiting, the scope of the invention is indicated by the appended claims, and all changes which are within the meaning and scope of equivalence are considered to be they are covered by them.

Claims (18)

1. A process for the simultaneous selective hydrogenation of diolefins and nitriles from a hydrocarbon feedstock, the process is characterized in that it comprises the steps of: (a) providing a hydrocarbon feedstock having a diolefin content of more than or equal to at about 0.1% by weight and a nitrile content of greater than or equal to about 2 ppm; (b) providing at least a first and second reactor zone, each containing a catalyst comprising a support material that is selected from the group consisting of inorganic oxide-zeolite composite material, carbon and zeolite, and a metal phase catalytically active which is selected from the group consisting of partially reduced group IB metals and completely reduced group VIII metals, the metallic phase is present in an amount of more than or equal to about 0.03% by weight, the catalyst has an activity of hydrogenation of the initial diolefin and the catalyst in the second reactor zone has a reduced diolefin hydrogenation activity; (c) mixing the raw material with hydrogen to provide a reaction feedstock having a ratio of hydrogen to diolefins and nitriles of less than about 3 times a stoichiometric amount necessary to selectively hydrogenate the diolefins and nitriles; (d) treating the reaction feedstock in the presence of the catalyst in the first reactor zone at a hydrogenation temperature and pressure until the catalyst in the first reactor zone has a reduced diolefin hydrogenation activity of not less than about 50% of the initial diolefin hydrogenation activity; (e) flushing the catalyst in the second reactor zone with an inert gas so that traces of hydrocarbon are removed from the catalyst and thus a washed catalyst is provided in the second reactor zone; (f) regenerating the washed catalyst in the reactor zone by the additional flow of the hydrogen washed catalyst so that a regenerated catalyst is provided in the second reactor zone having a regenerated diolefin hydrogenation activity which is greater than the reduced activity of diolefin hydrogenation; (g) treating the reaction feedstock in the presence of the catalyst in the second reactor zone at a hydrogenation temperature and pressure; until the catalyst has a reduced diolefin hydrogenation activity not less than about 50% of the initial hydrolenation activity of diolefin; (h) flushing the catalyst in the first reactor zone with an inert gas so that traces of hydrocarbon are removed from the catalyst and thus a washed catalyst is provided in the first reactor zone; (i) regenerating the washed catalyst in the first reactor zone by further flowing the hydrogen washed catalyst so that a regenerated catalyst is provided in the first reactor zone having a regenerated diolefin hydrogenation activity which is greater than the reduced hydrogenation activity of diolefin; and (j) repeating steps (d) to (i).

2. The process according to claim 1, characterized in that the regeneration step provides a regenerated catalyst having a regenerated diolefin hydrogenation activity of at least about 90% of the initial hydrolenation activity of diolefin.

3. The process according to claim 1, characterized in that the treatment step is carried out until the reduced diolefin hydrogenation activity is not less than about 50% of the initial hydrolenation activity of diolefin.

4. The process according to claim 3, characterized in that the treatment step is carried out until the reduced hydrolenation activity of diolefin is not less than about 80% of the initial hydrolenation activity of diolefin.

5. The process according to claim 1, characterized in that the treatment step comprises feeding the hydrocarbon feedstock to the catalyst in a feed direction, wherein the washing step is carried out by feeding the inert gas in a substantially opposite manner. the feeding direction, and wherein the regeneration step is carried out by feeding a reducing gas in the feed direction.

6. The process according to claim 1, characterized in that the abundant washing step and the regeneration step are carried out by sequentially feeding the inert gas and the reducing gas to the catalyst in substantially opposite directions.

7. The process according to claim 1, characterized in that steps (e) and (f) are carried out substantially simultaneously with step (d), and wherein steps (h) and (i) are carried out performed substantially simultaneously with step (g), whereby the catalyst in one of the first and second reactor zones is washed and regenerated while the catalyst in the other of the first and second reactor zones is used to treat the raw material of reaction.

8. The process according to claim 1, characterized in that the step of washing inert gas is carried out at a temperature of less than or equal to about 10 300 ° C.

9. The process according to claim 1, characterized in that the step of inert gas washing is carried out at a temperature between approximately subambiente until 15 approximately 300 ° C.

10. The process according to claim 1, characterized in that the abundant washing step of inert gas is carried out at a temperature between about room temperature to about 290 ° C.

11. The process according to claim 1, characterized in that the inert gas is selected from the group consisting of nitrogen, helium, argon, methane, ethane, propane, 25 hydrogen and mixture thereof.

12. The process according to claim 1, characterized in that the inert gas is nitrogen.

13. The process according to claim 1, characterized in that the regeneration step is carried out at a temperature between about 100 ° C and about 300 ° C.

14. The process according to claim 1, characterized in that the regeneration step is carried out at a pressure between about 10.5 kg / cm2 to about 46 kg / cm2 (150-650 psi).

15. The process according to claim 1, characterized in that the regeneration step comprises washing the washed catalyst abundantly with a volume of reducing gas of between about 5 and about 20 times an amount of reducing gas sufficient to substantially reduce the metallic phase of the catalyst.

16. The process according to claim 1, characterized in that the washing step is carried out at an inert gas space velocity of between about 100 to about 1000 h "1.

17. The process according to claim 1, characterized in that the regeneration step is carried out at a reducing gas space velocity of between about 20 h "1 and about 200 h" 1.

18. The process according to claim 1, characterized in that the reducing gas is hydrogen.