A PROCESS FOR REGENERATING A MONOFUNCTIONAL LARGE-PORE ZEOLITE CATALYST HAVING HIGH SELECTIVITY FOR PARAFFIN DEHYDROCYCLIZATION

Abstract: Process for regenerating a large-pore zeolitic catalyst that has been deactivated by the formation of Group VIII metal agglomerates on the catalyst surface. In the process, the Group VIII metal agglomerates are redispersed to produce agglomerates of small size. It comprises an oxychlorination step, a nitrogen purge step and a reduction step.

Description: A PROCESS FOR REGENERATING A MONOFUNCTIONAL LARGE-PORE ZEOLITE CATALYST HAVING HIGH 05 SELECTIVITY FOR PARAFFIN DEHYDROCYCLIZATION Field of Invention The present invention relates to regenerating contaminated catalysts. More specifically, this applica- J_Q tion is directed to regenerating large-pore zeolite cata¬ lysts. BACKGROUND OF THE INVENTION The invention described below relates to a pro¬ cess for regenerating large-pore zeolite catalysts having _5 a Group VIII metal which are used to reform petroleum feedstocks. Within the past few years such catalysts have become the object of considerable interest primarily due to their surprisingly high selectivity for paraffin dehy- drocyclization to produce aromatics under low pressure 0 reforming conditions. However, it has also been found that such catalysts are sensitive to certain types of contamination. Accordingly, there is an urgent need for a regeneration procedure for these catalysts. During reforming, conventional catalysts become 5 deactivated by changes in the physical state of the cata¬ lytic metal and the accumulation of carbonaceous matter (such as coke) on the catalyst surface. When deactivation occurs, it is common practice to regenerate the catalyst. U.S. Patent No. 3,496,096 granted on February 17, 1970 to 0 Kluksdahl, describes a catalyst regeneration procedure for a platinum/rhenium catalyst. The procedure involves three steps. In the first step the catalyst is contacted with an oxygen containing gas at a temperature of less than 427°C (800°F) which burns coke off the catalyst surface. 5 In the second step the catalyst is again contacted with a gas containing oxygen and a halide, but this time the temperature is between 427°C (800°F) and 482°C (900°F). In the final step the catalyst is contacted with a gas having a higher oxygen concentration and halide but at a 0 temperature above 482°C (900°F). The regenerated catalyst is then contacted with a gas containing hydrogen to reduce * -2- the valence states of the oxidized platinum and rhenium. Regeneration procedures such as this one have become known in the art as oxychlorination procedures (see also U.S. Patent No. 3,776,640 granted on December 4, 1973 to Moravec et al. which describes a similar procedure for removing coke) . One of their purposes is to redisperse platinum agglomerates which are formed during reforming or the coke burn. U.S. Patent No. 4,493,901 granted on January 15, 1985 to Bernard et al. discloses a regeneration procedure for a coke deactivated zeolite reforming catalyst. Patentees use a hydration step following a coke burn and an oxychlorination step. The hydration step is carried out while contacting the . catalyst with cool air after the oxychlorination step. Patentees add approximately 10 wt.% water to the cooling air. European Patent Application 0 142 352 (Publication Number) filed on November 9 , 1984 broadly describes a regeneration procedure for deactivated L-zeolite catalysts. The deactivation addressed by the disclosed procedure is caused by coke deposition and platinum agglomeration. Applicants employ a coke burn step and an oxychlorination step. However, when the redispersion procedures outlined in the European patent application are attempted on catalysts that have a binder, such as silica or alumina, the activity of the regenerated catalyst is substantially lower than that of the fresh catalyst- Sulfur may also cause catalyst deactivation. This is a particular problem for large-pore zeolite cata¬ lysts having a Group VIII metal. See U.S. Patent No. 4,456,527 granted June 26, 1984 to Buss et al. Accordingly, there is still a need for a proce¬ dure -which can restore the activity of large-pore zeolitic catalysts having an inorganic binder which have been deactivated in whole or in part by the formation of platinum agglomerates. This need has now been satisfied by the invention which is summarized and detailed below. SUMMARY OF THE INVENTION According to the present invention, a process is provided for redispersing platinum on a catalyst com¬ prising L-zeolite and an inorganic oxide binder. The process comprises (a) oxychlorinating the catalyst under oxychlorinating conditions; (b) contacting the catalyst with an inert gas; and (c) contacting the catalyst with dry hydrogen. The catalyst is preferably bound with clay, alumina, silica, or silica-alumina. Preferably, the hydrogen stream contains less than 1000 ppm water, more preferably less than 500 ppm water, most preferably less than 100 ppm water. It is also preferred that the inert gas is nitrogen and it preferably contacts the catalyst for a time between 10 minutes and 1 hour and 30 minutes. The process more preferably comprises (a) con¬ tacting the catalyst under oxychlorinating conditions with a gas comprising 1% to 21% oxygen, 1% to 4% water, and an effective amount of chlorine atoms to ,achieve a chlorine to platinum ratio between 4:1 and 1000:1; (b) contacting the catalyst with a gas comprising nitrogen, for a time between 10 minutes and 1-1/2 hours, at a gas flow rate of between 150 and 1500 GHSV, and at a temperature between 454°C (850°) and 510°C (950°F); and (c) contacting the catalyst with a gas comprising hydrogen having less than 1000 ppm water, at a temperature between 427°C (800°F) and 510°C (950°F) and a gas rate between 150 and 1500 GHSV. Among other factors, the process of the present invention is ba * sed on my finding that a catalyst having a Group VIII metal, an inorganic oxide binder, and L-zeolite can be regenerated to an unexpectedly high activity by using relatively low severity conditions in the reduction step of the process. Preferably, the lower severity con- ditions include the use of relatively lower temperature in the reduction step than is typical in prior art processes and also the use of substantially dry hydrogen in this step. Additionally, I have found that higher activity can be achieved if the inert gas purge time is limited in the process. Gas flow rates are also an important element of the catalyst regeneration process of the present inven- tion. I have found that the gas flow rate in steps (a), (b) and (c) of the process should be maintained at a rela¬ tively high level to attain regeneration of the catalyst to high activity. If the flow rate is diminished for step (a), (b) or (c) , then the exposure time preferably is increased to attain the high activity upon regeneration. DETAILED DESCRIPTION OF THE INVENTION The following discussion presents a more detailed discussion of the present invention. Monofunctional Large Pore Zeolite Catalysts As explained in the Summary section, the present invention is a procedure for regenerating large-pore zeolite catalysts. Hereinafter, the large-pore zeolite catalysts will simply be referred to as "catalysts". These catalysts generally co priset a large-pore zeolite; a Group VIII metal (such as a noble metal, or more specifically, platinum) ; preferably the zeolite also con¬ tains a metal from either Group IA or IIA. Preferably, the large-pore zeolite is L-zeolite. Large pore zeolites are defined as zeolites having an effective pore diameter between 6 and 15 Angstroms. Among the large-pore zeolites which have been found to be useful in the practice of the " present invention, type L zeolite, zeolite X, and zeolite Y are the most important and have apparent pore sizes on the order of 7 to 9 Angstroms. A composition of type L-zeolite, expressed in terms of mole ratios of oxides, may be represented as follows: (0.9-1.3)M2 n O:Al 2 O 3 (5.2-6.9)SiO 2 :yH 2 O wherein M designates a cation, n represents the valence of M, and y may be any value from 0 to 9. Zeolite L, its X-ray diffraction pattern, its properties, and method for its preparation are described in detail in U.S. Patent No. 3,216,789 which is hereby incorporated by reference in its entirety. The real formula may vary without changing the crystalline structure; for example, the mole ratio of silicon to aluminum (Si/Al) may vary from 1.5 to 3.5. The chemical formula for zeolite Y expressed in terms of mole oxides may be written as: (0.7-l.l)Na 2 O:Al2θ 3 :xSiO 2 :yH 2 O wherein x is a value between 3 and 6, and y may be a value up to about 9. Zeolite Y has a characteristic X-ray diffraction pattern which may be employed with the above formula for identification. Zeolite Y is described in more detail in U.S. Patent No. 3,130,007. U.S. Patent No. 3,130,007 is hereby incorporated by reference in its entirety to show a zeolite useful in the present inven¬ tion. Zeolite X is a synthetic crystalline zeolitic molecular sieve which may be represented by the formula: (0.7-1.1) 2 / n 0:Al 2 0 3 : (2.0-3.0)Si0 2 :yH 2 0 wherein M represents a metal, particularly alkali and alkaline earth metals, n is the valence of M, and y may have any value up to about 8 depending on the identity of M and the degree of hydration of the crystalline zeolite. Zeolite X, its X-ray diffraction pattern, its properties, and method for its preparation are described in detail in U.S. Patent No. 2,882,244. U.S. Patent No. 2,882,244 is hereby incorporated by reference in its entirety to show a zeolite useful in the present invention. These zeolites contain exchangeable cations. Common cations that are useful for catalysts of this invention are in Groups IA (alkali metals) and IIA (alkaline earth metals). When Group IA, alkali metals are used, sodium, potassium, lithium, rubidium, or cesium are preferred. When Group IIA, alkaline earth metals are used, either barium, calcium, or strontium is preferred. The alkaline earth metal can be incorporated into the zeolite by synthesis, impregnation or ion exchange. In the present regeneration process it is impor¬ tant for the catalysts of this invention to contain one or more Group VIII metals, e.g., ruthenium, rhodium, palla¬ dium^ iridium or platinum. The preferred Group VIII metals are iridium, palladium, and particularly platinum. (When reference is made to a specific Group VIII metal, such as platinum, in this application it is used as a representative of the group.) The preferred percentage of platinum, in the catalyst is between 0.1% and 5%, the lower limit corresponding to minimum practical catalyst activity and the upper limit to roughly the maximum possi¬ ble platinum utilization. Group VIII metals are introduced into the large-pore zeolite during synthesis, impregnation or exchange in an aqueous solution of an appropriate salt. If it is desired to introduce two Group VIII metals into the large-pore zeolite, the operation may be carried out simultaneously or sequentially. By way of example, platinum can be introduced by impregnating the large-pore zeolite with an aqueous solu- tion of tetrammineplatinum -(II) nitrate [Pt(NH 3 )^] (N0 ) 2 , tetrammineplatinum (II) chloride [Pt(NH 3 )^]Cl 2 , or dinitrodiamino-platinum [Pt(NH 3 ) 2 (N0 2 ) ] . In an ion- exchange process, platinum can be introduced by using cationic platinum complexes such as tetrammineplatinum (II) nitrate. The presence of a binder is important in the present process. An inorganic oxide is used as a matrix to bind the large-pore zeolite. This binder can be a natural or a synthetically produced inorganic oxide or combination of inorganic oxides. Typical inorganic oxide binders which can be used include clays, alumina, silica or mixtures thereof. Preferable binders are alumina, silica, or mixtures thereof. Acidic sites on the binder are preferably exchanged by cations which do not impart strong acidity (such as sodium, potassium, rubidium, cesium, calcium, strontium, or barium). After the desired metal or metals have been introduced, the catalyst should be calcined in air and then reduced in hydrogen. The catalyst may have a limited aqueous soak time and also be calcined in a steam-air mixture as specified in U.S. Patent No. 4,608,356 granted August 26, 1986 to Buss et al which is hereby incorporated by reference in its entirety. At this stage it is ready for use in the dehydrocyclization process. The regeneration process of the present inven¬ tion may be used on catalysts in the form of extrusions, pills, pellets, granules, broken fragments, or various other special shapes. The catalysts can become deacti¬ vated in any of the conventional types of eguipment used for catalytic reforming. Sulfur and Coke Contamination The present regeneration process is necessary due to platinum agglomeration which is a typical conse¬ quence of various types of contamination. For example, sulfur and coke contamination. The sulfur sensitivity of these catalysts is known from U.S. Patent No. 4,456,527 to Buss et al which is hereby incorporated by reference in its entirety. Sulfur contamination quickly lowers the catalytic activity for reforming reactions. To remove sulfur, various pro¬ cedures have been designed, for example, see U.S. Serial No. 944,403 which is hereby incorporated by reference in its entirety. Coke can also contaminate and deactivate the catalyst and can be generally described as an expected result of the reforming process. Hydrocarbons contact the catalyst and are dehydrogenated, some to the extent that only coke is left on the catalyst. As time increases, coke deposition forces an adjustment of the process con¬ ditions to maintain a certain target octane number. How¬ ever, there comes a time when the process conditions can no longer be adjusted to compensate for coke deposi¬ tion (much like sulfur contamination). It is at this point that the catalyst must be regenerated to restore its activity. Sulfur and Coke Removal Coke and sulfur removal processes are typically used prior to the present regeneration process. This removal preferably involves some type of oxidation at least. When sulfur is removed in the fashion described in U.S. Serial No. 944,403, the platinum particles are inten¬ tionally formed into large agglomerates. In this form, the catalyst is completely inactive for reforming. Conse- quently, the platinum must be redispersed to restore the catalytic properties of the catalyst. Likewise, when coke is removed from the catalyst by oxidation, platinum agglomerates are likely to form if they are not already present as a result of the reforming process itself. Typically, an oxidation step is used in advance of the basic oxychlorination process to burn coke off the catalyst. A preferred example is as follows: The catalyst is preferably contacted with a gas containing between 0.1 and 2.0 vol. % oxygen (for the purposes of this application gas concentrations are expressed as a percent of the total volume). When more than 0.5% 0 is present in-the gas, care should be taken to minimize the catalyst temperature until the carbon level has been sub¬ stantially reduced. Nitrogen or aiaother inert gas is preferably present in a sufficient amount to make up the remainder of the gas. The temperature is preferably between 260°C (500°F) and 427°C (800°F). The gas flow is preferably between 150 and 5000 GHSV, more preferably between 150 and 1500 GHSV. The pressure preferably ranges between 1 and 30 atmospheres, more preferably between 1 and 10 atmospheres. Water is preferred in a range between 0% and 10%. The catalyst is oxidized until sufficient coke has been removed. The time can preferably range between 15 minutes and 10 hours, more preferably between 30 minutes and 5 hours. After coke or sulfur removal, the average size of the platinum agglomerates can range from 10 to 300 Angstroms (depending on the conditions used for removing the coke or sulfur). Platinum agglomerates of this size must be redistributed over the catalyst to form particles smaller than apprbximately 10 Angstroms. This is necessary if the catalyst is to have an appreciable activity for aromatization. Oxychlorination The present regeneration process provides a method for redispersing Group VIII metal agglomerates by an oxychlorination procedure. Basically, the oxychlo- rination procedure comprises contacting the catalyst with an oxygen-containing qas arid a chloride-containing gas followed by a nitrogen purge and a reduction. The proce¬ dure involves three steps. In the first step the catalyst having platinum agglomerates is contacted with a mixture of air, ' water, and chloride or chlorine atoms. Oxygen is preferably present in a concentration of greater than 0.1%, more preferably between 1% and 21% of the total gas volume. Water is preferably present in a range of from 0.1% to 10%, more preferably from 1% to 4%, and most preferably from 2% to 3%. The chloride or chlorine atoms are prefer¬ ably present in an amount sufficient fco achieve a ratio of chlorine to platinum atoms of between 4:1 and 1000:1, more preferably between 5:1 and 200:1, and most preferably between 10:1 and 50:1. Examples of possible chlorine or chloride compounds are: chlorine gas; organic chlorides, such as carbon tetrachloride (CCl^); or hydrogen chloride (HC1). The temperature for the first step is preferably between 427°C (800°F) and 593°C (1100°F), more preferably between 482°C (900°F) and 538°C (1000°F), and most prefer¬ ably between 496°C (925°F) and 524°C (975°F). The time for the first step is preferably from 1 to 24 hours, more preferably 1 to 3 hours. The space velocity is preferably between 150 and 5000 GHSV, more preferably between 150 and 1500 GHSV. Pressure is preferably between 1 and 30 atmospheres, more preferably between 1 and 10 atmo¬ spheres. ι n the second step (also called a nitrogen purge) the catalyst is preferably contacted with a dry inert gas, more preferably nitrogen, for a time sufficient to purge the catalyst bed of oxygen. "Dry" means having preferably less than 1000 ppm water, more preferably less than 500 ppm water, and most preferably less than 100 ppm water. This nitrogen purge step is preferably between 10 minutes and 1-1/2 hours, more preferably between 10 minutes and 1 hour. The temperature is preferably between from 427°C (800°F) and 538°C (1000°F), more pre- ferably between 454°C (850°F) and 510°C (950°F), but most preferably between 469°C (875°F) and 496°C (925°F). The gas velocities and pressures should be in the same ranges as the first step. In the third and final step (also called a hydrogen reduction step), the catalyst is preferably con¬ tacted with dry hydrogen for a time sufficient to reduce all the exposed platinum. "Dry" means having preferably less than 1000 ppm water, more preferably less than 500 ppm water, and most preferably less than 100 ppm water. This time is dependent on the hydrogen flow and the reduction temperature. A shorter time is preferred based on commercial considerations, for example, prefer¬ ably less than 5 hours, or more preferably between 1 and 4 hours. The temperature is preferably between 316°C (600°F) and 538°C (1000°F), more preferably between 427°C (800°F) and 510°C (950°F) , and most preferably between 469°C (875°F) and 496°C (925°F). The gas velocities and pressures are preferably in the same ranges as the first and second steps. An oxygen post-treatment step can be inserted between the first and second steps. In the oxygen post- treatment, the catalyst is preferably contacted with an oxygen-containing gas having an oxygen concentration greater than 0.1%, more preferably between 1% and 21%. The temperature is preferably between 427°C (800°F) and 530°C (1000°F), more preferably between 482°C (900°F) and 524°C (975°F). Water is preferably present in an amount between 0 and 10%, more preferably between 1% and 4%, and most preferably between 2% and 3%. The gas velocities and pressures are preferably in the same ranges as the first, second and third steps. It has been surprisingly found that in the final hydrogen reduction step the hydrogen should preferably have less than 1000 ppm water, more preferably less than 500 ppm water, and most preferably, less than 100 ppm water. Also, the amount of hydrogen preferably should be greater than 2 moles H 2 /mole platinum, more preferably greater than 10 moles H 2 /mole platinum. Preferably, the hydrogen should have a total gas concentration of between 1 vol. % and 100 vol. %, more preferably 10% and 100%, and most preferably 50% and 100%. If there is less than 100% hydrogen, then an inert gas should preferably constitute the remainder of the gas. The following examples are presented here as specific embodiments of the overall concept of the present invention. They are intended to be exemplary and not restrictive in any way. EXAMPLES Example 1 The following example shows the regeneration of a sulfur contaminated catalyst according to the present invention. A catalyst comprising .8% platinum on a barium-potassium L-zeolite containing 8% barium was sul- fided until it accumulated 317 ppm of sulfur and was sub¬ stantially deactivated for paraffin dehydrocyclization [this is an isothermal test in which a light naphtha con¬ taining mostly g-Cg paraffins was reformed at 493°C (920°F), 100 psig and 6 liquid hourly space velocity] . Platinum atoms on the surface of the catalyst were observed by transmission electron microscopy (TEM) and occurred in groups which were 10 to 20 Angstroms in diameter. The deactivated catalyst was then subjected to a sulfur removal step which is as follows. The catalyst was contacted with a gaseous stream of 1% 0 2 in 99% N 2 at 482°C (900°F) and 250 GHSV for 24 hours. Then the cata¬ lyst was contacted with a gaseous stream of carbon monoxide which had been bubbled through a 32% HC1 solution to give 3.5% HC1, 1% H 2 0, 95.5% CO. This operation was conducted at 482°C (900°F) and 250 GHSV, for 24 hours. The sulfur concentration of the catalyst after treatment was 80 ppm. Platinum agglomerates, in the form of cubic crystals about 30 to 80 Angstroms in the edge length, were observed on the catalyst by TEM. The catalyst was com- pletely inactive for reforming reactions, including cyclo- hexane dehydrogenation. To restore activity to the catalyst, it was subjected to an oxychlorination step. This process was conducted as follows. The catalyst was contacted with wet air, at a flow rate of 1440 GHSV, and a temperature of 538°C (1000°F) for 1 hour. The wet air in this and later examples contained approximately 2% H 0 and was obtained by saturating air with water at room temperature. The pressure for this, and all further examples (unless noted) , was 1 atmosphere. Then the catalyst was contacted with a gaseous mixture of wet air at 1440 GHSV and a tem¬ perature of 482°C (900°F) for 2 hours, while chloride was injected as carbon tetrachloride (CCl^) at a ratio of approximately 20 chlorine atoms per 1 platinum atom. Thereafter, the wet air mixture was continued at 1440 GHSV and 482°C (900°F) for an additional hour but without the CCl^. Then, dry nitrogen was contacted with the catalyst at 1440 GHSV and 482°C (900°F) for 10 minutes. Following that, dry hydrogen was contacted with the catalyst at 1440 GHSV and a temperature of 482°C (900°F) for 1 hour. After this procedure, the catalyst was analyzed by TEM and it was observed that the only visible platinum was present in agglomerates of 10 Angstroms or smaller. After 20 ' hours onstream the catalyst was then tested for paraffin dehydrocyclization and it was found to have about 40% of the activity of the fresh catalyst also measured after 20 hours onstream. (K regenerated catalyst/K fresh catalyst = 0.40) (K = (selectivity) [In (1-conversion) ] ) . Example 2 The following example shows regeneration of a deactivated catalyst according to the present invention. Fresh, bound catalyst comprising .8% platinum on a barium-potassium L-zeolite containing 8% barium (metal concentrations are based on the weight of the zeolite, however, the catalyst was bound with 20% Si0 2 which changes the metal concentration for the bound catalyst) was reduced in H 2 at 482°C (900°F) for 1 hour, purged with N 2 and then heated in wet air for 1 hour at 538°C (1000°F). The resulting catalyst had a dehydrocyclization activity of /K fresh = 0.20. To restore the activity to the catalyst, it was subjected to the following oxychlorination step. The catalyst was contacted with a gaseous mixture of wet air at 1440 GHSV and a temperature of 510°C (950°F) for 2 hours, while chlorine was injected as carbon tetrachlo- ride (CCI4) at a ratio so that there were 20 chlorine atoms per 1 platinum atom. Then, dry nitrogen was injected at 1440 GHSV and 482°C (900°F) for 1 hour. Following that, dry hydrogen was contacted with the cata¬ lyst at 1440 GHSV and a temperature of 482°C (900°F) for 1 hour. The catalyst was then tested for paraffin dehydrocyclization and it was found that the activity was greater than the fresh catalyst (both measurements were made after 20 hours onstream) (K regenerated catalyst/K fresh catalyst = 1.15) (K = (selectivity) [1 (1-conver¬ sion) ] ) . The catalysts in the following examples con¬ tained .8 wt. % platinum on a barium-potassium L-zeolite containing 8 wt. % barium, the weight percent calculated based on L-zeolite without a binder. Bound catalysts contain 20 wt. % inorganic binder, which reduced the over¬ all platinum weight percent to .64% and the overall barium weight percent to 6.4%. Example 3 The following example shows a basic oxychlorina- tion pr <ocess using different conditions to achieve good results. It is not a strict example of the present inven¬ tion because the L-zeolite is not bound and wet hydrogen is used. Four fresh catalysts were taken and subjected to the following deactivation and regeneration conditions. Experiment No. 216 234 238 242 Fresh Catalyst L-Zeolite 238; no binder. Deactivation All catalysts were reduced in hydrogen Procedure at 482°C (900°F) for 1 hour. Then they wereoxidized in wet 1% 0 in the following conditions: 538°C 538°C 566°C 566°C (1000°F) (1000°F) (1050°F) (1050°F) for for for for 3 hrs. 3 hrs. 16 hrs. 16 hrs, Oxychlorination All the catalysts were contacted with Procedure wet (about 2% ' H 2 0) 1% 0 2 and CCl * (at a ratio of 20 Cl/Pt atom) at 510 S C (950°F) and 1440 GHSV for 2 hours. 0 2 Post All the catalysts were contacted with Treatment wet (about 2% H 2 0) 1% O, at 510°C (950°F) for 1 hour at 1440 GHSV. Purge All " the catalysts were contacted with * wet (about 2% H 2 0) 2 at 510°C (950°F) for 10 minutes at 1440 GHSV. H 2 Reduction All the catalysts were reduced in wet (about 2% H 2 0) hydrogen at 510°C (950°F) and 1440 GHSV for the following times: 1 hr. 2 hr. 2 hr.2 hr. Activity Test The following conversions* and selec- tivities* were noted for each catalyst for 3 hrs. onstream/20 hrs. onstream: Conversion: 78/69 79/71 77/69 78/69 Selectivity: 71/81 71/78 73/81 75/81 Conversion is defined as the fraction of the reac- tants that is converted to either aromatics or com¬ pounds with fewer than 6 carbon atoms. Selectivity is defined as the fraction of converted reactants that are converted to aromatics. Example 4 The following catalysts were treated in a similar manner to those in Example 3, but these were deactivated by coke fouling. Again, it is not a strict example of the present process because the zeolite is not bound and wet hydrogen is used. However, it is useful to show that the process will work on an unbound, coke con¬ taminated catalyst. Experiment No. 222 230 Fresh Catalyst L-Zeolite 238; no binder. Deactivation These catalysts were run in a pilot Procedure plant under standard reforming condi¬ tions until they were substantially deactivated for paraffin dehydrocycliz¬ ation. Coke Burn Both catalysts were contacted with 1% 0 2 at 316°C (600°F) for 1 hr. , then at 416°C (780°F) for 5 hrs. in the following amounts of H 2 0: About 2% 0% Oxychlorination The catalysts were contacted with wet Procedure 1% 0 2 for 2 hrs. at 510°C (950°F), 1440 GHSV and CC1 4 to achieve a 33:1 ratio of Cl/Pt. 0 2 Post The catalysts were contacted with wet Treatment 1% 0 2 for 1 hr. at 510°C (950°F) and 1440 GHSV. N 2 Purge Wet (about 2% H 2 0) 2 at 510°C (950°F) for 10 min. H 2 Reduction Both catalysts were subjected to wet (about 2%) hydrogen at 510°C (950°F) for 3 -hrs. Activity Test Conversion: 70/64 67/51 Selectivity: 76/80 71/76 Example 5 This example shows that unacceptable results are obtained when wet hydrogen is used in regenerating a coke contaminated, bound catalyst. The following catalysts were treated in a similar manner to those of Example 4, however, a binder was used to hold the catalyst powder together. Experiment No. 226 228 Fresh Catalyst L-zeolite L-zeolite 114 382 Binder Al 2 °3 SiO. Deactivation The catalysts were run i * a pilot plant Procedure under standard reforming conditions until they were substantially deactivated for paraffin dehydrocyclization. Coke Burn The catalysts were contacted with 1% 0 2 for 1 hr. then at 416°C (780°F) for 5 hrs. , both without H 2 0. Oxychlorination The catalysts were contacted with wet Procedure 1% 0 2 for 2 hrs. at 510°C (950°F) , 1440 GHSV and CC1 to achieve a ratio of 20:1 Cl/Pt. 0 2 Post The catalysts were contacted with wet Treatment 1% 0 2 for 1 hr at 510°C (950°F) at 1440 GHSV. Purge Wet 2 at 510°C (950°F) and 1440 GHSV for: 30 min. 10 min, H- Reduction The catalysts were contacted with wet (about 2%) hydrogen at 510°C (950°F) for 3 hrs. Activity Test Conversion: 53/39 52/39 Selectivity: 65/70 67/70 Example 6 This example shows that good results are obtained when dry N and dry H 2 are used at lower temperatures on a bound catalyst. Experiment No. 278 285 Fresh Catalyst L-zeolite L-zeolite 430 382 Binder SiO- SiO- Deactivation Catalyst was Coke fouling as Procedure reduced in Example 5. hydrogen for 1 hr. at 482°C (900°F) . Then it was oxidized in dry air at 538°C (1000°F) for 3 hrs. Coke Burn No. Coke burn as Example 5. Oxychlorination The catalyst was The catalyst was Procedure contacted with contacted with wet air at 510°C wet air at 538°C (950°F) for 2 hrs. , (1000°F) for 1 hr. 1440 GHSV, and Then wet air at enough CC1 4 to 510°C (950°F) for achieve a 20:1 Cl/Pt 2 hrs. with CC1 ratio. added to achieve 20:1 Cl/Pt. 0 2 Post The catalyst was The catalyst was Treatment contacted with contacted with wet wet air at 510°C air at 510°C (950°F) for 1 hr. (950°F) for 1 hr. N 2 Purge Dry at 482°C (900°F) for 1 hr. and 1440 GHSV. H Reduction Dry H 2 at 482°C (900°F) for 1 hr. and 1440 GHSV. Activity Test Conversion: 79/71 75/67 Selectivity: 82/88 81/87 Example 7 This example shows the effect of treating the catalyst with dry N 2 for varying times in the nitrogen purge step. Experiment No. 319 314 318 322 323 Fresh Catalyst L-zeolite 382 L-zeolite 485 Binder All catalysts had Si0 2 as a binder. Deactivation Coke fouling as Catalyst was Procedure Example 4. reduced in H 2 1 hr. , then oxidized in wet air at 538°C (1000°F) for 1 hr. Coke Burn Coke burn as No. Example 4. Oxychlorination 319 and 314 318, 322, and 323 were Procedure catalysts were contacted with wet air contacted with at 510°C (950°F) 1440 wet air at GHSV and CC1 4 to 538°C (1000°F) achieve a ratio for 1 hr. Then of 20:1 Cl/Pt atoms. wet air at 510°C (950°F) 1440 GHSV for 2 hrs. and CCl^ to achieve a ratio of 20:1 Cl/Pt atoms. 0 2 Post The catalyst were contacted with wet air Treatment at 510°C (950°F) for 1 hr. at 1440 GHSV. N 2 Purge All the catalysts were contacted wi th dry N 2 at 482 °C ( 900 °F ) for the following t ime pe riods : 1 hr. 2 hrs. 6 hrs. 16 hrs. 30 min. H 2 Reduction All the catalysts were contacted with dry H 2 at 482°C (900°F) for the following time periods: 1 hr. 4 hrs. 4 hrs. 4 hrs. 1 hr. Activity Test Conversion: 75/70 64/60 64/49 67/52 67/58 Selectivity: 82/88 85/89 81/87 83/89 83/89 Example 8 These experiments show the effect of a variety of flow rates. Experiment No. 285 292 287 Fresh Catalyst All catalysts were zeolite 382. Binder All catalysts used Si0 2 b-inder. Deactivation Coke fouling as in Example 4. Procedure Coke Burn Coke burn as in Example 5. Oxychlorination The catalyst was The catalysts were Procedure contacted with contacted with wet air wet air at 538°C at 510°C (950°F) for 2 (1000°F) for hrs. with CC1 4 added 1 hr. Then wet to achieve a 20:1 air at 510°C Cl/Pt ratio; at the (950°F) for 2 hrs. following rates: with CC1 4 added to achieve a 20:1 Cl/Pt 480 GHSV 140 GHSV ratio. A flow rate of 1440 GHSV was used. 0 2 Post The catalysts were contacted with wet air Treatmen at 510°C (950°F) for 1 hr. , but: 1440 GHSV 480 GHSV 140 GHSV Purge Dry N 2 at 482°C (900°F) for 1 hr. , but: 1440 GHSV 480 GHSV 140 GHSV H 2 Reduction Dry H 2 at 482°C (900°F) for 1 hr. , but: 1440 GHSV 480 GHSV 140 GHSV Activity Test Conversion: 75/67 57/42 13/5 Selectivity: 81/87 71/82 45/35 Example 9 These experiments show the effect of pressure. Experiment No. 778 811 Fresh Catalyst L—zeolite L-zeolite 436 488 Binder SiO. SiO- These two catalysts were treated identically to Exp. No. 285 in the: Deactivation Procedure, Coke Burn, 0 2 Post Treatment, N 2 purge, and H 2 Reduction. However, Exp. No. 778 was run at 0 psig and Exp. No. 811 was run at 150 psig. Other changes are listed below: Oxychlorination See Exp. N 285 See Exp. No. 292 Procedure in Example 8. • in Example 8, the Cl/Pt ratio was 115 and the time was 20 hours. Activity Test Conversion: 70/60 14/0 Selectivity: 83/88 50/0 Example 10 These experiments show a compensatory effect for a low flow rate. Experiment No. 297 298 Fresh Catalyst L-zeolite 382 Binder Si0 Both catalysts were treated the same as Exp. No. 285 in Example 8 for the: Deactivation Procedure; Coke Burn; Oxychlorination Procedure; and the Hydrogen Reduction, but the flow rate was 480 GHSV. Other changes are listed as follows: 0 2 Post The catalyst were contacted with 1% 0 Treatment at 510°C (950°F) and 480 GHSV for: 3 hrs. 1 hr. 2 Purge The catalyst was contacted with dry N at 482°C (900°F) and 480 GHSV for: 1 hr. 3 hrs, Activity Test Conversion: 67/57 72/64 Selectivity: 79/86 79/86 Experiment Nos. 297, 298, and 292 in Example 8 show how the times can be extended to compensate for the effect of low gas flow rate. The embodiments of this invention which are exemplified above are intended solely as illustrations of the invention. They should not be interpreted as limiting the scope of the invention to just those features which are exemplified. As those familiar with this area of research will appreciate there are numerous variations of the invention as defined in the followinq claims which have not been exemplified but which will achieve equiva¬ lent results.

Claims: -22- WHAT IS CLAIMED IS: l. A process for redispersing platinum on a cata¬ lyst comprising platinum, L-zeolite, and an inorganic oxide binder, which process comprises! (a) oxychlorinating the catalyst under oxychlorinat¬ ing conditions; (b) contacting the catalyst with an inert gas; and (c) contacting the catalyst with dry hydrogen. 2. The process as recited in Claim 1 wherein the binder is selected from the group consisting essentially of clays, silica, alumina, or silica-alumina. 3. The process as recited in Claim 1 wherein the catalyst is contacted with hydrogen having less than 1000 ppm water. 4. The process as recited in Claim 1 wherein the catalyst is contacted with hydrogen having less than • 500 ppm water. 5. The process as recited in Claim 1 wherein the catalyst is contacted with hydrogen having less than 100 ppm water. 6. The process as recited in Claim 1 wherein the inert gas is nitrogen and it*is in contact with the cata¬ lyst for a time period between 10 minutes to 1 hour and 30 minutes. 7. The process as recited in Claim 6 wherein the nitrogen is in contact with the catalyst for a time between' 30 minutes and 1 hour. 8. The process as recited in Claim 7 wherein the nitrogen stream contains less than 1000 ppm water. 9. The process as recited in Claim 1 wherein the oxychlorination step comprises contacting the catalyst with a gas comprising 0.1% to 21% oxygen, 0.1% to 10% water, and an effective amount of chlorine atoms to achieve a chlorine to platinum ratio of between 4:1 and 1000:1. 10. The process as recited in Claim 9 wherein the source of chlorine atoms is selected from the group con¬ sisting of hydrogen chloride, chlorine gas, or an organic chloride. 11. The process as recited in Claim 1 further com¬ prising contacting the catalyst with an oxygen-containing gas in an oxygen post-treatment step after the oxychlori¬ nation step but before the catalyst is contacted with the inert gas. 12. The process as recited in Claim 11 wherein the oxygen-containing gas comprises between 0.1% to 21% oxygen and is contacted with the catalyst at a temperature between 427°C (800°F) and 538°C (1000°F), at a gas flow rate between 150 and 1500 GHSV. 13. The process as recited in Claim 12 where the oxygen concentration is between 1% and 10%. « 14. The process as recited in Claim 1 wherein the catalyst is contacted with the inert qas and the dry hydrogen at a temperature between 316°C (600°F) and 538°C (1000°F) . 15. The process as recited in Claim 1 wherein the catalyst is contacted with the inert gas and the dry hydrogen at a temperature between 427°C (800°F) and 510°C (950°F). 16. The process as recited in Claim 1 wherein the catalyst is contacted with the inert gas and the dry hydrogen at a temperature between 469°C (875°F) and 496°C (925°F). 17. A process for red'ispersing platinum on a cata¬ lyst which comprises platinum, L-zeolite, and an inorganic binder, the process comprising: (a) contacting the catalyst under oxychlorination conditions with a gas comprising 1% to 21% oxygen, 1% to 4% water, and an effective amount of chlorine atoms to achieve a chlorine to platinum ratio between 4:1 and 1000:1; (b) contacting the catalyst with a gas comprising nitrogen for a time between 10 minutes and 1 hour and 30 minutes, at a gas flow rate of between 150 and 1500 GHSV and at a temperature between 454°C (850°F) and 510°C (950°F); and (c) contacting the catalyst with a gas comprising hydrogen having less than 1000 ppm water, at a temperature between 469°C (875°F) and 495°C (925°F), and a gas velocity between 150 and 1500 GHSV. 18. The process as recited in Claim 18 wherein the binder is selected from the group consisting essentially of clays, silica, alumina, or silica-alumina. 19. The process as recited in Claim 17 wherein the gas comprising hydrogen contains less than 500 ppm water. 20. The process as recited in Claim 17 wherein the nitrogen contact time is between 30 minutes and 1 hour. 21. The process as recited in Claim 1 further com¬ prising removing carbon from the catalyst prior to the oxychlorination procedure. 22. The process as recited in Claim 17 further com¬ prising removing carbon from the catalyst prior to the oxychlorination procedure. 23. The process as recited in Claim 1 further comprising removing sulfur (from the catalyst prior to the oxychlorination procedure. 24. The process as recited in Claim 17 further com¬ prising removing sulfur from the catalyst prior to the oxychlorination procedure.

Inventors: MOHR DONALD H, MOHR, DONALD, H.
Applicants: CHEVRON RES, CHEVRON RESEARCH COMPANY
Application year: 1987
Main classification: B01J29
IPC codes: B01J29