REGENERATION OF ZEOLITE CATALYST

Abstract: Catalysts comprising a crystalline zeolite of constraint index in the range of 1 to 12 are known to exhibit high selectivity to para-substituted products and processes such as xylene isomerisation, particularly when they manifest certain xylene sorption characteristics. According to the invention this selectivity is maintained or enhanced by regenerating such catalysts, when deactivated by deposi­ tion of coke during use, in a hydrogen - instead of an oxygen - containing atmosphere under specified condi­ tions.

Description: REGENERATION OF ZEOLITE CATALYST This invention relates to a method for regeneration of an aged crystalline zeolite catalysts by treatment with hydrogen under particular conditions. During the course of converting organic compounds involving reactions such as alkylation, disproportionation, isomerization, cracking, polymerization, aromatization, etc. employing a catalyst comprising a crystalline aluminosilicate zeolite having a silica to alumina mole ratio of at least 12, a constraint index between 1 and 12 and particular xylene sorption characteristics conducive to para selectivity. It has been observed that the catalyst aged during conversion. Aging has been attributed to the deposition of coke which forms during the conversion reaction and covers the active sites of the catalyst, thereby reducing its activity which in turn results in lower conversion. The usual method heretofore employed for regeneration of such catalysts to restore high product conversion has been to: (1) purge the system of organic compounds; (2) lower the temperature to about 700 F; (3) cautiously add air/nitrogen mixtures which contain about 1 percent oxygen at a rate to prevent the temperature, usually a hot zone progressing from top to bottom of the catalyst bed, from exceeding about 900 F as the coke is burned to form CO and H2O; (4) enrich the oxygen concentration gradually after the bulk of the coke has been burned until it reaches a level of from about -3 to 20 percent oxygen, the latter oxygen content corresponding to air, taking care not to exceed a temperature of about 9000F; (5) purge the system with nitrogen to remove any residual oxygen; and (6) begin reaction by restoring conditions and feeds. This method requires purging the reactor before and after coke burning. It is also necessary very carefully to monitor the temperature throughout the entire catalyst bed to prevent excessive temperatures which could permanently damage and deactivate the catalyst. This method has the further disadvantage of removing all coke from the catalyst, necessitating, where desired, the re-deposition of a controlled amount of coke on the catalyst surface to impart selectivity characteristics thereto as, for example; in the selective production of paraxylene by methylation of toluene described in U.S. 4,001 ,346. A simpler, faster and more effective way to regenerate an aged crystalline zeolite catalyst of the above type has now been discovered. The method of the ivention eliminates the undesirable purging and, where desired, coke re-deposition steps necessary in the catalyst regeneration procedure heretofore employed. According to the present invention a method of regenerating a catalyst bearing a deposit of coke as a consequence of use in an organic compound conversion process, said catalyst comprising a crystalline zeolite having a silica to alumina ratio of at least 12, a constraint index of 1 to 12; a xylene sorption capacity of at least 1g.l1COg. of zeolite and an o-xylene sorption time for 30 percent of said capacity greater than 10 minutes, said sorption capacity and time being measured at 1200C and a xylene pressure of 4.5 + 0.8 mm. Hg, comprises exposing the catalyst to a hydrogen-containing atmosphere at 425 to 6500C and C to 2000 p.s.i.g. The zeolite may have been modified before use by combination therewith of 0.5 to 40 weight percent of a difficulty reducible oxide and/or by controlled deposition thereon of at least 1 weight percent of coke. Coke deposition may be effected by contacting the catalyst with a thermally decomposable organic compound at conditions including a temperature above the decomposition temperature of that compound but below 12000 and a hydrogen/compound ratio between 0 and 1, said conditions being collectively more severe than those prevailing in said use. Preferably the catalyst is regenerated at a pressure of 10 to 1000 p.s.i.g.,still more preferably at a pressure of 50 to 450 p.s.i.g. In desirable embodiments the atmosphere contacts the catalyst at a weight hourly space velocity of 0.25 to 10, and the duration of the regeneration is 1 to 48 hours, preferably between 2 and 30 hours. The thermally decomposable organic compound may be an organic compound subjected to the conversion process, a frequently used such compound being toluene. The zeolite advantageously has a crystal size greater than 0.5 micron, and the preferred zeolite is ZSM-5. Suitable difficultly reducible oxides are those of antimony, boron, magnesium and/or phosphorus. In practice the zeolite is usually composited with a binder, such as alumina. The hydrogen regeneration which characterizes the invention applies particularly to conversion processes such as alkylation of an aromatic hydrocarbon, disproportionation of an alkyl aromatic hydrocarbon, xylene isomerisation or conversion of lower monohydric alcohols and or their corresponding ethers to an olefin-rich hydrocarbon mixture. The catalyst undergoing regeneration in accordance with the method described herein comprises a crystalline aluminosilicate zeolite which is a member of a novel class of zeolites exhibiting some unususal properties. These zeolites are in particular defined as those possessing a constraint index of 1 to 12 and the xylene sorption characteristics hereinabove set forth. The significance of that index and those characteristics, and techniques for their measurement, are fully set forth in many of our prior specifications, for instance DE-OS 2,714;239 (which is concerned with catalysts the zeolite in which is further characterized by an alpha value of 2 to 5000). The class of zeolites defined herein is exemplified by ZSM-5; ZSM-11; ZSM-12; ZSM-35 and ZSM-38, described respectively in U.S. specifications 3;702,886, 3,709,979, 3,832,449, 4,016;245 and 4;046;859. These zeolites, when prepared in the presence of organic cations, are catalytically inactive, possibly because the intracrystalline free space is occupied by organic cations from the forming solution. They may be activated by heating in an inert atmosphere at 100oF for one hour, for example; followed by base exchange with ammonium salts followed by calcination at 10000F in air. The presence of organic cations in the forming solution may not be absolutely essential to their formation; however, the presence of these cations does appear to favor the formation of this special type of zeolite. More generally, it is desirable to activate the zeolite by base exchange with ammonium salts followed by calcination in air at about 10000F for from about 15 minutes to about 24 hours. The base exchange should reduce the alkali metal content of the zeolite to below 1.5 weight percent, and replacing ions can, in addition to hydrogen/ammonium, be selected from groups IB to VIII of the Periodic Table including, by way of example, nickel, copper,zinc, palladium, calcium or rare earth. Preferably at least 50, and desirably more than 75, percent of the cationic sites of the zeolite are occupied by hydrogen ions. In a preferred aspect of this invention, the zeolites hereof are selected as those having a crystal framework density; in the dry hydrogen form, of not substantially below about 1.6 grams per cubic centimeter, as also set forth in the aforementioned DT-OS 2,714,239. The crystal size of the as synthesized zeolite is generally within the approximate range of .01 to 40 microns. Preferably; the crystal size of the zeolite employed in the process of the invention is greater than about 0.5 micron, usually in the approximate range of 1-20 microns and particularly in the range of 1-6 microns. With the use of crystals within such size range, distinctly higher selectivity for production of desired product has been observed as compared with comparable use of smaller size crystals. In practice the zeolite is frequently incorporated in another material resistant to the temperature and other conditions employed in the process, again as fully described in DT-CS 2,714,239. Modification of the zeolite with a difficultly reducible oxide or oxides can readily be effected by contacting the zeolite with a solution of an appropriate compound of the element to be introduced, followed by drying and calcining to convert the compound to its oxide form. Specific techniques for introducing the oxides of phosphorus and magnesium, which is an advantageous embodiment are present simultaneously, are described in aforementioned DT-OS 2,714,239. Boron oxide is also an effective modifying component. Representative boron-containing compounds include boric acid, trimethyiborate, boron hydride, boron oxide, boron sulfide, butylboron dimethoxide, butylboronic acid, dimethylboric anhydride, hexamethylborazine, phenylboric acid, triethylborane, tetramethylammonium borohydride, triphenyl boron and allylborate. Reaction of the zeolite with the boron compound is effected by contacting the zeolite with such compound. 'Where the treating boron compound is a liquid, such compound can be in solution in a solvent at the time contact with the zeolite is effected. Any solvent relatively inert with respect to the treating compound and the zeolite may be employed. Suitable solvents include water and aliphatic, aromatic or alcoholic liquids. Where the boron-containing compound is; for example, trimetylborate, a hydrocarbon solvent such as n-octane may be employed. The boron-containing compound may be used without a solvent, i.e., may be used as a neat liquid. Where the boron-containing compound is in the gaseous phase, such as where gaseous diborane is employed, the treating compound can be used by itself or can be used in admixture with a gaseous diluent inert to the boron-containing compound and the zeolite such as nitrogen or helium or with an organic solvent, such as octane. Prior to reacting the zeolite with the boron-containing compound, the zeolite may be dried. Drying can be effected in the presence of air. Elevated temperatures may be employed. However, the temperature should not be such that the crystal structure of the zeolite is destroyed. eating of the boron-containing catalyst subsequent to preparation and prior to use is also preferred. The heating can be carried out in the presence of oxygen, for example, air. Heating can be at a temperature of about 1500C. However, higher temperatures, i.e., up to about 5000C are preferred. Beating is generally carried out for 3-5 hours but may be extended to 24 hours or longer. While heating temperatures above about 5000C can be employed, they are not necessary. At temperatures of about 10000C, the crystal structure of the zeolite tends to deteriorate. The amount of boron incorporated with the zeolite should be at least about 0.5 percent by weight. However, it is preferred that the amount of boron in the zeolite be at least about 1 percent by weight when the same is combined with a binder, e.g., 35 weight percent of alumina. The amount of boron can be as high as about 20 percent by weight or more depending on the amount and type of binder present. Preferably, the amount of boron added to the zeolite is between about 1.5 and 10 percent by weight. Without being limited by any theoretical considerations, it is contemplated that boron is actually present in the zeolite in an oxidized state, such as B203. Antimony oxide may also be employed as a modifying component. The antimony oxide is presesnt as Sb203 alone or in admixture with other antimony oxides with or without metallic antimony or other antimony compounds being present. In all instances, regardless of the particular state of oxidation of the antimony, its content with respect to the zeolite is computed as if it were present as Sb203. Generally, the amount of Sb203 in the composite catalyst will be between about 6 and about 40 weight percent and preferably between about 10 and about 35 weight percent. Antimony derivations which may be used include: the hydrides SbH3; the halides t4X3; MX5(M=Sb, X=F, Cl, Br, I); organic alkyl and aryl stibines and their oxides R3Sb, R5Sb, RxSb=O(R-alkyl or aryl); -halogen derivatives RSbX2, R2SbX, RSbX4; R2SbX3, R3SbX2, R4SbX; the acids H3Sb03, HSbO2, HSb(OH)6; organic acids such as RSbO(OH)2, R2SbO OH, all with R and X defined as above noted. Also included are organic ethers such as R2SbOSbR2; esters and alcoholates such as Sb(OOCCH3)3; Sb(OC4H9)3, Sb(OC2H5)3; Sb(OCH3)3; and antimonyl salts as (SbO)SO4. (SbO)N03; K(SbO)C4H406, NaSbQ2 3H20. Enhancement of the above crystalline aluminosilicate zeolite catalyst modified by combination therewith of one or more of the above difficultly reducible oxides may further be obtained by steaming and/or precoking thereof. Steaming is effectively carried out using an atmosphere containing from about 5 to about 100 percent steam at a temperature of from about 250 to about 10000C for a period of between about 0.5 and about 100 hours under pressures ranging from sub-atmospheric to several hundred atmospheres. Controlled precoking, i.e., selectivation, may be carried out separately or prior to the specified steam treatment by exposing the catalyst to a thermally decomposable organic compound, e.g., toluene, under high severity conditions at a temperature in excess of the decomposition temperature of said compound, generally greater than 10000F, but less than about 12GOOF, at a hydrogen to organic compound mole ratio between 0 and 1 to deposit the desired quantity of coke thereon, generally an amount of at least about 1 percent by weight. For toluene and organic compounds of similar reactivity, the temperature employed is greater than 10000F. with organic compounds that are more readily decomposable than toluene, precoking can be carried out at temperatures of less than 1 C00 F. With the use of higher temperatures in the aforenoted range, the presence of hydrogen has not been found necessary. With temperatures of less than about 11000F, preferably some hydrogen, generally at least 0.2 mole of hydrogen per mole of organic compound is desirable. Organic materials, thermally decomposable under the above temperature conditions to provide coke deposition, encompass a wide variety of compounds including by way of example, hydrocarbons, such as paraffinic, cycloparaffinic, olefinic, cycloolefinic and aromatic; oxygen-containing organic compounds such as alcohols, aldehydes; ethers, ketones and phenols; heterocyclics such as furans, thiophenes, pyrroles and pyridines. Usually; it is contemplated that a thermally decomposable hydrocarbon, such as an alkyl-substituted aromatic, will be the source of coke and most preferably toluene. In the latter case, toluene is initially brought into contact under conditions of temperature and hydrogen concentration amenable to rapid coke formation. The amount of coke deposited on the catalyst, prior to conducting conversion therewith, will ordinarily be at least about 1 weight percent. Generally, the amount of coke deposited will not exceed about 60 weight percent. The optimum amount of coke employed will depend among other variables on the crystal size of the aluminosilicate zeolite used and the nature of the catalyst binder, if any, employed. It has been found that as a general rule, the smaller the zeolite crystal size, the greater the amount of coke deposition required to achieve comparable results. Thus, on a binder-free basis, it has been observed that with the use of small zeolite crystals, e.g. in the range of .02 to .05 micron size, greater than 20 weight percent of coke deposition was required to obtain results comparable to those obtained with larger zeolite crystals, e.g. in the range of 1 to 2 microns, having approximately 4 weight percent of coke deposited thereon. The organic compound conversion in which the above described crystalline aluminosilicate zeolite catalysts are employed; prior to regeneration, include those reactions wherein coke is inherently deposited on the catalyst as a consequence of the conversion taking place. Typical conversion processes, given by way of example, include the methylation of toluene described in Ù.S. 3,965,207; 3,965;208; 3,965;209; 3,965,210; 4,001,346; 4,002,697 and 4,002;698; disproportionation of toluene to produce benzene and xylenes rich in the para isomer described in U.S. 4,011,276; 4,016,219 and 4,097,543; isomerization of xylenes described in U.S. 3,856,872; hydrocarbon conversion described in U.S. 3;790,471; alkylation of aromatic hydrocarbons with olefins described in U.S. 3,751,504; 3,751,506; 3,755,483; 3,96-2,364 and 4,016,218; conversion of lower monohydric alcohols and their ethers, such as methanol and dimethyl ether to hydrocarbon mixtures rich in olefins described in U.S. 3,911,041 and 3,979,472; alkylation of olefins described in U.S. 3,906,054; ethylation of toluene or ethylbenzene to selectively produce the para ethyl derivative thereof described in U.S. 4,086,287 and selective production of para dialkyl substituted benzenes described in application Serial Number 841,073, filed October 11, 1977. In accordance with the regeneration method of the present invention, the aged catalyst resulting from use in catalyzing an organic compound conversion of the type indicated hereinabove and containing coke in an amount generally between about 0.5 and about 5 weight percent, in excess of any prior coke deposited to selectivate the catalyst; is exposed to an atmosphere rich in hydrogen. Chile the presence of inert contaminants, e.g.; nitrogen; may be tolerated, it is generally preferred that the regeneration atmosphere consist essentially of hydrogen. The regeneration conditions are important and critical to the success of the operation. Generally, a temperature between about 425 and about 6500C and preferably between about 500 and about 6000C will be employed, with the pressure being between about 10 and about 1000 psig and preferably between about 50 and about 450 psig. It is of interest to note that any coke which was deposited during the selectivation procedure, to obtain a catalyst which provides higher selectivities to a para oriented product, is essentially not removed by the hydrogen regeneration treatment described herein. Without being limited by any theory, it appears as if another and different type of coke is deposited during various conversions of organic compounds such as alkylation, disproportionation, isomerization, cracking, oligomerization, aromatization, etc. It is this latter coke which is selectively removed by hydrogen treatment under the conditions specified, essentially restoring the initial catalyst activity while maintaining the desired high selectivity. Such is not possible when oxygen-containing gases are used in which instance all of the coke is removed indiscriminately. The amount and nature of the binder composited with the crystalline aluminosilicate zeolite also has been found to have a marked effect on the amount of coke deposition required to obtain the desired selectivity characteristics. Thus, while binder-free zeolite of 1 to 2 micron size afforded high paraxylene selectivity with about 4 weight percent of coke deposited thereon, comparable use of a composite of such zeolite (65 percent) and alumina (35 percent) required an average of about 22 weight percent of coke deposition. With the use of small zeolite crystals (.02 to .05 micron) and alumina binder (35 percent), it is contemplated that 40 percent or more coke deposition would be required to obtain the desired high paraxylene selectivity. Also, increase in alumina content of the zeolite composite, which desirably is in the form of an extrudate, would be expected to require increased coke deposition to obtain comparable high selectivity. With the use of other binders, such as clay or silica, it is anticipated that the amount of coke required for comparable results may be somewhat less than in the case where alumina is the sole binding material. Figure 1 of the drawing depicts selectivity for para ethyltoluene and conversion of toluene with time on stream during alkylation of toluene with ethylene over a coke-selectivated crystalline aluminosilicate zeolite catalyst of the type used in the present invention. Figure 2 of the drawing depicts selectivity for paraxylene and conversion of toluene with time on stream during disproportionation of toluene over a coke-selectYvated crystalline aluminosilicate zeolite catalyst of the type used in the present invention. The following examples will serve to illustrate the process of the invention without limiting the same: EXAMPLE 1 ZSM-5 zeolite in the hydrogen form (60.5 grams) having a crystal size of about 2 microns, containing 35 weight percent alumina binder, in the form of 1/16" extrudate, was steamed at 6000C for 1 hour. The steamed material was then impregnated with a solution of 38.7 grams of diammonium acid phosphate in 100 ml of water, dried and calcined at 5000C overnight in an open dish. The resulting product was cooled and impregnated overnight with a solution of 195 grams of magnesium acetate tetrahydrate in 133 ml of water, dried and calcined at 5000C for about 19 hours. The final catalyst contained 4.93 percent magnesium and 3.48 percent phosphorus by weight. EXAlIPLE 2 Alkylation of toluene with ethylene was carried out in the presence of hydrogen and the catalyst of Example 1. The conditions used for alkylation included a temperature of 4250C, a pressure of 100 psig, toluene/ethylene/hydrogen feed WHSV of 29.3/1.16/.24 with the mole ratio of toluene/ethylene/hydrogen being 7.7/1/3. Initial run performance results are summarized in Table 1 below. TABLE I Stream Av. Selectivity % Run Time Conversion. % p-Et, % Other No. Hours Toluene C2H4 Total ET(a) p+m-ET(a) Gas(b) Liquid 1 22 10.5-10.1 85-77 96.1 94.2 1.1 4.8 B. Selctivate 21 hrs 2 25 5.2-3.7 46-34 99.9 95.6 1.6 2.8 C. Regenerate H2 2 hrs. 3 21 5.0-2.5 46-23 99.9 95.5 2.2 2.3 C. Regenerate H2 20 hrs. 4 6 4.7-4.9 44-46 99.9 96.0 1.7 2.3 C. Regenerate H2 17 hrs. 5 7 4.9-3.6 47-34 99.9 95.7 1.6 2.7 C. Regenerate H2 16 hrs. 6 7 4.9-3.6 50-34 99.9 96.0 1.6 2.4 D. Regenerate Air 13 hrs. 7 2 10.4 87-85 96.9 92.0 2.0 6.0 C. Selectivate 10.75 hrs. TABLE I (CONTINUED) Stream Av. Selectivity % Run Time Conversion. % p-Et, % Other No. Hours Toluene C2H4 Total ET(a) p+m-ET(a) Gas(b) Liquid 8 20 8.7-6.8 73-56 99.8 96.7 .9 2.5 9 117(d) 8.7-5.9 73-44 99.7 97 .8 2.2 C. Regerate H2 4 hrs. 10 18 8.3-7.6 66-61 99.7 94.1 2.3 3.6 ET = Ethyltoluene (a) No ortho isomer produced (b) C1-C4 paraffins and olefine (c) Benzene, ethylbenzene and p-xylene primarily (d) 450 C after first 20 hrs. The maximum toluene conversion, based on the amount of ethylene under the above conditions, was 13 percent. Approximately an 80 percent conversion of starting material was achieved in 22 hours of operation with a high selectivity to ethyltoluene and a very high amount of the para isomer in the ethyltoluene product. EXAMPLE 3 In order to increase the proportion of para isomer in the ethyltoluene ever further, the catalyst was treated with a toluene/hydrogen feed mixture, WHSV 29.3/0.8 with the mole ratio of toluene/hydrogen being 7.7/1 at 600 C and 100 psig pressure of 21 hours to deposit coke thereon. This treatment is referred to as the "selectivation" procedure. AS will be seen by reference to Run 2 of the above Table, the amount of p-isomer in the ethyltoluene product increased to 99.9 percent. However, the conversion decreased and the catalyst was found to age at a relatively high rate. EXAMPLE 4 In order to restore the catalyst activity, it was necessary to regenerate the catalyst. Hydrogen was used for this purpose at a temperature of 5500C, a pressure of 100 psig at a weight hourly space velocity (WHSV) of 0.24. After 2 hours of regeneration, the catalyst was again tested for alkylation under the conditions initially used, Run 3 of the above Table. It will be evident that the performance of the catalyst prior to regeneration (Run 2) was substantially restored. Thus; this technique for regeneration of the catalyst did not remove coke deposited during the selectivation procedure, Example 3, enhancing para selectivity but did remove the coke produced during the alkylation reaction which led to reduced catalyst alkylation ability. The initial reactivity of the selectivated catalyst was completely restored. EXAMPLE 5 The catalyst was regenerated with hydrogen in a manner similar to that described above and again tested for alkylation performance, Runs 4, 5 and 6 of the Table. It will be seen that the initial performance of the highly selectivated catalyst was substantially restored in every case to give 99.97o of the p-ethyltoluene in the ethyltoluene product. EXAMPLE 6 After Run 6; Table 1, -the catalyst was regenerated with air. In conducting such operation, the reactor was purged with nitrogen, and then air, initially diluted with nitrogen; was carefully and gradually admitted at 4500C at such a rate to avoid a temperature exotherm. The temperature was gradually raised to 5500C and the nitrogen flow diminished until pure air was flowing. The time of calcination was measured for conditions where pure air was used at 5500C. It will be evident from a comparison of the results of Runs 1 and 7 of the above Table that the described treatment resulted in alkylation performance substantially the same as that achieved with the original catalyst. In this case; it was apparent that all of the coke was removed, including that deposited by the selectivation procedure, and that produced during the alkylation reaction. EXAMPLE 7 The catalyst, after the conclusion of the operation described in Example 6, was selectivated by treatment with toluene and hydrogen for 10.75 hours and then tested for alkylation performance as described hereinabove. It will be seen from the results of Runs 8 and 9 of Table 1 that very high concentrations of para isomer in the ethyltoluene product, i.e., 99.7-99.8%, were obtained at relatively high conversions and selectivity. Regeneration of the catalyst with hydrogen for 4 hours under the conditions specified in Example 4 substantially restored the catalyst activity to its original value ("C" in Table I); as will be evident from a comparison of the results of Runs 8 and 10 of Table I. EXAMPLE 8 In a manner similar to that described in Example 1, a catalyst of HZSM-5 with an alumina binder (35% wt.) was prepared which contained 3.11 weight percent phosphorus and 4.01 weight percent magnesium. This catalyst was used in the alkylation of toluene with ethylene to produce ethyltoluene. After calcination with air for 16 hours, in a manner similar to that described in Example 6, the catalyst was used for alkylation under conditions similar to that described in Example 2. The results obtained are summarized in Table II below. TABLE II Stream p-ET Selectivity Run Time Conversion. % Total ET(a) ptm-ET(a) No. Hours Toluene C2H4 % % 1 24 10.5-10.1(b) 92-88 95.0-95.6 89.4-96.0 2 22 11.1-10.1 85-80 96.4-96.9 92.3-97.1 ET = Ethyltoluene (a) No ortho isomer was detected (b) Range shows value for initial and final hour for time period indicated. It will be seen that the results for the first 24 hours of operation are shown in Run 1 of the above Table. After a period of operation (358 hours) at temperatures from 400-4450C, the toluene and ethylene conversions were reduced to 4.7 percent and 34 percent respectively. The catalyst was then regenerated with hydrogen at a temperature of 5500C, a pressure of 150 psig and a weight hourly space velocity of .24 for 24 hours. Upon re-use of the catalyst for ethylation of toluene under the above conditions, it will be evident from a comparison of the results of Runs 1 and 2 of Table II that the catalyst activity as seen by conversion of starting materials, concentration of p-ethyltoluene product and selectivity to p-ethyltoluene was substantially restored to its original value. EXAMPLE 9 Alkylation of ethylbenzene with ethylene to produce diethylbenzene was carried out with the catalyst of Example 1. Such catalyst was calcined in air prior to use in a manner similar to that described in Example 6. Conditions of alkylation used included a temperature of 4250C, a pressure of 100 psig, an ethylbenzene/ethylene/hydrogen feed WHSV of 29.71/1.16/.24 with the mole ratio of ethylbenzene/ethylene/hydrogen being 6.8/1/3. After Runs 1 and 2, prior to Runs A and B, Table III the catalyst was selectivated by treating it with a mixture of toluene/hydrogen WHSV 30/.08 at 6000C, 100 psig for a period of about 11 hours. The conditions used to selectively regenerate with hydrogen before runs A and B was 5500C, 100 psig and UHSV of pure hydrogen of 0.24. Results are summarized in Table III below. TABLE III Stream Conversion, % p-DEB Selectivity Run Gas Time EB C2H4 Total DEB (a) ptm-DEB No. Diluent Hours % % Regenerate Air 20 hrs. 1 H2 50 21.9-16.3(b) 65-55 98.4-98.9 71.6-80.0 Regenerate Air 17 hrs. 2 N2 46 21.7-12.3 56-39 98.3-98.9 72.1-83.0 Regenerate Hydrogen 5 hrs. A H2 44 14,3-3,9 54-21 99.8-99.9 76.8-75.9 Regenerate Hydrogen 3 hrs. B N2 47 11.6-2.6 31-7 99.8-99.7 79.8-77.3 (a) None of the ortho isomer could be detected. (b) The range shows the result for the first and last hour of the time period tested. EB = Ethylbenzene, DEB = Diethylbenzene It will be seen from Run 1 of the above Table that the initial toluene conversion was 21.9% during the first hour of operation and was reduced to 16.3% durpg the 50th hour. It is to be noted that the maximum theoretical ethylbenzene conversion based on the amount of ethylene in the feed, and assuming that the only reaction was alkylation to diethylbenzene was about 14.8 percent. Under the conditions of reaction employed, however, ethylbenzene was also consumed by disproportionation to yield primarily benzene and paradiethlbenzene accounting for the additional conversion. As will further be evident, selectivity to the para isomer in the diethylbenzene product was very high, i.e., 98.4-98.9 percent. EXAMPLE 10 In a manner similar to Example 9, the alkylation and disproportionation of ethylbenzene was carried out with the same catalyst used in Example 9 but using a nitrogen diluent after regeneration of the catalyst in air. The conditions of temperature and pressure were the same as those used in the previous example. The ethylbenze/ethylene/nitrogen feed WHSV was 29.71/1.16/3.47 with the mole ratio of ethylbenze/ ethylene/nitrogen being 6.8/1/3. The results obtained are summarized in Table III, Run 2. It will be seen that the original catalyst activity was substantially restored but that catalyst aging was significantly greater with the nitrogen diluent as compared with the hydrogen diluent. EXAMPLE 11 In a manner similar to that described in Examples 9 and 10, except that hydrogen rather than air was used for the regenerations, catalyst performance was tested for the alkylation of ethylbenzene with ethylene to produce diethylbenzene. In this example; the catalyst had been selectivated with toluene and hydrogen prior to use, in a manner similar to that described in Example 3. Results are summarized in Runs A and B of Table III, from which it will be seen that the catalyst was regenerated with hydrogen in an overall manner similar to that observed for regeneration in air. The initial conversion obtained for Run B, i.e., 11 percent was less than that for Run A, i.e., 14.3 percent presumably due to the shorter time period for regeneration. Thus it can be seen that the coke deposited during the selectivation prior to Run A, Table III, which increased the selectivity to p-DEB to 99.8-99.9% was not removed during the regeneration with hydrogen following Run A; according to the conditions for regeneration described but did significantly increase activity from 3.9% (end of Run A) to 11.6% (beginning of Run B), by removing only the coke deposited during the alkylation reaction. EXAMPLE 1 2 In a manner similar to that described in Example 1, a sample of ZSM-5 was steamed and impregnated with diammonium acid phosphate and then magnesium acetate tetrahydrate to give a catalyst which contained 3.11% phosphorus and 4.01% magnesium, by weight. EXAMPLE 13 The catalyst described in Example 12 was calcined in air at 5500C for a period of 16 hours to remove all traces of carbon. It was then evaluated for its ability to catalyze the alkylation of toluene with ethylene, in the presence of hydrogen to produce ethyltoluenes. The conditions of reaction and results are summarized in Table IV. It is significant to note that hydrogen was present as a cofeed and that after 355 hours of operation the temperature was lowered to accelerate catalyst coking. After 381 hours of operation both toluene (10.5 4.7%) and ethylene (92 34%) conversions were significantly reduced. Treatment with pure hydrogen, however, effectively and substantially restored the catalyst activity and performance to that observed initially. TABLE IV Time Selectivity on p-ET To ET Stream Temp Pressure Tol/C2H4/H2 Feed Conversion, % Total ET p + m + o Hrs. C psig WHSV Mole Ratio Toluene C2H4 % % 1 425 100 30/1/0.2 8/1/3 10.5(a) 92 95.0 89.4 70 425 100 30/1/0.2 8/1/3 10.0 86 95.9 96.7 312 445 100 30/1/0.2 8/1/3 9.1 71 96.6 97.2 355 425(b) 100 30/1/0.2 8/1/3 8.0 57 97.3 97.1 381 400(b) 100 30/1/0.2 8/1/3 4.7 34 38.1 98.5 REGENERATE WITH HYDROGEN, WHSV = 0.24 550 C 150 psig 24 hrs. 382 425 100 30/1/0.2 8/1/3 11.1 85 96.4 92.3 427 425 100 30/1/0.2 8/1/3 9.8 76 97.1 97.6 (a) Maximum theoretical toluene conversion was 12.2% based on the limiting amount of ethylene in the feed (b) Temperature lowered to increase catalyst aging rate EXAMPLE 14 A sample of HZSM-5 (2.0 grams), characterized by a crystal size of 1-2 microns, in the form of an extrudate with 35 weight percent alumina, was selectivated with coke. Selectivation conditions included passing a stream of toluene and hydrogen over the zeolite for 25 hours at 11000F; 6.5 WHSV; 0.5 H2/toluene and 30 psig. EXAMPLE 15 The selectivated catalyst of Example 14 was tested for toluene disproportionation by passing a stream of toluene thereover at WHSV of 6.5, a pressure of 400 psig and a hydrogen/hydrocarbon ratio of 4 at a temperature of 9000F. At 17 percent conversion, the paraxylene content of the total xylenes produced was 75 percent. EXAMPLE 16 The catalyst used in Example 15 was then tested for ethylation of toluene by contacting with a toluene/ethylene/hydrogen stream at a weight hourly space velocity of 28/1.1/0.24; a temperature of 7970F and a pressure of 100 psig. At a toluene conversion of 55 percent of theory; there was observed 90 percent of para-ethyltoluene in the ethyltoluenes produced. Toluene conversion dropped to 30 percent after two days on- stream. EXAMPLE 17 The catalyst used in Example 16 was then regenerated by treating with hydrogen at a rate of 100cc of hydrogen per minute for 2 hours at 10000F. It was found that the catalyst could be restored to its initial activity and selectivity. The catalyst then aged during the next six days to 30 percent conversion. A two hour regeneration by treatment with hydrogen under the above conditions did not completely restore the initial catalyst activity. However, increasing the regeneration time to 16 hours restored the activity as did a subsequent 16 hour regeneration. The selectivity to para-ethyltoluene gradually increased from 90 to 93 percent during the 16 days on stream and was not affected by the hydrogen regeneration. The above results employing hydrogen regeneration are shown graphically in Figure 1. EXAMPLE 18 A sample of HZSM-5 (1.0g), characterized by a crystal size of 1-2 microns; in the form of an extrudate with 35 weight percent alumina, was selectivated with coke. Selectivation conditions included passing a stream of toluene over the extrudate particles for 112 hours at 10500F, 6.5 WHSV, 0.5 H2/HC and 30 psig. EXAMPLE 19 The selectivated catalyst of Example 18 was used for toluene disproportionation for six months by passing a stream of toluene thereover at a WHSV of 6.5, H2/HC = 4, and a pressure of 400 psig. During this period, catalyst aging was compensated by increasing the temperature from 9000F at the beginning to 9C50F at the end of the cycle. The toluene conversion was 24 percent. The paraxylene content of the total xylenes produced was 82 percent at the beginning and 93 percent at the end of the six month period. For comparison, the catalyst prior to coke selectivation gave xylenes containing only 30% p-xylene. EXAiPLE 20 The used catalyst of Example 19 was hydrogen regenerated by passing hydrogen thereover at 10000F and 400 psig for a total of 68 hours. After this regeneration; the catalyst produced 82 percent paraxylene in total xylenes at 24 percent conversion at a temperature of 9000F, i.e., at the test conditions at the beginning of the catalytic cycle of Example 6. The paraxylene selectivity changes for the catalyst materials of Example 18; 19 and 2C are summarized in Figure 2.

Claims: 1. A method of regenerating a catalyst bearing a deposit of coke as a consequence of use in an organic compound conversion process, said catalyst comprising a crystalline zeolite having a silica to alumina ratio of at least 12; a constraint index of 1 to 12, a xylene sorption capacity of at least 1g./100g. of zeolite and an o-xylene sorption time for 30 percent of said capacity greater than 10 minutes, said sorption capacity and time being measured at 1200C and a xylene pressure of 4.5 + 0.8 mm. Hg, said method comprising exposing the catalyst to a hydrogen-containing atmosphere at 425 to 6500C and 0 to 2000 psig. 2. A method according to claim 1 wherein said zeolite has been modified before use by combination therewith of 0.5 to 40 weight percent of a difficultly reducible oxide. 3. A method according to claim 1 wherein said catalyst has been modified before use by controlled. deposition thereon of at least 1 weight percent of coke. 4. A method according to claim 3 wherein said deposition is effected by contacting the catalyst with a thermally decomposable organic compound at conditions including a temperature above the decomposition temperature of that compound but below 12000F and a hydrogen/compound ratio between 0 and 1, said conditions being collectively more severe than those prevailing in said use. 5. A method according to any preceding claim wherein the catalyst is regenerated at a pressure of 10 to 1000 psig. 6. A method according to any preceding claim wherein the catalyst is regenerated at a pressure of 50 to 450 psig. 7. A method according to any preceding claim wherein said atmosphere contacts the catalyst at a weight hourly space velocity of 0.25 to 1C, 8. A method according to any preceding claim wherein the duration of the regeneration is 1 to 48 hours. 9. A method according to any of claims 4 to 8 wherein said thermally decomposable organic compound is also an organic compound subjected to said conversion process. 10. A method according to claim 9 wherein said compound is toluene. 11. A method according to any preceding claim wherein the zeolite is ZSM-5. 12. A method according to any preceding claim wherein the zeolite has a crystal size greater than 0.5 micron. 13. A method according to any of claims 2 to 12 wherein the difficultly reducible oxide is of antimony, boron, magnesium and/or phosphorus. 14. A method according to any preceding claim wherein the zeolite is composited with a binder, such as alumina. 15. A method according to any preceding claim wherein said conversion process is alkylation of an aromatic hydrocarbon, disproportionation of an alkyl aromatic hydrocarbon, xylene isomerisation or converison of lower monohydric alcohols and or their corresponding ethers to an olefin-rich hydrocarbon mixture.

Inventors: HAAG, WERNER OTTO, KAEDING, WARREN WILLIAM, OLSON, DAVID HAROLD, RODENWALD, PAUL GERHARD
Applicants: MOBIL OIL CORPORATION
Application year: 1979
Main classification: B01J29
IPC codes: C07C6, C07C2, B01J29, B01J38, C07C1, C07C5