METHOD OF PREPARING A ZEOLITIC CATALYST COMPOSITION OF IMPROVED SHAPE SELECTIVITY AND THERMAL STABILITY, AND USE THEREOF IN CATALYTIC HYDROCARBON CONVERSION PROCESS

Abstract: A method of preparing a thermally stable shape selective catalyst composition comprising a composite of a crystalline zeolite and a Group IIA or Group VIII metal, said zeolite having a silica to alumina ratio of at least about 12 and a constraint index, as hereinabove defined, within the approximate range of 1 to 12, which comprises impregnating and/or ion-­ exchanging said zeolite with Group IIA or Group VIII metal salts, followed by high temperature calcination, to the com­ positions produced thereby, and to the use thereof in catalytic hydrocarbon conversion processes.

Description: METHOD OF PREPARING ZEOLITIC CATALYST COMPOSITION OF IMPROVED SHAPE SELECTIVITY AND THERMAL STABILITY This invention relates to a method for preparing a crystalline aluminosilicate zeolite catalyst of improved shape selectivity and thermal stability, and to its use in catalytic hydrocarbon conversion processes. The disproportionation of aromatic hydrocarbons in the presence of zeolite catalysts has been described by Grandio et al in the Oil and Gas Journal, Vol. 69, No. 48 (1971). U.S. Patents 3,126,422; 3,413,374; 3,598,878; 3,598,879 and 3,607,961 show vapor-phase disproportionation of toluene over various catalysts. Alkylation of aromatic hydrocarbons with an olefin in the presence of a crystalline metallic aluminosilicate having uniform pore openings of about 6 to 15 Anstrom units is described in U.S. 2,290,607. U.S. 3,251,897 describes alkylation of aromatic hydrocarbons in the presence of X- or Y-type crystalline aluminosilicate zeolites, specifically such type zeolites wherein the cation is rare earth and/or hydrogen. U.S. 3,751,504 and 3,751,506 decribe vapor phase alkylation of aromatic hydrocarbons with olefins, e.g. benzene with ethylene, in the presence of a ZSt1-5 type zeolite catalyst. In these prior art processes, the xylene product produced has the equilibrium composition of approximately 24 percent para, 54 percent of meta and 22 percent of ortho. The alkylation of toluene with methanol in the presence of a cation exchanged zeolite Y has been described by Yashima t al In the Journal of Catalysis 16, 273-280 (1970). These workers reported selective production of paraxylane over the approximate temperature range of 200 to 2750C. with the maximum yield of para-xylene in the mixture of xylenes, i.e. about 50 percent of the xylene product mixture, being observed at 2250C. Higher temperatures were reported to result in an increase in the yield of meta-xylene and a decrease in the production of para- and ortho-xylkene. Transalkylation of toluene using a catalyst of faujasite or mordenite, a Group VIII metal, such as platinum, and an additional component of arsenic, antimony, bismuth, selenium, tellurium or -compounds thereof is described in U.S. 3,527,824. Of the xylene isomers, i.e. ortho, meta and para-xylene, meta-xylene is the least desired product, with ortho and para-xylene being the more desired products. Para-xylene is of particular value being useful in the manufacture of terephthalic acid which is an intermediate in the'manufacture of synthetic fibers, such as "Dacron". Mixtures of xylene isomers, either alone or in further admixture with ehylbenzene, generally containing a concentration of 'about 24 weight percent para-xylene in the equilibrium mixture, have previously been separated by expensive superfraction and multistage refrigeration steps. Such process, as will be realized, has 'involved high operation costs and has a limited yield. The ZSM-5 class of zeolite catalysts have been shown to be shape selective This shape selectivity can be further enhanced by the use of very large crystals, impregnation with Mg and P to reduce zeolite pore opening and coke selectivation. These modified zeolite catalysts have been very effective in such reactions as selective toluene disproportionation which yields predominantly p-xylene as the product and toluene-ethylene alkylation yielding primarily p-ethyltoluene. These modification procedures are quite complex and do not enhance in any way the stabiity of the zeolite catalyst. U.S. Patents 3,783,123 and 3,842,016 disclose thermally activated crystalline aluminosilicates at temperatures in excess of 4820C (900OF) for a period not substantially in excess of about 30 minutes. In accordance with the present invention, there now has been discovered an improved process for the selectivation and stabilization of a catalyst comprising a crystalline zeolite and a Group IIA or Group VIII metal, said zeolite being essentially characterized by a silica to alumina ratio of at least about 12 and a constraint index within the approximate range of 1 to 12, which comprises impregnating and/or ion exchanging said zeolite with the metal-containing salts, followed by high temperature calcination, about 6490C (12000F) or higher. The high temperature calcination step p a solid-state reaction between the metal and tne zeolite, not only improving shape selectivity but resulting in a crystalline structure more stable to further thermal and hydrothermal treatment than the starting zeolitic material. This procedure to produce a new zeolitic catalytic composition and the use of the product in hydrocarbon conversion is applicable to highly siliceous zeolites, SiO7/Al203 > 12 and meeting the constraint index of 1 to 12. The preparation of the selective stable catalyst of this invention useful in catalytIc hydrocarbon conversion processes comprises impregnating and/or ion exchanging a crystalline aluminosilicate zeolitic starting material having a silica/alumina ratio of at least about 12 and a constraint index, as hereinafter defined, within the approximate range of 1 to 12, with a Group IIA or Group VIII metal-containing salt, e.g. Mg, Co, Ni, in amounts between about 0.1 and 30 wt 7o with respect to said zeolite, preferably between about 0.5 and 15, still more preferably between about 0.6 and 6.1 wt %, and then calcining the resulting product at a temperature of at least about 6490C (1200 F) or higher. Representative magnesium and calcium containing compounds include the acetate, nitrate, benzoate, proprionate, 2-ethylhexoate, carbonate, formate, oxylate, amide, bromide, hydride, lactate, laurate, leate, palmitate, silicylate, stearate and sulfide forms thereof. Reaction of the zeolite with the treating magnesium or calcium compound is effected by contacting the zeolite with such compound. there the treating 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 metal compound and the zeolite may be employed. Suitable solvents include water and aliphatic, aromatic or alcoholic liquid. The treating compound may also be used without a solvent, i.e. may be used as a neat liquid. Where the treating compound is in the gaseous phase2 it can be used by itself or can be used in admixture with a gaseous diluent relatively inert to the treating compound and the zeolite such as helium or nitrogen or with an organic solvent, such as octane or toluene. The amount of metal oxide incorporated in the calcined zeolite should be at least about 0.1 percent by weight. However, it is preferred that the amount of magnesium oxide in the zeolite be at least about 0.5 percent by weight, particularly when the same is combined with a binder, e.g. 35 weight percent of alumina. The amount of metal oxide can be as high as about 30% percent by weight or more depending on the amount and type of binder present. Preferably, the amount of metal oxide added to the zeolite is between about 0.5 and about 15 percent by weight. A charge stock utilized in the process of this invention contains as a major reactant, at least one hydrocarbon, which can be toluene, a C2-C10 olefin, xylene, and benzene. Typical of the processes contemplated 2rein are the disproportionation of toioene te benzene an? xylenes, wherein the proportion of paraxylene obtained is greatly in excess of its normal equilibrium concentration. Such process is effectively carried out at a temperature of between about 400 and about 7500C at a pressure of between about 1 atmosphere and about 6996.09 kPa (1000 psig) utilizing a weight hourly space veolicty of between about 1 and about 20. Another process involves the rnethylation of toluene by reaction of the latter with a methylating agent, preferably methanol, at a temperature between about 2500C and about 7500C and preferably between about 4000C and about 6000C. The reaction generally takes place at atmospheric pressure, but the pressure may be within the approximate range of 1 atmosphere -to 6996.09 kPa (1000 psig). The molar ratio of methylatirig agent to toluene is generally between about .05 and about 5. When methanol is employed as the methylating agent a suitable molar ratio of methanol to toluene has been found to be approximately 0.1-2 moles of methanol per mole of toluene. With the use of other methylating agents, such as methylchioride, methylbromide, dimethylether, metylcarbonate, light olefins, or dimethylsulfide, the molar ratio of methylating agent to toluene may vary within the aforenoted range. Reaction is suitably accomplished utilizing a weight hourly space velocity of between about 1 and about 2000 and preferably between about 5 and about 1500. The reaction product consisting predominantly of para-xylene or a mixture of para- and orthoxylene, together with comparatively smaller amounts of meta-x.-ylene may be separated by any suitable means, such as by passing the same through a water condenser and subsequently passing the organic phase through a column in which chromatographic separation of the xylene isomers is accomplished. Another charge stock suitable for use in the process of the invention, is a stream high in C2-C10 olefin content. Thus, propylene, butenes, pentenes, hexenes, dienes such as butadiene, pentadienes, cycloolefins such as cyclopentene and cyclohexene, alkyl-substituted cycloolefins such as ethyl cyclopentene, cycipentadiene and cyclohexadiene can be effectively converted to a high yield of para-xylene utilizing the described catalyst comprising a composite of a specified crystalline aluminosilicate zeolite and antimony oxide. Conversicn utilizing such olefin feed is carried out at a temperature within the approximate range of 300 to 7000C, a pressure between atmospheric and 1500 psig employing a weight hourly space velocity between about 1 and about 1COO. As sources of the olefin reactant either substantially pure streams of the C2-C10 olefin may be employed or refinery or chemical streams high in such reactant, i.e. generally more than 50 volume percent may be used. It is also contemplated to amploy a dual catalyst bed process utilizing an initial paraffin and/or naphtha feed. In such embodiment, a charge of C2 to C10 paraffins is conducted to a first catalyst bed containing a catalyst suitable for effecting conversion of the paraffin charge to olefins. The catalyst employed in such bed is a crystalline aluminosilicate zeolite of the type hereinafter described which has not been composited with an alkaline earth oxide, e.g. HZSM-5; HZSM-11; HZSM-12; HZSM-38 or HZSM-35. These zeolites may have combined therewith a small amount of phosphorus as described in U.S. Patent 3,972,832 or may have undergone prior steaming as described in U.S. Patent 3,965,209. Conditions present in such bed include a temperature within the approximate rang ov 400 to 750 C, a pressure between atmospneric and 1'0-00 psig and a weight hourly space velocity of between ADONIS 0.5 and about 5000. The olefins formed in such operation are then passed through a second catalyst bed, maintained under conditions described hereinabove, containing the composite catalyst of crystalline aluminosilicate zeolite and alkaline earth oxide, which zeolite has a silica to alumina ratio of at least about 12 and a constraint index within the approximate range of 1 to 12. A still further charge stock which can be used in the process of the present invention to obtain high yields of para-xylene includes naphthenes, such as cyclopentane, cyclohexane and alkyl cyclopentanes having at least one alkyl group of 1 to 5 carbon atoms. Typical of the naphthene reactants are methyl cyclopentane, 1,2-dimethylcyclopentane, 1,3-dimethylcyclohexane. Another charge stock which can be effectively used in the present invention to selectively produce para-xylene includes paraffinic hydrocarbons having between 3 and 10 carbon atoms. Representative of such paraffins are butanes, pentanes, hexanes, heptanes, octanes and alkyl-sustituted derivatives of these paraffins. Utilizing a paraffinic and/or naphthenic charge stock, reaction conditions include contact with the composite catalyst of crystalline aluminosilicate zeolite and antimony oxide at a temperature of between about .400 to about 700 C, a pressure between about atmospheric and about 6996.09 kSa (1000 psig) and a weight hourly space velocity of 0.1 to 100. The catalyst has also been found useful in its selectivity for the synthesis of para-ethyltoluene, as will be seen in the examples below. The catalysts utilized in the process of this invention comprise in one embodiment composites of alkaine earth oxide, e.g. MgO, and a crystalline aluminosilicate zeolite more fully described below. Generally, the amount of MgO in the composite catalyst will be between about 0.1 and about 30 weight percent and preferably between about 0.5 and about 15 weight percent. The catalyst of this invention may be the product formed by impregnation of the zeolite powder or pellets with one or more alkaline earth compounds and/or ion exchanged with the same. Binders such as clays silica, or other inorganic oxides may be used, the zeolite constituting 1 to ga wt. of the resulting composite. The total catalyst composition should preferably contain at least 50 perent by weight of crystalline aluminosilicate zeolite. When the catalyst composition has the desired physical form, it is dried and then calcined at a temperature of at least about 6490C (12000F) or higher, preferably in an oxidizing atmosphere such as air. The zeolite catalyst herein described are m'embers of a novel class of zeolites exhibiting some unusual properties. These catalysts induce profound transformation of aliphatic hydrocarbons to aromatic hydrocarbons in commercially desirable yields and are generally highly effective in conversion reactions involving aromatic hydrocarbons. Although they have unusually low alumina contents, i.e. high silica to alumina ratios, they are very active even when the silica to alumina ratio exceeds 30. The activity is surprising since catalytic activity is generally attributed to framework aluminum atoms and cations associated with these aluminum atoms. These catalysts retain their crystallinity for long periods in spite of the presence ot steam at high temperature w'rA h n irreversible collapse of the framework of other zeolites, e.g. of the X and A type. Further more, carbonaceous deposits, when formed, may be sieemoved by burning higher than usual temperatures to restore activity. In many environments the zeolites of this class exhibit very low coke forming capability, conducive to very long times on stream between burning regenerations. An important characteristic of the crystal structure of this class of zeolites is that it provides cons trained access to, and egress from the intracrystalline free space by virtue of having a pore dimension greater than about 5 Angstroms and pore windows of about a size such as would be provided by 10-membered rings of oxygen atoms. It is to be understood, of course, that these rings are nose formed by the reguiar disposition of the tetrahedra making up the anionic framework of the crystalline aluminosilicate, the oxygen atoms themselves being bonded to the silicon or aluminum atoms at the centers of the tetrahedra. Briefly, the preferred type catalyst useful in this invention possess, in combination: a silica to alumina ratio of at least about 12; and a structure providing constrained access to the crystalline free space. The silica to alumina ratio referred to may be determined by conventionai analysis. This ratio is meant to represent, as closely as possible, the ratio in the rigid anionic framework of the zeolite crystal and to exclude aluminum in the binder or in cationic or other form within the channels. Although catalysts with a silica to alumina ratio of at least 12 are useful, it is preferred co use catalysts having higher ratios of at least about 3G. Such catalyst, after activation, acquire an intracrystalline- sorption capacity for normal hexane X ich is greater than that for water, i.e. they exhibit "hydrophobic" properties. The type zeolites useful in this invention freely sorb normal hexane and have a pore dimension greater than about 5 Angstroms. In addition, the structure must provide constrained access to larger molecules. It is sometimes poss-ible to judge from a known crystal structure whether such constrained access exists. For example, if the only pore windows in a crystal are formed by 8-membered rings of oxygen atoms, then access by molecules of larger cross-section than normal hexane is excluded and the zeolite is not of the desired type. Windows of 10-membered rings are preferred, although, in some instances, excessive puckering or pore blockage may render these catalysts ineffective. Twelve-membered rings do not generally appear to offer sufficient constraint to produce the advantageous conversions, although puckered structures exist such as TMA offretite which is a known effective zeolite. Also, structures can. be conceived, due to pore blockage or other cause, that may be operative. Rather than attempt to judge from crystal structure whether or not a catalyst possesses the necessary constrained access, a simple determination of the "constraint index" may be made by passing continuously a mixture of an equal weight of normal hexane and 3-methylpentane over a small sample, approximately 1 gram or less, of catalyst at atmospheric pressure accord to the following procedure. A sample of the catalyst, in the form of peilets or extrudate, is crushed to a particle size about that of coarse sand and mounted in a glass tube. Prior to testing, the catalyst is treated with a stream of air at 528 C (1000 F) for at least 15 minutes. The catalyst is then flushed with helium and the temperature adjusted between 288 C (550 F) and 510 C (950 F) to give an overall conversion between 10% and 60%, The mixture of hydrocarbons is passed at 1 liquid hourly space velocity (i.e. 1 volume of liquid hydrocarbon per volume of catalyst per hour) over the catalyst with Q helium dilution to 7ive a helium to total hydrocarbon mole ratio of 4:1. After 20 minutes on stream, a sample of the effluent is taken and analyzed, most conveniently by gas chromatrography, to determine the fraction remaining unchanged for each of the two hydrocarbons. The "constraint index" is calculated as follows: Constraint Index = log10(fraction of n-hexane remaining) log10(fraction of 3-methylpentane remaining) The constraint index approximates the ratio of the cracking rat constants for the two hydrocarbons. Catalysts suitable for the present invention are those having a constraint index in the approximate range of 1 to 12. Constraint Index (CI) values for some typical catalysts are: CAWS ZSM-5 8.3 ZSM-11 8.7 ZSM-12 2 ZSM-38 2 ZSM-35 4.5 TMA Offretite 3.7 Beta 0.6 ZSM-4 0.5 H-Zeolon 0.5 REY 0.4 Amorphous Silica-Alumina 0.6 Erionite 38 It is to be realized that the above constraint index values typically characterize the specified zeolites but that such are the cumulative result of several variables used in determination and calcualtion thereof. Thus, for a given zeolite depending on the temperature employed within the aforenoted range of 2880C (5500F) to 510 C (9500F), with accompanying conversion between 10% and 60%, the constraint index may vary within the indicated approximate range of 1 to 12. Likewise, other variables such as the crystal size of the zeolite, the presence of possibly occluded contaminants and binders intimately combined with the zeolite may affect the constraint index. It will accordingly be understood by those skilled in the art that the constraint index, as utilized herein, while affording a highly useful means for characterizing the zeolites of interest is approximate, taking into consideration the manner of its determination, with the probability, in some instances, of compounding variable extremes. However, in all instances, at a temperature within the above-specified range of 5500F to 9500F, the constraint index will have a value for any given zeolite of interest herein within the approximate range 12. The class o zeolites defined wherein is exemplified by ZSM-5 (U.S. Patent 3.702.886), ZSM-1 (U.S. Patent No. 3,709,979). ZSM-12 (U.S. Patent No 3,832,449). ZSM-35 (U.S. Patent No. 4,016,245), ZSM-38 (U.S. Paters No. 4,046,859), and other similar materials The specific zeolites described, 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 5380C (100O0F) for one hour, for example, followed by base exchange with ammonium salts followed by calcination at 5380C (1000 F) in air. The presence of organic cations in the forming solution may not be absolutely essential to the formation of this type zeolite; 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 this type catalyst by base exchange with ammonium salts followed by calcination in air at about 5380C (1000 F) for from about 15 minutes to about 24 hours. Natural zeolites may sometimes be converted to this type zeolite catalyst by various activation procedures and other treatments such as base exchange, steaming, alumina extraction and calcination, in combinations. Natural minerals which may be so treated include ferrierite, brewsterite, stilbite, dachiardite, epistilbite, heulandite, and clinoptilolite. In a preferred aspect of this invention, the catalysts hereof are selected as those having a crystal framework density, in the dry hydrogen form, of not substantially below about 1.t grams per cubic centimeter. It has been found that zeolites which satisfy all three of these criteria are most desired because they tend to maximize the production of gasoline boiling range hydrocarbon products. Therefore, the preferred catalysts of this invention are those having a constraint index as defined above of about 1 to about 12, a silica to alumina ratio of at least about 12 and a dried crystal density of not less than about 1.6 grams per cubic centimenter. The dry density for known structures may be calculated from the number of silicon plus aluminum atoms per 10CO cubic Angstroms, as given, e.g., on page 19 of the article on Zeolite Structure by W. M. Meir. This paper is included in "Proceedings of the Conference on Molecular Sieves, London, April 1967," published by the Society of Chemical Industry, London, 1968. When the crystal structure is unknown, the crystal framework density may be determined by classical pyknometer techniques. For example, it may be determined by immersing the dry hydrogen form of the zeolite in an organic solvent which is not sorbed by the crystal. It is possible that the unusual sustained activity and sus ability of this class of zeolites is associated with its high crystal anionic framework density of not less than about 1.6 grams per cubic centimeter. This high density, of course, must be associated with a relatively small amount of free space within the crystal, which might be expected to result in more stable structures. This free space, however, is important as the locus of catalytic activity. Crystal framework density cf some typical zeolites ara: Void Framework Zeolite Volume Densitv Ferrierlte 0.28 cc/cc 1.76 g/cc Mordenite .28 1.7 ZSM-5, -11 .29 1.79 Dachiarditel .32 1.72 L .32 1.61 Clinoptilolite .34 1.71 Laumontite .34 1.77 ZSM-4 (Omega) .38 1.65 Heulandite .39 1.69 P .41 1.57 Offretite .40 1.55 Levynite .40 1.54 Erionite .35 1.51 Gmelinite .44 1.46 Chabazite .47 1.45 A .5 1.2 Y .48 1.27 The conversion process described herein may be carried out as a batch type, semi-continucus or continuous operation utilizing a fixed or moving bed catalyst system. The catalyst after use is conducted to a regeneration zone wherein coke is burned from the catalyst in an oxygen-containing atmosphere, e.g. air, at an elevated temperature, after which the regenerated catalyst is recycled to the conversion zone for further contact with the charge stock. The following examples will aerve to illus trate the process of the invention without limiting the same EXAMPLES 1-4 Forty-five g. of ZSM-5 extrudates (65% ZSM-5 and 35% Al2O3) were impregnated with a solution of 30 g Mg(OAc)2 4 H2O and 25 g. H2O. The impregnated product was dries o-;ernight at 40 C followed by two hours final calcination at 871 C (1600 F) in N2 atmosphere. Th resultant catalyst was found to a very selective for the synthesis of PET (para ethyltoluene) as shown in Table 1. The Mg impregnated and calcined at 8710C (1600 F) sample has the highest selectivity to PET when compared to some catalysts prepared without the high temperature calcination, and to similar catalysts without the metal impregnation. The 8710C (16000F) is the approximate temperature for Mg impregnated 25M-5 extrudates at which it has been found by the DTA (differential thermal analysis) that a solid state exothermic reaction occurs. The reaction is thought to be between Mg and ZSM-5. Similar reactions between other metal compounds such as Ca, Zn, Cu, Pb and others are expected. Results are listed in Table 1 below. TABLE 1 PET TEST RESULTS Example 1 2 3 4 Zeolite ZMS-5 # # # SiO2/Al2O3 70 70 70 70 Binder 35% Al2O3 35%Al2O3 - 40% clay Impregnation Mg(OAc)2#4H2O # None None Mg. Wt.% 4 3.3 -- - Calcination 2 hrs (T-2) at 1600 F T-3-1000 F T-3-1000 F T-2-1600 Test Condition Temperature, C ( F) 427 427 427 427 427 (800) (800) (800) (800) (800) Toluene, g/Hr 26 13 26 26 26 Ethylenem g/Hr 1.125 0.563 1.125 1.125 1.125 TOS, Hr. 1 2 1 1 1 Test Result Toluene Conv., % 6.23 9.93 14.00 13.80 12.68 Total ET Prod., % 5.99 9.68 112.68 12.10 11.50 Normalized ET % PET 99.2 94.9 33.6 32.7 52.7 MET 0.8 5.1 63.1 63.6 46.6 OET 0 0 3.3 3.7 0.7 Catalytic cracking activity is indicated by the weight percent conversion of hexane to lower beilin C1-C3 hydrocarbons, while isomerisation activity is indicated by weight percent conversion to hexane isomerization. Cracking activity is also indicated quantitatively by the term alpha (&alpha; ;) whith is an indication of the relative catalytic cracking activity of the catalyst compared t7 a standard catalyst. &alpha; is the relative rate constant rate of n-hexane conversion per unit volume of oxides composition per unit time). It is based on the activity of highly active silica alumina cracking catalyst taken a * The test is further described in a letter to the editor entitled "Superactive Crystalline Aluminosilicate Hydrocarbon Cracking Catalysts" by P. B. Weisz and J. N. Miale, Journal of Catalysis, Vol.4, pp. 527-529 (August 1965). The following examples illustrate the advantages of Mg addition and high temperature calcination. EXAMPLES 5 and 6 A ZSM-5 sample of 40 SiO2/Al2O3 ratio was prepared into hydrogen form by the standard procedure. The as synthesized zeolite powder was pressed into thin tablets which was calcined in N2 for 3 hours at 5380C (10000F) and followed by NH4NO3 exchange to reduce its Na to less than 0.01% weight. The exchanged sample was sized to 14'25 mesh and air calcined for 3 hours at 5380C (1000 F). The activity of this finished catalyst was found to be 480. The finished catalyst was steamed wiFh 100% steam at 4820C (9000F), 790.8 kPa (100 psig) pressure for 48 hours. The steamed catalyst has an alpha activity of 3.8. EXAMPLE 7 The fresh H form catalyst in Example 5 was impregnated with Mg(NO3)2 solution to 2.84% Mg. The catalyst was steamed with 100% steam at 4820C (9000F) 790.8 kPa (100 psig) for 48 hours. The activity of the final catalyst was 11.7. EXAMPLE 8 (8a and 8b) The fresh H form catalyst in Example 5 was ion exchanged with Mg(NO3)2 solution to 1.4% Mg. The exchanged catalyst was calcined in air at 8710C (16000F) for 3 hours. The calcined sample was steamed with 100% steam at 4820C (9000F) 790.8 kPa (100 psig) for 24 and 48 hours respectively. The activities of the steamed catalysts are 31 and 23. The results of Examples 5-8 are summarized in Table 2. The resulted steam stability of Mg addition/combining with high temperature calcination is quite obvious. TABLE II N-HEXANE CRACKING ACTIVITY TEST Example 5 6 7 8a 8b Zeolire ZSM-5 -- -- -- - Metal O O Mg Mg Mg Method of Incorp. - - Impr. Ion Exchange Wt % Metal - - 2.84 1.40 1.40 SiO2/Al2O3 of zeolite 40 40 40 40 40 binder - - - - Steaming & Others fresh Temp. C ( F) 538 482 482 871 482 871 482 (1000) (900) (900) (1600) (900) (1600) (900) Presaure, kpa (psig) - 790.8 790.8 101.33 790.8 101.33 790.8 (100) (100) (0) (100) (0) (100) Time Hr 3 48 48 3 24 3 48 Steam. % Air 100 100 Air 100 Air 100 TABLE II (Continued) Test Condition Catalyst Vol, cc. 0.25 1.0 1 1 1 Carrier gas, cc/min 18 18 18 18 18 n C6 rate, cc/min 1 1 1 1 1 Temp, C ( F) 538 538 538 538 538 (1000) (1000) (1000) (1000) (1000) Time on Stream, min 5 5 5 5 5 LHSV 4 1 1 1 1 Test Results Conv. on n C6, wt % 96.8 10.4 28.5 58.6 48.6 C5- Products, wt % 78.4 10.4 28.5 57.1 47.6 Total Aromatics, wt % 18.4 - 0.1 1.5 1.1 KX10 , sec-1 4800 38.7 118 310 235 &alpha; 480 3.8 11.7 30.7 23.2 The following examples illustrate Mg, Co, and NI- impregnated catalysts. EXAMPLE 9 The Mg impregnated catalyst of Example 1 was also calcined at 704 C (1300 F) for one hour. The resultant catayst was also selective fox the synthesis of PET. Under the same test conditions, as example 1, the toluene conversion was 11.15%, ethyltoluene (ET) in product was 10.23%, and PET selective was 94.53%, EXAMPLE 10 The Mg impregnated catalyst of Example 1 was also calcined at 7600C (14000F) for 1 hour. The resultant catalyst was also selective for the synthesis of PET. Under the same test conditions the toluene conversion was 10.58% and the selectivity to PET was 95.9%. EXuAMPLE 11 The Mg impregnated catalyst of Example 1 was calcined at 6490C (12000F) for 2 hours. The resultant catalyst, was less active but still selective for the synthesis of PET. The toluene conversion ws 8.16% and PET selectivity was 91.8%. EXAMPLE 12 Twenty grams of ZSM-5 extrudates, 70/1 SiO2/A1203 (65% ZSM-5 and 35% Al203) were impregnated with a Ca(NO3)2#3H2O melt (ri1000C) for 0.5 hour, then the excess was drained off. The soaked extrudates were then dried overnight at room temperature. The final calcination was carried out in flowing N2, holding at 4820C (9000F) for 1 hour and then at 816 C (1500 F) for another hour. The resultant catalyst was selective for the synthesis of PET. The toluene conversion was 2.36% and PET selectivity was 100%. EXAMPLE 13 Twenty grams of ZSM-5 extrudates, Si02/Al203=70, (6370 ZSM-5 and 357J A1203) were soaked in Co(NO3)2#6H2O melt (#100 C) for 0.5 hour, then the excess molten salt was drained. The catalyst was dried at room temperature overnight and was then calcined in flowing N2 at 4820C (9000F) for 1 hour and at 8160C (15000F) for 1 hour. The resultant catalyst was active for the synthesis of PET. The toluene conversion was 6.83% and PET selectivity was 67%. Results of the foregoing examples are summarized in Table III. TABLE III PET TEST RESULTS EXAMPLE 9 10 11 12 13 Zeilite ZSM-5 # # # # Si8Al2O3 70 70 70 70 70 BiFPi 35%Al2O3 35%Al2O3 35%Al2O3 35%Al2O3 35%Al2O3 Im@@gnation Mg(OAc)2#4H2O # None Ca(NO3)2#3H2O Co(NO3)2#6H2O it % 4 4 - 6% Ca 9% Co Ca@@@nation C ( F) T-1 705 T-1 760 T-2 649 T-1 482(900) T-1 482(900) (1300) (1400) (1200) and and T-1 816(1500) T-1 816(1500) TABLE III (Continued) Test Condition Temperature, C ( F) 427 427 427 426 428 (800) (800) (800) (800) (800) Toluene, g/Hr 26 26 26 26 26 Ethylene, g/Hr 1.125 1.125 1.125 1.125 1.125 TOSm Hr. 1 1 1 1 1 Test Results Toluene Conv.% 11.15 10.58 8.16 2.4 6.8 Total ET Product, % 10.23 - - - Normalized ET % PET 94.53 95.9 91.8 100 67 MET - - - - OET - - - - - EXAMPLE 14 To further demonstrate the stability of the ZSM-5 samples which have been treated by metal (Ni) impregnation and high temperature calcination 871 C (1600 F). The following samples were prepared: A SiO2/Al2O3 ratio of 70 ZSM-5 extrudates (65% ZSM-5 and 35% Al2O3). One % Ni by weight was added to the extrudates which were then calcined for 3 hours in air at the following temperatures: 649 C (1200 F), 760 C (1400 F), 871 C (1600 F) and 982 C (1800 F). The &alpha; values of the above samples were 203, 133, 80 and 7, respectively The above calcined samples were steamed for 48 hours at 4820C (9000F), 790.8 kPa (100 psig), 100% steam and tested for &alpha; values again. The corresponding &alpha; values were 6, 13; 19 and 3, respectively. The 8710C (16000F) calcined samples is ;ncre stable than others. Results are summarized below. Ni Added ZSM-5 Extrudate (SiO2/Al2O3=70, 35% Al2O3) Ni 1% by weight based on Extrudate Calcination Temp 0C 649 760 871 982 (12000F) (14000) (15000F) (18000F) (in air) value 203 133 80 6.8 Steam Treatment l 48 790.8kPs 482 C (900 F), (100 psig), 100% (steam) value 6.3 13.3 19,0 2.5 (after steaming)

Claims: CLAIMS: 1. A method for preparing a thermally stable, shape selective catalyst composition comprising a composite of a crystalline zeolite and a Group IIA or Group VIII metal, said zeolite being characterized by a silica/alumina ratio of at least 12 and a constraint index within the range of 1 to 12, which comprises impregnating and/or ion-exchanging said zeolite with a Group IIA or Group VIII metal containing compound in amount of at least about 0.1 wt 7, with respect to said zeolite, as the oxide, then calcining the resultant metal impregnated and/or ion-exchanged zeolite at a temperature of a. least 6490C (12000F). 2. A method according to Claim 1 wherein said Group lIA metal is magnesium or calcium. 3. A method according to Claim 1 wherein said Group VIII metal is cobalt or nickel. 4. A method according to any preceding Claim wherein said zeolite is ZSM-5, ZSM-11, ZSM-12, ZSM-35 or ZSM-38. 5. A method according to any preceding claim wherein said composition also contains a binder for the zeolite. 6. A method according to any preceding claim wherein the amount of Group IIA or Group VIII metal is from 0.1 to 30% wt. with respect to zeolite. 7. A method according to claim 6 wherein said amount is from 0.5 to 15% wt. A process for converting hydrocarbons which comprises contacting the same, at conversion conditions, with a catalyst preparedd by the meth claimed in any of claims5 1 to 7. 9. A process according to claim 8, for effecting disproportionation of toluene to produce benzene and xylenes in which the proportion of para-xylene isomer is in excess of its normal equilibrium concentration wherein the disproportionation conditions include a temperature between 199 C (3900F) and 7600C (1400 F), a pressure between atmospheric and 6996.09 kPa (1000 psig) and a weight hourly space velocity between 0.08 and 20. 10. A process according to Claim 8, for the alkylation of toluene with ethylene to produce ethyltoluene in which the para-isomer is in excess of its normal equilibrium concentration, wherein the alkylation conditions include a temperature between 1990C (390 F) and 7600C (14000F), a pressure between atmospheric and 537.77 kPa (1000 psig) and a weight hourly space velocity between 0.08 and 20.

Inventors: CHU, POCHEN, DWYER, FRANCIS GERARD, SCHWARTZ, ALBERT B.
Applicants: MOBIL OIL CORPORATION
Application year: 1980
Main classification: B01J29
IPC codes: C07C15, C07C2, C07C67, C07C1, C07B61, B01J29, C09K3, C07C6