Substitution of Sn in place of Al in the framework of molecular sieve via treatment with fluoride salts

Molecular sieve abstract

Molecular sieve compositions are prepared by extracting aluminum and substituting chromium and/or tin for extracted aluminum to give molecular sieve products containing framework chromium and/or tin atoms. The process of preparing the chromium and/or tin-containing molecular sieves involves contacting a starting molecular sieve with a solution or slurry of at least one of a fluoro salt of chromium or a fluoro salt of tin under effective process conditions to provide for aluminum extraction and substitution of chromium and/or tin.

Molecular sieve claims

We claim as our invention:

1. A molecular sieve having a three-dimensional microporous framework structure which has an unit empirical formula on an anhydrous basis of:

said molecular sieve characterized in that it has a cation equivalency of at least about 0.8 and an oxygen adsorption capacity of at least 70% of its theoretical capacity as measured at 100 torr and 90.degree. K.

2. The molecular sieve of claim 1 having the characteristic X-ray powder diffraction pattern of zeolite Y.

3. The molecular sieve of claim 1 having the characteristic X-ray powder diffraction pattern of zeolite mordenite.

4. The molecular sieve of claim 1 having the characteristic X-ray powder diffraction pattern of zeolite LZ-202.

5. The molecular sieve of claim 1 having the characteristic X-ray powder diffraction pattern of zeolite L.

6. A molecular sieve having a three-dimensional microporous framework structure of tin, aluminum and silicon tetrahedral oxide units and which has a unit empirical formula on an anhydrous basis of

where u is the mole fraction of aluminum and ranges from about 0.01 to about 0.49 v is the mole fraction of silicon and ranges from about 0.5 to about 0.98 w is the mole fraction of tin and ranges from about 0.01 to about 0.49 [] is framework defect sites and z is the mole fraction of defect sites in the framework and ranges from greater than zero to about 0.2 characterized in that the molecular sieve has a cation equivalency of at least about 0.8 and an oxygen adsorption capacity of at least 70% of its theoretical capacity as measured at 100 torr and 90.degree. K.

7. The molecular sieve of claim 6 having the characteristic x-ray powder diffraction pattern of zeolite Y.

8. The molecular sieve of claim 6 having the characteristic x-ray powder diffraction pattern of zeolite mordenite.

9. The molecular sieve of claim 6 having the characteristic x-ray powder diffraction pattern of LZ-202.

10. The molecular sieve of claim 6 having the characteristic x-ray powder diffraction pattern of L.

11. A molecular sieve produced by the process of contacting a crystalline microporous aluminosilicate zeolite having a framework structure of aluminum and silicon tetrahedral oxide units, pore diameters of at least about 3 Angstroms and a molar ratio of SiO.sub.2 /Al.sub.2 O.sub.3 of at least 2 with a fluoro salt of tin, said fluoro salt being in the form of an aqueous solution or slurry at a pH of about 3 to about 7 whereby framework aluminum atoms of the zeolite are removed and replaced by extraneous tin atoms to give a molecular sieve having a framework structure of tin, aluminum and silicon tetrahedral oxide units, and an empirical formula on an anhydrous basis of

where "(a-N)" represents the mole fraction of aluminum atoms, "a" represents the mole fraction of aluminum atoms present in the framework of the zeolite and varies from about 0.01 to about 0.49 "N" represents the mole fraction of aluminum atoms removed from the framework of the zeolite and varies from about 0.01 to about 0.49 "b" represents the mole fraction of silicon and varies from about 0.5 to about 0.98 "c" represents the mole fraction of tin atoms and varies from about 0.01 to about 0.49; "[]" represents the framework defect sites; "z" represents the mole fraction of defect sites in the framework of the molecular sieve and varies from greater than zero to about 0.2; the molecular sieve characterized in that it has a cation equivalency of at least about 0.8 has retained at least 70% of the oxygen storage capacity of the zeolite at 100 torr and 90.degree. K. and the difference between the mole fraction of framework defect sites of the zeolite and the molecular sieve (.increment.z) is less than about 0.10.

12. The molecular sieve composition according to claim 11 where .increment.z is less than about 0.08.

13. The molecular sieve composition of claim 11 having the characteristic x-ray powder diffraction pattern of zeolite Y.

14. The molecular sieve composition of to claim 11 having the characteristic X-ray powder diffraction pattern of zeolite mordenite.

15. The molecular sieve composition of claim 11 having the characteristic X-ray powder diffraction pattern of zeolite LZ-202.

16. The molecular sieve composition of claim 11 having the characteristic X-ray powder diffraction pattern of zeolite L.

Molecular sieve description

FIELD OF THE INVENTION

The instant invention relates to molecular sieve compositions, the method for their preparation and to processes employing them. More particularly it relates to molecular sieve compositions topologically related to prior known molecular sieves but which are characterized as containing framework atoms of tin, and preferably having a very low content of defect sites in the structure, as hereinafter disclosed. In general the preparative process involves contacting a molecular sieve preferably with an aqueous solution of a fluoro salt of tin, preferably a fluoro salt which does not form insoluble salts with aluminum, under conditions suitable to insert tin for aluminum in the framework.

BACKGROUND OF THE INVENTION

The crystal structures of naturally occurring and as-synthesized zeolitic aluminosilicates are composed of AlO.sub.4.sup.- and SiO.sub.4 tetrahedra which are cross-linked by the sharing of oxygen atoms. The term AlO.sub.4.sup.-, SiO.sub.4 and the like, are used to depict the tetrahedral atoms Al, Si and others, in four-fold coordination with oxygen, within the framework of the zeolite. It is understood that each of the four oxygen atoms thus depicted is linked to an additional tetrahedral atom, thus completing the charge requirements placed on each tetrahedral unit. The electrovalence of each tetrahedron containing an aluminum atom is balanced by association with a cation. Most commonly this cation is a metal cation such as Na.sup.+ or K.sup.+ but organic species such as quaternary ammonium ions are also employed in zeolite synthesis and in some instances appear as cations in the synthesized product zeolite. In general the metal cations are, to a considerable extent at least, replaceable with other cations including H.sup.+ and NH.sub.4.sup.+. In many instances the organic cation species are too large to pass through the pore system of the zeolite and hence cannot be directly replaced by ion exchange techniques. Thermal treatments can reduce these organic cations to H.sup.+ or NH.sub.4.sup.+ cations which can be directly ion-exchanged. Thermal treatment of the H.sup.+ or NH.sub.4.sup.+ cationic forms of the zeolites can result in the substantial removal of these cations from their normal association with the AlO.sub.4.sup.- tetrahedra thereby creating an electrovalent imbalance in the zeolite structure which must be accompanied by structural rearrangements to restore the electrovalent balance. Commonly when AlO.sub.4.sup.- tetrahedra constitute about 40% or more of the total framework tetrahedra, the necessary structural rearrangements cannot be accommodated and the crystal structure collapses. In more siliceous zeolites, the structural integrity is substantially maintained but the resulting "decationized" form has certain significantly different properties from its fully cationized precursor.

The relative instability of aluminum in zeolites, particularly in the non-metallic cationic or the decationized form, is well recognized in the art. For example, in U.S. Pat. No. 3640681 issued to P. E. Pickert on Feb. 3 1972 there is disclosed a process for extracting framework aluminum from zeolites which involves dehydroxylating a partially cation deficient form of the zeolite and then contacting it with acetylacetone or a metal derivative thereof to chelate and solubilize aluminum atoms. Ethylenediaminetetraacetic acid has been proposed as an extractant for extracting aluminum from a zeolite framework in a process which is in some respects similar to the Pickert process. It is also known that calcining the H.sup.+ or NH.sub.4.sup.+ cation forms of zeolites such as zeolite Y in an environment of water vapor, either extraneous or derived from dehydroxylation of the zeolite itself, is effective in removing framework aluminum by hydrolysis. Evidence of this phenomenon is set forth in U.S. Pat. No. 3506400 issued Apr. 14 1970 to P. E. Eberly, Jr. et al.; U.S. Pat. No. 3493519 issued Feb. 3 1970 to G. T. Kerr et al.; and U.S. Pat. No. 3513108 issued May 19 1970 to G. T. Kerr. In those instances in which the crystal structure of the product composition is retained after the rigorous hydrothermal treatment infrared analysis indicated the presence of substantial hydroxyl groups exhibiting a stretching frequency in the area of about 3740 3640 and 3550 cm.sup.-1. The infrared analytical data of U.S. Pat. No. 3506400 is especially instructive in this regard. An explanation of the mechanism of the creation of these hydroxyl groups is provided by Kerr et al. in U.S. Pat. No. 3493519 wherein the patentees state that the aluminum atoms in the lattice framework of hydrogen zeolites can react with water resulting in the removal of aluminum from the lattice in accordance with the following equation: ##STR1##

The aluminum removed from its original lattice position is capable of further reaction with cationic hydrogen, according to Kerr et al. to yield aluminum-containing i.e., hydroxoaluminum, cations by the equation: ##STR2##

It has been suggested by Breck, D. W. and Skeels, G. W., "Zeolite Chemistry II. The Role of Aluminum in the Hydrothermal Treatment of Ammonium-Exchanged Zeolite Y, Stabilization", Molecular Sieves--II, A. C. S. Symposium Series 40 pages 271 to 280 (1977), that stabilization of NH.sub.4 Y occurs through hydrolysis of sufficient framework aluminum to form stable clusters of these hydroxoaluminum cations within the sodalite cages, thereby holding the zeolite structure together while the framework anneals itself through the migration of some of the framework silicon atoms.

It is alleged in U.S. Pat. No. 3594331 issued Jul. 20 1971 to C. H. Elliott, that fluoride ions in aqueous media, particularly under conditions in which the pH is less than about 7 are quite effective in extracting framework aluminum from zeolite lattices, and in fact when the fluoride concentration exceeds about 15 grams active fluoride per 10000 grams of zeolite, destruction of the crystal lattice by the direct attack on the framework silicon as well as on the framework aluminum can result. A fluoride treatment of this type using from 2 to 22 grams of available fluoride per 10000 grams of zeolite (anhydrous) in which the fluorine is provided by ammonium fluorosilicate is also described therein. The treatment is carried out for the purpose of improving the thermal stability of the zeolite. It is theorized by the patentee that the fluoride in some manner becomes attached to the constructional alkali metal oxide, thereby reducing the fluxing action of the basic structural Na.sub.2 O which would otherwise result in the collapse of the crystal structure. Such treatment within the constraints of the patent disclosure has no effect on either the overall silicon content of the zeolite product or the silicon content of a unit cell of the zeolite.

Since stability is quite obviously, in part at least, a function of the Al.sub.2 O.sub.3 content of the zeolite framework, it would appear to be advantageous to obtain zeolites having lower proportions of Al.sub.2 O.sub.3 while avoiding the structural changes inherent in framework aluminum extraction. Despite considerable effort in this regard, however, only very modest success has been achieved, and this has applied to a few individual species only.

A process for increasing the SiO.sub.2 /Al.sub.2 O.sub.3 ratio in zeolites is disclosed in: commonly assigned U.S. Pat. No. 4503023 issue date Mar. 5 1985; commonly assigned U.S. Pat. No. 4610856 issue date Sep. 9 1986 U.S. Pat. No. 4711770 issue date Dec. 8 1987 (U.S. patent application Ser. No. 880103 filed Jun. 30 1986), and in Skeels, G. W. and Breck, D. W. "Proceedings of the Sixth International Zeolite Conference", edited by David Olson and Attilio Bisio, Butterworth & Co. Ltd., pages 87 to 96 (1984). The process disclosed therein comprises inserting silicon atoms as SiO.sub.4 tetrahedra into the crystal lattice of an aluminosilicate having a SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of at least 3 and pore diameters of at least 3 Angstroms with a fiuoro- silicate salt in an amount of at least 0.0075 moles per 100 grams of the zeolitic aluminosilicate on an anhydrous basis, said fluorosilicate salt being in the form of an aqueous solution having a pH value within the range of 3 to about 7 and brought into contact with the zeolitic aluminosilicate at a rate sufficiently slow to preserve at least 60 percent of the crystallinity of the starting zeolitic aluminosilicate.

Commonly assigned U.S. Pat. No. 4892720 describes ammonium fluoride salts of the metal cations iron and/or titanium which are used to treat the zeolites in an aqueous medium. Framework aluminum is complexed by the fluoride and removed from the zeolite. The metal cation is inserted into the framework in place of the aluminum.

Various attempts have been made to substitute chromium or tin into a zeolite framework via primary synthesis methods but none have been truly successful so far. Attempts to synthesize zeolites of the pentasil family of zeolites (ZSM-5 like) with a number of ions other than aluminum have been made. In some cases chromium or tin is found with the zeolite but not in the framework of the zeolite. The likelihood that either chromium or tin is not a part of the zeolite framework in primary synthesis products rests on the fact that such a high pH is required for synthesis that it is probable that the chromium or tin are present as oxides and/or hydrous oxides. For example, in U.S. Pat. No. 4405502 (Klotz) discloses the presence of up to 12.40 weight percent of Cr.sub.2 O.sub.3 with the crystalline chromosilicate (Example IV), but the Cr.sub.2 O.sub.3 in the product is present as amorphous or crystalline oxides. The examples teach that the chromium, initially dissolved in water, is rapidly precipitated as the hydroxide before ever coming in contact with the silica source. Further, "these results show that as the chromium factor became larger, more and more Cr.sub.2 O.sub.3 was detected in the product." (Column 24 lines 15-17.)

Marosi et al., in German Patent No. 2831630 disclose the presence of between 0.50 weight percent and 3.00 weight percent of Cr.sub.2 O.sub.3 with a ZSM-5 type structure. The amount of chromium that would be included in the framework of the ZSM-5 if indeed it were located therein, would range from 0.4 to 2.5 atoms out of 100 framework tetrahedral atoms. In the only Example where a product composition is given (1), the solid product would contain only 0.7 Cr atoms out of 100 in the framework, a value less than the compositions of the present invention. In Example 2 of U.K. Patent Application GB 2024790 (Taramasso et al.), a 6.00 weight percent of Cr.sub.2 O.sub.3 with a ZSM-5 type structure was obtained and which was designated "TRS-28". While the claims teach that the chromium atoms either, "entered the crystalline lattice in place of silicon atoms" or "in the form of salts of bisilicic or polysilicic acids", the evidence presented in the examples fairly teach that the chromium is not within the lattice framework of the ZSM-5 product. Surface areas of all of the products of the invention are given which indicate that there is a substantial reduction relative to a typical ZSM-5. This is evidence of some amorphous or dense phase present with the zeolite. Typically ZSM-5 or its' more siliceous analog silicalite will have a surface area, (BET), of greater than 400 square meters per gram. The chromium containing product of the U.K. Patent Application GB 2024790 had a surface area (BET) of 380 square meters per gram, a value at least 5% less than what might be expected of a pure zeolite sample. Additionally, the chromium containing product of said invention containing 6.0 weight percent Cr.sub.2 O.sub.3 would be expected to have an ion exchange capacity of 0.79 meq/gram, providing all of the chromium atoms were to be positioned in the framework in tetrahedral coordination with four oxygen atoms. However, only 0.0058 meq/gram of cations were actually found in the calcined (550.degree. C.) product, a value at least two orders of magnitude less than what would be necessary to balance the framework negative charges, if chromium were indeed in the framework. In order for chromium to be in the framework in tetrahedral coordination with four oxygen atoms, it is a requirement that there be present a positively charged species or cation in order to balance the negative charge caused by the presence of the trivalent chromium ion sharing the negative charges on four separate oxygen atoms with silicon. Lacking the cation, it is not possible for the chromium to be tetrahedrally coordinated with oxygen in this way and hence, the chromium of this example is not in the framework of the zeolite synthesized in the example. The converse is not necessarily true, namely, that if a positively charged cation is found to balance the negative charge on the chromium to satisfy the requirement of tetrahedral coordination with oxygen, that the chromium is in the framework. It would be evident that the chromium is in tetrahedral coordination with oxygen, but it does not necessarily prove that the chromium is located in the zeolite framework. It is probable that, like amorphous aluminosilicates, the amorphous chromosilicates can have tetrahedrally coordinated chromium atoms and hence ion exchange capacity.

European Patent Application 13630 (Rubin et al.) discloses the presence of between 0.63 weight percent and 2.90 weight percent of Cr.sub.2 O.sub.3 with a ZSM-12 type structure. The samples described in the Tables of the patent application, particularly the products containing chromium, show a substantial loss of surface area. This indicates that the purity of the as-synthesized products is questionable and that they must contain amorphous material. A relative relationship can also be found in the Tables, namely that as the chromium content of the synthesis product increases, the reported X-ray crystallinity decreases.

In European Patent Application 14059 (Rubin et al.) between 0.09 weight percent and 1.26 weight percent of Cr.sub.2 O.sub.3 with a ZSM-11 type structure was obtained. Similar observations can be made with these products; that the products containing chromium have reduced X-ray crystallinity, substantially reduced adsorption capacity for n-hexane and cyclohexane and substantially lower surface areas when compared to a product which does not contain chromium. Each observation taken alone would not preclude the incorporation of chromium in the ZSM-11 framework. However, taken together, these data are substantive evidence for the precipitation of an amorphous chromium containing phase with the zeolite, which under the very basic synthesis conditions employed is the expected result.

Dwyer et al. in U.S. Pat. No. 3941871 disclose the presence of tin in place of or as part of the organic template in a ZSM-5 type of a structure but not as a part of the ZSM-5 framework structure itself. In U.S. Pat. No. 4329328 (McAnespic et al.) the synthesis of a stannosilicate is suggested, but no examples of such synthesis are given nor are any properties of such materials suggested.

The above-mentioned references, while they may suggest the incorporation of the chromium or tin metal ions into the frameworks of the respective zeolites, provide consistent evidence that the metal ions are not included in the framework, and are merely precipitated with the zeolite as some other probably amorphous phase during the course of the synthesis process. Tielen et al. in "Proceedings of the International Symposium on Zeolite Catalysis", Siofok, Hungary, May 13 1985 commented on isomorphic substitution in zeolites, stating that, "Generally speaking these new materials are claimed based upon their novel chemical composition or XRD spectrum or both. This novelty does not necessarily mean that the new materials contain the new element, or at least part of it, substituted in the zeolite framework. As far as we are aware, only in the case of boron substitution sound proof is available for its presence in the zeolite lattice." The reason for this failure is then obvious, since the very synthesis conditions used to synthesize the zeolite products are such that a nearly insoluble metal hydroxide precipitates thereby limiting the ability of the metal oxide to incorporate into the silicate units during crystal growth. This feature was only recently pointed out by Szostak et al. in Journal of Chemical Society, Faraday Trans. I, page 83 (1987). By recognizing the critical nature of the pH they were able to, for the first time, synthesize the ferrisilicate analog of ZSM-5.

It should be further pointed out that Tielen at the top of page 9 states "based on this table and the evidence mentioned in the introduction, elements with ionic radii between 0.020 and 0.061 are potential candidates for incorporation into a framework . . . " Using the values given for the Shannon references (radii in tetrahedral coordination) it is observed that Sn.sup.+4 has an ionic radius of 0.069 nm or 0.69 .ANG. (note that Shannon reports this value as the crystal radii) which is outside the range stipulated by Tielen and thus would not be expected to be in the framework. Although values for Cr.sup.+3 and Sn.sup.+2 are not provided in Tielen, they are provided by R. D. Shannon in his original paper (Acta Cryst. A 32 751-767 (1976)) as Cr.sup.+3 =0.755 and Sn.sup.+2 =1.36. It should be noted that the values for Cr.sup.+3 and Sn.sup.+2 are for octahedral coordination and the number for tetrahedral coordination would be expected to be smaller. Further, the numbers presented by Tielen are the crystal radii (see Shannon Table 1 page 752). Accordingly, none of these metal ions would be expected to be in the framework.

Another reference which has been cited in this art is Canadian Patent No. 1127134 to Morrison. This reference discloses an "alumino-silicate zeolite" which contains a metal oxide selected from the group consisting of indium, boron, ruthenium, platinum, chromium, rare earth, vanadium, palladium, molybdenum, mercury, tellurium, silver and mixtures thereof. However, there is no mention or hint that these metals are or could be in the framework. Indeed, on page 6 lines 1-7 the patentees state that it is not known whether the metal is present as a metal or as a metal compound. Given this uncertainty, it would be pure speculation to state that Morrison discloses an aluminosilicate zeolite where some of the aluminum in the framework has been replaced by chromium or some other metal. Accordingly, there is nothing in Morrison that suggests a zeolite having chromium as a framework metal.

Finally, U.S. Pat. No. 4933161 (Vaughan) issued Jun. 12 1990 discloses a process for replacing aluminum with tin (+4) in the zeolite framework. It is the inventor's contention that treating a zeolite with a tin compound under acidic hydrothermal conditions replaces some of the framework aluminum with tin. However, the conditions used by Vaughan would not result in framework aluminum being replaced by tin (+4). As will be shown in greater details in the examples, treating an ammonium Y zeolite by Vaughan's method gives a product that has lost a major fraction of its crystallinity and has virtually lost all of its cation equivalency indicating that considerable amounts of aluminum has been lost from the framework. In contrast, the molecular sieves of this invention retain at least 70% of their crystallinity and show only a small decrease in their cation equivalency. (See Examples 25 and 26).

The above mentioned references do suggest that it is desirable to synthesize zeolites or molecular sieves containing chromium or tin in the framework tetrahedral sites. However the methods employed in the references leave little doubt that the metal has been deposited with the zeolite either as an oxide or hydroxide or as an amorphous metal silicate. The references further demonstrate the difficulty involved in the incorporation of these metal ions in the zeolite tetrahedral framework positions. The uniqueness of the method of the current application which relies on the solubility of the chromium and tin metal ions in an acidic medium, and the Secondary Synthesis procedure to incorporate the metal ions into the framework is further demonstrated. As for the obviousness of the Secondary Synthesis procedure to incorporate any metal ion into the framework of an existing zeolite, all attempts to use this process with the ions of phosphorus or boron have thus far been unsuccessful. Boron is the only metal ion thus far that has been successfully incorporated into the pentasil zeolite framework via primary synthesis methods (Tielen et al.). Only by careful control of the Secondary Synthesis conditions can one be successful in incorporating iron and/or titanium, or chromium and/or tin into the framework of existing zeolites or molecular sieves.

Secondary Synthesis as used herein means a process whereby a molecular sieve product is treated by some method (Secondary Synthesis) to obtain a molecular sieve product that is either not obtainable by primary synthesis methods or is prepared with great difficulty or is not normally found in nature.

The present invention relates to novel zeolite compositions which contain significant framework tetrahedral atoms, which are not found to any significant level either in naturally occurring zeolites or in synthetic zeolites.

In the present invention, zeolite Y, zeolite L, mordenite and zeolite LZ-202 (an omega type zeolite prepared without the use of a templating agent as disclosed in U.S. Pat. No. 4840779) are treated with aqueous ammonium fluoride salts of either or both chromium or tin. During the treatment aluminum is removed from the molecular sieve framework and the metal ion is incorporated therein. By means of this invention, the metal ions of chromium and/or tin can be incorporated into molecular sieve frameworks where they are not normally found in nature.

DESCRIPTION OF THE FIGURES

FIG. 1A is a SEM (Scanning Electron Microscope) photograph for zeolite LZ-239 (Example 2), as hereinafter discussed.

FIG. 1B is an EDAX (Energy Dispersive Analysis by X-ray) Area scan for the photograph of FIG. 1A for zeolite LZ-239 (Example 2), as hereinafter discussed.

FIG. 2A is a SEM (Scanning Electron Microscope) photograph for zeolite LZ-239 (Example 2), as hereinafter discussed.

FIG. 2B is an EDAX (Energy Dispersive Analysis by X-ray) spot probe at point A in the photograph of FIG. 2A for zeolite LZ-239 (Example 2), as hereinafter discussed.

FIG. 2C is an EDAX (Energy Dispersive Analysis by X-ray) spot probe at point B in the photograph of FIG. 2A for zeolite LZ-239 (Example 2), as hereinafter discussed.

FIG. 3A is an EDAX (Energy Dispersive Analysis by X-ray) spot probe at point C in the photograph of FIG. 2A for zeolite LZ-239 (Example 2), as hereinafter discussed.

FIG. 3B is an EDAX (Energy Dispersive Analysis by X-ray) spot probe at point D in the photograph of FIG. 2A for zeolite LZ-239 (Example 2), as hereinafter discussed.

FIG. 4A is a SEM (Scanning Electron Microscope) photograph for zeolite LZ-239 (Example 2), as hereinafter discussed.

FIG. 4B is an EDAX (Energy Dispersive Analysis by X-ray) spot probe at point C in the photograph of FIG. 4A for zeolite LZ-239 (Example 2), as hereinafter discussed.

FIG. 5A is a SEM (Scanning Electron Microscope) photograph for zeolite LZ-239 (Example 3), as hereinafter discussed.

FIG. 5B is an EDAX (Energy Dispersive Analysis by X-ray) spot probe at point A in the photograph of FIG. 5A for zeolite LZ-239 (Example 3), as hereinafter discussed.

FIG. 5C is an EDAX (Energy Dispersive Analysis by X-ray) spot probe at point B in the photograph of FIG. 5A for zeolite LZ-239 (Example 3), as hereinafter discussed.

FIG. 6A is a SEM (Scanning Electron Microscope) photograph for zeolite LZ-239 (Example 4), as hereinafter discussed.

FIG. 6B is an EDAX (Energy Dispersive Analysis by X-ray) spot probe at point A in the photograph of FIG. 5A for zeolite LZ-239 (Example 4), as hereinafter discussed.

FIG. 7A is a SEM (Scanning Electron Microscope) photograph for zeolite LZ-252 (Example 10), as hereinafter discussed.

FIG. 7B is a SEM (Scanning Electron Microscope) photograph for zeolite LZ-252 (Example 10), as hereinafter discussed.

FIG. 8A is an EDAX (Energy Dispersive Analysis by X-ray) Area scan for the photograph of FIG. 7A for zeolite LZ-252 (Example 10), as hereinafter discussed.

FIG. 8B is an EDAX (Energy Dispersive Analysis by X-ray) spot probe at point B in the photograph of FIG. 7B for zeolite LZ-252 (Example 10), as hereinafter discussed.

FIG. 9 is a SEM (Scanning Electron Microscope) photograph for zeolite LZ-253 (Example 11), as hereinafter discussed.

FIG. 10A is a SEM (Scanning Electron Microscope) photograph for zeolite LZ-253 (Example 11), as hereinafter discussed.

FIG. 10B is an EDAX (Energy Dispersive Analysis by X-ray) spot probe at point B in the photograph of FIG. 10A for zeolite LZ-253 (Example 11), as hereinafter discussed.

FIG. 11A is a SEM (Scanning Electron Microscope) photograph for zeolite LZ-253 (Example 11), as hereinafter discussed.

FIG. 11B is an EDAX (Energy Dispersive Analysis by X-ray) Area scan for the photograph of FIG. 11A for zeolite LZ-253 (Example 11), as hereinafter discussed.

FIG. 12A is an EDAX (Energy Dispersive Analysis by X-ray) spot probe at point G in the photograph of FIG. 11A for zeolite LZ-253 (Example 11), as hereinafter discussed.

FIG. 12B is an EDAX (Energy Dispersive Analysis by X-ray) spot probe at point H in the photograph of FIG. 11A for zeolite LZ-253 (Example 11), as hereinafter discussed.

FIG. 13 is a ternary diagram wherein parameters relating to the instant compositions are set forth as mole fractions.

SUMMARY OF THE INVENTION

As stated this invention relates to a molecular sieve, a process for preparing the molecular sieve and processes which use the molecular sieve. Accordingly, one embodiment of the invention is a molecular sieve composition having a three-dimensional microporous framework structure which has a unit empirical formula on an anhydrous basis of:

______________________________________ Point w x y ______________________________________ A 0.49 0.01 0.50 B 0.01 0.49 0.50 C 0.01 0.01 0.98 ______________________________________

Another embodiment of the invention is a process for preparing a molecular sieve having a three dimensional microporous framework structure which has a unit empirical formula on an anhydrous basis of

where "w", "x" and "y" are the mole fractions of tin, aluminum and silicon, respectively, present as framework tetrahedral oxide units said mole fractions being such that they are within the triagonal area defined by points A, B, and C of FIG. 13 the process comprising contacting a crystalline microporous aluminosilicate zeolite having a framework structure of aluminum and silicon tetrahedral oxide units, pore diameters of at least about 3 Angstroms and a molar ratio of SiO.sub.2 /Al.sub.2 O.sub.3 of at least 2 with a fiuoro salt of tin, said fluoro salt being in the form of an aqueous solution or slurry, at a pH of about 3 to about 7 whereby framework aluminum atoms of the zeolite are removed and replaced by extraneous tin atoms.

Yet another embodiment of the invention is a molecular sieve prepared by the process described above and having an empirical formula on an anhydrous basis of

A further embodiment of the invention is a molecular sieve having a three-dimensional microporous framework structure of tin, aluminum and silicon tetrahedral oxide units and which has a unit empirical formula on an anhydrous basis of

These and other objects and embodiments will become more apparent after a more detailed description of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to new molecular sieve compositions and to the processes for their preparation. The molecular sieves of the instant invention have three-dimensional microporous crystal framework oxide structures of "MO.sub.2 ", AlO.sub.2 and SiO.sub.2 in tetrahedral units which have a unit empirical formula on an anhydrous basis of:

wherein "M" represents at least one of chromium or tin; and "w", "x" and "y" are as defined above represent the mole fractions of "M", aluminum and silicon, respectively, present as tetrahedral oxides.

The term "unit empirical formula" is used herein according to its common meaning to designate the simplest formula which gives the relative number of moles of chromium and/or tin (M), aluminum and silicon which form "MO.sub.2 ", AlO.sub.2 and SiO.sub.2 tetrahedral units within the molecular sieve. The unit empirical formula is given in terms of chromium and/or tin, aluminum and silicon as shown in Formula (1), above, and does not include other compounds, cations or anions which may be present as a result of the preparation or the existence of other impurities or materials in the bulk composition not containing the aforementioned tetrahedral units.

The instant process generally comprises a method for removing framework aluminum from zeolites having SiO.sub.2 /Al.sub.2 O.sub.3 mole ratios of about 2 or greater and substituting therefore one or more elements selected from the group consisting of chromium and/or tin. The resulting molecular sieves contain chromium and/or tin and have crystal structures similar to that of the initial zeolite.

The process of the invention comprises contacting a crystalline zeolite having pore diameters of at least about 3 Angstroms and having a molar SiO.sub.2 /Al.sub.2 O.sub.3 ratio of at least 2 with an effective amount of at least one of a fluoro salt of chromium or a fluoro salt of tin, preferably in an amount of at least 0.001 moles per 100 grams of zeolite starting material, said fluoro salt being in the form of an aqueous solution or slurry and brought into contact with the zeolite either incrementally or continuously at a slow rate (optionally in the presence of a buffer) whereby framework aluminum atoms of the zeolite are removed and replaced by chromium and/or tin atoms. It is desirable that the process be carried out such that at least 60 percent, preferably at least 80 percent, and more preferably at least 90 percent of the crystal structure of the starting zeolite is retained and that the Defect Structure Factor (hereinafter defined) is increased by less than 0.10 and preferably by less than 0.08.

Crystalline zeolite starting materials suitable for the practice of the present invention can be any naturally occurring or synthetically produced zeolite species which have pores large enough to permit the passage of water, chromium and/or tin fluoro salts and reaction products through their internal cavity system. These materials can generally be represented, in terms of molar ratios of oxides, as

wherein "M'" is a cation having the valence "n", "x" is a value of at least about 2 and preferably about 3 and "y" has a value of from zero to about 9. This value of "y" depends upon the degree of hydration and the capacity of the particular zeolite to hold adsorbed water. Alternatively, the framework composition of the naturally occurring or synthetic zeolite starting material can be expressed in terms of the mole fraction of framework tetrahedra, TO.sub.2 as:

wherein "a" is the mole fraction of framework tetrahedral sites occupied by aluminum atoms and "b" is the mole fraction of framework tetrahedral sites occupied by silicon atoms. Should the framework of the starting material contain atoms in addition to silicon and aluminum, these materials may be similarly expressed in terms of their "TO.sub.2 " formula in terms of their fractional occupation of the framework of the starting material. The algebraic sum of all of the subscripts within the brackets is equal to 1. In the above example, a+b=1.

Representative of the crystalline aluminosilicate zeolite molecular sieves include, but are not limited to erionite, mordenite, clinoptilolite, zeolite Y, zeolite L, zeolite LZ-202 (an omega type zeolite prepared without the use of a templating agent as disclosed in European Patent U.S. Pat. No. 4840779), zeolite omega, zeolite beta, zeolite TMA offretite, LZ-105 ZSM-5 ZSM-34 and ZSM-35. Zeolite Y is disclosed in U.S. Pat. No. 3130007; zeolite L is disclosed in U.S. Pat. No. 3216789; LZ-105 is disclosed in U.S. Pat. No. 4257885; zeolite omega is disclosed in U.S. Pat. No. 4241036; zeolite beta is disclosed in U.S. Pat. No. 3308069; ZSM-5 is disclosed in U.S. Pat. No. 3702886; ZSM-34 is disclosed in U.S. Pat. No. 4086186; and ZSM-35 is disclosed in U.S. Pat. No. 3992466. Both naturally occurring and synthetically prepared zeolite molecular sieves can be used.

For reasons more fully explained hereinafter, the starting zeolite should be able to withstand the initial loss of framework aluminum atoms to at least a modest degree without collapse of the crystal structure unless the process is to be carried out at a very slow rate, or the process is to be buffered. In general the ability to withstand aluminum extraction and maintain a high level of crystallinity is directly proportional to the initial SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of the zeolite. Accordingly, it is preferred that the SiO.sub.2 /Al.sub.2 O.sub.3 ratio is preferably at least about 2.0 and more preferably about 3. It is also preferred that at least about 50 percent, and more preferably at least 95 percent of the AlO.sub.4.sup.- tetrahedra of the naturally occurring or as-synthesized zeolite are present in the starting zeolite. Most advantageously the starting zeolite contains as many as possible of its original AlO.sub.4.sup.- tetrahedra, i.e. the starting zeolite has not been subjected to any post-formation treatment which either extensively removes aluminum atoms from their original framework sites or converts them from the normal conditions of 4-fold coordination with oxygen.

The cation population of the starting zeolite is not a critical factor insofar as substitution of chromium and/or tin for framework aluminum is concerned, but since the substitution mechanism may involve the in situ formation of salts of at least some of the zeolitic cations, it is generally advantageous that these salts be water-soluble to a substantial degree to facilitate their removal from the molecular sieve product. It is found that ammonium or hydronium cations form the most soluble salts in this regard and it is accordingly preferred that partially or at least 50 percent, most preferably 85 or more percent, of the zeolite cations be ammonium or hydronium cations. Sodium, one of the most common cations present in zeolites, is found to form Na.sub.3 AlF.sub.6 which is only very sparingly soluble in either hot or cold water. When this compound is formed as precipitates within the structural cavities of the zeolite it is quite difficult to remove by water washing. Its removal, moreover, is important if thermal stability of the molecular sieve product is desired since substantial amounts of fluoride can cause crystal collapse at temperatures as low as 500.degree. C.

For purposes of simplifying the description of the products of the above process, as above defined the framework composition of the zeolite starting material and the products of the instant process are expressed in terms of mole fractions of framework tetrahedra, i.e., the "TO.sub.2 ", where T represents the substituting tetrahedral atom in the framework. The starting zeolite may be expressed as:

whereas "a" is the mole fraction of aluminum tetrahedra in the framework; "b" is the mole fraction of silicon tetrahedra in the framework; "[]" denotes defect sites in the framework; and "z" is the mole fraction of defect sites in the zeolite framework. In many cases the "z" value for the starting zeolite is zero and the defect sites are simply eliminated from the expression, Numerically the sum of the values a+b+z=1.

If defect sites are present, the molecular sieves of this invention can have a unit empirical formula expressed in terms of the mole fractions of framework tetrahedra (TO.sub.2) of:

where u is the mole fraction of aluminum and ranges from about 0.01 to about 0.5 v is the mole fraction of silicon and ranges from about 0.5 to about 0.98 M is chromium, tin or mixtures thereof, w is the mole fraction of M and ranges from about 0.01 to about 0.49 [] is framework defect sites and z is the mole fraction of defect sites in the framework and ranges from greater than zero to about 0.2.

When the molecular sieves of this invention are prepared by the specific process of this invention, then the molecular sieve can have a unit empirical formula expressed in terms of the mole fractions of tetrahedra (TO.sub.2) of:

wherein: "N" is defined as the mole fraction of aluminum tetrahedra removed from the framework during the treatment and varies from about 0.01 to about 0.49; "a" is the mole fraction of aluminum tetrahedra present in the framework of the starting zeolite and varies from about 0.01 to about 0.49; "b" is the mole fraction of silicon tetrahedra present in the framework of the zeolite and varies from about 0.5 to about 0.98; "[]" is the framework defect sites; "z" is the mole fraction of defect sites in the framework and varies from greater than zero to about 0.2; "M" denotes chromium and/or tin; and "c" is the mole fraction of chromium and/or tin tetrahedra resulting from the fluoro salt treatment of the instant process and varies from about 0.01 to about 0.49. Numerically, the sum of the values:

The term "Defect Structure Factor" for any given zeolite is equivalent to the "z" value of that particular zeolite. The net change in Defect Structure Factors between the starting zeolite and the product zeolite is equivalent to ".increment.z".

.increment.z=z (product zeolite)-z (starting zeolite)

Theoretically, there should be no change in the silicon content and therefore "c" should equal (N.increment.z) where ".increment.z" is the net change in the mole fraction of defect sites in the zeolite framework resulting from the treatment. However, in reality fluoride does sometimes react with silicon of the molecular sieve particularly on the surface of the crystals of the more siliceous molecular sieves causing etching and transport of silicon atoms to other defect sites of the crystal. Hence "c" will not always be actually equal to (N.increment.z).

The chromium and/or tin-containing molecular sieve compositions prepared by the instant processes have framework aluminum removed from the starting zeolite with substitution of chromium and/or tin. The process generally comprises:

(a) contacting at effective process conditions a zeolite with an effective amount of at least one of a fluoro salt of chromium or a fluoro salt of tin; and

(b) isolating the chromium and/or tin-containing molecular sieve product from the reaction mixture.

The instant process generally comprises contacting a crystalline zeolite having a pore diameter of at least about 3 Angstroms and having a molar SiO.sub.2 /Al.sub.2 O.sub.3 ratio of at least 2 with at least 0.0075 moles of a fluoro salt of chromium or a fluoro salt of tin, per 100 grams of zeolite starting material, said fluoro salt being in the form of a solution or slurry. The fluoro salt is preferably provided as an aqueous solution or slurry but it is believed that solutions or slurries employing alcohols and other organic solvents may be employed.

It is necessary that the solution or slurry be maintained at an effective pH. The "effective pH" is a pH such that under effective process conditions; a) a monomeric species of the chromium and/or tin is present in the reaction solution; and b) the pH is high enough to avoid undue destructive acidic attack on the particular zeolite structure, apart from the intended reaction with an effective amount of the fluoro salt. The effective amount of fluoro salt is that amount which provides sufficient fluoride and chromium and/or tin for the process and the desired amount of chromium and/or tin in the final molecular sieve product. The effective pH value for this invention is generally greater than one (1), more preferably greater than 3 (three) and most preferably in the range of about 3 to about 7 (seven).

A pH of about 3 or more usually assures that no acid degradation of the zeolite occurs but it may not necessarily be the optimum pH for the formation of monomeric species of either chromium and/or tin in the solution. At pH values below about 3 crystal degradation of many zeolites is found to be unduly severe. Whereas at pH values higher than 7 insertion of the chromium and/or tin may be slow from a practical standpoint as a result of the solubility of chromium and/or tin at these pHs and as a result of certain polymerization reactions. A pH of 7 and above typically results in no monomeric species of either chromium and/or tin being present in the solution so that very little substitution of these metal atoms in the framework would occur. Frequently the polymeric species of chromium and/or tin will precipitate as solid oxides or hydrous oxides at pH 7 or above.

The fluoro salt solution or slurry is brought into contact with the zeolite either incrementally or continuously at a slow rate whereby framework aluminum atoms of the zeolite are removed and replaced by chromium and/or tin atoms from the fluoro salt.

The solution or slurry of the fiuoro salt, preferably aqueous, is brought into contact with the zeolite either incrementally or continuously at an effective rate such that a portion of the framework aluminum atoms are removed and replaced by chromium and/or tin atoms at a rate which preferably retains at least 80 percent and more preferably at least 90 percent of the crystal structure of the starting zeolite.

The fluoro salt used as the aluminum extractant and also as the source of chromium and/or tin, which is inserted into the zeolite structure in place of the extracted aluminum, can be any of the fluoro salts having the general formula:

where "M" is tin and "A" is a metallic or non-metallic cation, having the valence "b". Cations represented by "A" include alkylammonium, H.sup.+, NH.sub.4.sup.+, Mg.sup.++, Li.sup.+, Na.sup.+, K.sup.+, Ba.sup.++, Cd.sup.++, Cu.sup.+, Cu.sup.++, Ca.sup.++, Cs.sup.+, Fe.sup.++, Co.sup.++, Pb.sup.++, Mn.sup.++, Rb.sup.+, Ag.sup.+, Sr.sup.++, Tl.sup.+ and Zn.sup.++, or the formula A.sub.2/b MF.sub.5 where "M" is chromium. The ammonium and hydronium cation forms of the fluoro salt are generally preferred because of their solubility in water and also because these cations form water soluble by-product salts upon reaction with the zeolite, e.g., (NH.sub.4).sub.3 AlF.sub.6 and/or (NH.sub.4).sub.2 AlF.sub.5. Other salts which may be used include a combination of salts of MF.sub.3 and 3/2(NH.sub.4 HF.sub.2) or MF.sub.4 and NH.sub.4 HF.sub.2 where M is chromium or tin. Preferred fluoro salts are (NH.sub.4).sub.3 CrF.sub.5 ; CrF.sub.3 .multidot.3/2((NH.sub.4)HF.sub.2); NH.sub.4 SnF.sub.3 ; SnF.sub.2 .multidot.3/2(NH.sub.4 HF.sub.2) and SnF.sub.4 .multidot.NH.sub.4 HF.sub.2.

The manner in which the fluoro salt of chromium or the fluoro salt of tin and the starting zeolite are brought into contact and the overall process of substituting chromium and/or tin for aluminum in the zeolite framework is believed to be a two step process in which the aluminum extraction step tends to, unless controlled, proceed very rapidly while the insertion of chromium and/or tin is generally relatively slow. If dealumination becomes too extensive without the substitution of chromium and/or tin the crystal structure becomes seriously degraded and ultimately collapses. While not wishing to be bound by any particular theory, it appears that fluoride ion acts as the agent for extraction of framework aluminum in accordance with the equation: ##STR3##

It is important, therefore, that the initial dealumination step be inhibited and the step involving insertion of chromium and/or tin be promoted to achieve the desired molecular sieve product. It is found that the various zeolites have varying degrees of resistance toward degradation as a consequence of framework aluminum extraction without substitution of chromium and/or tin into the framework. Accordingly, for the reasons stated above the pH is preferably within the range of 3 to 7. The higher pH inhibits the rate and amount of dealumination. Also, increasing the reaction temperature tends to increase the rate of substitution of chromium and/or tin. Increasing the reaction temperature has been found to have less of an effect on dealumination than the pH of the solution. Therefore, the pH may be considered a means of controlling dealumination while temperature may be considered as a means of controlling the substitution rate.

Whether it is necessary or desirable to buffer the reaction system or select a particular fluoro salt concentration to control the pH is readily determined for each zeolite species by routine observation and evaluation. The question of whether the reaction system may advantageously be buffered will in large part depend on the selection of the particular starting zeolite, since zeolites have varying tolerances to acid and base media. For example, some zeolites such as mordenite and clinoptilolite can withstand very low pH conditions and a high level of dealumination without collapse of the crystal structure. When it is advantageous to buffer the reaction mixture in a particular pH range the reaction mixture may be buffered in a manner as generally heretofore employed in the art. The use of buffering salts, such as ammonium acetate, or use of an inert solid to react with excess acid or base, e.g. clays or aluminas, may be suitable to buffer the pH of the reaction mixture.

Theoretically, there is no lower limit for the concentration of fiuoro salt of chromium and/or tin in the aqueous solution or slurry employed. A slow rate of addition of the fluoro salt generally provides adequate time for the insertion of chromium and/or tin as a framework substitute for extracted aluminum before excessive aluminum extraction occurs with consequent collapse of the crystal structure. Practical commercial considerations, however, may require that the reaction proceed as rapidly as possible, and accordingly the conditions of reaction temperature and reagent concentrations will necessarily be optimized with respect to each zeolite starting material and with respect to commercial operation. In general it is believed that the more highly siliceous the zeolite, the higher the permissible reaction temperature and the lower the pH conditions which may be employed in the instant process. In general the preferred effective reaction temperature is within the range between about 10.degree. C. and about 99.degree. C., preferably between about 20.degree. C. and 95.degree. C., but temperatures of 125.degree. C. or higher and as low as 0.degree. C. are believed employable in some instances with some zeolite starting materials and with fluoro salts in a form other than aqueous solutions or slurries. The maximum concentration of fluoro salt in the aqueous solution employed is, of course, interrelated to the temperature and pH factors and also with the time of contact between the zeolite and the solution and the relative proportions of zeolite and fluoro salt. Solutions having fiuoro salt concentrations of between about 10.sup.-3 moles per liter of solution and up to saturation of the solution can be employed, but it is preferred that concentrations in the range of between about 0.5 and about 1.0 moles per liter of solution be used. In addition, as hereinbefore discussed, slurries of the fluoro salts of chromium and/or tin may be employed. The aforementioned concentration values are with respect to true solutions, and are not intended to apply to the total fluoro salts in slurries of the salts in water. Even very slightly soluble fluoro salts can be slurried in water and used as a reagent, the undissolved solids being readily available to replace dissolved molecular species consumed in reaction with the zeolite. As stated hereinabove, the amount of dissolved fluoro salts employed with respect to the particular zeolite being treated will depend to some extent upon the physical and chemical properties of the individual zeolites and other effective process conditions. However, the minimum value for the amount of fluoro salt to be added is preferably at least equivalent to the minimum mole fraction of aluminum to be removed from the zeolite.

In specifying the proportions of the zeolite starting material or adsorption properties of the zeolite product and the like herein, the "anhydrous state" of the zeolite will be intended unless otherwise stated. The term "anhydrous state" is employed herein to refer to a material substantially devoid of both physically adsorbed and chemically adsorbed water. In general a zeolite may be prepared in the anhydrous state by heating the zeolite in dry air at about 450.degree. C. for about 4 hours.

It is apparent from the foregoing that, with respect to effective process conditions, it is desirable that the integrity of the zeolite crystal structure be substantially maintained throughout the process, and that, in addition to having chromium and/or tin atoms inserted into the lattice, the zeolite retains at least 60 percent, preferably at least 70 and more preferably at least 90 percent of its original crystallinity. A convenient technique for assessing the crystallinity of the products relative to the crystallinity of the starting material is the comparison of the relative intensities of the d-spacings of their respective X-ray powder diffraction patterns. The sum of the peak heights, in terms of arbitrary units above background, of the starting material is used as the standard and is compared with the corresponding peak heights of the products. When, for example, the numerical sum of the peak heights of the molecular sieve product is 85 percent of the value of the sum of the peak heights of the starting zeolite, then 85 percent of the crystallinity has been retained. In practice it is common to utilize only a portion of the d-spacing peaks for this purpose, as for example, five of the six strongest d-spacings. In zeolite Y these d-spacings correspond to the Miller Indices 331 440 533 642 and 555. Products of the instant invention will have a certain fraction of the framework tetrahedra replaced by tin and/or chromium atoms. Because atoms of these heavier elements are incorporated there may be a decrease in the X-ray crystallinity values due to scatter because of the heavier elements. In this case, more reliable indicia of the crystallinity retained by the zeolite product are the degree of retention of surface area or the degree of retention of the adsorption capacity. Surface areas can be determined by the well-known Brunauer-Emmett-Teller method (B-E-T). See for example, Journal of American Chemical Society, Volume 60 page 309 (1938) using nitrogen as the adsorbate. In determining the adsorption capacity, the capacity for oxygen at 90.degree. K. (-183.degree. C.) and 100 Torr is preferred. Accordingly, the compositions of this invention are characterized in that they retain at least 60 preferably 70 and most preferably 90 percent of the capacity of the starting zeolite. Since it is preferred that the starting zeolite be highly crystalline and not have any defect, it is preferred that the instant compositions have at least 60 preferably 70 and most preferably 90 percent of its theoretical oxygen adsorption capacity as measured at 100 torr and 90.degree. K.

The present compositions are also characterized in that they have a cation equivalency of at least 0.8. Cation equivalency is the molar ratio of M'.sup.+ /Al in the molecular sieve.

Four-fold coordination of aluminum in the zeolite framework produces a net negative charge on the zeolite framework, requiring a cation M.sup.+ to balance the charge. The Cation Equivalent, M.sup.+ /Al, can be a direct measure of the amount of framework aluminum in the zeolite. Cations, here represented as the monovalent species, M.sup.+, can be any cation capable of entering the zeolite pores and balancing the framework charges. Representative of such cation species are Na.sup.+, K.sup.+, NH4.sup.+, Ca.sup.++, Mg.sup.++, Rare Earth.sup.+++, H.sup.+, and even hydroxoaluminum cation species Al(OH) 2.sup.+, Al(OH) 2.sup.+, AlO.sup.+, etc. Of course, hydroxoaluminum cations are not framework atoms, and thus when present they will have the effect of reducing the measured Cation Equivalent M.sup.+ /Al, since Al is taken to represent all of the aluminum present in the zeolite composition. Other non-cationic aluminum species such as forms of amorphous Al.sub.2 O.sub.3 may also be present with the zeolite composition. This form of amorphous Al.sub.2 O.sub.3 results from degradation to the zeolite that may occur as the result of a particular treatment. Presence of an amorphous Al.sub.2 O.sub.3 phase will also have the effect of reducing the value of the Cation Equivalent, M.sup.+ /Al, since Al is taken to represent all of the Al present in the zeolite composition. It is obvious then, that a low value for the Cation Equivalent indicates the presence of a substantial amount of zeolite degradation or the presence of a substantial amount of cationic aluminum. The higher the value for the Cation Equivalent, the greater the amount of the compositional Al present in the framework of the zeolite.

It is highly desirous that the residual Al be present in the framework of the molecular sieve instead of as an aluminum cation species or as amorphous Al.sub.2 O.sub.3 especially if the desired utility of the tin substituted product is in a catalytic application. Cation Equivalency can be directly related to the ion exchange capacity of the zeolite. The catalytic application would require that the Sn substituted zeolite product be acid exchanged (either H.sup.+ or an NH4.sup.+ form) to produce the catalytically active form of the zeolite on calcination. Since the Secondary Synthesis process has already reduced the aluminum content of the zeolite by substitution of the Sn for Al, it is important that as many as possible of the remaining Al be present at framework Al, thus insuring that the exchange capacity for the potential acidic species H.sup.+ and NH4.sup.+ is maximized.

It is advantageous to perform the routine chemical analysis on a form of the zeolite in which M' is an equivalent monovalent cation other than hydrogen. This avoids the uncertainty which can arise in the case of divalent or polyvalent metal zeolite cations as to whether the full valence of the cation is employed in balancing the net negative charge associated with each AlO.sub.4.sup.- tetrahedron.

Analysis of the Substitution Mechanism

The following is a hypothetical description of the mechanism involved and may not be the actual mechanism that is taking place. This description is based upon the present available data and analysis of the substitution products of this invention. This hypothetical description seems to be consistent with that data and may help to explain this unique process.

All available evidence, to date, indicates that the above described process of this invention is unique in being able to produce zeolites essentially free of defect structure and having chromium and/or tin inserted into the framework by a secondary synthesis process. In untreated, i.e. naturally occurring or as-synthesized zeolites the original tetrahedral structure is conventionally represented as ##STR4##

After treatment with a complexing agent such as ethylene-diamine-tetraacetic add (H.sub.4 EDTA) in which a stoichiometric reaction occurs whereby framework aluminum atoms along with an associated cation such as sodium is removed as NaAlEDTA, it is postulated that the tetrahedral aluminum is replaced by four protons which form a hydroxyl "nest", as follows: ##STR5##

In the practice of this invention, a two-step process is envisioned. In the first step of the treatment, tetrahedral aluminum atoms are first hydrolyzed and removed from the zeolite framework, whereupon they immediately react to form a more stable aluminum species or compound (i.e. aluminum fluoride species).

In the second step, ions of suitable size and coordination number are inserted into the vacant tetrahedral sites created by the dealumination.

Commonly assigned U.S. Pat. No. 4892720 involves replacement of framework aluminum by either iron and/or titanium. The present work involves replacement by either tin atoms or chromium atoms or both into vacant framework sites created by the dealumination.

The individual steps of the process can be accomplished in separate operations. However, it is more desirable to perform both steps in a single efficient operation. A particularly efficient class of compounds which can effect the dealumination and framework substitution steps in a single operation can be designated by J.sub.x TF.sub.y, where T represents the substituting tetrahedral atom. The substituting tetrahedral atom (T) when hydrolyzed in solution forms a hydroxylated species and an acid. The acid subsequently attacks the Al in the framework to cause the dealumination. The fluoride (F) serves to complex with the removed aluminum atoms, and J is the charge-balancing cation or cations. While the process is carried out in an aqueous system, it is not necessary that the J.sub.x TF.sub.y compound be dissolved in the solution. It is only necessary that it be sufficiently soluble to initiate the reaction with the zeolite. It is important that the reaction byproduct (the aluminum fluoride) be in a form that is readily removed from the zeolite by a washing step, subsequent to the substitution reaction. The presence of fluoride in the zeolite product in concentrations as low as 1 weight percent (or even lower), results in decreased thermal stability of the zeolite crystals. The residual fluoride can react with Si in the zeolite at elevated temperatures to cause the zeolite crystal to collapse.

Salts of the class of compounds J.sub.x TF.sub.y which have been used in the practice of this invention are:

Among the list of zeolites known to react with one or more of the above listed compounds to effect framework substitution are: the synthetic zeolite Y, mordenite, zeolite L and zeolite LZ-202 (an omega type zeolite prepared without the use of a templating agent as disclosed in (U.S. Pat. No. 4840779). With all of these zeolites, the reaction to dealuminate the starting zeolite and replace the removed aluminum atoms with a different tetrahedral atom did take place, at least to some extent, although the resulting zeolite may not have been the optimum product.

The chemistry of the process can be envisioned approximately in the following way. In the first step an aqueous slurry of the zeolite is contacted with a solution of J.sub.x TF.sub.y salt. In some cases, because of the limited solubility of J.sub.x TF.sub.y, the zeolite and the salt can be slurried together. The salt hydrolyzes in aqueous solution to form acid, H.sub.3 O.sup.+ and free fluoride. One example of this hydrolysis where T=Sn and J=NH.sub.4 can be depicted as follows:

The acid thus formed (H.sub.3 O).sup.+, reacts rapidly to dealuminate the zeolite. The removed aluminum rapidly reacts with the free fluoride to form aluminum fluoride salts such as AlF.sub.3 (NH.sub.4).sub.2 AlF.sub.5 and (NH.sub.4).sub.3 AlF.sub.6.

This reaction is the most crucial part of the process, since the dealumination step is very rapid. If too much dealumination occurs (without substitution into the vacant tetrahedral sites), the zeolite quickly loses its crystal structure. The use of a buffer such as ammonium acetate, thereby keeping the pH greater than about 6.0 can be used to slow down the hydrolysis so that the slower substitution step can take place. Another method of controlling the dealumination step is to add the J.sub.x TF.sub.y solution very slowly to the zeolite slurry. In this manner, some substitution can occur before the zeolite framework is excessively dealuminated to the point of causing crystal collapse. With the slow addition of the J.sub.x TF.sub.y solution, the zeolite itself acts as a "buffer" in the system.

The second step is the substitution of a new tetrahedral atom into the zeolite structure in place of the removed aluminum atom. This step has been found to be the overall rate-limiting or slow step. Increasing the temperature of the system increases the rate of substitution, but it may also speed up the rate of other undesirable side reactions such as the dealumination or the continued hydrolysis of T to form a polymeric species which will no longer be able to substitute in the framework defect sites. The exact chemistry of the substitution step is not known in detail. It can be suggested that dealumination of the zeolite leaves a hydroxyl nest in the vacant site, which in turn reacts with the hydrolyzed form of the substituting tetrahedral atom.

The stepwise reaction can be depicted as follows: ##STR6## the overall reaction can be stated as: ##STR7##

The Experimental Conditions

The infrared spectrum of the aluminum depleted zeolite will show a broad nondescript absorption band beginning at about 3750 cm.sup.-1 and extending to about 3000 cm.sup.-1. The size of this absorption band or envelope increases with increasing aluminum depletion of the zeolite. The reason that the absorption band is so broad and without any specific absorption frequency is that the hydroxyl groups in the vacant sites in the framework are coordinated in such a way that they interact with each other (hydrogen bonding). The hydroxyl groups of adsorbed water molecules are also hydrogen-bonded and produce a similar broad absorption band as do the "nest" hydroxyls. Also, certain other zeolitic hydroxyl groups, exhibiting specific characteristic absorption frequencies within the range of interest, will if present, cause infrared absorption bands in these regions which are superimposed on the band attributable to the "nest" hydroxyl groups. These specific hydroxyls are created by the decomposition of ammonium cations or organic cations present in the zeolite.

It is, however, possible to treat zeolites, prior to subjecting them to infrared analysis, to avoid the presence of the interfering hydroxyl groups and thus be able to observe the absorption attributable to the "nest" hydroxyls only. The hydroxyls belonging to adsorbed water are avoided by subjecting the hydrated zeolite sample to vacuum activation at a moderate temperature of about 200.degree. C. for about 1 hour. This treatment permits desorption and substantially complete removal of the adsorbed water. Complete removal of adsorbed water can be ascertained by noting when the infrared absorption band at about 1640 cm.sup.-1 the bending frequency of water molecules, has been removed from the spectrum.

The decomposable ammonium cations can be removed, at least in large part, by ion-exchange and replaced with metal cations, preferably by subjecting the ammonium form of the zeolite to a mild ion exchange treatment with an aqueous NaCl solution. The OH absorption bands produced by the thermal decomposition of ammonium cations are thereby avoided. Accordingly the absorption band over the range of 3745 cm.sup.-1 to about 3000 cm.sup.-1 for a zeolite so treated is almost entirely attributable to hydroxyl groups associated with defect structure and the absolute absorbance of this band can be a measure of the degree of aluminum depletion.

It is found, however, that the ion-exchange treatment, which must necessarily be exhaustive even though mild, required considerable time. Also the combination of the ion-exchange and the vacuum calcination to remove adsorbed water does not remove every possible hydroxyl other than defect hydroxyls which can exhibit absorption in the 3745 cm.sup.-1 to 3000 cm.sup.-1 range. For instance, a rather sharp band at 3745 cm.sup.-1 has been attributed to the Si-OH groups situated in the terminal lattice positions of the zeolite crystals and to amorphous (non-zeolitic) silica from which physically adsorbed water has been removed. For these reasons it is preferred to use a somewhat different criterion to measure the degree of defect structure in the zeolite products of this invention.

In the absence of hydrogen-bonded hydroxyl groups contributed by physically adsorbed water, the absorption frequency least affected by absorption due to hydroxyl groups other than those associated with framework vacancies or defect sites is at 3710.+-.5 cm.sup.-1. Thus the relative number of defect sites remaining in a zeolite product of this invention can be gauged by first removing any adsorbed water from the zeolite, determining the value of the absolute absorbance in its infrared spectrum at a frequency of 3710 cm.sup.-1 and comparing that value with the corresponding value obtained from the spectrum of a zeolite having a known quantity of defect structure. The following specific procedure has been arbitrarily selected and used to measure the amount of defect structure in the products prepared in the Examples appearing hereinafter. Using the data obtained from this procedure it is possible, using simple mathematical calculation, to obtain a single and reproducible value hereinafter referred to as the "Defect Structure Factor", denoted hereinafter by the symbol "z", which can be used in comparing and distinguishing the present novel zeolite compositions from their non-chromium and/or tin containing counter-parts.

DEFECT STRUCTURE FACTOR "Z"

(A) Defect Structure Zeolite Standard

Standards with known amounts of defect structure can be prepared by treating a crystalline zeolite of the same species as the product sample with ethylenediaminetetraacetic acid by the standard procedure of Kerr as described in U.S. Pat. No. 3442795. In order to prepare the standard it is important that the starting zeolite be well crystallized, substantially pure and free from defect structure. The first two of these properties are readily determined by conventional X-ray analysis and the third by infrared analysis using the procedure set forth in part (B) hereof. The product of the aluminum extraction should also be well crystallized and substantially free from impurities. The amount of aluminum depletion, i.e., the mole fraction of tetrahedral defect structure of the standard samples can be ascertained by conventional chemical analytical procedure. The molar SiO.sub.2 /Al.sub.2 O.sub.3 ratio of the starting zeolite used to prepare the standard sample in any given case is not narrowly critical, but is preferably within about 10% of the molar SiO.sub.2 /Al.sub.2 O.sub.3 ratio of the same zeolite species used as the starting material in the practice of the process of the present invention.

(B) Infrared Spectrum of Product Samples and Defect Structure Zeolite Standard

Fifteen milligrams of the hydrated zeolite to be analyzed are pressed into a 13 mm. diameter self-supporting wafer in a KBr die under 5000 lbs. pressure. The wafer is then heated at 200.degree. C. for 1 hour at a pressure of not greater than 1.times.10.sup.-4 mm Hg to remove all observable traces of physically adsorbed water from the zeolite. This condition of the zeolite is evidenced by the total absence of an infrared absorption band at about 1640 cm.sup.-1. Thereafter, and without contact with adsorbable substances, particularly water vapor, the infrared spectrum of the wafer is obtained on an interferometer system at 4 cm.sup.-1 resolution over the frequency range of at least 3745 to 3000 cm.sup.-1. Both the product sample and the standard sample are analyzed using the same interferometer system to avoid discrepancies in the analysis due to different apparatus. The spectrum, normally obtained in the transmission mode of operation is mathematically converted to and plotted as wave number vs. absorbance.

The defect structure factor (z) is calculated by substituting the appropriate data into the following formula: ##EQU1## wherein AA .sub.(ps) is the infrared absolute absorbance measured above the estimated background of the product sample at 3710 cm.sup.-1 ; AA .sub.(std) is the absolute absorbance measured above the background of the standard at 3710 cm.sup.-1 and the mole fraction of defects in the standard are determined in accordance with part (A) above.

Once the defect structure factor, z, is known, it is possible to determine from the wet chemical analysis of the product sample for SiO.sub.2 Al.sub.2 O.sub.3 chromium and/or tin and the cation content as M.sub.2/n O whether chromium and/or tin has been substituted for aluminum in the zeolite as a result of the treatment and also the efficiency of the substitution of chromium and/or tin.

The essential X-ray powder diffraction patterns appearing in this specification and referred to in the appended claims are obtained using either: 1) standard X-ray powder diffraction techniques; or 2) computer based techniques using copper K-alpha radiation and using Siemens D-500 X-ray powder diffractometers with Siemens Type K-805 X-ray sources, available from Siemens Corporation, Cherry Hill, N.J., with appropriate computer interface. When employing the standard X-ray technique the radiation source is a high-intensity, copper target, x-ray tube operated at 50 Kv and 40 ma. The diffraction pattern from the copper K alpha radiation and graphite monochromator is suitably recorded by an X-ray spectrometer scintillation counter, pulse-height analyzer and strip-chart recorder. Flat compressed powder samples are scanned at 2.degree. (2 theta) per minute, using a 2 second time constant. Interplanar spacings (d) are obtained from the position of the diffraction peaks expressed as 2 theta, where 2 theta is the Bragg angle as observed on the strip chart. Intensities are determined from the heights of diffraction peaks after subtracting background.

All of the zeolite samples were evaluated according to standard analytical procedures. The x-ray crystallinity of most samples was measured using the Siemens D-500 where peak areas as well as peak intensities of all major reflections were measured and compared against untreated samples of the starting materials. It was expected that the product of a successful experiment would maintain a major fraction of its x-ray crystallinity. Unit cell values were measured on materials possessing cubic unit cells (a.sub.o).

Framework infrared spectra of the treated zeolites were compared to the framework spectra of the respective starting materials. A general overall shift of the framework absorption frequencies to higher wave numbers is a good indication of a higher silicon content in the framework. Shift of the asymmetric stretch band at about 950-1250 cm.sup.-1 accompanies dealumination. The symmetric stretch band, 750-835 cm.sup.-1 is more sensitive to the actual silicon content in the framework, shifting to higher wave numbers as the silicon content increases. Very little is known about the effect of substitution of atoms other than silicon into the zeolite framework on the position of these bands. Very little effect on the position of the symmetric stretch band has been observed as a result of simple dealumination. However, because there are not studies of the effect of dealumination on the positions or shifts of the framework infrared bands with zeolites other than Y and perhaps mordenite; the lack of a substantial shift of the symmetric stretch band was not used as the sole criterion to judge the degree of metal atom substitution.

More specifically, there are no studies of the effect of substituting either chromium or tin or both for aluminum in the zeolite framework on shifts of framework infrared bands. A general assumption would be that ions larger than Al would increase the unit cell size causing a decrease in framework infrared absorption band positions. Conversely, substitution of ions smaller than Al into the zeolite framework would cause a decrease in unit cell size and an increase in framework infrared absorption band positions.

The hydroxyl region infrared spectrum was used to evaluate the relative amount of framework defect sites in the zeolite product of this invention. For a more thorough description of this method of evaluation see U.S. Pat. No. 4503023. Briefly, using standard procedures, the absolute absorbance (above background) at 3710 cm.sup.-1 was measured and compared to a standard sample of aluminum-depleted NaY which contained a known number of defects. The defect structure factor (z) of the reference standard was 0.140 and gave rise to an absolute absorbance value of 0.330 at 3710 cm.sup.-1 of the infrared spectrum. The reference value of z in this case is the mole fraction of vacant tetrahedral sites in the zeolite framework of the aluminum-depleted NaY. Fourteen percent of all of the tetrahedral sites do not contain a tetrahedral atom (Si or Al), but rather, some form of hydrogen-bonded OH groups.

EXAMPLES

The following examples are provided to illustrated the invention and are not intended to be limiting thereof.

Practice of the invention is demonstrated by the following examples. After the substitution of Sn and Cr in place of Al in the framework of zeolites via treatment with aqueous ammonium fluoride salts, all the zeolite products were washed well in hot distilled water following reaction. Samples of the dried powders were examined by x-ray powder diffraction techniques for retention of crystallinity. Those samples judged to be crystalline were further examined by differential thermal analysis methods (DTA), measurement of O.sub.2 adsorption isotherms at -183.degree. C. (90.degree. K.), measurement of H.sub.2 O adsorption capacity at 4.6 torr and 25.degree. C., infrared analyses of both the OH region and the mid-range (framework) region, and finally by complete chemical analysis.

In some of the X-ray patterns reported, the relative intensities of the d-spacings are indicated by the notations vs, s, m, w and vw which represent very strong, strong, medium, weak and very weak, respectively.

Examples 1 through 5 disclose the substitution of Cr.sup.3+ in the framework of Zeolite Y and the resulting product was designated LZ-239.

EXAMPLE 1

Two gm NH.sub.4 Y (anhydrous weight) containing 8.544 millimoles of Al were slurried in 100 ml distilled water heated at 75.degree. C. Fifty ml of a second solution containing 21.36 millimoles CrF.sub.3 and 64.08 millimoles NH.sub.4 HF.sub.2 in 250 ml distilled water, was added incrementally to the zeolite slurry at a rate of 2 ml every 5 minutes. Following the addition of the chrome solution, the temperature was raised to 95.degree. C. and the slurry was digested for 3 hours at 95.degree. C. A green colored product was obtained which was filtered, washed free of soluble fluoride with hot distilled water, dried and characterized. The product contained 11 weight percent Cr.sub.2 O.sub.3 it showed substantially reduced X-ray crystallinity, and an estimated unit cell value of 24.55.ANG. and and a substantial increase in the Defect Structure Factor, z. Reduced crystallinity may have been caused by two factors in this case. A certain amount of apparent disorder in the structure is to be expected due to the larger chromium cation which can be present both in the framework and as a hydroxylated cation [Cr(OH).sup.2+, Cr(OH).sub.2.sup.+ ]. Incorporation of the heavier chromium atoms into the structure should cause loss of peak intensity and area due to the scattering of X-rays by the heavier atoms of chromium. In addition, the acidic nature of the bifluoride anion probably caused some degradation to the acid sensitive Y zeolite framework structure.

The framework mole fractions of oxides are set forth below for the starting NH.sub.4 Y and the LZ-239 product.

(a) Mole fractions of oxides (TO.sub.2):

Starting NH.sub.4 Y: (Al.sub.0.277 Si.sub.0.705[]0.018)O.sub.2

LZ-239 Product: (Al.sub.0.115 Cr.sub.0.075 Si.sub.0.634[]0.176)O.sub.2

(b) Mole Fraction of Aluminum Removed, N: 0.162

(d) Change in Defect Structure Factor, z: 0.158

(e) Moles of Chromium Substituted per Mole of Aluminum Removed, c/N : 0.463

PROCESS APPLICATIONS

The molecular sieves compositions of this invention have unique surface characteristics making them useful as molecular sieves and as catalyst or as bases for catalysts in a variety of separation, hydrocarbon conversion and oxidative combustion processes. These composition can be impregnated or otherwise associated with catalytically active metals by the numerous methods known in the art and used, for example, in fabricating catalysts compositions containing alumina or aluminosilicate materials.

The instant molecular sieve compositions may be employed for separating molecular species in admixture with molecular species of a different degree of polarity or having different kinetic diameters by contacting such mixtures with a molecular sieve composition having pore diameters large enough to adsorb at least one but not all molecular species of the mixture based on the polarity of the adsorbed molecular species and/or its kinetic diameter. When the instant compositions are employed for such separation processes the compositions are at least partially activated whereby some molecular species selectively enter the intracrystalline pore system thereof.

The hydrocarbon conversion reactions which may be catalyzed by the instant molecular sieve compositions include; cracking, hydrocracking; alkylation of both the aromatic and isoparaffin types; isomerization (including xylene isomerization); polymerization; reforming; hydrogenation; dehydrogenation; transalkylation; dealkylation; and hydration.

When catalyst composition containing the instant molecular sieve compositions also contains a hydrogenation promoter, such promoter may be platinum, palladium, tungsten, nickel or molybdenum and may be used to treat various petroleum stocks including heavy petroleum residual stocks, cyclic stocks and other hydrocrackable charge stocks. These stocks can be hydrocracked at temperatures in the range of between about 400.degree. F. and about 825.degree. F. using molar ratios of hydrogen to hydrocarbon in the range of between about 2 and about 80 pressures between about 10 and about 3500 p.s.i.g., and a liquid hourly space velocity (LHSV) of between about 0.1 and about 20 preferably between about 1.0 and about 10.

Catalyst compositions containing the instant molecular sieve compositions may also be employed in reforming processes in which the hydrocarbon feedstocks contact the catalyst at temperatures between about 700.degree. F. and about 1000.degree. F., hydrogen pressures of between about 100 and about 500 p.s.i.g., LHSV values in the range between about 0.1 and about 10 and hydrogen to hydrocarbon molar ratios in the range between about 1 and about 20 preferably between about 4 and about 12.

Further, catalysts containing the instant molecular sieve compositions which also contain hydrogenation promoters, are also useful in hydroisomerization processes wherein the feedstock(s), such as normal paraffins, is converted to saturated branched-chain isomers. Hydroisomerization processes are typically carried out at a temperature between about 200.degree. F. and about 600.degree. F., preferably between about 300.degree. F. and about 550.degree. F. with an LHSV value between about 0.2 and about 1.0. Hydrogen is typically supplied to the reactor in admixture with the hydrocarbon feedstock in molar proportions of hydrogen to the feedstock of between about 1 and about 5.

Catalyst compositions similar to those employed for hydrocracking and hydroisomerization may also be employed at between about 650.degree. F. and about 1000.degree. F., preferably between about 850.degree. F. and about 950.degree. F. and usually at somewhat lower pressures within the range between about 15 and about 50 p.s.i.g. for the hydroisomerization of normal paraffins. Preferably the paraffin feedstock comprises normal paraffins having a carbon number range of C.sub.7 -C.sub.20. The contact time between the feedstock and the catalyst is generally relatively short to avoid undesirable side reactions such as olefin polymerization and paraffin cracking. LHSV values in the range between about 0.1 and about 10 preferably between about 1.0 and about 6.0 are suitable.

The low alkali metal content of the instant compositions make them particularly well suited for use in the conversion of alkylaromatic compounds, particularly for use in the catalytic disproportionation of toluene, xylene, trimethylbenzenes, tetramethylbenzenes and the like. In such disproportionation processes it has been observed that isomerization and transalkylation can also occur. The catalysts containing the instant molecular sieve compositions and employed for such processes will typically include Group VIII noble metal adjuvants alone or in conjunction with Group VI-B metals such as tungsten, molybdenum and chromium which are preferably included in such catalyst compositions in amounts between about 3 and about 15 weight-percent of the overall catalyst composition. Extraneous hydrogen can, but need not be present in the reaction zone which is maintained at a temperature between about 400.degree. and about 750.degree. F., pressures in the range between about 100 and about 2000 p.s.i.g. and LHSV values in the range between about 0.1 and about 15.

Catalysts containing the instant molecular sieve compositions may be employed in catalytic cracking processes wherein such are preferably employed with feedstocks such as gas oils, heavy naphthas, deasphalted crude oil residues etc. with gasoline being the principal desired product. Temperature conditions are typically between about 850.degree. and about 1100.degree. F., LHSV values between about 0.5 and about 10 pressure conditions are between about 0 p.s.i.g. and about 50 p.s.i.g.

Catalysts containing the instant molecular sieve compositions may be employed for dehydrocyclization reactions which employ paraffinic hydrocarbon feedstocks, preferably normal paraffins having more than 6 carbon atoms, to form benzene, xylenes, toluene and the like. Dehydrocyclization processes are typically carried out using reaction conditions similar to those employed for catalytic cracking. For such processes it is preferred to use a Group VIII non-noble metal cation such as cobalt and nickel in conjunction with the molecular sieve composition.

Catalysts containing the instant molecular sieve compositions may be employed in catalytic dealkylation where paraffinic side chains are cleaved from aromatic nuclei without substantially hydrogenating the ring structure at relatively high temperatures in the range between about 800.degree. F. and about 1000.degree. F. at moderate hydrogen pressures between about 300 and about 1000 p.s.i.g. with other conditions being similar to those described above for catalytic hydrocracking. Catalysts employed for catalytic dealkylation are of the same type described above in connection with catalytic dehydrocyclization. Particularly desirable dealkylation reactions contemplated herein include the conversion of methylnaphthalene to naphthalene and toluene and/or xylenes to benzene.

Catalysts containing the instant molecular sieve compositions may be used in catalytic hydrofining wherein the primary objective is to provide for the selective hydrodecomposition of organic sulfur and/or nitrogen compounds without substantially affecting hydrocarbon molecules present therewith. For this purpose it is preferred to employ the same general conditions described above for catalytic hydrocracking. The catalysts are the same typically of the same general nature as described in connection with dehydrocyclization operations. Feedstocks commonly employed for catalytic hydroforming include: gasoline fractions; kerosenes; jet fuel fractions; diesel fractions; light and heavy gas oils; deasphalted crude oil residua; and the like. The feedstock may contain up to about 5 weight-percent of sulfur and up to about 3 weight-percent of nitrogen.

Catalysts containing the instant molecular sieve compositions may be employed for isomerization processes under conditions similar to those described above for reforming although isomerization processes tend to require somewhat more acidic catalysts than those employed in reforming processes. Olefins are preferably isomerized at temperatures between about 500.degree. F. and about 900.degree. F., while paraffins, naphthenes and alkyl aromatics are isomerized at temperatures between about 700.degree. F. and about 1000.degree. F. Particularly desirable isomerization reactions contemplated herein include the conversion of n-heptane and/or n-octane to isoheptanes, iso-octanes, butane to iso-butane, methylcyclopentane to cyclohexane, meta-xylene and/or ortho-xylene to para-xylene, 1-butene to 2-butene and/or isobutene, n-hexene to isohexane, cyclohexane to methylcyclopentene etc. The preferred cation form is a combination of a molecular sieve of this invention and polyvalent metal compounds (such as sulfides) of metals of Group II-A, Group II-B and rare earth metals. For alkylation and dealkylation processes the instant molecular sieve compositions having pores of at least 5 are preferred. When employed for dealkylation of alkyl aromatics, the temperature is usually at least 350.degree. F. and ranges up to a temperature at which substantial cracking of the feedstock or conversion products occurs, generally up to about 700.degree. F. The temperature is preferably at least 450.degree. F. and not greater than the critical temperature of the compound undergoing dealkylation.

Pressure conditions are applied to retain at least the aromatic feed in the liquid state. For alkylation the temperature can be as low as 250.degree. F. but is preferably at least 350.degree. F. In alkylation of benzene, toluene and xylene, the preferred alkylation agents are olefins such as ethylene and propylene.

The molecular sieve compositions of this invention may be employed in conventional molecular sieving processes as heretofore have been carried out using aluminosilicate, aluminophosphate or other commonly employed molecular sieves. The instant compositions are preferably activated, e.g. calcined in air or nitrogen, prior to their use in a molecular sieve process.

The molecular sieve compositions of this invention are also useful as adsorbents and are capable of separating mixtures of molecular species both on the basis of molecular size (kinetic diameters) and based on the degree of polarity of the molecular species. When the separation of molecular species is based upon selective adsorption based on molecular size, the instant molecular sieve composition is chosen in view of the dimensions of its pores such that at least the smallest molecular species of the mixture can enter the intracrystalline void space while at least the largest species is excluded. When the separation is based on degree of polarity it is generally the case that the more hydrophilic molecular sieve composition will preferentially adsorb the more polar molecular species of a mixture having different degrees of polarity even though both molecular species can communicate with the pore system of the molecular sieve composition.

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