Method of Preparing Crystalline Zeolite

This invention relates to an improved method of preparing crystalline zeolite materials using a new class of compounds 1-alkyl, 4-aza, 1-azonia-bicyclo(2,2,2)octane, 4-oxide, halides.

Zeolitic materials, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversions. Certain zeolitic materials are ordered, porous crystalline aluminosilicates having a definite crystalline structure within which there are a large number of channels. These cavities and channels are precisely uniform in size. Since the dimensions of these pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as "molecular sieves" and are utilized in a variety of ways to take advantage of these properties.

Such molecular sieves, both natural and synthetic, include a wide variety of positive ion-containing crystalline aluminosilicates. These aluminosilicates can be described as a rigid three-dimensional framework of SiO.sub.4 and AlO.sub.4 in which the tetrahedra are cross-linked by the sharing of oxygen atoms whereby the ratio of the total aluminum and silicon atoms to oxygen is 1:2. The electrovalence of the tetrahedra containing aluminum is balanced by the inclusion in the crystal of a cation, for example, an alkali metal or an alkaline earth metal cation. This can be expressed wherein the ratio of aluminum to the number of various cations, such as Ca/2, Sr/2, Na, K or Li is equal to unity. One type of cation may often be exchanged either entirely or partially by another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchange, it has been possible to vary the properties of a given aluminosilicate by suitable selection of the cation. The spaces between the tetrahedra are usually occupied by molecules of water prior to dehydration.

Prior art techniques have resulted in the formation of a great variety of synthetic aluminosilicates. These aluminosilicates have come to be designated by letter or other convenient symbols, as illustrated by zeolite A (U.S. Pat. No. 2,882,243), zeolite X (U.S. Pat. No. 2,882,244), zeolite Y (U.S. Pat. No. 3,130,007), zeolite ZK-5 (U.S. Pat. No. 3,247,195), zeolite ZK-4 (U.S. Pat. No. 3,314,752) zeolite ZSM-5 (U.S. Pat. No. 3,702,886), zeolite ZSM-11 (U.S. Pat. No. 3,709,979), zeolite ZSM-12 (U.S. Pat. No. 3,832,449), zeolite ZSM-20 (U.S. Pat. No. 3,972,983), zeolite ZSM-35 (U.S. Pat. No. 4,016,245), zeolite ZSM-21 and 38 (U.S. Pat. No. 4,046,859), and zeolite ZSM-23 (U.S. Pat. No. 4,076,842), merely to name a few.

The novel class of compounds discovered to be useful in the present zeolite synthesis are described in co-pending U.S. Application Ser. No. 073,766 filed Sept. 10, 1979 filed concurrently herewith.

The present invention relates to an improved method of preparing synthetic crystalline zeolite materials having a constraint index between 1 and 12 and a SiO.sub.2 /Al.sub.2 O.sub.3 ratio greater than 5. More particularly the present invention relates to an improved method of preparing the zeolites ZSM-5, ZSM-11, ZSM-12, ZSM-21, ZSM-23, ZSM-35, ZSM-38 and ZSM-48 described in our copending U.S. Application Ser. No. 13,640 filed Feb. 21, 1979.

Still more particularly, the present invention is directed to an improved method for preparing a group of crystalline zeolite materials hereinafter designated as ZSM-5 and an unidentified crystalline material which comprises crystallizing the substantially pure zeolite material from a silica and alumina (optional) gel mixture in the presence of a new class of compounds 1-alkyl, 4-aza, 1-azonia-bicyclo (2,2,2)octane, 4-oxide, halides and the zeolite products produced thereby.

Zeolite ZSM-5, for example, has the formula, in terms of mole ratios of oxides as follows:

wherein M is at least one cation having a valence n, Y is at least 5 and z is 0-40. M can be an alkali metal, e.g. sodium, and tetralkylammonium cations, the alkyl group containing 2-5 carbon atoms.

Members of the family of zeolites designated herein as ZSM-5 have an exceptionally high degree of thermal stability thereby rendering them particularly effective for use in processes involving elevated temperatures. In this connection, ZSM-5 zeolites appear to be one of the most stable families of zeolites known to date.

Members of the family of ZSM-5 zeolites possess a definite distinguishing crystalline structure whose X-ray diffraction pattern shows the following significant lines:

The unidentified crystalline material also produced crystallizes into large irregularly-shaped particles which are agglomerates of very small platelets. The crystalline product is relatively unstable and undergoes a loss in crystallinity and a large decrease in lattice parameter on calcination. Crystallite size may have a bearing thereon.

The X-ray diffraction pattern of the unidentified crystalline material of the present invention has the following values:

These values for ZSM-5 and the unidentified material were determined by standard techniques. The radiation was the K-alpha doublet of copper and a diffractometer equipped with a scintillation counter and a strip chart recorder was used. The peak heights, I, and the positions as a function of 2 theta, where theta is the Bragg angle, were read from the diffractometer chart. From these, the relative intensities, 100 I/I.sub.o, where I.sub.o is the intensity of the strongest line or peak, and d(obs), the interplanar spacing in A, corresponding to the recorded lines, were calculated. In the tables the relative intensities are given in terms of the symbols VS=Very Strong, S=Strong, M=Medium, W=Weak, and VW=Very Weak, or numerically. It should be understood that each X-ray diffraction pattern is characteristic of all the species of each zeolite structure, i.e. ZSM-5 and the unidentified product, respectively.

The sodium form of ZSM-5 as well as other cationic forms reveal substantially the same pattern with some minor shifts in interplanar spacing and variation in relative intensity. Other minor variations can occur depending on the silicon to aluminum ratio of the particular sample, as well as if it has been subjected to thermal treatment.

ZSM-5 can be used either in the alkali metal form, e.g. the sodium form, the ammonium form, the hydrogen form or another univalent or multivalent form. When used as a catalyst it will be subjected to thermal treatment to remove part or all of any organic constitutent.

Zeolites ZSM-5, ZSM-11 and ZSM-12 have, for example, been originally crystallized in the presence of quaternary ammonium compounds or precursors thereof, e.g. ZSM-5, tetrapropylammonium ions, ZSM-11, tetrabutylammonium ions, and ZSM-12, tetraethylammonium (TEA) ions. We have found the methyl ANOxide cation to be effective in zeolite synthesis. Depending upon the mixture composition, the product will be ZSM-5 in low SiO.sub.2 /Al.sub.2 O.sub.3 mixtures, the unidentified crystalline component in very high SiO.sub.2 /Al.sub.2 O.sub.3 mixtures, and a mixture of the two at intermediate SiO.sub.2 /Al.sub.2 O.sub.3.

By this invention it has been found that the crystalline materials crystallize in the presence of the novel compounds 1-alkyl, 4-aza, 1-azonia-bicyclo(2,2,2)octane, 4-oxide, halides.

The crystalline zeolites and the unidentified crystalline material can be prepared from a reaction mixture containing a source of silica, optionally alumina, alkyl ANOxide cations (RNO), an alkali metal oxide, e.g. sodium, and water, and having a composition in terms of mole ratios of oxides, falling within the following ratios:

the zeolites formed by the present invention form a class characterized in their preparation by reaction mixtures of lower alkalinity and by a zeolite product of SiO.sub.2 /Al.sub.2 O.sub.3 >5. In addition they have a constraint index of between 1 and 12.

The constraint index is calculated as follows: ##EQU1##

The constraint index approximates the ratio of the cracking rate constants for the two hydrocarbons. Catalysts suitable for the present invention are those having a constraint index in the approximate range of 1 to 12. Constraint Index (CI) values for some typical catalysts are:

Crystallization can be carried out at either static or stirred condition. In our examples static conditions were employed using polypropylene jars at 100.degree. C. or stainless steel autoclaves at 160.degree. C. The total useful range of temperatures is 80.degree. C. to 180.degree. C. for about 6 hours to 150 days. Thereafter, the zeolite crystals are separated from the liquid and recovered. The composition can be prepared utilizing materials which supply the appropriate oxides. Reaction mixtures can include sodium silicate, silica hydrosol, silica gel, silicic acid, and sodium hydroxide, and of course, the alkyl ANOxide cations heretofore described. The reaction mixture can be prepared either batch-wise or continuously. Crystal size and crystallization time of the zeolite compositions will vary with the nature of the reaction mixture employed and the crystallization conditions.

As indicated above, the zeolite crystals prepared by the instant invention are shaped in a wide variety of particle sizes. Generally speaking, the particles can be in the form of a powder, a granule, or a molded product, such as an extrudate having particle size sufficient to pass through a 2 mesh (Tyler) screen and be retained on a 400 mesh (Tyler) screen. In cases where the catalyst is molded, such as by extrusion, the catalyst crystals can be extruded before drying or dried or partially dried and then extruded.

The zeolites prepared can also be used as a catalyst in intimate combination with a hydrogenating component such as tungsten, vanadium, molybdenum, rhenium, nickel, cobalt, chromium, manganese, or a noble metal such as platinum or palladium where a hydrogenation-dehydrogenation function is to be performed. Such component can be exchanged into the composition, impregnated therein or physically intimately admixed therewith. Such component can be impregnated in or on to it such as, for example, by, in the case of platinum, treating the zeolite with a solution containing a platinum metal-containing ion. Thus, suitable platinum compounds include chloroplatinic acid, platinous chloride and various compounds contianing the tetrammineplatinum complex.

The above zeolite crystals especially in their metal, hydrogen, and ammonium forms can be beneficially converted to a catalytically applicable form by thermal treatment. This thermal treatment is generally performed by heating one of these forms in an atmosphere such as air, nitrogen, steam etc., at a temperature of at lest 700.degree. F. for at least 1 minute and generally not more than 20 hours to remove part or all of the water and the organic constituent. While subatmospheric pressure can be employed for the thermal treatment, atmospheric pressure is desired for reasons of convenience. The thermal treatment can be performed at a temperature up to about 1700.degree. F. The thermally treated product is particularly useful in the catalysis of certain hydrocarbon conversion reactions.

In the case of many catalysts it is desired to incorporate the zeolite with another material resistant to the temperatures and other conditions employed in organic conversion processes. Such materials include active and inactive materials and synthetic or naturally occurring zeolites as well as inorganic materials such as clays, silica and/or metal oxides. The latter may be either naturally occurring or in the form of gelatinous precipitates or gels including mixtures of silica and metal oxides. Use of a material in conjunction with the zeolite material, which is active, tends to improve the conversion and/or selectivity of the catalyst in certain organic conversion processes. Inactive materials suitably serve as diluents to control the amount of conversion in a given process so that products can be obtained economically and orderly without employing other means for controlling the rate of reaction. These materials may be incorporated into naturally-occurring clays, e.g. bentonite and kaolin, to improve the crush strength of the catalyst under commercial operating conditions. Said material, i.e. clays, oxides, etc., function as binders for the catalyst. It is required to provide a catalyst having good crush strength because in commercial use it is desirable to prevent the catalyst from breaking down into powder-like materials. These clay binders also improve the crush strength of the catalyst.

Naturally-occurring clays which can be composited with the zeolite crystals include the montmorillonite and kaolin family, which families include the subbentonites, and the kaolins commonly known as Dixie, McNamee, Georgia and Florida clays or others in which the main mineral constituent is halloysite, kaolinite, dickite, nacrite, or anauxite. Such clays can be used in the raw state as originally mined or initially subjected to calcination, acid treatment or chemical modification. Binders useful for compositing with the catalyst also include inorganic oxides, notably alumina.

In addition to the foregoing materials, the zeolite catalysts can be composited with a porous matrix material such as silica-alumina, silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia, silica-titania as well as ternary compositions such as silica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesia and silica-magnesia-zirconia. The relative proportions of finely divided catalyst and inorganic oxide gel matrix vary widely with the zeolite content ranging from about 1 to about 90 percent by weight and more usually, particularly when the composite is prepared in the form of beads, in the range of about 2 to about 50 percent by weight of the composite.

In order to more fully illustrate the nature of the invention and the manner of practicing same, the following examples are presented, wherein ZSM-5, the unidentified crystalline material, and mixtures of both were obtained.

In the examples which follow whenever adsorption data are set forth for comparison of sorptive capacities for water, cyclohexane and n-hexane, they were determined as follows:

A weighed sample of the calcined adsorbent was contacted with the desired pure adsorbate vapor in an adsorption chamber, evacuated to <1 mm and contacted with 12 mm Hg water vapor or 20 mm Hg of cyclohexane or n-hexane vapor, pressures less than the vapor-liquid equilibrium pressure of the respective adsorbate at room temperature. The pressure was kept constant (within about .+-.0.5 mm) by addition of adsorbate vapor controlled by a manostat during the adsorption period which did not exceed about eight hours. As adsorbate was adsorbed by the silico-crystal, the decrease in pressure caused the manostat to open a valve which admitted more adsorbate vapor to the chamber to restore the above control pressures. Sorption was complete when the pressure change was not sufficient to activate the manostat. The increase in weight was calculated as the adsorption capacity of the sample in g/100 g of calcined adsorbent.

The following examples, compiled as Table III, immediately hereinbelow, give details as to formulation, and reaction conditions, and the products obtained.

Hydrocarbon sorptions were conducted on the various products of Examples 1-3 at different calcination temperatures. Results are compiled in Table IV.

Note that when the unidentified component of the product of Example 2 is collapsed by calcination at 600.degree. C., the n-hexane sorption more than doubles (5.9 vs 2.6) suggesting higher catalytic activity.