~1~16 ~CTIVITY ENHANCEi/i~lT OF ~I~H SILICA Z~OLITES
Backgroun~ of The Invention This invention relates to a method of enhanclng the acid activity of certain hiyh silica-containing crystalline materials by a process which involves contacting them with aluminum chloride (AlC13) vapors, followed by hydrolysis and calcination.
~iyh silica-containing zeolites are well known in the art, and it is yenerally accepted that the ion exchange capacity of a crystalline alumino-silicate is directly dependent upon its aluTninum content. Thus, for example, th~ more aluminum there is in a crystalline structure, the rnore cations are required to balance the electronegativity thereof, and when such cations are of the acidic type such as hydrogen, they impart tremendous catalytic activity to the crystalline material. On the other hand, hi~h silica-containing zeolites havin~ little or substantially no aluminum have many important properties and characteristics and a high degree of structural stability such that they have become candidates for use in various processes including catalytic processes. Materials of this type are known in the art and include hiyh silica-containing aluminosilicates such as ZSM-5 (U.S. Patent 3,702,886), ZSM-ll (U.S. Patent 3,709,979), and zeolite ZSM-12 (U.S. Patent 3,832,449) to rnention a few.
The silica-to-alumina ratio of a yiven zeolite is often variable; for example, zeolite X can be synthesized with silica-to-alumina ratio of ~rom 2 to 3; zeolite Y from 3 to about 6. In some zeolites, the upper limit of silica-to-alur,lina ratio was virtually unboun~ed. ZSM-5 is one such exarnple ~2~Z~
wherein the silica-to-alumina ratio is at least 5.
U. S. Patent 3,941,~71 discloses a crystalline Inetal or~anosilicate essentially free of aluminum and exhibiting an x-ray diffraction pattern characteristlc of ZSM-5 type aluminosilicates. U.S.
Patents 4,061,724; 4,073,865; and 4,104,294 describe microporous crystalline silicas or oryanosilicates wherein the alur,linum content present is at impurity levels.
Because of tlle extremely low aluminum content of these silica-containing zeolites, their ion exchange capacity is not as great as materials with a higher aluminurm content. Therefore, w~en these rnaterials are contacted with an acidic solution and thereafter are processed in a conventional manner, they are not as catalytically actlve as their higher aluminum-containing counterparts.
The novel process of this invention yermits the preparation o~ certain high silica-containing materials which have all the desirable yroperties inherently possessed by such high silica materials and, yet, have an acid activity which heretofore has only been possible to be achieved by r.laterials having a higher aluminum content ln thelr "as synthesized~
Description of The Prior Art It is to be immediately understood that there are yatents relating to contactin~ crystalline aluminosilicate zeolites with alumlnum chloride followed by hydrolysis, i.e. United States 3,354,07 and United States 3,644,220. However, neither of these two yatents is in any way concerned with treatment of crystalline materials having a silica to ~z~
alumina ratio of at least 100 and even more desirably of at least 500 which have been synthesized from a forming solution containing quarternary ammonium cations. The novel process of this invention results in introducing the aluminum within the intracrystalline structure such that its constraint index is substantially unaltered.
Description of the Invention As has heretofore been stated, the novel pro-cess of this invention is concerned with the treatment of high silica-containing crystalline material. The expression "high silica-containing crystalline material' is intended to define a crystalline structure which has a silica-to-alumina ratio greater than 100 and more preferably greater than 500, up to and including those highly siliceous materials where the silica-to-alumina ratio is infinity or as reasonably close to infinity as practically possible. This latter group of highly siliceous materials is exemplified by U.S. Patents 3,941,871; 4,061,724; 4,073,865; 4,104,294 wherein the materials are prepared from reaction solutions which involve no deliberate addition of aluminum. However, trace quantities of aluminum are usually present due to the impurity of the reaction solutions. It is to be understood that the expression "high silica-containing crystalline material" also specifically includes those materials which have other metals besides silica and/or alumina associated therewith, such as boron, iron and chromium, etc. Thus, the only requirements with regard to the starting materials utilized in the novel process of this invention is that they have a silica to alumina ratio greater than about 100 (irrespective of what other materials or metals are present in the crystal structure) and that they be synthesized from a reaction miXtlJre con-taining tetraalkylammonium ions. It has been found that the novel process of this invention is not applicable to high silica-containing crystalline materials which have been synthesized with diamines.
The novel process of this invention is simple in nature and easy to carry out, although the results therefrom are dramatic. The novel process of this in-vention is carried out simply by ca]cining a high silica crystalline material having a silica to alumina ratio of at least 100 and preferably of at least 500 which has been prepared from a reaction mixture containing tetra-alkylammonium ions by heating the same at a temperaturewithin the range of about 200-600C in an atmosphere such as air, nitrogen, etc. and at atmospheric, super-atmospheric, or subatmospheric pressures for between 1 and about 4~ hours. The calcined zeolite is thereafter treated with aluminum chloride vapors at elevated tem-peratures, preferably admixed with an inert gas such as nitrogen at a temperature ranging from 100 to 600C.
The amount of aluminum chloride vapor which is utilized is not narrowly critical but usually 0 01 to 1 gram and preferably about 0.5 of aluminum chloride is used per gram of high silica crystalline material. Following the treatment with aluminum chloride, the crystalline material is then hydrolyæed in water, preferably at a temperature ranging from 20 to 100C, followed by a final calcination preferably at a temperature ranging from 200 to 600C, more preferably from 450 to 550C.
The activity enhanced high silica-containing crystalline materials prepared by the present process are useful as catalyst components for acld catalyzed hydro-carbon conversion reactions. Such reactions include, as a non-limiting example, cracking of hydrocarbon compounds under reaction conditions including a temperature of from about 300C to about 650C, a pressure of from about atmos-pheric to about 200 psig and a weight hourly space velocity of from about 0.5 to about 50 hr 1.
In practicing a particularly desired chemical con-version process, it may be useful to incorporate the above-described activity enhanced crystalline zeolite with a matrix comprising another material resistant to the temperature and other conditions employed in the process. Such matrix material is useful as a binder and imparts greater resistance to the catalyst for the se~ere temperature, pressure and reactant feed stream velocity conditions en-countered in many cracking processes.
Useful matrix materials include both synthetic and naturally occurring substances, as well as inorganic materials such as clay, 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. Naturally occurring clays which can be composited with the zeolite include those of the montmorillonite and kaolin families, which families include the sub-bentonites and the kaolins commonly known as Dixie, McNamee, Georgia and Florida clays or others in which the main mineral con-stituent 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.
In addition to the foregoing materials, the zeolites employed herein may be composited with a porous matrix material, such as alumina, silica-alumina, silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia, and silica-titania, as well as ternary compositions, such as silica-alumina-tharia, silica-alumina-zirconia, silica-alumina-magnesia and silica-magnesia-zirconia. The matrix may be in the form of a cogel. The relative proportions of activity enhanced zeolite component and inorganic oxide gel matrix, on an anhydrous basis, may vary widely with the zeolite content ranging from between about 1 to about 99 percent by weight and more usually in the range of about 5 to about 80 percent by weight of the dry composite.
~ 7 EXAMPL~
Four differen~ high silica containiny zeolites were used in this example -- all of which were syntIlesized from reaction rnixtures containing tetraalkylammonium ions. These included three crystalline materials havlny the x-ray diffraction uattern of ZSM-5, having silica-to-alurnina ratios of 600, 2900 and greater than 50,U00 respectively. one sa~ple of a crystalline material having the x-ray diffraction pattern of ZSM-ll and having a silica-to-alumina ratio of about l,056 was also utilized.
The above as synthesized zeolites were calcined in either air or nitrogen at 1C per minute to about 540C where the temperature was maintained for about 10 hours. Two ~rams of each of the calcined zeolites were ~laced in a horizontal tube on one side of a fritted disc and one grarn of aluminum chloride was placed on the other side. Dry nitrogen at 50-100 cc per minute was introduced from the direction of the zeolite while heating at 100C for one hour. The direction of the nitroyen flow was then reversed and the temperature raised to 500C at 2C per minute and maintained at 500C for 1/2 hour.
After cooliny, the zeolite was transferred to another reactor and again heated to 500C in nitrogen to remove any residual unreacted alurninum chloride.
Each of the four zeolites was then hydrolyzed at lO0 ml of water at roonl telnperature for at least two hours. The hydrolyzed samples were filtered, washed well with water, air-dried, and then finally calcined at 540C for ten hours.
The results obtained, as well as the properties o the aluminum enhanced zeolites are shown in the following table:
Properties of Aluminum-Enhanced Zeolites zeolite Type ZSM-5 ZSM-5 ZSM-5 ZSM-ll Si/Alz 6U0 2900 -- 5U,UU0 1056 % Al (oriy.) 0.15% 0.03% ~ U.01% - 0.1%
% Al (after treatment) 2.55% 1.63% 1.55% 1.93%
% Crystallinity (after treatment) n.d. n.d. 74%
Alpha (orig. in E~-form) 17 ~est.) 4 (est.) O.OU4 lU (est.) Alpha ~after treatment) 102 75 70 101 g~
Increase in Alpha 85 71 70 91 Constraint Index (after treatlnent) n.d. n.d. 4.1 4.8 As can be seen, the alpha value of each of the four zeolites was considerably raised in accordance with the novel process of this invention.
Furtherlnore, this enhanced acid activity was clearly intrazeolitic as evidenced by the shape selective constraint index values.
As is well known in the aet, the alpha activity yives an approximate indication of the catalytic cracking activity of the catalyst compared to a standard catalyst and it gives the relative ra~e constant (rate of normal hexane conversion per volume of oxide composition per unit time). It is based on the activity of the highly active silica alunlina crackin~ catalyst taken as an alpha of 1. This test is described in U. S. 3,354,078 an~ in The Journal of Catalysis, Vol. 4, pp. S22-529, August 1965.
The constraint index is a measure of the selectivity of a ~articular catalyst and it involves conversion of normal hexane and 3-methylpentane.
This test is described in many issued United States patents, including U. S. 4,231,899.