NZ205275A - Treating zeolites with ammoniacal alkali metal aluminate - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £05275 2 *"2 ' .■> £- V Priority Date(s): Complete Specification Filed: .

Class: .. 89/<A$?M ...

P.O. Journal, No: . .42?/ II ffiS NEW ZEALAND PATENTS ACT, 1953 No.: Date: COMPLETE SPECIFICATION TREATMENT OF ZEOLITES fc/We, MOBIL OIL CORPORATION/ a corporation organised under the laws of the State of New York, United States of America, of 15 0 East 4 2nd Street, New York, State of New York, United States of America, hereby declare the invention for which i / we pray that a patent may be granted to owa/us, and the method by which it is to be performed, to be particularly described in and by the following statement: - (followed by page la) -F--13 46 • - 1*- TREATMENT OF ZEOLITES 7 This invention relates to the treatment of zeolites to enhance their activity.

High-silica zeolites are well known in the art 5 and it is generally accepted that the ion exchange capacity of a crystalline a luminosi I icate is directly dependent upon its aluminum content. Thus, for example, the more aluminum there is in a crystalline structure, the more cations are required to balance the electronegativity 10 thereof, and when such cations are of the acidic type such as hydrogen, they impart high catalytic activity to the crystalline material. On the other hand, high-silica zeolites having little or substantially no aluminum have many important properties and characteristics and a high 15 degree of structural stability and have become candidates for use in various processes including catalytic processes. Materials of this type are known in the art and include high si I ica-containing a luminosiIicates such as ZSM-5 (US-A-3,702,886), ZSM-11 (US-A-3,709,979), and 20 zeolite ZSM-12 (US-A-3,832,449) to mention a few.

The si1ica-to-alumina ratio of a given zeolite is often variable; for example, zeolite X can be synthesized with silica-to-alumina ratio of from 2 to 3; zeolite Y from 3 to about 6. In some zeolites, the upper 25 limit of si I ica-1o-a I urnina ratio was unbounded. ZSM-5 is one such example wherein the silica-to-alumina ratio is at least 5. US-A-3,9 41,871 discloses a crystalline metal organosi I icate essentially free of aluminum and exhibiting an X-ray diffraction pattern characteristic 30 of ZSM-5 type aluminosiIicates. US-A-4,061,724; 4,073,865; and 4,104,294 describe microporous crystalline silicas or organosi1icates wherein the aluminum content present is at impurity levels.

Because of the extremely low aluminum content of 35 these silica-containing zeolites, their ion exchange capacity is not as great as materials with a higher aluminum content. Therefore, when these materials are contacted with an acidic solution and thereafter are processed in a conventional manner, they are. not as 7 O :" / / "sw-.' * cat a ly t i ca L Ly active as their higher a I urn i rium- c ont a i n i ng counterparts.

This invention permits the preparation of high silica-containing materials which have all the desirable properties inherently possessed by such high silica materials yet have an acid activity which heretofore has only been manifested by materials having a higher aluminum content.

This invention is concerned with the treatment of high-silica zeolites, namely those of silica-to-alumina ratio greater than 500, preferably greater than 1000, and including those highly siliceous materials where the silica-to-alumina ratio is inifinity or as reasonably close to infinity as practically possible.

This latter group of highly siliceous materials is exemplified by US-A-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 invention includes those materials which have other metals besides silica and/or alumina associated therewith, such as boron, iron and chromium, etc. . Thus, the only requirement with regard to the starting materials utilized in a novel process of this invention, is that they have a si Iica-1o-a lumina ratio greater than about 500, irrespect' ive of what other materials or metals are present in the crystal structure. They' usually have a constraint index in the range 1 to 12. The particularly preferred starting materials for the novel process of this invention are those crystalline materials which have an X-ray diffraction pattern characteristic of ZSM-5, ZSM-11, and ZSM-12 irrespective of their chemical composition other than the minimum si lie a-to-alumina ratio. The preferred starting material for the novel process of this invention is a high siIica-containing ZSM-5.

The invention is simple in nature and easy to carry out, although the results obtained are dramatic.

The invention is carried out simply by contacting a high-silica zeolite either as crystallized or after calcination with an ammoniacal alkali metal aluminate solution, preferably an ammoniacal sodium aiumin.ate solution, at 5 a pH of about 8 to 14, preferably a pH greater than 10. A particularly preferred technique involves contacting the zeolite with the ammoniacal alkali metal aluminate solution by vacuum impregnation.

The amount of solution utilized to treat the 10 zeolite is not narrowly critical and the solution to zeolite ratio can vary from 0.3 to < 10 grams of solution per gram of zeolite. The amount of solution will vary as a furiction of its concentration and the desired enhancement of activity.

The process is carried out by treating the zeol ite with the above described solution at temperatures ranging from 20 to 50°C , preferably from 20 to 3 5 °C , for periods of time ranging from 20 minutes to 30 days, preferably from 1/2 hour to 5 days.

Following the above treatment, the zeolite is processed into its catalytically active form by conventional techniques, such as base exchange with appropriate cations such as hydrogen, ammonium, rare earth, and mixtures thereof. The zeolite may then be calcined by heat-25 ing to a temperature in the range of 200-600°C in an atmosphere such as air, nitrogen, etc. at atmospheric, subatmospheric, or superatmospheric pressures for between 1 and 48 hours. The zeolite can, if desired, be incorporated in a matrix by techniques well known in the art. 30 Conventional matrices include inorganic oxides, such as silica, alumina, silica alumina, etc.

The following examples will illustrate the novel process of this invention.

EXAMPLE 1 A 2-g. sample of ZSM-5 zeolite having a silica- to-alumina ratio of about 26,000 and a sodium content of about 0.23 weight percent was impregnated with 3 grams of 5 weight percent sodium aluminate solution and calcined in air at 538°C for 20 hours.

• V v' $ >w. <US>' * EXAMPLE 2 The product of Example 1 was treated with a 1-N 8 weight percent solution of ammonium nitrate.

EXAMPLE 3 A sample of the same ZSM-5 used above was vacuum impregnated with a solution of sodium aluminate which was diluted by an equal volume of concentrated (12N) NH^OH. The pH was 12.4. After 30 minutes, the sample was dried and submitted to three cycles of 1N NH4NO3 treat-10 ment followed by hot water washing. The sample was dried and calcined at 538°C prior to testing.

The products of Examples 1-3 were evaluated for alpha activity. The Alpha test is described in Journal of Catalysis, Vol. 4, pp. 522-529, August 1965. 15 The results are shown in the following table: Table 1 Activity of High SiOj ZSM-5 After Treatment Examp le Alpha 1 NaA lOg t reat 0.4 2 NaA 102/NH4N03 treat 0.2 3 NaAl02/NH40H imp+ 12 NH4NO3 treat From the above table, it can be seen that the novel process of this invention resulted in a dramatic 25 increase of activity.. The procedure of Examples 1 and 2 did not result in any significant improvement, whereas the process of this invention (Example 3) did enhance activity. 205275

Claims (8)

WHAT WE CLAIM IS:

1. A method for enhancing the activity of a zeolite having a silica-to-alumina ratio greater than 500 which comprises contacting said material with an ammoniacal solution of an alkali metal aluminate for a period of time ranging from 1/2 hour to 5 days at a temperature of from 20 to 50°C and at a pH of at least 10.

2. The method of claim 1 wherein the alkali metal aluminate is sodiurn aluminate.

3. The method of claim 1 or claim 2 wherein the zeolite has a silica-to-alumina ratio in excess of 1000.

4. The method of any preceding claim wherein the zeolite is one synthesized from a reaction mixture in which aluminum is present only as impurity.

5. The method of any preceding claim wherein the ammoniacal alkali metal aluminate is applied to the zeolite by vacuum impregnation.

6. The method of any preceding claim wherein the zeolite is one having a constraint index of 1 to 12.

7. The method of any preceding claim wherein the zeolite is ZSM-5.

8. A method for enhancing the activity of a zeolite having a silica-to-alumina ratio greater than 500 according to any one of claims 1 to 7 substantially as hereinbefore described with reference to the Examples.