GB2202838A - Synthesis of ZSM - 23 type 3 eolite - Google Patents

Abstract

Synthesis of a ZSM-23 type zeolite from a reaction mixture containing a source of silica, optionally a source of alumina, a source of alkali metal oxide and an octane - 1,8- bis(trimethylammonium) compound.

Description

Zeolite Synthesis The present invention relates to a novel and improved method for the synthesis of a zeolite of the type designated ZSM-23.

Aluminosilicate zeolites are now widely used in industry. Some occur only in nature, others are only available as a result of chemical synthesis and some are available in both natural and synthetic forms. Synthetic zeolites are attracting more and more attention and it is becoming more and more possible to control the preparation of such zeolites and to tailor their properties to particular needs.

In recent years much attention has focussed on so-called "high silica" zeolites, that is zeolites which have a silica to alumina mole ratio which is greater than about 10:1. Many such zeolites have been described, among them the zeolite which has been designated "ZSM-23".

Zeolite ZSM-23 and a method for its synthesis have been described in US Patent No 4,076,842 where ZSM-23 is defined as having a composition in the anhydrous state, expressed in terms of mole ratios of oxides of: (0.58 to 3.4 )M20 : A1203 : (40 to 250) SiO2 wherein M is at least one cation having a valence n, the zeolite having the X-ray diffraction lines of Table 1 below.

TABLE 1

I d(A) I I/Io I d(A) I I/Io I 111.2 + 0.23 I Medium I 3.44 + 0.07 I Strong I 110.1 + 0.20 I Weak I 3.36 + 0.07 I Weak I 1 7.87 + 0.15 I Weak 1 3.16 + 0.07 I Weak I 1 5.59 + 0.10 I Weak I 3.05 + 0.06 I Weak I 1 5.44 + 0.10 I Weak I 2.99 + 0.06 I Weak I 1 4.90 + 0.10 I Weak I 2.85 + 0.06 I Weak 1 4.53 + 0.10 I Strong I 2.54 + 0.05 I Medium I 1 3.90 + 0.08 I Very strong 1 2.47 + 0.05 I Weak I 1 3.72 + 0.08 I Very strong 1 2.40 + 0.05 I Weak I i 3.62 + 0.07 I Very strong 1 2.34 + 0.05 I Weak I 1 3.54 + 0.07 1 Medium l l I USP 4,076,842 also describes a method of preparation of zeolite ZSM-23 which comprises preparing a mixture containing sources of an alkali metal oxide, a nitrogen containing organic cation, an oxide of aluminium, an oxide of silicon and water having a composition, in terms of mole ratios of oxides, falling within the ranges: R+/(R++M+) : 0.85 to 0.95 OH-/Si02 : 0.01 to 0.049 H20/0H : 200 to 600 Si02/A1203 : 55 to 70 wherein R is a nitrogen-containing cation derived from pyrrolidine and M is an alkali metal ion, and maintaining the mixture at a temperature of above 2800F until the crystals of ZSM-23 are formed.

The present Applicants have encountered some difficulty in synthesising ZSM-23 from pyrrolidine-containing mixtures of the above composition but they have now surprisingly found that use of another organic nitrogen-containing cation enables members of the ZSM-23 family of zeolites to be prepared rather more easily.

Accordingly the present invention comprises a method for the synthesis of a ZSM-23 type zeolite which comprises preparing a reaction mixture containing a source of silica, optionally a source of alumina, a source of alkali metal oxide and an octane-1,8bis(trimethylammonium) compound, the mixture having the molar composition: SiO2/A1203 at least 15:1, preferably in the range 15:1 to 500:1 H20/Si02 10:1 to 100:1, preferably 30:1 to 70:1 M20/SiO2 0.03:1 to 0.5:1, preferably 0.05:1 to 0.25:1.

QO/SiO2 at least 0.03:1 and preferably in the range 0.08:1 to 0.5:1 where M is one or more alkali metal, ammonium or hydrogen and Q is the octane -1,8-bis(trimethylammonium) compound (hereinafter referred to for convenience as octamethonium compound).

M and/or Q may be present as hydroxides or salts of inorganic or organic acids The preferred alkali metal is sodium but sources of the other alkali metals may also be used in the reaction mixture.

The silica source can be any of those commonly considered for use in synthesising zeolites, for example powdered solid silica, silicic acid, colloidal silica or dissolved silica. Among the powdered silicas usable are precipitated silicas, especially those made by precipitation from an alkali metal silicate solution, such as the type known as "KS 300 made by AKZO, and similar products, aerosil silicas, fumed silicas such as those sold under the name "CAB-O-SIL" and silica gels suitably in grades for use in reinforcing pigments for rubber or silicone rubber. Colloidal silicas of various particle sizes may be used, for example 10 tol5 or 40 to50 microns, as sold under the registered Trade Marks "LUDOX", "NALCOAG" and "SYTON".

The usable dissolved silicas include commercially available waterglass silicates containing 0.5 to 6.0, especially 2.0 to 4.0 mols of SiO 2 per mol of alkali metal oxide, "active" alkali metal silicates, as defined in UK Patent 1,193,254, and silicates made by dissolving silica in an alkali metal hydroxide or quaternary ammonium hydroxide or a mixture thereof.

The optional alumina source is most conveniently sodium aluminate, but can be aluminium, an aluminium salt, for example the chloride, nitrate or sulphate, an aluminium alkoxide or alumina itself, which should preferably be in a hydrated or hydratable form such as colloidal alumina, pseudoboehmite, boehmite, gamma alumina or the alpha or beta trihydrate.

The reaction mixture is usually reacted under autogenous pressure, optionally with added gas, e.g. nitrogen, at a temperature between 85 and 250"C until crystals of zeolite ZSM-23 form, which can be from 1 hour to many months depending on the reactant composition and the operating temperature. Agitation is optional, but is preferable since it reduces the reaction time.

At the end of the reaction, the solid phase is collected on a filter and washed and is then ready for further steps such as drying, dehydration and ion-exchange.

The product of the reaction will contain alkali metal ions, and these have to be at least partly removed in order to prepare the hydrogen form of the ZSM-23 type zeolite.. This can be done by ion exchange with an acid, especially a strong mineral acid such as hydrochloric acid or by way of the ammonium compound, made by ion exchange with a solution of an ammonium salt such as ammonium chloride. Ion exchange can be carried out by slurrying once or several times with the ion-exchange solution. The zeolite is usually calcined after ion exchange but this may be effected before ionexchange or during ion-exchange if the latter is carried out in a number of stages.

In general, the cation(s) of zeolite ZSM-23 type zeolites prepared according to this invention can be replaced by any cation(s) of metals, and particularly those in Groups IA, IB, IIA, IIB, III (including rare earths) VIII (including noble metals) and by lead, tin, and bismuth. (The Periodic Table is in Abridgements of Specifications" published by the UK Patent Office). Exchange is carried out using any water soluble salts containing the appropriate cation.

The method of this invention is illustrated by the following Examples.

Example 1 Solution A was prepared by dissolving 9.93g of sodium hydroxide and 3.967g of sodium aluminate (composition 1.31Na20 : A1203 : 5.25H20) in 250g of deionised water.

Solution B was prepared by diluting 144g of octamethonium bromide solution (39%) with a further 180g of de-ionised water.

Solutions A and B were mixed and the mixture was then added to a dispersion containing 51.5g of silica (CAB-O-SIL) and 250g deionised water. Mixing was continued to give a smooth gel of composition: 10Na20 : 10 Octa Br2 : A1203 : 60 SiO2 : 3000H20 where "Octa" refers to octamethonium.

The gel was transferred to a 1 litre autoclave and reacted therein at 1800C for 170 hours. On discharge, the material was filtered, washed and then dried overnight at 1100C.

Inorganic analysis showed the material to have the composition: 0.16 Na20 : A1203 : 47Si02 The material had the X-ray diffraction pattern shown in Figure 1 and it was identified as being a ZSM-23-type zeolite.

Example 2 Example 1 was repeated except that the gel had a composition: 10Na20 : 10 OctaBr2 : 0.6Al203 : 60 SiO2 : 3000 H20 and the scale of the experiment was slightly different. Thus, the CAB-O-SIL dispersion contained 45.2g of CAB-O-SIL and the amounts of the components in solutions A and B were adjusted accordingly. The gel was reacted at 1800C for 171 hours. X-ray analysis of the product showed it to be largely composed of ZSM-23 type zeolite together with someo & -quartz.

Claims (8)

Claims

1. A method for the synthesis of a ZSM-23 type zeolite which comprises preparing a reaction mixture containing a source of silica, optionally a source of alumina, a source of alkali metal oxide and an octane-1,8-bis(trimethylammonium) compound, the mixture having the molar composition: SiO2/A1203 at least 15:1 H20/SiO2 10:1 to 100:1 M20/SiO2 0.03:1 to 0.5:1 QO/SiO2 at least 0.03:1 where M is one or more alkali metal, ammonium or hydrogen and Q is the octane -1,8-bis(trimethylammonium) compound.

2. A method as claimed in claim 1 wherein the molar ratio of SiO2/A1203 in the reaction mixture is in the range 15:1 to 500:1.

3. A method as claimed in claim 1 or 2 wherein the molar ratio of H20/SiO2 in the reaction mixture is in the range 30:1 to 70:1.

4. A method as claimed in any one of the preceding claims wherein the molar ratio of M20/SiO2 in the reaction mixture is in the range 0.05:1 to 0.25:1.

5. A method as claimed in any one of the preceding claims wherein the molar ratio of QO/SiO2 in the reaction mixture is in the range 0.08:1 to 0.5:1.

6. ZSM-23 type zeolite whenever prepared by the method of any one of claims 1 to 5.

7. A catalyst comprising a ZSM-23 type zeolite whenever prepared by a method as claimed in any one of claims 1 to 5.

8. A catalytic process employing the catalyst claimed in claim 7.