GB2190910A - Synthesis of ZSM-23 - Google Patents

Abstract

This invention relates to a novel synthesis of ZSM-23 using diisopropanolamine as the template. The zeolite can be used as such or as a support for catalysing hydrocarbon conversion reactions. The zeolite is formed by crystallisation of a gel composition comprising a silica source, an alumina source, an alkali metal source, water and the template in which the silica:alumina mole ratio is at least 50:1 sec.

Description

SPECIFICATION Synthesis of ZSM-23 The present invention relates to a method of preparing ZSM-23.

Zeolites, both natural and synthetic, have been shown to have catalytic properties for various types of hydrocarbon conversion. Zeolites are ordered porous crystalline aluminosilicates having a definite crystalline structure within which there are a large number of small cavities which are interconnected channels. These cavities and channels are uniform in size, and are capable of sorbing molecules of certain dimensions while rejecting those of larger dimensions. These materials have therefore been used as molecular sieves. Zeolites have been described as having a rigid three-dimensional network of SiO4 and Al04 in which the tetrahedra are cross-linked by the sharing of oxygen atoms whereby the ratio of the total aluminium and silicon atoms to oxygen is 1:2.The electrovalence of the aluminium-containing tetrahedra is balanced by the inclusion of cations, for example, alkali metal or alkaline earth metal cations. This can be expressed by a formula in which the ratio of Al to the number of the various cations, such as Ca/2, Sr/2, Na, K or Li, is equal to unity. One type of cation can be exchanged in entirety or partially by another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchange, it is possible to vary the size of the pores in the given aluminosilicate. The void volumes in the cavities and channels may be occupied by molecules of water in the uncalcined form of the zeolite. More recently, the structure of these zeolites has been characterised by their X-ray diffraction patterns.A list of the various types of zeolites as characterised by their crystal structures can be found in the book by Meier, W.M. and Olson, D.H. entitled, "Atlas of Zeolite Structure Types", published by the Structure Commission of the International ZeoliteAssociation (1978) and distributed by Polycrystal Book Service, Pittsburgh, Pa, USA.

Zeolite ZSM-23 is one such zeolite and its method of preparation and physical characteristics such as XRD pattern is described and claimed in USP 4076842 (Mobil). In the synthesis, reported in this patent, the only template used is pyrrolidone. However, we have found it difficult to synthesise ZSM-23 under the conditions described in this patent using pyrollidone as the template. Similar difficulty in reproducing the examples in USP 4076842 has also been reported in EP-A-0042226 and EP-A-0063436, both in the name of ICI.

It has now been found that ZSM-23 can be repeatably produced by crystallization from a mixture containing a source of silica, a source of alumina, a source of alkali metal(s), water and an organic nitrogen containing base, by a careful choice of tem plate and gel composition.

Accordingly, the present invention provides a process for synthesizing ZSM-23 which has the following composition in terms of the mole ratios of the oxides: 0.9 + 0.2 M2XnO: Al203: xSiO2: yH2O wherein M is at least one cation having a valance n, x is at least 50 and y/x is between 0 to 25, wherein ZSM-23 in the as synthesised form has an X-ray diffraction pattern substantially as set forth in Table A of the specification, said process comprising mixing a source of silica, a source of alumina, a source of alkali metal(s), water and an organic template to form a gel composition followed by crystallisation thereof, characterised in that in the gel composition the silica to alumina mole ratio is at least 50:1 and the organic template is diisopropanolamine.

Preferably, ZSM-23 in the calcined hydrogen-form has an X-ray diffraction pattern substantially as set forth in table B of the specification.

By the "calcined hydrogen-form" is meant throughout this specification that ZSM-23 is in the calcined state and that the cation M is hydrogen.

The cation M in ZSM-23 may be selected from H+, ammonium, alkali metal cations, alkaline earth metal cations, organic nitrogen containing cations, aluminium cations, gallium cation and mixtures thereof.

The cations present in ZSM-23 may be replaced using conventional ion exchange techniques either wholly or partially by other cations e.g. hydrogen ions or metal cations.

The calcined hydrogen-form of ZSM-23 may be produced by known methods such as exchange with acidic or ammonium cations or a combination of the two followed by one or more calcination stages.

The specific values in Tables A and B below for ZSM-23 were determined using copper K-alpha radiation and a computer step scan.

The peak heights, I, and their position as a function of 2 theta, where theta is the Bragg angle, were read from the spectrometer output. From this output the relative intensities 100 x Illo, where lo is the intensity of the strongest peak, and d the inter-planar spacing in A, corresponding to the recorded peaks were calculated.

It will be understood by those skilled in the art that the X-ray diffraction pattern of ZSM-23 may vary in the values of 111o and the d-spacing depending for example upon whether the sample being examined is calcined or uncalcined, upon the temperature of calcination, upon the nature of the cation present in ZSM-23, the mole ratio of silica to alumina, and the particle size of ZSM-23.

ZSM-23 is produced from an initial mixture containing a source of silica, a source of alumina, a source of alkali metal(s), water and diisopropanolamine as the template and in which the silica to alumina mole ratio is at least 50:1.

The silica to alumina mole ratio and the free alkali metal(s) hydroxide to water mole ratio, defined as: [(Number of moles of total alkali metal(s) - (Number of moles of alkali metal(s) required to convert alumina present to alkali metal aluminate(s), i.e. MAlO2)] Number of moles of water present are preferably greater than 50:1 and greater than 2 x 10-3:1 respectively. Even more preferably the silica to alumina mole ratio is in the range 60:1 to 500:1 and the free alkali metal(s) hydroxide to water mole ratio is in the range 2 x 10-3:1 to 8 x 10:1. The mole ratio of water to silica may suitably be in the range 4:1 to 100:1, preferably in the range 6:1 to 30:1, even more preferably in the range 9:1 to 30:1.

Using diisopropanolamine as the nitrogen containing organic base, ZSM-23 substantially free from other crystalline aluminosilicates, e.g. ZSM-5, can be produced at a silica to alumina mole ratio greater than 60:1 and a free alkali metal(s) hydroxide to water ratio less than 8 x 10-3:1 in the initial mixture.

ZSM-23 is suitably prepared by forming a mixture of all the reactants, by simply mixing them together while maintaining the mixture suitably at a temperature from 0 to 1000C, preferably from 20 to 600C, until a homogeneous gel is formed and crystallising the mixture so-formed at a temperature above 70"C, preferably between 100 and 220"C for a period of at least 2 hours, preferably for 6 to 240 hours. The optimum crystallisation period can vary and may depend upon such factors as the temperature, pH and gel composition. Preferabiy the source of silica is an amorphous silica sol which is diluted with water. It is preferred that the silica source is added to the other reagents in such a way as to commence gelation at a relatively high pH.

The product obtained in this manner contains cations which may be hydrogen, alkali metal(s), aluminium, or organic nitrogen containing cations or any combination thereof.

The cations in the ZSM-23 product may be converted to the hydrogen ion to give rise to the hydrogen-form of the product. This may be achieved by techniques known to those skilled in the art, e.g. (a) ammonia exchange followed by calcination, (b) acid exchange or a combination of (a) and (b).

The ZSM-23 product or the hydrogen-form thereof may also be loaded with a metal or metal compound suitable for imparting a specific type of catalytic activity. The metal compounds which may be used for loading may be compounds of any one of the following metals or groups of metals, namely those belonging to Groups IB, IIB, IIIA, IVA, VA, VIB, VIIB and VIII according to the Periodic Table published in pages 448 and 449 of the Handbook of Chemistry and Physics, Ed. by C.D. Hodgman et al, 44th Edition (1963) and published by the Chemical Rubber Publishing Company, Cleveland, Ohio, USA. Specifically, compounds of copper, silver, zinc, aluminium, gallium, indium, thallium, lead, antimony, bismuth, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum and rhenium are preferred.

ZSM-23 may be bound in a suitable binding material before or after loading with one of the aforementioned metals or metal compounds to produce an attrition resistant catalyst. The binder for this purpose may be any one of the conventional alumina or silica binders.

ZSM-23 may be used, whether or not loaded with additional catalytic metals or compounds, as catalysts for any of the following reactions. Alkylation, dealkylation, dehydrocyclodimerisation, aromatisation, transalkylation, isomerisation, dehydrogenation, hydrogenation, cracking, cyclisation, oligomerisation, polymerisation and dehydration reactions, the last named in particular with reference to dehydration of alcohols and ethers.

ZSM-23 is particularly suitable as a catalytic component in selective cracking of alkanes, especially linear alkanes to alkenes, and for the restructuring of olefins, especially linear olefins to the isomeric isoolefins or disproportionation products thereof which are desirable gasoline blending components. ZSM-23 may be used as such or as a component of a catalyst mixture containing other active or inactive components. ZSM-23 may also be used in admixture with other zeolites. The catalysts may be used in the form of fixed, fluidised or moving beds.

TABLE A ZSM-23 (Product of Example 1) d(A) I/lo x 100 11.04 62 10.75 62 9.86 35 7.72 31 6.02 6 5.55 7 5.38 6 4.85 11 4.48 75 4.39 16 4.22 72 4.12 12 3.86 100 3.71 53(S) 3.67 76 3.59 57 3.51 33 3.41 33 3.27 2 3.14 8 2.96 3 2.82 7 (S) Shoulder TABLE B HZSM-23 Product of example 1 (after calcination) d(A) I/lo x 100 11.03 100 10.70 90 9.87 28 7.72 34 6.01 1 5.54 10 5.37 11 4.86 7 4.47 76 4.21 57 4.11 8 3.86 71 3.71 45(S) 3.67 57 3.58 44 3.51 34 3.40 34 3.27 2 3.14 7 3.02 3 2.96 1 2.82 8 (S) Shoulder The present invention is further illustrated with reference to the following Examples.

Example 1 A solution was prepared containing 3.0g sodium aluminate (by wt 40% Al2O3, 30% Na2O and 30% H2O), 1.5g of sodium hydroxide and 150g of water. 60g of diisopropanolamine (CH3.CH(OH).CH2)2NH, which is hereafter referred to as "DIPA", was added to the solution, with stirring. 1 50g of commercial silica solution "Ludox AS40" (Registered Trade Mark) which contains 40% by weight silica was then added and stirring continued for 20 minutes. The resultant hydrogel had the following composition : 2.8 Na2O:38.9 DIP : Al203: 85.0 Six2:1133 H2O 1009 of this hydrogel was transferred into a stainless steel pressure vessel and crystallisedwith stirring for40 hours.

The product was filtered, washed and dried at 90"C. It was found that the as synthesised material had an XRD shown in Table A which is consistent with ZSM-23 zeolite without any detectable inpurities.

Example 2 A hydrogel was prepared as described in Example 1 except that the hydrogel composition was: 3.1 Na2O : 38.3 DIPA : Awl203: 85.0 Six2:1133 H2O It was transferred into a stainless steel pressure vessel and crystailised with stirring for 16 hours.

The product was filtered, washed and dried at 90"C and upon analysis was found to be consistent with the XRD of ZSM-23 zeolite with a little cristobalite.

Example 3 A hydrogel was prepared as described in Example 1 except that the hydrogel composition was: 4.8 Na2O : 68.5 DIPA : Awl203: 121 Six2:1821 H2O The hydrogel was crystallised at 175"C for 72 hours. The product was filtered, washed and dried at 90"C. Upon analysis it was found to be consistent with the XRD of ZSM-23 with some cristobalite.

Comparative Test 1 A hydrogel was prepared as described in Example 1 except that the gel composition was: 2.1 Na2O 16.0 DIPA : Awl203: 28.3 SiO2 : 425 H2O and crystallised as in Example 1 but at 175"C for 72 hours. The product was filtered, washed and dried at 90"C.

It was found by X-ray diffraction to be ZSM-5 zeolite.

Comparative Test2 A hydrogel was prepared as described in Example 1 except that diethanolamine (DEA) was used instead of diisopropanolamine and the gel composition was: 3.1 Na2O : 33.1 DEA: Awl203: 77.3 Six2:1159 H2O and crystallised at 175"C for 120 hours. The product was filtered, washed and dried at 90"C. It was found by X-ray diffraction to be mainlyTheta-1 (according to our EP-A-0057049) and a little cristobalite.

Claims (5)

1. A process for synthesising ZSM-23 which has the following composition in terms of the mole ratios of the oxides: 0.9 + 0.2 Mu,O : Al203: xSiO2: yH2O wherein M is at least one cation having a valence n, xis at least 50 and y/x is between 0 to 25, wherein ZSM-23 in the as synthesised form has an X-ray diffraction pattern substantially as set forth in Table A of the specification, said process comprising mixing a source of silica, a source of alumina, a source of alkali metal(s), water and an organic template to form a gel composition followed by crystallisation thereof, characterised in that in the gel composition the silica to alumina mole ratio is at least 50:1 and the organic template is diisopropanolamine.

2. A process according to claim 1 wherein the gel composition has the various reactants in the following mole ratio ranges: silica to alumina greater than 50:1 free alkali metal(s) hydroxide to water greater than 2 x 10-3:1 water to silica 4:1 to 100:1

3. A process according to claim 1 or 2 wherein the gel composition has the various reactants in the following mole ratio ranges: silica to alumina 60:1 to 500:1 free alkali metal(s) hydroxide to water 2 x 10-3:1 to 8 x 10-3:1 waterto silica 9:1 to 30:1

4. A process according to any one of the preceding claims wherein the various reactants in the gel composition are mixed together while maintaining the temperature of said gel from 0 to 100 C until a homogeneous gel is formed and crystallising the resultant homogeneous gel at a temperature above 70"C for 6240 hours.

5. A method synthesising ZSM-23 according to claim 1 as hereinbefore described with reference to the Examples.