Large crystal ZSM-5, its synthesis and use

Details Large crystal ZSM-5, its synthesis and use Large crystal ZSM-5, its synthesis and use

1997-11-04

2000-01-11

Bell, Mark L.

Chemistry of inorganic compounds

Zeolite

Organic compound used to form zeolite

423705, 423706, 423708, 423716, 423DIG22, C01B 3940

Patent

active

060132396

DESCRIPTION:

BRIEF SUMMARY
This invention relates to large crystal ZSM-5, its synthesis and its use in catalytic processes.


BACKGROUND OF THE INVENTION

ZSM-5 and its synthesis using tetrapropylammonium (TPA) cations as a directing agent are disclosed in U.S. Pat. No. 3,702,886. EP-A-21674 teaches that large crystal ZSM-5, having a crystal size in excess of 1 micron, can be prepared from a reaction mixture containing TPA cations provided the OH-/SiO.sub.2 ratio is maintained within the range 0.01-0.07.
Large crystal ZSM-5 (>0.5 micron) usually can be prepared without difficulty when the aluminum content in the synthesis mixture is low. As a result, with large crystal ZSM-5, although SiO.sub.2 /Al.sub.2 O.sub.3 ratios of 100 or higher are relatively easily attainable, SiO.sub.2 /Al.sub.2 O.sub.3 ratios of 40 or lower are difficult to attain.
In conventionally prepared, large ZSM-5 crystals, the aluminum distribution tends to be non-uniform with a significantly higher aluminum concentration (>20%) being found on the outer surface, as compared with the interior, of the crystal. Aluminum zoning in ZSM-5, especially in large crystals, has been reported. See "Zoned Aluminum Distribution in Synthetic Zeolite ZSM-5", R. von Ballmoos & W. M. Meier, Nature 1981, 289, 782-3; "Aluminum Distribution in Large ZSM-5 Crystals", K. J. Chao & J. Y. Chern, Zeolites, 1988, 8, 82; "Aluminum Zoning in ZSM-5 As Revealed by Selective Silica Removal", R. M. Dessau, E. W. Valyocsik & N. H. Goeke, Zeolites, 1992, 12, 776.


SUMMARY OF THE INVENTION

Unexpectedly it has now been found that by using amino acids as the directing agent, large crystal ZSM-5 of high aluminum content, SiO.sub.2 /Al.sub.2 O.sub.3 =25-40, can readily be obtained. Moreover, the resultant large ZSM-5 crystals have essentially the same SiO.sub.2 /Al.sub.2 O.sub.3 ratios in bulk (as measured by elemental and NMR analyses) and on the surface (as measured by x-ray photoelectron spectroscopy analysis (XPS) which determines the surface concentration and oxidation state of all detectable elements.)
It is to be appreciated that, although ZSM-5 is normally synthesized as an aluminosilicate, the framework aluminum can be partially or completely replaced by other trivalent elements, such as boron, iron and/or gallium, and the framework silicon can be partially or completely replaced by other tetravalent elements such as germanium.
In one aspect, the invention resides in a synthetic porous crystalline material having the structure of ZSM-5 and a composition involving the molar relationship: gallium, preferably aluminum; Y is a tetravalent element such as silicon and/or germanium, preferably silicon; and n is greater than about 12, and wherein the crystals have a major dimension of at least about 0.5 micron and a surface framework YO.sub.2 /X.sub.2 O.sub.3 ratio which is no more than 20% less than the bulk framework YO.sub.2 /X.sub.2 O.sub.3 ratio of the crystal.
Preferably, the crystals have a major dimension of at least about 1 micron.
Preferably, the surface framework YO.sub.2 / X.sub.2 O.sub.3 ratio is no more than 10% less than the bulk framework YO.sub.2 /X.sub.2 O.sub.3 ratio of the crystal.
Preferably, n is less than about 100 and more preferably is about 25 to about 40.
Preferably, the crystalline material exhibits a sorption time for 2,2-dimethylbutane for 30% of its capacity, as measured at 120.degree. C. and 60 torr (8 kPa) hydrocarbon pressure, of at least 5 minutes, preferably at least 10 minutes.
In a further aspect, the invention resides in a synthetic porous crystalline material having the structure of ZSM-5 and a Toluene Disproportionation Index (as hereinafter defined) of less than 430, and preferably less than 400.
In yet a further aspect, the invention resides in a method of synthesizing said porous crystalline material having the structure of ZSM-5 comprising the steps of forming a reaction mixture containing sources of an alkali or alkaline-earth metal oxide, a trivalent metal oxide X.sub.2 O.sub.3, a tetravalent metal oxide YO.sub.2, water, and an amino acid or salt t

REFERENCES:
patent: 4088605 (1978-05-01), Rollmann
patent: 4203869 (1980-05-01), Rollmann
patent: 4331641 (1982-05-01), Hinnenkamp et al.
patent: 4650656 (1987-03-01), Dwyer et al.
patent: 5365002 (1994-11-01), Wallau et al.
patent: 5573746 (1996-11-01), Chen
"Concerning the Aluminum Distribution Gradient in ZSM-5 Zeolites", Derouane et al., Journal of Catalysis, 1981, vol 71, pp. 447-8 (No Month).

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