Catalyst – solid sorbent – or support therefor: product or process – Zeolite or clay – including gallium analogs – And group viii containing
Patent
1992-06-30
1996-02-13
Pal, Asok
Catalyst, solid sorbent, or support therefor: product or process
Zeolite or clay, including gallium analogs
And group viii containing
208135, 423716, 502 60, 502 66, 585407, B01J 2930, C01B 3334, C07C 276
Patent
active
054911192
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a zeolite of the L type, and a process for its production. This zeolite is a good catalyst base for a variety of organic reactions, especially hydrocarbon conversions, and may be regenerated after use.
BACKGROUND OF THE INVENTION
Zeolite L has been known for some time as an adsorbent and in U.S. Pat. No. 3,216,789 is described as an alumino-silicate of the formula: having a characteristic X-ray diffraction pattern.
EP-A-96479 describes a zeolite L which is particularly useful as a catalyst base in hydrocarbon conversions such as aromatization. The zeolite comprises crystallites in the form of cylinders with a mean diameter of at least 0.1 micron, preferably at least 0.5 micron and with an aspect ratio (ratio of cylinder length to diameter) of at least 0.5. The gel from which the zeolite is obtained comprises the following ratios of components: 2.4 to 3.0 moles K.sub.2 O, 0.6 to 1.3 moles Al.sub.2 O.sub.3, 8 to 12 moles of SiO.sub.2 and 120 to 240 moles H.sub.2 O. A particularly preferred gel has the following compositions:
The potassium form of zeolite L, hereinafter identified as zeolite KL, may also contain caesium, as described in EP-A-323892.
Typically the zeolite is loaded with one or more metals such as platinum, tin, germanium, rhenium or iridium, particularly platinum, to prepare the desired catalyst.
New forms of zeolite KL are sought which are particularly useful as a catalyst base for aromatization and which permit regeneration of spent catalyst. Imperfections in the zeolite crystals and relatively long uni-directional zeolite channels result in poor utilization of Pt, poor maintenance of catalyst activity, and undesirable secondary reactions. To improve the properties of such a zeolite the channel length of the zeolite should be decreased to well below one micron, but at the same time the surface area of the zeolite crystal should be maintained as large as is practicable, and the crystals should be well-formed i.e. without a significant level of crystal imperfections.
These features are present if well-formed zeolite crystals can be made in the form of very flat cylinders. The present invention provides a zeolite whose crystals have the requisite properties; the present invention also provides a process for producing such zeolites.
SUMMARY OF THE INVENTION
Accordingly the present invention provides a zeolite of the KL-type in which the crystals are cylindrical and have an average length of 0.6 microns or less and an average length: diameter ratio of less than 0.5 and have substantially flat basal planes.
It is believed that in such a zeolite the flatness of the basal planes is an indication of the intrinsic quality of the crystals and the shortness of the crystal length makes for less meandering channels.
DESCRIPTION OF PREFERRED EMBODIMENTS
The cylindrical crystal particles are substantially in the form of cylinders of circular cross-section, and preferably substantially in the form of right circular cylinders where the base is normal to the cylinder axis.
The crystals are coin or hockeypuck shaped and have a relatively large diameter and short length. The "length" of a crystal is a measurement of the outer edge of the crystal perpendicular to the basal plane containing the diameter. The length is typically 0.1 to 0.6 preferably 0.1 to 0.3 microns and the diameter is generally 0.3 to 1.5 microns preferably 0.4-1.0 microns. When the length/diameter ratio is 0.2-0.5 the crystal shape is termed herein as "hockeypuck". When the ratio is less than 0.2 the shape is termed herein as "coin".
The crystals thus possess the advantages of a short channel length and of a relatively large diameter which gives increased selectivity and/or yield when it is used as a base for a catalyst. The average length of time over which the catalyst remains active i.e. the run length of the process before the catalyst requires regeneration is longer with the present form of zeolite than with previous zeolites L of larger channel length and crystal size. Ano
REFERENCES:
patent: 4544539 (1985-10-01), Wortel
patent: 4680280 (1987-07-01), Pandey et al.
patent: 4894214 (1990-01-01), Verduijn et al.
patent: 5051387 (1991-09-01), Koetsier et al.
patent: 5242675 (1993-09-01), Verduijn
Exxon Chemical Patents Inc.
Pal Asok
Sherer Edward F.
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