Chemistry of inorganic compounds – Zeolite – Isomorphic metal substitution
Patent
1993-10-25
1995-12-05
Bell, Mark L.
Chemistry of inorganic compounds
Zeolite
Isomorphic metal substitution
423716, 423DIG28, 502 66, 502 74, 208138, C01B 3906, C01B 3932, B01J 29068, C10G 35085
Patent
active
054726816
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a zeolite KL containing iron and of improved morphology compared with a zeolite produced from the same synthesis mixture, but not containing iron. The present invention also relates to a process for producing such a zeolite, a reforming catalyst comprising the zeolite, and a reforming process using this catalyst.
The reforming of hydrocarbons, and in particular the aromatisation of paraffins, frequently uses a catalyst comprising a zeolite KL on which has been loaded a metal such as platinum, or a mixture of platinum and another metal, e.g. iridium. The size and shape i.e. the morphology of the zeolite crystals affects the performance of the catalyst. Another factor which contributes to catalyst performance is the overall electronegativity of the zeolite. A reduction in the electronegativity can improve the catalyst performance. Zeolites are commonly formed of an alumino-silicate structure. The electronegativity of this may be reduced by replacing at least a part of the aluminum in this structure with another metal.
It has now surprisingly been found that zeolite EL which has been crystyallized from a synthesis mixture of low alkalinity, conveniently expressed in terms of a ratio of K.sub.2 O/SiO.sub.2, and containing Fe.sup.3+ ions shows an enhanced morphology, in particular compared with a zeolite crystallised from the corresponding synthesis mixture which does not contain Fe.
EP-A-198721 and EP-A-198720 (Chevron Research Company) disclose zeolite reforming catalysts comprising platinum metal and at least one promoter metal selected from iron, cobalt and titanium. If the promoter metal is iron, it may be present in the synthesis mixture in an amount of e.g. up to around 1100 ppm of Fe. The exemplified reforming catalysts were obtained from synthesis mixtures containing up to 221 ppm of Fe. However, the iron in these reforming catalysts was used as a promoter for the platinum to be loaded on the zeolite. The alkalinity of the synthesis mixture used and the quantities of iron used, are such that the morphology of the crystals is the same, whether or not iron is present in the synthesis mixture.
SUMMARY OF THE INVENTION
The present invention provides an Fe-containing zeolite KL which has a reduced crystal size and flatter basal planes than the corresponding zeolite which was not synthesised in the presence of added iron, and in particular one in which the zeolite synthesis mixture does not contain iron and has a higher alkalinity.
The present invention provides an Fe-containing zeolite KL obtainable by heating a synthesis mixture comprising a source of K.sub.2 O, a source of SiO.sub.2, a source of Al.sub.2 O.sub.3 and a source of Fe.sup.3+, in which the K.sub.2 O/SiO.sub.2 molar ratio is 0.18 to 0.36 and in which the iron is present in an amount such that the average length of the zeolite crystals produced is not more than 80% of the average length of zeolite crystals produced by heating under the same conditions the corresponding synthesis mixture in the absence of iron.
The present invention also provides a process for reducing the average crystal length of a zeolite comprising including a source of Fe.sup.3+ in a synthesis mixture comprising a source of K.sub.2 O, a source of SiO.sub.2 and a source of Al.sub.2 O.sub.3, the K.sub.2 O/SiO.sub.2 molar ratio being 0.18 to 0.36 and the Fe.sup.3+ being included in an amount sufficient to reduce the average length of the zeolite crystals.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows scanning electron micrographs (SEMS) of zeolite crystals made in accordance with Examples 1-3 and Reference Example A.
FIG. 2 shows SEMS of zeolite crystals made in accordance with Example 4 and Reference Examples B.
FIG. 3 shows an SEM of zeolite crystals made in accordance with Reference Example C.
FIG. 4 shows an SEM of zeolite crystals made in accordance with Example 5.
FIG. 5 shows an SEM of zeolite crystals made in accordance with Example 6.
FIG. 6 shows SEMS of zeolite crystals made in accordance with the processes of prior art U.S. Pa
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Bell Mark L.
Exxon Chemical Patents Inc.
Sample David
Sherer E. F.
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