Chemistry of inorganic compounds – Zeolite – Organic compound used to form zeolite
Patent
1995-05-15
1998-07-21
Bell, Mark I.
Chemistry of inorganic compounds
Zeolite
Organic compound used to form zeolite
423704, 423705, 423708, 423716, 423709, 423DIG22, 502 77, C01B 3940, C01B 3334
Patent
active
057833214
DESCRIPTION:
BRIEF SUMMARY
ZSM-5ZEOLITE
The present invention relates to a form of ZSM-5 zeolite, processes for its production, processes for its use in the production or conversion organic compounds, and processes for its use as a selective absorbent.
ZSM-5 is an MFI-type zeolite, usually an aluminosilicate zeolite, which has been found useful as a catalyst in a variety of processes for preparing, converting, separating or purifying organic compounds. The earliest ZSM-5 zeolites were prepared using an organic template in the synthesis mixture which directed the formation of the ZSM-5 structure. Known ZSM-5 zeolites prepared using an organic template generally have an SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of at least 60 and frequently considerably greater than 60 (see e.g. U.S. Pat. No. 4,797,267). So-called "inorganic" ZSM-5 zeolites, made in the absence of an organic template, were prepared in the 1980 's. Typically these have an SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of from 20 to about 30 to 40. SiO.sub.2 /Al.sub.2 O.sub.3 ratios of up to 80have been reported (e.g. Zeolites 1989Vol. 9 363-370).
The morphology of ZSM-5 crystals produced using an organic template can vary. For example, Studies in Surface Science and Catalysis 33, "Synthesis of High Silica Aluminosilicate Zeolites" (Elsevier), Peter A. Jacobs and Johan A. Martens illustrates ZSM-5 crystals which are large elongated hexagonal prisms, whose corners may be rounded. Crystals of ZSM-5 zeolite which are agglomerates of smaller, elementary hexagonal crystallites are also illustrated. In the presence of an extremely high proportion of silica (e.g. U.S. Pat. No. 4,797,267), ZSM-5 crystals may be rod shaped i.e. elongated crystals with substantially parallel sides and blunt ends. The morphology of inorganic ZSM-5 crystals tends, according to Zeolites (ibid), to be ellipsoidal.
There is evidence to suggest that inorganic ZSM-5 zeolite and ZSM-5 zeolites produced by organic templated synthesis differ in terms of the relative positions of atoms in their structures. In templated synthesis, there is evidence for occurrence of aluminium zoning (see e.g. Jacobs and Martens, ibid). In inorganic ZSM-5 it is believed that the Al atoms are homogeneously distributed over the T-atom sites. NMR spectra of ZSM-5 zeolites prepared using an organic template, specifically .sup.29 Si NMR spectra, show two peaks: one at -111 ppm corresponding to Si with no Al neighbours, and one at -105 ppm corresponding to Si with one Al atom as a nearest neighbour in a T-atom site.
The applicants have now identified a novel form of ZSM-5 zeolite. The zeolites of the present invention are tectosilicates. They contain silicon and aluminium, although some or all of the aluminium may be replaced with another element e.g. gallium, boron, iron, zinc or copper. For simplicity the following text will refer to aluminium but unless otherwise stated this should not be taken to imply a limitation.
The present invention provides a crystalline ZSM-5 zeolite, preferably an aluminosilicate zeolite, which comprises substantially needle-shaped agglomerates.
By needle-shaped it is intended to mean that the agglomerates are substantially rod-shaped having gently tapering ends (i.e. not blunt ended like coffin-shaped crystals) and where the average ratio of length to diameter (measured at the thickest part of the needle) is at least 2.5, preferably at least 3.
The ends of the agglomerate taper, preferably so that the length of the portion of the agglomerate having a diameter less than the maximum diameter, is at least 50%, preferably at least 60%, more preferably at least 70% of the total length of the agglomerate. Typically the average length of the needle-shaped agglomerates is of the order 0.2 to 10 .mu.m, preferably 0.4 to 5 .mu.m. Substantially all the ZSM-5 zeolite agglomerates may be needle-shaped, i.e. at least 80%, preferably at least 90%, more preferably at least 95% of the agglomerates are needle-shaped.
Each needle-shaped agglomerate may be made up of much smaller crystals agglomerated together. The smaller crysta
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Martens Johan Adriaan
Martens Luc Roger Marc
Verduijn Johannes Petrus
Bell Mark I.
Exxon Chemical Patents Inc.
Sherer Edward F.
Troilo Louis M.
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