Chemistry of inorganic compounds – Zeolite – Seed used
Reexamination Certificate
2001-08-10
2004-11-23
Sample, David (Department: 1755)
Chemistry of inorganic compounds
Zeolite
Seed used
C423S716000
Reexamination Certificate
active
06821503
ABSTRACT:
This invention relates to molecular sieves and processes for their manufacture. More especially it relates to processes in which synthesis mixtures are seeded to control process conditions and product characteristics. The invention relates primarily to the manufacture of zeolites and other crystalline molecular sieves. Examples of the latter include phosphorus-containing molecular sieves whether or not they have zeolite analogues.
It is well-known that seeding a molecular sieve synthesis mixture frequently has beneficial effects, for example in controlling the particle size of the product, avoiding the need for an organic template, accelerating synthesis, and improving the proportion of product that is of the intended structure type. Colloidal seeds have proved especially effective—see, for example, International Application Nos. WO 97/03020 and 03021, and EP-A-753483, 753484 and 753485.
Whereas procedures for the preparation of colloidal dispersions of certain structure types have been described in the above-mentioned references, and similar procedures are effective in the preparation of colloidal dispersions of crystalline molecular sieves of other structure types, these procedures have proved ineffective in the preparation of colloidal dispersions of certain further structure types, especially LEV.
As used in this specification, the term “structure type” is used in the sense described in the Structure Type Atlas, Zeolites 17, 1996.
It has now been found that for many structure types a process for manufacturing a crystalline molecular sieve produces a product of a desired, larger, particle size, which 35 particles have much smaller particles, of a size suitable for use as seeds in subsequent manufacturing processes, adhering loosely to them.
The present invention accordingly provides in a first aspect a process for the manufacture of seed crystals of a molecular sieve, which comprises synthesizing the molecular sieve by treatment f an appropriate synthesis mixture, separating from the treated synthesis mixture a crystalline molecular sieve comprising particles of a first, larger, particle size in admixture with particles of a second, smaller, size suitable for use as seed crystals, and treating the crystalline molecular sieve to separate the larger particles from the smaller particles.
In a second aspect, the invention provides a process for the manufacture of a crystalline molecular sieve by treatment of a synthesis mixture appropriate for the formation of that molecular sieve, wherein the mixture contains as seeds separated smaller particles obtainable by, and preferably obtained by, the process of the first aspect of the invention.
In a third aspect, the invention provides the use of seed crystals obtainable by, and preferably obtained by, the process of the first aspect to accelerate the rate of production of a crystalline molecular sieve by treatment of a synthesis mixture.
In a fourth aspect, the invention provides the use of seed crystals obtainable by, and preferably obtained by, the process of the first aspect to control a characteristic, for example the purity, the phase purity, the particle shape, the particle size, or the particle size distribution, of a crystalline molecular sieve produced by treatment of a synthesis mixture.
In a fifth aspect, the invention provides the use of seed crystals obtainable by, and preferably obtained by, the process of the first aspect to facilitate the manufacture of a crystalline molecular sieve by treatment of a synthesis mixture substantially free from organic structure-directing agent (template).
In a sixth aspect, the invention provides the use of seed crystals obtainable by, and preferably obtained by, the process of the first aspect to facilitate the manufacture of a crystalline molecular sieve by treatment of a synthesis mixture, without stirring, at least after the desired synthesis temperature has been reached.
Referring now in more detail to the first aspect of the invention, it will be appreciated that it is applicable to all crystalline molecular sieve structure types, and to all processes for the manufacture of a crystalline molecular sieve of such a structure type, in which the initial product of synthesis is a product containing smaller particles adhering to the larger particles. To establish applicability requires only a simple routine experiment. In one such routine experiment, which is also a preferred method of obtaining the seed crystals, the synthesis mixture containing the crystalline molecular sieve product is centrifuged and the solids washed in, advantageously deionized, water, a two-stage procedure which is repeated a number of times. If the first aspect of the invention is applicable, the supernatant water after washing will not be clear.
It has been observed that in some systems while the first wash water may sometimes be clear, and may contain no or very few dispersed crystalline molecular sieve particles, the second or subsequent wash water is in contrast not clear, and has a measurable solids content.
The procedure yields hazy supernatants after various numbers of repetitions (depending both on the system and the relative sizes of the sample and the washing water); with some systems as many as 8 may be required; 2 to 5 is typical.
Among the structure types to which the first aspect of the invention is applicable, there may be mentioned LEV, FER, TON, MFI, MFS and MOR.
Among the specific examples within the structure types, there may be mentioned Levyne, ZK-20, NU-3 and ZSM-45 (LEV), ferrierite, ZSM-21, ZSM-35, ZSM-38, NU-23, FU-9, or ISI-6, (FER), ZSM-22, NU-10, ISI-1 or KZ-2 (TON), TS-1 (MFI), ZSM-57 (MFS) and Mordenite (MOR). Using the specific examples of the products of the first aspect of the invention, there may be prepared, in the remaining aspects, those specific examples and, in addition, many others.
As indicated above, separation of the smaller particles, hereinafter termed “washwater seeds”, from the larger particles may be carried out by repeated washing of the crystalline product obtained from the synthesis mixture until the supernatant wash water is hazy. Advantageously, the seeds are recovered not earlier than the second wash to limit contamination by unreacted starting materials remaining in the synthesis mixture, and preferably the suspension of washwater seeds is substantially free of such materials.
Other separations may be effected by subjecting the synthesis mixture to fractionation, low speed centrifuging, gel permeation, surfactant treatment, ammonia treatment, or: a combination of the two last mentioned.
(Although separation is advantageously complete, it is, within the scope of the invention to produce washwater seeds admixed with a small proportion of the larger particles.)
The washwater seeds, however separated, are found to have particle sizes in the range 20 to 500 nm (the smallest dimension being measured), and as such can be regarded as colloidal. The particle size of the recovered seeds may be controlled by, for example, varying the speed of the centrifuge. The seeds are advantageously used in the form of a dispersion in the separating medium, advantageously water although, in a presently less preferred alternative, they may be dried and added to a subsequent synthesis mixture in any form, provided they are not treated in any way, for example calcining, that reduces their seeding activity.
As used herein, the term “colloidal”, when used of a suspension, refers to one containing discrete finely divided particles dispersed in a continuous liquid phase and preferably refers to a suspension that is stable, in the sense that no visible separation occurs or sediment forms, in a period sufficient for the use intended, advantageously for at least 10, more advantageously at least 20, preferably at least 100, and more preferably at least 500, hours at ambient temperature (23° C.)
In each of the second and subsequent aspects of the invention, the washwater seeds are incorporated in a In synthesis mixture that is otherwise as known in the art or as described in the literature fo
Berge Jannetje Maatje van den
Janssen Marcel Johannes
Maria Van Oorschot Cornelis Wilhelmus
Mertens Machteld Maria Wilfried
Mortier Wilfried Jozef
Berge Jannetje Maatje van den
ExxonMobil Chemical Patents Inc.
Sample David
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