Molecular sieve layers and processes for their manufacture

Details Molecular sieve layers and processes for their manufacture Molecular sieve layers and processes for their manufacture

1996-02-12

1998-03-03

Lewis, Michael

Catalyst, solid sorbent, or support therefor: product or process

In form of a membrane

502 64, 502 71, 502 77, B01J 2028

Patent

active

057233977

DESCRIPTION:

BRIEF SUMMARY
This invention relates to molecular sieves, more especially to crystalline molecular sieves, and to layers containing them. More especially, the invention relates to a layer, especially a supported layer, containing particles of a crystalline molecular sieve, and a process for its manufacture.
Molecular sieves find many uses in physical, physico-chemical, and chemical processes, most notably as selective sorbents, effecting separation of components in mixtures, and as catalysts. In these applications, the crystallographically-defined pore structure within the molecular sieve material is normally required to be open, and it is then a prerequisite that any structure-directing agent, or template, that has been employed in the manufacture of the molecular sieve be removed, usually by calcination.
Numerous materials are known to act as molecular sieves, among which zeolites form a well-known class. Examples of zeolites and other materials suitable for use in the invention will be given below.
When molecular sieves are used as sorbents or catalysts they are often in granular form. Such granules may be composed entirely of the molecular sieve or be a composite of a binder or support and the molecular sieve, with the latter distributed throughout the entire volume of the granule. In any event, the granule usually contains a non-molecular sieve pore structure which improves mass transfer through the granule.
The support may be continuous, e.g., in the form of a plate, or it may be discontinuous, e.g., in the form of granules. The molecular sieve crystals may be of such a size that, although the pores of the support are occupied by the crystals, the pores remain open. Alternatively, the molecular sieve may occupy the pores to an extent that the pores are effectively closed; in this case, when the support is continuous a molecular sieve membrane may result.
Thus, depending on the arrangement chosen and the nature and size of the material to be contacted by the molecular sieve, material may pass through the bulk of the molecular sieve material entirely through the pores of the molecular sieve material, or entirely through interstices between individual particles of the molecular sieve material, or partly through the pores and partly through the interstices.
Molecular sieve layers having the permeation path entirely through the molecular sieve crystals have been proposed for a variety of size and shape selective separations. Membranes containing molecular sieve crystals have also been proposed as catalysts having the advantage that they may perform catalysis and separation simultaneously if desired.
In our earlier European Patent Application No. 93.303 187.4, and a corresponding PCT Application No. PCT/E94/01301 filed simultaneously with this application, the disclosures of which are incorporated herein by reference, there are described a supported inorganic molecular sieve layer having a controllable thickness that may, if desired, be of a thickness of the order of only a few microns, and processes for its manufacture.
Such a layer and a process for its manufacture make possible the production of a number of useful products, including membranes, which because of their uniformity and thinness will have predictable properties, and will permit a high flux.
One process according to our earlier application comprises preparing a synthesis mixture comprising a source of silica and an organic structure directing agent in the form of a hydroxide in a proportion sufficient to effect substantially complete dissolution of the silica source in the mixture at the boiling temperature of the mixture, immersing the support in the synthesis mixture, crystallizing zeolite from the synthesis mixture onto the support, and if desired or required calcining the crystallized layer.
This process gives a uniform layer which is of sufficient thickness for many purposes. For other purposes, however, a layer of greater thickness is desirable.
The present invention provides a process for the manufacture of a layer comprising a crystalline molecular

REFERENCES:
patent: 5019263 (1991-05-01), Haag et al.
patent: 5258339 (1993-11-01), Ma et al.
patent: 5266542 (1993-11-01), Hashimoto et al.
Journal of Membrane Science, Vol. 73, 1992, pp. 111-128 (no month).

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