Molecular sieves and processes for their manufacture

Details Molecular sieves and processes for their manufacture Molecular sieves and processes for their manufacture

1997-04-03

2000-07-18

Fortuna, Ana

Liquid purification or separation

Processes

Liquid/liquid solvent or colloidal extraction or diffusing...

210650, 210490, 210506, 21050025, 96 8, 96 10, 96 11, 96 12, 4274432, 427244, B01D 6100, B01D 2900

Patent

active

060902892

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/EP95/02704, filed oil Jul. 10, 1995, which claims priority of GB Application No. 9413863.3.
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 a crystalline molecular sieve and to a structure comprising such a layer.
Molecular sieves find many uses in physical, physicochemical, 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 present invention will be given below.
In our earlier International Application WO 94/25151 we have described a supported inorganic layer comprising optionally contiguous particles of a crystalline molecular sieve, the mean particle size being within the range of from 20 nm to 1 .mu.m. The support is advantageously porous. When the pores of the support are covered to the extent that they are effectively closed, and the support is continuous, a molecular sieve membrane results; such membranes have the advantage that they may perform catalysis and separation simultaneously if desired.
While the products of the earlier application are effective in many separation processes, the crystals of the layer are not ordered, and as a result diffusion of materials through the membrane may be hampered by grain boundaries. Further, there are voids between the crystals.
Other literature describing supported inorganic crystalline molecular sieve layers includes U.S. Pat. No. 4,699,892; J. C. Jansen et al, Proceedings of 9th International Zeolite Conference 1992 (in which lateral and axial orientations of the crystals with respect to the support surface are described), J. Shi et al, Synthesis of Self-supporting Zeolite Films, 15th Annual Meeting of the British Zeolite Association, 1992, Poster Presentation (in which oriented Gmelinite crystal layers are described); and S. Feng et al, Nature, Apr. 28, 1994, p 834, which discloses an oriented zeolite x analogue layer.
WO93/19840 describes a process for the deposition of zeo-type material on a porous support; the support may be pre-treated with a solution of silicic acid. WO94/25152 discloses a process for deposition on a support of a molecular sieve layer wherein the solution temperature is increased during deposition. WO93/08125 describes colloidal zeolite materials and methods of their preparation. EP 0 481 660 describes a method of manufacture of zeolite membranes in which a number of deposition stages are used to build up the membrane thickness. WO94/01209 discloses a continuous gastight film of zeolite on a porous underlayer and a process for its manufacture. WO94/09902 describes a structured catalyst system wherein a structured support is covered with a layer of molecular sieve crystals. FR 2 365 520 describes a process for the deposition of a zeolite on a support.
Related copending PCT Applications are PCT/US95/0851 1, PCT/US95/08513, and PCT/US95/08514.
The present invention provides, in a first aspect, a structure comprising a support, an intermediate layer, and an upper layer, the intermediate layer comprising a crystalline molecular sieve having a crystal size of at most 1 .mu.m, and the upper layer comprising a crystalline molecular sieve of crystals having at least one dimension greater than the dimensions of the crystals of the intermediate layer.
In a second aspect, the present invention provides a structure comprising a support, an intermediate layer, and an upper layer, the intermediate la

REFERENCES:
patent: 4214020 (1980-07-01), Ward et al.
patent: 4699892 (1987-10-01), Suzuki et al.
patent: 5362522 (1994-11-01), Barri et al.
patent: 5716527 (1998-02-01), Deckman et al.

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