Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Patent
1995-02-27
1997-01-07
Spear, Frank
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
210490, 21050025, 21050026, 427245, B01D 7102
Patent
active
055913458
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a membrane based on molecular sieve material for separating small molecules from mixtures and to a method for the production thereof, according to which method a porous support is treated with a solution which contains the appropriate metalate ions such as aluminate and silicate ions, and optionally alkali metal or alkaline earth metal ions.
BACKGROUND OF THE INVENTION
German Patent Application 3,827,049 discloses a membrane which is produced by applying a crystallisation-promoting layer to a support, for example a metal or ceramic support, and allowing zeolite A to grow thereon from a solution which contains silicate, aluminate and sodium.
In addition, European Patent Application 135,069 discloses a composite membrane which consists of a porous support on which a continuous zeolite layer has been applied, which membrane can be obtained by depositing a gel which contains zeolite constituents on a porous support and allowing the gel to crystallise at elevated temperature.
U.S. Pat. No. 5,019,263 discloses a non-composited microporous membrane consisting of crystalline molecular sieve material, in particular silicon dioxide or zeolite. This membrane is produced by depositing crystalline material of the desired composition from a solution onto an auxiliary carrier, removing the crystalline material from the auxiliary carrier and calcining it. Because of the small thickness (0.1-400 .mu.m) the residual membrane is difficult to handle and has little resistance to substantial differences in pressure.
A method for the production of crystalline zeolite is disclosed in U.S. Pat. No.3,119,660. According to this method amorphous kaolin is pressed to give mouldings and the mouldings are treated at elevated temperature with an alkaline solution which also contains the zeolite constituents; this zeolite is intended for absorption and not for gas separation.
SUMMARY OF THE INVENTION
A separating membrane has now been found which has a pore size which can be accurately adjusted so that a sharp separation of components from a mixture can be achieved. The membrane has a permeability and thickness such that a high separation rate can be achieved and the pressures which may be needed for this separation can be withstood.
The separating membrane according to the invention consists virtually exclusively of molecular sieve crystals, has a thickness of 0.01-10 mm and has a separating top layer with a thickness of 0.01-10 .mu.m and an effective pore size of the separating layer of less than 1.5 nm.
The molecular sieve material can be of a common type. Useful molecular sieve materials are zeolites, which are composed of silicon oxides (silicates), mostly aluminium oxides (aluminates) and often alkali metal or alkaline earth metal ions. The ratio of silicon to aluminium atoms in the zeolites is generally 1 or higher. The aluminium atoms may be partly or entirely exchanged by other trivalent atoms, in particular boron, gallium or iron, whereas the silicon atoms may be partly or entirely exchanged by other tetravalent atoms, in particular titanium or germanium.
The molecular sieve material may also be of the aluminophosphate type, i.e. molecular sieves composed of aluminium oxides (aluminates) and phosphoric oxides (phosphates), optionally together with other oxides such as silicates (silicoaluminophosphates) and oxides of other metals such as Ti, Ge, As, Zr, Mo, Sn, Sb and the like (metaloaluminophosphates or metaloaluminophosphosilicates).
Preferably, the zeolite crystals are of the synthetic type A having the formula {M.sup.n+.sub.12
[Al.sub.12 Si.sub.12 O.sub.48 ]. 27H.sub.2 O}.sub.8, X having, for example, the formula M.sup.n+.sub.5
[Al.sub.86
Si.sub.106 O.sub.304 ]. 264H.sub.2 O or Y having, for example, the formula M.sup.n+.sub.56
[Al.sub.56 Si.sub.136 O.sub.384 ]. 250H.sub.2 O, in which M is an alkali metal (n=1) or an alkaline earth metal (n=2). The pore system of these zeolites is three-dimensional. The zeolite can also be of the ZSM-5 or silicalite type.
The thi
REFERENCES:
patent: 3421948 (1969-01-01), Webb
patent: 5019263 (1991-05-01), Haag et al.
patent: 5362522 (1994-11-01), Barri et al.
Engelen Charles W. R.
Van Leeuwen Willem F.
Spear Frank
Stichting Energieonderzoek Centrum Nederland
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