Membrane for separating off small molecules and method for the production thereof

DETAILED DESCRIPTION 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/n [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/n [Al.
sub.
86/n Si.
sub.
106 O.
sub.
304 ].
264H.
sub.
2 O or Y having, for example, the formula M.
sup.
n+.
sub.
56/n [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)