Liquid purification or separation – Filter – Supported – shaped or superimposed formed mediums
Patent
1993-04-21
1994-08-30
Spear, Frank
Liquid purification or separation
Filter
Supported, shaped or superimposed formed mediums
21050025, 21050026, 21050042, B01D 7102
Patent
active
053425219
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a reverse osmosis or nanofiltration membrane or diaphragm more particularly usable in the agroalimentary and pharmaceutical industries.
It more specifically relates to organomineral membranes having high permeability levels and a good resistance to high pressures and aggressive chemical treatments such as steam sterilization at 120.degree. C. and washing by acid or basic solutions.
It is pointed out that a semipermeable membrane is a membrane having an active layer with the property of permitting the selective diffusion of certain species, so as to retain the selected species such as sodium chloride.
A nanofiltration membrane is a membrane making it possible to retain substances having a molecular weight above a certain threshold falling within the range 50 to 1000.
Organomineral membranes are membranes having an inorganic material porous support on which is located an organic polymer active layer. Organomineral membranes are in particular described in U.S. Pat. No. 4,861,480, EP-A-250 327 and Japanese patent application published under No. 59-206008 in the name of the TDK Corporation.
In U.S. Pat. No. 4,861,480, these organomineral membranes are semipermeable membranes constituted by an inorganic material porous support having an outer microporous layer with a thickness of 1 to 2 .mu.m, covered with a semipermeable, dense organic layer based on a polyvinylidine fluoride polymer or copolymer having functional groups giving the membrane a selective permeability with respect to water or other solvents. These membranes are more particularly usable as reverse osmosis membranes for e.g. retaining sodium chloride.
EP-A-250 327 describes an ultrafiltration, hyperfiltration or demineralization element having an inorganic material porous support and an asymmetrical, partitioned, microporous, organic polymer membrane, formed on one of the faces of the porous support and fitted into the pores of the porous support flush with said surface without projecting beyond the same. This element can be used for the demineralization of water by the Donnan effect. In this element, the separating layer is fitted into the surface pores of a porous support, which makes it possible to treat effluents without prefiltration, because the separating layer is slightly set back with respect to the surface of the support, so that it is insensitive to impacts of any solid suspended particles.
In this document, the thickness of the separating layer is 25 to 200 .mu.m, which leads to permeabilities to water of 0.05 to 2.5.multidot.10.sup.-5 m.d.sup.-1 .multidot.Pa.sup.-1.
Although the membranes described in these two documents have satisfactory properties, it would be of interest to be able to further improve their permeability to the treated solutions.
Japanese patent application 59-206008 describes a filter having a ceramic porous support on which is located a semipermeable, thin organic membrane usable for reverse osmosis. In this case, the thickness is at least 1 .mu.m. Thus, it is possible to obtain good permeability levels, but the organic materials used are not appropriate for the separation of solutes in the molecular weight range 50 to 1000.
The present invention relates to a reverse osmosis or nanofiltration organomineral membrane having improved properties compared with the membranes described hereinbefore.
According to the invention, the reverse osmosis or nanofiltration membrane comprises an inorganic material porous support coated on one face with a first inorganic material mesoporous layer having a mean pore radius below 10 nm and a second active layer placed on the first mesoporous layer and having a thickness of 0.1 to 1 .mu.m, being made from an organomineral polymer or an organic polymer chosen from within the group including sulphonated polysulphones, polybenzimidazolones, polyvinylidine fluorides grafted by diaminoethyl methacrylate and perfluorine ionomers.
In this membrane, the choice of polymers constituting the second active layer more particularly makes it possible to obtain even thin
REFERENCES:
patent: 4741744 (1988-05-01), Wu et al.
patent: 4861480 (1989-08-01), Berardo et al.
patent: 4865930 (1989-09-01), Kindler et al.
I.E.C. Product Research and Developement, vol. 2, No. 3, Sep. 1981, American Chemical Society, (Washington, US) H. Murakami et al.: "PBIL tubular reverse osmosis. Application as low-energy concentrators", pp. 501-508.
Bardot Colette
Carles Maurice
Desplantes Rene
Shrive Luc
Commissariat a l''Energie Atomique
Spear Frank
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