Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2001-09-28
2003-05-27
Bell, Bruce F. (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S627000, C204S630000, C204S518000, C204S520000, C204S521000, C204S523000, C204S529000, C521S027000, C205S618000
Reexamination Certificate
active
06569301
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a cation exchange membrane which is useful for concentration or separation of an aqueous electrolyte solution or for production of demineralized water employing an ion exchange membrane, and a method for its production. More particularly, it relates to a cation exchange membrane selectively permeable to monovalent cations, which permits cations having small electric charges to readily permeate particularly selectively, and which is useful for concentration or separation of an aqueous electrolyte solution or production of demineralized water, by electrodialysis, and a method for its production.
BACKGROUND ART
Concentration or separation of an aqueous electrolyte solution, or production of demineralized water, employing an ion exchange membrane, is carried out in various fields. Especially in Japan, in order to establish a salt production technique of concentrating seawater by electrodialysis, many membranes selectively permeable to monovalent ions, which are capable of selectively concentrating sodium chloride from various seawater components, have been proposed and are being practically used. Further, their applications to areas other than concentration of seawater, have also been attempted.
The following methods may be mentioned as conventional methods for imparting selective permeability to monovalent cations, to cation exchange membranes.
(1) A method of making the surface portion of a cation exchange membrane to have a dense structure (for example, making the surface layer to be a layer having a high cross-linking degree or a layer having a high fixed ion concentration);
(2) A method of forming an electrically neutral thin layer containing no ion exchange groups, on the surface of a cation exchange membrane;
(3) A method of forming a thin layer having an opposite electrical charge, on the surface of a cation exchange membrane.
(4) A method of employing two or more of the above methods (1) to (3) in combination.
Among the above methods, method (1) is usually excellent in durability, but has a drawback that the electrical resistance is high, and method (2) is inadequate in selective permeability. Whereas, method (3) usually has a merit in that selectivity to monovalent ions is excellent, and the electrical resistance is low, but the initially proposed method (JP-704599) had drawbacks that the molecular weight of the material forming the opposite electric charge layer was low, the durability of the selectivity to monovalent cations was inadequate, and if the opposite electrical charge layer was made to increase the durability or the selectivity, an increase in the direct current resistance or a decrease in the limiting current density was likely to be led.
Many proposals have been made to overcome such drawbacks, and one of such proposals is a method of forming a selective layer by an opposite electrical charge compound having the solubility controlled, such as a non-crosslinkable substance having anion exchange groups and having a specific HLB value and molecular weight (JP-A-55-8838) or a polymer having anion exchange groups and having a specific solubility to seawater (JP-A-9-48861). By such a method, the durability under application of electric current can be improved, but there is a problem that in a state where application of electric current has been stopped, the selective layer tends to gradually elute from the membrane, whereby the selectivity tends to deteriorate.
Further, as a method to prevent such a drawback, a method of treating a cation exchange membrane immersed in a mixture of an organic solvent and water, with the opposite electrical charge compound (JP-B-6-49786), or a method of treating it with a high molecular amine in an electrically non-charged state (JP-A-4-90828) for the purpose of improving the durability by permitting the opposite electrical charge layer to penetrate into the membrane, but such a method has not necessarily been adequate.
Further, there is a method in which a compound having an opposite electrical charge or convertible to have an opposite electrical charge, is polymerized on the surface of a cation exchange membrane to form an insolubilized layer (JP-A-62-205135, etc.). By this method, the durability of the selectivity to monovalent cations can be improved to a large extent, but there is a problem such that the direct current resistance of the membrane is likely to be high at the time of concentration of seawater, while the alternate current resistance of the membrane is low.
DISCLOSURE OF THE INVENTION
The present invention has been made to solve the above problems, and the cation exchange membrane selectively permeable to monovalent cations of the present invention, is characterized by having, on at least one side of the cation exchange membrane, a surface treated by contact with high molecular cations in the presence of anions of an oxyacid or ions of an organic sulfonic acid.
Further, the method for producing a cation exchange membrane selectively permeable to monovalent cations of the present invention, is characterized by contacting at least one surface of a cation exchange membrane with high molecular cations in the presence of anions of an oxyacid and ions of an organic sulfonic acid (hereinafter, these acids may sometimes be referred to as an oxyacid, etc., and their ions may sometimes be referred to as oxyacid anions, etc.).
In the present invention, as described above, at least one surface of the cation exchange membrane is brought in contact with high molecular cations in the presence of anions of an oxyacid or ions of an organic sulfonic acid. However, the reason why such a contact is effective, has not yet been clarified, but the effects are evident from Examples given hereinafter.
BEST MODE FOR CARRYING OUT THE INVENTION
The cation exchange membrane selectively permeable to monovalent cations of the present invention is one having, on at least one side of the cation exchange membrane, a surface treated by contact with high molecular cations in the presence of anions of an oxyacid or ions of an organic sulfonic acid, as mentioned above. As cation exchange membranes prior to the treatment to impart the selective permeability to monovalent cations, the following membranes may, for example, be mentioned, and they can be used without any particular restriction.
(1) A cation exchange membrane obtained by impregnating a reinforcing cloth with styrene/divinyl benzene, followed by polymerization and then by sulfonization.
(2) A heterogeneous cation exchange membrane formed in a membrane-shape from a kneaded blend of a cation exchange resin powder and a binder.
(3) A cation exchange membrane obtained by graft-polymerizing a monomer convertible to a cation exchange group or having a cation exchange group to a polyolefin or fluorine type film.
(4) A perfluoro type cation exchange membrane useful as a sodium chloride electrolytic membrane for an ion exchange membrane method.
To prepare the cation exchange membrane selectively permeable to monovalent cations of the present invention, at least one side of a cation exchange membrane as listed above, is contacted with high molecular cations in the presence of anions of an oxyacid or ions of an organic sulfonic acid. The high molecular cations in the present invention are defined to be a high molecular electrolyte, of which the average molecular weight (the average formula weight) of cations charged positively during the use of the cation exchange membrane, is at least 5,000. As the high molecular electrolyte which gives such high molecular cations, a water-soluble polymer may, for example, be mentioned, such as polyethyleneimine, polyallylamine, a polyamizine, a hexamethylenediamine/epichlorohydrin polycondensate, a dicyandiamide/formalin polycondensate, a guanidine/formalin polycondensate, a polyvinyl benzyl trimethylammonium chloride, a poly(4-vinyl pyridine), a poly(2-vinyl pyridine), a poly(dimethylaminoethyl acrylate), a poly(dimethylaminoethyl methacrylate), a poly(1-vinyl imidazole), a poly(2-vinyl pyrazine), a poly(4-butenyl pyr
Aoki Yoshiharu
Fukui Motoo
Sugaya Yoshio
Asahi Glass Company Limited
Bell Bruce F.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Cation exchange membrane selectively permeable to monovalent... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cation exchange membrane selectively permeable to monovalent..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cation exchange membrane selectively permeable to monovalent... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3080219