Cation exchange membrane and method for producing same

Patent metadata

Field	Value
Publication number	US-9833742-B2
Application number	US-201514681209-A
Country	US
Kind code	B2
Filing date	Apr 8, 2015
Priority date	Oct 10, 2012
Publication date	Dec 5, 2017
Grant date	Dec 5, 2017

Abstract

Provided is a cation exchange membrane having a stable ion exchange performance during usage, being excellent in basic properties such as membrane resistance and ion transportation as well as strength, and useful for electrodialysis and a method for producing the same. The cation exchange membrane is composed of a polyvinyl alcohol copolymer including an anionic group-containing anionic polymer segment and a vinyl alcohol polymer segment, and having a microphase separation structure having a domain size (X) in a range from 0 nm<X≦150 nm. The method is composed of forming a membrane from a polyvinyl alcohol copolymer which is adjusted to contain salts in a proportion that the salt weight (C) relative to the polyvinyl alcohol copolymer weight (P) is [(C)/(P)] of 4.5/95.5 or lower.

First claim

What is claimed is:

1. A cation exchange membrane, comprising a polyvinyl alcohol copolymer, wherein:
the polyvinyl alcohol copolymer comprises an anionic group-containing anionic polymer segment and a vinyl alcohol polymer segment; the content of the anionic group-containing monomer units is in the range of 0.1 to 50 mol % based on the total number of monomer units in the polyvinyl alcohol copolymer; and
the polyvinyl alcohol copolymer has a microphase separation structure having a domain size (X) satisfying 0 nm<X≦150 nm.

2. The cation exchange membrane as claimed in claim 1 , further comprising a polyvinyl alcohol homopolymer or copolymer without an anionic group.

3. The cation exchange membrane as claimed in claim 2 , consisting essentially of the polyvinyl alcohol copolymer and the polyvinyl alcohol homopolymer or copolymer without an anionic group.

4. The cation exchange membrane as claimed in claim 1 , wherein the polyvinyl alcohol copolymer has a crosslinking structure introduced thereinto.

5. The cation exchange membrane as claimed in claim 1 , wherein the polyvinyl alcohol copolymer is an anionic block copolymer comprising a vinyl alcohol polymer block and an anionic group-containing anionic polymer block.

6. The cation exchange membrane as claimed in claim 1 , wherein the polyvinyl alcohol copolymer is an anionic graft copolymer comprising a vinyl alcohol polymer block and an anionic group-containing anionic polymer block.

7. The cation exchange membrane as claimed in claim 1 , wherein the cation exchange membrane has an ion exchange capacity of 0.30 meq/g or higher.

8. The cation exchange membrane as claimed in claim 1 , wherein the cation exchange membrane has a membrane resistance of 10 Ωcm 2 or lower.

9. The cation exchange membrane as claimed in claim 1 , wherein the domain size (X) satisfies 1 nm<X≦150 nm.

10. The cation exchange membrane as claimed in claim 1 , wherein the domain size (X) satisfies 3 nm<X≦150 nm.

11. The cation exchange membrane as claimed in claim 1 , consisting essentially of the polyvinyl alcohol copolymer.

12. A method for producing a cation exchange membrane recited in claim 1 , comprising:
forming a membrane from a polyvinyl alcohol copolymer which is adjusted to contain salts in a proportion that the salt weight (C) relative to the polyvinyl alcohol copolymer weight (P) is [(C)/(P)] of 4.5/95.5 or lower.

13. The method as claimed in claim 12 , wherein the salts are inevitable impurities in the polyvinyl alcohol copolymer.

14. The method as claimed in claim 12 , wherein the salt is removed by carrying out precipitation or re-precipitation from a solution of the polyvinyl alcohol copolymer containing the salt to adjust a weight ratio of the salt based on the polyvinyl alcohol copolymer to a predetermined value or lower.

15. The method as claimed in claim 12 , wherein after membrane formation, the obtained membrane is crosslinked.

16. The method as claimed in claim 12 , further comprising:
preparing a film from a polyvinyl alcohol copolymer solution containing a salt,
heat-treating the obtained film at a temperature of 100° C. or higher,
conducting crosslinking treatment of the heated film with a dialdehyde compound under acidic condition in water, an alcohol, or a mixed solvent thereof, and
washing the crosslinked resultant with water to obtain a membrane.

Assignees

• Kuraray Co
• Univ Yamaguchi

Inventors

• Nakashima Takahiro
• Jikihara Atsushi
• Wakui Takashi
• Higa Mitsuru

Classifications

• B01D2325/42

  Ion-exchange membranes · CPC title

• B01J39/19

  obtained otherwise than by reactions only involving unsaturated carbon-to-carbon bonds · CPC title

• C08J2329/04

  Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids · CPC title

• C02F1/4693

  electrodialysis · CPC title

• B01D71/82

  characterised by the presence of specified groups, e.g. introduced by chemical after-treatment · CPC title