Electrodialysis

Patent metadata

Field	Value
Publication number	US-9969628-B2
Application number	US-201414904534-A
Country	US
Kind code	B2
Filing date	Jun 12, 2014
Priority date	Jul 12, 2013
Publication date	May 15, 2018
Grant date	May 15, 2018

Abstract

An electrodialysis unit comprising at least two electrodialysis stacks (ED 1 and ED 2 ) connected in series, wherein: (a) stacks ED 1 and ED 2 comprise anion exchange membranes and cation exchange membranes; and (b) the anion exchange membranes in stack ED 1 have a lower electrical resistance than the anion exchange membranes in stack ED 2 and the cation exchange membranes in stack ED 1 have a lower electrical resistance than the cation exchange membranes in stack ED 2 . Also claimed is a process for purifying liquids, e.g. for desalinating sea water or brackish water.

First claim

The invention claimed is:

1. An electrodialysis unit comprising at least two electrodialysis stacks (ED 1 and ED 2 ) connected in series, wherein:
(a) stacks ED 1 and ED 2 comprise anion exchange membranes and cation exchange membranes;
(b) the anion exchange membranes in stack ED 1 have a lower electrical resistance than the anion exchange membranes in stack ED 2 and the cation exchange membranes in stack ED 1 have a lower electrical resistance than the cation exchange membranes in stack ED 2 ;
(c) the water-permeability of the cation exchange membranes in stack ED 2 is 2 to 20 times lower than the water-permeability of the cation exchange membranes in stack ED 1 ; and
(d) the water-permeability of the anion exchange membranes in stack ED 2 is 2 to 20 times lower than the water-permeability of the anion exchange membranes in stack ED 1 .

2. The electrodialysis unit according to claim 1 wherein the electrical resistance of the anion exchange membranes in stack ED 1 is lower than 4 ohm·cm 2 .

3. The electrodialysis unit according to claim 1 wherein the electrical resistance of the cation exchange membranes in stack ED 1 is lower than 5 ohm·cm 2 .

4. The electrodialysis unit according to claim 1 wherein the electrical resistance of the cation exchange membranes in stack ED 1 is 1.5 to 20 times lower than the electrical resistance of the cation exchange membranes in stack ED 2 and the electrical resistance of the anion exchange membranes in stack ED 1 is 1.5 to 25 times lower than the electrical resistance of the anion exchange membranes in stack ED 2 .

5. The electrodialysis unit according to claim 1 wherein the water-permeability of the anion exchange membranes in stack ED 2 is less than 30×10 −12 m 3 /m 2 ·s·kPa and the water-permeability of the cation exchange membranes in stack ED 2 is less than 30×10 −12 m 3 /m 2 ·s·kPa.

6. The electrodialysis unit according to claim 1 which further comprises a third electrodialysis stack ED 3 comprising anion exchange membranes and cation exchange membranes and being located downstream of stack ED 2 and wherein stack ED 3 is connected in series to stack ED 2 .

7. The electrodialysis unit according to claim 6 wherein the anion exchange membranes in stack ED 2 have a lower electrical resistance than the anion exchange membranes in stack ED 3 and the cation exchange membranes in stack ED 2 have a lower electrical resistance than the cation exchange membranes in stack ED 3 .

8. The electrodialysis unit according to claim 6 wherein the anion exchange membranes in stack ED 3 have a lower water-permeability than the anion exchange membranes in stack ED 2 and the cation exchange membranes in stack ED 3 have a lower water-permeability than the cation exchange membranes in stack ED 2 .

9. The electrodialysis unit according to claim 1 wherein the electrodialysis stacks are free from particulate ion exchange resins.

10. An apparatus for purifying water comprising an electrodialysis unit according to claim 1 and an electrodeionization unit located downstream of the electrodialysis unit.

11. A process for purifying an aqueous feed liquid comprising passing the feed liquid through an electrodialysis unit according to claim 1 such that the feed liquid is separated into a concentrate and a diluate.

12. The process according to claim 11 wherein the feed liquid passes through stack ED 1 to form a diluate and a concentrate and then the diluate exiting stack ED 1 is fed into stack ED 2 in order to further lower the concentration of ions dissolved therein.

13. The process according to claim 11 wherein the average current density applied to stack ED 1 is higher than the average current density applied to stack ED 2 .

14. The process according to claim 11 wherein the aqueous feed liquid is or comprises sea water or brackish water.

15. The process according to claim 11 wherein the diluate is potable water.

16. A electrodialysis unit according to claim 1 wherein:
(a) the electrical resistance of the anion exchange membranes in stack ED 1 is lower than 4 ohm·cm 2 ;
(b) the electrical resistance of the cation exchange membranes in stack ED 1 is lower than 5 ohm·cm 2 ;
(c) the electrical resistance of the cation exchange membranes in stack ED 1 is 1.5 to 20 times lower than the electrical resistance of the cation exchange membranes in stack ED 2 ; and
(d) the electrical resistance of the anion exchange membranes in stack ED 1 is 1.5 to 25 times lower than the electrical resistance of the anion exchange membranes in stack ED 2 .

17. The electrodialysis unit according to claim 16 wherein the water-permeability of the anion exchange membranes in stack ED 2 is less than 30×10 −12 m 3 /m 2 ·s·kPa and the water-permeability of the cation exchange membranes in stack ED 2 is less than 30×10 −12 m 3 /m 2 ·s·kPa.

18. An apparatus for purifying water comprising an electrodialysis unit according to claim 17 and an electrodeionization unit located downstream of the electrodialysis unit.

19. An apparatus for purifying water comprising an electrodialysis unit according to claim 16 and an electrodeionization unit located downstream of the electrodialysis unit.

20. The electrodialysis unit according to claim 1 wherein stack ED 2 is located downstream of stack ED 1 .

Assignees

• Fujifilm Mfg Europe Bv

Inventors

• Bhikhi Vinodnarain
• Van Baak Willem

Classifications

• C02F2103/08

  Seawater, e.g. for desalination · CPC title

• B01D2317/04

  Elements in parallel · CPC title

• B01D61/54

  Controlling or regulating · CPC title

• B01D2317/02

  Elements in series · CPC title

• C02F2201/46135

  Voltage · CPC title