Process and apparatus for treatment of fluids, particularly demineralization of aqueous solutions

• US 4,687,561 A
• Filed: 05/20/1985
• Issued: 08/18/1987
• Est. Priority Date: 05/13/1982
• Status: Expired due to Term

• Current Assignee: U.S. Filter/Ionpure, Inc. (Evoqua Water Technologies LLC)
• Original Assignee: Gerhard Kunz
• Inventors: Kunz, Gerhard
• Primary Examiner(s): NOT, DEFINED
• Application Number:
  US06/736,198
• Time in Patent Office: 820 Days
• Field of Search: 204/573, 204/301, 204/182.5, 204/180 P, 204/180 B
• US Class Current: 204/524
• CPC Class Codes: B01J 47/08 subjected to a direct electric current
• CPC Class Codes: B01J 49/30 Electrical regeneration
• CPC Class Codes: C02F 1/4604 for desalination of seawater or brackish water
• CPC Class Codes: C02F 1/469 by electrochemical separation, e.g. by electro-osmosis, electrodialysis, electrophoresis

Abstract

Process and apparatus are provided for demineralizing aqueous solutions without using regenerating chemicals. Oppositely charged ions are electrolytically generated within electrode chambers and diffused into the stream of aqueous solution to be demineralized flowing in cross-current thereto. In their migration in response to the application of an electric potential, the ion streams are subjected to displacement steps in cation and anion exchange masses separated by selectively permeable ion exchange membranes. The aqueous solution alternately passes through the cation and anion exchange masses resulting in a demineralized aqueous stream and an enriched brine stream.

Claims

1. A process for demineralizing an aqueous liquid containing salts, comprising:

(a) passing the liquid through at least a first means for exchanging cations, a means for exchanging anions, and a second means for exchanging cations;

the cation-exchange means containing hydrogen ions and the anion-exchange means containing hydroxyl ions, whereby cations and anions dissociated from the salts are exchanged for the hydrogen ions and the hydroxyl ions, thereby reducing the concentration of salts in the outflowing liquid;

(b) applying electric potential across the direction of flow of the liquid whereby hydrogen ions and hydroxyl ions migrating in opposite directions are exchanged for the cations and anions in the means for exchanging ions thereby restoring said hydrogen and hydroxyl ions to the means, and whereby the displaced cations and anions are caused to migrate in opposite directions; and

(c) passing a flushing solution across the direction of the ion migration capable of receiving the cations migrating out from said first means for exchanging cations and the anions migrating out from the means for exchanging anions, whereby salts are formed and discharged with the flushing solution.

2. The process of claim 1 wherein the liquid to be demineralized is raw water.

3. The process of claim 1 wherein the liquid to be demineralized is pre-softened.

4. The process of claim 1 wherein

the first and second means for exchanging cations are cation-exchange resins;

and

the means for exchanging anions is an anion-exchange resin.

5. The process of claim 1 wherein the flushing solution is a salt solution.

6. The process of claim 3 wherein the liquid in step (a) is passed through a second means for exchanging anions.

7. The process of claim 3 wherein the liquid in step (a) is alternately and sequentially passed through two cation exchange means and two anion exchange means.

8. The process of claim 1 wherein the electric potential in step (b) generates a stream of cations which travels from an anode towards a cathode through the liquid and the flushing solution during the residence thereof in the following sequence:

(I) liquid in said second means for exchange of cations, (II) liquid in said first means for exchange of cations, (III) said flushing solution, and (IV) liquid in said first means for exchange of anions; and

a stream of anions which travels from the cathode towards the anode through the liquid and the flushing solution in a sequence opposite to the current of cations.

9. The process of claim 3 wherein steps (a) through (c) are conducted simultaneously.

10. A continuous process for demineralizing an aqueous liquid comprising conducting steps (a) through (c) of the process of claim 3 in a continuous manner.

11. The process of claim 1 wherein said migrating cations and anions access said flushing solution approximately simultaneously.

12. The process of claim 8 wherein

the cations are substantially prevented from migrating out of the means for exchanging anions into a liquid surrounding the cathode by a means for selectively permeating only anions;

and

the anions are substantially prevented from migrating out of the means for exchanging cations into a liquid surrounding the anode by a means for selectively permeating only cations.

13. The process of claim 1 wherein

the liquid to be demineralized is heated in order to increase its temperature during demineralization.

14. The process of claim 12, wherein

the means for selectively permeating anions is an anion-permeable membrane;

and

the means for selectively permeating cations is a cation-permeable membrane.

15. The process of claim 12 wherein at least one of said means for selectively permeating ions is a double ion permeable membrane substantially impermeable to counter-ions.

16. An apparatus for demineralizing an aqueous liquid containing salts, comprising:

at least one anode,

at least one cathode,

at least one means for exchanging cations,

at least one means for exchanging anions,

at least one flushing means,

said means for exchanging ions and said flushing means being separated from each other by means for selectively permeating ions;

means creating an electric potential between said anode and said cathode whereby the means for exchanging ions are regenerated by hydrogen and hydroxyl ions migrating in opposite directions from said electrodes; and

means for causing said cations and anions migrating toward said flushing means to enter said flushing means at substantially the same rate.

17. An apparatus for demineralizing a pre-softened aqueous liquid containing salts, which comprises:

a cathode;

an anode;

a flushing means;

a means for exchanging anions; and

a first and a second means for exchanging cations, said first means for exchanging cations positioned between said flushing means and said second means for exchanging cations;

and further comprising, means for passing the liquid sequentially through the first means for exchanging cations, the means for exchanging anions, and therefrom through the second means for exchanging cations before exiting the apparatus.

18. The apparatus of claim 17 wherein

the means for exchanging cations is a cation exchange resin, and

the means for exchanging anions is an anion exchange resin.

19. The apparatus of claim 17 wherein the flushing means is a dilute salt solution.

20. The apparatus of claim 17 wherein the apparatus is insulated to retain heat within said apparatus.

21. The apparatus of claim 17 wherein

said means for selectively permeating cations is a cation-permeable membrane which is substantially impermeable to anions, the liquid and a flusing solution;

and

said means for selectively permeating anions is an anion-permeable membrane which is substantially impermeable to cations, the liquid and the flushing solution.

22. The apparatus of claim 17, containing

two anodes,

one cathode,

two means for exchanging cations, and

two means for exchanging anions, wherein

said first means for exchanging cations is positioned between the first anode and a first flushing means;

said first means for exchanging anions is positioned between the first flushing means and the cathode;

said second means for exchanging cations is positioned between a second flushing means and the second anode; and

said second means for exchanging anions is positioned between the cathode and the second flushing means;

said apparatus further comprising means for transferring the liquid from the first means for exchanging of cations to the first means for exchanging anions, therefrom to the second means for exchanging cations before exiting the apparatus.

23. The apparatus of claim 17, further comprising at least one heat exchange means for transfer of heat from solutions exiting said apparatus to said aqueous liquid to be demineralized prior to passing into the first means for exchanging cations.

24. A multi-compartmented apparatus for demineralizing an aqueous liquid containing salts, which comprises in combination:

(a) a cathode chamber containing a cathode;

(b) an anode chamber containing an anode;

(c) a flushing chamber positioned between said anode chamber and said cathode chamber;

(d) a first ion exchange chamber containing cation exchange resins on one side of said flushing chamber and separated from said flushing chamber by a cation permeable membrane;

(e) a second ion exchange chamber containing anion exchange resins on the other side of said flushing chamber and separated from said flushing chamber by an anion permeable membrane;

(f) a third ion exchange chamber containing cation exchange resins positioned between said first anion exchange chamber and said anode chamber and separated from each by a cation permeable membrane;

(g) means to impress a direct electric current across said cathode and said anode to create an electric potential in said first ion exchange chamber, said second ion exchange chamber, said third ion exchange chamber, and said flushing chamber;

(h) means to pass the liquid to be treated sequentially through said first ion exchange chamber, said second ion exchange chamber, and said third ion exchange chamber; and

(i) means for passing a flushing solution through said flushing chamber.

25. The multi-compartmented apparatus of claim 24 wherein the first ion exchange chamber, the second ion exchange chamber, and the third ion exchange chamber are sized so as to cause cations and anions to enter said flushing chamber at substantially the same rate.

26. The multi-compartmented apparatus of claim 24 and further including heat means to increase the temperature of the liquid to be treated.

27. The multi-compartmented apparatus of claim 24 wherein the outside of said apparatus is insulated in order to retain latent heat therein.

28. The multi-compartmented apparatus of claim 24 and further including means for automatically controlling the flow of the flushing solution passing through the flushing chamber.

29. The multi-compartmented apparatus of claim 24 wherein the aqueous liquid containing salt has been pre-softened.

32. The multi-compartmented apparatus of claim 24 and further including means for recombining oxygen and hydrogen gases generated at the anode and cathode.

33. The apparatus of claim 32 wherein the means for combining the oxygen and hydrogen gases forms water for reuse in said apparatus.

30. A method of simultaneously decreasing the salt content of a first solution and increasing the salt content of a second solution which comprises:

(a) passing the first solution sequentially through at least a first means for exchanging cations, a first means for exchanging anions, and a second means for exchanging cations;

the cation exchange means containing hydrogen ions and the anion exchange means containing hydroxyl ions, whereby cations and anions disassociated from the salt content of said first solution are exchanged for the hydrogen ions and the hydroxyl ions, thereby reducing the salt content in the first solution;

(b) establishing an electric potential across the ion exchange means in order to migrate hydrogen ions and hydoxyl ions in opposite directions for exchange with the cations and anions in the means for exchanging ions thereby restoring said hydrogen and hydroxyl ions to the means, and in order to migrated displaced cations and anions in opposite directions; and

(c) passing said second solution across the direction of the ion migration in order to receive the cations migrating out from said first means for exchanging cations and the anions migrating out of the means for exchanging anions, whereby the salt content of said second solution is increased.

31. The method of claim 30 wherein said first solution is pre-softened water.

34. A multi-compartmented apparatus for demineralizing a pre-softened aqueous liquid containing salts including chlorine ions, which comprises:

a cathode;

an anode;

a flushing chamber positioned between said anode and said cathode;

a first ion exchange chamber containing cation exchange resins on one side of said flushing chamber and a second ion exchange chamber containing anion exchange resins on the other side of said flushing chamber;

a third ion exchange chamber containing cation exchange resins positioned between said anion exchange chamber and said anode; and

means to impress a direct electric current across said cathode and said anode to create an electric potential in said first, second, and third ion exchange chambers and said flushing chamber, the position of said third ion exchange chamber between said second ion exchange chamber and said anode insulating against the migration of chloride ions to said anode to prevent chlorine formation.

35. A process for demineralizing an aqueous liquid containing salts, comprising:

(a)sequentially passing the liquid through means for exchanging cations containing hydrogen ions and means for exchanging anions containing hydroxyl ions whereby cations and anions disassociated from the salts are exchanged for the hydrogen ions and the hydroxyl ions thereby reducing the concentration of salts in the outflowing liquid;

(b) applying electric potential across the direction of flow of the liquid whereby hydrogen ions and hydroxyl ions migrating in opposite directions are exchanged for the cations and anions in the ion exchanging means thereby restoring said hydrogen and hydroxyl ions to the means, and causing the displaced cations and anions to migrate in opposite directions; and

(c) passing a series of flushing solutions across the direction of the ion migration, one solution capable of receiving the cations migrating out from said means for exchanging cations and another solution capable of receiving the anions migrating out from the means for exchanging anions whereby salts are formed and discharged with the flushing solutions.

36. The process of claim 35 in which the first two flushing solutions are mixed to form a third flushing solution which passes across the direction of the ion migration between the first and second flushing solutions.

37. The process of claim 35 wherein the liquid to be demineralized is raw water.

38. An apparatus for demineralizing an aqueous liquid containing salts, which comprises:

a cathode and an anode,

means for exchanging cations and means for exchanging anions,

means for passing the liquid sequentially through the means for exchanging cations and the means for exchanging anions before exiting the apparatus; and

flushing means including a first flushing solution to receive the cations migrating out from said means for exchanging cations, a second flushing solution to receive the anions migrating out from said means for exchanging anions, and a third flushing solution to supply anions and cations, respectively, to said first and second flushing solutions.

39. The apparatus of claim 38 and further including a mixing means for mixing the first and second flushing solutions to form the third flushing solution.