Method and apparatus for capacitive deionization and electrochemical purification and regeneration of electrodes

• US 6,309,532 B1
• Filed: 04/12/1999
• Issued: 10/30/2001
• Est. Priority Date: 05/20/1994
• Status: Expired due to Fees

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Farmer, Joseph C., Murguia, Laura, Tran, Tri D.
• Primary Examiner(s): Gorgos, Kathryn
• Assistant Examiner(s): Feely, Michael J
• Application Number:
  US09/289,876
• Time in Patent Office: 932 Days
• Field of Search: 204/551, 204/554, 204/555, 204/647, 204/660, 204/661, 204/663, 204/267, 204/269, 204/278.5, 360/500, 205/687, 205/688
• US Class Current: 205/687
• CPC Class Codes: B01D 15/36 involving ionic interaction
• CPC Class Codes: B01D 15/361 Ion-exchange
• CPC Class Codes: B01D 15/362 Cation-exchange
• CPC Class Codes: B01D 15/363 Anion-exchange
• CPC Class Codes: B01J 47/08 subjected to a direct electric current
• CPC Class Codes: B01J 49/30 Electrical regeneration
• CPC Class Codes: C02F 1/42 by ion-exchange ion-exchange in general B01J
• CPC Class Codes: C02F 1/46104 Devices therefor; Their operating or servicing
• CPC Class Codes: C02F 1/46109 Electrodes
• CPC Class Codes: C02F 1/4691 Capacitive deionisation
• CPC Class Codes: C02F 2001/46119 Cleaning the electrodes
• CPC Class Codes: C02F 2001/46123 Movable electrodes
• CPC Class Codes: C02F 2001/46128 Bipolar electrodes
• CPC Class Codes: C02F 2001/46138 Electrodes comprising a substrate and a coating
• CPC Class Codes: C02F 2001/46152 characterised by the shape or form electrodes in particulate form or with conductive or non-conductive particles between them C02F1/46114
• CPC Class Codes: C02F 2001/46161 Porous electrodes
• CPC Class Codes: C02F 2101/006 Radioactive compounds
• CPC Class Codes: C02F 2201/4611 Fluid flow
• CPC Class Codes: C02F 2201/46115 Electrolytic cell with membranes or diaphragms
• CPC Class Codes: C02F 2201/4612 Controlling or monitoring
• CPC Class Codes: C02F 2201/46125 : Electrical variables
• CPC Class Codes: C02F 2201/46145 : Fluid flow
• CPC Class Codes: C02F 2201/46175 : Electrical pulses
• CPC Class Codes: C02F 2209/001 : Upstream control, i.e. monitoring for predictive control
• CPC Class Codes: C02F 2209/003 : Downstream control, i.e. outlet monitoring, e.g. to check the treating agents, such as halogens or ozone, leaving the process
• CPC Class Codes: C02F 2209/02 : Temperature
• CPC Class Codes: C02F 2209/05 : Conductivity or salinity
• CPC Class Codes: C02F 2209/06 : pH
• CPC Class Codes: C02F 2303/16 : Regeneration of sorbents, filters
• CPC Class Codes: G01N 2030/0035 : electrical field
• CPC Class Codes: G01N 2030/645 : electrical conductivity detectors
• CPC Class Codes: G01N 2030/8881 : Modular construction, specially adapted therefor
• CPC Class Codes: G01N 30/02 : Column chromatography
• CPC Class Codes: G01N 30/60 : Construction of the column
• CPC Class Codes: G01N 30/6095 : Micromachined or nanomachined, e.g. micro- or nanosize
• CPC Class Codes: G01N 30/96 : using ion-exchange G01N30/02, G01N30/90 take precedence

Abstract

An electrically regeneratable electrochemical cell (30) for capacitive deionization and electrochemical purification and regeneration of electrodes includes two end plates (31, 32), one at each end of the cell (30). A new regeneration method is applied to the cell (30) which includes slowing or stopping the purification cycle, electrically desorbing contaminants and removing the desorbed contaminants. The cell (30) further includes a plurality of generally identical double-sided intermediate electrodes (37-43) that are equidistally separated from each other, between the two end electrodes (35, 36). As the electrolyte enters the cell, it flows through a continuous open serpentine channel (65-71) defined by the electrodes, substantially parallel to the surfaces of the electrodes. By polarizing the cell (30), ions are removed from the electrolyte and are held in the electric double layers formed at the carbon aerogel surfaces of the electrodes. The cell (30) is regenerated electrically to desorb such previously removed ions.

Claims

1. An electrochemical method for deionizing a fluid comprising ions and regenerating electrodes employed in said method, said method comprising:

(1) flowing said fluid through at least one open channel defined between at least three pair of intermediate electrodes of a battery of electrochemical cells to deionize said fluid to produce a deionized fluid, said open channel having no dimension open to the exterior of said battery;

(2) slowing or stopping the flow of said fluid;

(3) contacting said electrodes with a regenerant fluid and regenerating said electrodes of said battery to produce a waste fluid comprising said ions; and

(4) flowing more of said fluid through said battery after step (3) to deionize more of said fluid.

2. The method of claim 1 wherein said fluid is passed through said cells of said battery in a serpentine path and said regenerating includes electrically discharging the electrodes to release accumulated ions from said electrodes.

3. The method of claim 2 wherein said electrodes comprise a carbon aerogel composite.

4. The method of claim 2 wherein said regenerating of said electrodes in step (3) is conducted by shorting said cells of said battery or reversing the polarity of said cells of said battery from that of a polarity applied to said cells in step (1).

5. The method of claim 4 wherein said regenerant fluid is selected from the group consisting of an oxidizing agent, chelating agent, organic acid, and surfactant, and is contacted with said electrodes in step (3).

6. The method of claim 2 further comprising step (5), stopping or slowing the deionization of more of said fluid flowing through said battery during step (4), to regenerate said electrodes of said battery.

7. The method of claim 1 wherein said cells comprise a plurality of double-sided intermediate electrodes and said regenerant comprises an oxidizing agent selected from the group consisting of ozone, hydrogen peroxide, Fenton'"'"'s reagent, silver (II), cobalt (III), iron (III), hypochlorite (ClO⁻

), peroxymonosulfate and peroxydisulfate (S₂O₈<sup>−

2</sup>).

8. The method of claim 1 wherein said flow is stopped for at least 5 minutes in step (3) and said electrodes are soaked in said regenerant fluid.

9. The method of claim 1 wherein said regenerant fluid comprising a concentration of ions which is the same or less than that contained in said fluid is passed through said battery in step (3).

10. The method of claim 1 wherein said regenerant fluid comprising a concentration of ions which is the same or greater than that in said fluid is passed through said battery in step (3) at a rate at least as fast as a flow rate of said fluid through said battery in step (1), to regenerate said electrodes.

11. The method of claim 1 wherein said regenerant fluid is passed through said battery subsequent to step (2) in step (3) at a flow rate which is greater than that of said fluid passed through said battery in step (1).

12. The method of claim 1 wherein said regenerant fluid is selected from the group consisting of deionized water, recycled deionized fluid obtained from step (1), and recycled portions of said waste fluid obtained from step (3).

13. The method of claim 1 wherein said fluid is passed through said cells of said battery in a serpentine path.

14. The method of claim 13 wherein said electrodes comprise a carbon aerogel composite.

15. An electrochemical method for deionizing a fluid comprising ions and regenerating electrodes employed in said method, said method comprising:

(1) flowing said fluid through an open channel defined between at least three pair of intermediate electrodes of a battery of electrochemical cells to deionize said fluid, said open channel having no dimension open to the exterior of said battery;

(2) interrupting the flow of said fluid;

(3) contacting said electrodes with a regenerant fluid comprising an oxidizing agent to regenerate said electrodes of said battery; and

(4) flowing more of said fluid through said battery after step (3) to deionize more of said fluid.

16. The method of claim 15 wherein said fluid is passed through said cells of said battery in a serpentine path and said electrodes are electrically regenerated in step (3).

17. The method of claim 16 wherein said cells comprise a plurality of double-sided intermediate electrodes and said flow is stopped for at least 15 minutes in step (2) and said electrodes are soaked in said regenerant fluid in step (3).

18. The method of claim 15 wherein in step (3) includes electrically regenerating said electrodes by shorting said cells of said battery or reversing the polarity of said cells of said battery from a polarity applied to said cells in step (1).

19. The method of claim 15 wherein said electrodes comprise an carbon aerogel composite.

20. The method of claim 15 wherein said regenerant comprises an oxidizing agent selected from the group consisting of ozone, hydrogen peroxide, Fenton'"'"'s reagent, silver (II), cobalt (III), iron (III), hypochlorite (ClO⁻

), peroxymonosulfate and peroxydisulfate (S₂O₈<sup>−

2</sup>).

21. An electrochemical method for deionizing a fluid comprising ions and regenerating electrodes employed in said method, said method comprising:

(1) flowing said fluid through at least one open channel defined between at least three pair of intermediate electrodes of a battery of electrochemical cells to deionize said fluid at a given applied polarity above about 1.2 V to about 1.8V across said open channels, said open channels having no dimension open to the exterior of said battery and said electrodes comprising a carbon aerogel composite;

(2) slowing or stopping the flow of said fluid for a period of at least 5 minutes;

(3) contacting said electrodes with a regenerant fluid and regenerating said electrodes of said battery at a shorted or reversed polarity to produce a waste fluid comprising said ions;

(4) flowing more of said fluid through said battery after step (3) to deionize more of said fluid; and

(5) interrupting said flow of more of said fluid to electrically regenerate said electrodes in the presence of a second regenerant fluid comprising (a) recycled portions of said waste fluid, (b) inleted or recycled portions of said fluid and/or (c) a fluid comprising a lower concentration of said ions than contained in said waste fluid.

22. The method of claim 21 wherein said waste fluid is fast flushed from said battery.

23. A capacitive deionization-regeneration system adapted for operating a deionization cycle and a regeneration cycle, comprising in combination:

(1) a battery of at least four electrochemical cells, each cell comprising at least one pair of adjacent electrodes including an electrosorptive medium having a high specific surface area and sorption capacity, formed on one or more surfaces of said electrodes;

each pair of said adjacent electrodes including at least one aperture; and

each pair of said adjacent electrodes forming an open channel, said open channel adapted to fluidly communicate with a subsequent open channel via said aperture to allow a fluid to flow across said electrosorptive medium and through the battery in a serpentine path,

(2) an electrical circuit for controlling the operation of said battery of cells, said electrical circuit adapted for shorting or switching the polarity of each pair of said electrodes during said regeneration cycle of said electrodes; and

(3) a fluid circuit for regulating the flow of a fluid through said battery under the control of said electrical circuit, in order to slow or stop a fluid flow through said cells for predetermined time intervals during said regeneration cycle, said fluid circuit comprises an outlet adapted for deionized fluid obtained from a deionization cycle operable at a given polarity, and a second outlet adapted for regenerated waste fluid obtained from said regeneration cycle operable at a shorted or reversed polarity relative to said given polarity and at a slower flow rate than the one used during said deionization cycle.

24. The system of claim 23 wherein said electrosorptive medium of said electrodes comprise a carbon aerogel composite.

25. The system of claim 23 wherein said electrosorptive medium is composed essentially of any, or a combination of:

carbon aerogel composite;

a packed volume of particulate carbon, carbon aerogel, metal, or Buckminster fullerene;

a carbide or a composite of carbides that are stable at high temperatures, chemically resistant, and highly conductive with a resistivity ranging between about 10 μ

ohm-cm and 2000 μ

ohm-cm, selected from a group consisting essentially of TiC, ZrC, VC, NbC, TaC, UC, MoC, WC, Mo₂C, Cr₃C₂, or Ta₂C;

a packed volume of porous titanium, platinum or other metal;

a metal sponge, or metallic foam;

reticulated vitreous carbon (RVC) impregnated in resorcinal/formaldehyde carbon aerogel;

or a porous, conductive screen including an array of holes that have been photolithographically formed to optimize the volumetric specific surface area of said screen.

26. The system of claim 23 wherein said fluid circuit comprises a recycle conduit from said second outlet for said waste fluid to a fluid inlet to said battery.

27. The system of claim 23 wherein said fluid circuit comprises a recycle conduit from said second outlet for said waste fluid to an inlet to said battery.

28. The system of claim 23 wherein said fluid circuit comprises a recycle conduit from said outlet for said deionized fluid to an inlet to said battery.

29. An electrically regeneratable electrochemical cell for use in a capacitive deionization apparatus, said cell comprising the following corrosion resistant components:

two end plates, one at each end of the cell;

two end electrodes comprising ceramics, one at each end of the cell, adjacent to the end plates;

an insulator layer interposed between one end plate and an adjacent one of said end electrodes;

an insulator layer interposed between the other end plate and the other one of said end electrodes;

two or more intermediate electrodes comprising ceramics, disposed between said two end electrodes;

each end electrode and intermediate electrodes including an electrosorptive medium having a high specific surface area and sorption capacity; and

wherein said corrosion resistant components adapted to withstand deleterious effects of oxidative regenerants contacting said end electrodes or said intermediate electrodes.

30. An electrochemical method for deionizing a fluid comprising ions and regenerating electrodes employed in said method, said method comprising:

(1) flowing said fluid through at least one open channel defined between at least three pair of intermediate electrodes of a battery of electrochemical cells to deionize said fluid to produce a deionized fluid, said open channel having no dimension open to the exterior of said battery;

(2) contacting said electrodes with a regenerant fluid added to said fluid and regenerating said electrodes of said battery to produce a waste fluid comprising said ions; and

(3) flowing said regenerant fluid through said battery at a faster rate than said flowing of said fluid through said battery in step (1).