Electrolyzer and a method of operating the same

• US 5,766,438 A
• Filed: 02/18/1997
• Issued: 06/16/1998
• Est. Priority Date: 12/26/1990
• Status: Expired due to Fees

• Current Assignee: Unitika Limited
• Original Assignee: Unitika Limited
• Inventors: Kano, Hiroshi, Sasaki, Masanori, Obara, Hideto, Ishibashi, Tadaya
• Primary Examiner(s): Phasge, Arun S.
• Assistant Examiner(s): STARSIAK, JOHN S
• Application Number:
  US08/801,557
• Time in Patent Office: 483 Days
• Field of Search: 204/520, 204/522, 204/525, 204/528, 204/581, 204/627, 204/630, 204/633, 204/640
• US Class Current: 204/520
• CPC Class Codes: B01D 61/00 Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor separation of gases or vapours by diffusion B01D53/22
• CPC Class Codes: B01D 61/44 Ion-selective electrodialysis
• CPC Class Codes: B01D 61/464 comprising the membrane sequence CC
• CPC Class Codes: B01D 61/52 Accessories; Auxiliary operation
• CPC Class Codes: C02F 1/469 by electrochemical separation, e.g. by electro-osmosis, electrodialysis, electrophoresis
• CPC Class Codes: C02F 2201/003 Coaxial constructions, e.g. a cartridge located coaxially within another
• CPC Class Codes: C23F 1/36 for etching aluminium or alloys thereof
• CPC Class Codes: C23G 1/36 Regeneration of waste pickling liquors

Abstract

In an electrolyzer provided according to this invention, the polarity of electrodes is periodically inverted at very short intervals. This has the effect of allowing gases to be generated uniformly all over the surface of each electrode in the form of extremely small bubbles instead of being formed in specific positions in the form of large bubbles as is the case with a conventional electrolyzer in which a direct current is allowed to flow without changing the flow direction. Thus the surfaces of electrodes are prevented from being covered with bubbles, and the flow of liquids along the surfaces of electrodes is not disturbed by the bubbles any more.

Claims

1. A method for operating an electrolyzer for treating an object liquid, said electrolyzer comprising:

a cylindrical anode formed as an outer wall and having an inner surface comprising a corrosion-resistant metal;

a cylindrical cathode coaxially arranged at a position close to said inner surface of said anode;

a plurality of ion exchange membranes coaxially arranged between said anode and cathode standing oppositely for functioning as electrically conductive partition diaphragms to control selection of ions electrophoretically passing therethrough;

said anode and one of said membranes forming an anode chamber, said cathode electrode and another one of said membranes forming a cathode chamber, and isolating chamber means defined by any two of said ion exchange membranes for selectively electrophoretically separating and removing and concentrating said ions;

circumferential passage means in flow communication with said isolating chamber for uniformly discharging said object liquid from said isolating chamber means after said object liquid has been subjected to treatment in said isolating chamber means;

said method comprising;

applying to the anode a polarity which is periodically and repeatedly inverted so that a percentage of time during which the anode electrode plate is anodic relative to the cathode electrode plate is 60 to 99.9 percent, while a percentage of time during which the anode electrode plate is cathodic relative to the cathode electrode plate is 0.1 to 40 percent, and said time during which the anode electrode plate is anodic relative to the cathode electrode plate is 10 ms (milliseconds) to 1,000 min (minutes), while said time during which the anode electrode plate is cathodic relative to the cathode electrode plate is 1 ms (millisecond) to 10 min (minutes);

monitoring a wave form of a voltage applied during the respective polarities from a power source having a function capable of changing the respective times being used;

flowing a first liquid into said cathode chamber and flowing a second liquid into said anode chamber; and

flowing said second liquid out of said anode chamber and flowing said first liquid out of said cathode chamber, respectively, into said passage means;

whereby very small bubbles generated all over surfaces of said cathode and anode are discharged by each of said first and second liquids, and sedimentation of different kinds of substances onto surfaces of said anode and cathode is suppressed.

2. A method of operating an electrolyzer as set forth in claim 1 for treatment of said object liquid wherein said object liquid comprises transition metal cations, halogen compounds, and sodium or potassium containing alkaline agents being added to said object liquid, said halogen compounds forming halogen ions accompanied by metallic ions which are electrophoretically moved into said cathode chamber, whereby soluble halides are formed from said halogen compounds and insoluble metal compounds are formed from said metallic ions, separating said soluble halides from said insoluble metal compounds, essentially continuously removing said first liquid containing said separated soluble halides from said electrolyzer, and analyzing said first liquid to maintain a concentration of said halides in said cathode chamber of said electrolyzer at a saturated concentration or less.

3. A method of operating an electrolyzer as set forth in claim 2 wherein said object liquid comprising said halogen compounds is isolated from said anode chamber by said ion exchange membranes, and said second liquid is selected to protect the inner surface of said anode electrode plate from corrosion by halogen ions diffusedly moved into said anode chamber.

4. A method of operating an electrolyzer as set forth in claim 3 wherein said object liquid is obtained from washings discharged from an operating line of a pickling tank in equipment for surface treatment of steel materials in an acid bath, wherein said object liquid comprises a mixture of nitric acid and hydrofluoric acid, said nitric acid is replenished to said acid bath for metal treatment and is supplied from said anode chamber to said acid bath, said quantity supplied to said acid bath being selected to maintain a concentration of halogen ions at 500 milligrams per liter or less in said acid bath.

5. A method of operating an electrolyzer as set forth in claim 2 wherein said object liquid is obtained from washings discharged from an operating line of a pickling tank in equipment for surface treatment of steel materials in an acid bath, wherein a concentrated liquid of said soluble halides is added to said second liquid continuously taken out of said cathode chamber and then the resulting mixed liquids are supplied to another electrolyzer, where cations are diffused into a cathode chamber of said other electrolyzer, and remaining anions are recovered in the form of free acids, sodium ions or potassium ions, which have been electrophoretically moved into the cathode chamber of said other electrolyzer, whereby sodium hydroxide or potassium hydroxide are formed, and an alkaline agent composed of said sodium hydroxide or potassium hydroxide is recovered for use as a neutralizing agent for said washings.

6. A method for operating a plurality of electrolyzers for treating an object liquid comprising a target substance, said electrolyzer comprising:

a cylindrical anode formed as an outer wall and having an inner surface;

a cylindrical cathode coaxially arranged at a position close to said inner surface of said anode;

a single or a plurality of ion exchange membranes coaxially arranged between said anode and cathode standing oppositely for functioning as electrically conductive partition diaphragms to control selection of ions electrophoretically passing therethrough;

isolating chamber means composed of said cylindrical anode, said cylindrical cathode and said single or plurality of ion exchange membranes for selectively electrophoretically separating and removing and concentrating said ions;

circumferential passage means in flow communication with said isolating chamber for uniformly discharging said object liquid from said isolating chamber means after said object liquid has been subjected to treatment in said isolating chamber means;

said method comprising;

using said plurality of said electrolyzers, the number of said electrolyzers constituting said plurality being determined by;

supplying an electric current to an electrode surface of a selected one of said electrolyzers and passing said electric current through said selected electrolyzer;

determining a quantity of electricity required for said selected electrolyzer;

determining a quantity of electricity per unit time required for electrophoretically separating the target substance divided by said quantity of electricity required for said selected electrolyzer;

determining a number of said electrolyzers required; and

arranging the required number of said electrolyzers in series, with cathode terminals and anode terminals of respective said electrolyzers being alternately connected in series, and said terminals on both final ends being connected with an electrical power source.

7. A method of operating electrolyzers as set forth in claim 6, wherein an oxygen gas and a hydrogen gas are formed by electrolysis of water molecules during electrolytic reactions at said cathode and anode electrodes, and wherein said gases are introduced into an oxidizing catalyzer for conversion into water, or said gases are released into the atmosphere.

8. A method of operating electrolyzers as set forth in claim 7, wherein concentrations of the target substances and compositions of the respective liquids are simultaneously analyzed by analytical control means provided in a liquid-supply line supplying at least one of said electrolyzers to monitor operating conditions of said electrolyzer.

9. A method of operating electrolyzers as set forth in claim 6, wherein concentrations of the target substances and compositions of the respective liquids are simultaneously analyzed by analytical control means provided in a liquid-supply line supplying said electrolyzer to monitor operating conditions of said electrolyzer.