WO2013035762A1 - Electrolysis system and electrolysis method for the same - Google Patents

Electrolysis system and electrolysis method for the same Download PDF

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Publication number
WO2013035762A1
WO2013035762A1 PCT/JP2012/072668 JP2012072668W WO2013035762A1 WO 2013035762 A1 WO2013035762 A1 WO 2013035762A1 JP 2012072668 W JP2012072668 W JP 2012072668W WO 2013035762 A1 WO2013035762 A1 WO 2013035762A1
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WO
WIPO (PCT)
Prior art keywords
cathode
anode
electrolysis system
cation exchange
compartment
Prior art date
Application number
PCT/JP2012/072668
Other languages
French (fr)
Inventor
Hideo Nitta
Masashi Hosonuma
Yasunori Fukushima
Ryojin OBINATA
Original Assignee
Aquaecos Ltd.
Permelec Electrode Ltd.
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Filing date
Publication date
Application filed by Aquaecos Ltd., Permelec Electrode Ltd. filed Critical Aquaecos Ltd.
Priority to KR1020147009212A priority Critical patent/KR20140074927A/en
Priority to JP2013548687A priority patent/JP5716100B2/en
Priority to CN201280043774.1A priority patent/CN103781731A/en
Publication of WO2013035762A1 publication Critical patent/WO2013035762A1/en

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    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
    • C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
    • C02F1/46104—Devices therefor; Their operating or servicing
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
    • C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
    • C02F1/46104—Devices therefor; Their operating or servicing
    • C02F1/46109—Electrodes
    • C02F2001/46119—Cleaning the electrodes
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
    • C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
    • C02F1/46104—Devices therefor; Their operating or servicing
    • C02F1/46109—Electrodes
    • C02F2001/46133—Electrodes characterised by the material
    • C02F2001/46138—Electrodes comprising a substrate and a coating
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
    • C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
    • C02F1/46104—Devices therefor; Their operating or servicing
    • C02F1/46109—Electrodes
    • C02F2001/46133—Electrodes characterised by the material
    • C02F2001/46138—Electrodes comprising a substrate and a coating
    • C02F2001/46142—Catalytic coating
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
    • C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
    • C02F1/46104—Devices therefor; Their operating or servicing
    • C02F1/46109—Electrodes
    • C02F2001/46133—Electrodes characterised by the material
    • C02F2001/46138—Electrodes comprising a substrate and a coating
    • C02F2001/46147—Diamond coating
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2201/00—Apparatus for treatment of water, waste water or sewage
    • C02F2201/46—Apparatus for electrochemical processes
    • C02F2201/461—Electrolysis apparatus
    • C02F2201/46105—Details relating to the electrolytic devices
    • C02F2201/46115—Electrolytic cell with membranes or diaphragms
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2201/00—Apparatus for treatment of water, waste water or sewage
    • C02F2201/46—Apparatus for electrochemical processes
    • C02F2201/461—Electrolysis apparatus
    • C02F2201/46105—Details relating to the electrolytic devices
    • C02F2201/46195—Cells containing solid electrolyte

Definitions

  • the present invention relates to an electrolysis system and an electrolysis method for the same in which non-purified water containing a trace amount of alkali earth metal ions, such as calcium ion and magnesium ion is applied as raw material, having a construction in which the raw material water is supplied to a cathode compartment, featuring that scale of hydroxide and others of the alkali earth metals can be prevented from depositing on the cathode surface.
  • non-purified water containing a trace amount of alkali earth metal ions such as calcium ion and magnesium ion
  • the water treatment applying electrolysis reaction is widely employed for such purposes as production of functional water by electrolysis, ozone water and electrolysis water, sterilization, and decomposition removal of toxic substance.
  • the reactor which is used for these processes has a construction generally having an anode, a cathode and an ion exchange membrane disposed inbetween or a porous diaphragm accommodated in a case and is called an electrolyzer or an electrolytic cell.
  • This type of electrolyzer or electrolytic cell comprises a diaphragm, an anode compartment separated by the diaphragm, a cathode compartment separated by the diaphragm, an anode provided in the anode compartment and a cathode provided in the cathode compartment, and a two-compartment type electrolysis system and a three-compartment type electrolysis system are known.
  • the two-compartment type electrolysis system includes the diaphragm process electrolysis system, the cation exchange membrane process electrolysis system and the solid polymer electrolyte process electrolysis system as a special process of this type.
  • the diaphragm process electrolysis system applies a porous diaphragm as diaphragm
  • the cation exchange membrane process electrolysis system applies a cation exchange membrane as diaphragm
  • the solid polymer electrolyte process electrolysis system applies a cation exchange membrane with the anode and the cathode tightly attached on each surface of the cation exchange
  • membrane as solid polymer electrolyte, to constitute an electrolysis system that can electrolyze even purified water with a small electric conductivity.
  • the three-compartment type electrolysis system is provided with a cation exchange membrane and an anion exchange membrane as diaphragm to separate the anode compartment and the cathode compartment to form an intermediate compartment between the cation exchange membrane and the anion exchange membrane.
  • Various kinds of functional water and ozone water are produced by these electrolysis systems.
  • the present invention relates to an electrolysis system and an electrolysis method for the same in which non-purified water containing a trace amount of alkali earth metal ions, such as calcium ion and magnesium ion is applied as raw material to be electrolyzed; more in details, the present invention proposes a system and a method for the same which can ameliorate the deposition problem of hydroxide and others on the cathode for an ozone water production system by electrolysis and an ozone water production method for the same, a functional water production system and a functional water production method for the same and an electrolysis water production system and an electrolysis water production method for the same, a sterilization process, a waste water treatment process, etc., applying non-purified water as raw material water. Further, the electrolysis system and the electrolysis method for the same by the present invention can contribute to solving similar problems in other fields of applications.
  • non-purified water containing alkali earth metal ions such as calcium ion and magnesium ion is applied as raw material in the waste fluid treatment process or the production processes of function waters including alkaline ionized water.
  • alkali earth metal ions such as calcium ion and magnesium ion
  • the pH value of the catholyte increases with time of electrolysis first from the cathode surface and alkali earth metal ions deposit with a trace amount of calcium as the chief element in the form of hydroxide, oxides and carbonate of them on the cathode surface as non-conducting scale (water scale), causing dysfunction of electrolysis.
  • PTL 1 and PTL 2 propose a method of applying acid for the cathode compartment solution; however the construction becomes complicated and safety operation becomes difficult.
  • PTL 3 proposes suppression of cathode deposit by proving the production system of electrolysis water with an auxiliary tank and a multiple number of electrode assemblies for alternating use at a preset time interval. This system design, however, needs a large installation, leading to increased costs.
  • PTL 4 describes, in detail, the method for removing deposits by acid cleaning, etc. to be made at a regular shut-down of the system operation, which causes complicated procedures of operation.
  • PTL 5 suggests prevention of deposition on the cathode by acidifying the non-diaphragm electrolytic cell with hydrochloric acid. This process applies strong acid chemical solutions including hydrochloric acid, which is not only disadvantageous in operation safety or cost but strong acidity may be unacceptable depending on application.
  • PTL 6 introduces such operation manner that the anode and the cathode of the electrolytic cell are reversed at the time of deterioration in electrolysis performance so as to recover the performance through reverse current.
  • cathode functions as anode temporarily with applied reverse current and constituent metal elements elute.
  • highly corrosion resistant valve metals may be employed for the cathode.
  • an expensive precious metal coating is required on the cathode surface to decrease electrolytic overvoltage.
  • the cathodic reduction of the anode which temporarily turns to the cathode and the deterioration due to concomitant hydrogen embrittlement are feared.
  • PTL 7 introduces the production process of hypochlorite through electrolysis of an aqueous solution of chloride by a non-diaphragmatic electrolysis method, applying a cathode covered with a reduction preventive film coated on a low hydrogen overvoltage layer formed on the conductive substrate.
  • An organic cation exchange membrane substance or an inorganic cation exchange membrane substance or a substance of the mixture of these is used as the reduction preventive film.
  • This reduction preventive film is to prevent hypochlorous acid ion from reducing at the cathode in the non-diaphragmatic electrolysis method, in which the product at the anode directly contacts the cathode, not to prevent cathode deposition, chiefly alkali earth metal hydroxide.
  • any reduction preventive film is not required unlike PTL 7, to prevent hypochlorous acid ion, the product at the anode, from reducing.
  • the present invention aims to provide an electrolysis system and an electrolysis method of the same which can prevent scales of hydroxide and others of the alkali earth metal from depositing on the cathode surface, when non-purified water containing alkali earth metal ions is applied as raw material for the electrolysis method and the electrolysis system using a diaphragm.
  • the present invention prevents scales of hydroxide and others of the alkali earth metal from depositing on the cathode surface, by covering substantially the entire surface of the cathode with the cation exchange resin-contained, alkali earth metal scale- preventive film in the electrolysis system having a configuration comprising a diaphragm, an anode compartment separated by the diaphragm, a cathode compartment separated by the diaphragm, an anode provided in the anode compartment, a cathode provided in the cathode compartment, and raw material water containing alkali earth metal ions supplied to the cathode compartment
  • the present invention constructs a diaphragm process electrolysis system applying a porous diaphragm as the diaphragm.
  • the present invention constitutes a cation exchange membrane process electrolysis system applying cation exchange membrane as the diaphragm.
  • the present invention constitutes a solid polymer electrolyte type electrolysis system, wherein the anode and the cathode are adhered to each surface of the cation exchange membrane, respectively.
  • the present invention constitutes a three-compartment type electrolysis system comprising a cation exchange membrane and an anion exchange membrane provided between the anode compartment and the cathode compartment as diaphragm to separate the anode compartment and the cathode compartment to form an intermediate compartment between the cation exchange membrane and the anion exchange membrane.
  • the present invention applies conductive diamond, lead dioxide, precious metal or precious metal oxide as anode catalyst for the anode.
  • the present invention provides a current-carrying member for the anode and the cathode.
  • the present invention mixes filler in fiber or powder form comprising inorganic or organic materials in the cation exchange resin-contained, alkali earth metal scale- preventive film as a reinforcing material of the film.
  • the present invention mixes ceramics particles having the cation exchange function in the cation exchange resin-contained, alkali earth metal scale-preventive film.
  • the present invention applies at least one kind of ceramics particles from among apatite, perovskite type oxide and zeolite, as the ceramics particles having the cation exchange function.
  • the present invention applies a plate material, a porous metal, a fiber metal form, a mesh or a hole-punched metal, as the cathode substrate.
  • the present invention provides an electrolysis method to electrolyze raw material water containing alkali earth metal ions including calcium ion and magnesium ion, by applying the electrolysis system.
  • the electrolysis system and the electrolysis method of the same applying a diaphragm can suppress depositions including hydroxide, without relying on various means of conventional technologies, by covering substantially the entire surface of the cathode with the cation exchange resin-contained, alkali earth metal scale-preventive film and also can suppress concomitant rise of electrolysis voltage, when non-purified water containing alkali earth metal ions is applied as raw material. As a result, a long time, stable electrolysis operation becomes available, compared with the case not according to the present invention.
  • alkali earth metal scale- preventive film As the reason, if the cation exchange resin-contained, alkali earth metal scale- preventive film is not used, a trace amount of alkali metal ions in the raw material water, such as Na + , is drawn to the surface of cathode catalyst, where the cathode surface becomes alkaline by the cathode reaction, Na + +H 2 O+e ⁇ ⁇ NaOH+ (1/2)H 2 and alkali earth metal ions such as Ca 2+ contained as impurities like Na + cause alkali deposit as Ca(OH) 2 on the surface of the cathode catalyst, depositing as scale covering the cathode catalyst.
  • alkali earth metal ions such as Ca 2+ contained as impurities like Na + cause alkali deposit as Ca(OH) 2 on the surface of the cathode catalyst, depositing as scale covering the cathode catalyst.
  • alkali earth metal ions such as Ca 2+ contained as impurities like Na + cause alkali deposit near the cation exchange resin-contained, alkali earth metal scale-preventive film and becomes Ca(OH) 2 before reaching the surface of the cathode catalyst in opposition to the anode because Ca 2+ has a smaller transport number in the cation exchange resin than Na + .
  • Cathode deposits including Ca(OH) 2 do not directly deposit on the surface of the cathode catalyst.
  • the cathode deposits not only precipitate near the cation exchange resin-contained, alkali earth metal scale-preventive film, but also near the cathode catalyst in opposition to the anode, and almost uniformly on the entire surface of the cathode including the rear surface.
  • the cathode catalyst surface is prevented from being preferentially covered directly by the layer of Ca(OH) 2 deposit and electrolysis will continue. Hydrogen gas generated from the cathode surface is dispersed outside through micro gaps in the cation exchange resin-contained, alkali earth metal scale-preventive film.
  • the present invention features that when the cathode is covered with the cation exchange resin-contained, alkali earth metal scale-preventive film, weaker adhesion of the deposit to the cathode surface and therefore, more natural falling off are observed than when electrolysis is carried out with the cathode catalyst exposed directly to the solution without covering.
  • Micro gaps of the cation exchange resin-contained, alkali earth metal scale-preventive film, as the vent route for hydrogen molecules formed at the cathode surface, are gradually narrowed and the cell voltage eventually rises, but the rising rate is significantly milder compared with the systems without covering the cathode by the cation exchange resin-contained, alkali earth metal scale-preventive film.
  • Fig. 1 is a longitudinal section drawing of the SPE (registered trademark) type electrolysis system as one example of a two-compartment type electrolysis system as one embodiment of the present invention.
  • Fig. 2 (a) is a sectional view of the examples of the anode applied in the present invention.
  • Fig. 2 (b) is a sectional view of the examples of the cathode applied in the present invention.
  • Fig. 3 is a longitudinal section view of a diaphragm process electrolysis system as another embodiment of the present invention.
  • Fig. 4 is a longitudinal sections view of an example of a three-compartment type electrolysis system as other embodiments of the present invention.
  • Fig. 5 is a graph showing the electrolysis time vs. cell voltage of Example 1 of the present invention and Comparative Example 1.
  • Fig. 6 is a graph showing the electrolysis time vs. cell voltage of Example 2 of the present invention and Comparative Example 2.
  • Fig. 7 is a graph showing the electrolysis time vs. cell voltage of Example 3 of the present invention and Comparative Example 3. Description of Embodiments
  • the present invention prevents scales of hydroxide and others of the alkali earth metal from depositing on the cathode surface, by covering substantially the entire surface of the cathode with the cation exchange resin-contained, alkali earth metal scale-preventive film in the electrolysis system having a construction comprising a diaphragm, an anode compartment separated by the diaphragm, a cathode compartment separated by the diaphragm, an anode provided in the anode compartment, a cathode provided in the cathode compartment, and raw material water containing alkali earth metal ions including calcium ion and magnesium ion supplied to the cathode compartment.
  • the electrolysis system by the present invention is applied to a diaphragm- installed electrolyzer, such as two-compartment type electrolysis system or three- compartment type electrolysis system.
  • the two-compartment type electrolysis system includes the diaphragm process electrolysis system, the cation exchange membrane process electrolysis system and the solid polymer electrolyte process electrolysis system as a special process of this type.
  • the diaphragm process electrolysis system applies a porous diaphragm as diaphragm
  • the cation exchange membrane process electrolysis system applies a cation exchange membrane as diaphragm
  • the solid polymer electrolyte process electrolysis system applies a cation exchange membrane as solid polymer electrolyte, with the anode and the cathode tightly attached on each surface of the cation exchange membrane to constitute an electrolysis system that can
  • the three- compartment type electrolysis system is provided with a cation exchange membrane and an anion exchange membrane as a diaphragm to separate the anode compartment and the cathode compartment to form an intermediate compartment between the cation exchange membrane and the anion exchange membrane.
  • Fig. 1 is a longitudinal section drawing of the solid polymer electrolyte type electrolysis system as one example of the two-compartment type electrolysis system, comprising the cathode compartment 1 , the cathode 2, the anode compartment 3, the anode 4, the cation exchange membrane 5, the current- carrying member 6 for the cathode 2 and the current-carrying member 7 for the anode 4.
  • Fig. 2 (a) is an example of the anode 4 applying an expanded mesh as the anode substrate 4a and the anode catalyst 4b is coated on the surface.
  • Fig. 2 (b) is a sectional view of an example of the cathode 2 applying an expanded mesh as the cathode substrate 2a, as with the case of the anode substrate 4a and the cation exchange resin-contained, alkali earth metal scale- preventive film 8 is coated on the substantially entire surface.
  • the material for the cathode substrate 2a of the cathode 2 for the present invention can be selected suitably from among irons and alloy thereof including stainless steel, nickel and alloy thereof, copper and alloy thereof, aluminum and alloy thereof, titanium, zirconium, molybdenum, tungsten, silicon and those alloys and carbides, carbon and allotrope thereof. Also, depending on the application, precious metal or precious metal oxide is applicable as coating material for the electrode catalyst.
  • the shape and form for the cathode substrate 2a of the cathode 2 for the present invention include plate, hole-punched metal, mesh, porous metal, fiber metal (ex. bibili fiber sintered body). Also, for the substrates in other shapes and form, if the effective surface of the cathode substrate 2a is coated with the cation exchange resin-contained adhesion-preventive film against alkali earth metal scale, the effect by the present invention can be expected without problems.
  • the material for the anode substrate 4a of the anode 4 can be selected from among such metals as tantalum, niobium, titanium, zirconium, and silicon and alloys thereof, which form a stable passivation film in the treatment solution and depending on the application, conductive diamond, lead dioxide, precious metal or precious metal oxide can be coated as the anode catalyst 4b for the anode substrate 4a, as suitably selected material in view of catalytic activity for the reaction.
  • ferrite, amorphous carbon or graphite alone is applicable.
  • cation exchange resin In order to form the cation exchange resin-contained, alkali earth metal scale- preventive film 8 over the substantially entire surface of the cathode substrate 2a, dispersion of cation exchange resin is coated on the surface of the cathode substrate 2a, followed by baking.
  • the cation exchange groups for dispersion of the cation exchange resin include sulfonic acid group, carboxylic acid group, phosphonic acid group and phosphate group.
  • suitable dispersion is that by perfuorosulfonic acid type cation exchange resin, having sulfonic acid group superior in chemical stability.
  • the perfuorosulfonic acid type cation exchange resin does not dissolve completely in a solvent, and is considered to be existing as colloid with a relatively large size around 10 nm diameter in the solvent.
  • the prepared dispersion of the resin is coated on the surface of the cathode substrate 2a by a spray, roller, brush, or sponge, followed by drying of the solvent at a room temperature being left for a prefixed time. At this time, leveling of the dispersion dripped from a nozzle or a tip can be left to the spreading wetting.
  • the electrode substrate with a dispersion coating in state of dried membrane is heated at 120-350 degrees Celsius. Heating may be conducted by a dryer, muffle furnace or a heating gun, or may be done on a hot plate. Heating is made not only for vaporizing solvent but also for sintering coagulating colloid. If applied temperature is too high, polymer molecules may change in quality. A preferable range will be 150-250 degrees Celsius. During the time, the micro gap may be formed.
  • Powder coating method is also applicable, in which the powder of the cation exchange resin is coated, followed by heat treatment to semi-dissolution for close coating.
  • a reinforcing agent for the cation exchange resin-contained, alkali earth metal scale-preventive film cross-linking agent of fluororesin, fluororesin or ion exchange resin filler is added in the dispersion. Then, after the heat treatment, the cation exchange resin-contained, alkali earth metal scale-preventive film can be reinforced.
  • the mechanical strength can be enhanced without impeding movement of cation within this film.
  • the cation exchange resin-contained, alkali earth metal scale-preventive film is installed on the both faces of the electrode substrate, constituting an envelope-state structure with the periphery and multiple
  • FIG. 3 illustrates an example of the diaphragm process electrolysis system, comprising the cathode compartment 1 , the cathode 2, the anode compartment 3, the anode 4, the current-carrying member 6 for the cathode 2, the current-carrying member 7 for the anode 4, and the hydrophilic porous diaphragm 9. Expanded mesh is applied for the anode substrate 4a of the anode 4, on the surface of which the anode catalyst 4b is coated.
  • FIG. 4 illustrates an example of the three-compartment type electrolysis system, comprising the cathode compartment 1 , the cathode 2, the anode compartment 3, the anode 4, the current-carrying member 6 for the cathode 2, the current-carrying member 7 for the anode 4, and the cation exchange resin-contained, alkali earth metal scale-preventive film 8, the anion exchange membrane 10, the cation exchange membrane 11 and the intermediate compartment 12.
  • Expanded mesh is applied for the anode substrate 4a of the anode 4, on the surface of which the anode catalyst 4b is coated. Similarly to the anode substrate 4a, expanded mesh is applied for the cathode substrate 2a of the cathode 2, on the substantially entire surface of which the cation exchange resin-contained, alkali earth metal scale- preventive film 8 is coated.
  • the functional water means "aqueous solutions having acquired reproducible, useful functions by means of artificial treatments to which the scientific grounds for the treatment and the function has been elucidated or is about to be elucidated".
  • functional waters including electrolysis water and ozone water.
  • Electrolysis water is defined and classified, as follows, in the home page of Functional Water Foundation, Japan.
  • Electrolysis water is a generic name of aqueous solution which is obtained through electrolyzing tap water or weak brine at a small DC voltage.
  • Various kinds of electrolysis water are produced by different equipment and under different conditions. Based on the application purposes, electrolysis water is roughly divided into two categories: germicidal electrolysis water used for the sanitary supervision like the washing disinfection, etc. including strong acid and slightly acid electrolysis water and electrolytic sodium hypochlorite water regarded as diluted sodium hypochlorite and alkaline electrolysis water (alkaline ionized water) with clear effect on the stomach and intestines symptom by continued drinking.
  • Acid electrolysis water is a generic name of electrolysis water of 6.5 or less of pH, which shows wide, strong sterilizing properties to various pathogenic bacteria and those drug resistant bacteria (MRSA etc.), and is used in various fields like the medical treatment, dentistry, food or agriculture, etc.
  • the main bactericidal factor is hypochlorite generated by electrolysis.
  • hypochlorite generated by electrolysis.
  • Strong acid electrolysis water is the electrolytic water of pH 2.7 or below having hypochlorous acid as main element (available chlorine density of 20-60ppm) generated on the anode, prepared by electrolyzing brine (NaCI) of 0.1 % or less in a two-compartment type electrolyzer, which is partitioned by a diaphragm into the anode and the cathode.
  • Slightly acid electrolysis water is an aqueous solution of hypochlorous acid of pH 5-6.5 and with available chlorine at 10-30 ppm, prepared by electrolyzing hydrochloric acid water of 2-6 % in a single-compartment type electrolyzer, which is not partitioned by a diaphragm into the anode and the cathode, featuring that all the generated water is sterilization water.
  • Alkaline ionized water is an alias of the electrolysis drinking water with a weak alkalinity (pH9-10), prepared by electrolyzing potable water using a household electrolysis water generator commonly called an alkali ion water purifier.
  • the household electrolysis water generator is a name of the medical apparatus for home use classified into "Apparatus and machine 83 for generating materials for the medical treatment" in the Pharmaceutical Affairs Act- Enforcement Order.
  • ozone water is an electrolysis product that chiefly contains ozone gas that is obtained by electrolyzing purified water or tap water, processed sterilization liquids, wastewater, waste fluid, etc. by using electrolytic cells by the present invention.
  • Ozone water also means ozone gas-contained water that contains, besides ozone gas, OH radical, oxygen radical such as super oxide anions, hydrogen peroxide and other oxidants.
  • ozone gas becomes the subject of oxidation and in a high pH (alkaline), ozone gas is resolved and then oxidation by the formed OH radical proceeds, exhibiting a stronger oxidation action, even if the total chemical equivalent for oxidation is the same.
  • the present invention can be applied to an electrolysis system for producing hydrogen, oxygen, ozone water, alkaline ionized water, acid water, and slightly acid water and for waste water treatment.
  • the effect is achieved most suitably for the method to flow catholyte including alkali earth metal ion regularly, but also for the method to replace non-refined catholyte including alkali earth metal ion regularly.
  • Example 1 SPE type electrolyzer (SPE is a registered trademark of Permelec Electrode Ltd.) was used as a solid polymer electrolyte type electrolysis system, as one example of the two-compartment type electrolysis system shown in Fig. 1.
  • SPE is a registered trademark of Permelec Electrode Ltd.
  • SUS304 mesh Mesh specification: plate thickness 1mm, SW 3.5mm, and specific surface area 1.1 m 2 /m 2
  • Commercially available cation exchange resin 5% dispersion (Trade name : National (registered trademark) DE520 - Nation is a registered trademark of E. I.
  • du Pont de Nemours and Company was coated on the substantially entire surface of the cathode 2, excluding the connection part to the current-carrying member 6, followed by baking at 170 degrees Celsius, thus the substantially entire surface of the cathode 2 being coated with the cation exchange resin-contained, alkali earth metal scale-preventive film 8.
  • the anode 4 was prepared by a Ti-mesh of the same shape coated with Pt.
  • the cation exchange membrane 5 (trade name: Nafion 117, registered trademark of E. I. du Pont de Nemours and Company) was inserted. Tap water was supplied at 300 mL/min.
  • Example 1 it took 26 hours before the cell voltage reached 20V, proving the suppression effect to voltage rise by the cation exchange resin coating on the cathode.
  • Example 1 showed relatively a sharp voltage rise. As the reasons, it is considered that the applied current value was larger and that there was the cation exchange resin membrane between the anode and the cathode which was poorer in adherence compared with the cation exchange resin coating in Example 2, resulting in deposition of hydroxide and others of alkali earth metal ion in a minute inter- electrode gap and of alkali earth metal ion within the membrane.
  • Example 1 assuming ordinary water electrolysis to produce oxygen and hydrogen, the electrolysis was conducted by applying the anode with Pt coating at relatively a low current density. By electrolysis at a high current density or by applying any materials with a high oxygen generation overvoltage, such as conductive diamond, ozone water can be generated through the following reactions.
  • Ozone formation is by the following reaction equation.
  • the ozone generation reaction is a competing reaction with oxygen generation reaction, under which oxygen with a low generation potential will evolve
  • electrolysis is performed at a high potential by high current density electrolysis.
  • Comparative Example 1 tests were conducted using an electrolysis system as with Example 1 , except that as the cathode, SUS 304 mesh without coating of the cation exchange resin-contained, alkali earth metal scale-preventive film 8 was used. In Comparative Example 1 , also, SPE electrolysis was conducted by the presence of cation exchange resin membrane. The results were as shown in Fig. 5, in which the voltage of Comparative Example 1 started to rise from right after the electrolysis operation and reached 20V in approx. 8 hours. This indicates that continued operation for a long time is difficult in the tap water electrolysis using an ordinary electrolytic cell under the applied conditions.
  • Example 2 the diaphragm process electrolysis system as shown in Fig. 3 was used.
  • Ti mesh Mosh specification: plate thickness 1mm, SW 3.5mm, and specific surface area 1.1 m 2 /m 2 ) of 16mm ⁇ 16mm in the size was used.
  • Commercially available cation exchange resin 5% dispersion (Trade name: Nafion (registered trademark) DE520 - Nafion is a registered trademark of E. I. du Pont de Nemours and Company) was coated on the substantially entire surface of the cathode 2, followed by baking at 150 degrees Celsius, thus forming the cation exchange resin-contained, alkali earth metal scale-preventive film 8.
  • the cathode 2 and the anode 4 were disposed in parallel at an interval of approx. 1.5mm and separated by the hydrophilic porous diaphragm 9 (neutral membrane ) of 20mm x 20mm. These were disposed at the center of the cathode compartment 1 and the anode compartment 3 of the diaphragm process electrolysis system.
  • compartment 1 of the electrolysis system respectively, at a flow rate of 12mL/min. and electrolysis tests were conducted at 0.03A at room temperature. During the tests, the voltage between the cathode 2 and the anode 4 was monitored as electrolytic cell voltage at an interval of 30 seconds.
  • Example 2 the voltage was constantly stable in a range of 20-26V and suppression effect to voltage rise by the cation exchange resin-contained, alkali earth metal scale-preventive film 8 for the cathode was clearly indicated.
  • Example 2 the construction of the diaphragm process electrolysis system in Example 2 is identical to the construction of alkali ion water purifier.
  • the electrode substrate is a plate and catholyte is passed swiftly through the gap of approx. 1mm between the cathode and the porous diaphragm, by which mixing of catholyte and anolyte through the porous diaphragm is suppressed.
  • the average pH value of catholyte at the outlet of the cathode compartment monitored three times at approx. every 24 hours was 8.75, and the average pH value similarly monitored in Comparative Example 2 was 8.98.
  • Comparative Example 2 the cathode 2 coated with Pt on Ti mesh (Mesh specification: plate thickness 1mm, SW 3.5mm, and specific surface area 1.1 m 2 /m 2 ) of 16mm ⁇ 16mm in the size without coating of the cation exchange resin- contained, alkali earth metal scale-preventive film 8, was used. Tests were conducted using an electrolysis system having a construction as with Example 2, except the cathode, and results were given in Fig. 6. The cell voltage started to rise from right after the electrolysis operation and reached 42V in 100 hours.
  • Example 3 the three-compartment type electrolysis system, as shown in Fig. 4 was used.
  • the three-compartment type electrolysis system comprises the anode 4 and the cathode 2 prepared as with Examplel , the anion exchange membrane 10 (Trade name: TOSFLEX SF48 - registered trademark of Tosoh
  • This configuration is a device that mimics a production system to produce so-called strong acid water containing hypochlorous acid at the anode compartment 3 and alkaline ionized water at the cathode compartment, with brine being supplied as raw material.
  • Dilute brine kept at 30 g/L was circulated to the intermediate compartment 12 of the electrolyzer, and tap water was supplied to the anode compartment 3 and the cathode compartment 1 , respectively, at a flow rate of 500mL/min. Electrolysis tests were conducted under a current supply at 0.5A. During the test, the voltage between the anode and the cathode was monitored as electrolytic cell voltage at a fixed interval.
  • JP2006-281013A for example, a treatment method of organic-contained waste effluent by electrolysis is described.
  • domestic wastewater and industrial wastewater containing alkali earth metal ions, such as Ca ion, as impurities are assumed for treatment.
  • alkali earth metal ions such as Ca ion
  • hydroxides, etc. of these impurities ions will deposit on the cathode unless otherwise special means is provided.
  • JP2003-126860A proposes electrolytic methods to remove dissolved persistent substances, such as aromatic compounds, PCB, and dioxin.
  • Raw material water resulting in waste fluid including dioxin is commonly supplied from groundwater or city water, which is non-purified water, in view of availability and economy.
  • These raw material waters contain alkali earth metal elements, such as Ca ion, as impurities, and hydroxides of them deposit in the cathode, hampering a continuous operation for a long time without maintenance including periodical acid cleaning.
  • the electrolytic cell by the present invention can suppress deposition on the cathode, achieving long-term continuous operation at a significantly reduced maintenance cost.
  • JP2002-316155A discloses also the means to dissolve and remove the scale deposit of the cathode.
  • the deposition including hydroxide can be intrinsically reduced.
  • non-purified water such as tap water is supplied to the cathode of the ozone water generation system, comprising a conductive diamond electrode as anode and the interleaved cation exchange membrane.
  • Deposition such as hydroxide on the cathode is a problem. According to the present invention, however, the amount of deposition can be greatly reduced.

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Abstract

The present invention provides an electrolysis system and an electrolysis method for the same in which non-purified water containing a trace amount of alkali earth metal ions, such as calcium ion and magnesium ion is applied as raw material, having a configuration in which the raw material water is supplied to the cathode compartment (1), featuring that scale of the alkali earth metals including hydroxide can be prevented from depositing on the surface of the cathode (2) provided in the cathode compartment (1). The present invention prevents scales of hydroxide and others of the alkali earth metal from depositing on the cathode surface (2), by covering the substantially entire surface of the cathode (2) with the cation exchange resin-contained, alkali earth metal scale-preventive film in the electrolysis system having a configuration comprising a diaphragm (5), an anode compartment (3) separated by the diaphragm (5), a cathode compartment (1) separated by the diaphragm (5), an anode (4) provided in the anode compartment (3), a cathode (2) provided in the cathode compartment (1), and raw material water containing alkali earth metal ions supplied to the cathode compartment

Description

DESCRIPTION
Title of Invention
ELECTROLYSIS SYSTEM AND ELECTROLYSIS METHOD FOR THE SAME
Technical Field
The present invention relates to an electrolysis system and an electrolysis method for the same in which non-purified water containing a trace amount of alkali earth metal ions, such as calcium ion and magnesium ion is applied as raw material, having a construction in which the raw material water is supplied to a cathode compartment, featuring that scale of hydroxide and others of the alkali earth metals can be prevented from depositing on the cathode surface.
Background Art
The water treatment applying electrolysis reaction is widely employed for such purposes as production of functional water by electrolysis, ozone water and electrolysis water, sterilization, and decomposition removal of toxic substance. The reactor which is used for these processes has a construction generally having an anode, a cathode and an ion exchange membrane disposed inbetween or a porous diaphragm accommodated in a case and is called an electrolyzer or an electrolytic cell. This type of electrolyzer or electrolytic cell comprises a diaphragm, an anode compartment separated by the diaphragm, a cathode compartment separated by the diaphragm, an anode provided in the anode compartment and a cathode provided in the cathode compartment, and a two-compartment type electrolysis system and a three-compartment type electrolysis system are known. The two-compartment type electrolysis system includes the diaphragm process electrolysis system, the cation exchange membrane process electrolysis system and the solid polymer electrolyte process electrolysis system as a special process of this type. The diaphragm process electrolysis system applies a porous diaphragm as diaphragm, the cation exchange membrane process electrolysis system applies a cation exchange membrane as diaphragm, and the solid polymer electrolyte process electrolysis system applies a cation exchange membrane with the anode and the cathode tightly attached on each surface of the cation exchange
membrane as solid polymer electrolyte, to constitute an electrolysis system that can electrolyze even purified water with a small electric conductivity.
The three-compartment type electrolysis system is provided with a cation exchange membrane and an anion exchange membrane as diaphragm to separate the anode compartment and the cathode compartment to form an intermediate compartment between the cation exchange membrane and the anion exchange membrane. Various kinds of functional water and ozone water are produced by these electrolysis systems. The present invention relates to an electrolysis system and an electrolysis method for the same in which non-purified water containing a trace amount of alkali earth metal ions, such as calcium ion and magnesium ion is applied as raw material to be electrolyzed; more in details, the present invention proposes a system and a method for the same which can ameliorate the deposition problem of hydroxide and others on the cathode for an ozone water production system by electrolysis and an ozone water production method for the same, a functional water production system and a functional water production method for the same and an electrolysis water production system and an electrolysis water production method for the same, a sterilization process, a waste water treatment process, etc., applying non-purified water as raw material water. Further, the electrolysis system and the electrolysis method for the same by the present invention can contribute to solving similar problems in other fields of applications.
In general, non-purified water containing alkali earth metal ions, such as calcium ion and magnesium ion is applied as raw material in the waste fluid treatment process or the production processes of function waters including alkaline ionized water. In these electrolysis processes applying non-purified water, the pH value of the catholyte increases with time of electrolysis first from the cathode surface and alkali earth metal ions deposit with a trace amount of calcium as the chief element in the form of hydroxide, oxides and carbonate of them on the cathode surface as non-conducting scale (water scale), causing dysfunction of electrolysis.
To cope with them, PTL 1 and PTL 2 propose a method of applying acid for the cathode compartment solution; however the construction becomes complicated and safety operation becomes difficult. PTL 3 proposes suppression of cathode deposit by proving the production system of electrolysis water with an auxiliary tank and a multiple number of electrode assemblies for alternating use at a preset time interval. This system design, however, needs a large installation, leading to increased costs. PTL 4 describes, in detail, the method for removing deposits by acid cleaning, etc. to be made at a regular shut-down of the system operation, which causes complicated procedures of operation. PTL 5 suggests prevention of deposition on the cathode by acidifying the non-diaphragm electrolytic cell with hydrochloric acid. This process applies strong acid chemical solutions including hydrochloric acid, which is not only disadvantageous in operation safety or cost but strong acidity may be unacceptable depending on application.
PTL 6 introduces such operation manner that the anode and the cathode of the electrolytic cell are reversed at the time of deterioration in electrolysis performance so as to recover the performance through reverse current. In this case, cathode functions as anode temporarily with applied reverse current and constituent metal elements elute. Most of Ion from the eluted metals, such as Cr and Ni, are not only undesirable as ions contained in the process liquid but also penetrate the solid polymer electrolyte membrane to deteriorate the ion transport ability of it. For this reason, highly corrosion resistant valve metals may be employed for the cathode. In this case, however, an expensive precious metal coating is required on the cathode surface to decrease electrolytic overvoltage. Moreover, the cathodic reduction of the anode which temporarily turns to the cathode and the deterioration due to concomitant hydrogen embrittlement are feared.
PTL 7 introduces the production process of hypochlorite through electrolysis of an aqueous solution of chloride by a non-diaphragmatic electrolysis method, applying a cathode covered with a reduction preventive film coated on a low hydrogen overvoltage layer formed on the conductive substrate. An organic cation exchange membrane substance or an inorganic cation exchange membrane substance or a substance of the mixture of these is used as the reduction preventive film. This reduction preventive film, however, is to prevent hypochlorous acid ion from reducing at the cathode in the non-diaphragmatic electrolysis method, in which the product at the anode directly contacts the cathode, not to prevent cathode deposition, chiefly alkali earth metal hydroxide. On the other hand, in the electrolysis method and the electrolysis system applying a diaphragm as in the present invention, any reduction preventive film is not required unlike PTL 7, to prevent hypochlorous acid ion, the product at the anode, from reducing.
In the conventional electrolysis method and the electrolysis system applying a diaphragm, when non-purified water containing alkali earth metal ions is applied as raw material, metal ions ionized as cation are concentrated on the cathode surface and the pH increases, and scale of hydroxide as chief material is formed as cathode deposit substance. Thus formed scale obstructs electrolysis operation. Conventionally proposed techniques to suppress formation of scale are
disadvantageous, requiring cost and manpower or sacrificing performance partially. Further improvements are needed.
Citation List Patent Literature
PTL 1 : JP2002-173789A
PTL 2: JP2005-177671A
PTL 3: JP2011-050807A
PTL 4: JP10-130876A
PTL 5: JP2008-200667A
PTL 6: JP2008-150665A
PTL 7: JP08-104991A Summary of Invention
Technical Problem
In order to solve the drawback of the conventional methods, the present invention aims to provide an electrolysis system and an electrolysis method of the same which can prevent scales of hydroxide and others of the alkali earth metal from depositing on the cathode surface, when non-purified water containing alkali earth metal ions is applied as raw material for the electrolysis method and the electrolysis system using a diaphragm. Solution to Problem
As the first solution to solve the above-mentioned problems, the present invention prevents scales of hydroxide and others of the alkali earth metal from depositing on the cathode surface, by covering substantially the entire surface of the cathode with the cation exchange resin-contained, alkali earth metal scale- preventive film in the electrolysis system having a configuration comprising a diaphragm, an anode compartment separated by the diaphragm, a cathode compartment separated by the diaphragm, an anode provided in the anode compartment, a cathode provided in the cathode compartment, and raw material water containing alkali earth metal ions supplied to the cathode compartment As the second solution to solve the above-mentioned problems, the present invention constructs a diaphragm process electrolysis system applying a porous diaphragm as the diaphragm.
As the third solution to solve the above-mentioned problems, the present invention constitutes a cation exchange membrane process electrolysis system applying cation exchange membrane as the diaphragm. As the fourth solution to solve the above-mentioned problems, the present invention constitutes a solid polymer electrolyte type electrolysis system, wherein the anode and the cathode are adhered to each surface of the cation exchange membrane, respectively. As the fifth solution to solve the above-mentioned problems, the present invention constitutes a three-compartment type electrolysis system comprising a cation exchange membrane and an anion exchange membrane provided between the anode compartment and the cathode compartment as diaphragm to separate the anode compartment and the cathode compartment to form an intermediate compartment between the cation exchange membrane and the anion exchange membrane.
As the sixth solution to solve the above-mentioned problems, the present invention applies conductive diamond, lead dioxide, precious metal or precious metal oxide as anode catalyst for the anode.
As the seventh solution to solve the above-mentioned problems, the present invention provides a current-carrying member for the anode and the cathode. As the eighth solution to solve the above-mentioned problems, the present invention mixes filler in fiber or powder form comprising inorganic or organic materials in the cation exchange resin-contained, alkali earth metal scale- preventive film as a reinforcing material of the film.
As the ninth solution to solve the above-mentioned problems, the present invention mixes ceramics particles having the cation exchange function in the cation exchange resin-contained, alkali earth metal scale-preventive film. As the tenth solution to solve the above-mentioned problems, the present invention applies at least one kind of ceramics particles from among apatite, perovskite type oxide and zeolite, as the ceramics particles having the cation exchange function. As the eleventh solution to solve the above-mentioned problems, the present invention applies a plate material, a porous metal, a fiber metal form, a mesh or a hole-punched metal, as the cathode substrate.
As the twelfth solution to solve the above-mentioned problems, the present invention provides an electrolysis method to electrolyze raw material water containing alkali earth metal ions including calcium ion and magnesium ion, by applying the electrolysis system.
Advantageous Effects of Invention
According to the present invention, the electrolysis system and the electrolysis method of the same applying a diaphragm can suppress depositions including hydroxide, without relying on various means of conventional technologies, by covering substantially the entire surface of the cathode with the cation exchange resin-contained, alkali earth metal scale-preventive film and also can suppress concomitant rise of electrolysis voltage, when non-purified water containing alkali earth metal ions is applied as raw material. As a result, a long time, stable electrolysis operation becomes available, compared with the case not according to the present invention.
As the reason, if the cation exchange resin-contained, alkali earth metal scale- preventive film is not used, a trace amount of alkali metal ions in the raw material water, such as Na+ , is drawn to the surface of cathode catalyst, where the cathode surface becomes alkaline by the cathode reaction, Na++H2O+e~→NaOH+ (1/2)H2 and alkali earth metal ions such as Ca2+ contained as impurities like Na+ cause alkali deposit as Ca(OH)2 on the surface of the cathode catalyst, depositing as scale covering the cathode catalyst.
On the contrary, if the cathode is covered by the cation exchange resin- contained, alkali earth metal scale-preventive film by the present invention, NaOH and H2 gas formed on the cathode catalyst disperses within the cation exchange resin-contained, alkali earth metal scale-preventive film, leaches from the surface of the film, and further disperses into the raw material water. At this time, alkali earth metal ions, such as Ca2+ contained as impurities like Na+ cause alkali deposit near the cation exchange resin-contained, alkali earth metal scale-preventive film and becomes Ca(OH)2 before reaching the surface of the cathode catalyst in opposition to the anode because Ca2+ has a smaller transport number in the cation exchange resin than Na+. Cathode deposits including Ca(OH)2 do not directly deposit on the surface of the cathode catalyst. Moreover, it has been confirmed from a visual inspection or a magnifying glass observation of the cathode after a long time electrolysis operation that the cathode deposits not only precipitate near the cation exchange resin-contained, alkali earth metal scale-preventive film, but also near the cathode catalyst in opposition to the anode, and almost uniformly on the entire surface of the cathode including the rear surface. Thus, the cathode catalyst surface is prevented from being preferentially covered directly by the layer of Ca(OH)2 deposit and electrolysis will continue. Hydrogen gas generated from the cathode surface is dispersed outside through micro gaps in the cation exchange resin-contained, alkali earth metal scale-preventive film.
In addition to suppressing precipitation of the deposits of hydroxide and others (Ca(OH)2, etc.) of the alkali earth metal on to the cathode surface, the present invention features that when the cathode is covered with the cation exchange resin-contained, alkali earth metal scale-preventive film, weaker adhesion of the deposit to the cathode surface and therefore, more natural falling off are observed than when electrolysis is carried out with the cathode catalyst exposed directly to the solution without covering. Micro gaps of the cation exchange resin-contained, alkali earth metal scale-preventive film, as the vent route for hydrogen molecules formed at the cathode surface, are gradually narrowed and the cell voltage eventually rises, but the rising rate is significantly milder compared with the systems without covering the cathode by the cation exchange resin-contained, alkali earth metal scale-preventive film.
When the entire cathode surface is covered by a film applying porous resin only without ion exchange capacity, including fluororesin, instead of the cation exchange resin-contained, alkali earth metal scale-preventive film, the exposed area of the cathode surface is decreased and electrolytic current concentrates at the slightly remaining exposed part and the pH value sharply increases. As a result, non-conductive scales including hydroxide are formed and the cell voltage increases rapidly, showing an adverse effect. Brief Description of Drawings
Fig. 1 is a longitudinal section drawing of the SPE (registered trademark) type electrolysis system as one example of a two-compartment type electrolysis system as one embodiment of the present invention.
Fig. 2 (a) is a sectional view of the examples of the anode applied in the present invention.
Fig. 2 (b) is a sectional view of the examples of the cathode applied in the present invention.
Fig. 3 is a longitudinal section view of a diaphragm process electrolysis system as another embodiment of the present invention.
Fig. 4 is a longitudinal sections view of an example of a three-compartment type electrolysis system as other embodiments of the present invention.
Fig. 5 is a graph showing the electrolysis time vs. cell voltage of Example 1 of the present invention and Comparative Example 1.
Fig. 6 is a graph showing the electrolysis time vs. cell voltage of Example 2 of the present invention and Comparative Example 2.
Fig. 7 is a graph showing the electrolysis time vs. cell voltage of Example 3 of the present invention and Comparative Example 3. Description of Embodiments
The present invention prevents scales of hydroxide and others of the alkali earth metal from depositing on the cathode surface, by covering substantially the entire surface of the cathode with the cation exchange resin-contained, alkali earth metal scale-preventive film in the electrolysis system having a construction comprising a diaphragm, an anode compartment separated by the diaphragm, a cathode compartment separated by the diaphragm, an anode provided in the anode compartment, a cathode provided in the cathode compartment, and raw material water containing alkali earth metal ions including calcium ion and magnesium ion supplied to the cathode compartment.
The electrolysis system by the present invention is applied to a diaphragm- installed electrolyzer, such as two-compartment type electrolysis system or three- compartment type electrolysis system. The two-compartment type electrolysis system includes the diaphragm process electrolysis system, the cation exchange membrane process electrolysis system and the solid polymer electrolyte process electrolysis system as a special process of this type.
The diaphragm process electrolysis system applies a porous diaphragm as diaphragm, the cation exchange membrane process electrolysis system applies a cation exchange membrane as diaphragm, and the solid polymer electrolyte process electrolysis system applies a cation exchange membrane as solid polymer electrolyte, with the anode and the cathode tightly attached on each surface of the cation exchange membrane to constitute an electrolysis system that can
electrolyze even purified water with a small electric conductivity. The three- compartment type electrolysis system is provided with a cation exchange membrane and an anion exchange membrane as a diaphragm to separate the anode compartment and the cathode compartment to form an intermediate compartment between the cation exchange membrane and the anion exchange membrane.
Fig. 1 is a longitudinal section drawing of the solid polymer electrolyte type electrolysis system as one example of the two-compartment type electrolysis system, comprising the cathode compartment 1 , the cathode 2, the anode compartment 3, the anode 4, the cation exchange membrane 5, the current- carrying member 6 for the cathode 2 and the current-carrying member 7 for the anode 4.
Fig. 2 (a) is an example of the anode 4 applying an expanded mesh as the anode substrate 4a and the anode catalyst 4b is coated on the surface.
Fig. 2 (b) is a sectional view of an example of the cathode 2 applying an expanded mesh as the cathode substrate 2a, as with the case of the anode substrate 4a and the cation exchange resin-contained, alkali earth metal scale- preventive film 8 is coated on the substantially entire surface.
The material for the cathode substrate 2a of the cathode 2 for the present invention can be selected suitably from among irons and alloy thereof including stainless steel, nickel and alloy thereof, copper and alloy thereof, aluminum and alloy thereof, titanium, zirconium, molybdenum, tungsten, silicon and those alloys and carbides, carbon and allotrope thereof. Also, depending on the application, precious metal or precious metal oxide is applicable as coating material for the electrode catalyst.
The shape and form for the cathode substrate 2a of the cathode 2 for the present invention include plate, hole-punched metal, mesh, porous metal, fiber metal (ex. bibili fiber sintered body). Also, for the substrates in other shapes and form, if the effective surface of the cathode substrate 2a is coated with the cation exchange resin-contained adhesion-preventive film against alkali earth metal scale, the effect by the present invention can be expected without problems. The material for the anode substrate 4a of the anode 4 can be selected from among such metals as tantalum, niobium, titanium, zirconium, and silicon and alloys thereof, which form a stable passivation film in the treatment solution and depending on the application, conductive diamond, lead dioxide, precious metal or precious metal oxide can be coated as the anode catalyst 4b for the anode substrate 4a, as suitably selected material in view of catalytic activity for the reaction. As the anode substrate 4a for the anode 4, ferrite, amorphous carbon or graphite, alone is applicable.
In order to form the cation exchange resin-contained, alkali earth metal scale- preventive film 8 over the substantially entire surface of the cathode substrate 2a, dispersion of cation exchange resin is coated on the surface of the cathode substrate 2a, followed by baking. The cation exchange groups for dispersion of the cation exchange resin include sulfonic acid group, carboxylic acid group, phosphonic acid group and phosphate group. Among them, suitable dispersion is that by perfuorosulfonic acid type cation exchange resin, having sulfonic acid group superior in chemical stability. The perfuorosulfonic acid type cation exchange resin does not dissolve completely in a solvent, and is considered to be existing as colloid with a relatively large size around 10 nm diameter in the solvent.
The prepared dispersion of the resin is coated on the surface of the cathode substrate 2a by a spray, roller, brush, or sponge, followed by drying of the solvent at a room temperature being left for a prefixed time. At this time, leveling of the dispersion dripped from a nozzle or a tip can be left to the spreading wetting. The electrode substrate with a dispersion coating in state of dried membrane is heated at 120-350 degrees Celsius. Heating may be conducted by a dryer, muffle furnace or a heating gun, or may be done on a hot plate. Heating is made not only for vaporizing solvent but also for sintering coagulating colloid. If applied temperature is too high, polymer molecules may change in quality. A preferable range will be 150-250 degrees Celsius. During the time, the micro gap may be formed.
Powder coating method is also applicable, in which the powder of the cation exchange resin is coated, followed by heat treatment to semi-dissolution for close coating. As a reinforcing agent for the cation exchange resin-contained, alkali earth metal scale-preventive film, cross-linking agent of fluororesin, fluororesin or ion exchange resin filler is added in the dispersion. Then, after the heat treatment, the cation exchange resin-contained, alkali earth metal scale-preventive film can be reinforced.
If ceramics particles having cation exchange capacity including apatite, perovskite type oxide and zeolite is added to the cation exchange resin-contained film, the mechanical strength can be enhanced without impeding movement of cation within this film. Further, it is also possible that the cation exchange resin-contained, alkali earth metal scale-preventive film is installed on the both faces of the electrode substrate, constituting an envelope-state structure with the periphery and multiple
intermediate points, as needed, tightly attached. Such structure can be
manufactured by hot pressing. At this time, it is necessary to provide minute openings to release gases including hydrogen gas generated at the cathode surface. In this case, a structure with openings only at the top is preferable. Fig. 3 illustrates an example of the diaphragm process electrolysis system, comprising the cathode compartment 1 , the cathode 2, the anode compartment 3, the anode 4, the current-carrying member 6 for the cathode 2, the current-carrying member 7 for the anode 4, and the hydrophilic porous diaphragm 9. Expanded mesh is applied for the anode substrate 4a of the anode 4, on the surface of which the anode catalyst 4b is coated. Similarly to the anode substrate 4a, expanded mesh is applied for the cathode substrate 2a of the cathode 2, on the substantially entire surface of which the cation exchange resin-contained, alkali earth metal scale-preventive film 8 is coated. Fig. 4 illustrates an example of the three-compartment type electrolysis system, comprising the cathode compartment 1 , the cathode 2, the anode compartment 3, the anode 4, the current-carrying member 6 for the cathode 2, the current-carrying member 7 for the anode 4, and the cation exchange resin-contained, alkali earth metal scale-preventive film 8, the anion exchange membrane 10, the cation exchange membrane 11 and the intermediate compartment 12. Expanded mesh is applied for the anode substrate 4a of the anode 4, on the surface of which the anode catalyst 4b is coated. Similarly to the anode substrate 4a, expanded mesh is applied for the cathode substrate 2a of the cathode 2, on the substantially entire surface of which the cation exchange resin-contained, alkali earth metal scale- preventive film 8 is coated.
In these electrolysis systems, various kinds of functional water and ozone water are produced.
For the present invention, the functional water means "aqueous solutions having acquired reproducible, useful functions by means of artificial treatments to which the scientific grounds for the treatment and the function has been elucidated or is about to be elucidated". There are various kinds of functional waters including electrolysis water and ozone water.
Electrolysis water is defined and classified, as follows, in the home page of Functional Water Foundation, Japan.
Electrolysis water is a generic name of aqueous solution which is obtained through electrolyzing tap water or weak brine at a small DC voltage. Various kinds of electrolysis water are produced by different equipment and under different conditions. Based on the application purposes, electrolysis water is roughly divided into two categories: germicidal electrolysis water used for the sanitary supervision like the washing disinfection, etc. including strong acid and slightly acid electrolysis water and electrolytic sodium hypochlorite water regarded as diluted sodium hypochlorite and alkaline electrolysis water (alkaline ionized water) with clear effect on the stomach and intestines symptom by continued drinking.
Acid electrolysis water is a generic name of electrolysis water of 6.5 or less of pH, which shows wide, strong sterilizing properties to various pathogenic bacteria and those drug resistant bacteria (MRSA etc.), and is used in various fields like the medical treatment, dentistry, food or agriculture, etc. The main bactericidal factor is hypochlorite generated by electrolysis. When strong acid electrolysis water and slightly acid electrolysis water were specified as food additive in 2002 in Japan for their harmless nature to human health, the name, "hypochlorous acid water" was given.
Strong acid electrolysis water (strong acid hypochlorous acid water) is the electrolytic water of pH 2.7 or below having hypochlorous acid as main element (available chlorine density of 20-60ppm) generated on the anode, prepared by electrolyzing brine (NaCI) of 0.1 % or less in a two-compartment type electrolyzer, which is partitioned by a diaphragm into the anode and the cathode. The electrolyzed water of strong alkaline (pH11-11.5) generated on the cathode side at the same time, is called strong alkali electrolysis water.
Slightly acid electrolysis water is an aqueous solution of hypochlorous acid of pH 5-6.5 and with available chlorine at 10-30 ppm, prepared by electrolyzing hydrochloric acid water of 2-6 % in a single-compartment type electrolyzer, which is not partitioned by a diaphragm into the anode and the cathode, featuring that all the generated water is sterilization water.
Alkaline ionized water is an alias of the electrolysis drinking water with a weak alkalinity (pH9-10), prepared by electrolyzing potable water using a household electrolysis water generator commonly called an alkali ion water purifier. The household electrolysis water generator is a name of the medical apparatus for home use classified into "Apparatus and machine 83 for generating materials for the medical treatment" in the Pharmaceutical Affairs Act- Enforcement Order. As a result of the strict controlled clinical trials, the following effects of the alkaline ionized water, which are approved as medical devices, have been confirmed. That is, it is effective for "chronic diarrhea, dyspepsia, abnormal fermentation in stomach and intestines, antacid and hyperacid". Also to constipation, enhanced effect was recognized. It has been renewed that there is "Ameliorating effect of the stomach and intestines symptom" along with the revision of Pharmaceutical Affairs Act (2005) now. In the present invention, ozone water is an electrolysis product that chiefly contains ozone gas that is obtained by electrolyzing purified water or tap water, processed sterilization liquids, wastewater, waste fluid, etc. by using electrolytic cells by the present invention. Ozone water also means ozone gas-contained water that contains, besides ozone gas, OH radical, oxygen radical such as super oxide anions, hydrogen peroxide and other oxidants. As an action of this ozone water, in a low pH (acidic), ozone gas becomes the subject of oxidation and in a high pH (alkaline), ozone gas is resolved and then oxidation by the formed OH radical proceeds, exhibiting a stronger oxidation action, even if the total chemical equivalent for oxidation is the same.
The present invention can be applied to an electrolysis system for producing hydrogen, oxygen, ozone water, alkaline ionized water, acid water, and slightly acid water and for waste water treatment.
As the operation mode, the effect is achieved most suitably for the method to flow catholyte including alkali earth metal ion regularly, but also for the method to replace non-refined catholyte including alkali earth metal ion regularly.
Examples
The following are examples of the present invention; provided however, the present invention shall not be limited to them.
[Example 1]
In Example 1 , SPE type electrolyzer (SPE is a registered trademark of Permelec Electrode Ltd.) was used as a solid polymer electrolyte type electrolysis system, as one example of the two-compartment type electrolysis system shown in Fig. 1. For the anode substrate 4a and the cathode substrate 2a, SUS304 mesh (Mesh specification: plate thickness 1mm, SW 3.5mm, and specific surface area 1.1 m2/m2) of the expanded metal of 30mm χ 30mm in the size was used. Commercially available cation exchange resin 5% dispersion (Trade name : Nation (registered trademark) DE520 - Nation is a registered trademark of E. I. du Pont de Nemours and Company) was coated on the substantially entire surface of the cathode 2, excluding the connection part to the current-carrying member 6, followed by baking at 170 degrees Celsius, thus the substantially entire surface of the cathode 2 being coated with the cation exchange resin-contained, alkali earth metal scale-preventive film 8. Also, the anode 4 was prepared by a Ti-mesh of the same shape coated with Pt. Between the anode 4 and the cathode 2, the cation exchange membrane 5 (trade name: Nafion 117, registered trademark of E. I. du Pont de Nemours and Company) was inserted. Tap water was supplied at 300 mL/min. to the anode compartment 3 and the cathode compartment 1 of this electrolysis system, and electrolysis tests were conducted at a supply current of 1.8A. During the tests, the voltage between the anode and the cathode was monitored as electrolytic cell voltage at a fixed interval. The results were shown in Fig. 5. In Example 1 , it took 26 hours before the cell voltage reached 20V, proving the suppression effect to voltage rise by the cation exchange resin coating on the cathode.
Compared with Example 2 and Example 3 described in latter part, Example 1 showed relatively a sharp voltage rise. As the reasons, it is considered that the applied current value was larger and that there was the cation exchange resin membrane between the anode and the cathode which was poorer in adherence compared with the cation exchange resin coating in Example 2, resulting in deposition of hydroxide and others of alkali earth metal ion in a minute inter- electrode gap and of alkali earth metal ion within the membrane.
In Example 1 , assuming ordinary water electrolysis to produce oxygen and hydrogen, the electrolysis was conducted by applying the anode with Pt coating at relatively a low current density. By electrolysis at a high current density or by applying any materials with a high oxygen generation overvoltage, such as conductive diamond, ozone water can be generated through the following reactions.
Ozone formation is by the following reaction equation.
Ozone generation reaction (anode):
Figure imgf000021_0001
E°=+1.51V
Oxygen generation reaction (anode): 2H2O=O2+4H++4e"
E°=+1.23V
Hydrogen generation reaction (cathode): 2H++2e" =H2
The ozone generation reaction is a competing reaction with oxygen generation reaction, under which oxygen with a low generation potential will evolve
preferentially, resulting in a low current efficiency. In case that an anode with a high overvoltage, such as lead oxide or conductive diamond electrode is used to suppress oxygen generation, or in case that platinum-coated electrode is used, electrolysis is performed at a high potential by high current density electrolysis.
[Comparative Example 1]
In Comparative Example 1 , tests were conducted using an electrolysis system as with Example 1 , except that as the cathode, SUS 304 mesh without coating of the cation exchange resin-contained, alkali earth metal scale-preventive film 8 was used. In Comparative Example 1 , also, SPE electrolysis was conducted by the presence of cation exchange resin membrane. The results were as shown in Fig. 5, in which the voltage of Comparative Example 1 started to rise from right after the electrolysis operation and reached 20V in approx. 8 hours. This indicates that continued operation for a long time is difficult in the tap water electrolysis using an ordinary electrolytic cell under the applied conditions.
[Example 2]
In Example 2, the diaphragm process electrolysis system as shown in Fig. 3 was used. For the cathode 2 and the anode 4, Ti mesh (Mesh specification: plate thickness 1mm, SW 3.5mm, and specific surface area 1.1 m2/m2) of 16mm χ 16mm in the size was used. Commercially available cation exchange resin 5% dispersion (Trade name: Nafion (registered trademark) DE520 - Nafion is a registered trademark of E. I. du Pont de Nemours and Company) was coated on the substantially entire surface of the cathode 2, followed by baking at 150 degrees Celsius, thus forming the cation exchange resin-contained, alkali earth metal scale-preventive film 8. The cathode 2 and the anode 4 were disposed in parallel at an interval of approx. 1.5mm and separated by the hydrophilic porous diaphragm 9 (neutral membrane ) of 20mm x 20mm. These were disposed at the center of the cathode compartment 1 and the anode compartment 3 of the diaphragm process electrolysis system.
Tap water was supplied to the anode compartment 3 and the cathode
compartment 1 of the electrolysis system, respectively, at a flow rate of 12mL/min. and electrolysis tests were conducted at 0.03A at room temperature. During the tests, the voltage between the cathode 2 and the anode 4 was monitored as electrolytic cell voltage at an interval of 30 seconds.
The results were shown in Fig. 6. In Example 2, the voltage was constantly stable in a range of 20-26V and suppression effect to voltage rise by the cation exchange resin-contained, alkali earth metal scale-preventive film 8 for the cathode was clearly indicated.
Meanwhile, the construction of the diaphragm process electrolysis system in Example 2 is identical to the construction of alkali ion water purifier. In a
commercially available alkali ion water purifier, the electrode substrate is a plate and catholyte is passed swiftly through the gap of approx. 1mm between the cathode and the porous diaphragm, by which mixing of catholyte and anolyte through the porous diaphragm is suppressed. For reference, in Example 2, the average pH value of catholyte at the outlet of the cathode compartment monitored three times at approx. every 24 hours was 8.75, and the average pH value similarly monitored in Comparative Example 2 was 8.98. [Comparative Example 2]
In Comparative Example 2, the cathode 2 coated with Pt on Ti mesh (Mesh specification: plate thickness 1mm, SW 3.5mm, and specific surface area 1.1 m2/m2) of 16mm χ 16mm in the size without coating of the cation exchange resin- contained, alkali earth metal scale-preventive film 8, was used. Tests were conducted using an electrolysis system having a construction as with Example 2, except the cathode, and results were given in Fig. 6. The cell voltage started to rise from right after the electrolysis operation and reached 42V in 100 hours.
[Example 3]
In Example 3, the three-compartment type electrolysis system, as shown in Fig. 4 was used. The three-compartment type electrolysis system comprises the anode 4 and the cathode 2 prepared as with Examplel , the anion exchange membrane 10 (Trade name: TOSFLEX SF48 - registered trademark of Tosoh
Corporation) as the diaphragm for the anode compartment 3 and the intermediate compartment 12 and the cation exchange membrane 11 (Trade name: Nafionl 17 - registered trademark of E. I. du Pont de Nemours and Company) between the intermediate compartment 12 and the cathode compartment 1. This configuration is a device that mimics a production system to produce so-called strong acid water containing hypochlorous acid at the anode compartment 3 and alkaline ionized water at the cathode compartment, with brine being supplied as raw material.
Dilute brine kept at 30 g/L was circulated to the intermediate compartment 12 of the electrolyzer, and tap water was supplied to the anode compartment 3 and the cathode compartment 1 , respectively, at a flow rate of 500mL/min. Electrolysis tests were conducted under a current supply at 0.5A. During the test, the voltage between the anode and the cathode was monitored as electrolytic cell voltage at a fixed interval.
As a result, as shown in Fig. 7, electrolytic cell voltage stopped at approx.12V in Example 3, proving the clear effect of the present invention.
[Comparative Example 3]
In Comparative Example 3, SUS 304 mesh without a coating of the cation exchange resin-contained, alkali earth metal scale-preventive film 8 was used for the cathode 2. Tests were conducted by the electrolysis system of the same configuration as with the Example 3, except the cathode. As a result, as shown in Fig. 7, electrolytic cell voltage which had been less than 7V in an early period increased to 18V in 480 hours.
Industrial Applicability
The present invention is applicable to the fields mentioned below, provided however, it shall not be necessarily limited to them.
1. Wastewater and waste effluent treatment
1) Processing equipment for organic-contained, high BOD■ COD effluent
In JP2006-281013A, for example, a treatment method of organic-contained waste effluent by electrolysis is described. In this publication, domestic wastewater and industrial wastewater containing alkali earth metal ions, such as Ca ion, as impurities are assumed for treatment. However, even if the specifications do not mention clearly, it is apparent that hydroxides, etc. of these impurities ions will deposit on the cathode unless otherwise special means is provided.
2) Decomposition of dissolved persistent substance
JP2003-126860A proposes electrolytic methods to remove dissolved persistent substances, such as aromatic compounds, PCB, and dioxin. Raw material water resulting in waste fluid including dioxin is commonly supplied from groundwater or city water, which is non-purified water, in view of availability and economy. These raw material waters contain alkali earth metal elements, such as Ca ion, as impurities, and hydroxides of them deposit in the cathode, hampering a continuous operation for a long time without maintenance including periodical acid cleaning.
Whereas, the electrolytic cell by the present invention can suppress deposition on the cathode, achieving long-term continuous operation at a significantly reduced maintenance cost.
2. Production of electrolysis water
A variety of methods and devices that assume non-purified water such as tap water to be raw material are proposed to produce electrolysis water including alkaline ionized water by electrolysis. In those devices, deposition including hydroxide in the cathode is a common problem. JP2002-316155A discloses also the means to dissolve and remove the scale deposit of the cathode. However, according to the present invention, the deposition including hydroxide can be intrinsically reduced.
3. Ozone water production
In general, non-purified water such as tap water is supplied to the cathode of the ozone water generation system, comprising a conductive diamond electrode as anode and the interleaved cation exchange membrane. Deposition, such as hydroxide on the cathode is a problem. According to the present invention, however, the amount of deposition can be greatly reduced.
Reference Signs List
1 : cathode compartment
2 : cathode
2a : cathode substrate
3 : anode compartment
4 : anode
4a : anode substrate
4b : anode catalyst
5 : cation exchange membrane : current-carrying member for cathode 2
: current-carrying member for anode 4
: cation exchange resin-contained, alkali earth metal scale-preventive film : hydrophilic porous diaphragm
: anion exchange membrane
: cation exchange membrane
: intermediate compartment

Claims

1. An electrolysis system having a configuration comprising a diaphragm, an anode compartment separated by the diaphragm, a cathode compartment separated by the diaphragm, an anode provided in the anode compartment, a cathode provided in the cathode compartment, and raw material water containing alkali earth metal ions supplied to the cathode compartment, wherein the substantially entire surface of the cathode is coated with a cation exchange resin- contained, alkali earth metal scale-preventive film to prevent hydroxides and others of alkali earth metal from depositing on the cathode surface.
2. The electrolysis system as in Claim 1 constituting a diaphragm process electrolysis system, wherein a porous diaphragm is applied as the diaphragm.
3. The electrolysis system as in Claim 1 comprising a cation exchange membrane process electrolysis system, wherein a cation exchange membrane is applied as the diaphragm.
4. The electrolysis system as in Claim 1 or 3 constituting a solid polymer electrolyte type electrolysis system, wherein the anode and the cathode are closely adhered to each surface of the cation exchange membrane, respectively.
5. The electrolysis system as in Claim 1 constituting a three-compartment type electrolysis system comprising a cation exchange membrane and an anion exchange membrane provided between the anode compartment and the cathode compartment as the diaphragm to separate the anode compartment and the cathode compartment to form an intermediate compartment between the cation exchange membrane and the anion exchange membrane.
6. The electrolysis system as in one of Claims 1-5, wherein conductive diamond, lead dioxide, precious metal or precious metal oxide is applied as anode catalyst for the anode.
7. The electrolysis system as in one of Claims 1-6, wherein a current-carrying member is provided for the anode and the cathode.
8. The electrolysis system as in one of Claims 1-7, wherein filler in fiber or powder form comprising inorganic or organic materials is mixed in the cation exchange resin-contained, alkali earth metal scale-preventive film as a reinforcing material of the film.
9. The electrolysis system as in one of Claims 1-8, wherein ceramics particles having the cation exchange function is mixed in the cation exchange resin- contained, alkali earth metal scale-preventive film.
10. The electrolysis system as in Claims 9, wherein at least one kind of ceramics particles selected from among apatite, perovskite type oxide and zeolite is applied as the ceramics particles having the cation exchange function.
1 . The electrolysis system as in one of Claims 1-10, wherein a plate material, a porous metal, a fiber metal form, a mesh or a hole-punched metal, is applied as the cathode substrate.
12. An electrolysis method wherein raw material water containing alkali earth metal ions including calcium ion and magnesium ion is electrolyzed by using the electrolysis system as in one of Claims 1-11.
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