Method for producing oxidized water for sterilization use without adding electrolyte

Abstract

A method for producing oxidized water for sterilization use which contains chlorine dioxide, said method comprising: electrolyzing tap water containing chlorine ions using a three-chamber-type electrolysis vessel, in which an intermediate chamber is located between an anode chamber and a cathode chamber; trapping the chlorine ions dissolved in the tap water; and electrolytically oxidizing the trapped chlorine ions on an anode electrode. A partitioning membrane that isolates the anode chamber from the intermediate chamber is composed of a fluorine-containing cation exchange membrane and an anion exchange membrane, wherein a porous anode electrode is adhered onto the fluorine-containing cation exchange membrane in the partitioning membrane. A partitioning membrane that isolates the cathode chamber from the intermediate chamber is composed of a cation exchange membrane or an anion exchange membrane, wherein a porous cathode electrode is adhered onto the partitioning membrane; and an anion exchange resin is filled in the intermediate chamber.

Claims

1. A method for producing oxidized water for sterilization use which contains chlorine dioxide, comprising: electrolyzing tap water containing chlorine ions using a three-chamber-type electrolysis vessel in which an intermediate chamber is located between an anode chamber and a cathode chamber and is formed by providing partitioning membranes between the anode chamber and the cathode chamber; trapping the chlorine ions dissolved in the tap water; and electrolytically oxidizing the trapped chlorine ions on the anode electrode; wherein a partitioning membrane that isolates the anode chamber from the intermediate chamber has a fluorine-containing cation exchange membrane and an anion exchange membrane and a porous anode electrode is adhered onto the fluorine-containing cation exchange membrane in the partitioning membrane, wherein a partitioning membrane that isolates the cathode chamber from the intermediate chamber has a cation exchange membrane or an anion exchange membrane and a porous cathode electrode is adhered onto the partitioning membrane, wherein the intermediate chamber is filled with an anion exchange resin, and wherein a planar permeable member is provided on an anode chamber side of the porous anode electrode to efficiently perform an oxidation reaction of chlorine ions into chlorine dioxide.

2. The method for producing oxidized water for sterilization use according to claim 1, wherein the electrolysis vessel that has a structure in which the fluorine-containing cation exchange membrane having pores with a diameter of 1 micron or more is adhered onto the porous anode electrode is used to increase the concentration of the chlorine dioxide.

3. The method for producing oxidized water for sterilization use according to claim 1, wherein a system provided with a bypass line parallel to a supplying line in the anode chamber of the three-chamber-type electrolysis vessel is utilized to increase the concentration of the chlorine dioxide.

4. The method for producing oxidized water for sterilization use according to claim 1, wherein raw water purified by a water-softening system filled with a cation exchange resin is utilized as water to be supplied to the intermediate chamber.

5. The method for producing oxidized water for sterilization use which contains chlorine dioxide according to claim 1, wherein the planar permeable member is a porous partitioning plate.

6. The method for producing oxidized water for sterilization use which contains chlorine dioxide according to claim 1, wherein the planar permeable member is a non-woven fabric.

7. The method for producing oxidized water for sterilization use according to claim 1, wherein a chlorine ion aqueous solution tank is provided, and a chlorine ion salt aqueous solution is supplied to the intermediate chamber by a metering pump, if necessary, resulting in electrolytic oxidation, to increase the concentration of the chlorine dioxide.

8. The method for producing oxidized water for sterilization use according to claim 1, wherein water obtained by causing raw water to pass through a cation exchange resin tower is supplied to the intermediate chamber to maintain the electrolysis efficiency for a long period of time, to thereby cause the water to contain chlorine dioxide.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic view illustrating a two-chamber-type electrolysis vessel.

(2) FIG. 2 is a schematic view illustrating a three-chamber-type electrolysis vessel.

(3) FIG. 3 is a plan view of a porous electrode.

(4) FIG. 4 is a schematic view illustrating a three-chamber-type electrolysis vessel used in Example 1.

(5) FIG. 5(a) is a schematic view illustrating a three-chamber-type electrolysis vessel used in Example 2.

(6) FIG. 5(b) is a schematic view illustrating a three-chamber-type electrolysis vessel used in Example 2.

(7) FIG. 6 is a schematic view illustrating a three-chamber-type electrolysis vessel used in Example 3.

(8) FIG. 7 is a flow view in Examples 4 and 5.

(9) FIG. 8 is a flow view in Example 6.

(10) FIG. 9 is a flow view according to another embodiment of Example 6.

(11) FIG. 10 is a schematic view illustrating a three-chamber-type electrolysis vessel used in Example 7.

DESCRIPTION OF EMBODIMENTS

(12) In tap water or the like, chlorine ions are dissolved at the maximum concentration of 200 ppm. When electrolysis is performed in a two-chamber-type electrolysis vessel shown in FIG. 1 or a simple three-chamber-type electrolysis vessel shown in FIG. 2 utilizing chlorine ions in such tap water, the residual chlorine concentration is 0.1 ppm or less, and is so low that the sterilization effect is not expected. When tap water is electrolyzed using the electrolysis vessel, the electric conductivity of tap water is insufficient to obtain target sterilization effect by electrolysis. Therefore, the electrolysis voltage is as high as 100 V or more at a current density of about 10 mA/cm2. Thus, a problem remains in practical terms. For practical use, it is preferred that a target chlorine concentration be achieved at an electrolysis voltage of about 30 V or less.

(13) As described in Example 4, a method for decreasing the electrolysis voltage is a method of filling an intermediate chamber of the three-chamber-type electrolysis vessel in FIG. 2 with a cation exchange resin. The filled cation exchange resin makes it possible to decrease the electrolysis voltage at about 10 mA/cm2 to 20 V or less. However, the residual chlorine concentration is as low as about 0.1 ppm even in this case.

(14) In order to increase the residual chlorine concentration, the electrolysis vessel is improved as shown in FIGS. 4 to 6.

(15) In FIG. 4, the intermediate chamber partitioned by an ion exchange membrane in FIG. 2 is filled with an anion exchange resin. As a partitioning membrane on an anode chamber side, an anion exchange membrane is used. When tap water is allowed to pass through the intermediate chamber, halogen ions such as chlorine ions are retained in the anion exchange resin and concentrated. When electrolysis is performed in this state, the residual chlorine concentration can be increased.

(16) The anion exchange resin and a fluorine-containing cation exchange membrane used in the present invention will be described below. An amino group is bonded to the anion exchange resin as a functional group.

(17) Such an anion exchange resin includes two kinds of exchange resins that are strong basic and weakly basic. In order to efficiently collect chlorine ions and the like in tap water, a strongly basic ion exchange resin is suitable. The strongly basic resin includes two kinds of I type that is bonded to a trimethylammonium group, and II type that is bonded to a dimethylethanolammonium group. The I type strongly basic resin is effective in terms of an efficiency of trapping chlorine ions and the like. Specifically, a strongly basic I-type anion exchange resin that is available from Mitsubishi Chemical Corporation is preferred.

(18) On the other hand, in the fluorine-containing cation exchange membrane, a sulfate ion group is bonded to a fluorine resin as a functional group. Under an environment of fluorine resin, H.sup.+ ions bonded to the sulfate ion groups are easily dissociated, and the H.sup.+ ions can act as carriers during electrolysis. Therefore, it has been reported that pure water is also electrolyzable. As such a cation exchange membrane, Nafion 117 available from DuPont Co., and the like are useful. It has been reported that when an anode electrode is adhered onto the fluorine-containing cation exchange membrane and anode electrolysis is performed, ozone are generated (Proton exchange membrance fuel cell systems based on aromatic hydrocarbon and partially fluorinated disulfonated poly(Arlene ether)copolymers). Since the fluorine-containing cation exchange membrane is swelled in water, chlorine ions may pass through the membrane with high probability.

(19) In order to increase the concentration of residual chlorine containing chlorine dioxide, the membrane permeability of chlorine ions may be important. In this case, when pores of 1 to 1,000 microns are given in the fluorine-containing cation exchange membrane, a reactivity of ozone with chlorine ions can be enhanced.

(20) In FIG. 4, when the fluorine-containing cation exchange membrane is provided as the partitioning membrane on the anode chamber side between the anion exchange membrane and the anode electrode, the residual chlorine concentration can be further enhanced.

(21) It has been known that when the anode electrode is specifically adhered onto the fluorine-containing cation exchange membrane and electrolysis is performed, the generation efficiency of ozone is increased. Produced ozone is subjected to an oxidation reaction with chlorine ions to produce high-order chlorine oxides, as shown by the following formula. (JPH08-134677, and JP2000-234191)
[Chemical Formula 2]
Cl.sup.+O.sub.3.fwdarw.ClO.sub.3.sup.(3)

(22) From the high-order chlorine oxides, chlorine dioxide is produced.
[Chemical Formula 3]
2ClO.sub.3.sup.+O.sub.2.sup.+4H.sup.+.fwdarw.2ClO.sub.2+3H.sub.2O(4)
ClO.sub.3.sup.+OH.+3H.sup.+.fwdarw.ClO.sub.2+2H.sub.2O(5)
2ClO.sub.3.sup.+2Cl.sup.+4H.sup.+.fwdarw.2ClO.sub.2+2H.sub.2O+Cl.sub.2(6)

(23) Cl.sub.2, ClO.sup., and ClO.sub.2 have oxidative power, and an effect of sterilizing microorganisms. The substances contribute to the residual chlorine concentration, and exhibit sterilizing power.

(24) Thus, when chlorine ions are directly added to residual chlorine generated by an electrolytic oxidation reaction, resulting in an oxidation reaction of the chlorine ions due to ozone, the residual chlorine concentration can be increased. Specifically, as shown in FIG. 6, the reaction efficiency of ozone produced at the anode electrode with chlorine ions is intended to be increased by locating a porous substance at the anode electrode on the anode chamber side in the anode chamber.
[Chemical Formula 4]
Cl+O.sub.3.fwdarw.ClO.sub.3.sup.(7)
Cl.sub.2+2H.sub.2O2H.sup.++2Cl+O.sub.2(8)

(25) In order to efficiently perform an oxidation reaction of halogen ions, a planar permeable member is provided on an anode chamber side of a porous anode electrode. This configuration prevents direct contact of supplied water with the anode electrode, and increases the reaction efficiency of chlorine ions with ozone or the like. Furthermore, a reaction substance is supplied through pores of a non-woven fabric to a side of anode water.

(26) Examples of the planar permeable member used in the present invention may include a porous partition plate, a porous film, and a non-woven fabric.

(27) The porous partition plate or the porous film is a plate or a film that has many fine pores. The porous partition plate may constitute a porous partitioning membrane. In order to prevent a decrease in halogen ion concentration due to direct supply of raw water of the anode chamber to the anode electrode, in the planar permeable member, the porous partition plate is provided on the anode chamber side of the anode electrode. The porous partition plate or the porous film is desirably formed from a synthetic resin such as polypropylene and polyethylene as a material since the material is unlikely to cause deterioration such as rust due electrolytically oxidized water. As the plate or film that is formed from the resin, a plate or a film in which many pores with a diameter of 1 mm or less are formed is used. The pores may be mechanically formed, or a porous film having pores with a diameter of 100 m or more may be used.

(28) The non-woven fabric is a sheet-shaped fabric in which polymeric fibers are entangled without weaving. In general, fibers of polyethylene, polypropylene, polyethylene terephthalate, or the like are used. Since in the present invention, the non-woven fabric is combined with the anode electrode, resistance to oxidation is required. For this reason, a polytetrafluoroethylene (PTFE) resin non-woven fabric is suitable for the present invention. The pore size of the non-woven fabric is suitably 10 to 1,000 m.

(29) In order to promote the reaction of the oxidizable substance such as ozone produced on a surface of the anode electrode with unreacted chlorine ions or the like as described above, the anode chamber is divided by the planar permeable member.

(30) In Table 1, the anode electrode side is called a mixing chamber. This planar permeable member prevents direct supply of raw water to the surface of the anode electrode and may improve the reaction efficiency of ozone with chlorine ions or the like.

(31) The present invention aims to produce oxidized water for sterilization use by electrolytic oxidation of raw water which can be used for drinking such as tap water. However, the raw water generally includes dissolved divalent metal ions of alkaline earth metal such as calcium and magnesium. It has been known that the divalent metal ions are attached to a cathode electrode, and the cathode electrode is contaminated to increase the electrolysis voltage. Thus, an electrolysis operation is made difficult. In the present invention, when the concentration of the divalent metal ions in the raw water supplied to the intermediate chamber of the three-chamber-type electrolysis vessel is high, the raw water is allowed to pass through a cation exchange resin tower before supply of the raw water to the intermediate chamber to prevent contamination of the cathode electrode.

Example 1

(32) As shown in FIG. 4, in a three-chamber electrolysis vessel that was provided with an intermediate chamber between an anode chamber 2 and a cathode chamber 4, a porous anode electrode 1 was adhered onto a partitioning membrane 1 (31) as an anion exchange membrane, and a porous cathode electrode was adhered onto a partitioning membrane 2 as a cation exchange membrane. An intermediate chamber 6 was provided between the partitioning membrane 1 and the partitioning membrane 2 (32), and was filled with an anion exchange resin 9. In the anion exchange resin 9, halogen ions such as chlorine ions, bromine ions, and iodine ions in tap water are trapped. As halogen ions contributing to electrolysis, the trapped halogen ions are used to perform oxidative decomposition. Use of the trapped ions improves an efficiency of producing Cl.sub.2, Br.sub.2, and I.sub.2 which are sterilizable.

Example 2

(33) In the anion exchange membrane of the partitioning membrane 1 (31) in the three-chamber-type electrolysis vessel of FIG. 4, it has been known that oxidation generally promotes deterioration. Therefore, a fluorine-containing cation exchange membrane 33 was interposed between the partitioning membrane 1 (31) including the anion exchange membrane and a porous anode electrode, as shown in FIG. 5(a). The presence of the fluorine-containing cation exchange membrane extends the life span of the anion exchange membrane. Further, it is important that the fluorine-containing cation exchange membrane is known to be swelled with water, also easily allow anions to pass, and have high generation efficiency of ozone. The generated ozone has sterilization property. By the ozone, chlorine ions are oxidized to produce chlorine dioxide (Cl.sub.2O).

(34) Furthermore, since the concentration of halogen ions such as chlorine ions is low, efficient use of the ions is required in the present invention. As shown in FIG. 5(b), a porous partitioning wall 35 is provided on a water communication side of the porous anode electrode to increase the concentration of halogen ions around the porous anode electrode in the three-chamber-type electrolysis vessel. In the present invention, a chamber separated by the anode electrode 1 and the porous partitioning membrane 35 is called a mixing chamber. When the porous partitioning membrane is provided, supply water to be supplied to anode water makes it possible to prevent a decrease in the concentration of halogen ions around the anode electrode. Thus, the electrolytic oxidation reaction efficiency is improved, and the residual chlorine concentration is improved.

Example 3

(35) In order to improve the reactivity of ozone with chlorine ions in the three-chamber-type electrolysis vessels as shown in FIGS. 5(a) and 5(b), a surface of the anode electrode 1 was covered with a porous film in the three-chamber-type electrolysis vessel as shown in FIG. 6. Specifically, a fluorine-containing non-woven fabric 36 was used as the cover. The provision of the non-woven fabric makes it possible to increase the reaction efficiency of generated ozone gas with chlorine ions.

Example 4

(36) As shown in FIG. 3, platinum-plating titanium porous anode and cathode electrodes of 86 cm.sup.2 were used, and the thickness of the intermediate chamber was 1 cm. The efficiencies of producing an oxidizable substance in the electrolysis vessels shown in FIGS. 2, 4, 5, and 6 were compared and investigated. A system shown in FIG. 7 was used as a test device. In the system of FIG. 7, tap water having a chlorine ion concentration of about 100 ppm is first allowed to pass through a cation exchange resin tower 10 to remove divalent metal ions that may considerably contaminate the cathode electrode. The divalent metal ion-filtered water was supplied to the intermediate chamber of each of the electrolysis vessels shown in FIGS. 2, 4, 5, and 6. A tap water inlet 12 is installed to inject tap water into the cation exchange resin tower 10. The ion exchange resin is efficiently regenerated by regularly adding a salt or the like as a regenerated salt from a regenerated salt addition port 11 and stirring an aqueous solution of regenerated salt using a stirring pump 101.

(37) The electrolysis current was 8 A in each electrolysis vessel. The flow rate of tap water supplied to the anode chamber is 0.5 L/min, and the flow rate of tap water supplied to the intermediate chamber is 2.0 L/min.

(38) When the simple three-chamber-type electrolysis vessel of FIG. 2 was used for comparison, the electrolysis voltage was increased and the electrolysis current was decreased to 1 A or less, and the residual chlorine concentration was 0.01 ppm or less. When the intermediate chamber of the three-chamber-type electrolysis vessel of FIG. 2 was filled with a cation exchange resin, the electrolysis voltage was decreased to 20 V or less, but the residual chlorine concentration was about 0.1 ppm. When the three-chamber-type electrolysis vessel in which the intermediate chamber was filled with an anion exchange resin as shown in FIG. 3 was used, the residual chlorine concentration became about 1.5 pm. From comparison of the values, an effect caused by charging the intermediate chamber with the anion exchange resin was revealed.

(39) In order to enhance the durability of the anion exchange membrane of the partitioning membrane and effectively use ozone, a membrane in which the fluorine-containing cation exchange membrane and the anion exchange membrane were overlapped as shown in FIG. 5 so that the fluorine-containing cation exchange membrane was adhered onto the anode electrode was used as the partitioning membrane. When this electrolysis vessel was used, the residual chlorine concentration was about 2.0 ppm. In order to increase the transmittance of chlorine ions, 35 pores of about 0.5 microns were formed in this fluorine-containing cation exchange membrane.

(40) When the electrolysis vessel in which the surface of the anode electrode was covered with the non-woven fabric as shown in FIG. 6 was used, the residual chlorine concentration in oxidized water produced became about 4.0 ppm. From these data, effectiveness of the present invention was exhibited.

(41) TABLE-US-00001 TABLE 1 RESIDUAL RATIO OF STRUCTURE OF CHLORINE CHLORINE ELECTROLYSIS MIXING PARTITIONING INTERMEDIATE CONCENTRATION DIOXIDE VESSEL CHAMBER MEMBRANE CHAMBER (ppm) (%) pH THREE- FIG. 2 ANION ~0.1 0 6.1 CHAMBER- EXCHANGE TYPE MEMBRANE THREE- FIG. 2* ANION ~0.1 0 6.5 CHAMBER- EXCHANGE TYPE MEMBRANE THREE- FIG. 4 ANION ANION ~0.2 0 4.8 CHAMBER- EXCHANGE EXCHANGE TYPE MEMBRANE RESIN THREE- FIG. 5 FLUORINE-CONTAINING ANION ANION ~2.0 25 4.5 CHAMBER- CATION EXCHANGE EXCHANGE EXCHANGE TYPE MEMBRANE MEMBRANE RESIN THREE- FIG. 6 NON- FLUORINE-CONTAINING ANION ANION ~4.0 65 4.2 CHAMBER- WOVEN CATION EXCHANGE EXCHANGE EXCHANGE TYPE FABRIC MEMBRANE MEMBRANE RESIN The mark *represents that an intermediate chamber of a three-chamber-type electrolysis vessel shown in FIG. 2 is filled with a cation exchange resin.

Example 5

(42) FIG. 8 shows an example of a system capable of appropriately exchanging and supplying both of purified tap water and a salt solution to an intermediate chamber of a three-chamber-type electrolysis vessel. In this example, the electrolysis vessel shown in FIG. 5(b) was built in. In this electrolysis vessel, a partitioning membrane structure having the anion exchange membrane 31 and the fluorine-containing cation exchange membrane 33 is used, and the partitioning membrane of this structure is adhered onto the anode electrode 1. A porous partitioning membrane 35 is provided on a side of the anode chamber 2 that is an opposite side of the partitioning membrane structure. For the intermediate chamber of the electrolysis vessel, a method of supplying tap water having passed through the ion exchange resin tower 10 and a method of supplying a salt solution from a salt solution tank 13 using a metering pump 150 to the intermediate chamber can be selected.

(43) In the system of FIG. 8, the salt solution tank was filled with a 15% salt solution, and the salt solution was supplied to the intermediate chamber at about 3 mL/min. The dimension of an electrode built in the electrolysis vessel was 68 cm.sup.2, and the electrolysis current was 10 A. The flow rate of tap water supplied was 1 L/min. The residual chlorine concentration of electrolytically oxidized water produced was measured to be about 45 ppm. The ratio of chlorine dioxide in the oxidized water was 72%. In the measurement of chlorine dioxide, colorimetry using glycine and diethyl-p-phenylene diamine (DPD) was used.

Example 6

(44) A system that is basically the same as the system of FIG. 8 and is provided with a bypass line that circumvents the anode chamber of the electrolysis vessel is shown in FIG. 9. When this system is used, the flow rate of tap water as raw water in the anode chamber can be largely decreased while the whole flow rate of oxidized water is maintained. When the flow rate in the anode chamber was restricted to 0.2 L/min and the whole flow rate of tap water was 1 L/min under the same electrolysis condition as in Example 5, the residual chlorine concentration was increased to 85 ppm.

Example 7

(45) Herein, a structure in which the three-chamber-type electrolysis vessel is improved so as to decrease the use amount of water is shown in FIG. 10. As shown in FIG. 10, a cathode chamber is removed, and an air electrode is used as a cathode electrode. When a fluorine-containing cation exchange membrane is used for a partitioning membrane on a cathode side, water in an intermediate chamber is partially transferred to a side of porous cathode electrode due to swelling property that is a property of the fluorine-containing cation exchange membrane. Therefore, electrolysis can be continually performed.

INDUSTRIAL APPLICABILITY

(46) According to the present invention, oxidized water for sterilization/disinfection use in a neutral range can be produced. Therefore, the present invention is extremely useful for processing of foods or in a clinical setting.

REFERENCE SIGNS LIST

(47) 1 porous anode electrode 2 anode chamber 21 anode chamber outlet 22 anode chamber inlet 31 partitioning membrane 1 32 partitioning membrane 2 33 fluorine-containing cation exchange membrane 35 porous partitioning plate 36 non-woven fabric 4 cathode chamber 41 cathode chamber outlet 42 cathode chamber inlet 5 porous cathode electrode 6 intermediate chamber 61 intermediate chamber inlet 62 intermediate chamber outlet 9 anion exchange resin