JPH08246180A - Electrolytic method - Google Patents

Abstract

PURPOSE: To obtain an improved water small in the quantity of metallic impurities and having a specific oxidation-reduction potential and pH with excellent electrolytic efficiency by electrolyzing while supplying an electrolyte containing an acid and a non-metallic salt to an anode chamber side of a two chamber type high molecular solid electrolyte type electrolytic cell. CONSTITUTION: A porous anode 7 composed of a noble metal or noble metal oxide powder and a porous cathode 8 composed of Ni or the like are provided respectively with an anode and cathode surface of a cation exchange membrane 2 in close contact state and current is supplied through an anode and cathode collecting body 9, 10. Passages 11, 15 are formed inside of an anode and cathode chamber wall plate 5, 6. An anolyte, which is fed from an inlet 12 and in which NH4 Cl or the like is dissolved, enters to the anode chamber from an opening part 13, is brought into contact with the anode 7, oxidized by a compound having high oxidation force and high oxidation-reduction potential of >=1000mV such as hypochlorous acid and taken out from an outlet 14 as the improved water having pH<=3. And if necessary, a deionized water supplied from the inlet 16 enters to the cathode chamber from the opening part 17, is brought into contact with the cathode 8 with an ion-containing water transferred from the anode, reduced to form an alkaline water, which is taken out from the outlet 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has a high oxidizing power and a high pH.
TECHNICAL FIELD The present invention relates to an electrolysis method for producing reformed water having a low water content, and more particularly to an electrolysis method for providing cleaning water with excellent detergency that can be used in a semiconductor cleaning process, and alkaline water with excellent reducibility.

[0002]

2. Description of the Related Art Conventionally, it has been widely practiced to modify water by electrolysis to produce acidic water or alkaline water, but recently, their applications have been particularly widespread, and water treatment, medical treatment, etc. Modified water is widely used in various fields such as sterilization for food and food industry. Of the reforming water produced by conventional electrolysis, the acidic water generated in the anode chamber is the redox potential (ORP).
Has an oxidizing power of 1000 mV or more, and has an effect of dissolving and removing metal precipitates. On the other hand, the alkaline water generated on the cathode chamber side has a reducing power of about −600 mV as an oxidation-reduction potential, and has a function of dissolving and removing the precipitated oxide.

In order to carry out ordinary electrolysis, an appropriate supporting electrolyte is added to the electrolyte to provide ionic conductivity. In many cases, this supporting electrolyte is a metal salt and remains in the reforming water in which metal ions are generated even when the electrolytic solution containing the metal salt is electrolyzed. Inconvenience arises in that the metal ions of (3) adhere to the surface of the semiconductor as impurities to cause insulation failure. When a neutral diaphragm is used as a diaphragm that separates the anode chamber and the cathode chamber, both electrodes sandwiching the diaphragm are placed close to each other in order to reduce the electrolytic voltage. However, even with such an arrangement, since the gas-liquid permeability of the diaphragm is high, various products generated in each electrode chamber are transferred to the counter electrode chamber and reoxidized or reduced to cause a reduction in efficiency. Generally, the electrolyte concentration is low, so the electrical resistance is high,
Even with a very low current density of 1 A / dm ^2, the gap between the electrodes is 1 m
The voltage may be 10 V or more at about m. This defect can be solved to some extent by increasing the distance between the poles, but it is not perfect.In addition, the increase in the power consumption resulting from the increase in the resistance with the increase in the pole distance becomes remarkable, and the heat generated by this resistance loss is often large. There has been a problem that the liquid needs to be cooled and extra power consumption occurs.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, that is, impurities such as metals are easily mixed in the reforming water generated by electrolysis, and the electrolysis efficiency is low and the power consumption is apt to increase. It is intended to provide an electrolysis method.

[0005]

In the present invention, a cation exchange membrane is used as a diaphragm, and a noble metal or a noble metal oxide anode and a cathode are placed on both sides of the cation exchange membrane in a state of being substantially adhered to the cation exchange membrane. Electrolysis is performed while supplying an electrolytic solution containing an acid and / or a non-metallic salt to the anode chamber side of a two-chamber solid polymer electrolyte type electrolytic cell, and the redox potential is 1000 m in the anode chamber.
The electrolyzing method is characterized in that reformed water having a pH of 3 or more and a pH of 3 or more is obtained.

Hereinafter, the present invention will be described in detail. In the present invention, a polymer solid electrolyte type electrolytic cell using a cation exchange membrane as a diaphragm, a noble metal or noble metal oxide anode as an anode, and an acid and / or a non-metal salt as a supporting electrolyte are used.

Since the solid polymer electrolyte type electrolytic cell equipped with the cation exchange membrane of (1) is used, the present invention can avoid the efficiency decrease due to the mixing of the anolyte and the catholyte and save energy by the low voltage operation. Can be achieved. Further, it becomes possible to operate under a high current density, and it becomes possible to produce the same amount of reforming water with a small device. Although the reason is not clear, the consumption of the electrode material is reduced, in other words, the contamination of the reforming water due to the mixing of the electrode material is avoided. This is because the conductivity of the electrolyte is good so that the uneven distribution of current is eliminated and the electrical resistance is reduced even if partially, and the temperature rise is suppressed.
It can be inferred that this is because the portion in contact with the membrane functions three-dimensionally and the load on the electrode is substantially reduced.

Empirically, when the electrode material is platinum, in the case of non-solid electrolyte type, the degree of consumption in salt water electrolysis with sodium chloride concentration of about 1000 ppm is 10 to 30 mg / KAH, whereas in the case of solid electrolyte type. In case of 0.5 to 3 mg / KAH
It can be reduced to 1/10 to 1/20 of wear. When the electrode material is iridium oxide, the consumption is even smaller, 0.05-0.3
It becomes mg / KAH. The suppression of the mixing of impurities into the modified water due to the reduction of the consumption amount of the electrode material is particularly important in the case of a semiconductor in which the mixing of conductive solids is required to be minimized.

[0009] The use of perfluorocarbon sulfonic acid type ion exchange membrane as a cation exchange membrane, the anode side in a highly oxidizing hypochlorous acid ions (ClO ^-) and persulfate ion (S ₂ O ₈ ^-) is generated Even so, stable operation can be performed with extremely strong resistance to it. Further, the cation exchange membrane has high conductivity and is stable against electrolysis even in a diluted electrolytic solution or pure water. Furthermore, it exhibits extremely high resistance to many chemicals in addition to the above-mentioned highly oxidizable products.

Next, in the present invention, a noble metal or noble metal oxide anode is used as the anode as described above. This noble metal or noble metal oxide itself consumes very little electricity, and in addition to the use of the polymer solid electrolyte type electrolytic cell described above, the use of these electrode substances can further reduce the pollution of the obtained reformed water. it can. For example, when carbon, which is a conventional electrode material other than the electrode material, is used as the anode material, the carbon is oxidized by the anodic reaction to generate carbon dioxide, which causes a problem of weakening the electrode.

In the noble metal or noble metal oxide anode, the oxidizability obtained can be controlled depending on the kind of the noble metal anode used. That is, when a substance containing platinum is used as an electrode when sulfate ions are present during electrolysis, the sulfate ions can be oxidized to persulfuric acid to further increase the redox potential. When a platinum group noble metal oxide is used as an electrode material when chlorine ions are present during electrolysis, the chlorine ions can be oxidized to hypochlorite ions and the redox potential can be further increased. Furthermore, at this time,
Since hydrogen ions are generated, the pH can be lowered sufficiently in any case. In either reaction, the main reaction is the oxygen generation reaction, and does not consume itself as in the case of the carbon electrode described above.

In the present invention, as described above, an acid and / or a nonmetallic salt is used as the supporting electrolyte. Specifically, hydrochloric acid and sulfuric acid can be used as the acid, and ammonium chloride and ammonium sulfate can be used as the non-metallic salt. The ammonium salt contained in the electrolytic solution can be used as a component of the cleaning solution because ammonium ions, which are cations, are transferred to the cathode chamber by electrolysis. Also, in the case of hydrochloric acid or sulfuric acid, the cation is a hydrogen ion, and therefore no inconvenience occurs even if it remains.

The concentration of these supporting electrolytes is 100 to 10,000.
It is desirable to adjust the content to be ppm, and if it is less than 100 ppm, the acidity or alkalinity of the resulting reformed water tends to be insufficient, acid water with an oxidation-reduction potential of 1000 mV or more and a pH of 3 or less cannot be obtained, and the current efficiency of the reaction is also descend. On the other hand, when the concentration of the supporting electrolyte exceeds 10,000 ppm, both the oxidation-reduction potential and the pH reach a satisfactory level, but an undesirable side reaction may occur. That is, when chlorine ions are contained, the generation of chlorine gas becomes active and problems such as corrosion due to chlorine gas easily occur. Further, in the case of sulfate ions, the concentration of persulfate ions produced becomes too high, which may corrode the electrolytic cell itself, auxiliary equipment, piping and the like.

When an electrolytic solution containing an acid and / or a non-metallic salt is electrolyzed using the electrolytic cell thus constructed,
The reformed water can be obtained with high current efficiency under the low power consumption which is characteristic of the polymer solid electrolyte type electrolysis. At this time, since the supplied electrolytic solution does not contain metal ions, there is no metal in the obtained reformed water, and in the reformed water, the presence of metal ions causes a problem such as poor insulation. It can be effectively used as washing water for semiconductors. In addition, since the noble metal or noble metal oxide electrode that hardly consumes is used as the anode, it is possible to prevent the increase of impurities due to the mixing of the electrode material.

Next, an example of an electrolytic cell which can be used in the electrolysis method according to the present invention will be described with reference to the accompanying drawings. Figure 1
It is a schematic sectional drawing which shows an example of the electrolytic cell which can be used for the method of this invention. The electrolyzer 1 for producing reformed water has a frame-shaped anode chamber gasket 3 and cathode chamber gasket 4 that sandwich the periphery of the cation exchange membrane 2, and the surface of each gasket 3 and 4 opposite to the cation exchange membrane 2. It is constituted by an anode chamber wall plate 5 and a cathode chamber wall plate 6 which are installed in close contact with each other and have an electrolytic solution circulation function.

On the anode surface of the cation exchange membrane 2, platinum,
A porous anode 7 made of a platinum group metal such as ruthenium, iridium or rhodium or a platinum group metal oxide powder such as ruthenium oxide or iridium oxide is placed in close contact, while nickel is provided on the cathode surface of the cation exchange membrane 2. A porous cathode 8 made of, for example, is installed in a close contact state. The anode 7 and the cathode 8 have an anode current collector 9 and a cathode current collector 10, respectively.
Are connected, and electricity is supplied through the current collector. An anolyte flow passage 11 is formed inside the anodic chamber wall plate 5, and the anolyte, which is supplied from the anolyte inlet 12 and dissolves ammonium chloride or the like, enters into the anodic chamber through an anodic chamber opening 13 to form the anodic liquid 7 Is contacted with, and is oxidized into a compound having a high oxidation-reduction potential such as hypochlorous acid and having a strong oxidizing power, and is taken out from the anolyte outlet 14 as reforming water having a high pH value.

Further, a catholyte flow passage 15 is formed inside the cathode chamber wall plate 6, and deionized water supplied as needed from a catholyte inlet 16 enters the cathode chamber through an opening 17 of the cathode chamber. It is brought into contact with the cathode 7 together with the transition water from the anode containing ions to be reduced to generate alkaline water, which is taken out from the catholyte outlet 18.

[0018]

EXAMPLES Next, examples of the electrolysis method according to the present invention will be described, but the examples do not limit the present invention.

EXAMPLE 1 Porous platinum plate electrode area is 0.053 dm ² as the anode, a porous platinum plate electrode area is 0.053 dm ² as the cathode, as a cation exchange membrane Nafion (trade name) 117, respectively It was used to construct the electrolytic cell shown in FIG. Concentrations of 1000 ppm and 30 as anolyte respectively
Three kinds of ammonium chloride aqueous solutions of 00 ppm and 10000 ppm were prepared.

While maintaining other conditions constant, the concentration of the anolyte was changed to 1000 ppm, 3000 ppm and 10000 ppm, and the pH of the reformed anolyte (acidic water), the redox potential of the reformed anolyte, of the changes, The influence of the pH of the modified catholyte (alkaline water) and the redox potential of the modified catholyte was measured. The results are shown in FIGS. 2 (a), 3 (a), 4 (a) and 5 (a), respectively. Then, while maintaining other conditions constant, the current density was 10 A / dm ² , 20 A / dm ² and 30 A / dm ^2.
And the effect of the change on the pH of the reforming anolyte (acidic water), the redox potential of the reforming anolyte, the pH of the reforming catholyte (alkaline water) and the redox potential of the reforming catholyte. It was measured. The results are shown in FIG. 2 (b), FIG. 3 (b), FIG. 4 (b) and FIG.
Each is shown in (b).

While maintaining the other conditions constant, the flow rate of the anolyte was changed to 4 cc / min, 8 cc / min and 12 cc / min, and the pH and the reforming of the anolyte (acidic water) were modified by the changes. Redox potential of anolyte, pH of modified catholyte (alkaline water)
And the effect of the modified catholyte on the redox potential was measured. The results are shown in FIGS. 2 (c), 3 (c), 4 (c) and 5 (c), respectively. Finally, while maintaining other conditions constant, the circulation flow rate of the cathode chamber liquid was set to 2 cc / min, 7 cc / min and
The change was changed to 11 cc / min, and the effect of the change on the pH of the modified catholyte (alkali water) and the redox potential of the modified catholyte was measured. The results are shown in FIGS. 4 (d) and 5 (d), respectively.

As can be seen from FIG. 2, when the ammonium chloride concentration is in the range of 1000 to 10000 ppm, the pH of the modified anolyte is
Was maintained below 3 at all times, and similarly the pH of the modified anolyte was maintained below 3 at current densities in the range of 10-30 A / dm ² and anolyte flow rates in the range of 4-12 cc / min. See also Figure 3
As can be seen, the redox potential of the reforming anolyte is 1000 mV when the ammonium chloride concentration is in the range of 10,000 to 10,000 ppm, the current density is in the range of 10 to 30 A / dm ² and the anolyte flow rate is in the range of 4 to 12 cc / min. Maintained above.

As can be seen from FIG. 4, 1000 to 10000 p
Ammonium chloride concentration in the range of pm, 10-30 A / dm ²
The pH of the modified catholyte was maintained at 8 or higher at a current density in the range of 4 to 12 cc / min, and a catholyte flow rate of 2 to 11 cc / min. As can be seen from FIG. 5, 1000
Ammonium chloride concentration in the range of ~ 10000 ppm, 10 ~ 30
Current density in the range of A / dm ^2, the redox potential of the reforming catholyte anolyte flow rate and 2～11Cc / min catholyte flow rate range 4～12Cc / min was maintained below -680 mV.

[0023]

Comparative Example 1 Electrolysis was carried out in the same manner as in Example 1 with an ammonium chloride concentration of 10 ppm and a current density of 30 A / dm ^2. The pH of the obtained modified anolyte was 6.5 and its redox potential was 400. mV, the pH of the catholyte was 8.0, and its redox potential was −680 mV, which were far inferior to the pH and redox potential of the anolyte obtained in the examples.

[0024]

[Comparative Example 2] Electrolysis was carried out in the same manner as in Example 1 except that a neutral diaphragm was used as the diaphragm instead of Nafion, the ammonium chloride concentration was 1000 pH, the current density was 1 A / dm ² , and the cell voltage was 20 V. Now, the pH of the anolyte is 4.2,
The redox potential was 700 mV, and neither was satisfactory.

[0025]

According to the method of the present invention, a cation exchange membrane is used as a diaphragm, and a noble metal or a noble metal oxide anode and a cathode are placed on both sides of the membrane in a state of being substantially adhered to the cation exchange membrane. Electrolysis is carried out while supplying an electrolytic solution containing an acid and / or a non-metallic salt to the anode chamber side of the molecular solid electrolyte type electrolytic cell, and the pH is set at a redox potential of 1000 mV or more in the anode chamber.
Is a reforming water of 3 or less.

In the method of the present invention, a polymer solid electrolyte type electrolytic cell equipped with a cation exchange membrane and a noble metal or noble metal oxide electrode with almost no wear as an anode is used, and a salt containing no metal or an electrolyte is used. Since an acid is used, it is possible to obtain reformed water with high current efficiency under low power consumption, and further, there is no metal in the reformed water, and the reformed water has particularly no metal ion. It can be effectively used as cleaning water for semiconductors that causes problems such as poor insulation.

Hydrochloric acid or sulfuric acid can be used as the acid, and ammonium chloride or ammonium sulfate can be used as the non-metallic salt. The concentration of these substances during electrolysis is 100 to 10000 pp.
It is desirable to set m. The above-mentioned acid or non-metallic salt is electrolyzed to generate chlorine ions, perchlorate ions, persulfate ions, etc., and these ions increase the redox potential of the resulting acidic water to improve the desired characteristics. Can provide quality water.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of an electrolytic cell that can be used in an electrolysis method according to the present invention.

FIG. 2 is a graph showing the influence of each factor on the pH of the acidic water obtained in Example 1.

FIG. 3 is a graph showing the influence of each factor on the redox potential of the acidic water obtained in Example 1.

FIG. 4 is a graph showing the influence of each factor on the pH of alkaline water obtained in Example 1.

FIG. 5 is a graph showing the influence of each factor on the redox potential of the alkaline water obtained in Example 1.

[Explanation of symbols]

1 ... Electrolyzer for producing reforming water 2 ... Cation exchange membrane 3, 4 ... Gasket 5 ... Anode chamber wall plate 6 ...
..Cathode chamber wall plate 7 ... Anode 8 ... Cathodes 9 and 10
..Current collector 11 ... Anode liquid flow passage 15 ... Cathode liquid flow passage

Claims (4)

[Claims] 1. A two-chamber solid polymer electrolyte type electrolysis in which a cation-exchange membrane is used as a diaphragm, and a noble metal or a noble metal oxide anode and a cathode are placed on both sides of the cation-exchange membrane in a state of being substantially adhered to the cation-exchange membrane. Electrolysis is performed while supplying an electrolytic solution containing an acid and / or a non-metallic salt to the side of the anode chamber of the tank to obtain reformed water having a redox potential of 1000 mV or more and a pH of 3 or less in the anode chamber. Electrolysis method. 2. The acid is hydrochloric acid and / or sulfuric acid.
The electrolysis method described in. 3. The electrolysis method according to claim 1, wherein the non-metallic salt is ammonium chloride and / or ammonium sulfate. 4. The concentration of acid and / or non-metallic salt is 100-.
The electrolysis method according to claim 1, wherein the electrolysis is 10000 ppm.