JPH09220573A - Electrolytic method using two-chamber type electrolytic cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the mixing of impurities such as metal into modified water, the lowering of electrolytic efficiency and an increase in power consumption by electrolyzing a soln. containing ammonium ions or aq. ammonia while supplying the same to the cathode chamber of a two-chamber electrolytic cell to obtain acidic water of which the redox potential and pH are specific values in an anode chamber. SOLUTION: Porous platinum plates are used as an anode 7 and a cathode 8 and an anion exchange membrane 2 is inserted into the space between both electrodes to constitute an electrolytic cell 1. A current is supplied across the anode 7 and the cathode 8 while a soln. containing ammonium ions, for example, ammonium chloride aq. soln. or aq. ammonia is supplied into an anode chamber to electrolyze the soln. containing ammonium ions or aq. ammonia. Acidic water with redox potential of 1000V or higher and pH of 4 or less is formed in the anode chamber while alkali water is formed in a cathode chamber. By this constitution, modified water can be obtained with high current efficiency under low power consumption.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is free from salts and metals,
Acidic water with high oxidizing power and low pH or high reducing power p
The present invention relates to an electrolysis method for simultaneously producing alkaline water having a high H content, and more particularly to an electrolysis method for providing acidic water or alkaline water having excellent detergency that can be used in a semiconductor cleaning process.

[0002]

2. Description of the Related Art Conventionally, reforming water by electrolysis to produce reformed water such as acidic water and alkaline water has been widely practiced in the past. Modified water is widely used in various fields such as clean water treatment, medical sterilization, and food industry. Of the reformed water produced by conventional electrolysis, alkaline water produced in the cathode chamber has a reducing power of -600 mV or more as an oxidation-reduction potential (ORP),
It has a function of dissolving and removing the precipitated oxide. At the same time, acidic water having a pH of 3 or less and an oxidation-reduction potential (ORP) of 1.2 V or more is usually produced in the anode chamber of the electrolytic cell.

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 for partitioning the anode compartment and the cathode compartment, the two electrodes sandwiching the diaphragm are arranged close to each other 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 an extremely low current density of 1 A / dm ^2, a voltage of 10 V or more may occur with a gap of about 1 mm. This defect can be solved to some extent by increasing the distance between the electrodes, but it is not perfect.In addition, the increase in the power consumption resulting from the increase in the resistance due to the increase in the distance between the electrodes becomes remarkable, and the heat generated by this resistance loss is often large. However, there is a problem in that 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]

The present invention is directed to a two-chamber type electrolytic cell in which an anode and a cathode are closely attached to both sides of the ion exchange membrane divided into an anode chamber and a cathode chamber by a cation exchange membrane. Electrolysis is performed while supplying a solution containing ammonium ions or ammonia water to the cathode chamber, and acidic water having an oxidation-reduction potential of 1000 mV or more and a pH of 4 or less is obtained in the anode chamber, and alkaline water is obtained in the cathode chamber. This is an electrolysis method using a two-chamber electrolysis cell.

Hereinafter, the present invention will be described in detail. The reason why acidic water or alkaline water is obtained by electrolysis in which pure water or the like is added to the anode chamber and ammonium ions or ammonia is added to the cathode chamber is presumed as follows. When pure water (deionized water) or diluted acidic water is added to the anode chamber, and ammonium ions (solution containing ammonium salt or ammonia water) are added to the cathode chamber and electricity is applied, the ammonium ions in the cathode chamber are diffused due to the concentration gradient. Part of it permeates the cation exchange membrane and moves to the side of the anode chamber. The transferred ammonium ions again move to the cathode chamber side by electrophoresis. Therefore, the transfer rate of hydrogen ions generated by water electrolysis at the anode is reduced by that amount, and the pH on the anode chamber side is reduced. Since oxygen or ozone is generated and dissolved at the anode, the equilibrium potential is changed to be noble and acidic water with high activity is obtained. When ammonium chloride or ammonium sulfate is used as an ammonium salt, chloride ions and sulfate ions are generated in the catholyte solution, but these ions remain in the cathode chamber because they cannot pass through the cation exchange membrane and affect the acidic water generated in the anode chamber. Don't give. When ammonia water is used as the electrolyte, only hydroxide ions exist as anions in the electrolytic cell, and reformed water containing very few impurities can be obtained.

In the cathode chamber, the hydrogen generation reaction from water progresses due to the shortage of hydrogen ions transferred from the anode chamber side, the pH shifts to the alkaline side, and the highly active alkaline water is generated due to the dissolution of the hydrogen gas generated at the cathode. can get. In the present invention, an electrolytic cell using a cation exchange membrane as a diaphragm, preferably a solid polymer electrolyte type electrolytic cell, preferably a platinum group metal or platinum group metal oxide anode as an anode, preferably a platinum group metal as a cathode Alternatively, a carbon cathode is further used, and an ammonium salt or an alkali is used as an electrolyte, and a solution of the electrolyte is supplied to the cathode chamber of the electrolytic cell.

Since the electrolytic cell equipped with the cation exchange membrane is used, in the present invention, it is possible to avoid the efficiency decrease due to the mixing of the anolyte and the catholyte, and to achieve the energy saving by the low voltage operation. 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. Further, as described above, even when cations such as chlorine ions and sulfate ions are supplied to the cathode chamber, the cation exchange membrane prevents the cations from permeating into the anode chamber, and acidic water free from contamination such as metals. Is obtained. 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, and the portion in contact with the membrane functions three-dimensionally. It can be speculated that this is due to the fact that the burden on the

Empirically, in the case of the non-solid electrolyte type in which the electrode material is platinum, the degree of consumption in salt water electrolysis with a sodium chloride concentration of about 1000 ppm is 10 to 30 mg / KAH, whereas in the case of the solid electrolyte type 0.5 to 3 mg / KAH and 1 /
It can be reduced to 10 to 1/20 consumption. When the electrode material is iridium oxide, the consumption is even smaller, 0.05-0.3m
It becomes g / 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. When a solid electrolyte is used, the solid electrolyte also has a function as a diaphragm, has high selectivity for ions, and is likely to be suitable for both anolyte and catholyte.

As the cation exchange membrane, a perfluorocarbon sulfonic acid type cation exchange membrane or the like can be used, and by using the ion exchange membrane, the resistance to corrosive substances is extremely strong and stable operation can be performed. Further, the cation exchange membrane has high conductivity and is stable against electrolysis even in a diluted electrolytic solution or pure water. Further, the ion exchange membrane has extremely high resistance to many chemicals.

Next, in the present invention, it is preferable to use a platinum group metal or platinum group metal oxide anode as the anode as described above. This platinum group metal or platinum group metal oxide itself has a very small consumption due to electrolysis, and in addition to the use of the desirable polymer solid electrolyte described above, the use of these electrode materials further reduces the pollution of the obtained reformed water. be able to. 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 present invention, it is preferable to use a polymer solid electrolyte type electrode, but the present invention is not limited to this, and it is also possible to use, for example, a porous plate-shaped platinum electrode or the like.

In the present invention, a platinum group metal or carbon cathode is preferably used as the cathode as described above. These materials are stable in highly concentrated alkaline water and have excellent hydrogen generating ability. Next, as described above, an ammonium salt solution, specifically, ammonium chloride, ammonium sulfate, or ammonia water is used as an electrolyte, and this is supplied to the cathode chamber of the electrolytic cell. Ammonium salt contained in the electrolytic solution, ammonium ions which are cations remain in the cathode chamber by electrolysis, and can be used as a component of the cleaning solution,
Further, since it is volatile, it can be easily removed when unnecessary. Further, since it does not contain metal ions, it is not necessary to take special measures for removing the metal ions, and the deterioration of purity due to the mixing of the metal is eliminated.

The concentration of these electrolytes is 100-10000 ppm
If less than 100 ppm, the electrolytic reaction becomes insufficient and the ORP of the acidic water obtained in the anode chamber is 1000 m.
It does not rise above V, the pH is insufficiently lowered, and the current efficiency of the reaction is lowered. On the other hand, if it exceeds 10,000 ppm, both ORP and pH easily reach satisfactory levels, but undesirable side reactions 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. However, the above drawbacks can be solved by supplying pure water to the electrolytic cell and adjusting the concentration thereof.

When electrolysis is performed while supplying a solution containing ammonium salt or aqueous ammonia to the cathode chamber using the electrolytic cell thus constructed, particularly the solid polymer electrolyte type electrolytic cell, the solid polymer electrolyte type electrolysis is performed. The reformed water can be obtained with high current efficiency under the low power consumption which is characteristic of the above. 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.

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. FIG.
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 with the cathode surface of the anion exchange membrane 2 and nickel. 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 anolyte such as ion-exchanged water supplied from an anolyte inlet 12 enters into the anodic chamber through an anodic chamber opening 13 to form an anode 7. It comes into contact with and is taken out from the anolyte outlet 14 as high pH reforming water.

A cathode liquid flow passage 15 is formed inside the cathode chamber wall plate 6, and an ammonium chloride aqueous solution or ammonia water supplied from a cathode liquid inlet 16 enters the cathode chamber through an opening 17 in the cathode chamber. As a result, the ammonium salt permeates to the anode chamber side through the cation exchange membrane 2 to give modified water having a high pH value to the anode chamber as described above, and the alkaline water generated in the cathode chamber becomes the cathode. It is taken out from the liquid 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 as an anode is 0.053 dm ^2, the porous platinum plate electrode area is 0.053 dm ² as the cathode, DuPont Nafion 117 (trade name cation exchange membrane ) Were used to construct the electrolytic cell shown in FIG. An ammonium chloride aqueous solution with a concentration of 3000 ppm was supplied as the catholyte at 12 cc / min, and ion-exchanged water as the anolyte was supplied at 12 cc / min, respectively, while energizing between both electrodes so that the current density was 30 A / dm ^2. Acidic water having a pH of 4 and an ORP of 1000 mV was obtained from the chamber.

[0019]

[Comparative Example 1] Electrolysis was carried out under the same conditions as in Example 1 except that ammonium chloride was not added as an electrolyte. The obtained acidic water had a pH of 5.6 and an ORP of 230 m.
V.

[0020]

Example 2 Electrolysis was carried out under the same conditions as in Example 1 except that the ammonium chloride aqueous solution having a concentration of 3000 ppm was replaced with ammonia water having a concentration of 3000 ppm.
At 9.3 alkaline water with an ORP of -800 mV was obtained.

[0021]

According to the method of the present invention, the cathode chamber of the two-chamber electrolytic cell in which the anode and the cathode are closely attached to both sides of the ion exchange membrane divided into the anode chamber and the cathode chamber by the cation exchange membrane is used. Electrolysis is performed while supplying a solution containing ammonium ions or ammonia water, and the redox potential is increased in the anode chamber.
This is an electrolysis method using a two-chamber electrolysis cell, wherein acidic water having a pH of 4 or less at 1000 mV and alkaline water is obtained in a cathode chamber.

According to the method of the present invention, acidic water is obtained in the anode chamber and alkaline water is simultaneously obtained in the cathode chamber by transferring ammonium ions from the cathode chamber to the anode chamber and further from the anode chamber to the cathode chamber. Furthermore, in the present invention, an electrolytic cell equipped with a cation exchange membrane, particularly a solid polymer electrolyte type electrolytic cell is used, and since an ammonium salt solution or ammonia water is used as an electrolytic solution, under low power consumption, It is possible to obtain reformed water with high current efficiency, and further, metal does not exist in the acidic water, and the acidic water can be effectively used as washing water for semiconductors in which metal ions particularly cause problems such as poor insulation. . Also, in the electrolysis where chlorine ions and sulfate ions are present in the anode chamber, chlorine gas, hypochlorous acid, persulfuric acid, etc. may be generated,
Stimulation of these living bodies may not be preferable, but in the method of the present invention, since the chlorine ions and the like do not exist in the anode chamber, no irritating odor or the like is generated. Further, in electrolysis in which ammonia water is supplied to the cathode chamber, only hydroxide ions exist as anions in the electrolytic cell, and reformed water containing very few impurities can be obtained.

[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.

[Explanation of symbols]

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

Claims (1)

[Claims] 1. A solution containing ammonium ions in the cathode chamber of a two-chamber electrolysis cell in which an anode and a cathode are closely attached to both sides of the ion exchange membrane divided into an anode chamber and a cathode chamber by a cation exchange membrane. Alternatively, electrolysis using a two-chamber electrolysis cell is characterized in that electrolysis is performed while supplying aqueous ammonia, acidic water having an oxidation-reduction potential of 1000 mV or more and pH 4 or less is obtained in the anode chamber, and alkaline water is obtained in the cathode chamber. Method.