JP3299250B2 - Pure water electrolysis tank with an intermediate chamber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is directed to pure water or ultrapure water, which has a small electric conductivity, and is provided with a new intermediate chamber in the middle of a tank provided with two positive and negative electrodes. An electrolytic cell with improved electrolysis efficiency, and a method for removing impurities in a solution using the same, more specifically, a granular solid electrolyte between a cathode chamber and an anode chamber,
For example, by providing an intermediate tank filled with H-type fluororesin cation exchange resin, etc., it is possible to prevent highly oxidizing substances such as oxygen and ozone generated at the anode from diffusing and moving to the cathode chamber. The present invention also relates to an electrolytic cell capable of easily generating hydrogen in a cathode chamber and obtaining a catholyte having a strong reducing property.

[0002]

BACKGROUND OF THE INVENTION In recent years, adverse effects on the environment of various cleaning agents have become a problem, and studies have been made from various angles. A typical example is chlorofluorocarbon, which has been used in semiconductors and many other fields due to its strong cleaning power. However, since it has been reported that fluorinated solvents such as chlorofluorocarbons have a risk of destroying the ozone layer of the earth, the use thereof has been increasingly restricted on a global scale. As an alternative to these solvents, the safest solvent, water, is again in the limelight. Cleaning water used in the semiconductor field and the like is so-called pure water. Pure water is generally confirmed by electric conductivity, and a substance having a conductivity ρ smaller than 10 μS · cm is often referred to as pure water, and a substance smaller than 0.055 μS · cm is referred to as ultrapure water. Follow this. The redox properties and purity of these pure waters, particularly impurities such as polar organic substances, will be described below.

[0003] The redox properties of water are highly dependent on the substances involved. Dissolved oxygen (D
O) is contained in about 8 ppm. Therefore, it is known that when a surface such as silicon is washed with the pure water, the surface is partially oxidized and dissolved. For this reason, an ultrapure water production apparatus that achieves low DO by bubbling (foaming) nitrogen gas for the purpose of reducing DO has been developed. However, when this degassing method is used, DO decreases relatively quickly to 50 ppb (0.005 ppm), but it takes time to reduce DO to 50 ppb or less. In addition, the gas for degassing is required to be of extremely high purity so as not to contaminate ultrapure water. For this, a more efficient method is required.

[0004] As another field, a boiling water reactor (BWR) of nuclear power plants uses water near the ultrapure water level as cooling water. It is known that a radionuclide such as cobalt 60 generated during power generation is taken into an oxide film formed on the inner surface of a BWR primary stainless steel pipe. Since the dose rate around the pipe C _o ⁶⁰ adheres to the piping is increased, C _o
It is desirable to remove ⁶⁰ occasionally. In order to remove _Co ⁶⁰ , it is necessary to dissolve and remove the oxide film incorporating _Co ⁶⁰ . It is known that the oxide film of stainless steel formed in a BWR environment has an increased dissolution rate under a reducing condition of 1 ppb of DO. Normally, chemicals are added to remove _Co ⁶⁰ , but the primary system is contaminated with the chemicals, and the purification operation takes a lot of time, and the amount of radioactive waste increases. Therefore, by enhancing the reducibility of cooling water close to ultrapure water, _Co
If a technique to increase the removal rate of ⁶⁰ can be established, this technique is very promising from the viewpoint of safety. In addition, this technology is not limited to BWR, and when removing iron-based oxide film,
Since no waste of chemicals is discharged, this is an advantageous technique in terms of measures against reflux.

At present, an apparatus for producing ultrapure water comprises an ion exchange resin tower, a polisher resin tower, a filter, a reverse osmotic pressure apparatus, an ultrafiltration module, and an ultraviolet sterilizer. Among the purity of ultrapure water, the electrical conductivity is approaching the theoretical value of only H ⁺ and OH ⁻ ions generated by dissociation of a part of water molecules. K ⁺ , Na ⁺ , Cu ^{2 +}
And the concentration of impurities such as Zn ²⁺ ions is reduced to the order of several ppb, but is not completely removed. In particular, the transition metal ion becomes electrically neutral as a whole due to the hydrolysis, and it becomes difficult to remove it with an ion exchange resin. The organic impurities are about 50 ppb, and the residual amount is larger than the ionic impurities. Therefore, in order to further improve the purity of ultrapure water, it was necessary to develop a new purification method.

[0006] As a candidate for a new purification method, J.-K. H. St
rohl and K.R. L. There is a method utilizing an electrochemical process reported by Dunlap (see * below). According to this report, the adsorption phenomenon of a nonionic polar organic substance depends on the potential of the substance to be adsorbed, and specifically adsorbs at a potential specific to the organic substance. However, this report uses an electrolyte solution and cannot be applied directly to purification of ultrapure water (* JHStrohland KLDunlap Anal.Chem., 44 (A
72) 2166, Elechosorption AND Separation of Quinones
on a Column of graphite particles).

[0007] An electrolytic reduction method is known as a technique for reducing the DO of water and improving the reducibility without using chemicals. However, the conductivity of pure water or ultrapure water is extremely low at 10 µS · cm or less. Since it is small, in order to obtain an electrolytic effect, the electrolysis voltage is several hundred volts or more, which is not suitable for industrial implementation. Conventionally, the electrolytic reduction method has not been applied to pure water or ultrapure water.

A technique for obtaining gaseous ozone (O ₃ ) or high-concentration ozone water by electrolyzing pure water at a low voltage has recently been developed. It is noteworthy as one of the technologies for electrolyzing water.

Although not related to the object of the present invention, the outline of the above proposal for obtaining the ozone water will be briefly described below. In this method, as shown in FIG. 7, for example, an electrolytic cell 104 having a structure in which a cathode electrode 102 and an anode electrode 103 are adhered to both sides of an ion exchange resin 101 is used. The cathode chamber 109 has an inlet 105 and an outlet 1
06 is provided, and the anode chamber 110 has an inlet 107.
And an outlet 108 is provided. In such a configuration, for example, a cation exchange group (—SO ₃ H
The use of a cation-exchange membrane into which the base has been introduced allows the electrolysis voltage to be reduced to several volts (V). In an electrolytic cell having such a structure, it is known that the current efficiency for generating ozone at the anode electrode 103 depends on the electrode material. In general, platinum (Pt), lead oxide (β-Pb
O ₂ ) and the like are often used.

When electricity is supplied to the electrolytic cell having this structure, (O ₃ ) and (O ₂ ) are generated at the anode electrode 103, and hydrogen (H ₂ ) is generated at the cathode electrode 102. The following chemical reaction formulas have been estimated for these electrochemical processes.

[0011] _{H 2 O + O 2 → O} 3 + 2H + + 2e - Eo = 2.07V (1) 3H 2 O → O 3 + 6H + + 6e - Eo = 1.51V (2) 2H 2 O → O 2 + 4H + + 4e - Eo = 1.23V (3) where Eo is a standard oxidation-reduction potential.

The H formed according to these chemical formulas
^{It is considered that +} ions move to the cathode electrode side through the cation exchange membrane and are reduced to H ₂ gas.

By the way, when this electrolytic cell 104 is used,
Although it is possible to electrolyze pure water at a low voltage, however, the cation exchange membrane, which is a solid electrolyte, partially permeates O _{2 and the} like, so that the reduction performance of the cathode electrolyte is reduced. It cannot be applied for the purpose of the present invention.

[0014]

SUMMARY OF THE INVENTION The present invention relates to ozone (O
_An object of the present invention is to provide an electrolytic cell capable of controlling the oxidation-reduction property and purity of pure water, not the production of ₃ ).

[0015] When using the electrolytic cell having the structure shown in FIG. 7 described above, the O ₃ or O ₂ is generated in the anode electrode 103, oxidizing water gives the anode compartment, whereas,
Since H ₂ is generated in the cathode electrode 102, reducing water is obtained in the cathode chamber. Here, if the wish to obtain a greater reduction of the water at the cathode side, in addition to the generation of a reducing agent such as H _2, it is necessary to remove the oxidizing agent, such as O2. O2 is generally dissolved even in pure water, and oxidizing substances generated on the anode
Therefore , the removal of O2 is desired in order to improve the reducibility.

As shown in the following chemical reaction formula, O ₂ is converted into a reducing substance by a reduction reaction, and thus the electrolytic reduction method is one of the effective methods for removing O ₂ .

O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O Eo = 1.23V (4) O ₂ + H ⁺ + e ⁻ → HO ₂ Eo = −0.13V (5) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O ₂ Eo = −0.69 V (6) By the way, in the electrolysis method, the oxidation reaction at the anode electrode and the reduction reaction at the cathode electrode are paired, so if the cation exchange membrane has gas permeability between the electrodes, As described above, the oxidizing substance such as O ₂ generated by the oxidation reaction moves to the cathode electrode side via the ion exchange membrane. This phenomenon is a disadvantage of the electrolytic reduction method.

When the electrolytic cell 104 shown in FIG. 7 is used, trace metal ions in pure water move to the cathode electrode side which is a negative electrode, and conversely, anions move to the anode electrode side which is a positive electrode .

[0019]

As described above, in the electrolytic cell 104 having the structure shown in FIG. 7 proposed for producing the above-described high-concentration ozone water, O ₃ generated at the anode electrode is used.
Inevitably, O ₂ and O ₂ move to the cathode electrode side, and this is a major problem when this is applied to the object of the present invention.

Therefore, the inventor has conducted research on avoiding this problem, and has completed the present invention described in each of the claims.

The principle of the present invention will be described below with reference to FIG. In the electrolytic cell 15 of FIG. 1, 1 and 2 are ion exchange membranes, 3 is a cathode electrode, 4 is an anode electrode, 5 is an inlet of the cathode chamber 11, 6 is an outlet thereof, and 7 is an anode chamber 1
Reference numeral 2 denotes an inlet, 8 denotes the same outlet, 9 denotes an inlet of the intermediate chamber 13, and 10 denotes the same outlet.

The pure water passing through the intermediate chamber can sufficiently lower the dissolved oxygen concentration (DO) by bubbling high-purity nitrogen N ₂ (or argon Ar) gas (generally, conductivity of 50 ppb or less). , Preferably 10 ppb or less). When this pure water is used in a circulating manner, O ₂ and O ₃ that migrate from the anode chamber 12 to the intermediate chamber 13 are removed by this bubbling operation.

One of the features of the present invention is that the above-described intermediate chamber 13 is provided.
To fill the solid electrolyte. This is the middle room 1
When the pure water is filled into the sample No. 3, the conductivity of the pure water becomes 10%.
While the electrolysis voltage is extremely large because it is as small as μS · cm or less, it is effective to reduce the electrolysis voltage by increasing the conductivity by filling the intermediate chamber with a solid electrolyte (for example, ion exchange resin). Because it becomes. As the solid electrolyte for lowering the electrolysis voltage, a fluorine ion exchange resin is suitable for filling the intermediate chamber as in the case of the ion exchange membrane. In particular, an ion exchange resin in which a —SO ₃ H group is bonded to a fluorine resin, specifically, The Nafion NR- made by DuPont
50 and the like can be cited as typical examples, but are not limited thereto. Other examples of the solid electrolyte include a sulfonic acid group (-
Ion exchange resins to which SO ₃ H) is bound, specifically Amberlite IR-116, IR-118, IR-12
1, IR-122, 252, 200C, 200CT (manufactured by Organo Corporation), Diaion SK102, SK104,
SK10, SK110, SK116, SK208, PK
208, PK212, PK216, PK220, PK2
28 (manufactured by Mitsubishi Plastics), Dowex HCR ₂ , HC
RS, HGR-W, MSH-1 (manufactured by Dow Chemical Company)
And a carboxylic acid group (—COO) is added to a resin composed of methacrylic acid or acrylic acid and divinylbenzene.
H) bonded resin, specifically Amberlite IRC
-50, DP-1, IRC-84 (manufactured by Organo), Diaion WK10, WK11, WK20 (manufactured by Mitsubishi Plastics), Dowex CCR-2 (manufactured by Dow Chemical), and the like. The solid degree of filling of the electrolyte, the electrolyte per unit area ^1g / cm ^{2 ~10g} / cm 2
Is appropriate. In addition to the solid electrolyte being granular, for example, a block-shaped porous body having a pore diameter of 50 μm or more that allows appropriate water flow is also preferably used.

The speed at which water passes through the intermediate chamber is a linear speed.
It is preferable that the thickness be about 0.1 cm / sec to 100 cm / sec.

The number of intermediate chambers is not limited to one, but it is desirable to increase the number of intermediate chambers when it is highly necessary to suppress the diffusion of oxidizing substances. For example, when the temperature of pure water is increased (for example, 80 to 100 ° C.), the permeability of O ₂ passing through the diaphragm increases. Therefore, the diffusion of O ₂ is more effectively prevented by providing a plurality of intermediate chambers. be able to.

A voltage can be applied by energizing the granular ion exchange resin in the intermediate chamber. As a result, the potential on the surface of the granular ion exchange resin is widely distributed from plus to minus. Furthermore, since the filling of the intermediate chamber is granular, the probability of contact with organic matter increases. From these points, the use of the intermediate chamber facilitates adsorption and removal of a plurality of nonionic polar organic substances. Since the cations contained as impurities move to the cathode electrode side and the anions move to the anode electrode side, the intermediate chamber is also suitable for removing ionic substances.

In addition, the configuration in which one of the ion exchange membranes 1 is removed from the electrolytic cell 15 having the structure shown in FIG. 1 is also effectively used, whereby the structure in which the cathode electrode and the granular or porous solid electrolyte are in close contact with each other is a transition type. The collection amount of metal ions is improved. A specific example of the structure is shown by the electrolytic cell 31 in FIG. 2, and members common to those in FIG. That is, 22 in FIG. 2 is a cathode electrode, 23 is an anode electrode, 21 is a cation exchange membrane, and 24 is an intermediate chamber filled with a granular or porous solid electrolyte.
Reference numeral 25 denotes an inlet of water to the intermediate chamber 24 for the purpose of purification, and reference numeral 26 denotes an outlet of the generated water from the cathode chamber 29.
7 is an inlet of water to the anode chamber 30, and 28 is an outlet thereof.

The solid electrolyte is the same as that shown in FIG. 1, and a fluorine-based cation exchange resin is suitable. When electrolytic reduction is performed using an electrolytic cell having this structure, metal ions as impurities are first deposited on the electrode surface and then also deposited on the solid electrolyte. As a result, the collection amount of metal ions is improved, and the life of the device is extended.

[0029]

According to the conventional electrolysis method of pure water, it is not easy to remove dissolved gas such as dissolved oxygen from the solution, and it passes through metal ions and pores of the membrane which are electrically neutralized by hydrolysis. It is difficult to remove cluster-like metal ions as small as possible by using an ion exchange resin or a membrane, and activated carbon has a limit in the amount of adsorption. However, if the electrolytic cell of the present invention and a pure water production apparatus are used in combination, Impurities that could not be removed by conventional pure water production equipment or ultrapure water production equipment can be efficiently removed, and an active reducing substance can be injected into the solution by electrolysis. There is an effect that suitable water can be obtained.

The water produced by using the electrolytic cell of the present invention is particularly suitable for the final stage cleaning of a silicon wafer which needs to extremely reduce impurities and needs to prevent the surface from being oxidized and dissolved. ing.

Further, the present invention is useful for reducing impurities required for reducing radioactive substances contained in primary cooling water of a boiling water nuclear power plant, and is also suitable for preventing corrosion damage to materials in a furnace. ing.

[0032]

EXAMPLE 1 In the electrolytic cell 15 shown in FIG. 1, a porous rectangular carbon electrode (90 × 70 × 30 m) was used as the cathode electrode 3.
m), and 80 mesh mesh platinum (80 × 60 mm) was used as the anode electrode 4. About 160 g of Nafion NR-50 manufactured by DuPont was filled in the intermediate chamber, and Nafion 117 was used for the diaphragm. As the water, pure water having a conductivity of an ultrapure water level of 0.06 μS · cm was used.
The size of the cathode chamber and the size of the anode chamber are each 90 × 70
× 30mm), the size of the intermediate chamber is (90 × 70 × 25m)
m).

Such an electrolytic cell was combined with the pure water producing apparatus shown in FIG. 6 to perform pure water electrolysis.

The DO in pure water was previously reduced to 50 ppb by bubbling N ₂ gas.
This low dissolved oxygen water is added to the cathode chamber and the intermediate chamber 13 for 20 minutes.
circulating at a flow rate of cc / sec and a current density of 5-20 mA /
The current was supplied at cm ² .

The relationship between the DO measured at the cathode chamber outlet 6 and the current density is shown by the curve in FIG. As is apparent from this figure, it is understood that the cathodic electrolysis reduces DO.

For comparison, an experiment using an electrolytic cell except for the intermediate chamber shown in FIG. 1 was performed. Except for the absence of an intermediate chamber, the test conditions were exactly the same as those described above. D at the exit
The O measurement changed as shown by the curve in FIG. DO
Was lower than before the cathode electrolysis, but the DO reduction rate was smaller than when the intermediate chamber was provided.

From the above results, the effectiveness of the present invention was confirmed. Example 2 As in Example 1, the electrolytic cell 15 shown in FIG. 1 was used. In the intermediate chamber 13, nonionic polar organic molecules were dissolved and water was flowed. Water was collected at the inlet 9 and outlet 10 of the intermediate chamber, and the concentration of polar organic molecules was measured. As the polar organic molecule, 2-hydroxy-1,4-naphthoquinone (HNQ) was used.
Electrolysis conditions were set as follows. Since the adsorption phenomenon is known to depend on the potential, in this experiment, constant potential electrolysis was performed instead of constant current electrolysis. Electrolysis voltage is 0 to 25V
Was changed within the range. H of ^{10 -6} M as a stock solution using
A solution in which NQ was dissolved in ultrapure water was used. 10 parts of this stock solution
Water was passed through the intermediate chamber at a rate of ml / min. The concentration in the solution sampled at the outlet of the intermediate chamber was measured using an ultraviolet absorption spectrometer.

FIG. 4 shows the electrolytic voltage dependence of the concentration of HNQ at the outlet 10 of the intermediate chamber. As can be seen from this figure, HNQ was removed from ultrapure water or 90% or more by applying electrolysis to the intermediate chamber 13. In other words, the amount of HNQ adsorbed on the ion exchange resin increases. The experiment was performed under the same conditions as in Example 2 except that the ion exchange membrane on the cathode electrode side was removed using the electrolytic cell shown in FIG.
The HNQ removal rate was 10% or less in the range of 25 V to 25 V. These results show that the electrolytic cell having the structure of the present invention is effective for removing polar organic molecules in the aqueous solution. Example 3 In the electrolytic cell 31 shown in FIG. 2, an 80 mesh platinum electrode was used as the cathode electrode 22, and the same platinum electrode was used as the anode electrode 23. Nafion NR50 manufactured by DuPont was filled as the solid electrolyte, and Nafion 117 was used as the diaphragm 21. As a comparative example, an electrolytic cell 104 having a structure shown in FIG. 6 was used. The electrolytic cell 104 of the comparative example is exactly the same as the electrolytic cell 31 of the present example except for Nafion NR50.

As raw water, an ultrapure water level of 0.055 μm
S / cm of water was used. 10 ppb of iron (Fe
³⁺ ) The solution in which the ions were dissolved was subjected to the test. The current density was set to 20 mA / cm ² and the flow rate was set to 0.5 l / min. FIG. 5 shows a change in the iron ion concentration at the outlet 26. The curve in this figure shows the result using the electrolytic cell 31 of the present example, and the curve shows the result of the comparative example. As is apparent from this figure, the metal ion collecting ability of the present invention is excellent. Example 4 By using a system in which the electrolytic cell 15 shown in FIG. 1 and the electrolytic cell 31 shown in FIG. 2 are connected in series, nonionic and nonionic polar organic substances in pure water can be effectively removed. Can be.

Specifically, a system in which the outlet 10 of the electrolytic cell 15 shown in FIG. 1 is connected to the inlet 25 of the electrolytic cell 31 shown in FIG.

With this system, the first-stage electrolytic cell 15
To remove non-ionic polar organic substances, and metal ions can be removed by electrophoresis in the second electrolytic bath 31. Fifth Embodiment By attaching a filter after the outlet 26 of the electrolytic cell 31 shown in FIG. 2 described in the third embodiment, the purity of pure water can be further improved. This is because there is a risk that metal deposited on the cathode electrode, the granular or porous solid electrolyte may be partially peeled off by the action of the flow. Therefore, if a filter is provided after the flow of the pure water, even if the metal is peeled off from the scale, it can be removed by the filter. The filter is desirably as small as possible with a pore size of 0.45 μm, and a microfiltration membrane, ultrafiltration membrane, reverse osmosis membrane, or the like can be used.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a configuration outline of an electrolytic cell of the present invention.

FIG. 2 is a diagram showing another configuration outline of the electrolytic cell of the present invention.

FIG. 3 is a diagram showing the results of Example 1.

FIG. 4 is a diagram showing the results of Example 2.

FIG. 5 shows the results of Example 3.

FIG. 6 is a diagram showing an example of a configuration outline of a pure water production apparatus having the electrolytic cell of FIG.

FIG. 7 is a diagram showing a schematic configuration of an electrolytic cell of a comparative example.

[Explanation of symbols]

1, 2 ... ion exchange membrane, 3 ... cathode electrode, 4 ... anode electrode, 5 ... cathode chamber inlet, 6 ... cathode chamber outlet, 7
... Anode chamber inlet, 8 ... Anode chamber outlet, 9 ... Intermediate chamber inlet, 10 ... Intermediate chamber outlet, 11 ... Cathode chamber, 12 ... Anode chamber, 13 ... Intermediate chamber, 15 ... Electrolyzer, 21 ... Ion exchange membrane, 22 ... Cathode electrode, 23 ... Anode electrode, 24
... Intermediate chamber 25 ... Inlet, 26 ... Outlet, 27 ... Anode chamber inlet, 28 ... Anode chamber outlet, 29 ... Cathode chamber, 30 ...
Anode chamber, 31 ... electrolyzer.

Continuation of front page (56) References JP-A-64-90088 (JP, A) JP-A-61-14232 (JP, A) JP-A-54-15361 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) C25B 9/00 C25B 13/08 C02F 1/46 B01J 47/12

Claims (3)

(57) [Claims] 1. A structure in which an anode chamber provided with an anode electrode and a cathode chamber provided with a cathode electrode are separated by a pair of juxtaposed diaphragms and have a conductivity ρ of 10 μS · cm or more. A small value pure water electrolysis tank, wherein an intermediate chamber filled with a granular or porous solid electrolyte is provided between the pair of diaphragms, and a means for passing water through the intermediate chamber is connected; A pure water electrolytic cell provided with means for collecting a liquid from a chamber. 2. The pure water electrolytic cell according to claim 1, wherein the diaphragm is a cation exchange membrane. 3. The pure water electrolysis tank according to claim 1, wherein the solid electrolyte filled in the intermediate chamber is a cation exchange resin.