JPS6136074B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the economical production of alkali hydroxide in an alkali chloride electrolysis method using an ion exchange membrane method. More specifically, when producing alkali hydroxide by electrolyzing alkali chloride in an electrolytic cell divided into an anode chamber and a cathode chamber using a cation exchange membrane, cations with metal fixed to at least one side by a chemical plating method are used. A method for producing alkali hydroxide by electrolysis of alkali chloride with a low electrolysis voltage, using an exchange membrane and incorporating the cation exchange membrane into an electrolytic cell so that the metal-fixed surface faces the cathode side. It is.

Several attempts have been made to lower the electrolysis voltage in electrolysis methods using cation exchange membranes. Reducing the distance between the anode and cathode is considered to be an effective method for lowering the voltage.
It is disclosed in JP-A-80974 and JP-A-50-109899. Furthermore, Japanese Patent Application Laid-Open No. 54-47877 proposes mechanically bringing the negative and positive electrodes into close contact with the cation exchange membrane using the force of a spring, but in both cases the voltage drop is insufficient. A high level of manufacturing precision is required for special devices such as springs and electrodes, which poses an economical problem.

The present inventors used a cation exchange membrane to which metal was fixed using a chemical plating method, assembled it in an electrolytic cell made of transparent acrylic resin so that the metal surface was on the cathode side, electrolyzed it, and observed it in detail. It was surprisingly found that almost no air bubbles were attached to the surface to which the metal was fixed, and the electrolytic voltage was significantly lowered.
Furthermore, in electrolytic cells using ordinary cation-exchange membranes that do not have metals fixed to them, the phenomenon of an increase in electrolytic voltage and instability that is often observed when the distance between the anode and cathode is reduced is also caused by this metal. It was found that there was no difference when using a cation-exchange membrane with

The reason why the electrolytic voltage is reduced when using a cation exchange membrane to which metal is fixed is that hydrogen gas bubbles generated by electrolysis are difficult to adhere to the cathode surface of the membrane.
This is because the increase in electrolytic voltage due to the adhesion of air bubbles to the membrane surface is due to shielding by the air bubbles, obstruction to the diffusion of highly concentrated alkali hydroxide in the vicinity of the membrane, and the like.

On the other hand, chlorine gas generated at the anode due to electrolysis has a much larger bubble size than hydrogen gas and is difficult to adhere to the anode surface of the cation exchange membrane, so it is not necessary to fix metal to the anode side. do not have.

The chemical plating method in the present invention is a commonly used method and is not particularly limited. For example, a metal salt solution to be plated is placed on the cathode side of a cation exchange membrane, and a reducing agent solution is placed on the anode side, and the membrane is plated. Method of plating using the difference in penetration speed of
(No. Publication), a method in which a membrane is immersed in a metal salt solution to impregnate the membrane with the metal salt, and then immersed in a reducing agent to deposit metal on the membrane surface, a method using an electroless plating solution, etc. It can be selected as appropriate, and the above methods may be combined. The metal fixed to the membrane may be any metal as long as it can withstand the environment in which it is used, such as platinum, palladium, iridium, ruthenium, nickel, or a mixture thereof.

The cation exchange membrane in the present invention may be any cation exchange membrane that is commonly used when producing alkali hydroxide by electrolysis of an aqueous alkali metal chloride solution, but in particular, the surface of the cation exchange membrane facing the anode may be Using a fluorocarbon polymer having a sulfonic acid group and a carboxylic acid group on the surface facing the cathode, a metal is fixed to the surface having the carboxylic acid group by a chemical plating method, and the surface is placed in an electrolytic cell with the surface facing the cathode. In this case, the effects of the present invention are significant. The cathode used in the present invention may be one that can withstand the environment in which it is used, has a sufficient catalytic effect on the reaction, and has a structure that does not hinder the escape of the produced gas, and may be any commonly used cathode. If you have enough, you can achieve your goal. For example, materials such as iron, mild steel, nickel, stainless steel, etc., and porous materials such as wire mesh, expanded metal, lattice shape, vertical rail shape, punched metal, etc. may be mentioned, but are not limited to these. .

As for the anode, a normal anode that can withstand the usage environment and has sufficient catalytic action for the desired reaction is used. A porous anode coated with a platinum group metal such as , palladium, ruthenium, or iridium, an oxide of a platinum group metal, or a mixture of an oxide of a platinum group metal and an oxide of a valve metal is used.

The following polymers can be used for producing the cation exchange membrane that can be used in the present invention.

For example; the following general formula [However, R = CF ₃ , -CF ₂ -O-CF ₃ n = 0 or 1 to 5 m = 0 or 1 o = 0 or 1 p = 1 to 6 X = SO ₂ F, SO ₂ Cl, COOR ₁ (R ₁ = 1
~5 alkyl group) CN, COF] Also, a polymer obtained by adding a third component or a fourth component to the above-mentioned two-component system can also be used. Specifically, the following can be shown, for example.

In these, it is preferable to adjust the exchange group capacity to 0.5 meq/g dry resin to 1.5 meq/g dry resin.

The cation exchange membrane used in the present invention uses these films, for example, one side of the film of Group 1A is treated with an oxidizing agent.

2. After hydrolyzing the film of Group A, it is treated with hydrochloric acid, then treated with a sulfonyl chloride agent, etc., and then one side is treated with an oxidizing agent or reducing agent.

3 Glue the film of group A and the film of group B together.

It can be obtained by means such as.

Of course, the cation exchange membrane used in the present invention is
It is not limited only to these.

The cation exchange membrane used in the present invention is generally used with a thickness of 50μ to 500μ, and an appropriate thickness is selected in consideration of the membrane's specific conductivity and current efficiency.
Further, such a cation exchange membrane may be reinforced with Teflon fiber cloth or the like for the purpose of improving the mechanical properties of the membrane.

The cation exchange membrane is usually in contact with and supported by the anode or structure.

In the present invention, for membrane protection, ease of maintenance, and economical reasons, the anode side of the cation exchange membrane is brought into contact with and supported by the anode, while the cathode side of the cation exchange membrane is supported. The surface is assembled into an electrolytic cell so as to maintain a gap with the cathode, and electrolysis is performed.

Contact between the cation exchange membrane and the electrode can be easily achieved by the pressure difference between the anode and cathode chambers. For example, methods are used to slightly reduce the pressure in the anode chamber or to pressurize the cathode chamber. In particular, by increasing the level of extraction of aqueous alkali hydroxide from the cathode chamber, the cathode chamber is pressurized and the anode and membrane are separated. A method of contacting is a preferred form.

There are no particular limitations on the conditions for carrying out the present invention, such as current density, alkali metal chloride concentration and pH in the anode chamber, caustic alkali concentration in the cathode chamber, etc. Furthermore, the interval between the anode and cathode can be set arbitrarily. The effects of the present invention are particularly noticeable when operating at a high current density of 20 A/dm ² or higher.

As described above, the method of the present invention does not require special devices such as springs, nor does it require high mechanical precision for electrodes, electrolytic cells, etc., and the spacing between the anode and cathode can be arbitrarily selected. Therefore, 1. The electrolytic cell is simple, and the operating conditions, operation, and maintenance management are easy.

2. Electrolysis can continue as long as the membrane itself is not damaged.

3. There is little risk of mechanical damage to the membrane.

4 Applicable to existing ion exchange membrane electrolyzers.

5. It is an extremely economical and engineering method that has new advantages such as being economically superior.

An example of the effect will be shown below using a specific example. Note that the present invention is not limited to these specific examples.

Example 1 The monomer with 1,1,2-trichloro-1,
A copolymer was obtained using perfluoropropionyl peroxide as an initiator in 2,2-trifluoroethane (the exchange capacity as a sulfonic acid group was
0.91 meq/g dry resin) (A polymer).

in the same way (exchange capacity as carboxylic acid group is 1.1 meq/g) (polymer B).

Next, polymer A was molded into films with a thickness of 100 μm and polymer B with a thickness of 75 μm, and these two films were stacked together and bonded under heat.
It was made into one film. Then the film is concentrated
10% by weight NaOH/methanol (1/1 weight ratio)
Hydrolysis was carried out at 80°C for 6 hours to obtain a cation exchange membrane.

After impregnating the carboxylic acid base layer of the membrane with platinum salt,
After reduction using NaBH ₄ , chemical plating was performed using a platinum electroless plating solution containing dimethylamine borane (hereinafter referred to as DMAB).

Titanium expanded metal coated with ruthenium oxide was used as the anode, and expanded iron metal was used as the cathode. The distance between the anode and cathode was set to 3 mm, and the level at which the aqueous alkali hydroxide solution was extracted from the cathode chamber was set 20 cm higher than the liquid level in the anode chamber so that the surface of the membrane to which platinum was not fixed was in contact with the anode. When electrolysis was carried out at a temperature of 80°C and a current density of 30 A/ ^dm2 while supplying saturated saline solution to the anode chamber and a 35% by weight aqueous caustic soda solution to the cathode chamber, the voltage was 3.3 V and the current efficiency was 93%. .

Comparative Example 1 When an electrolytic cell was assembled and electrolysis was performed in the same manner as in Example 1 without chemical plating of platinum, the voltage was
The voltage was 3.8V and the current efficiency was 93%.

Example 2 Chemical plating was performed in the same manner as in Example 1, except that nickel salt was used instead of the platinum salt used in Example 1.

Next, electrolysis was carried out in the same manner as in Example 1.
The voltage was 3.4V and the current efficiency was 93%.

Example 3 and 1,1,2-trichloro-1,2,2-trifluoroethane using perfluoropropionyl peroxide as an initiator to obtain a copolymer, which was then molded into a film with a thickness of 250 μm.

Next, 20wt% KOH-methanol (weight ratio 1/
1), a cation exchange membrane with an exchange capacity of 0.91 meq/g dry resin was obtained by hydrolysis at 90°C.

After the cation exchange membrane thus obtained was treated with hydrochloric acid, only one side was reacted in phosphorus pentachloride-phosphorus oxychloride (weight ratio 1/1), and SO ₃ H
A film with a phase layer of 150μ and an SO ₂ Cl layer of 100μ was obtained. Next, it was subjected to a reaction treatment with hydroiodic acid (58%) at 90°C for 5 days.

Next, 20wt% KOH-methanol (weight ratio 1/
Hydrolyzed in step 1). The obtained film has an SO ₃ K layer.
A two-layer membrane with a thickness of 150μ and a COOK layer of 100μ was obtained.
Next, the carboxylic acid base layer of the film was impregnated with a platinum salt, and then reduced using NaBH ₄ , and then chemically plated with a platinum electroless plating solution containing DMAB.

Using the same electrolytic cell as used in Example 1, instead of supplying the cathode chamber with a concentration of 35% by weight caustic soda,
When operated under the same conditions as in Example 1 except for supplying 32% by weight caustic soda, the voltage was
The voltage was 3.3V and the current efficiency was 93%.

Comparative Example 2 When an electrolytic cell was assembled and electrolysis was performed in the same manner as in Example 3 without platinum plating on the cation exchange membrane used in Example 3, the voltage was 3.7V and the current efficiency was 93%. It was hot.

Claims (1)

[Claims] 1. When producing alkali hydroxide by electrolyzing an aqueous solution of alkali metal chloride in an electrolytic cell divided into an anode chamber and a cathode chamber by a cation exchange membrane,
A metal is fixed by a chemical plating method to the surface of the cation exchange membrane facing the cathode, the other surface to which no metal is fixed is supported in contact with the anode, and a gap is provided between the membrane and the cathode, A method for producing alkali hydroxide, which comprises electrolyzing an aqueous solution of alkali metal chloride. 2. The cation exchange membrane is made of a fluorocarbon polymer having a carboxylic acid group on one side and a sulfonic acid group on the other side, and the surface to which metal is fixed by chemical plating is the side having the carboxylic acid group. The method described in item 1. 3. The method according to claim 1 or 2, wherein the metal fixed to the cation exchange membrane by the chemical plating method is platinum, palladium, iridium, ruthenium, or nickel, singly or in a mixture thereof.