JPH0143026B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a cation exchange membrane with metals fixed on its surface, and relates to its preparation and use in aqueous solution, particularly halide electrolysis.

In recent years, energy-saving development has been progressing in the method of producing alkali hydroxide by electrolyzing alkali chloride in an electrolytic cell divided into an anode chamber and a cathode chamber by a cation exchange membrane (ion exchange membrane method).
From this point of view, in this type of technology, efforts are being made to lower the electrolysis voltage as much as possible. Various methods have been proposed in the past, such as considering the material, composition, and shape of the anode and cathode, or specifying the composition of the ion exchange membrane used and the type of ion exchange group. Although all of them have certain effects, they are not necessarily fully satisfactory industrially.

On the other hand, in recent years, a technology called SPE electrolysis has been attracting attention. This is aimed at reducing the electrolysis voltage by integrating the electrode layer and the cation exchange membrane, and has achieved considerable effects. Furthermore, a method has been proposed in which a cation exchange membrane and a porous layer having no electrode activity, such as a metal oxide, are integrated, and this is used as a diaphragm in salt electrolysis. (JP-A-56-75583, JP-A-56-112487, JP-A-56-108888, etc.).

As described above, one method for reducing the electrolysis voltage is to cover the surface of the cation exchange membrane with a layer made of certain metals, metal oxides, etc.
It is becoming a trend.

As a method for covering a cation exchange membrane with a layer containing metal and/or metal oxide, there is a dry method (Japanese Unexamined Patent Application Publication No. 1983-1983) in which catalysts and particles are sintered and formed using a binder such as PTFE, and then hot-pressed onto the membrane surface. -52297), etc., a wet method in which metal is deposited on the membrane surface in a solution using a reducing agent, the so-called chemical plating method (Japanese Patent Publication No. 56-36873,
JP-A-56-136985) is known.

From the above points of view, the present inventors developed a dry method,
As a result of intensive research on the electrolytic performance of diaphragms using the wet method, we came to the following conclusions.

1. In the dry method, it is difficult to uniformly adhere the metal layer onto the membrane surface, and in turn, it is difficult to achieve reproducibility in the electrolytic performance of the membrane. Furthermore, during electrolysis, the metal layer cannot be avoided from detaching from the film surface.

2. It is easier to obtain reproducibility with wet methods than with dry methods. However, since the metal is non-uniformly deposited only on the film surface, the degree of metal separation is higher than that of the dry method. Furthermore, if the fixing conditions are made stricter for the purpose of improving this point, the current efficiency will be lowered.

Based on these conclusions, the present inventors conducted further research and found that the membrane surface was impregnated with polyamine or polyamine hydrochloride, and then negative metal complex ions were added to the membrane to form metal complexes. The present inventors have discovered that by impregnating the membrane with salt and applying chemical plating, it is possible to obtain a cation exchange membrane having a metal layer bonded very firmly and uniformly to the cation exchange membrane, thereby completing the present invention. .

Even when this membrane was used as a diaphragm for salt electrolysis, there was almost no separation of the metal layer, and it exhibited low voltage and high current efficiency over a long period of time.

The reason why the effects of the present invention are produced can be roughly considered as follows.

When positive metal complex ions are used, when the ions enter the membrane, they preferentially enter sites where they are easy to move, making it impossible to introduce the ions uniformly into the membrane surface or into the membrane. . On the other hand, when negative metal complex ions were used, they had the disadvantage that they could not be adsorbed into the film due to electrical repulsion, and chemical plating could not proceed.

However, as in the present invention, polyamine or
When polyamine hydrochloride is used, because the polyamine molecules are large, they do not penetrate into the membrane and are adsorbed on the membrane surface, so negative metal complex ions are uniformly adsorbed on the membrane surface at a high concentration. It is thought that chemical plating allows the metal to be formed uniformly and with good adhesion on the film surface.

It goes without saying that this description does not limit the present invention in any way.

The cation exchange membrane that can be used in the present invention is a perfluorocarbon polymer membrane that can be obtained from the following polymers and has a cation exchange group and/or a group that can become a cation exchange group. These groups include sulfonic acid groups (-SO ₃ M, where M is a hydrogen atom or metal atom), -SO ₂ F, -SO ₂ Cl, which are precursors of sulfonic acid groups, and carboxylic acid groups (-COOM, where M is a hydrogen atom or a metal atom). M is a hydrogen atom or a metal atom), which is a precursor of a carboxylic acid group.
COF, -COOR (R is an alkyl group having 1 to 5 carbon atoms)
and -CN. Examples of the polymer include polymers represented by 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 ₃ M (M is hydrogen atom or metal atom), -SO ₂ F, -SO ₂ Cl -COOM (M is a hydrogen atom or metal atom), -COOR ₁ (R ₁ = alkyl group of 1 to 5), -CN, -COF] or A polymer obtained by adding a third component or a fourth component to the above two-component system can also be used. More specifically, the following can be shown, for example.

(Group A) (Group B) In these polymers, the exchange group capacity is 0.5meq/
It is preferable to adjust the amount to 1.5 meq/g dry resin to 1.5 meq/g dry resin.

In the present invention, these polymers molded into a membrane can of course be used alone, but
A polymer having a mixture of a sulfonic acid group or a group that can be converted into this group and a carboxylic acid group or a group that can be converted into this group, preferably a polymer having a sulfonic acid group or a group that can be converted into this group, and a carboxylic acid group or a group that can be converted into this group. A polymer having a group that can be converted into a group formed in a layer on each side can also be used.

Such a film-like material is composed of a polymer having a sulfonic acid group or a group that can be converted into this group (for example, a group (A) polymer), and a polymer having a carboxylic acid group or a group that can be converted to this group (for example, (B) polymers) can be obtained by forming each into a film shape and then gluing the two together.Also, it is possible to obtain polymers having only sulfonic acid groups or groups that can be converted into such groups. It can also be obtained by chemically treating only one side of the membrane to convert these groups into carboxylic acid groups.

Furthermore, it can also be obtained by chemically treating only one side of a polymer film having only carboxylic acid groups or groups that can be converted into carboxylic acid groups to convert these groups into sulfonic acid groups. The thickness of the membrane used is
50μ to 500μ is generally used, and the specific conductivity of the membrane,
Select an appropriate thickness considering current efficiency. In the first step of the present invention, the surface of the ion exchange membrane obtained from such a polymer membrane is impregnated with a polyamine or a hydrochloride of a polyamine. Examples of the polyamines used include ethylenediamine, 1,2-diaminopropane, 1,3-diaminopropane, triethylenetetramine, tetraethylenepentamine, and polyethyleneimine. A temperature range of room temperature to 100°C is sufficient for impregnating the polyamine or polyamine hydrochloride onto the membrane surface.

In the second step, the membrane surface is impregnated with a metal salt that forms negative metal complex ions in solution.

Examples of metal salts that form negative metal complex ions in solution include PdCl ₂ dissolved in hydrochloric acid;
Aqueous solution of H ₂ ptCl ₆ , K ₂ [Ni(CN) ₄ ] aqueous solution, K ₄
Examples include an aqueous solution of [Ru(CN) ₆ ] and a mixture thereof.

The third stage is chemical plating. The method of chemical plating itself is not particularly limited and can be achieved by a method of depositing metal on the surface of the film by immersing it in a reducing agent. As the reducing agent, for example, an aqueous solution of hydrazine, NaBH ₄ or NaH ₂ PO ₂ can be used, and chemical plating is immersed in these reducing agents for several seconds or several hours, and then repeated until the desired deposit is obtained. conduct.

Example 1 copolymer with (exchange capacity 0.92 meq/g dry)
film (5 mil) and CF ₂ = CF ₂ and Copolymer with (conversion capacity 0.96 meq/g dry)
film (2 mil) and then hydrolyzed to obtain a membrane with a two-layer structure of carboxylic acid groups and sulfonic acid groups. The membrane was then treated with boiling water for 5 hours and then set in a cell so that only the carboxylic acid base layer could be treated. Then NH ₂ −CH ₂ −CH ₂
-NH- _CH2 - _CH2 -NH- _CH2 - _CH2 - _NH2 was treated with hydrochloric acid to convert it into a hydrochloride salt, and then the solution was brought into contact with the membrane surface of the membrane for 5 hours. After washing with water,
0.5% solution _{of H2PtCl6} in contact for 2 hours, then 10
Reduction treatment was performed with a vol% hydrazine aqueous solution. This operation was repeated three times. Then 60% with 10 wt% NaOH
Treated at ~80°C for 5 hours.

A salt electrolyte layer was assembled so that the carboxylic acid layer of the ion exchange membrane, on which platinum was fixed on the carboxylic acid layer obtained above, faced the cathode. Titanium expanded metal coated with ruthenium oxide as anode,
An expanded iron metal was used as the cathode. The anode and the membrane were brought into contact with each other under pressure, and the cathode and the membrane were brought into contact with each other under pressure. When saturated saline was supplied to the anode chamber and water was supplied to the cathode chamber to maintain the concentration of caustic soda in the cathode chamber at 35% by weight, electrolysis was carried out at a temperature of 90°C and a current density of 30A/ ^dm2.The voltage was 3.25 volts and the current was 3.25 volts. The efficiency was 95%. Also, even after 6 months of operation, the voltage is 20 mv.
It just rose.

Note that when a membrane not subjected to the above treatment was used, the voltage was 3.45 volts and the current efficiency was 96%.

Example 2 Copolymer with (exchange capacity 1.4 meq/g dry)
A cation exchange membrane was obtained by forming a film with a thickness of 7 mil and then hydrolyzing it. After fixing platinum using the present cation exchange membrane under the same conditions as shown in Example 1,
It was operated under similar conditions.

The voltage is 3.33 volts and the current efficiency is 95%, 6
Even when driving for a month, the increase was only 30mv.

When using a membrane that has not been subjected to the treatment of the present invention,
The voltage was 3.52 volts and the current efficiency was 95%.

Example 3 After obtaining a copolymer using perfluoropropionyl peroxide in 1,1,2-trichloro-1,2,2-trifluoroethane as an initiator,
A 7 mil thick film was cast.

Next, a cation exchange membrane with an exchange capacity of 0.91 meq/g dry was obtained by hydrolysis at 90° C. in a 20% by weight KOH-methanol solution (weight ratio 1/1). 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).
A film was obtained with a SO ₃ H layer of 5 mil and an SO ₂ Cl layer of 2 mil. Then, at 90 °C in hydroiodic acid (58% by volume),
The reaction treatment was carried out for 5 days. Next, it was hydrolyzed with a 20% by weight KOH-methanol solution (weight ratio 1/1).
The resulting membrane had a SO ₃ K layer of 5 mils and a COOK layer of 2 mils.
A two-layer membrane of the mill was obtained.

Next, after subjecting the membrane to boiling water treatment for 5 hours,
The cell was set so that only the carboxylic acid layer could be treated. Next, tetraethylenepentamine was treated with hydrochloric acid to convert it into a hydrochloride salt, and then the solution was brought into contact with the membrane surface of the membrane for 5 hours.

After washing with water, add 0.5 wt% aqueous solution of H ₂ PtCl ₆ to
The mixture was brought into contact for a period of time, and then reduced with a 0.01% by weight aqueous solution of NaBH ₄ . This operation was repeated four times.
Next, it was treated with 10% by weight NaOH at 60-80°C for 5 hours.

A salt electrolytic cell was assembled so that the carboxylic acid layer of the ion exchange membrane, on which platinum was fixed on the carboxylic acid layer obtained above, faced the cathode. Titanium expanded metal coated with ruthenium oxide as anode,
An expanded iron metal was used as the cathode. The anode and the membrane were brought into contact with each other under pressure, and the cathode and the membrane were brought into contact with each other under pressure. When saturated saline was supplied to the anode chamber and water was supplied to the cathode chamber to maintain the concentration of caustic soda in the cathode chamber at 33% by weight, electrolysis was carried out at a temperature of 90°C and a current density of 30A/ ^dm2.The voltage was 3.25 volts and the current was 3.25 volts. The efficiency was 95%. Also, the voltage is 30 mv even after 6 months of operation.
It just rose.

Note that when a membrane not subjected to the above treatment was used, the voltage was 3.40 volts and the current efficiency was 95%.

Claims (1)

[Claims] 1. A method for fixing a metal on the surface of a cation exchange membrane, in which the surface of the membrane is impregnated with a polyamine or a hydrochloride of a polyamine in advance,
A method for fixing a metal to the surface of a cation exchange membrane, which is then impregnated with a metal salt that forms a negative metal complex ion in a solution and subjected to chemical plating. 2 Claim 1 in which a cation exchange membrane consisting of sulfonic acid groups is used as the cation exchange group
The method described in section. 3 Claim 1 in which a cation exchange membrane consisting of a carboxylic acid group is used as the cation exchange group
The method described in section. 4. The method according to claim 1, which uses a cation exchange membrane having a multilayer structure of sulfonic acid groups and carboxylic acid groups as cation exchange groups. 5. The method according to claim 1, 2, 3 or 4, wherein the metal to be fixed is selected from platinum, palladium, ruthenium, nickel, or a mixture thereof.