JPS6154116B2 - - 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 the 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, Japanese Patent Publication No. 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 deposited only on the film surface, the degree of metal removal 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 this conclusion, the present inventors conducted further research and surprisingly found that by pre-embedding metal particles on the film surface and then chemically plating the film surface, The present inventors have discovered that a cation exchange membrane having a metal layer bonded very strongly and uniformly on its surface can be obtained with good reproducibility, leading to 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.

That is, the present invention provides cation exchange groups and/or
Alternatively, after pressing a metal onto a perfluorocarbon polymer membrane that has a group that can become a cation exchange group, if a group that can become a cation exchange group is used, convert it to a cation exchange group, and then chemical plating. It is a method that consists of doing things.

The perfluorocarbon polymer that can be used in the present invention has a cation exchange group and/or a group that can become a cation exchange group, and these groups include a sulfonic acid group (-SO ₃ M, where M is a hydrogen atom). or metal atoms), −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 metal atom), -COF, which is a precursor of a carboxylic acid group, -
COOF (R is an alkyl group having 1 to 5 carbon atoms) and -
CN can be mentioned. Furthermore, examples of the polymer include a polymer 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.

Specifically, the following can be shown, for example.

In these polymers, the exchange group capacity is 0.5meq/g
It is preferable to adjust the amount of 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 one 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) group polymers) can be obtained by forming them into a membrane and then gluing them together.Also, it is possible to obtain polymers having only sulfonic acid groups or groups that can be converted into sulfonic acid groups. It can also be obtained by chemically treating only one side of the membrane and converting these groups into carboxylic acid groups or groups that can be converted into carboxylic acid groups.

Furthermore, by chemically treating only one side of the polymer film having only carboxylic acid groups or groups that can be converted into such groups, these groups can be converted into sulfonic acid groups or groups that can be converted into such groups. You can get it even if you twist it. Also, the thickness of the membrane used is 50μ
~500μ is generally used, and an appropriate thickness is selected by considering the specific conductivity and current efficiency of the film.

The first step of the invention is the compression of metal onto the membrane surface. The metal used is preferably in the form of particles of 1 μ to 100 μ, and metal particles may be formed into a thin film using a binder such as PTFE in advance to ensure uniform dispersion on the film surface. .
For pressure bonding, it is necessary to uniformly disperse the metal particles on the film surface by using a sieve or the like or by using a thin film of the metal particles described above with a binder. If this uniformity is not sufficient, the resulting metal fixation state will be non-uniform and its contribution to improving electrolytic performance will be reduced.

The amount of metal to be crimped is preferably in the range 0.1 mg to 100 mg per 10 m ² . The amount of metal to be crimped
If it is less than 0.1 mg/cm ² , the uniformity of the chemical plating performed in the next step and the adhesion strength of the deposited metal to the film surface will be insufficient. Furthermore, if the amount of metal to be crimped is 100 mg/cm ² or more, even if chemical plating is performed in the next step, the drawbacks seen in the dry method described above cannot be compensated for.

For crimping, a normal hot press used for plastic molding can be used,
Continuous embedding is also possible by passing the membrane and metal powder simultaneously between two rolls. The temperature, pressure and time required for crimping at this time are:
Of course, it varies depending on the type and amount of exchange groups present in the membrane or groups that can be converted into exchange groups, and the molecular weight and molecular weight distribution of the polymer, but usually,
Temperature 50℃~350℃, Pressure 5Kg/cm ² ~500Kg/cm ² hours 1
Conditions from seconds to 10 minutes are selected.

The second stage of the present invention is a stage in which metal is buried in the first stage and chemical plating is applied on the film surface. however,
If the polymer membrane contains a group that can become a cation exchange group, it is converted into a cation exchange group by chemical treatment and then enters the second stage.

The chemical plating method referred to in the present invention is a commonly used method and is not particularly limited. For example,
A method of plating by placing a metal salt solution to be plated on one side of the membrane and a reducing agent solution on the other side, taking advantage of the difference in permeation speed into the membrane (Special Publications 1983-
36873), 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 that is fixed on the film surface in the above manner may be selected from metals that can withstand the usage environment, such as platinum group metals such as platinum, palladium, ruthenium, and iridium, gold, silver, and nickel. Ru. Furthermore, the metal embedded in the film in the first step of the present invention may be different from the metal plated in the second step, and when chemical plating is performed in several steps, the metal embedded in the film in the first step may be different from the metal plated in the second step. It does not matter if the metal types are different.

The metal fixation of the present invention may be applied to only one side of the membrane, or may be applied to both sides. When metal fixing is applied to both sides, the metals on both sides may be the same or different.

When metal fixing is applied to only one side of the membrane, it is preferable that this side is the membrane side facing the cathode during salt electrolysis.

The cation exchange membrane with fixed metal obtained as described above can be used as a diaphragm for dividing an anode chamber and a cathode chamber in a salt electrolysis process. The cathode used in this case may be one that can withstand the operating environment, has a sufficient catalytic effect for the reaction, and has a structure that does not hinder the escape of the produced gas, and may be any commonly used cathode. Bye. For example, iron, mild steel, nickel,
Materials such as stainless steel and porous materials such as wire mesh, expanded metal, lattice, vertical lattice, and punched metal may be used, but the material is not limited thereto.

As for the anode, a normal anode that can withstand the usage environment and has sufficient catalytic activity for the desired reaction is used. A porous anode coated with a platinum group metal such as platinum, 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.
During electrolysis, these electrodes may be in contact with the membrane surface or the fixed metal on the membrane surface, or they may be separated.

The method of the present invention will be explained below using specific examples. Note that the present invention is not limited to these specific examples.

Example 1 were copolymerized in 1,1,2-trichloro-1,2,2-trifluoroethane using perfluoropropionyl peroxide as an initiator to obtain a polymer (exchange capacity as sulfonic acid group was 0.91 meq/g). dry resin). This is called Polymer A.

in the same way (Exchange capacity as carboxylic acid group was 1.1 meq/g). This will be referred to as B polymer.

Next, Polymer A was molded into films with a thickness of 100 μm and Polymer B with a thickness of 75 μm, respectively, and these two films were stacked and thermocompressed to form one film. This will be referred to as film 1.

50ml of 50mg of platinum fine particles (average particle size 5-10μ)
A suspension of polytetrafluoroethylene (PTFE) was added to this in such a manner that the weight ratio of PTFE to platinum was 1/6, and after stirring, the suspension was The film was suctioned onto a porous PTFE sheet to obtain a film with a thin layer of platinum particles uniformly dispersed on the PTFE. The film is called Film 2.
shall be.

Platinum was contained in the thin layer at a rate of 5 mg/cm ² .

Place film 2 on the B polymer side of film 1 so that the thin platinum layer is in contact with polymer B, and in this state pressurize with a hot press at 160°C, 100 kg/cm ² for 1 minute, and press the thin platinum layer onto the film. After that, the porous PTFE membrane was removed to obtain a polymer membrane in which platinum was adhered to the membrane surface. Subsequently, the polymer film was immersed in a mixture of 20% NaOH aqueous solution and methanol at 70°C for 15 hours to remove the - present in the film.
An ion exchange membrane was prepared by hydrolyzing SO ₂ F and -COOCH ₃ .

Thereafter, the ion exchange membrane was immersed in a platinum electroless plating solution containing dimethylamine borane to chemically plate platinum on the platinum fine particles on the membrane surface.

In the manner described above, an ion exchange membrane having a carboxylic acid-sulfonic acid two-layer structure in which platinum was uniformly and firmly adhered to the carboxylic acid layer was obtained.

Example 2 50mg of nickel fine particles (average particle size 30μ or less)
Suspend it in 50ml of water, add a suspension of polytetrafluoroethylene (STFE) so that the weight ratio of PTFE to nickel is 1/9, and after stirring, add the suspension to porous PTFE. A thin layer of nickel particles uniformly dispersed on the PTFE sheet was obtained by suctioning the film onto the sheet. This film will be referred to as film 3.

Film 3 was pressure-bonded onto Film 1 obtained in Example 1 in the same manner as in Example 1 to obtain a polymer film in which nickel adhered to the film surface. Subsequently, the polymer was subjected to the same hydrolysis conditions as in Example 1 to form an ion exchange membrane.

The thus obtained ion exchange membrane with nickel adhered to the membrane surface was further immersed in an electroless plating bath containing nickel chloride and sodium borohydride to chemically plate nickel on the nickel fine particles on the membrane surface.

In the manner described above, an ion exchange membrane having a carboxylic acid-sulfonic acid two-layer structure in which platinum was uniformly and firmly adhered to the carboxylic acid layer was obtained.

Example 3 The same procedure as in Example 1 was carried out except that the amount of platinum contained in the platinum thin film was changed from 5 mg/cm ² to 1 mg/cm ² . Carboxylic acid-sulfonic acid 2 with tightly adhered
An ion exchange membrane with a layered structure was obtained.

Example 4 Two films 2 were prepared in Example 1, and film 1 was sandwiched from both sides so that the porous PTFE was on the outside. Pressure was applied under the same conditions to attach a thin platinum layer to both sides of film 1. After that, the porous PTFE membrane was removed to obtain a polymer membrane with platinum adhered to both sides of the membrane. Subsequently, the polymer membrane was subjected to the same hydrolysis conditions as in Example 1 to obtain an ion exchange membrane.
Thereafter, in the same manner as in Example 1, platinum was chemically plated on the platinum fine particles on the film surface.

As described above, an ion exchange membrane having a carboxylic acid-sulfonic acid two-layer structure in which platinum was uniformly and firmly adhered to both sides of the membrane was obtained.

Comparative Example 1 Film 1 obtained in Example 1 was hydrolyzed to obtain an ion exchange membrane. Thereafter, an attempt was made to electrolessly plate platinum on the ion exchange membrane under the same conditions as in Example 1. However, almost no platinum was deposited on the membrane surface, and the deposited portions had almost no adhesion to the membrane and were easily peeled off simply by immersion in hot water.

Reference Example 1 The ion exchange membrane having a carboxylic acid-sulfonic acid two-layer structure in which platinum was fixed on the carboxylic acid layer obtained in Example 1 was placed in a salt electrolytic cell so that the carboxylic acid layer faced the cathode.

Titanium expanded metal coated with ruthenium oxide was used as the anode, and expanded iron metal was used as the cathode. 3mm between anode and cathode
In addition, in order to bring the surface of the membrane to which platinum is not adhered into contact with the anode, the level at which the caustic soda aqueous solution is extracted from the cathode chamber is set at 20% relative to the liquid level in the anode chamber.
cm higher.

Supply saturated saline to the anode chamber and water to the cathode chamber.
When electrolysis was carried out at a temperature of 80°C and a current density of 30 A/dm ² while maintaining the concentration of caustic soda in the cathode chamber at 35%, the voltage was 3.2 volts and the current efficiency was 96%. or,
This value was maintained during 6 months of operation, and no peeling of the metal adhered to the membrane was observed.

On the other hand, in Example 1, using an ion exchange membrane with only a platinum thin film crimped on it without electroless plating,
When the same salt electrolysis as above was carried out, the voltage was
The voltage was 3.55 volts, and the current efficiency was 96%, but after 10 days of operation, the voltage had increased to 3.5 volts, and peeling of the platinum film from the surface was observed.

Claims (1)

[Scope of Claims] 1. Particles of 1 μ to 100 μ of a metal selected from platinum group metals, gold, silver, and nickel on a perfluorocarbon polymer membrane having a cation exchange group and/or a group capable of becoming a cation exchange group. 0.1 per ^10m2
mg~100mg, 50~350℃, 5~500Kg/ ^cm2 , 1 second~10
Cation exchange, which consists of crimping under conditions of 10 minutes, then converting the group into a cation exchange group if a group capable of becoming a cation exchange group is used, and chemically plating with a metal selected from the above metals. A method of fixing metal onto a membrane. 2. The method according to claim 1, which uses a perfluorocarbon polymer membrane in which the cation exchange groups consist of sulfonic acid and/or carboxylic acid groups. 3 Groups that can become cation exchange groups are -SO ₂ F, -
The method according to claim 1, wherein the method is selected from _SO2Cl , -COF, -COOR (R is an alkyl group having 1 to 5 carbon atoms) and -CN.