JPS6256183B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a roughened cation exchange membrane.

A method of producing alkali hydroxide by electrolyzing an aqueous alkali chloride solution in an electrolytic cell divided into an anode chamber and a cathode chamber by a cation exchange membrane (ion exchange membrane method)
In recent years, many attempts have been made to save energy, and in particular, methods of reducing electrolysis power by lowering the electrolysis voltage as much as possible are attracting attention.

Conventionally, this method involves determining the material of the anode and cathode,
Various methods have been proposed, such as considering the composition and shape, or specifying the composition of the cation exchange membrane used and the type of ion exchange group, but although all of these methods have certain effects, they are not necessarily suitable for industrial use. was not completely satisfactory.

On the other hand, in recent years, a method has become mainstream in which the anode and cathode are brought as close as possible to minimize the electrolytic voltage portion due to the resistance of the electrolytic solution or bubbles existing between the two electrodes. As an ideal method, a method called SPE electrolysis has been proposed, which attempts to minimize the resistance between the electrodes by integrating the cation exchange membrane and the anode and cathode, but there are still many problems that need to be solved. Therefore, industrialization is difficult.

Therefore, instead of integrating the membrane and electrode, it has been proposed to bring the electrode and membrane as close as possible or to treat the membrane surface in order to bring them into close contact for electrolysis. For example, methods for roughening the membrane surface (JP-A-55-110786, JP-A-56-116891, JP-A-57-
70285), a method of forming a porous layer made of metal oxide on the surface (Japanese Patent Application Laid-Open No. 108888/1983), etc.

Surface-treated membranes prepared by any of the above methods can prevent a large voltage increase due to electrolytically generated bubbles that normally occur when the electrode and membrane are brought close to each other.

However, according to the studies of the present inventors, the roughened film using the blasting method often damages the film because particles collide with the film at high speed to form unevenness during blasting. This method results in a decrease in current efficiency and is not yet a perfect method.

In addition, even if the surface is roughened by removing particles such as aluminum, zinc, tin, or nickel after being heated and compressed, the voltage reduction value will be small if you try to maintain high current efficiency. However, it is still not a satisfactory method.

Furthermore, embossing, which is a common surface treatment method for plastic films, cannot form desired irregularities, and it is often difficult to completely prevent voltage increases that occur when the electrode and film are brought close together.

As described above, it is difficult to simply apply surface roughening, which is a long-known method for making a film surface hydrophilic, as seen in British Patent No. 851021, to cation exchange membranes.

On the other hand, when a porous layer made of metal oxide is formed on the surface, there always remains the problem that the attached porous layer peels off over time.

The present inventors continued their research into a method for manufacturing a membrane that does not have these disadvantages but has the electrolytic voltage as low as possible, and found that granular materials such as aluminum, zinc, tin, and nickel are heated and bonded together. In the surface roughening method where the surface is roughened and then removed, many of the roughened surfaces were examined in detail using an electron microscope, and the cause that seemed to reduce the current efficiency was discovered.
We came to the following conclusion.

When forming a particle layer with zinc, tin, etc., a binder is used to make it easier to remove when drying, so the particle layer becomes hard, and the bulk density of these particles is large, so the particle layer becomes hard. When this particle layer is heated and compressed, the pressure is not properly transmitted to the membrane surface, and a lateral force is applied to the membrane surface, or a strong force is applied to a part of the membrane surface, causing the membrane surface to tighten. This results in the formation of crack-like marks or deep holes, which lowers the current efficiency.In order to successfully form a rough surface, it is necessary to apply pressure to the particle layer when applying pressure to the particle layer. The conclusion is that it is important to form a particle layer consisting of particles with a low bulk density in order to have a uniformizing effect.

Based on this conclusion, we conducted further research, selected specific powder particles, heated and compressed the particle layer on the surface of the cation exchange membrane, and then removed this particle layer, thereby reducing the voltage even when the electrode and membrane were brought close together. We have found a method that can be economically scaled up without causing any increase in current efficiency while maintaining high current efficiency.

Using this method, it became possible to perform surface treatment on cation exchange membranes with good reproducibility, and a method for producing roughened cation exchange membranes was completed.

That is, in the present invention, silica powder and water are mixed to form a suspension or paste mixture, the mixture is supported on art paper or paper, and the silica powder layer formed by drying is coated with cation exchange groups and Surface roughening characterized by heating and press-bonding the surface of a perfluorocarbon polymer membrane having a group that can become a cation exchange group and removing the silica powder formed on the surface of the membrane using a water-soluble caustic alkali solution. This is a method for manufacturing cation exchange membranes that not only prevents a large increase in voltage when the electrode and membrane are brought close together in the electrolysis of aqueous alkali chloride solutions using cation exchange, but also reduces the electrolysis voltage and produces high quality products. The present invention provides a roughened cation exchange membrane for producing caustic alkali.

The cation exchange membrane used in the present invention has heat resistance,
A perfluorocarbon polymer with excellent chemical resistance and mechanical strength is used.

The perfluorocarbon polymer 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 a metal atom),
−SO ₂ F, − which is a precursor of sulfonic acid group
SO ₂ Cl, carboxylic acid group (-COOM, where M is a hydrogen atom or metal atom), -COF, -COOR (R has 1 to 1 carbon atoms), which is a precursor of a carboxylic acid group
5) and -CN. Furthermore, 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-mentioned two-component system can also be used.

Specifically, the following can be shown, for example.

(Group A) (Group B) The ion exchange capacity of these polymers is
It is preferable to adjust the amount to 0.5 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) 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.

When roughening the surface of a cation exchange membrane, it is most important to select the type of powder particles and the paper that is the carrier for the powder.

As the powder particles, silica having an average particle diameter of 0.01 to 20μ, preferably 0.1 to 10μ is used. The silica powder is once formed as a particle layer on the carrier. If silica powder is directly formed on the cation exchange membrane by coating or the like, the cation exchange membrane will wrinkle or the particle layer will crack, making it impossible to obtain the desired surface roughening.

Paper or art paper (product name) as carrier
Use. With other types of paper, it is difficult to obtain a uniform silica particle layer, and if the particle layer is handled after drying, the particles may fall off or the particle layer may crack, which is undesirable.

In addition, powders other than silica, such as aluminum,
When powder particles such as zinc, nickel, tin, etc. are used, even if paper or art paper is used, if the particle layer is dried and handled, the particles may fall off or the particle layer may crack, making it unsuitable as a surface roughening material. do not have.

As described above, only the combination of silica and paper or art paper can form an optimal surface roughening particle layer.

The thickness of the particle layer formed on the carrier is 5μ to 250μ
μ is preferred. If it is less than 5μ, it is difficult to uniformly roughen the surface of the cation exchange membrane;
If it is more than μ, cracks will occur in the silica particle layer, which is not preferable. Within this range, a sufficient surface treatment effect can be obtained even if the depth of the unevenness is different.

If the particle layer formed on the carrier contains water, it may generate water vapor during heating and pressure bonding, which may destroy the particle layer, so it is necessary to dry it beforehand.

The silica powder particle layer formed on paper or art paper is heated and pressed onto the base cation exchange membrane to form such a particle layer on the surface of the cation exchange membrane.

The pressure bonding method may be either a press method or a roll method, which is appropriately selected depending on the membrane form of the base cation exchange membrane.

The pressure bonding conditions are a temperature of 100 to 200°C and a pressure of 5 to 100 Kg/ ^cm2 , which are appropriately selected depending on the form of the cation exchange group.
is preferred.

The silica particle layer formed on the surface of the cation exchange membrane is heated in a caustic soda aqueous solution with a concentration of 1 to 30% by weight.
Dissolve and remove at 20-90℃.

The roughened surface formed on the surface of the cation exchange membrane by the above treatment has an average depth or height of 0.1 to 20 μ from the membrane surface, and an average of 10 3 to 10 ³ per cm ² of the membrane surface.
It consists of 10 ^{to 15} minute irregularities, and its cross-sectional shape is
It has an irregular circular shape.

These surface irregularities can be roughly measured using a surface profile measuring device (roughness meter), but in order to accurately judge the extent of the effect, a method is used to determine the depth or height and density from surface and cross-sectional photographs taken using an electron microscope. It's better to do so.

The surface roughening of the present invention can be applied to only one side of the membrane, or can be applied to both sides. When applying to both sides, it is preferable to heat and press the silica powder layer on both sides at the same time. When only one side is roughened, it is used by arranging it so that the roughened side faces the cathode side.

The surface-treated cation exchange membrane obtained as described above is used as a diaphragm for dividing an anode chamber and a cathode chamber in an electrolysis process of an aqueous alkali chloride solution. 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. Examples include, but are not limited to, materials such as iron, mild steel, nickel, and stainless steel, and porous materials such as wire mesh, expanded metal, lattice, vertical rail, and punched metal. isn't it.

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 may be apart.

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

Similarly, CF ₂ = CF ₂ (exchange capacity as carboxylic acid group was 1.1 meq/g). This will be referred to as B polymer.

Next, polymer A is formed into a film with a thickness of 100μ and polymer B with a thickness of 75μ, respectively.Then, these two films are stacked and thermocompressed to form a single film, which is used as a base cation exchange membrane. .

Fine silica powder with an average particle size of about 5 μm was kneaded with water to form a paste of 15% by weight, and then applied onto art paper to obtain a silica particle layer with a thickness of about 50 μm.

The art paper carrying the silica particle layer was applied to both sides of the base cation exchange membrane, and heated and pressed at 160° C. and 60 kg/cm ² .

Then, in a 5% by weight aqueous solution of caustic soda at a temperature of 80°C.
The silica powder pressed onto the surface of the cation-exchange membrane was removed under conditions of 100°C, and at the same time hydrolysis was carried out to obtain a roughened cation-exchange membrane.

The B polymer side of the cation exchange membrane was placed in an electrolytic cell with the side facing the cathode, and titanium expanded metal coated with ruthenium oxide was used as the anode, and iron expanded metal was used as the cathode, the distance between the anode and cathode was 1 mm, and the cathode chamber was The extraction level of the caustic soda aqueous solution was set 20 cm higher than the level of the anode chamber, and electrolysis was carried out with the membrane in contact with the anode.

Supply saturated saline to the anode chamber and water to the cathode chamber.
The caustic soda concentration in the cathode chamber was maintained at 33% by weight, and the temperature
When electrolyzed at 90° C. and a current density of 40 A/dm ² , the voltage was 3.33 V and the current efficiency was 96.5%.

The salt concentration in the 33% by weight caustic soda product is
It was as low as 10ppm.

Comparative Example 1 Zinc powder with an average particle size of 7 μm was suspended in water to a concentration of 2% by weight, and a layer of zinc powder particles was formed on paper by the filtration method. was heated and crimped.

Next, the zinc powder was dissolved and removed in a 20% by weight aqueous sodium hydroxide solution at 80°C, and then treated for 24 hours in a 10% by weight aqueous sodium hydroxide solution at 90°C for hydrolysis.

Electrolysis was carried out under exactly the same conditions as in Example 1, with a current density of 40 A/dm ² , a voltage of 3.30 V, and a current efficiency of 94.0%.
I got the result.

Comparative Example 2 In Example 1, electrolysis was carried out in exactly the same manner as in Example 1 without any treatment on both sides of the cation exchange membrane at a current density of 40 A/dm ² , voltage of 3.65 V, and current efficiency.
Obtained a result of 96.0%.

Example 2 Fine silica powder with an average particle size of 5 μm was suspended in water to a concentration of 0.3% by weight, and a layer of silica particles with a thickness of about 70 μm was formed on paper by a filtration method.

After drying the paper carrying this silica particle layer, it was applied to both sides of the same base cation exchange membrane as in Example 1, and heated and pressed under the conditions of 160° C. and 20 kg/cm ² .

After that, the same process as in Example 1 is performed, and Example 1
Electrolysis was carried out under the same conditions. Current density 40A/ ^dm2
We obtained a voltage of 3.35V and a current efficiency of 96.5%.

The salt concentration in the product 33% by weight caustic soda is 8ppm
There were very few.

Claims (1)

[Claims] 1. Mix silica powder and water to form a suspension or paste mixture, support the mixture on art paper or paper, and dry it to form a silica powder layer. A roughened cation exchange membrane characterized by heating and press-bonding the surface of a perfluorocarbon polymer membrane having a group capable of becoming an ion exchange group, and removing silica powder formed on the membrane surface with a caustic aqueous solution. manufacturing method.