JPS6316420B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a roughened cation exchange membrane suitable for electrolysis of an aqueous alkali chloride solution.

A method for producing alkali hydroxide by electrolyzing an aqueous alkali chloride solution in an electrolytic cell divided into an anode chamber and a cathode chamber using 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 group used and the type of ion exchange membrane, 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 form of this, a method called SPE electrolysis has been proposed, which attempts to minimize the resistance between the electrodes by integrating the cation exchange membrane with the anode and cathode, but there are still many problems to be solved. industrialization is difficult.

Therefore, instead of integrating the membrane and electrode, it has been proposed to treat the membrane surface in order to bring the electrode and membrane as close as possible or in close contact for electrolysis. For example, methods for roughening the membrane surface (Japanese Unexamined Patent Publications No. 55-110786, No. 56-116891, No.
57-70285), a method of forming a porous layer made of a 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 conducted by the present inventors, the roughened film using the blasting method often damages the film because particles collide with the film at high speed during blasting, forming unevenness. This method results in a decrease in efficiency and is not yet a perfected method.

Furthermore, even if the surface is roughened by removing granular materials such as aluminum, zinc, tin, or nickel after being heated and crimped, the voltage reduction value will be However, it is still not a satisfactory method.

Furthermore, embossing, which is a common surface processing 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 to each other.

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 and has the electrolytic voltage as low as possible, and found that by selecting specific powder particles, a particle layer was formed on the surface of the cation exchange membrane. By removing this particle layer after heating and pressure bonding, we have found an economically viable method for increasing the size of the membrane without causing a voltage increase even when the electrode and membrane are brought close to each other, while maintaining high current efficiency.

This method has made it possible to perform surface treatment on cation exchange membranes with good reproducibility;
As they continued their improvement research, they discovered a method that could further reduce the voltage, and completed the present invention.

That is, the present invention heats and presses a powder particle layer made of silica powder on the surface of a perfluorocarbon polymer having a cation exchange group and/or a group that can become a cation exchange group, and then injects the silica powder into a caustic aqueous solution. Further, in a mixture of a caustic aqueous solution and a C ₁ to _{C 3} lower alcohol,
This is a method for producing roughened cation exchange membranes that is characterized by heating from 40℃ or higher to the boiling point of _C1 to _C3 lower alcohols, and the voltage range when the electrode and membrane are brought close together. The purpose of the present invention is to provide a surface-treated cation exchange membrane that not only prevents the electrolysis voltage from increasing, but also effectively reduces the electrolytic voltage and produces high-quality caustic alkali.

For the cation exchange membrane used in the present invention, a perfluorocarbon polymer is used in consideration of heat resistance, chemical resistance, mechanical strength, etc.

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, which is a precursor of a carboxylic acid group, -COOR (R has 1 to 1 carbon atoms)
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 two-component system can also be used.

Specifically, the following can be shown, for example.

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 20 μm, preferably 0.1 to 10 μm or less 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 means such as coating, the cation exchange membrane will wrinkle or the particle layer will crack, making it impossible to obtain the desired surface roughening.

As the carrier, it is preferable to use paper or art paper (trade name). 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, an optimal surface roughening particle layer can be formed when using a combination of silica and paper or silica and art paper.

The thickness of the particle layer formed on the carrier is preferably 5μ to 250μ. If it is less than 5μ, it is difficult to uniformly roughen the surface of the cation exchange membrane, and if it is more than 250μ, 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.

A silica powder particle layer formed on paper or art paper is heated and pressed onto a 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.

Crimping conditions are temperature 100~200℃, pressure 5~100Kg/
^cm2 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℃.

By further treating the cation exchange membrane whose surface has been roughened by the above method in the next step, a high-performance surface-treated ion exchange membrane with a reduced absolute value of voltage can be obtained.

This process involves heating a roughened cation exchange membrane in a mixture of a caustic aqueous solution and a C ₁ to C ₃ lower alcohol to a temperature from 40°C or higher to the boiling point of the C ₁ to C ₃ lower alcohol. It is to be.

Organic solvents other than those of the present invention are not preferred because they do not exhibit a voltage reduction effect, are difficult to handle, are expensive, and the like.

Even when heating is performed using only a lower alcohol without the presence of an aqueous caustic alkali solution, the degree of swelling of the cation exchange membrane increases, the water content increases, and the current efficiency decreases, which is not preferable.

In other words, only the treatment using the liquid mixture of the present invention can effectively reduce the voltage.

The concentration of caustic alkali and lower alcohol in the mixed solution is determined based on solubility and processing effect, but the concentration of caustic alkali is preferably 5 to 20% by weight, and the concentration of lower alcohol is preferably 20 to 80% by volume.

If the above conditions are exceeded, for example, if the concentration of caustic alkali increases, the voltage reduction effect will decrease,
If the proportion of lower alcohol becomes too high, the cation exchange membrane will swell too much, which is undesirable, especially since the current efficiency immediately after the start of electrolysis may become low and the anode may be damaged.

If the heating temperature is less than 40° C., no voltage reduction effect will be obtained, and if the heating temperature is higher than the boiling point of the C ₁ -C ₃ lower alcohol, the current efficiency will decrease, which is not preferable.

After heat treatment under the conditions of the present invention, the cation exchange membrane was taken out, washed with water, and placed in the air at a temperature of 5 to 50℃.
It is further preferable to dry under mild conditions at .degree.

By adding such drying treatment, stable performance can be exhibited immediately after the start of electrolysis.

Note that even if a membrane that has not been subjected to surface roughening treatment is heat treated in a mixed solution of a caustic alkali aqueous solution and a C ₁ to _{C 3} lower alcohol, no voltage reduction effect can be expected.

The rough 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 ¹⁵ per cm ² of the membrane surface.
The cross-sectional shape is an irregular circle.

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, there is a method of determining the depth or height and density from surface and cross-sectional photographs taken using an electron microscope. It is better to adopt it.

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 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 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 0.91meq/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 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 30 kg/cm ² . Thereafter, in a 5% by weight aqueous sodium hydroxide solution at a temperature of 80° C., the silica powder pressed onto the surface of the cation exchange membrane was dissolved and removed, and at the same time hydrolysis was carried out.

Next, the cation exchange membrane was placed in a mixture of 20% by weight aqueous caustic soda and methanol at 60°C.
After heat treatment for 5 hours, it was heated in air at 25℃ for 2 hours.
Dry for days.

The obtained roughened cation exchange membrane was immersed in a 2% by weight aqueous sodium hydroxide solution overnight, and the cation exchange membrane was placed in an electrolytic cell with the B polymer side facing the cathode, and titanium coated with ruthenium oxide was used as the anode. An expanded metal made of iron was used as the cathode, the distance between the anode and cathode was 1 mm, the extraction level of the caustic soda aqueous solution in the cathode chamber was 20 cm higher than the level in 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 3.25 V and the current efficiency was 96.5%.

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, and both sides of the base cation exchange membrane used in Example 1 were suspended. 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, both sides of the cation exchange membrane were not treated in any way, and electrolysis was carried out in exactly the same manner as in Example 1, with a current density of 40 A/dm ² , a voltage of 3.65 V, and a current efficiency of 96.0%. I got the result.

Example 2 A membrane having a carboxylic acid layer with a thickness of about 40μ was prepared by chemically treating one side of a Nafion 117 cation exchange membrane commercially available from DuPont, USA.
A cation exchange membrane with a SO ₃ H/COOH two-layer structure was obtained.

Using this membrane, the surface was roughened in exactly the same manner as in Example 1, and electrolysis was performed under the same conditions as in Example 1, resulting in a voltage of 3.30 V and a current efficiency of 96.5%.

Example 3 Fine silica powder with an average particle size of 3 μm or less 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.

The paper carrying the silica particle layer was applied to both sides of the same base cation exchange membrane as in Example 1, and heated at 160°C and 60°C.
Heating and compression bonding was carried out under conditions of Kg/cm ² . then 5% by weight
The silica particles pressed onto the surface of the cation exchange membrane were dissolved and removed in a caustic soda aqueous solution at a temperature of 80°C.

Next, the cation exchange membrane was placed in a mixture of equal amounts of 20% by weight caustic soda aqueous solution and ethanol at 60°C.
Heat treatment was performed for 5 hours.

Electrolysis was performed under the same conditions as in Example 1 using the obtained roughened cation exchange membrane. Initially, both voltage and current efficiency were low, and it took about a week for performance to recover.
After that, stable performance was maintained. The electrolysis performance on the seventh day was a voltage of 3.23V and a current efficiency of 96.0%.

Comparative Example 3 In Example 1, the silica powder pressed onto the surface of the cation exchange membrane was dissolved and removed and hydrolyzed at the same time, and then the cation exchange membrane was placed in an electrolytic cell and electrolysis was carried out in the same manner as in Example 1. I went.

Current density 40A/ ^dm2 , voltage 3.33V, current efficiency
The voltage increased to 96.5%.

Comparative Example 4 In Example 2, the silica powder pressed onto the surface of the cation exchange membrane was dissolved and removed and simultaneously hydrolyzed, and then the cation exchange membrane was incorporated into an electrolytic cell and electrolyzed in the same manner as in Example 2. I went to

Current density 40A/ ^dm2 , voltage 3.38V, current efficiency
The voltage increased to 96.5%.

Comparative Example 5 In Example 3, after dissolving and removing the silica particles pressed onto the surface of the cation exchange membrane, the cation exchange membrane was incorporated into an electrolytic cell, and electrolysis was performed in the same manner as in Example 3.

Although it showed stable voltage and current efficiency from the beginning,
The electrolytic performance was higher at voltage 3.31V and current efficiency 96.0%.

Claims (1)

[Claims] 1. A silica powder layer formed by mixing silica powder and water to form a suspension or paste mixture, supporting the mixture on art paper or paper, and drying the silica powder layer. A rough surface obtained by heating and pressing the surface of a perfluorocarbon polymer membrane having an exchange group and/or a group capable of becoming a cation exchange group, and eluting the silica powder formed on the membrane surface with a caustic aqueous solution. The chemical cation exchange membrane is heated from 40°C or higher to C ₁ - _{C 3} in a mixture of aqueous caustic alkaline solution and C ₁ - C 3 lower alcohol.
A method for producing a roughened cation exchange membrane characterized by heating to a temperature up to the boiling point of a _C3 lower alcohol. 2. The manufacturing method according to claim 1, which comprises heating in a mixed solution of a caustic alkali aqueous solution and a _C1 to _C3 lower alcohol, followed by washing with water and drying.