JPS5989328A - Manufacture of cation exchange membrane having roughened surface - Google Patents

Abstract

PURPOSE:To obtain the titled exchange membrane suitable for electrolytic use, by applying a silica powder layer to the surface of cation exchange membrane substrate, dissolving the silica powder with an aqueous solution of a caustic alkali, and boiling the membrane in an aqueous solution of caustic alkali having a specific concentration. CONSTITUTION:Silica powder is mixed with water to obtain a suspension or pasty mixture, applied to a sheet of coated paper or filter paper, and dried. The obtained silica powder layer is transferred with heat and pressure to the surface of a perfluorocarbon polymer membrane having a cation exchange group and/or a group which can be converted to cation exchange group. The silica powder transferred to the surface of the exchange membrane is dissolved with an aqueous solution of caustic alkali to obtain a cation exchange membrane having roughened surface, which is converted to the objective cation exchange membrane by boiling in an aqueous solution of caustic alkali having a concentration of 1-10wt%.

Description

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

In recent years, energy conservation has been actively attempted in the 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 particular, methods of reducing the electrolytic power by lowering the electrolytic voltage as low as possible are attracting attention. Conventionally, methods for this include considering the composition and shape of the material of the anode and cathode, or using Various methods have been proposed, such as specifying the composition of the cation exchange membrane and the species of the ion exchange group, but although all of them have some effect, they are not necessarily fully satisfactory industrially. .

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 still need to be solved. 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, a method of roughening the membrane surface (Japanese Patent Laid-Open No. 55-110786, 116891-1989, 70285-1985), a method of forming a porous layer made of metal oxide on the surface (Japanese Patent Laid-Open No. 57-70285), 56-108888) etc.

In any of the above-mentioned methods, the electrode and the membrane were brought close to each other. In this case, it is possible to eliminate the large voltage rise caused by the electrolytically generated bubbles that normally occur.

However, according to studies conducted by the inventors, the surface-roughening treatment film using the blasting method causes particles to collide with the film at high speed during blasting, forming unevenness, which often causes damage to the surface of the film, which can cause damage to the electrode. This method results in a decrease in efficiency and is not yet a perfected method. Even if the surface is roughened by removing such particulate matter after aluminum heating and crimping, the voltage reduction value will be small if you try to maintain high current efficiency, and this is still not a satisfactory method. I don't get it.

However, embossing, which is a common surface treatment method for plastic films, does not create the desired unevenness, and it is often difficult to completely prevent the rise in voltage that kills insects when the electrode and membrane are brought close together. Thus, for example, British Patent 851.0
It is difficult to simply apply surface roughening, which is a long-known method of making a film surface hydrophilic, as seen in No. 21, 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 of peeling off of the attached porous layer over time.

The present inventors have developed a membrane that does not have these disadvantages and also has a reduced electrolytic voltage as much as possible. Continuing research into manufacturing methods, we found that by selecting specific powder particles, heating and pressing a particle layer onto the surface of the base cation exchange membrane, and then removing the particle layer, the electrode and membrane could be brought close together. We have found a method that can be economically scaled up and maintains high current efficiency without causing a voltage increase. Using this method, it became possible to perform surface treatment on cation exchange membranes with good reproducibility, but while continuing research for further improvements, they discovered a method that could further reduce the voltage and completed the present invention. .

That is, in the present invention, silica powder is heated on the surface of a base cation exchange membrane used for aqueous alkali chloride electrolysis.

After the silica powder is crimped, the roughened cation exchange membrane obtained by eluting the silica powder with a caustic alkali aqueous solution is boiled in a 1-10% caustic alkali aqueous solution. This is a method of manufacturing an exchange membrane, which not only prevents a large increase in voltage when the electrode and membrane are brought close together.
The present invention provides a surface-treated cation exchange membrane that effectively reduces electrolysis voltage and produces high quality caustic alkali.

For the base cation exchange membrane used in the present invention, a perfluorocarbon polymer having excellent heat resistance, chemical resistance, mechanical strength, etc. is usually used.

Perfluorocarbon polymers have cation exchange groups and/or
or has a group that can become a cation exchange group,
These groups include sulfonic acid groups (505M, where M is a hydrogen atom or a metal atom).

18o2F, which is a precursor of sulfonic acid groups.

-5o2at, carboxylic acid group (-000M, where M is a hydrogen atom or a metal atom), 100F, which is a precursor of a carboxylic acid group, -00OR (R is an alkyl group having 1 to 5 carbon atoms), and -CNwo can be mentioned.

Furthermore, examples of the polymer include polymers represented by the following general formula.

CF2 1 Small F2 "0F-R' [However, R' = -CF3. -0F2-0-01
7'.

n=0 or 1-5 m=o or 1 0 = 0 or 1 p=1-6 X = -80, M (M is a hydrogen atom or a metal atom), -8o, F, -6o20A-OOOM (M hydrogen atoms or metal atoms).

10OOR, (F, 1=1-5 alkyl group -aN, -
00F] A polymer obtained by adding a third component or a fourth component to the above two-component system can also be used.

Specifically, for example, be able to show the following:

(A'n) CIl +CF2-C! F'2 ther 10 F2-0F na nl, ml [OF, -0F-QC! F2-CF2-8o3HOF.

+2l-(-0'E'2-OF'2→→0F2-CF←
n2, ~2 Ward 0F2-OF-00F2-OF2-8o2FOF.

hmm Doo F2 0F-OF.

OF2-0F2-8o□F (J2 0F-OF'2-0-OF.

[ 0F2-OF2-8o2F F2 0F2-8o2F (Group B) F2 (JC!F3 0-(3F2-(1!00H C'P2 F2 0F2-0000H.

CF2-CF2-0F2-C! F2-(3000H30
F,,-OF2-00F 1 CF'2-OF-QC! F2-CF2-00C'OH3
CF3 000H3 C! F30'P2-OF2-C! F2-C0FCF3
0F2-CF, -0F2-C000H3 ○ 0 CF3 0F2-OF2-00FOF,
OF2 CF-CF3 0-0F2-CF2 (30F 0 0000H3 CF3 In these polymerizations, the ion father exchange capacity is 0.5 meq/
9 dry resin ~t 5 meq/? It is preferable to adjust the resin so that it becomes a dry resin.

In the present invention, it is of course possible to use these polymers formed into a membrane alone, but a group that can be converted into a sulfonic acid group or several groups and a group that can be converted into a carboxylic acid group or several groups are mixed. A polymer having a sulfonic acid group or a group that can be converted into several groups and a polymer having a group that can be converted into a carboxylic acid group or several groups can be layered on each side. can.

Such a film-like material is a polymer having a sulfonic acid group or a group that can be converted into several groups (for example, (A, polymers of group 1)
and a polymer having a carboxyl/acid group or a group that can be converted into several groups (for example, a polymer of group (B)) can be obtained by forming each into a film shape and then gluing the two together. It can also be obtained by chemically treating only one side of a polymer film having only sulfonic acid groups or groups that can be converted into several groups, and converting these groups into carboxylic acid groups or groups that can be converted into several groups. be able to.

Furthermore, by chemically treating only one side of the polymer film having only carboxylic acid groups or groups that can be converted into several groups, and converting these groups into sulfonic acid groups or groups that can be converted into several groups. You can also get In addition, the thickness of the membrane used is generally 50μ to 500μ,
Specific electrical conductivity of the membrane.

Select an appropriate thickness considering current efficiency.

When roughening the surface of a cation exchange membrane, the type of powder particles,
The choice of paper as a carrier for the powder is most important.

As the powder particles, silica having an average particle size of 0.01 to 20 μm, preferably Q, 1 to 10 μm is used. The silica powder is once formed as a particle layer on the carrier. If silica powder is directly formed on the base 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 a carrier,
It is preferable to use filter paper or art paper (trade name). With other papers, it is difficult to obtain a uniform silica particle layer, and if the particle layer is dried and handled, the particles may fall off or the particle layer may crack, which is undesirable.

Also, powders other than silica, such as aluminum.

When powder particles of zinc, nickel, tin, etc. are used, even if filter 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, resulting in a roughening material. It's not nice.

As described above, in the case of a combination of silica and filter paper or silica and art paper, an optimal particle layer for surface roughening can be formed.

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, there is a risk that water vapor will be generated and the particle layer will be destroyed during heating and compression bonding, so it is necessary to dry it beforehand.

The silica powder particle layer formed on Oki paper or art paper is heated and pressed onto the base cation exchange membrane, and the particle layer is formed on the surface of the base 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 compression conditions are appropriately selected depending on the form of the cation exchange group, but preferably a temperature of 100 to 200° C. and a pressure of 5 to 100 kg/momme 2.

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

By treating the cation exchange membrane 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.

Such a step means that the roughened cation exchange membrane Z concentration is 1 to 10.
It is a boiling treatment under normal pressure in a dilute aqueous caustic alkaline solution containing % fi. The processing time is preferably 5 to 10 hours. If boiling in water instead of a dilute caustic aqueous solution causes the roughened cation exchange membrane to swell too much, resulting in high water content, the current efficiency will be low (especially immediately after the start of electrolysis), and there is a risk of damaging the anode. However, the current efficiency does not recover easily.

If the concentration of the dilute aqueous caustic solution exceeds 10%, there will be no treatment effect and no voltage reduction effect can be expected. Further, if the treatment temperature is lowered to, for example, 80 to 9°C under normal pressure, the voltage reduction effect cannot be obtained, which is not preferable. Furthermore, it is preferable to take out the boiling-treated membrane and dry it in the air under mild conditions at a lake temperature of 10 to 50°C. If such a drying step is performed, high current efficiency can be obtained immediately after the start of electrolysis.

The roughening applied to the surface of the cation exchange membrane through the above treatment means that the depth or height from the membrane surface is on average 0.1 to 2.
0 μ, average 103 to 10 per 1 CIrL2 membrane surface
It consists of 5 minute concavities and convexities, and its cross-sectional shape is irregularly circular.

These surface irregularities can be approximately measured using a surface profile measuring device (roughness meter), but in order to accurately judge the extent of the effect, there is a method to determine 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 may be applied to only one side of the membrane, or may 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, the roughened side is used facing toward the cathode.

The surface-treated cation exchange membrane obtained as described above is
It is used as a diaphragm to separate an anode chamber and a cathode chamber in the electrolysis process of aqueous alkali chloride solutions. In this case, the cathode used should be one that can withstand the operating environment, has sufficient catalytic activity for the reaction, and has a structure that does not impede the escape of the produced gas. 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. It is not limited.

As for the anode, a normal anode that can withstand the operating environment and has sufficient catalytic activity for the desired reaction is used, such as graphite, titanium, tantalum, tungsten,
A porous anode in which the surface of a metal such as zirconium or niobium is 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 pulp metal. is used.

During electrolysis, these electrodes may be in contact with the membrane surface,
Also, they can be apart.

Hereinafter, the present invention will be explained in detail using specific examples.

It should be noted that the present invention is not limited in any way to these specific examples.

Example 1 0F2=OF2 and 0F2=CF-0-C! F, -CF-
0-OF2-OF2-EI02FFs was copolymerized in 1.1.2-)lichloro-1,2,2 trifluoroethane using perfluoropropionyl peroxide as an initiator to obtain a polymer (as a sulfonic acid group). Exchange capacity is 0.91 meq/dry resin).

Let's call this polymer A.

Similarly, OF,, =OF, and OF, =OF'-0-OF'2-
A copolymer with OF-0-OF, -cF2-coocn3CF3 was obtained (exchange capacity as carboxylic acid group was 1.1 meq7'?). This will be referred to as B polymer.

Next, add polymer A to a thickness of 100 μm and polymer B to a thickness of 75 μm.
After forming each film into a film with a thickness of μ, two of these 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 approximately 5 μm was kneaded with water to form a paste of 15% by weight, and then applied onto art paper to a thickness of approximately 50 μm.
A layer of μ silica particles was obtained. The art paper carrying the silica particle layer was applied to both sides of the base cation exchange membrane at 160°C.
20kl? Heating and compression bonding were carried out under the conditions of /cTt2. 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 performed.

Next, the cation exchange membrane was boiled in a 2% by weight aqueous sodium hydroxide solution for 6 hours, washed with water, and dried in air at 25° C. for 2 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 assembled into an electrolytic cell toward the B polymer side cathode, and coated with ruthenium oxide as an anode. Using titanium extracted band metal and iron extracted band metal as the cathode, the distance between the anode and cathode is
i 11 m, and the extraction level of the caustic soda aqueous solution in the cathode chamber is 2OcIrL higher than the level in the anode chamber.
Electrolysis was performed with the membrane in contact with the anode.

When saturated saline was supplied to the anode chamber and water was supplied to the cathode chamber to maintain the caustic soda concentration in the cathode chamber at 66% by weight, electrolysis was carried out at a temperature of 90°C and a current density of 40 A/dm2, the voltage was 3.25.
V, 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 the paper by the Okinawa method to form the base cation exchange membrane used in Example 1. heating on both sides of the
It was crimped.

Next, the zinc powder was dissolved and removed in a 20% by weight aqueous sodium hydroxide solution at 80°C, and hydrolyzed by treatment for 24 hours in a 1ON aqueous sodium hydroxide solution at 90°C.

Example 1 and all (electrolysis was carried out under the same conditions, current density 40
With A/Blood 2, a voltage of 430 V and a current efficiency of 94.0% were obtained.

Comparative Example 2 The roughened cation exchange membrane was treated in exactly the same manner as in Example 1, except that it was boiled in water for 3 hours instead of the 2% by weight aqueous caustic soda solution, and electrolysis was carried out under the same conditions as in Example 1. ,
At a current density of 40 A/lbn'', a voltage of 3.24 V and a current efficiency of 95.0% were obtained.

Comparative Example 6 The roughened cation exchange membrane 7 was treated in the same manner as in Example 1 except that it was boiled for 6 hours in a 20% by weight caustic soda aqueous solution instead of the 72% by weight caustic soda aqueous solution.
Electrolysis was performed under the same conditions as above, and results were obtained with a current of 40 A/blood 2, a voltage of 154 V, and a current efficiency of 96.5%.

Example 2 Fine silica powder with an average particle size of 3 μm or less was suspended in water to a concentration of 70.3% by weight, and was spread on paper to a thickness of about 70 μm using a filtration method.
A layer of silica particles was formed. The tear paper carrying the silica particle layer was applied to both sides of the same base cation exchange membrane as in Example 1, heated at 160 ° C. and 100 kg/CrrL2,
It was crimped. Thereafter, the silica powder pressed onto the surface of the cation exchange membrane was dissolved and removed in a 5% by weight aqueous sodium hydroxide solution at a temperature of 80°C.

Next, the cation exchange membrane was boiled in a 75% by weight aqueous sodium hydroxide solution for 6 hours, and then dried in air at 25° C. for 2 days. The obtained roughened cation exchange membrane was immersed overnight in a 2% by weight aqueous solution of caustic soda, and then electrolyzed under the same conditions as in Example 1, with a current density of 40 A/blood 2 and a voltage of 3.
．． A result of 21 V and a current efficiency of 96.0% was obtained.

Example 3 ■Nafion 117 commercially available from Devon, USA
Approximately 4cm thick, made by chemically treating one side of a cation exchange membrane.
A cation exchange membrane having a 5o3H/C0OH two-layer structure having a 0μ carboxylic acid layer was obtained. The membrane was subjected to surface roughening treatment in exactly the same manner as in Example 2, and electrolysis 2 was performed under the same conditions as in Example 2, at a current density of 4°A/blood 2 and a voltage of 3.28 V.
A current efficiency of 9Zo% was obtained.

Example 4 The surface was roughened in the same manner as in Example 1 except that the drying step after the boiling treatment was omitted, and electrolyzed under the same conditions as in Example 1. Initially, both voltage and current efficiency were low, and it took about a week to recover the performance.The electrolysis performance for 7 days was at a voltage of 3.24V
, the current efficiency was 96%, and this performance was maintained over a long period of 6 months.

Comparative Example 4 Electrolysis was carried out in exactly the same manner as in Example 1, without any treatment on both sides of the cation exchange membrane, and the current density was 40A.
/Blood 2, the voltage was 3.65V and the current efficiency was 96.0%.

Patent applicant: Toyo Soda Kogyo Co., Ltd.

Claims (1)

[Claims] (1: A silica powder layer formed by mixing silica powder and water to form a suspension or paste-like mixture, allowing the mixture to be supported on art paper or plain paper, and drying. The silica powder formed on the membrane surface is heated and pressed onto the surface of a perfluorocarbon polymer membrane having a cation exchange group and/or a group that can become a cation exchange group, and the silica powder formed on the membrane surface is eluted with a caustic alkali aqueous solution. A method for producing a roughened cation exchange membrane, characterized in that the roughened cation exchange membrane is boiled in a 1 to 10 wt/f1'% caustic alkali aqueous solution. (2) After the boiling treatment, washing with water Claims that dry (1)
) method described in section.