JPS627217B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a cation exchange membrane. More specifically, a film of a mixture of a perfluorocarbon polymer having a group capable of becoming a sulfonic acid group and a perfluorocarbon polymer having a group capable of becoming a carboxylic acid group, and a perfluorocarbon polymer having a group capable of becoming a carboxylic acid group. This is a method for producing a cation exchange membrane, which is characterized by laminating the films together, and then converting groups capable of becoming carboxylic acid groups and groups capable of becoming sulfonic acid groups into carboxylic acid groups and sulfonic acid groups, respectively. As a diaphragm for electrolyzing alkali metal halides, a cation exchange membrane has appeared that has a sulfonic acid group as an exchange group and is based on a perfluorocarbon polymer. A typical example of this is a sulfonic acid type membrane made of a perfluorocarbon polymer commercially available from DuPont. However, although this membrane had no problems with durability, the cation transfer number in an electrolyte solution containing hydroxide ions was still not satisfactory. Therefore, various methods to improve these problems have been studied and are currently being studied. Here are some examples: (1) Making the exchange group concentration on the surface facing the cathode chamber lower than that on the surface facing the anode chamber (2) Moving the exchange group on the surface facing the cathode chamber toward the anode chamber. A method of making the surface weaker than that of the facing surface (3) This method uses a weakly acidic exchange group. In general, it is well known that production costs are greatly influenced not only by electricity costs but also by the decomposition rate of the alkali metal halide used and the concentration of the alkali hydroxide produced. If the purity of the alkali metal hydroxide is low, it will not be viable industrially. In order to operate efficiently and industrially, it is necessary to fully consider the balance between these factors and further develop membranes that are compatible with this balance. When performing electrolysis using the improved cation exchange membrane described above to increase the decomposition rate of alkali metal halides and produce highly concentrated alkali metal hydroxides, not only the current efficiency decreases, but also the production It is often experienced that alkali metal halides are mixed into alkali metal hydroxides. In order to solve these problems, the inventors of the present invention continued their intensive research and completed the present invention. That is, a film of a mixture of a perfluorocarbon polymer having a group capable of becoming a sulfonic acid group and a perfluorocarbon polymer having a group capable of becoming a carboxylic acid group, and a film of a perfluorocarbon polymer having a group capable of becoming a carboxylic acid group. The object of the present invention is to provide a method for producing a cation exchange membrane, which comprises laminating the above groups together and then converting the groups into sulfonic acid groups and carboxylic acid groups. Although it is not clear why the method of the present invention showed excellent results, it can be explained as follows. As the decomposition rate of the alkali metal halide in the anode chamber increases, the swelling of the membrane surface on the anode chamber side increases accordingly. For this reason, the aqueous solution of alkali metal halide infiltrates into the membrane, resulting in an increase in the water content in the membrane, lowering the fixed ion concentration and lowering the current efficiency, and causing the alkali metal halide in the membrane to enter the cathode chamber. , reducing the purity of the alkali metal hydroxide produced. Furthermore, if the swelling property of the surface facing the cathode chamber is designed to be extremely small, the difference in swelling within the membrane will become large and the membrane will be destroyed. For this purpose, it is necessary to reduce the swelling of the membrane surface on the anode chamber side. Furthermore, increasing the decomposition rate of alkali metal halides in the anode chamber will decrease the concentration of alkali metal halides, while increasing the concentration of alkali metal hydroxides produced in the cathode chamber. In this case, the swelling of the membrane surface on the anode chamber side becomes larger than the swelling of the membrane surface on the cathode chamber side, which is thought to cause the unfavorable results described above. Examples of fluorocarbon polymers that can be used to produce the cation exchange membrane of the present invention include the following. For example, a polymer represented by the following general formula can be mentioned. [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 ₂ F, SO ₃ Cl, COOR ₁ (R ₁ =1-5 alkyl group) CN, COF] Also, 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 is a perfluorocarbon polymer having a group that can become a sulfonic acid group, and Group B is a perfluorocarbon polymer that has a group that can be a carboxylic acid group. In the present invention, the exchange capacity of groups that can become sulfonic acid groups in the perfluorocarbon polymer as sulfonic acid groups is 0.5 to 1.0 meq/g, and that of groups that can become carboxylic acid groups as carboxylic acid groups.
0.8 to 1.5 meq/g can be used. In mixing a perfluorocarbon polymer having a group capable of becoming a sulfonic acid group and a perfluorocarbon polymer having a group capable of becoming a carboxylic acid group, the weight ratio thereof is 0.5 to 20. The method for forming a film from the above polymer is as follows:
Already known methods can be used. That is, press molding, roll molding, extrusion molding, dispersion molding, powder molding, and the like.
The molding temperature is in the range of 150°C to 300°C, particularly preferably in the range of 160 to 250°C. There are press or roll methods for gluing each film together, and the gluing temperature varies.
The temperature ranges from 150℃ to 300℃. The thickness of the layer containing carboxylic acid groups usually ranges from 0.01 to 80%, preferably from 0.1 to 50% of the total thickness. Further, the thickness of the membrane-like material is 4 to 12 mil, and reinforcing fibers may be introduced into these for the purpose of improving the mechanical strength of the membrane. Further, these groups that can become carboxylic acid groups and groups that can become sulfonic acid groups can be converted into carboxylic acid groups and sulfonic acid groups by hydrolysis. EXAMPLES The present invention will be explained in more detail below with reference to Examples, but it goes without saying that the present invention is not limited by these explanations. Example 1 The monomer with 1,1,2-trichloro-1,
A copolymer was obtained using perfluoropropionyl pereoxide as an initiator in 2,2-trifluoroethane (exchange capacity as sulfonic acid group 0.91 me
q/g) (A polymer). Similarly, CF ₂ = CF ₂ and copolymer (exchange capacity as carboxylic acid groups 1.1
meq/g) was obtained (Polymer B). Next, polymer A and polymer B were mixed in a weight ratio of 4:
After mixing at a ratio of 1:1 (C polymer), a film with a thickness of 4 mil was prepared. A film with a thickness of 3 mil was also produced from a copolymer of polymer B. Next, a film made from polymer C and a film made from polymer B were bonded together by thermocompression to produce a single film, and subsequently, the film was made positively by hydrolyzing with methanol/10 wt% caustic soda (weight ratio 1/1). An ion exchange membrane was obtained. The cation exchange membrane thus obtained was used as a diaphragm to separate the anode chamber and the cathode chamber with the carboxylic acid layer facing the cathode chamber side, an electrolytic cell with an effective area of 30 x 30 cm ² was constructed, and saturated sodium chloride was placed in the anode chamber. Supply water and the outlet concentration
180g/, and the outlet concentration in the cathode chamber is 32% by weight.
Water was supplied so that the electrolysis was carried out at a current density of 30 A/dm ² and a temperature of 85°C. Table 1 shows the current efficiency, voltage, and salt concentration in the caustic soda aqueous solution under stable operating conditions.

[Table] Comparative Example 1 A 4 mil film obtained from polymer A and a 3 mil film obtained from polymer B were bonded together by thermocompression to produce one film, and then methanol/
A cation exchange membrane was obtained by hydrolysis with 10wt% caustic soda (weight ratio 1/1). The obtained membrane was operated under the same operating conditions as in Example 1, and the results were as follows.

[Table] Comparative Example 2 A 7 mil film obtained from polymer B was hydrolyzed in the same manner as in Example 1, and then operated under the same conditions as in Example 1. The results are shown in Table 3.

[Table] Example 2 CF ₂ = CF ₂ and CF ₂ = CF-O-CF ₂ - CF ₃ and terpolymer (exchange capacity as carboxylic acid group)
1.4meq/g) to 1,1,2-trichloro-1,
Perfluoropropionyl peroxide was obtained as an initiator in 2,2-trifluoroethane (D
polymer). After mixing Polymer A and Polymer D at a weight ratio of 5:1 (Polymer E), a film with a thickness of 4 mil was prepared. In addition, a film with a thickness of 3 mil was prepared from a terpolymer of C polymer. Next, a film made of E polymer and a film made of D polymer were bonded together by thermocompression to produce a single film, and then hydrolyzed with methanol/10wt% caustic soda (weight ratio 1/1) to exchange cations. A membrane was obtained. The cation exchange membrane thus obtained was used as a diaphragm to separate the anode chamber and the cathode chamber with the carboxylic acid layer facing the cathode chamber side, an electrolytic cell with an effective area of 30 x 30 cm ² was constructed, and saturated sodium chloride was placed in the anode chamber. Supply water and the outlet concentration
180g/, and the outlet concentration in the cathode chamber is 38% by weight.
Water was supplied so that the electrolysis was carried out at a current density of 30 A/dm ² and a temperature of 85°C. Table 4 shows the current efficiency, voltage, and salt concentration in the caustic soda aqueous solution under stable operating conditions.

[Table] Comparative Example 3 A 4 mil film obtained from Polymer A and a 3 mil film obtained from Polymer D were bonded under heat to produce one film, and then methanol/10 wt% caustic soda (weight ratio 1 /1) to obtain a cation exchange membrane. The obtained membrane was operated under the same operating conditions as in Example 2, and the results were as follows.

[Table] Comparative Example 4 A 7 mil film obtained from polymer D was hydrolyzed in the same manner as in Example 1, and then operated under the same conditions as in Example 2. The results are shown in Table 6.

【table】

Claims (1)

[Scope of Claims] 1. A film of a mixture of a perfluorocarbon polymer having a group capable of becoming a sulfonic acid group and a perfluorocarbon polymer having a group capable of becoming a carboxylic acid group, and a perfluorocarbon polymer having a group capable of becoming a carboxylic acid group. A method for producing a cation exchange membrane, which comprises laminating a fluorocarbon polymer film together, and then converting a group capable of becoming a carboxylic acid group and a group capable of becoming a sulfonic acid group into a carboxylic acid group and a sulfonic acid group, respectively. 2. The production method according to claim 1, wherein the perfluorocarbon polymer has a group capable of becoming a sulfonic acid group, and the exchange capacity of the group as a sulfonic acid group is 0.5 to 1.0 meq/g. 3. The production method according to claim 1 or 2, wherein the perfluorocarbon polymer has a group capable of becoming a carboxylic acid group, and the exchange capacity of the group as a carboxylic acid group is 0.8 to 1.5 meq/g. 4. Claims 1, 2 or 4, wherein the mixing ratio of the perfluorocarbon polymer having a group capable of becoming a sulfonic acid group and the perfluorocarbon polymer having a group capable of becoming a carboxylic acid group is 0.5 to 20 by weight. The manufacturing method described in Section 3.