JPS634573B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an economically advantageous fluorine-based cation exchange membrane used for electrolysis of alkali chloride by an ion exchange membrane method. More specifically, it is a fluorine-based composite membrane in which two membranes with different equivalent weights (dry resin weight per equivalent of ion exchange group) and/or types of ion exchange groups and a reinforcing fabric are integrated. The layer in which the reinforcing fabric of the membrane is not embedded and which will be on the cathode side when incorporated into the electrolytic cell is ground, and the layer at the intersection of the fibers constituting the reinforcing fabric is ground. The layer thickness (Tk) is 1 micron or more, and the ratio of Tk to the thickness (Tw) of the reinforcing fabric at the void part is 0.9.
The present invention relates to a fluorine-based composite membrane having a low electrolytic voltage and a long membrane life, which is characterized by the following characteristics. In the present invention, for the sake of simplicity, a composite membrane formed by integrating (laminating) two membranes with different equivalent weights and/or types of ion exchange groups is simply referred to as a "composite membrane", and the membrane is also referred to as a "composite membrane". The layer that will become the anode side and the layer that will become the cathode side when installed in the tank are labeled “A” respectively.
layer” and “C layer”. Fluorine-based cation exchange membranes, which have excellent heat resistance, chemical resistance, and mechanical strength, are advantageously used industrially when producing alkali hydroxide by electrolyzing alkali chloride. In order to improve the electrolysis power consumption rate, many attempts have been made to increase the current efficiency of fluorine-based cation exchange membranes and to lower the electrolysis voltage. The current efficiency of an ion exchange membrane varies depending on the equivalent weight and water content of the membrane, and generally the current efficiency can be increased by lowering the water content. However, lowering the water content across the entire thickness of the membrane increases the electrolytic voltage, so lower the water content only on the cathode side of the membrane and increase the water content on the anode side of the membrane to lower the electrolytic voltage of the membrane. It is preferable. As such a membrane, a composite membrane in which a membrane with a high moisture content and a membrane with a low moisture content are laminated has been proposed. The composite membrane is attached to the battery case so that the layer with the lower water content is on the cathode side. For example, a method of laminating a film with high equivalent weight and a film with low equivalent weight
18994), and a method of laminating a membrane made of a sulfonic acid group and a membrane made of a mixture of sulfonic acid groups and carboxylic acid groups (US Pat. No. 4,176,215). The thickness of such a fluorine-based composite membrane is preferably 1000 microns or less in order to lower the electrolytic voltage.
Since the membrane has an insufficient mechanical strength of 200 microns or less, reinforcing material is embedded to add strength to the membrane. Embedding the reinforcement is usually done at the same time as laminating the membrane. As the reinforcing material, a woven fabric of fibers such as polytetrafluoroethylene, tetrafluoroethylene/hexafluoropropylene copolymer, and tetrafluoroethylene/ethylene copolymer is used. The woven fabric has a cross structure of fibers such as plain weave, leno weave, and twill weave, and the porosity of the woven fabric is 30 to 80%. The term "voids" refers to the proportion of voids between fiber structures constituting a woven fabric per unit area of the woven fabric, expressed as a percentage. The current efficiency is higher when the reinforcing fabric is inside layer A than when it is inside layer C of the composite membrane. Therefore, it is common practice to select manufacturing conditions such that the reinforcing woven fabric is wrapped inside the A layer. A method for lining an ion exchange membrane with a reinforcing woven fabric is a method of stacking a heat-fusible ion exchange membrane intermediate and the woven fabric, heat pressing, and embedding the woven fabric in the membrane (heat press lamination method; JP After hydrolyzing only one side of the heat-melting ion-exchange membrane intermediate to make it heat-insoluble, the other side was brought into contact with a woven fabric, and the entire surface was heated while the surface that was in contact with the woven fabric. Reduce the pressure to
Method of embedding woven fabric in membrane (vacuum lamination method; Special Publication 1977-
16470), etc. Both sides of the composite membrane lined with reinforcing fabric by hot press lamination are flat, and the boundaries between layer A and layer C of the membrane are parallel to both sides. In addition, in a composite membrane lined with a reinforcing woven fabric using the vacuum lamination method, the surface of the A layer is flat, but the surface of the C layer has large irregularities due to the fibers that make up the woven fabric. The boundary is C
parallel to the plane of the layer. Composite membranes lined with reinforcing woven fabric using these methods have two thicknesses: the thickness of the C layer at the intersection of the fibers that make up the woven fabric (Tk) and the thickness of the C layer at the voids in the woven fabric. (Tw) are almost equal.
The reason for this is that when layer A and layer C are laminated and the reinforcing fabric is embedded, layer A is thermally melted and flows, but layer C is not substantially deformed by heat. be. Although the mechanical strength of a fluorine-based composite membrane backed with such a reinforcing woven fabric is sufficiently satisfactory, most of the ions flow through the voids of the woven fabric due to the shielding effect of the woven fabric. Current distribution within the film becomes non-uniform. Therefore, the electrolytic voltage is higher than that of a composite membrane not lined with woven fabric, and the degree of electrolytic voltage is correlated to the void area. Further, if electrolysis is continued for a long time, the fine structure of the membrane changes and the current efficiency gradually decreases.
In particular, when electrolyzing at a high current density, the current efficiency tends to decrease. Therefore, in a composite membrane lined with a reinforcing woven fabric, current concentrates in the voids of the woven fabric, reducing the current efficiency in these areas and shortening the life of the membrane. In order to eliminate such adverse effects, a method has been proposed in which a fibrillated fluororesin and an ion exchange polymer are kneaded instead of a reinforcing woven fabric (Japanese Patent Application Laid-Open No. 1989-1999).
No. 1283), but the reinforcing effect of the membrane is inferior to that of woven fabric. The present inventors have conducted intensive studies to reduce the bias in the current distribution within the membrane due to the fabric of the fluorine-based composite membrane lined with a reinforcing fabric, lower the electrolytic voltage, and extend the life of the membrane. As a result, the C layer of the composite membrane was ground, and the thickness (Tk) of the C layer at the intersection of the fibers constituting the woven fabric was 1 micron or more, and the thickness of the C layer at the gap between Tk and the woven fabric was determined. (Tw) The ratio Tk/Tw is
It has been found that this can be achieved by creating a composite membrane with a value of 0.9 or less. The reason why it is possible to reduce the electrolytic voltage and extend the membrane life by grinding a composite membrane in which Tk and Tw are approximately equal is as follows: (1) When Tk/Tw is 0.9 or less, the current distribution within the membrane is relatively uniform. Electrolysis voltage is low and membrane life is extended. (2) Grinding the composite membrane reduces the electrolytic voltage because the membrane thickness becomes thinner. (3) When the fluorine composite membrane is attached to an electrolytic cell and alkali chloride is electrolyzed, hydrogen gas bubbles adhere to the surface of the C layer, increasing the electrolysis voltage. However, minute irregularities of several microns or less are formed on the surface of the ground C layer, which suppresses the adhesion of hydrogen gas bubbles during electrolysis, resulting in a decrease in electrolysis voltage. etc. can be mentioned. In the present invention, the values of Tk and Tk/Tw are important. Tk is 1 micron or more, preferably 5 microns to 50 microns. Grinding until Tk is less than 1 micron is not preferred because the current efficiency tends to decrease. Furthermore, when grinding a large film industrially, the grinding depth tends to vary and the Tk tends to be less than 1 micron in some parts, so the thickness is preferably 5 microns or more. Tk/Tw is 0.9 or less, preferably 0.8 to 0.05. If Tk/Tw exceeds 0.9, it is not preferable because the bias in current distribution within the film cannot be sufficiently improved. Tk and Tw of the present invention are measured by the following method.
A thin section is cut from the composite membrane lined with reinforcing fabric using a sharp razor, and the cross section of the membrane is observed under a microscope. Sections were stained prior to observation, and two parts of the composite membrane were stained.
It is desirable to dye the layers separately. Dyeing is carried out by appropriately changing the type of dye, pH of the dyeing solution, etc., depending on the composition of the A layer and C layer of the composite membrane. The thickness of the C layer at the intersection of the fibers constituting the reinforcing woven fabric is Tk, and the thickness of the C layer at the voids of the woven fabric is Tw. FIG. 1 shows a plan view of a composite membrane lined with a plain-woven reinforcing fabric using a vacuum lamination method (unground membrane). The shaded area is the reinforcing fabric. The composite membrane is k−k′ and w
-W' cross-sectional views are shown in Figures 2 and 3, respectively. The thickness of the C layer at the intersection of the fibers constituting the woven fabric in FIG. 2 is Tk, and the thickness of the C layer at the void portion of the woven fabric in FIG. 3 is Tw. Tk and Tw are measured at more than 30 different locations on the sample, and the obtained values are averaged. Methods for grinding a futuristic composite membrane lined with a reinforcing fabric include (1) a method of grinding the surface of the membrane with an abrasive material; (2) A method in which an abrasive is sprayed onto the membrane using compressed air (dry blasting method). (3) A method in which an abrasive suspended in water is sprayed onto the membrane using compressed air (liquid honing). (4) Metal brushes, sandpaper, abrasive belts,
A method of grinding by bringing a polishing device such as a polishing roll into contact with the surface of the membrane. Examples include, but are not limited to. In industrial practice, dry blasting or liquid honing methods are advantageous. The surface of the C layer of the fluorine-based composite membrane lined with a reinforcing woven fabric using a vacuum lamination method has large irregularities due to the fibers constituting the woven fabric. For this reason, the current distribution within the membrane during electrolysis is highly biased, and the effect of the grinding of the present invention is particularly remarkable. When the C layer of such a film is ground by the method described above, Tk/Tw can be made 0.9 or less because the grinding speed of the convex portions is higher than that of the concave portions. In particular, when selectively grinding the intersections (protrusions) without grinding too much the voids (concavities) of the fibers of the reinforcing woven fabric, grinding with an abrasive material or contacting the abrasive machine with the surface of the membrane is recommended. A method of grinding is advantageous.
However, since the C layer of the fluorine-based composite membrane backed with a reinforcing fabric by the hot press lamination method is flat, in order to grind the membrane using the above method to reduce Tk/Tw to 0.9 or less,
Special measures are required to create a difference in the grinding force between the voids and fibers of the woven fabric. Since fluorine-based cationic polymers are not crosslinked, they tend to be elastically deformed by external stress. Taking advantage of this property, by placing a sponge, brushed cloth, non-woven fabric, coarse wire mesh, etc. on the opposite side of the grinding surface of a composite membrane lined with reinforcing woven fabric using the heat press lamination method, the woven fabric The resin in the voids is elastically deformed and the grinding force is reduced, but the resin in the fibers is restrained from deformation by the fibers, so it is difficult to elastically deform and is easily ground. As a result
Tk/Tw can be made 0.9 or less. The composite membrane of the present invention is produced by forming a polymer obtained by copolymerizing monomers of the first group and monomers of the second group and/or the third group described below, and then adjusting the equivalent weight and/or ion It can be obtained by laminating two membranes with different types of exchange groups and then hydrolyzing them. Monomers of the first group: vinyl fluoride, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, etc. Second group of monomers; CF ₂ = CF (CF ₂ ) _l SO ₂ X,

[Formula] (l is an integer of 0 to 8, m is an integer of 0 to 3, n is an integer of 1 to 8, X is F or Cl, Y is F or CF ₃ ), etc. Monomers of the third group; CF ₂ = CF (CF ₂ ) _p A,

[Formula] (p is an integer of 0 to 12, q is an integer of 0 to 3, r is an integer of 1 to 8, A is COOR [R is an alkyl group having 1 to 3 carbon atoms], Y is F or CF ₃ )etc. To line the composite membrane of the present invention with a reinforcing fabric,
This is carried out simultaneously with or after lamination by a vacuum lamination method or a hot press lamination method. In the present invention, the composite membrane can be used as it is without chemical treatment, but it can also be chemically treated depending on the purpose. Of course, the following chemical treatment can be performed on the C layer before or after grinding the fluorine-based membrane lined with the reinforcing fabric, but the effect of the chemical treatment must be ensured. In order to obtain this, it is preferable to carry out chemical treatment after grinding. A preferred chemical treatment method is, for example, after integrating two films with different equivalent weights with a reinforcing woven fabric using a copolymer film of monomers of the first group and monomers of the second group. , (1) A method of treating the surface of the C layer with ammonia, alkyl monoamine or diamine (Japanese Patent Laid-Open No. 1973-
No. 44360, No. 50-66488, No. 51-64495, 51-
No. 64496). (2) A method of reducing the surface of the C layer (Unexamined Japanese Patent Publication No. 1983-
24175, 52-24176, 52-24177). (3) A method of oxidizing the surface of the C layer with organic solvent vapor (Japanese Patent Application Laid-open No. 83932/1983). (4) A method of treating the surface of the C layer with a compound having an amino group or a basic aqueous solution containing ammonium ions (JP-A-54-21478, 54-41287)
issue). (5) A method in which the surface of the C layer is reacted with iodine in the presence of a radical generator and then treated with a phosphorus compound (Japanese Patent Application Laid-open No. 82684/1984). The examples include, but are not limited to these. A method for electrolyzing alkali chloride using the composite membrane of the present invention will be described below. Examples of the alkali chloride include lithium chloride, sodium chloride, potassium chloride, and the like. Furthermore, examples of the alkali hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, and the like. When installing the ground fluorine-based composite membrane of the present invention in an electrolytic cell, the ground C layer must be placed on the cathode side. A preferable electrolytic cell and electrolytic conditions will be described when electrolyzing alkali chloride using the composite membrane of the present invention. Salt water is supplied to the anode chamber, and water or dilute alkali hydroxide solution is supplied to the cathode chamber while electrolysis is carried out to adjust the concentration of alkali hydroxide at the outlet of the cathode chamber. The brine supplied to the anode chamber is purified in a manner similar to conventional chloride alkaline electrolysis. In other words, the return salt water that circulates and returns from the anode chamber undergoes dechlorination, saturation dissolution of alkali chloride, sedimentation separation of magnesium, calcium, iron, etc., and neutralization, but these processes are performed using conventional methods. It is done in the same way. However, if necessary, the supplied brine may be further purified with a granular ion exchange resin, especially a chelate resin.
Calcium tolerable limits, preferably
It is desirable to keep it below 1ppm. The concentration of salt water is
Preferably rich and close to saturation. The utilization rate of alkali chloride supplied to the anode chamber is 5
~95%, which varies depending on the current density and heat removal method, but generally higher values are desirable. Electrolysis can be carried out at a temperature of 20 to 100°C. Since heat is generated by electrolysis, the anolyte or a portion of the catholyte is cooled to remove the heat. Chlorine and hydrogen are generated in the anode chamber and the cathode chamber, respectively. In particular, an electrolytic cell designed to guide the generated gas to the back side of the electrode and raise it has the effect that there is no space occupied by the gas between the electrode and the membrane surface, which reduces the electrolysis voltage and reduces power consumption. There is. Regarding the flow rate in each chamber, it is desirable that the liquid in the chamber is stirred by the gas generated in the cathode chamber and the anode chamber in addition to the flow rate supplied from the outside. It is desirable to use a large number of electrodes to move and circulate the liquid in each chamber with the upward flow of gas. From the viewpoint of overvoltage, the electrode is preferably iron or iron plated with nickel or a nickel compound as a cathode. The anode is generally preferably a metal mesh electrode coated with an oxide of a noble metal such as ruthenium. Examples will be specifically described below, but the present invention is not limited thereto. Example 1-4 Tetrafluoroethylene and perfluoro-3,6-dioxa-4-methyl-7-octensulfonyl fluoride were copolymerized to have an equivalent weight of 1100 (Polymer A).
and 1500 (polymer B) were obtained. These copolymers were heat molded to 120 and 50 microns, respectively.
It was made into a film-like substance with microns. After laminating the film-like material, it was lined with a plain-woven reinforcing fabric using a vacuum lamination method. At that time, manufacturing conditions were selected such that the reinforcing woven fabric was wrapped inside the layer of polymer A. Then, it was hydrolyzed with caustic soda to obtain a sulfonic acid type cation exchange membrane. C layer (polymer B with larger equivalent weight) of the thus obtained multilayer structure fluorine cation exchange membrane
was ground with an abrasive. As the abrasive material, silicon carbide (trade name, GC-240 manufactured by Fujimi Abrasive Industries KK) with an average particle size of 80.5 microns was used, and the surface of the film was ground by brush-twisting with a nylon brush. Grinding time is 1 minute, 3 minutes per ^cm2 of membrane,
5 minutes, 7 minutes. The ground film obtained in this way
Tk and Tw values were measured. The results are shown in Table 1. In addition, these films were assembled into an electrolytic cell with the ground C layer facing the cathode side, and the current density
Edible temperature electrolysis was performed at 50 A/dm ² and an electrolysis temperature of 90°C.
The anode is a dimensionally stable electrode made of a titanium substrate coated with ruthenium oxide, and the cathode is an iron wire mesh. A 3N saline solution with a pH of 2 was supplied to the anode chamber, and 5.0N caustic soda was supplied to the cathode, and the electrolysis voltage and current efficiency were measured. The results are shown in Table 1. Comparative Example 1 A cation exchange membrane produced in the same manner as in Example 1-4 was treated with Tk without undergoing the treatment of the present invention.
The Tw value was measured, and the product was incorporated into an electrolytic cell and electrolyzed in the same manner as in Example 1, and the electrolytic voltage and current efficiency were measured. The results are shown in Table 1.

[Table] Example 5-7 Tetrafluoroethylene and perfluoro-3,6-dioxa-4-methyl-7-octensulfonyl fluoride were copolymerized to have an equivalent weight of 1100 (Polymer A)
A polymer of and 1350 (B′ polymer) was obtained. These copolymers were heat molded to 100 microns and 40 microns, respectively.
It was made into a film-like substance with microns. After laminating the membrane, a Teflon woven fabric was embedded in the layer of polymer A and hydrolyzed with caustic soda to obtain a sulfonic acid type cation exchange membrane. Next, the surface of the C layer (the surface of the B' polymer) of the cation exchange membrane was ground by a liquid honing method. The liquid honing method is a method of polishing by spraying an abrasive material suspended in water onto the object to be ground using compressed air. An aqueous solution in which abrasives (manufactured by Fujimi Abrasives Industry KK) were suspended was sprayed with 6.5 kg/cm ² of compressed air. Spraying time is 8.0 per 1 ^dm2 of membrane
minutes, 4.0 minutes, and 2.0 minutes. The membrane was treated with phosphorus pentachloride to convert the sulfonic acid groups to sulfonyl chloride groups, and then the surface of the B′ polymer was reduced with hydroiodic acid to convert the sulfonyl chloride groups to carboxylic acid groups. . Then, after hydrolyzing the membrane with caustic soda, pH=1
It was confirmed that a 10-micron layer on the surface that had been stained with a malachite green solution and subjected to reduction treatment had been converted to carboxylic acid groups. The Tk and Tw of the ground film thus obtained were measured. The results are shown in Table 2. In addition, these membranes were assembled into an electrolytic cell with the C layer facing the cathode side, and salt electrolysis was performed. Current density
40A/dm ² , Caustic soda concentration 6.5N supplied to the cathode chamber
All other conditions were the same as in Examples 1-4. Table 2 shows the electrolysis voltage and current efficiency after one week and one year. Comparative Example 2 The grinding treatment of the present invention was not applied, and the other conditions were Examples 5-7.
The Tk of the cation exchange membrane prepared in the same manner as
The Tw value was measured. The results are shown in Table 2. Furthermore, the membrane was assembled into an electrolytic cell so that the C layer was on the cathode side, and electrolyzed in the same manner as in Examples 5-7.
Table 2 shows the electrolysis voltage and current efficiency after one week and one year.

[Table] Example 8 Tetrafluoroethylene and perfluoro-3,6-dioxa-4-methyl-7-octensulfonyl fluoride were copolymerized to obtain a polymer with an equivalent weight of 1100 (Polymer A) . Also, tetrafluoroethylene and CF ₂
= CFOCF ₂ CF (CF) ₃ OCF ₂ CF ₂ COOCH ₃ was copolymerized to obtain a polymer having an equivalent weight of 1100 (C polymer). Polymer A and polymer C were blended well at a weight ratio of 1:2 and then heated and molded to a thickness of 50 mm.
A micron film was obtained. Separately, only Polymer A was heat-molded to obtain a 100 micron thick film.
After laminating these membrane-like materials, a Teflon woven fabric was embedded from the surface of the polymer A by a vacuum lamination method. Hydrolysis was performed with caustic soda to obtain a fluorine-based cation exchange membrane having a multilayer structure consisting of a sulfonic acid layer and a layer containing a mixture of carboxylic acid groups and sulfonic acid groups. The surface of the layer consisting of polymer A and polymer C was ground using a liquid honing method. As the abrasive material, alumina (product name WA#3000, manufactured by Fujimi Abrasive Industry KK) with an average particle size of 5.3 microns was used.
Compressed air of 6.5 kg/cm ² was sprayed onto the surface of layer C (the surface of the layer consisting of polymer A and polymer C). The spraying time was 15 minutes per 1 dm ² of film. The Tk of the membrane thus obtained is 7μ, Tw is 28μ,
Tk/Tw was 0.25. Further, the membrane was electrolyzed in the same manner as in Examples 5-7. The electrolysis voltage is
3.72V, current efficiency was 94%. Comparative Example 3 The multilayered fluorine-based cation exchange membrane of Example 8 was subjected to salt electrolysis in the same manner as in Example 8 without being subjected to the treatment of the present invention. The electrolysis voltage was 3.9V, and the current efficiency was 94%. Further, the Tk of the film was 50 microns, the Tw was 51 microns, and the Tk/Tw was 0.98. Example 9 Tetrafluoroethylene and perfluoro-3,6-dioxy-4-methyl-7-octensulfonyl fluoride were copolymerized to produce a polymer (Polymer A) with an equivalent weight of 1100 and a polymer (Polymer A) with an equivalent weight of 1400. Polymer B″)
I got it. These polymers are heated and molded to achieve their respective thicknesses.
100 microns (polymer A) and 50 microns (polymer
B″) was made into a two-layer laminate, and a Teflon woven fabric was further embedded from the polymer A side by a vacuum lamination method.The C layer side of the film (layer consisting of polymer B″) was
Grinded with a metal brush. Furthermore, only the surface of the C layer was treated with n-butylamine to produce a 10 micron sulfonamide layer. The Tk of the membrane thus obtained was 15 microns.
Tw was 40 microns and Tk/Tw = 0.38. Further, when this membrane was subjected to salt electrolysis under the same conditions as in Example 1-4, the electrolytic voltage was 3.94 V and the current efficiency was 93%. Comparative Example 4 After the grinding process in Example 9, a sulfonamide type cation exchange membrane that had not been subjected to the grinding process was used instead of the amine-treated sulfonamide type cation exchange membrane, but in the same manner as in Example 9. Electrolyzed. Electrolysis voltage is 4.18V, current efficiency is 93%
It was hot.

[Brief explanation of the drawing]

Figure 1 is a plan view of a composite membrane lined with a plain-woven reinforcing fabric using the vacuum lamination method. FIG. 1... Ion exchange resin membrane, 2... Reinforcing woven fabric,
3... Fibers constituting the reinforcing woven fabric, 4... C layer,
5...A layer.

Claims (1)

[Scope of Claims] 1. A fluorine-based composite membrane formed by integrating two membranes with different equivalent weights and/or types of ion exchange groups and a reinforcing woven fabric, wherein the reinforcing woven fabric of the membrane is The layer in which the fabric is not embedded and which will be on the cathode side when attached to the battery case is ground so that the thickness (Tk) of this layer at the intersection of the fibers that make up the reinforcing fabric is 1 micron. A fluorine-based composite membrane having the above structure and having a ratio Tk/Tw of Tk to the thickness (Tw) of the reinforcing woven fabric at the void portion of 0.9 or less. 2. The membrane according to claim 1, which is lined with a reinforcing woven fabric using a vacuum lamination method. 3. The membrane according to claim 1, wherein Tk is from 5 microns to 50 microns. 4. The membrane according to any one of claims 1 to 3, wherein Tk/Tw is 0.8 to 0.05. 5. According to any one of claims 1 to 4, the cation exchange membrane is a membrane ground by using an abrasive or an abrasive device such as metal brush sandpaper, an abrasive roll, or an abrasive belt. membrane. 6. The membrane according to any one of claims 1 to 4, wherein the ion exchange membrane is a membrane ground by a liquid honing method or a dry blasting method. 7. The film according to any one of claims 1 to 6, wherein the ground surface is chemically treated after the grinding process.