JP2504135B2 - Cation exchange membrane for electrolysis - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cation exchange membrane for electrolysis, particularly a cation exchange membrane suitable for electrolysis of an aqueous solution such as water, an acid or alkali aqueous solution, an alkali halide or an alkali carbonate aqueous solution. Regarding an ion exchange membrane.

[Prior Art] A method for obtaining caustic alkali and chlorine by electrolyzing the above aqueous solution, for example, an aqueous solution of alkali chloride, has recently replaced the mercury method with a diaphragm method from the viewpoint of pollution prevention, and has a higher purity and a higher concentration. A method using an ion exchange membrane has been put into practical use for the purpose of obtaining caustic alkali with high efficiency.

On the other hand, from the viewpoint of energy saving, in this type of electrolysis, an ion exchange membrane capable of minimizing current efficiency and electrolysis voltage is required, and various membranes therefor have been proposed. As one form among them, a film using a polymer having a sulfonic acid group as the first film of the fluoropolymer having a cation exchange group and a polymer having a carboxylic acid group as the second film. Is known and has been put to practical use. However, since the compatibility of the copolymer having a sulfonic acid group and the copolymer having a carboxylic acid group is low and the adhesiveness between them is weak, the sulfonic acid group of the copolymer used in the first film is It is known that the compound is chemically modified to have a carboxylic acid group, or a multilayer film is obtained by means such as co-extrusion lamination. Therefore, the ion exchange capacity of the copolymer having a carboxylic acid group is limited,
Alternatively, a laminated film having a thin film having a second film layer thickness of 10 μm for coextrusion lamination, and 3
There is a problem that it is difficult to manufacture a multilayer film having more layers.

On the other hand, according to Japanese Examined Patent Publication No. 62-1652, (A) CF ₂ -CFX, as a second film in the above two-layer multilayer film, Copolymers consisting of are known.

Here, X is —F, —Cl, or —CF ₃ , Rf is a perfluoroalkyl group having 1 to 10 carbon atoms, M is hydrogen or an alkali metal, and Y is selected from the following. In the general formula of, x and y are 1 to 10 and Z is -F or Rf. In addition, B / (A + B + C) (molar ratio) and C / (A + B)
+ C) (molar ratio) is 0.01 to 0.3 and 0.05 to 0.5, respectively.

CF _{2 x} , OCH _{2 x} However, in this, (C) Is described for production of low-concentration (20-30%) caustic soda, and production of high-concentration caustic soda in excess of 30%, which is generally performed industrially, is not yet known. .

[Problems to be Solved by the Invention] A membrane using a fluorinated copolymer having a sulfonic acid group as the first film is used in order to perform conventional electrolysis with high current efficiency and high efficiency of low electrolysis voltage. A fluorinated copolymer having a carboxylic acid group is used as the second film. For this reason, it is difficult to laminate the above two layers. Therefore, a complicated and expensive laminating apparatus such as conventional coextrusion is used, or one side of the copolymer having a sulfonic acid group, specifically, the cathode side can be chemically reacted. , It was necessary to convert to a carboxylic acid layer.

Further, the copolymer used in the second film is a conventional tetrafluoroethylene. However, it is known that the amount of NaCl contained in the caustic soda produced in the cathode chamber is relatively large when the aqueous solution of NaCl is electrolyzed in the laminated film using this copolymer. ing.

[Means for Solving Problems] The present invention has been made to solve the above problems, and includes a first film of a fluoropolymer having a sulfonic acid group and the following (A): , (B), (C) comprising a fluorinated polymer having a carboxylic acid group as an exchange group having a repeating unit and having a thickness of 5 to 50 μm smaller than that of the first film
And a cation exchange membrane for electrolysis, which is characterized in that it is laminated with a second film having a large ion exchange capacity of 0.05 to 0.20 meq / g dry resin.

(A) CF ₂ -CF ₂ Here, Rf is a perfluoroalkyl group having 1 to 5 carbon atoms, M is hydrogen or an alkali metal, and (B + C)
/ (A + B + C) (molar ratio) is 0.12-0.25.

The ion exchange membrane of the present invention has excellent performance in electrolysis, that is, high current efficiency and low electrolysis voltage, and has the property of reducing the NaCl content in NaOH generated in the cathode chamber, and at the same time, it has a sulfonic acid group. A first film of a copolymer having the above and a second film having a carboxylic acid group,
It also has the excellent property that it can be laminated by a simple method such as roll press lamination. This is because the second film constituting the cation exchange membrane according to the present invention is formed from a fluorine-containing polymer having a carboxylic acid group having repeating units (A), (B) and (C) as described above. Due to that. That is, first of all, an extremely thin film having an ion exchange capacity of 1.1 meq / g or less, such as 5 to 40 μm, which was conventionally difficult to obtain with a fluoropolymer of this kind, can be easily produced by extrusion molding or the like. As a result, high current efficiency and low electrolysis voltage are achieved.

In addition, as a second point, CF ₂ = CFO (CF ₂ ) _{1 to 5} COOCH ₃ having a short pendant side chain is used as a monomer having a carboxylic acid group that constitutes the copolymer used in the second film. , Long side chain monomers eg The ion exchange capacity is 0.85 compared to the copolymer containing
Even if it is set as high as ~ 1.30 meq / g, high current efficiency can be obtained. The inventor believes that the use of the ion exchange membrane of the present invention can reduce the NaCl content in NaOH produced by electrolysis as follows, but this description does not limit the present invention in any way. is not. That is, since the pendant side chain of the copolymer of the second film is short and the ion exchange capacity can be set high, the fixed ion concentration is increased, the Donnan exclusion force is increased, and NaCl diffusion is prevented.

Thirdly, since the constituent element of the copolymer used for the second film contains a specific amount of the (B) unit, the ion exchange capacity is such that high current efficiency is exhibited and the ion exchange capacity is larger than that of the first film. Even if it has a capacity, the crystallinity of the polymer can be lowered. In the binary copolymer which does not include the unit (B) and is composed only of the units (A) and (C), the crystallinity is high at a low ion exchange capacity where a high current efficiency is exhibited, so that the formability of the thin film is remarkable. Poor and poor adhesion to the first film, causing swelling or peeling during hydrolysis or electrolysis.

If the second film according to the present invention is used, a two-layer film can be easily formed by laminating the first film with the first film, for example, by roll pressing. Further, since the layers can be laminated by roll pressing, it is possible to easily form a multi-layered structure having three or more layers and to reinforce with a cloth, and it is possible to produce a higher performance ion exchange membrane.

In the present invention, the sulfonic acid group-containing fluoropolymer film forming the first film preferably has a large ion exchange capacity and a small specific electric resistance as long as the mechanical strength is sufficient. The content of this sulfonic acid group is preferably 0.7 to 1.5 meq.
/ g dry resin Especially preferably, it is made to be 0.8 to 1.2 meq / g dry resin.

The above-mentioned fluoropolymer is preferably a perfluoropolymer, and a preferable example thereof is CF ₂ = CF ₂ . Copolymer with CF ₂ = CF ₂ and CF ₂ = CFO (CF ₂ ) _2-5 SO ₂ F
And copolymers thereof. The composition ratio of the monomers forming the polymer is selected so that the fluoropolymer has the above-mentioned ion exchange capacity.

In the present invention, the fluoropolymer having a carboxylic acid group as an exchange group which forms the second film has the following (A),
It has repeating units of (B) and (C).

(A) CF ₂ -CFX Here, X, Rf, and M are as described above, but among them, perfluoro polymers are preferable, and examples thereof include CF ₂ ═C
A terpolymer of F ₂ , CF ₂ = CFORf (Rf is a perfluoroalkyl group having 1 to 5 carbon atoms), and CF ₂ = CFO (CF ₂ ) ₃ COOCH ₃ can be mentioned.

Repeating units (A), (B) in the fluoropolymer,
The composition ratio of (C) is important because it determines the properties of the film. That is, (B + C) / (A + B + C) (molar ratio)
Is related to the ease of film formation and the adhesion to the first film, but preferably the ratio is 0.12 to 0.25,
Especially, it is set to 0.15 to 0.20. When the ratio is small, the improvement of the film forming property becomes small, and conversely when the ratio is large, the mechanical strength of the film is lowered. Further, from the viewpoint of the adhesiveness with the first film, the film has an appropriate crystallinity. A ratio is selected. On the other hand, C / (A + B + C)
The (molar ratio) is related to the exchange capacity of the film, and the ratio is selected as an appropriate ion exchange capacity in relation to the concentration of caustic alkali to be produced by electrolysis. The ion exchange capacity is 0.05 to 0.20 meq / g dry resin greater, preferably 0.90 to 1.30 meq / g dry resin, preferably 0.95 to 1.20 meq / g dry resin.

The fluoropolymers of the first and second films are produced by various methods. If necessary, these films can be reinforced with a cloth, a non-woven fabric, a fibril, a porous body or a metal mesh, a porous body, or the like, which is preferably made of a fluoropolymer such as polytetrafluoroethylene. When reinforced with a cloth or the like, a copolymer film having a sulfonic acid group having a thickness of 5 to 50 μm may be laminated further on the anode side of the first film.

In the present invention, the films of the first and second fluoropolymers are used in order to maximize the ion exchange membrane performance.
The first film is preferably 130-300μ, the second film is preferably 5-50μ, and the first film /
The thickness ratio of the second film is preferably 2.0 to 30,
Especially, it is set to 5 to 20. If the second film is very thin, it is preferred that the reinforcing material described above be incorporated into the first film.

Any appropriate means may be adopted for laminating the first film and the second film, but in any case, it is necessary to integrate the two film-shaped materials by laminating. Thus,
For example, preferably at a temperature of 100 to 350 ° C and a pressure of 0.5 to 100.
By pressing at kg / cm ² , such lamination is carried out. In the present invention, two or more kinds of one or both of the first film and the second film can be used in the present invention for lamination. In addition, the lamination of both films is preferably performed in an acid or ester type in the form of an appropriate ion exchange group that does not cause decomposition of the cation exchange group, for example, in the case of a carboxylic acid group, In the case of a sulfonic acid group, it is preferable to use the —SO ₂ F type.
The thickness of the cation exchange membrane after lamination is preferably 80 to 50.
It is preferably 0 μ, particularly preferably 100 to 300 μ.

The cation exchange membrane obtained by laminating the first film and the second film of the present invention exhibits excellent performance as it is, but if necessary, one or both membrane surfaces may be exposed to gas and gas. Porous layer containing particles having liquid-permeable electrode activity (see, for example, US Pat. No. 4224121)
Alternatively, a porous layer containing gas and liquid permeable particles having no electrode activity (see, for example, British Published Patent Specification No. 2064586) can be provided to further improve the properties.

The cation exchange membrane of the present invention can be used for electrolysis of various aqueous solutions including an aqueous solution of alkali chloride as described above. For example, when used for electrolysis of an aqueous solution of alkali chloride, the cation exchange membrane of the present invention can be arranged so that the first film surface faces the anode side and the second film surface faces the cathode side. In this case, the cation exchange membrane of the present invention exerts its maximum performance.

The process conditions for electrolyzing an aqueous solution of alkali chloride using the ion-exchange membrane of the present invention include those described in JP-A-
Known conditions such as those in Japanese Patent Publication 54-112398 can be adopted. For example, the anode chamber is preferably 2.5-5.0 normal (N)
Is supplied, and water or diluted alkali hydroxide is supplied to the cathode chamber, and electrolysis is carried out at preferably 80 to 120 ° C. and current density of 10 to 100 A / dm ² . In such a case, heavy metal ions such as calcium and magnesium in the aqueous solution of alkali chloride cause deterioration of the ion exchange membrane, so it is preferable to make them as small as possible. Further, an acid such as hydrochloric acid can be added to the aqueous alkali chloride solution in order to minimize generation of oxygen at the anode.

In the present invention, the electrolytic cell may be a monopolar type or a bipolar type as long as it has the above configuration. Further, the material constituting the electrolytic cell is, for example, in the case of electrolysis of an aqueous solution of alkali chloride, in the case of the anode chamber, a material resistant to the aqueous solution of alkali chloride and chlorine, such as valve metal or titanium, and in the case of the cathode chamber. Is used for iron, stainless steel, nickel, etc., which are resistant to alkali hydroxide and hydrogen.

When the electrodes are arranged in the present invention, the electrodes may be arranged in contact with the ion exchange membrane, or may be arranged at an appropriate interval.

In the above, the use of the membrane of the present invention has been described mainly with respect to electrolysis of an aqueous solution of alkali chloride, but the same applies to electrolysis of water, halogen acid (hydrochloric acid, hydrobromic acid), and alkali carbonate. Of course.

Next, the present invention will be described with reference to Examples, but it goes without saying that the present invention is not limited thereto.

[Example] Example 1 6500 g of ion-exchanged water, 13 g of C ₈ F ₁₇ COONH ₄ and 13 g of Na ₂ HPO ₄ · 12H ₂ O were placed in a pressure resistant reaction vessel made of stainless steel with an internal volume of 10 l.
32.3 g, and NaH ₂ PO ₄ · 2H ₂ O and _{18.9g (NH 4) 2 S 2} O 8 5.14
0.39 g of g and n-hexane was charged, and then 984 g of CF ₂ = C
FO (CF ₂ ) ₃ COOCH ₃ and 316 g of CF ₂ = CFOC ₃ F ₇ were charged.
After sufficiently degassing, the polymerization temperature was raised to 57 ° C. and the pressure was raised to a predetermined pressure of 11.7 kg / cm ² with ethylene tetrafluoride to carry out the reaction. Polymerization is carried out while introducing tetrafluoroethylene,
The pressure was kept at a predetermined pressure. After 5 hours, the reaction was stopped, the obtained latex was agglomerated with concentrated sulfuric acid, and then the polymer was thoroughly washed with water, then, in methanol, at 65 ° C.,
Ion exchange capacity is 1.
1.42 kg of a terpolymer of 01 meq / g was obtained. The terpolymer was extruded at 220 ° C. to form a thin film having a thickness of 20 μm.

Then, in the same reaction vessel, 1,1,2-trichloro, 1,2,2-
Trifluoroethane was charged with 3.09 kg α, α′-azobisisobutyronitrile 13.5 g, and then, 4.41kg was charged. After sufficiently degassing, polymerization temperature 70
The temperature was raised to ℃ and the pressure was raised to a predetermined pressure of 12.4 kg / cm ² with ethylene tetrafluoride, and the reaction was allowed to proceed. Polymerization was performed while introducing tetrafluoroethylene, and the pressure was maintained at a predetermined pressure. After 7.0 hours, the reaction was stopped, and the obtained polymer was thoroughly washed and dried to give a copolymer having an ion exchange capacity of 0.91 meq / g of 1.1.
I got 5kg. The copolymer was formed into a film at 220 ° C. to obtain a film having a thickness of 160 μ.

Then, these two kinds of films were laminated at 220 ° C. by using a roll to form a two-layer film, which was then hydrolyzed in an aqueous solution of 30% by weight of dimethyl sulfoxide and 11% by weight of caustic potash, and then 2N. -The membrane was immersed in an aqueous NaCl solution. Next, using this film, electrolysis was performed as follows.

Effective film area 0.25 dm ² , anode RuO ₂ / Ti expanded metal, cathode active nickel / Fe expanded metal, gap 3 mm
Electrolysis test was performed at 90 ° C. and current density of 30 A / dm ² while supplying 200 g / l NaCl and water to the anode chamber and the cathode chamber using a small tank consisting of. As a result, the current efficiency was 96% at the generated caustic concentration of 35% NaOH. Also, Na in the catholyte
The Cl content was 15 ppm.

Comparative Example 1 C ₂ F ₄ and CF ₂ = CFO (CF ₂ ) ₃ COOCH ₃ were copolymerized to give respective ion exchange capacities of 1.01,1.04,1.08,1.12,1.25 (meq / g).
And a thin film with a thickness of 20 μm was obtained by extrusion molding. The copolymer having an ion exchange capacity of 1.01 meq / g is
High crystallinity made it difficult to form a thin film.

Next, ion exchange capacity 1.04,1.08,1.12,1.25 (meq / g)
And the sulfonic acid group-copolymer membrane used in Example 1 were laminated with a roll at a temperature of 220 ° C. in the same manner as in Example 1 and then hydrolyzed. 2N-N
When immersed in an aCl solution, the thin film layer has an ion exchange capacity of 1.04 (meq / g). A laminated film using a copolymer causes delamination at the lamination interface and has an ion exchange capacity of 1.08 (meq / g). Caused blister at the laminated interface.

When a laminated film using a copolymer having an ion exchange capacity of 1.12 (meq / g) was electrolyzed in the same manner as in Example 1, the current efficiency was 95.5%. However, because the voltage gradually increased, disassembling and examining the membrane, 20 days after electrolysis,
Some peeling occurred at the laminated interface.

When a laminated film using a copolymer having an ion exchange capacity of 1.25 (meq / g) was electrolyzed in the same manner as in Example 1, the current efficiency was 90.5%.

Comparative Example 2 With C ₂ F ₄ To obtain a copolymer with an ion exchange capacity of 0.91 (mea / g), which was extruded at 220 ° C to a thickness of 20
A thin film of μ was obtained.

Next, the sulfonic acid group-containing copolymer film used in Example 1 was laminated in the same manner as in Example 1, hydrolyzed and then electrolyzed in the same manner as in Example 1.
96.0%, NaCl content in the catholyte was 30 ppm. 30
After electrolysis for a day, the film was taken out and observed. As a result, some peeling was observed on the laminated surface.

Comparative Example 3 In the same container as in Example 1, 6500 g of ion-exchanged water and C ₈ F
₁₇ COONH ₄ 13g, Na ₂ HPO ₄・ 12H ₂ O 32.3g, NaH ₂ PO ₄・ 2H
₂ O 18.9 g (NH ₄ ) ₂ S ₂ O ₈ 3.43 g, n-hexane 0.4
Charge 6g, then 850g CF ₂ = CFO (CF ₂ ) ₃ COOCH ₃ , CF
₂ = 450 g of CFOC ₃ F ₇ was charged, polymerization temperature 57 ° C, polymerization pressure 11.
Polymerization was carried out at 9 kg / cm ^{2 for} 7 hours in the same manner as in Example 1 to obtain 1.4 kg of a terpolymer having an ion exchange capacity of 0.84 meq / g. The terpolymer was extruded at 220 ° C to form a film with a thickness of 20 μm.
Was obtained. The terpolymer was extruded at 220 ° C. to form a film, and a 20 μm thick film was obtained. This thin film and Example 1
The sulfonic acid group-containing copolymer film used in Example 1 was laminated in the same manner as in Example 1.

This membrane was subjected to hydrolysis and hydrophilization on the surface in the same manner as in Example 2 and then subjected to an electrolytic test. As a result, the current efficiency at a generated caustic soda concentration of 35% is 92%,
The cell voltage was 3.5V.

Example 2 The two types of films obtained in Example 1 were
Lamination lamination was performed using a roll press at ℃. next,
29.0% by weight of zirconium oxide having an average particle size of 1μ, 1.3% by weight of methylcellulose, 4.6% by weight of cyclohexanol,
A paste composed of 1.5% by weight of cyclohexanone and 63.6% by weight of water was transferred to the first layer side (copolymer layer having a sulfonic acid group) of the laminated film by roll pressing.

The amount of zirconium oxide attached at this time was 20 g / m ² . Next, this film was hydrolyzed in the same manner as in Example 1, and then 10 g / m ^{2 of} zirconium oxide particles was adhered to the second layer side of the laminated film by a spray method.

To this film, an anode coated with a solid solution of ruthenium oxide, iridium oxide, and titanium oxide on a punched metal of Ti, and a cathode electrodeposited with Raney nickel containing ruthenium on a punched metal made of stainless steel were respectively brought into contact with each other, and 200 g / anode chamber was provided. l
The aqueous sodium chloride solution was subjected to an electrolytic test at a current density of 30 A / dm ² and a temperature of 90 ° C. while supplying water to the cathode chamber. As a result, the current efficiencies at the generated caustic soda concentrations of 32% and 35% were both 96.0%, and the cell voltage was 2.94 V and respectively.
2.97V, the salt content in the catholyte was both 15 ppm.

EFFECTS OF THE INVENTION The present invention provides a fluororesin cation in which the first layer has a sulfonic acid group and a polymer having a specific composition is used in the second film layer, which is particularly suitable for alkaline halide electrolysis. It is intended to provide an exchange membrane, which enables production of a salt, for example, a caustic alkali having a low NaCl content, with a possible high current efficiency and electrolysis at a low electrolysis voltage. In addition, it is extremely epoch-making that the first film and the second film can be easily adhered to each other relatively easily by a roll press or the like.

Claims (1)

(57) [Claims] 1. A first film of a fluorine-containing polymer having a sulfonic acid group and a fluorine-containing polymer having a carboxylic acid group having the following repeating units (A), (B) and (C) as an exchange group. Composed of a united body and having a thickness smaller than that of the first film
It has 50μ and has an ion exchange capacity of 0.05 to 0.20 meq.
A cation exchange membrane for electrolysis, which is characterized in that it is formed by laminating a second film which is large only by a dry resin. (A) CF ₂ -CF ₂ Here, R _f is a perfluoroalkyl group having 1 to 5 carbon atoms, M is hydrogen or an alkyl metal, and (B + C)
/ (A + B + C) (molar ratio) is 0.12-0.25.