JP4815788B2 - Method for producing fluorine-based cation exchange membrane - Google Patents

Description

  The present invention relates to a method for producing a fluorinated cation exchange membrane having a gas release layer on its surface, which is used for alkaline chloride electrolysis.

A method of producing alkali hydroxide and chlorine by electrolyzing an aqueous alkali chloride solution using an ion exchange membrane as a diaphragm is known.
In the above manufacturing method, there is a problem that an electrolysis voltage rises due to the gas generated during electrolysis adhering to the surface of the ion exchange membrane, resulting in energy loss.

  Conventionally, in order to solve this problem, a method of providing a hydrophilic function by providing a gas release layer on the surface of an ion exchange membrane is known. According to this method, it is possible to suppress the gas from adhering to the film and to reduce the electrolysis voltage. This gas release layer is spray-coated on the film surface with a liquid in which fine powder particles mainly composed of oxides, nitrides and carbides of Group 4 elements of the periodic table are dispersed in an alcohol solvent. The layer composed of the fine particles previously formed into a film shape is formed on the surface of the ion exchange membrane by a method of pressure-transferring the film to the film with a roll press or the like.

However, the adhesive force between the gas release layer and the film is not always sufficient. Particularly, those formed by a spray method have a problem that peeling easily occurs due to physical external forces such as scratching and friction.
Moreover, in an ion exchange membrane incorporated in an electrolytic cell, the gas release layer may be consumed due to fluctuations in the internal pressure during long-term operation or electrolytic cell operation, and the electrolysis voltage may increase. there were.

  Several methods have been proposed to solve these problems. For example, Patent Document 1 reports that the gas release layer can be adhered uniformly and with sufficient adhesive force by reducing the particle size of the inorganic particles that are the main components of the gas release layer to 0.01 to 0.2 μm. ing. In Patent Document 2, it is reported that the adhesion of the gas release layer can be enhanced by heating to 130 ° C. or higher after forming the gas release layer.

  However, the durability between the electrode and the membrane surface is not always sufficient against long-term operation in a zero-gap electrolytic cell with a small gap between the membrane and the electrode, and the friction between the electrode and the membrane surface caused by the influence of pressure vibration in the electrolytic cell Did not have.

JP-A-3-137136 (Claims) JP 2000-336187 A (Claims)

  The present invention is an ion exchange membrane having excellent adhesion between the gas release layer and the membrane, and does not peel even when a physical external force is applied. An object is to provide a fluorine-based cation exchange membrane in which peeling does not occur.

The present invention provides a first step of producing a film made of a perfluorocarbon polymer having an ion exchange group or a precursor group of an ion exchange group, a dispersion containing inorganic particles and a fluoropolymer having a sulfonic acid group , And a second step of heating and removing the aprotic polar solvent after applying the aprotic polar solvent to the membrane surface, and when the perfluorocarbon polymer has a precursor group of an ion exchange group, There is provided a method for producing a fluorine-based cation exchange membrane having a gas release layer on the surface, which has a third step of converting the precursor group into an ion exchange group.

  By applying an aprotic polar solvent to the membrane surface and removing it by heating, a strong adhesion can be imparted to the gas release layer. The reason for this is not necessarily clear, but the high-boiling aprotic polar solvent causes the binder polymer to swell so that the inorganic particles are closely surrounded, and the gel surface layer composed of the binder polymer and the inorganic particles on the film surface. Next, it is inferred that the aprotic polar solvent is vaporized by heating, whereby the binder polymer is denatured.

  This is a phenomenon that is clearly different from the case where the volatilization of the alcoholic solvent proceeds from the middle of application to the film surface when only an alcoholic solvent such as ethanol is used as the dispersion solvent.

  The fluorine-based cation exchange membrane obtained by the present invention is less likely to cause abrasion or peeling of the gas release layer even when membrane vibration occurs during long-term operation. Therefore, when electrolysis of an aqueous alkali chloride solution is performed using the ion exchange membrane, the electrolysis voltage does not increase and it is possible to operate stably for a long period of time.

  The film formed in the first step of the present invention includes a layer made of a perfluorocarbon polymer having a carboxylic acid group or a carboxylic acid precursor group (hereinafter referred to as a first layer), a sulfonic acid group or a sulfonic acid. Examples include a laminated film in which at least two layers of a perfluorocarbon polymer having a group of precursor groups (hereinafter referred to as a second layer) are laminated.

The perfluorocarbon polymer forming the first layer is a copolymer of a polymer unit based on the monomer represented by Formula 1 and a polymer unit based on the monomer represented by Formula 2, or the What converted the Y into -COOH by hydrolyzing the copolymer is preferable.
CF ₂ = _CX a _X b ··· Formula 1,
CF ₂ = CF (OCF ₂ CFX _c ) _n O (CF ₂ ) _m Y Formula 2

In Formula 1, _Xa and _Xb are each independently a fluorine atom, a chlorine atom, a hydrogen atom, or a trifluoromethyl group. In Formula 2, _Xc is a fluorine atom or a trifluoromethyl group, m is an integer of 1 to 3, n = 0 or 1, and Y is a precursor group that can be converted into a carboxylic acid group by hydrolysis in an alkaline medium. It is. Y is preferably -COOR (R is an alkyl group having 1 to 4 carbon atoms), -CN, or -COZ (Z is a halogen atom).

Preferably _CF 2 = CF ₂ as the monomer of the formula 1, the monomer represented by Formula _{2, CF 2 = CFOCF 2 CF} (CF 3) OCF 2 CF 2 COOCH 3, CF 2 = CFOCF ₂ CF ₂ COOCH ₃ , CF ₂ = CFOCF ₂ CF ₂ CF ₂ COOCH ₃ , CF ₂ = CFOCF ₂ CF ₂ CF ₂ OCF ₂ CF ₂ COOCH ₃ , CF ₂ = CFOCF ₂ CF ₂ CF ₂ CF ₂ CF ₂ COOCH ₃ , CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ CF ₂ COOCH ₃ is preferred.

  The ion exchange capacity of the first layer constituting the laminated film is preferably 0.7 to 1.05 meq / g dry resin. Moreover, it is preferable that the thickness of this 1st layer is 5-50 micrometers, especially 10-35 micrometers.

On the other hand, as the perfluorocarbon polymer forming the second layer, a copolymer of a polymer unit based on the monomer represented by the above formula 1 and a polymer unit based on the monomer represented by the formula 3, or those converting W into -SO 3 _H by hydrolysis of the copolymer is preferred.
CF ₂ = CF (OCF ₂ CFX _d ) _s O (CF ₂ ) _t W Formula 3
In Formula 3, X _d = a fluorine atom or a trifluoromethyl group, an integer of s = 1 to 3, t = 0, 1, or 2, W is a precursor that can be converted into a sulfonic acid group by hydrolysis in an alkaline medium It is a body group. The _{W, -SO 2 X e (X} e is a fluorine atom, a chlorine atom or a bromine atom), - _SO 2 R (R is an alkyl group having 1 to 4 carbon atoms) are preferred.

Examples of the monomer represented by Formula _{3, CF 2 = CFOCF 2 CF} (CF 3) OCF 2 CF 2 CF 2 SO 2 F, CF 2 = CFOCF 2 CF (CF 3) OCF 2 CF 2 SO 2 FCF 2 = CFOCF ₂ CF ₂ CF ₂ SO ₂ F, CF ₂ = CFOCF ₂ CF ₂ SO ₂ F are preferred.

  The ion exchange capacity of the second layer constituting the laminated film is preferably 0.9 to 1.15 meq / g dry resin. From the viewpoint of preventing separation between the first layer and the second layer, the difference in ion exchange capacity between the first layer and the second layer is preferably as small as possible. The thickness of the second layer is preferably 45 to 140 [mu] m, particularly 60 to 100 [mu] m, from the viewpoint of providing sufficient strength.

  The laminated film may further have a layer made of a perfluorocarbon polymer having a sulfonic acid group or a sulfonic acid group precursor group as the third layer, in which case the third layer constitutes the second layer. It is preferably selected from polymers having the same structure as the polymer. The ion exchange capacity of the third layer is preferably the same as that of the second layer or higher from the viewpoint of reducing the electrolysis voltage. The thickness of the third layer is preferably 10 to 60 μm. When the thickness of the third layer is 10 μm or less, the reinforced woven fabric is difficult to be accommodated in the laminated film and easily peeled, and when it is 60 μm or more, the film resistance increases.

  The fluorine-based cation exchange membrane in the present invention is preferably one in which a woven fabric is laminated from the viewpoint of improving the strength of the membrane. When the film produced in the first step is a laminated film having a three-layer structure, the woven fabric is composed of the second layer and the third layer of the laminated film formed by laminating the first layer, the second layer, and the third layer in this order. It is preferably embedded between the layers.

Such a laminated film can be produced, for example, by the following method.
First, a laminated film of a first layer made of a polymer having a carboxylic acid group precursor group and a second layer made of a polymer having a sulfonic acid group precursor group is obtained by a coextrusion method. A third layer made of a polymer having a sulfonic acid group precursor group is obtained by a layer extrusion method. Subsequently, it arrange | positions in order of the laminated film of a 3rd layer, a woven fabric, and a 1st layer and a 2nd layer, and these are laminated | stacked using a lamination roll or a vacuum lamination apparatus. At this time, the laminated film of the first layer and the second layer is arranged so that the second layer side faces the woven fabric side.

  The cation exchange membrane is obtained by hydrolyzing the precursor group of the carboxylic acid group and the precursor group of the sulfonic acid group of the laminated film thus obtained to convert each into a carboxylic acid group and a sulfonic acid group. Is obtained. As a hydrolysis method, for example, a method using a mixture of a water-soluble organic compound and an alkali metal hydroxide as described in JP-A-1-140987 is preferable. Thus, the hydrolysis is preferably performed before the gas release layer is formed.

  In the second step of the present invention, the dispersion containing inorganic particles and the binder polymer and the aprotic polar solvent are applied to the surface of the film obtained in the first step, and then the aprotic polar solvent is added. Remove by heating. The layer made of the inorganic particles and the binder polymer formed thereby has a role of a gas release layer.

As the inorganic particles, those having excellent corrosion resistance against an electrolytic solution and the like and having hydrophilicity are preferable. Specific examples include Group 4 element or Group 14 element oxides, nitrogen compounds or carbides, and SiO ₂ , SiC, ZrO ₂ and ZrC are particularly preferable.
The average particle diameter of the inorganic particles is preferably 0.5 to 2.0 μm in terms of secondary average particle diameter from the viewpoint of adhesion to the binder polymer.

  As the binder polymer, those having excellent corrosion resistance with respect to an electrolytic solution and having hydrophilicity are preferable. For example, a fluorine-based polymer or copolymer into which a carboxylic acid group or a sulfonic acid group is introduced is preferable. In particular, a fluoropolymer having a sulfonic acid group is preferably used.

  The content ratio of the inorganic particles in the dispersion containing the inorganic particles and the binder polymer is preferably 20 to 500 parts by mass with respect to 100 parts by mass of the binder polymer, and from the viewpoint of developing a sufficient gas release function, It is preferable to set it as 80-160 mass parts.

  In general, the dispersion preferably contains a dispersion medium from the viewpoint of uniformly coating the dispersion in a film shape. As the dispersion medium, for example, when the binder polymer is a fluorinated polymer having a sulfonic acid group, an alcohol solvent is preferably used, and ethanol, isopropyl alcohol, or the like can be used.

  Although the content rate of the dispersion medium in the said dispersion liquid is not specifically limited, It is preferable to set it as about 30-95 mass%. When the content ratio of the dispersion medium is in the above range, the binder polymer is excellent in dispersibility and has an appropriate viscosity, which is suitable when the dispersion is applied to the film surface by a spray method.

As the aprotic polar solvent, those having a boiling point of 140 ° C. or higher and a melting point of 25 ° C. or lower are preferable, and those having a boiling point lower than the melting point of the polymer constituting the film are preferable. .
Specific examples of the aprotic polar solvent include dimethyl sulfoxide, formamide, N, N-dimethylacetamide, and N, N-dimethylformamide. Among them, dimethyl sulfoxide has been conventionally used in the hydrolysis step of a fluorine-based ion exchange membrane, and is preferably used because it is easy to handle.

As a method for forming a gas release layer comprising inorganic particles and a binder polymer on the surface of the film obtained in the first step, the following method is preferred.
(1) A method in which a dispersion containing inorganic particles and a binder polymer is applied to the film surface, and then an aprotic polar solvent is applied, followed by heating to remove the aprotic polar solvent.
(2) A method in which a dispersion containing inorganic particles and a binder polymer and a mixed solution of an aprotic polar solvent are applied to the membrane surface and then heated to remove the aprotic polar solvent.
The dispersion liquid in (1) and the liquid mixture of the dispersion liquid and the aprotic polar solvent in (2) can be adjusted by a known method such as mixing in a container equipped with a stirring blade or mixing using a ball mill. .

In addition, as a method of applying the dispersion liquid in (1), the aprotic polar solvent in (1), or the mixed liquid of the dispersion liquid and the aprotic polar solvent in (2) to the film surface, a spray method or a roll is used. The method by the coater method etc. is mentioned.
The aprotic polar solvent is added in an amount of 1 to 70 mass%, particularly 10 to 50 mass%, based on the total amount of the dispersion containing the inorganic particles and the binder polymer and the aprotic polar solvent. It is preferable to add so that it becomes.

The heating temperature at the time of removing the aprotic polar solvent is not particularly limited, but it is preferably 30 ° C. or higher, preferably higher than the boiling point of the aprotic polar solvent used. Generally, when the heating temperature is lower than the boiling point of the aprotic polar solvent used, the aprotic polar solvent tends to remain on the membrane surface, but depending on the type, the solvent is sufficient even when heated below the boiling point due to the vapor pressure. Can be volatilized.
On the other hand, when the heating is performed at a temperature equal to or higher than the melting point of the polymer constituting the film, care must be taken so that the thickness of the film does not become uneven. Is preferred.

  As the heating method, a method using a heating roll, a method of heating in an oven, and the like can be applied, but industrially, a method of continuous treatment with a roll press machine equipped with a heating drum is preferable. The pressure applied by the roll press is not particularly limited, but is preferably a linear pressure of 0.2 MPa or less from the viewpoint of power reduction.

  In the present invention, when a film made of a perfluorocarbon polymer having an ion exchange group precursor group is produced in the first step and then a gas release layer is formed in the second step, the second step is followed by Then, a third step of converting the precursor group into an ion exchange group is performed. The second step and the third step may be performed in parallel. Conversion to an ion exchange group can be carried out by hydrolyzing the precursor group in an alkaline aqueous solution.

[Examples 1 to 5]
<Preparation of cation exchange membrane>
CF ₂ ═CF ₂ and CF ₂ ═CFOCF ₂ CF ₂ CF ₂ COOCH ₃ are copolymerized and hydrolyzed to give a polymer having an ion exchange capacity of 0.95 meq / g dry resin (hereinafter referred to as polymer A) .) Also, CF ₂ = CF ₂ and CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ SO ₂ F are copolymerized and hydrolyzed, the ion exchange capacity is 1.0 meq / g dry resin The following polymer (hereinafter referred to as polymer B) was obtained. Further, a polymer (hereinafter referred to as polymer C), which is the same copolymer as polymer B and has an ion exchange capacity of 1.0 meq / g dry resin when hydrolyzed, was prepared.

  Using an apparatus equipped with two extruders, a film die for coextrusion, and a take-up machine, a 17 μm thick A layer (first layer) composed of polymer A and a 67 μm thick B composed of polymer B A two-layer film AB obtained by laminating a layer (second layer) was obtained. A film C (third layer) made of polymer C and having a thickness of 30 μm was obtained using a film die for single layer extrusion.

On the other hand, on a film made of polyethylene terephthalate (hereinafter referred to as PET), a paste in which zirconium oxide is dispersed in a 1% by mass methylcellulose aqueous solution is applied by a gravure roll method so as to have a dry weight of 8 g / m ^2. A processed film D was obtained.

  Further, a 100 denier yarn made of polytetrafluoroethylene was used as the reinforcing yarn, a 30 denier 6 filament yarn made of polyethylene terephthalate was used as the sacrificial yarn, the density of the reinforcing yarn was 10 pieces / cm, and the density of the sacrificial yarn was 20 A plain weave woven fabric having a line / cm was obtained.

  Next, using a laminated roll of a pair of metal rolls and rubber lining rolls, a film D, a film C, a woven fabric, and a two-layer film AB at a temperature of 200 ° C., a linear pressure of 40 kg / cm, and a speed of 0.4 m / min. A composite film having a zirconium oxide particle layer on one side was obtained by laminating and integrating in this order. At this time, the film D was disposed with the coated surface of zirconium oxide facing the film C side, and the two-layer film AB was disposed with the B layer facing the woven fabric side.

The obtained composite membrane was immersed in an aqueous solution containing 30% by mass of dimethyl sulfoxide (DMSO, boiling point 189 ° C.) and 15% by mass of potassium hydroxide at 90 ° C. for 12 minutes, and COOCH ₃ groups and SO ₂ F groups were added. Hydrolysis and conversion to ion exchange groups. Next, this was washed with water and then dried in a hot air dryer at 90 ° C.

  On the other hand, a polymer obtained by converting the same copolymer as the polymer B into an acid form and having an ion exchange capacity of 1.1 meq / g was prepared as a binder polymer. This polymer was dissolved in ethanol to prepare a 7.4% by mass ethanol solution. Zirconium oxide having a secondary average particle diameter of 1 μm was added to this ethanol solution and dispersed uniformly using a ball mill to obtain a suspension containing 10.8% by mass of zirconium oxide.

  Next, DMSO was added to this suspension in a proportion of 0% by mass (Example 1, Comparative Example), 10% by mass (Example 2), 20% by mass (Example 3), 30% by mass (Example). 4) and 40% by mass (Example 5) were added, and zirconium oxide was further uniformly dispersed by a ball mill to obtain five types of dispersions.

  Each dispersion was applied by spraying to the two-layer film AB surface side of the dried composite membrane, and a zirconium oxide particle layer was also formed on the two-layer film AB surface. Next, the composite film was heated at a temperature of 160 ° C., a linear pressure of 1.5 kg / cm, and a speed of 0.04 m / min, using a pair of metal rolls and rubber lining rolls. Furthermore, the composite membrane was immersed in a 4% by mass aqueous sodium hydrogen carbonate solution at a temperature of 40 ° C., and an equilibrium treatment was performed.

<Friction test>
The five kinds of cation exchange membranes obtained as described above were subjected to a friction test according to the following method. As a friction tester, a simple type wear resistance tester IMC-1558-1 manufactured by Imoto Seisakusho was used, and as a friction body, a foamed urethane sheet (density: 22 kg / m ³ ) manufactured by Inoac Corporation was used. A friction body was brought into contact with the two-layer film AB surface side of the cation exchange membrane, a load of 50 g was applied to the friction body, and a 100 reciprocating friction acceleration test was performed.
After the friction test, the amount of zirconium oxide remaining on the surface of the two-layer film AB side of the cation exchange membrane was measured using a fluorescent X-ray measuring device, and the residual rate was calculated. The results are shown in Table 1.

<Electrolysis test (durability test)>
On the other hand, the same cation exchange membrane as that used in Example 1 was placed in the electrolytic cell so that the two-layer film AB side, that is, the A layer (first layer) side having a carboxylic acid group, faces the cathode. The sodium chloride aqueous solution was electrolyzed with the acid group-containing film C (third layer) side facing the anode. As the electrolytic cell, an electrolytic cell having an effective energization area of 0.25 dm ² was used. As the anode, DSE manufactured by Permerek Electrode Co., Ltd. was used. As the cathode, Raney nickel plating cathode manufactured by Chlorine Engineers Co., Ltd. was used.

An aqueous sodium chloride solution was supplied to the anode chamber while adjusting to 200 g / L, and electrolysis was performed at a current density of 4 kA / m ² and a temperature of 85 ° C. while maintaining the sodium hydroxide concentration discharged from the cathode chamber at 32% by mass. went. As a result, the initial voltage was 3.02 V, the current efficiency was 97.2%, the voltage 6 months after the start of operation was 3.05 V, and the current efficiency was 97.1%. Moreover, when the film | membrane used for 6 months was removed from the electrolytic cell and the residual amount of the zirconium oxide was measured using the fluorescent X ray measuring device, the residual rate was 95%.
Similar electrolysis tests were performed using the same cation exchange membranes used in Examples 2-5. The results are shown in Table 1.

[Examples 6 to 10 (Comparative example)]
Prepare a cation exchange membrane that was treated in the same manner as in Examples 1 to 5 except that the zirconium oxide dispersion was applied to the two-layer film AB side of the cation exchange membrane and then the heat treatment at 160 ° C. was not performed. A friction test was performed on each cation exchange membrane in the same manner as in Examples 1-5. The results are shown in Table 2.

[Examples 11 to 15]
A cation exchange membrane having a zirconium oxide particle layer on its surface was prepared in the same manner as in Examples 2 to 5 except that each solvent shown in Table 3 was used instead of DMSO and the content ratio of each solvent was 50% by mass. Then, the friction test was performed in the same manner as in Examples 2-5. The results are shown in Table 3.

The fluorine-based cation exchange membrane obtained by the production method of the present invention is used for alkali chloride electrolysis.

Claims (4)

First step for producing a film comprising a perfluorocarbon polymer having an ion exchange group or a precursor group of an ion exchange group, a dispersion containing inorganic particles and a fluoropolymer having a sulfonic acid group , and an aprotic system A second step of heating and removing the aprotic polar solvent after applying the polar solvent to the membrane surface, and when the perfluorocarbon polymer has a precursor group of an ion exchange group, the precursor group A method for producing a fluorine-based cation exchange membrane having a gas release layer on the surface, wherein the method comprises a third step of converting the water into an ion exchange group. The fluorine- containing cation according to claim 1, wherein in the second step, a dispersion containing inorganic particles and a fluorine- containing polymer having a sulfonic acid group is applied to the surface of the membrane, and then an aprotic polar solvent is applied. An exchange membrane manufacturing method. 2. The fluorine- containing cation according to claim 1, wherein in the second step, a dispersion containing inorganic particles and a fluorine- containing polymer having a sulfonic acid group , and a mixture of an aprotic polar solvent are applied to the membrane surface. An exchange membrane manufacturing method.   The method for producing a fluorine-based cation exchange membrane according to claim 1, 2, or 3, wherein the aprotic polar solvent is dimethyl sulfoxide.