JPH0756079B2 - Method for producing alkali hydroxide - Google Patents

Description

The present invention relates to a method for producing alkali hydroxide by ion exchange membrane electrolysis. More specifically, it relates to a method of stably electrolyzing at a high current efficiency and low voltage over a wide range of alkali hydroxide concentration of 20 to 52% by weight, especially 42% by weight.
The present invention relates to a method for producing a high-concentration alkali hydroxide.

[Prior Art] In the so-called ion exchange membrane method alkaline electrolysis, in which a fluorine-containing resin ion exchange membrane is used as a diaphragm and an alkali chloride aqueous solution is electrolyzed to produce alkali hydroxide and chlorine, high purity alkali hydroxide Since it can be manufactured with a lower energy consumption than the conventional methods up to the above, it has become popular internationally in recent years.

In such an ion exchange membrane method alkaline electrolysis, in the early days, a fluorinated ion exchange membrane having a sulfonic acid group as an ion exchange group was used, but in recent years it is not possible to increase the current efficiency, It was changed to a cation exchange membrane with a carboxylic acid group as an ion exchange group, and as a result, the current efficiency in electrolysis reached almost 93 to 97%, reaching an industrially almost completed range.

However, it has been found that when the above-mentioned carboxylic acid cation exchange membrane is used, although excellent current efficiency is obtained for a long period of time, it is suitable for producing an alkali hydroxide having a concentration of up to 36% by weight. . According to the research of the present invention, when the concentration of the produced alkali hydroxide exceeds 36% by weight, the current efficiency is high at the beginning of the operation, but the current efficiency is increased when the operation is performed for a long period of one month to one year. There was a phenomenon that it gradually decreased. Thus, the carboxylic acid cation exchange membrane is not always suitable for industrially producing the above-mentioned high-concentration alkali hydroxide.

On the other hand, a method for producing an alkali hydroxide having a concentration of 30% by weight or more using a sulfonic acid group of a sulfonic acid cation exchange membrane of a fluorine-containing resin has been proposed. In that case, the current efficiency is reduced. That is, the initial current efficiency of 91-93% gradually increases to 87-90%.
Will be reduced to%.

Further, US Pat. No. 4,455,210 (Japanese Patent Laid-Open No. 58-179236) discloses a cation exchange membrane in which a fluoropolymer film having a sulfonic acid amide group is laminated with a fluoropolymer film having a sulfonic acid group on the cathode side. It has been proposed to use to produce high concentrations of alkali hydroxide. However, in this method, not only the initial current efficiency is low in the first place, but also the current efficiency is further lowered when the operation is performed for a long period of time. Further, JP-A-52-105598 exemplifies that an alkali hydroxide is produced by providing a porous membrane of a fluoropolymer having a sulfonic acid group on the cathode side of a fluoropolymer layer having a sulfonic acid group. ing. In this case, the electrolysis voltage is high because of the three-chamber type electrolysis consisting of two diaphragms, and in order to obtain high current efficiency, it is necessary to supply diluted alkali to the intermediate chamber under pressure, and the electrolysis operation is very complicated. Will be.

[Problems to be Solved by the Invention] The present invention uses an ion exchange membrane which can give a wide range of concentrations of alkali hydroxide not only high current efficiency in the initial stage but also high current efficiency even when it is operated for a long time. It is an object to provide a method for producing alkali hydroxide. In particular, by providing the production of 42% by weight or more of alkali hydroxide, which has been difficult with the prior art, it is possible to provide a method of producing high-concentration alkali hydroxide that does not require a process of concentrating an electrolytic solution by an evaporator. To aim.

[Means for Solving the Problem] Thus, in the present invention, in producing an alkali hydroxide by ion exchange membrane electrolysis, an ion exchange capacity of 0.8 to 2.0 meq / g dry resin having a -COOM group as an ion exchange group, Use of a fluorinated cation exchange membrane having a multi-layer structure of an ion exchange layer having a thickness of 5 to 300 μm and an asymmetric porous layer which is present on the cathode side of the layer and has a lower water permeability as it is closer to the cathode side. The present invention provides a method for producing an alkali hydroxide characterized by the above.

In the fluorine-containing resin cation exchange membrane used in the present invention, due to the multilayer structure of the ion exchange layer and the asymmetric porous layer, a wide range of alkali hydroxide, particularly 42% by weight or more of high concentration water Alkali oxide is stably produced over a long period of time with high current efficiency and low voltage. This object cannot be achieved even if one of the above layers is missing. The ion exchange layer is a layer exhibiting high current efficiency, but if there is no asymmetric porous layer, the current efficiency will decrease with time.

The ion exchange layer having the above-COOM group has an ion exchange capacity of 0.
It is selected from 8 to 2.0 / g dry resin and a thickness of 5 to 300 μm. Among them, in the present invention, the smaller the ion exchange capacity, the better the stability over long-term operation, and the smaller the thickness, the smaller the membrane resistance. Therefore, the ion exchange capacity is preferably 0.9.
~ 1.5 milliequivalent / g dry resin, thickness is preferably 10 ~ 60μ
selected from m.

The asymmetric porous layer present on the cathode side of the ion exchange layer preferably has a structure in which the water permeability becomes smaller toward the cathode side, and is preferably formed of at least two layers.
When the porous layer to be present on the cathode side of the ion exchange layer does not have an asymmetric structure, that is, when the porous layer has a symmetrical structure and has uniform porosity and water permeability throughout the porous layer, the porosity of the porous layer and When the water permeability is small, a high current efficiency can be obtained, but the electrolysis voltage is very high. When the porosity and water permeability are large, the electrolysis voltage is low but high current efficiency cannot be obtained.

When the asymmetric porous layer is formed of two layers, the first porous layer in contact with the ion exchange layer preferably has a porosity of 5 to 95.
%, Water permeability of 1 × 10 ^{−2 to} 5 × 10 ² cc / hr · cm ² · atom is used. When the porosity is 5% or less, a high current efficiency cannot be obtained, the electrolysis voltage is high, and the electrolysis condition causes peeling from the ion exchange layer. Therefore, the porosity is preferably 10 to 85%.
Those having a porosity of are used. Furthermore, water permeability is 1 ×
Since 10 ^-2 or less lead to separation of the ion exchange layer depending high also electrolysis conditions electrolysis voltage, preferably 1 × 10 ^-1 ~
A material having a water permeability of 1 × 10 ² hr · cm ² · atom is used.

The first porous layer has SO ₃ M groups (M represents hydrogen or an alkali metal) because the first porous layer has a higher water permeability than the second porous layer arranged on the cathode side, so that the current passes through the pores. It does not matter whether the fluorine-containing ion exchange polymer is contained or not. However, when it is contained, it can be formed into a film by various methods, which is preferable. For example, SO ₃ M
A method of forming a porous film by mixing inorganic particles in a fluoropolymer having a group, kneading, and then forming a porous film, or by decomposing and extracting a pore-forming agent and a fluoropolymer that can be extracted, and then forming a thin film, and after decomposition and extraction It can also be a porous film. As the pore-forming agent, for example, SiO ₂ , polycarbonate, cotton, rayon, nylon, polyethylene terephthalate, polyacrylonitrile, etc., which can be dissolved when hydrolyzed with an alkaline aqueous solution, can be extracted with a solvent, such as ethyl cellulose, alkylnaphthalene, and sodium chloride. Water-soluble salts, etc. are listed. Porosity and water permeability are controlled by the content and particle size of inorganic particles and pore-forming agents. As the ion exchange capacity of the fluoropolymer containing SO ₃ M groups, 0.5 to 1.5 meq / g dry resin is used. When the formation of the porous layer does not contain a fluorine-containing ion exchange polymer, an alkali resistant porous body, for example, asbestos solidified with a fluororesin, a polytetrafluoroethylene porous membrane, or the like can be used. . The thickness of the porous layer is 20 to reduce the membrane resistance.
0 μm or less is adopted, and preferably 100 μm or less is selected. On the cathode side of the first porous layer forming the asymmetric porous layer, the porosity is 80% or less, preferably 60% or less, and the water permeability is 1 × 10 ^{−3 to 5} cc / hr · cm ² · atom, preferably 5 x 10 ^-3
A second porous layer having ~ 2cc / hr · cm ² · atom is disposed. Since the second porous layer has a smaller water permeability than the first porous layer, it is preferably a fluorine-containing ion exchange polymer having an SO ₃ M group in order to form a current passage portion other than the pores in the porous layer. A porous layer containing is used.

When the porosity of the second porous layer is higher than 80% or the water permeability is higher than 5 cc / hr · cm ² · atom, high current efficiency cannot be obtained, and the water permeability is 1 × 10 ^−3. ~ 5cc / hr
・ If it is smaller than cm ² · atom, the current efficiency is low, and peeling may occur depending on the electrolysis conditions. The second porous layer can be formed by the same method as the above-mentioned first porous layer,
In the case of a composite of a fluorinated ionic polymer and other components (inorganic particles, etc.), the fluorinated polymer is a porous layer forming material.
The content is 30 vol% or more, preferably 50 vol% or more. 30vol
When the content of the fluoropolymer is not more than%, it is difficult to stably obtain high current efficiency even if the porosity and the water permeability are within the above range. The thickness of the second porous layer is selected to be 100 μm or less, preferably 50 μm or less in order to reduce the membrane resistance. The ion-exchange layer thus formed and the asymmetric porous layer can be laminated, and the first and second porous layers forming the asymmetric porous layer can be laminated by an ordinary hot press or the like. In addition, when a solution of a fluorine-containing ion exchange polymer having a SO ₃ M group is used for forming the porous layer, the layers can be laminated by a wet film forming method.

The ion exchange layer forming the fluorine-containing ion exchange membrane of the present invention can be composed of a single layer of the above-mentioned fluorine-containing polymer having a —COOM group, but is preferably a fluorine-containing polymer layer having the —COOM group. And a multilayer of the ion-exchange group-containing fluoropolymer present on the anode side.

As the anode side layer, a single layer or multiple layers of a fluoropolymer having a COOM group and / or a SO ₃ M group is used, and the thickness is 10 to
300 μm, preferably 50 to 200 μm is selected. In order to impart high strength, a reinforcing cloth made of a fluorine-containing polymer having corrosion resistance can be adopted for the ion exchange layer. The fluoropolymer constituting the ion exchange layer is composed of a copolymer of at least two kinds of monomers, preferably a copolymer having the following polymer units (a) and (b).

_{(I) - (CF 2 -CXX ')} -, Here, X and X ′ are —F, —Cl, —H or —CF ₃ ,
A is, -SO ₃ M, -CRfRf'OM or -CO ₂ M (M is hydrogen, a alkali metal or hydrolysis, etc., .Rf represents a group converted into these groups, Rf 'from 1 to 10 carbon atoms The perfluoroalkyl group, Y, is selected from the following, where Z,
Z'is -F or a perfluoroalkyl group having 1 to 10 carbon atoms, and _{X, Y and Z each} represent an integer of 1 to 10.

-(CF ₂ ) _X -,-O- (CF ₂ ) _X- , The composition ratio (molar ratio) of (a) / (b) forming the polymer is selected so that the fluoropolymer forms the ion exchange capacity.

The above-mentioned fluoropolymer is preferably a perfluorocarbon polymer, and preferred examples thereof include CF ₂ = CF ₂ and CF ₂ = CFO (CF ₂ CF (CF ₃ ) OCF ₂ CF ₂ SO ₂ F. Copolymer CF ₂ = CF ₂ and CF ₂ = CFO (CF ₂ ) _2-5 SO ₂ F Copolymer CF ₂ = CF ₂ and CF ₂ = CFO (CF ₂ ) _1-5 COOCH ₃ Copolymer Copolymer CF ₂ = CF ₂ and CF ₂ = CFO (CF ₂ ) _2-5 CO ₂ CH ₃ Copolymer Furthermore, CF ₂ = CF ₂ and CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF An example is a copolymer with ₂ COOCH ₃ .

The above-mentioned fluorine-containing cation exchange membrane can be used as it is, but preferably at least one surface of the cation exchange membrane, particularly preferably at least the anode side surface of the ion exchange membrane is subjected to a treatment for releasing chlorine gas. Thereby, the long-term stability of current efficiency can be further improved.

The reason why the chlorine gas release property of the surface of the ion exchange membrane on the anode side contributes to the long-term stability of current efficiency is not always clear, but it is believed that it is probably due to the following reason.

That is, when chlorine gas adheres to the surface of the anode, the chlorine gas penetrates into the film and comes into contact with caustic alkali from the cathode side to generate alkali chloride. When the caustic alkali concentration is low, the produced alkali chloride is eluted without depositing in the film, but when producing an alkali hydroxide having an alkali hydroxide concentration of more than 36% by weight, the produced alkali chloride is in the film. It is described that it precipitates on the surface and impairs the long-term stability of the current efficiency. However, it goes without saying that the present invention is not limited to the above description.

As a method for treating the surface of the ion exchange membrane for releasing gas, a method of forming fine irregularities on the membrane surface (Japanese Patent Publication No. Sho 60).
-26495), a method of supplying a liquid containing iron, zirconia, etc. to the electrolytic cell to deposit hydrophilic inorganic particles on the membrane surface (Japanese Patent Laid-Open No. 56-152980), gas and liquid permeable electrode activity. A method of providing a porous layer containing particles not having the particles (JP-A-56
-75583 and JP-A-57-39185).
The gas releasing layer on the surface of such an ion exchange membrane can improve the voltage under electrolysis in addition to the effect of improving the long-term stability of current efficiency.

As the process conditions for electrolyzing an aqueous solution of alkali chloride using the fluorine-containing cation exchange membrane of the present invention, known conditions as described in JP-A-54-112398 can be adopted. For example, preferably 2.5 to 5.0 normal (N) aqueous solution of alkali chloride is supplied to the anode chamber, and water or diluted alkali hydroxide is supplied to the cathode chamber, preferably at 50 to 120 ° C.
It is electrolyzed at 5 to 100 A / dm ² . In such a case, heavy metal ions such as calcium and magnesium in the alkali chloride cause deterioration of the ion exchange membrane, and therefore it is preferable to make them as small as possible. In addition, a salt such as hydrochloric acid can be added to the aqueous solution of alkali chloride in order to prevent the generation of oxygen at the anode as much as possible.

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

When the electrode is arranged in the present invention, the electrode may be arranged in contact with the multilayer film or may be arranged at an appropriate interval, but particularly in the case of the present invention, the electrode is arranged in contact with the diaphragm. In this case, an advantageous cell voltage with low membrane resistance can be achieved without hindrance.

[Operation and Effect of the Present Invention] In the present invention, the reason why an ion exchange membrane having a multilayer structure of an ion exchange layer and an asymmetric porous layer contributes to good current efficiency and long-term stability of electrolysis voltage is not always clear. However, it is believed that this is probably due to the following reasons. It is considered that the current is mainly passing through the high resistance fluorine-containing ion exchange polymer portion in the second porous layer portion having relatively small water permeability on the cathode side of the first porous layer in contact with the ion exchange layer. To be The balance of the current passing through the fluoropolymer and the current passing through the ion-exchange layer is considered to determine the alkali concentration in the pores of the first porous layer in contact with the ion-exchange layer. In order to make it manifest, it is necessary to keep the alkali hydroxide concentration in contact with the ion exchange layer uniform. Therefore, it is considered that high porosity and high water permeability are required for the first porous layer in contact with the ion exchange layer. Also, when the water permeability of the second porous layer is large,
If the high-concentration alkali in the cathode chamber flows into the first porous layer, the ion exchange layer cannot function sufficiently, and if the water permeability of the second porous layer is extremely small, the ion exchange layer and porous layer are It is believed that delamination occurs between the layers resulting in reduced current efficiency.

[Examples] Hereinafter, the present invention will be described in more detail, but the present invention is not limited to these examples. Incidentally, the electrolysis in Examples and Comparative Examples is effective energization area 0.25dm ²
The electrolytic cell used was a titanium punched metal (short diameter 4 mm, long diameter 8 mm) coated with ruthenium oxide, iridium oxide, and titanium oxide solid solution as the anode, and SUS 304 punched metal as the cathode. (Short diameter 4 mm, long diameter 8 mm)
Was used in a 52 wt% caustic soda aqueous solution at 150 ° C. for 52 hours for etching. The electrolysis is arranged so that the anode / membrane / cathode are in contact, and while supplying 5N sodium chloride aqueous solution to the anolyte and water to the cathode chamber, the sodium chloride concentration in the anode chamber is set to 3.5N and the caustic soda in the cathode chamber is supplied. While keeping the concentration at 20-50% by weight, 90 ℃,
The current density was 30 A / dm ² .

Example 1 CF ₂ = CF ₂ / CF ₂ = CFOCF ₂ CF ₂ CF ₂ CO ₂ CH ₃ Ion exchange capacity 1.44 meq / g dry resin, 140 μm thick CF ₂ = CF ₂ / CF ₂ = CFOCF ₂ CF ₂ CF ₂ CO ₂ CH _{3 An} ion exchange capacity of 1.25 meq / g dry resin 20μ consisting of a copolymer was thermocompression bonded to obtain a laminated film as an ion exchange layer.

On the other hand, a mixture of methylcellulose containing 30% by weight of ZrO ₂ having a particle size of 5 μm, water, and cyclohexanolcyclohexane is kneaded to form a paste, and the paste is applied onto a mylar film and dried to obtain ZrO ₂ particles. To form a porous layer having 4 mg per cm ² of the film surface. Porous layer 2 attached on the mylar film
Between the two, CF ₂₀ / CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ SO ₂ F copolymer, ion exchange capacity 1.1 meq / g 20 μm thick film made of dry resin is sandwiched from both sides. The porous layer A containing the fluorine-containing ion exchange polymer was formed by transferring the porous layer on the Mylar film by heating and pressure bonding.

Furthermore, CF ₂ = CF ₂ / CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ -SO ₂ F copolymer, ion exchange capacity 1.1 meq / g dry resin mixed with polyethylene terephthalate in a volume ratio of 35% And then thickness 20
A precursor for porous layer B, which becomes a porous layer after elution of polyethylene terephthalate, was formed into a thin film having a thickness of μ. These porous layers A and B were arranged in the order of A and B from the ion exchange layer side on the ion exchange capacity 1.25 meq / g dry resin side of the laminated membrane to be the above ion exchange layer, and after stacking, 25% NaOH , At 70 ℃ 16
Hydrolyzed for hours.

The above-mentioned porous layers A and B were separately hydrolyzed separately, and the porosity and water permeability were examined. The porosity was A = 24.
%, B = 35%, and water permeability is A = 20cc / hr ・ cm ²・ ato
m and B were 0.2 cc / hr · cm ² · atom. The thus-obtained fluorine-containing ion exchange membrane was electrolyzed with an aqueous sodium chloride solution in an electrolytic cell in which the sides of the porous layers A and B faced the cathode side.

As a result of electrolysis, when the concentration of sodium hydroxide obtained from the cathode chamber was 49%, the voltage was 3.68V and the current efficiency was 95.5%.

[Example 2] The same procedure as in Example 1 was repeated except that the same fluorine-containing ion exchange membrane as that used in Example 1 was used, except that the ZrO ₂ particles were added per 1 cm ^{2 of the} film surface. A bubble release layer consisting of a porous layer having 1 mg attached was formed by thermocompression bonding.

The fluorine-containing ion exchange membrane thus obtained was electrolyzed with an aqueous sodium chloride solution in the same manner as in Example 1. The results are shown in Table-1.

Comparative Example 1 In Example 2, a multilayer film of an ion exchange layer, a ZrO ₂ porous layer, which is the same as in Example 2 except that the porous layer B is not provided,
A membrane was experimentally produced using the porous layer A, and electrolysis was performed. The results are shown in Table 2.

Comparative Example 2 The same procedure as in Example 2 except that the polyethylene terephthalate content of the porous layer B was 25 vol%, and a membrane using the same ion-exchange layer multilayer film, ZrO ₂ porous layer, and porous layer A was used. Was prototyped. However, the concentration of caustic soda in the cathode chamber was 49%.
When electrolysis was carried out at 1, the peeling occurred between the multilayer film and the porous layer A, the voltage was as high as 3.57 V and the current efficiency was as low as 89.5%. When the water permeability of the porous layer B was measured separately, it was 8 × 10.
^{It was -4} cc / hr · cm ² · atom.

Example 3 A mixture of fine powder of polytetrofluoroethylene (hereinafter referred to as PTFE) and white kerosene as a liquid lubricant was formed into a film. White kerosene was removed and then stretched in two orthogonal directions to obtain a PTFE porous body having a porous structure stabilized by heat treatment, having a pore size of 2 μ, a porosity of 70%, and a film thickness of 120 μ.

Then, the above PTFE porous material / CF ₂ = CF ₂ / CF ₂ = CFOCF ₂ CF ₂ CF ₂ CO
₂ CH ₃ copolymer membrane (ion exchange capacity 1.44 meq / g dry resin, thickness 20μ) / CF ₂ = CF ₂ / CF ₂ = CFOCF ₂ CF ₂ CF ₂ CO ₂ CH ₃ copolymer membrane (ion exchange capacity 1.25 meq / g dry resin, thickness
40 μ) was laminated by heating and compression to obtain a 170 μ-thick three-layer diaphragm.

The ion exchange capacity of this three-layer diaphragm was 1.25 meq / g dry resin, and the porous layer A used in Example 1 and CF ₂ = CF ₂ / CF
₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ SO ₂ F copolymer, ion exchange capacity
1.1 meq / g dry resin (Copolymer A) with 2μ particle size SiO
_Two particles were kneaded at a volume ratio of 50%, and then thinned to a thickness of 15 μm, and a precursor of a porous layer B to be a porous layer after elution of SiO ₂ was laminated in this order.

Next, 4 parts of copolymer A and 8 parts of zirconyl chloride were mixed with 57 parts of ethanol.
Parts and 31 parts of water to dissolve in a mixed solvent to obtain a mixed solution. Immediately after impregnating the porous body of the laminated film with such a mixed solution, immediately 1 part of sodium oleate, 65 parts of ethanol, and 35 parts of water were used.
The laminated film impregnated with the mixed solution was dipped in a surfactant solution consisting of 1 part to coagulate and fix the copolymer and the inorganic compound.

Furthermore, a dispersion of 13% ZrO ₂ having an average particle size of 5 μ was prepared in a 25 ethanol solution of the acid-type polymer of copolymer A, and the dispersion was sprayed on both sides of the laminated film to 1 cm ³
A coating consisting of 0.9 mg of ZrO ₂ and Copolymer A was applied.

The membrane was hydrolyzed at 25% NaOH, 70 ℃ for 16 hours and then treated with PTFE.
Electrolysis was performed with the surface of the porous body facing the anode. With a current efficiency of 95.2% and a voltage of 3.15V, 49% caustic soda was obtained.
Even if electrolysis was continued for 30 days, neither current efficiency nor voltage changed.

Incidentally, when the porous layer B was decomposed by itself and examined for porosity and water permeability, the porosity was 50% and the water permeability was 0.2 cc / hr · cm ² atom.

Example 4 In Example 2, the porosity obtained by adhering an emulsion of terrafluoroethylene and hexafluoropropyleneno copolymer to asbestos in the porous layer A and firing the mixture.
%, Water permeability 190 cc / hr · cm ² · atom, the same multilayer film as in Example 2 except that a porous layer having a thickness of 40 μm was used, a ZrO ₂ porous layer,
A membrane was made as a prototype using the porous layer B and electrolysis was performed. Current efficiency also
95.6% and 49% caustic soda were obtained at a voltage of 3.29V, and the current efficiency and voltage did not change even after electrolysis for 130 days.

Comparative Example 3 In Example 4, a membrane was experimentally produced using the same multilayer film, ZrO ₂ porous layer, and asbestos porous layer as in Example 4 except that the porous layer B was not provided, and electrolysis was performed. The cathode caustic soda concentration was 49%, the current efficiency was 81%, and the voltage was 3.18V.

Example 5 In Example 2, CF ₂ = CF ₂ / CF ₂ = CFOCF ₂ CF (C
F ₃ ) OCF ₂ CF ₂ SO ₂ F copolymer, ion exchange capacity 1.0 meq /
g Dry resin, 10 μm thick film, ZrO _{2 of} Example 1
A multilayer film, a ZrO ₂ porous layer, and a porous layer similar to those of Example 2, except that the porous layer B prepared by thermocompression bonding the porous layer having a ZrO ₂ particle attachment amount of 2 mg / cm ² was used. A film was prepared using A, and electrolysis was performed. The results are shown in the third.

When the porous layer B was hydrolyzed alone and the porosity and water permeability were examined, the porosity was 12% and the water permeability was 0.4 cc / hr · cm ² · atom.

Comparative Example 4 In Example 5, except that the thickness of the fluorine-containing ion exchange polymer film forming the porous layer B was 5 μm.
A multi-layer film, a ZrO ₂ porous layer, and a porous layer A similar to those in Example 5 were used as a prototype to perform electrolysis. The results are shown in Table 4.

Claims (6)

[Claims] 1. When producing an alkali hydroxide by electrolysis using an ion exchange membrane method, a --COOM group (M
Represents hydrogen or an alkali metal) having an ion exchange capacity of 0.8 to 2.0 meq / g dry resin and a thickness of 5 to 300 μm, and the water permeability becomes smaller as it is closer to the cathode side. A method for producing an alkali hydroxide, which comprises using a fluorine-containing cation exchange membrane having a multilayer structure with an asymmetric porous layer. 2. The asymmetric porous layer is in contact with the ion exchange layer and has a porosity of 5 to 95% and a water permeability of 1 × 10 ^{−2 to} 5 × 10 ² cc / hr.
cm ² · atom first layer, water permeability lower than the first layer, porosity 80% or less, water permeability 1 × 10 ^{-3 to 5} cc / hr · cm ² · a
The method of claim 1 comprising a second porous layer of tom. 3. The asymmetric porous layer has an ion exchange capacity of 0.5-.
-SO ₃ M group of 1.5 meq / g dry resin (M is the same as above)
The method according to claim (1) or (2), which further comprises a fluorine-containing ion exchange polymer having: Wherein the first layer and -COOM group greater thickness 10~300μm moisture content than the first layer was present on the anode side having an ion exchange layer is -COOM group, -SO ₃ M and / Or the method of (1), (2) or (3), which comprises a layer containing an ion-exchange group consisting of a mixed system thereof. 5. The method according to claim 1, wherein a bubble releasing layer made of inorganic particles is bonded to the surface of the ion exchange membrane on the anode side and / or the cathode side. 6. The method according to claim 1, wherein the concentration of the alkali hydroxide is 42% by weight or more.