JPH0254791A - Production of alkali hydroxide - Google Patents

Abstract

PURPOSE:To produce alkali hydroxide at a specified concn. with high current efficiency by electrolyzing alkali chloride in the anode chamber of an electrolytic cell with a membrane consisting of a layer contg. a specified cation exchanger on the cathode side and a specified perfluorocarbon polymer layer. CONSTITUTION:A fluorine-contg. cation exchange membrane is composed of a first layer of an alkali-proof cation exchanger having >=5mum thickness and a second layer of a perfluorocarbon polymer having 2-7% water content in 45wt.% aq. NaOH soln., >=5mum thickness and -CO2M groups (M is an alkali metal). The first layer is a porous layer of a cation exchanger contg. dispersed alkali-proof inorg. matter or short fibers, a porous layer of a cation exchange resin having low penetrability of pores or a porous layer of a cation exchanger contg. an embedded alkali-proof polymer having no ion exchange group. The cation exchange membrane is stretched in an electrolytic cell so that the first layer confronts the cathode. Alkali chloride is fed into the anode chamber of the cell and electrolyzed. Alkali hydroxide is efficiently obtd. in the wide concn. range of 20-55%.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a method for producing an aqueous alkali hydroxide solution, and particularly in an ion exchange membrane method, a single membrane can produce two
0 to 55% by weight, especially less than 45% by weight, especially 42% by weight
The present invention relates to a method for producing alkali hydroxide in a wide range from less than 20% by weight to more than 20% by weight with high current efficiency.

[Prior art] In the so-called ion-exchange removal method alkaline electrolysis, which uses a fluorine-containing cation exchange membrane as a diaphragm and electrolyzes an aqueous alkali chloride solution to produce alkali hydroxide and chlorine, high-purity alkali hydroxide is It has become popular internationally in recent years because it can be manufactured with lower energy consumption than conventional methods.

In the early days of such ion-exchange removal method alkaline electrolysis, fluorine-containing cation exchange membranes with sulfonic acid groups as ion exchange groups were used, but in recent years they have not been used due to the inability to increase current efficiency. The membrane is replaced with an ion exchange membrane (both have carboxylic acid groups on the cathode side),
As a result, the current efficiency in electrolysis is approximately 92-97%.
It has reached an almost industrial level of perfection.

However, when using the above carboxylic acid type cation exchange membrane, excellent current efficiency can be obtained at low voltage over a long period of time only when producing alkali hydroxide with a concentration of approximately 36 to 40% by weight. It was discovered that According to the research conducted by the present inventor, a high electrolytic efficiency of 94 to 98% can be obtained when the concentration of alkali hydroxide reaches approximately 40% by weight, but when the concentration is higher than that, the current efficiency suddenly decreases. Served. In addition, when the concentration is high, the membrane resistance suddenly increases and the electrolytic voltage increases, and when operated for a long period of - weeks to a year, the current efficiency gradually decreases (a phenomenon that is not observed). When we measured the ion exchange capacity of the cathode surface of a membrane operated for a long period with such a high concentration of alkali hydroxide, it was clear that the ion exchange capacity of the surface decreased due to the decomposition of the carboxylic acid groups. Thus, in a cation exchange membrane having a carboxylic acid group on the cathode side of the membrane, it is not preferable to industrially produce alkali hydroxide at such a high concentration as described above.

On the other hand, U.S. Patent No. 4,455,210 discloses that a cation exchange membrane in which a fluorine-containing polymer film having sulfonamide groups is laminated on the cathode side of a fluorine-containing polymer film having sulfonic acid groups is used to achieve high concentration of hydroxide. It has been proposed to produce alkali. However, in this method, not only the initial current efficiency is low to begin with, but the current efficiency further decreases when operated for a long period of time.

Japanese Patent Publication No. 57-9589 discloses a method for obtaining 40% by weight of NaOH using a fluorine-containing cation exchange membrane having a sulfonic acid group-containing layer of about 2 μm on the cathode side of the carboxylic acid group-containing layer. There is. Other examples having a thin sulfonic acid group-containing layer on the cathode side of the membrane are also found in JP-A No. 58-83030, JP-A No. 60-23776, and JP-A No. 59-Sho.
No. 22930 describes an example in which a mixed layer of a sulfonic acid group-containing cation exchanger and zirconia was provided on both sides of the membrane, but both of these layers contained about 35% by weight of NaO.
This concerns the reduction of electrolytic voltage when obtaining t(.

According to the research of the present inventor, when the cathode side sulfonic acid group-containing layer is thin, 40% by weight of alkali hydroxide is 95%
Although high current efficiencies were obtained around 45% by weight or more, in the case of alkali hydroxide of 45% by weight or more, current efficiencies of only around 90% were obtained, and it became clear that the current efficiency decreased over time.

If such highly concentrated alkali hydroxide can be produced with high current efficiency and low electrolytic voltage, the energy conventionally required for concentrating alkali hydroxide can be saved or eliminated.

On the other hand, so far we have referred to conventional techniques for producing high concentration alkali hydroxide, but ion exchange membranes are also used to produce alkali hydroxide at concentrations such as 20 to 30% by weight. The alkali hydroxide concentration is determined by comprehensively considering various operating conditions. In this case, the ion exchange membrane is generally one that exhibits high current efficiency within a predetermined alkali hydroxide concentration range. Therefore, various ion exchange membranes suitable for the alkali hydroxide concentration are selected.
Traditionally, it was selected each time. However, 45% by weight
20 to 55% by weight, including less than 42% by weight
Once it became possible to manufacture a wide range of alkali hydroxides with a single membrane with high current efficiency, it became possible to produce a specified amount of alkali hydroxide while continuously operating the same electrolytic cell without changing the ion exchange membrane. It becomes possible to produce alkali hydroxide of any concentration.

[Problems to be Solved by the Invention] The present invention has a concentration of 20 to 55% by weight, preferably 25 to 50% by weight.
Less than 45% by weight, especially less than 42% by weight, 20% by weight
In producing the above alkali hydroxides, it is possible to not only provide high current efficiency initially, but also maintain high current efficiency even after long-term operation, and to produce alkali hydroxides of the various concentrations mentioned above using a single ion exchange membrane. The purpose is to provide a manufacturing method.

[Means for solving the problem] A first layer containing a cation exchanger selected from the following (a) to (c) with a thickness of 5 μm or more and having alkali resistance, and a 45% by weight NaOH aqueous solution. -CO2M group (
A fluorine-containing cation exchange membrane consisting of at least two layers including a second layer of a perfluorocarbon polymer having M (alkali metal) is placed in an anode chamber of an electrolytic cell with the first layer facing the cathode side. A method for producing alkali hydroxide characterized by supplying an alkali and performing electrolysis.

(a) A porous layer made of a cation exchanger containing dispersed alkali-resistant inorganic particles or fibrils (b) A porous layer made of a cation exchange resin with small pore penetration (c) Ions The first layer of the present invention has a thickness of 5 μm or more, preferably 1 μm or more.
It is 0 to 200 μm. 20 if thinner than 5μm
When producing alkali hydroxide of 25% by weight or more, sufficient current efficiency cannot be obtained, and deterioration of carboxylic acid groups due to high concentration of alkali cannot be sufficiently prevented. If it exceeds 200 μm, the membrane resistance becomes large and the electrolytic voltage becomes high, which is not preferable.

The alkali-resistant cation exchange resin forming the first layer is preferably a hydrocarbon cation exchange resin such as a sulfonated styrene/divinylbenzene copolymer or a hydroxystyrene/divinylbenzene copolymer. −
A perfluorocarbon polymer having an SO3M group or an -OM group (M is an alkali metal) is used.

The cation exchange resin forming the second layer has a thickness of 5
A perfluorocarbon polymer preferably containing -CO2M groups (M is an alkali metal) with a size of .mu.m or more is used. −
The second layer of perfluorocarbon polymer having CO2M groups (M is an alkali metal) has a water content in a 45 wt NaOH aqueous solution of 2 to 7% by weight, preferably 2.5 to 5%.
Preferably, it is in the range of % by weight. Outside this range, sufficiently high current efficiency cannot be obtained. Here, in the present invention, the water content in 45% NaOH means that the cation exchange membrane is immersed in a 45% NaOH aqueous solution for 16 hours,
After cooling to 5℃, the weight after wiping off the alkano water (liquid '8) on the membrane surface is ag.The membrane was immersed in ion-exchanged water at 90℃ for 16 hours, and then vacuum-dried at 130℃ for 16 hours. When the weight of bg is taken as bg, the water content (%) = (a-b) /bx100.

In the present invention, the ion exchange resin forming the first layer is preferably a perfluorocarbon polymer having -SO3M group or -'OM group, and the ion exchange capacity of the -SO3M group-containing perfluorocarbon polymer is preferably is 0.6 to 1.8 meq/g dry resin, especially 0.8
5-1.6 meq/g dry resin, 45 wt% N
a Ot (with a moisture content of preferably at least 3%, more preferably less (both 5%) than that of the second layer).
Although it is large, it is preferable that it is not larger than 30%, preferably not larger than 25%. - The ion exchange capacity of the M group-containing perfluorocarbon polymer is preferably 0.6 to 2.8.
milliequivalents/g dry resin, particularly 0.85 to 2.5 milliequivalents/g dry resin.

The second layer is preferably made of a perfluorocarbon polymer having a -CO2M group (M is an alkali metal), and has an ion exchange capacity of preferably 0.6 to 1.8 milliequivalents/g dry resin, especially is 0.85 to 1.6 mm
t/g dry resin.

In the present invention, the perfluorocarbon polymer refers to a polymer in which fluorine atoms account for 90% or more of the hydrogen atoms or halogen atoms bonded to carbon atoms, and the -5O, M group or -OM group mentioned above. The first layer of perfluorocarbon polymer having -CClaM group and the second layer of perfluorocarbon polymer having -CCaM group are composed of a small amount of perfluorocarbon polymer (both are composed of a copolymer of two types of monomers, Preferably, it consists of a copolymer having the following polymerized units (a) and (b).

(4) -(CF, -CXX')-, (0)
-(CFa-CX)-↓-9 Cocote, x, x' are -F, -C1, -■ or -CFa
With Te, A is -303M, -CRfRf'OM
or -CO2M (M is hydrogen, alkali metal, Rf, Rf
' represents a perfluoroalkyl group having 1 to 10 carbon atoms) or a group that can be converted into these groups by hydrolysis or the like, and 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 IO.

Furthermore, in addition to the polymerized units (a) and (b), the following polymerized units may be included.

The content of (b) in the above polymer is selected so that the fluorine-containing polymer forms the above ion exchange capacity.

The above-mentioned fluoropolymer is preferably a perfluorocarbon polymer in a hydrolyzed form,
Preferred examples are CFa=CF2 and CF
2=CFOCF2CF (CF3)OCF2(:FzS
Copolymer with OzF, CF,=CF2 and CF2=CFOfCF,
) copolymer with 2-ssO□F, CF2:(:F2 and CF, =CFOCF
Copolymer with 2CF2C(CF,)20H, CF2”CF2 and CF2=CFO(CF
z) copolymer with 2-6CO□CL, furthermore, CFa=(:F2 and (:F1=(:FOCF2CFCCF,)0(CF2)
2CO□CH.

An example is a copolymer with

In the present invention, the inorganic particles or fibrils dispersed and contained in the first layer (a) preferably have alkali resistance and do not dissolve in a 45% by weight NaOH aqueous solution at the electrolysis temperature. Such alkali-resistant inorganic substances are preferably those of the long-period table (7) Il, , Ill +,
, Ivl, , Vb, ill, , IV, selected from oxides, nitrides, carbides, hydroxides, or boron carbide of elements in the third period or later of groups, alone or in mixtures thereof, and specifically preferred among them Examples are selected from oxides, nitrides, carbides, hydroxides of titanium, zirconium, niobium, hafnium, tantalum, indium, tin, etc., nitrides and carbides of silicon, alone or in mixtures. The alkali-resistant inorganic substance preferably accounts for 20 to 80% in terms of volume ratio (volume of alkali-resistant inorganic substance/(volume of alkali-resistant inorganic substance + volume of cation exchange resin)) in the first M.
More preferably, it is appropriate to uniformly contain 20 to 60%. In this case, the average particle diameter of the particles or the average wire diameter of the fibrils is preferably one or less of the thickness of the first layer and 20 Itm or less, particularly 10 μm or less. If it deviates from this range, the current efficiency or durability will decrease, although the reason is not clear.

The porous body of the cation exchange resin in the first layer of the present invention has a porosity of 5 to 95%, particularly 10 to 80%. Here, the porosity refers to the specific gravity of the cation exchange resin ρ (g/c
m”), the weight per unit area is a (g/cm2),
When the thickness of the porous body is d (cm 2 ), it is given by the following formula.

Porosity (%) = a/p - d Preferably, inorganic substances, hydrocarbon-based or fluorine-containing low-molecular-weight organic compounds, polymers, surfactants, etc. (hereinafter referred to as pore-forming agents) are used as the cation exchanger forming the first layer or its precursor. A method of forming a film containing 5 to 95% by volume, particularly 20 to 80% by volume, and immersing the film in a solution containing an alkali and/or water to elute the pore-forming agent. The porous layer thus obtained is
It is preferable that the permeability of the pores is small, at least in a state where the film is not wet with a liquid such as water or an aqueous alkaline solution after film formation. In the present invention, the permeability of the pores is determined by the Gurley number for the porous body in a dry state after film formation, that is,
It is evaluated by the number of seconds it takes for 100 ml of air to pass through an area of 6.45 c+n'' under a pressure difference of 0.0132 kg/cm'', and it is preferable that the value is 350 or more. A porous body with higher permeability is not preferable because alkali hydroxide will penetrate from the cathode chamber to the surface of the carboxylic acid layer. Under actual electrolytic conditions, the porous layer may have fine pores in some cases due to the influence of ion flow.

In the present invention, the alkali-resistant polymer having no ion exchange group embedded in the first layer (c) includes an alkali-resistant polymer containing a hydrocarbon polymer having substantially no ion exchange group, Its presence reinforces the mechanical strength, particularly the brittleness, of the first layer and further improves its creep properties. The material is preferably fluoro,
In particular, it is a perfluorocarbon polymer, and various shapes such as webs such as nonwoven fabrics and woven fabrics disclosed in Japanese Patent Publication No. 54-19909, etc., and small fibers (fibrils) can be used. Non-woven and woven webs are
The porosity is preferably 30-95%, especially 40-85
%, and its thickness is preferably 1% within the range of the first layer.
Selected from 0 to 200 μm. The thickness of the web is measured, for example, by sandwiching the woven fabric between thin films of known thickness made of polyethylene terephthalate and measuring the overall thickness with a micrometer. '(g/cm"), web thickness d
'(am), and the weight per unit area a'(g/
cm'') is calculated using the following formula.

Porosity (%) = a'/ρ'・d'
Publication No. Preferred perfluorocarbon polymers include polytetrafluoroethylene, tetrafluoroethylene/hexafluoropropylene copolymer, and tetrafluoroethylene/hexafluoropropylene copolymer.
Examples include perfluoropropyl vinyl ether copolymer and tetrafluoroethylene/perfluoromethyl vinyl ether copolymer.

The cation exchange membrane of the present invention can be produced by a wet film forming method similar to conventional extrusion film forming, in which films of a first layer and a second layer that have been produced in advance are laminated. For example, a mixture of alkali-resistant inorganic particles or fibrils dispersed in a solution or dispersion of a perfluorocarbon polymer having a -3OJ' group (M' is Hl or an alkali metal) is added to the second layer or its precursor. The first layer film and the second layer obtained by directly coating and drying on the film forming the second layer, or by coating the above mixture onto another substrate or film, etc. and drying it. It can be laminated preferably by hot pressing after combining with a layer consisting of the material or its precursor. Furthermore, layers other than the first layer can also be formed by wet film formation.

Polymer liquids in which these fluorine-containing polymers are dissolved or dispersed are disclosed in, for example, JP-A-56-72022 and JP-B-Sho 4g-13.
No. 333 and Japanese Unexamined Patent Publication No. 57-192464, which can be used.

In the present invention, the first layer not only contains dispersed alkali-resistant inorganic particles or small fibers as described above, but also employs, for example, a porous membrane, cloth, or fibril made of polytetrafluoroethylene. By reinforcing the cation exchanger or the cation exchanger containing other alkali-resistant substances, the resistance to peeling and cracking of the core layer is improved compared to membranes without reinforcement of the core layer. This not only improves the mechanical strength of the entire membrane (but also provides a cation exchange membrane with even better long-term stability in current efficiency).

In the fluorine-containing cation exchange membrane used in the present invention, in addition to the first layer and the second layer, a third layer can be further laminated if necessary. As such a preferred example, a thickness can be laminated on the anode side of the second layer. By stacking such third and fourth layers, the mechanical strength and other properties of the film can be further increased (stabilized) compared to a film consisting of only the first and second layers. Can be done.

Furthermore, in addition to the above, the fluoropolymer used in the present invention has the necessary properties in order to firmly laminate the first layer, second layer, third layer, and even fourth layer. A bonding layer can be provided by. Such a bonding layer may be a layer formed by blending a fluorine-containing polymer having a sulfonic acid group or a hydroxyl group and a fluorine-containing polymer having a carboxylic acid group, preferably in a weight ratio of 4/1 to 1/4; It consists of a fluoropolymer having both a sulfonic acid group or a hydroxyl group and a carboxylic acid group, preferably in a ratio of 2/1 to 1/2. Thickness is preferably 5
A layer of ~50 μm is chosen. Such a bonding layer is inserted at the time of bonding the first layer, the second layer, and even the third layer, and
Heated and fused.

In addition, the fluorine-containing cation exchange membrane of the present invention preferably has a second, third or fourth layer near the anode side, if necessary, for example, a web of woven fabric or non-woven fabric such as polytetrafluoroethylene. It is also possible to embed reinforcement material.

The thus formed fluorine-containing cation exchange membrane used in the present invention preferably has an overall thickness of 50 to 600 μm.
m, particularly preferably from 150 to 400 μm.

The above-mentioned fluorine-containing cation exchange membrane can be used as is, but preferably, at least one surface of the cation exchange membrane is provided with a chlorine gas open property on the anode side and a hydrogen gas open property on the cathode side. Particularly preferably, the long-term stability of current efficiency can be further improved by subjecting at least the surface of the ion exchange membrane on the anode side to a treatment for releasing chlorine gas.

As a method of treating the surface of the ion exchange membrane for gas release, a method of forming fine irregularities on the membrane surface (Japanese Patent Publication No. 6)
0-26495), a method of depositing hydrophilic inorganic particles on the membrane surface by supplying a liquid containing iron, zirconia, etc. to an electrolytic cell (Japanese Patent Application Laid-Open No. 152980/1983), electrode activity permeable to gas and liquid A method of providing a porous layer containing particles that do not have
9185) etc. are exemplified. The gas-opening layer on the surface of such an ion exchange membrane not only has the effect of improving the long-term stability of current efficiency, but also can further reduce the voltage during electrolysis.

As the process conditions for electrolyzing an aqueous alkali chloride solution using the fluorine-containing cation exchange membrane of the present invention, known conditions such as those disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 112398/1988 can be employed. For example, preferably 2.
Supplying an aqueous alkali chloride solution of 5 to 5.0 normal (N),
Water or diluted alkali hydroxide is supplied to the cathode chamber as necessary, preferably at 50 to 120°C and 5 to 100 A/
It is electrolyzed in dm2. In such cases, heavy metal ions such as calcium and magnesium in alkali chloride cause deterioration of the ion exchange membrane (so it is preferable to minimize them as much as possible. In addition, in order to prevent the generation of oxygen at the anode as much as possible, hydrochloric acid can be added to the aqueous alkali chloride solution.

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

In the case of arranging the electrodes in the present invention, the electrodes may be arranged in contact with the multilayer membrane or at appropriate intervals, but in particular in the case of the present invention, the electrodes may be arranged in contact with the diaphragm In this case, advantageous sliding voltages can be achieved without disturbance (with low membrane resistance).

[Example] Example 1 A polytetrafluoroethylene porous body with a pore diameter of 2 μm and a membrane thickness of 120 μm, and an ion exchange capacity of 1.2 milliequivalents/
g CF2=CF2/CF2=CFO(CFz
) A 40 μm thick film made of a 5-COoCH-copolymer (copolymer A) was laminated, and an ion exchange capacity of 1.0 milliequivalent/g dry resin was added to the copolymer A layer.
CF2/CF,=CFOCF2CF(CF,)0(CF2),5
Copolymer B and ZrO with a thickness of 50 μm were coated and dried by applying an ethanol mixture containing O3H (copolymer B) and ZrO particles with an average particle size of 5 μm at a volume ratio of 3/2.
□ A mixed layer was formed and hot pressed at 120°C. Next, by impregnating the inside of the porous body with a solution containing copolymer B and zirconyl chloride, and then drying,
A multilayer diaphragm was obtained in which the inner wall of the porous body was made hydrophilic.

Next, a solution in which ZrO2 particles were dispersed in a solution of copolymer B was spray-coated on both sides of the multilayer membrane, and the ZrO
□ A multilayer diaphragm to which fine particles were attached was obtained.

After hydrolyzing the thus obtained multilayer membrane with an aqueous caustic soda solution, a layer of 50 mm thick consisting of copolymer B and ZrO□ was formed.
On the μm layer side, a low hydrogen overvoltage cathode obtained by etching SO3304 punched metal in a 52% by weight caustic solder aqueous solution at 150°C for 52 hours, and on the opposite side of the extraction, a titanium punched metal is etched. A low chlorine overvoltage anode coated with a solid solution of ruthenium oxide, iridium oxide, and titanium oxide is placed in contact with the metal, and the N a O in the cathode chamber is
t (210 g in the anode chamber while keeping the concentration at 45% by weight)
/l of saline solution at 90°C and current density of 30 A.
/dm" for 3 months, the catholyte concentration was changed to 42% by weight, 38% by weight, 35% by weight, 32% by weight, 4% by weight.
Set in the order of 5% by weight and 49% by weight, and at each concentration 5 to 49% by weight.
Electrolysis was carried out for 10 days. After continuing electrolysis at 49% by weight for about one month, the electrolysis was stopped. As a result of membrane observation, no abnormalities such as blistering or peeling were observed in the membrane.The electrolytic evaluation results are shown in Table 1. The moisture content in %NaOH was 3.1% and 16.6%, respectively.The Gurley number of the porous copolymer B layer was 30.
It was over 00.

Table 1 Comparative Example 1 Same as in Example 1 except that a layer of copolymer B having no porous material was formed on the cathode side of the copolymer A layer to a thickness of 50 μm by applying a solution of the copolymer. When tested, the current efficiency was 95% and the sliding voltage was 3 Ov. The current efficiency after 3 months of electrolysis was 93%. When the sample was removed from the electrolytic cell, peeling of the copolymer B layer was observed in a part of the vicinity of the electrolytic surface.

Comparative Example 2 In Example 1, copolymer B was added to the cathode side of the copolymer A layer.
An electrolytic test was conducted in the same manner, except that a layer consisting of a porous material made of polytetrafluoroethylene and a polytetrafluoroethylene porous material was not provided.
Initial current efficiency 92%, sliding voltage 3. IV, the current efficiency decreased to 87% after one month.

Example 2 An electrolytic test similar to that of Example 1 was conducted except that no treatment for releasing chlorine and hydrogen bubbles was performed, and the initial current efficiency was 95% and the sliding voltage was 3.5 V.

Comparative Example 3 In Example 1, copolymer B was added to the cathode side of the copolymer A layer.
A similar test was conducted, except that a mixed layer of ZrO and ZrO□ was not provided, and no treatment was performed to release chlorine and hydrogen bubbles, and the initial current efficiency was 92% and the sliding voltage was 3.
At 6 V, the current efficiency decreased over time.

Example 3 In Example 1, instead of the polytetrafluoroethylene porous membrane on the anode side of the copolymer A layer, CF*=CF
2/CFz=CFOCFzCF (CFz)O(CFz
) Ion exchange capacity made of xsOxF copolymer 1.1
A test was conducted in the same manner as in Example 1 except that a film having a dry resin thickness of 160 μm per milliequivalent/g was used, and the performance was stable for one month at a current efficiency of 95% and a sliding voltage of 3.2 V.

Example 4 In Example 1, the average wire diameter was 4μ instead of ZrO2 particles.
A test was conducted in the same manner as in Example 1, except that SiC whiskers of 1.0 m were used at a volume ratio of 40% to copolymer B, and the current efficiency was 94% and the sliding voltage was 3. It was Ov.

Examples 5 to 8 Instead of the ZrO□ particles in Example 1, electrolytic tests were conducted using membranes in which various inorganic particles were dispersed in copolymer B in various proportions. The results are shown in Table-2.

Table 2 Example 9 Ion exchange capacity 1.2 meq/g CF of dry resin
2=CF, /CF2=CFOfCF2) 3COOC1
13 copolymer (copolymer A) with a thickness of 20+ zm and an ion exchange capacity of 1.5 mm/g dry resin cF
2=cF2/CF,=CFO(CF2) IC0OC:
The thickness of the H3 copolymer (copolymer C) is 150 μm, and the copolymer C and ion exchange capacity u 1 are placed on the copolymer C side of the laminated film.
．． CF2=CFz/CF2=CFOC:F2CF(CF3)0(CF, ),
1:l blend membrane 30 with SO,F (copolymer B)
A multilayer film (1) was obtained by hot pressing a 10 μm thick film consisting of um and copolymer B, with the copolymer B layer being the outermost layer.

Next, 3 layers of ZrO□ were added to the copolymer B layer side of the multilayer film (1).
A Zr(h) porous layer formed from a paste consisting of methyl cellulose containing 0% by weight, water, cyclohexanol, and cyclohexanone was laminated by hot pressing to obtain a multilayer film (2) with a chlorine gas release layer. Further, on the copolymer A side of the multilayer film, an ethanol solution of acidified copolymer B and 5 μm particle size ZrO□ particles (40vo1%) were added.
A composite membrane (3) was obtained by applying a mixed paste consisting of the above, drying and hot pressing.

After hydrolyzing the composite membrane (3) thus obtained in a caustic soda aqueous solution, 52% by weight of caustic soda was added to the ZrO□-containing copolymer B layer layer laminated on the copolymer A side with SUS 304 punched metal. A low hydrogen overvoltage cathode obtained by etching at 150°C for 52 hours in an aqueous solution is placed on a punched titanium metal plate with ruthenium oxide on the opposite side of the extraction.
A low chlorine overvoltage anode coated with a solid solution of iridium oxide and titanium oxide is arranged so as to be in contact with each other, and two
Current density 30 A while supplying 10 g/l saline
/dm2. Electrolysis was performed at a temperature of 90° C. while changing the concentration of caustic soda in the catholyte. The results are shown in Table-3.

Table 3 Example 10 In the multilayer film of Example 10, ZrO□-containing copolymer B
In place of i, a 5ins-containing (40vo 1%) copolymer B' layer consisting of a paste of 2 μm of SiO□ mixed with an ethanol solution of acidified copolymer B was formed.
A film was formed in the same manner and hydrolyzed. After hydrolysis, SiO2 was completely eluted and the B' layer was made porous. Electrolysis was performed in the same manner as in Example 10, with the following results obtained. Ta.

The results are shown in Table 4.

Example 11 Electrolysis was carried out in exactly the same manner as in Example 1O, except that 170-180 g/l of potassium chloride aqueous solution was supplied instead of 210 g/l of saline solution, and Table 5
I got a result like this.

Table-5 Table-4 Toshiko Hiraishi (Representative rlP person (on patent attorney))

Claims (17)

[Claims] (1) When producing 20 to 55% by weight alkali hydroxide, the thickness is 5 μm selected from the following (a) to (c).
A first layer containing a cation exchanger having alkali resistance as described above and a water content of 2 to 7 in a 45% by weight NaOH aqueous solution.
-CO_2M in the range of % by weight and with a thickness of 5 μm or more
An anode chamber of an electrolytic cell in which a fluorine-containing cation exchange membrane consisting of at least two layers including a second layer of a perfluorocarbon polymer having a group (M is an alkali metal) is arranged with the first layer facing the cathode side. A method for producing alkali hydroxide, which comprises supplying alkali chloride to and electrolyzing it. (a) A porous layer made of a cation exchanger containing dispersed alkali-resistant inorganic substances or fibrils (b) A porous layer with small pore penetration made of a cation exchange resin (c) Ion exchange A porous layer of cation exchanger embedded with an alkali-resistant polymer without groups (2) The alkali-resistant inorganic substances contained in the first layer (a) are II_a, III_b, IV_b, V_ of the long periodic table.
Selected from oxides, nitrides, carbides, hydroxides, or boron carbide of elements in the third and later periods of groups b, III_a, and IV_a, singly or in combination, and each having an average particle size or average wire diameter of 20 μm or less Claim (1) consisting of particles or fibrils that are not more than half the thickness of the first layer.
the method of. (3) The method according to claim (1), wherein the content of the inorganic particles contained in the first layer (a) is 20 to 80% by volume. (4) The method according to claim (1), wherein the porous body of the cation exchange resin in the first layer (b) is a fluorine-containing cation exchanger with a Gurley number of 350 or more and a porosity of 5 to 95%. . (5) Claims in which the alkali-resistant polymer having no ion exchange groups in the first layer (c) is a fluorocarbon polymer, and the shape thereof is a web, fibrils, or particles (
Method 1). (6) Claim (1) in which the first layer consists of a combination of at least two or more of (a), (b), and (c).
)the method of. (7) The alkali-resistant cation exchanger constituting the first layer is a perfluorocarbon polymer having -SO_3M group or -OM group (M is an alkali metal), and the thickness of the film is 10 to 200 μm. The method according to claim (1). (8) The second layer has a thickness of 5 to 300 μm and an ion exchange capacity of 0.85 to 1.6 meq/g of dry resin -CO_2
The method according to claim (1), wherein the layer is made of an M group-containing perfluorocarbon polymer. (9) Claims ( Method 1). (10) The fluorine-containing cation exchange membrane is made of a perfluorocarbon polymer having a cation exchange group on the anode side of the second layer, and has a specific resistance smaller than that of the second layer and a thicker third layer. The method of claim (1) comprising a layer. (11) A fluorine-containing cation exchange membrane is provided on the anode side of the second layer or the third layer with a thickness of 10 to 450 μm and a porosity of 30 to
95%, and the fourth layer is made of a porous fluoropolymer whose surface and interior are made hydrophilic (
Method 1). (12) Claims comprising means for opening gas bubbles on at least one surface of the fluorine-containing cation exchange membrane (
Method 1). (13) The method according to claim (1), comprising means for opening hydrogen gas bubbles on at least one surface of the fluorine-containing cation exchange membrane. (14) The method according to claim (1), comprising means for opening chlorine gas bubbles on the surface of the fluorine-containing cation exchange membrane. (15) The method according to claim (14), wherein the means for opening gas bubbles is fine irregularities on the surface of the membrane. (16) The method according to claim (14), wherein the means for opening gas bubbles is a deposit of hydrophilic inorganic particles. (17) The method according to claim (14), wherein the means for opening gas bubbles is a porous layer containing gas- and liquid-permeable particles having no electrode activity on the membrane surface.