JPS6123875B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an ion exchange membrane electrolytic cell, particularly an ion exchange membrane electrolytic cell used when electrolyzing an aqueous alkali chloride solution to obtain caustic alkali at low voltage. As a method for obtaining caustic alkali by electrolyzing an aqueous alkali chloride solution using a diaphragm method, a method using an ion exchange membrane has been proposed to replace the method of using asbestos as a diaphragm for the purpose of obtaining a higher purity and higher concentration of caustic alkali. There is. On the other hand, in recent years, energy conservation has been progressing worldwide, and from this point of view, it is desired to reduce the electrolysis voltage as much as possible in this type of technology. Various methods have been proposed to lower the electrolytic voltage, such as considering the material, composition, and shape of the anode and cathode, or specifying the composition of the ion exchange membrane used and the type of ion exchange group. . Although all of these methods have certain effects, most of them have an upper limit where the concentration of the caustic alkali obtained is not so high.
If this value is exceeded, the electrolytic voltage suddenly increases, the current efficiency decreases, or the sustainability and durability of the electrolytic voltage drop phenomenon deteriorates, so that the electrolytic voltage is not always fully satisfactory industrially. Furthermore, a method has been proposed for producing caustic alkali by electrolyzing an aqueous alkali chloride solution in an electrolytic cell in which a gas- and liquid-permeable anode and a cathode are bonded to the surface of a fluorine-containing cation exchange membrane. (Unexamined Japanese Patent Publication No. 54-112398
(Refer to the publication) This method reduces the electrical resistance caused by the electrolyte, which was previously thought to be unavoidable in this type of technology,
This method is promising as a means to perform electrolysis at a lower voltage than conventional methods because it can minimize the electrical resistance caused by bubbles generated from hydrogen and chlorine gas. In this method, the anode and cathode are bonded to and embedded in the surface of the ion exchange membrane, and the gas generated by electrolysis at the contact interface between the membrane and electrode easily leaves the electrode, and the electrolyte permeates. It is made permeable to gases and liquids so that it can be used. Such porous electrodes usually consist of a uniform mixture of active particles as an anode or a cathode, and a substance that binds them, preferably graphite or other conductive material.
It consists of a porous body formed into a thin layer. However, according to studies conducted by the present inventors, when using an electrolytic cell in which such an electrode is directly bonded to an ion exchange membrane, for example, the anode in the electrolytic cell comes into contact with hydroxide ions that diffuse back from the cathode chamber. Therefore, in addition to the conventional chlorine resistance, alkali resistance is also required, which necessarily requires special and expensive materials.In addition, since the electrode and ion exchange membrane are directly connected, the electrode reaction It has been found that the generated gas may cause partial bulges in the ion exchange membrane, deteriorating membrane performance, and making stable operation difficult over a long period of time. As a result of various studies and examinations aimed at eliminating such drawbacks and finding a means to obtain caustic alkali with as low a cell voltage as possible, the present inventor discovered that a gas having no electrode activity on the surface of a cation exchange membrane. By using an electrolytic cell in which a liquid-permeable porous layer is formed and an anode or a cathode is disposed through the porous layer,
It was discovered that the above purpose could be achieved, and a patent application has already been filed.
It was proposed as No. 55-13012. In this electrolytic cell, the electrolyte is preferably placed in contact with or near the cation exchange membrane, but in such a case, how can hydrogen and chlorine gas generated by electrolysis be transferred smoothly and sufficiently to the electrodes? It is required to be able to remove the ion exchange membrane from the body, and to prevent deformation of the ion exchange membrane during electrolysis without increasing cell voltage. In view of the above, the present inventor conducted various studies with the aim of obtaining an electrolytic cell that allows good gas release and prevents deformation of the ion exchange membrane without increasing cell voltage. The closer the wire is to the electrode surface, the finer the mesh and the thinner the wire diameter, and the farther away from the electrode surface, the coarser the wire diameter.Made by laminating multiple sheets of expanded metal or wire mesh coated as necessary. It has been found that the above object can be achieved by arranging the electrode body. Thus, the present invention provides an electrode vessel in which an electrode body is placed in contact with or in the vicinity of a gas and liquid permeable porous layer that has no electrode activity and is formed on the surface of an ion exchange membrane. An ion exchange membrane characterized in that the electrode body is constructed by laminating a plurality of expanded metals or wire meshes with coarse meshes and large wire diameters in sequence from expanded metals or wire meshes with fine meshes and thin wire diameters. It's in the electrolytic tank. In the present invention, when expanded metal is used as the electrode material that comes into direct contact with the ion exchange membrane surface, the physical properties of the expanded metal are such that the long diameter of the pores is 1.0 to 1.
20mm, short diameter 0.5~10mm, wire diameter 0.1~1.5mm, open area ratio
It is appropriate to have about 30 to 90%. If these physical properties deviate from the above ranges, the cell voltage will increase or the ion membrane will be greatly warped, which is undesirable.
Among these physical properties, the long diameter of the pores is 0.1 to 10
mm, short axis 0.5 to 5 mm, wire diameter 0.2 to 1.3 mm, open area ratio 35
It is particularly preferable to use a ratio of 85% to 85%, since a good gas desorption effect can be expected and stable electrolytic operation can be performed with virtually no increase in cell voltage. Similarly, when wire mesh is used as the electrode body material, its physical properties are 5 to 160 mesh, wire diameter 0.1
It is appropriate to adopt a thickness of about 2 mm. If 6 to 100 meshes and wire diameters of 0.15 to 1.8 mm are used, a good gas release effect can be expected, and there will be virtually no increase in cell voltage, resulting in stable electrolysis operation. This is particularly preferable because it can be done. In addition, the physical properties of the electrode body material located furthest away from the ion exchange membrane surface, so to speak, are such that when it is made of expanded metal, the long diameter of the pores is 6 to 150 mm, and the short diameter is 3 to 60 mm. , wire diameter 0.4~11
It is appropriate to adopt a hole area ratio of 30 to 93%.
If these physical properties deviate from the above ranges, gas release may be impaired or fine mesh may not be retained sufficiently. Among these, the long axis of the hole is 7 to 140 mm, the short axis is 4 to 50 mm, the wire diameter is 0.6 to 10 mm,
It is particularly preferable to use a porosity of 40 to 90%, since a sufficient gas release effect and a sufficient retention effect can also be expected. Further, when a wire mesh is used, it is appropriate to use a wire mesh having physical properties of 4 to 100 mesh and a wire diameter of about 0.1 to 3 mm. In particular, it is particularly preferable to use 5 to 80 meshes and a wire diameter of 0.2 to 2 mm. These expanded metals and wire meshes can be used in appropriate combinations, and the expanded metals and wire meshes located in the middle are selected as appropriate from those with small physical properties to those with large physical properties as described above. . When stacking these electrode bodies, it is possible to use, for example, a structure in which the laminate is fitted and fixed in advance using a suitable frame, or ion exchange is performed each time during use. It is also possible to arrange them sequentially from narrow to coarse on the membrane surface and integrate them during use or when assembling the electrolytic cell by means described later. The expanded metal or wire mesh material constituting these electrode bodies includes, for example, stainless steel, nickel, or iron for the cathode side, and titanium, tantalum, niobium, zirconium, platinum group metals, and alloys thereof, and the like for the anode side. Coatings of platinum group metal oxides and mixtures thereof may be used. In the present invention, the porous layer used in conjunction with the ion exchange membrane is at least one of the anode side and the cathode side. Such a porous layer is a thin layer that is permeable to liquid and gas, and its physical properties include an average pore diameter of 0.01 to 200μ and a porosity of
10-99%, thickness 0.01-100μ, preferably average pore diameter 0.1-100μ, porosity 20-95%, thickness 0.1-50
It is appropriate to have μ. In order to obtain such a porous layer, for example, powder or granules of a porous layer-forming material are formed into a thin layer using a binder made of a fluorine-containing polymer such as polytetrafluoroethylene, if necessary. do. As the porous layer-forming material, any material can be used as long as it has corrosion resistance under the conditions of use, but in particular, materials from Group A of the periodic table (preferably germanium, germanium,
-B group (preferably titanium, zirconium, hafnium), -B group (preferably niobium, tantalum), iron group metals (iron, cobalt, nickel), chromium, manganese, etc. Alternatively, its oxide, hydroxide, nitride or carbide may be used. In this way, the porous layer having no electrode activity formed on the surface of the ion-exchange membrane preferably contains 0.01 to 100 mg of particulate matter having no electrode activity in the porous layer.
cm ² , particularly 0.1 to 10 mg/cm ² . In the electrolytic cell of the present invention, as a specific means for using the electrode body, preferably, for the porous layer,
It is used by bringing the electrode body into contact and pressing lightly, for example, at a pressure of up to 1 kg/cm ² . Examples of means for contacting and pressing include using a suitable frame and tightening it with springs or screws, or pressing the electrode chamber from the opposite membrane surface (electrode chamber) side of the ion exchange membrane surface. Other appropriate means, such as pressing the porous layer on the electrode with liquid pressure, may be employed. However, in the electrolytic cell of the present invention, the electrode body does not necessarily need to be placed in contact with the porous layer;
Depending on the case, they may be arranged at intervals of, for example, 0.1 to 5 mm. The ion exchange membrane used in the present invention is made of a polymer containing a cation exchange group such as a carboxyl group, a sulfonic acid group, a phosphonic acid group, or a phenolic hydroxyl group, and such polymers include fluorine-containing polymers. It is particularly preferable to employ combination. Examples of fluorine-containing polymers containing ion-exchange groups include those that react with vinyl monomers such as tetrafluoroethylene and chlorotrifluoroethylene and ion-exchange groups such as sulfonic acid, carboxylic acid, and phosphoric acid groups, or that can be converted into ion-exchange groups. A copolymer with a perfluorinated vinyl monomer having a functional group is preferred.
Also usable are trifluoroethylene membrane polymers into which ion exchange groups such as sulfonic acid groups have been introduced, and styrene divinylbenzene into which sulfonic acid groups have been introduced. Among these, it is preferable to use polymers having the following structures (a) and (b), respectively. (a) (−CF ₂ −CXX′)−

[Formula] Here, X is F, Cl, H or -CF ₃ , and X' is
or CF ₃ (CF ₂ )m, where m is 1 to 5,
Y is selected from the following: (-( _CF2 ) _-x -A,-O( _-CF2 ) _-xA , x, y, z are all 1 to 10, and Z, R _f is -F
or a group selected from _-C1-10 perfluoroalkyl groups. A is −COOM, −SO ₃ M or −CN, −COF, −
SO ₂ F, −COOR ₁ , −COOM, −CONR ₂ R ₃ , −
By hydrolysis or neutralization of SO ₂ NR ₂ R ₃ , etc., -
Indicates a functional group that can be converted to COOM or _-SO3M .
R ₁ is a C _1-10 alkyl group, M is hydrogen, an alkali metal, or a quaternary ammonium group, R ₂ ,
_R3 represents H or a _C1-10 alkyl group. In the present invention, the concentration of carboxylic acid groups in the film per gram of dry resin made of these copolymers is
It has been found that when a fluorine-containing cation exchange membrane having a fluorine content of 0.5 to 4.0 milliequivalents is used, the intended purpose of the present invention can be particularly fully achieved. When the concentration of carboxylic acid groups per dry resin is 0.8 to 2.0 milliequivalents, the objects of the present invention can be sufficiently and stably achieved, and in particular, the durability of performance can be improved.
It is preferable because it can increase durability. In order to achieve such ion exchange capacity, the above (a) and
In the case of a polymer consisting of polymerized units of (b), preferably (b)
Suitably, the proportion of polymerized units is 1 to 40 mol %, particularly 3 to 20 mol %. Preferred cation exchange membranes used in the present invention are often composed of non-crosslinkable copolymers, and their molecular weight is preferably about 100,000 to 200,000.
10,000, especially preferably 150,000 to 1,000,000. Various methods can be used to produce the polymer forming the ion exchange membrane, but preferably one or more of the monomers (a) and (b) are used, and if necessary, a third monomer is used. It can also be produced by copolymerizing the monomers. For example, as the third monomer, CF ₂ =
By selecting CFOR _f (R _f is a C _1-10 perfluoroalkyl group), flexibility can be imparted to the obtained film, or CF ₂ =CF−CF=CF ₂ , CF ₂ =
By using a divinyl monomer such as CFO(CF ₂ ) _1-3 CF=CF ₂ in combination, the resulting copolymer can be crosslinked and mechanical strength can be imparted to the membrane. Copolymerization of the fluorinated olefin monomer and a polymerizable monomer having an ion exchange group or a functional group convertible into the group, and further a third monomer can be carried out by any known method. . That is, polymerization can be carried out by catalytic polymerization, thermal polymerization, radiation polymerization, etc., using a solvent such as a halogenated hydrocarbon, if necessary.
Furthermore, there is no particular limit to the method for forming an ion exchange membrane from a polymer, such as press molding, roll molding,
Any known means such as extrusion molding, solution casting, dispersion molding, powder molding, etc. may be employed as appropriate. The thickness of the membrane thus obtained is between 50 and 500 mm.
μ, preferably 100 to 400 μ. In addition, if the copolymerizability is not the ion exchange group itself but a functional group that can be converted into the group before or after the polymer film formation process, preferably after film formation, by appropriate treatment according to the copolymerizability, These functional groups are converted into ion exchange groups. For example −CN, −
In the case of COF, -SO ₂ F, -COOR ₁ (M, R ₁ to _{R 3} are the same as above), it is converted into a carboxylic acid group by hydrolysis or neutralization with an acid or alkaline alcohol solution, or When the functional group is a double bond
It is converted into a carboxylic acid group by reacting with COF ₂ . Furthermore, the cation exchange membrane used in the present invention is
If necessary, during film formation, an olefin polymer such as polyethylene or polypropylene, preferably a fluorine-containing polymer such as polytetrafluoroethylene or a copolymer of ethylene and tetrafluoroethylene, may be mixed and molded. Further, it is also possible to use a cation exchange membrane reinforced with a reinforcing material such as a metal wire, net, or a synthetic resin net, or provided with dimensional stability. Note that FIG. 1 is a schematic explanatory diagram of the ion exchange membrane electrolytic cell of the present invention. In FIG. 1, 1 is an ion exchange membrane, and 2 and 3 are porous layers on the anode side and the cathode side, respectively, which have no electrode activity and are bonded to the ion exchange membrane. These porous layers are preferably contacted with a fine-mesh anode body 4 and a cathode body 5. The fine-mesh anode body and cathode body each have a coarse-mesh anode body 6
and cathode body 7 are laminated to hold the fine-mesh anode body and cathode body. In the case of alkaline chloride electrolysis, the anode chamber is supplied with an aqueous alkali chloride solution (MCl+H ₂ O), while the cathode chamber is supplied with water (H ₂ O) or diluted caustic alkali. At the anode, chlorine is generated by electrolysis, and alkali metal ions (M ⁺ ) are transferred to the cathode chamber through the ion exchange membrane. In the cathode chamber, hydrogen is generated by electrolysis, and hydroxide ions are also generated. These hydroxide ions react with alkali metal ions transferred from the anode to produce caustic alkali. In the above, the present invention has been particularly described as an electrolytic cell for electrolyzing an aqueous alkali chloride solution, but the electrolytic cell of the present invention can be similarly applied to other water electrolysis, electrolysis of an aqueous hydrogen halide solution such as hydrochloric acid, and an electrolytic cell for an aqueous alkali carbonate solution. Of course, it can be used for. The present invention will be explained in more detail below. Example 1 10 g of titanium oxide, 1.0 g of polytetrafluoroethylene with a particle size of 1 μm or less, 10 c.c. of water, and 10 c.c. of isopropyl alcohol were mixed and kneaded to obtain a paste. The paste has an ion exchange capacity of 1.45meq/g
A dry resin, screen printed on one side of a cation exchange membrane made of a copolymer of polytetrafluoroethylene and CF ₂ = CFO (CF ₂ ) ₃ COOCH ₃ with a thickness of 220 μ, and titanium oxide of 1.5 mg/cm ² A porous layer containing was obtained. Next, a porous layer containing iron oxide at a rate of 1 mg/cm ² and having a porosity of 90% was deposited on the other side of the ion exchange membrane in the same manner. Then 150℃, 20Kg/cm ²
These porous layers were pressed onto the ion exchange membrane under the following conditions, and then immersed in a 25% by weight aqueous sodium hydroxide solution at 90° C. for 16 hours to hydrolyze the ion exchange membrane. Next, the above porous layer made of titanium oxide was used as a cathode body with a short diameter of 2 mm and a total size of 20 cm x 25 cm.
Smooth nickel expanded metal with a long diameter of 5 mm, wire diameter of 0.3 mm, and thickness of 0.3 mm, a short diameter of 10 mm, and a long diameter of 20 mm.
A cathode body made of a layered layer of smooth nickel expanded metal with a wire diameter of 2.0 mm, a wire diameter of 2.0 mm, and a thickness of 2.0 mm was pressed against a porous layer made of titanium oxide with the expanded metal of fine mesh. Also, ruthenium oxide
The anode body is made from a laminate of two expanded metals that are coated with iridium oxide-titanium oxide (3:1:4) and have the same shape and dimensions as the cathode body above, except that the material is titanium. The narrow expanded metal side was pressed against the porous layer made of iron oxide. Then use such a configuration to add 5N to the anode chamber.
Water was supplied to the -NaCl aqueous solution into the cathode chamber, and electrolysis was carried out while maintaining the sodium chloride concentration in the anolyte at 4N and the caustic soda concentration in the catholyte at 35% by weight, and the following results were obtained. Current density (A/dm ² ) Cell voltage (V) 20 2.96 40 3.20 Furthermore, when electrolysis was carried out at a current density of 40 A/dm ² , the current efficiency for producing caustic soda was 93%. Example 2 In the same manner as in Example-1, an ion exchange membrane in which a porous layer made of titanium metal and tantalum oxide was combined was used on the anode side and the cathode side, respectively, and the electrolyte used in Example-1 was used. Electrolysis was carried out in exactly the same manner as in Example 1, except that the laminates were placed at a distance of 1.5 mm from the porous surface without contacting the porous surface, and the following results were obtained. Obtained. Current density (A/dm ² ) Cell voltage (V) 20 3.08 40 3.35 In addition, when electrolysis was carried out at a current density of 40 A/dm ² , the current efficiency for producing caustic soda was 94.5%. Comparative Example The same ion exchange membrane structure as in Example 1 was used, and the cathode was laminated with a 5 mm thick nickel perforated plate with 20 mesh nickel wire mesh and 50 mesh holes with an aperture ratio of 60%. The former was placed in contact with the ion exchange membrane, and similarly the anode was made of ruthenium oxide - iridium oxide - titanium oxide (3:1:
4) Similar titanium wire mesh coated with (20 mesh)
Electrolysis was carried out in exactly the same manner as in the example except that a titanium perforated plate (50 mesh) and a titanium perforated plate (50 mesh) were placed in contact with the ion exchange membrane, and the following results were obtained. Current density (A/dm ² ) Cell voltage (V) 20 3.03 40 3.31 Furthermore, when electrolysis was carried out at a current density of 40 A/dm ² , the current efficiency for producing caustic soda was 86%.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of an electrolytic cell using the electrode body of the present invention. 1... Ion exchange membrane, 2, 3... Porous layer on the anode side, porous layer on the cathode side, respectively, 4, 5... Fine anode, cathode, respectively, 6, 7... Coarse anode, cathode, respectively. .

Claims (1)

[Claims] 1. An electrolytic cell in which an electrode body is placed in contact with or in the vicinity of a gas and liquid permeable porous layer having no electrode activity formed on the surface of an ion exchange membrane, wherein the electrode body is An ion-exchange membrane electrolytic cell characterized in that it is constructed by laminating a plurality of expanded metals or wire meshes with fine meshes and thin wire diameters, followed by a plurality of expanded metals or wire meshes with coarse meshes and thick wire diameters.