JPS6340876B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a cation exchange membrane for electrolysis, and particularly to a cation exchange membrane suitable for electrolysis of aqueous solutions such as water, acid or alkali aqueous solutions, alkali halides, and alkali carbonate aqueous solutions. The method for obtaining caustic alkali and chlorine by electrolyzing the above aqueous solution, especially aqueous alkali chloride solution, has recently been replaced by the mercury method from the viewpoint of pollution prevention, and the diaphragm method has been adopted.
Furthermore, a method using an ion exchange membrane has been put into practical use for the purpose of obtaining highly purified and highly concentrated caustic alkali with high efficiency. On the other hand, from the viewpoint of energy saving, it is required in this type of electrolysis to lower the electrolysis voltage as much as possible, and various means have been proposed for this purpose.
Even now, the purpose has not been fully achieved because the voltage reduction effect is not sufficient or the electrolytic cell is complicated. The present inventor continued his research in order to perform electrolysis of an aqueous solution with as low a load voltage as possible, and found that a conductive or non-conductive material was added to the surface facing at least one of the anode or the cathode of the cation exchange membrane. It has surprisingly been found that by using a cation exchange membrane having a porous layer formed by bonding microfibers, the above object can be satisfactorily achieved. The effect of reducing electrolytic voltage by using a cation exchange membrane having such a porous layer on its surface varies depending on the material and formation of the microfibers, and the porosity and thickness of the porous layer formed by the fibers. however,
The porous layer does not have electrical conductivity as described below,
It is an unexpected phenomenon that such a reduction effect is exhibited even when the fibers are formed from microfibers that do not have ion exchange performance. Furthermore,
When using an ion exchange membrane having such a porous layer, the electrode does not necessarily need to be placed in contact with the membrane, and even if it is placed away from the membrane surface, the electrolytic voltage can be reduced. The microfibers bound to the surface of the cation exchange membrane preferably have a diameter of 0.01 to 50μ, especially 0.1 to 50μ.
40μ and lengths from 0.1 to 300μ, in particular from 1 to 200μ, are used. and asbestos ratio (length/diameter ratio)
Those with a number of 5 or more, especially 10 or more are preferably used. The amount of these microfibers attached to the membrane surface varies depending on the porosity and thickness of the porous layer to be formed, and also varies depending on the shape and material of the fibers. It has been found that it is preferable to use from 0.001 to 50 mg, in particular from 0.005 to 10 mg, per cm ² of area. If the amount of fibers attached is too small, the desired effect cannot be achieved. On the other hand, if the amount of attached fibers is too large, it may lead to an increase in the electrolytic voltage, which is not preferable. The fibers forming the gas- and liquid-permeable porous layer provided on the surface of the cation exchange membrane of the present invention are made of a conductive or non-conductive material as described above. Such fibers preferably have a high crystalline content, therefore high hardness, and also high corrosion resistance and heat resistance. When forming a porous layer on an ion exchange membrane using fibers made of such materials, each fiber always maintains a stable fiber shape, and as a result, a porous layer that always has predetermined physical properties is obtained, making it an excellent choice. performance is achieved. The fibers used in the present invention include metal fibers, carbon (graphite, carbon) fibers, organic polymer fibers,
Non-oxide ceramic fibers are preferably used.
The metal fiber is preferably -B in the synchronous table.
Group (copper, silver, etc.), -A group (aluminum, thallium, etc.), -B group (titanium, zircon, hafnium, etc.), -B group (niobium, tantalum),
Fibers of single or alloyed iron group metals (iron, cobalt, nickel, etc.) or fibers of their oxides are used. In addition, graphite fibers and carbonaceous fibers are both used as carbon fibers, and fluorine-containing polymer fibers, polypropylene fibers, polysulfone fibers, polyimide fibers, polyphenylene oxide fibers, etc. are used as organic polymer fibers. Ru. Further, as the non-oxide ceramic fibers, preferably carbide, nitride, silicide, boride or sulfide fibers are used. And for example,
Carbides include HfC, TaC, SiC, B ₄ C, WC,
Examples include TiC, CrC, UC, and BeC, examples of nitrides include BN, Si ₃ N ₄ , TiC, and AlN, and examples of silicides include Cr, Mo, W, Ti, and Nb.
Or Zr silicide is exemplified, and borides include Ti, Zr, Hf, Ce, Mo, W, Ta, Nb or
Examples include borides of La, and sulfides include:
Examples include Fe ₃ S ₄ and MoS ₂ . Among them, SiC,
_B4C , BN, _Si3N4 , TiN, _AlN , _MoSi2 , _LaB6
Fibers are often used. The form used in the present invention may be a monofilament (single thread) or a multifilament such as a twisted yarn, and either form may be used. When these conductive or non-conductive fibrils are bonded to the surface of an ion exchange membrane to form a porous layer, it is preferably done as follows. That is, the fine fibers forming the porous layer are prepared by preparing a dispersion, syrup, or paste containing the fibers using appropriate auxiliary agents or media as necessary, and ionizing them in such a form. Applied to the exchange membrane surface. When preparing such fiber-containing dispersions, syrups, or pastes, polytetrafluoroethylene or the like is used in combination with a fluoropolymer as a binder, although it is not essential, if necessary. Furthermore, thickeners such as celluloses such as carboxymethyl cellulose, methyl cellulose, and hydroxyethyl cellulose, and water-soluble substances such as polyethylene glycol, polyvinyl alcohol, polyvinyl pyrrolidone, sodium polyacrylate, polymethyl vinyl ether, casein, and polyacrylamide are used. Ru. These binders or thickeners are preferably used in an amount of 0 to 50% by weight, particularly 0.5 to 30% by weight, based on the powder. In addition, if necessary, a suitable surfactant such as a long-chain hydrocarbon or a fluorinated hydrocarbon may be added to facilitate the formation of the porous layer. The bonding of the microfibers forming the porous layer to the cation exchange membrane can be achieved by, for example, the above-mentioned fibrous material and, if necessary, a binder,
This is carried out by thoroughly mixing a thickener in a suitable medium such as alcohol, ketone, hydrocarbon, etc. to obtain a paste of the mixture, and transferring or printing this onto the membrane surface. Furthermore, in the present invention, the fibers can be attached to the ion exchange membrane surface by spraying or spraying a syrup or slurry containing the fibers directly onto the membrane surface instead of using the paste-like mixture containing the fibers. It will be done. The fibrous material forming the porous layer attached to the ion exchange membrane surface is then heated preferably at 80-220°C and 1-150°C, preferably using a press or roll.
It is heated and pressed onto an ion exchange membrane at a pressure of Kg/cm ² to preferably embed a portion of the fibers or fiber groups in the membrane surface. The porous layer formed from the fibers or groups of fibers thus bonded to the membrane surface preferably has a porosity of 10%.
In particular, the thickness should preferably be 0.01 to 200μ, particularly 0.1 to 100μ. In the present invention, the ion exchange membrane in which a porous layer is formed on the membrane surface has a cation exchange group such as a carboxylic acid group, a sulfonic acid group, a phosphonic acid group, or a phenolic hydroxyl group, preferably a fluorine-containing polymer. Membranes consisting of coalescence are preferred. Such a film is
For example, those having a copolymer structure of a vinyl monomer such as tetrafluoroethylene or chlorotrifluoroethylene and a fluorovinyl monomer containing an ion exchange group such as a sulfonic acid, carboxylic acid, or phosphoric acid group are preferable. In particular, it is particularly preferable to use polymers having the following structures (a) and (b). (a) (−CF ₂ −CXX′) −, (b)

[Formula] Here, X is F, Cl, H or -CF ₃ , X' is X or CF ₃ (CF ₂ ) - _n , m is 1 to 5,
Y is selected from the following: ( _-CF2 ) _-x A, -O( _-CF2 ) _-x A,

[Formula] −CF ₂ −O(−CF ₂ )− _x A,

【formula】

X, Y, and Z are all 0 to 10, and Z, R _f
is selected from -F perfluoroalkyl groups having 1 to 10 carbon atoms. In addition, A is _-SO3M , -COOM or _-SO2F , which can be converted into these groups by hydrolysis,
-CN, -COF or -COOR, M represents hydrogen or an alkali metal, and R represents an alkyl group having 1 to 10 carbon atoms. The cation exchange membrane used in the present invention preferably has an ion exchange capacity of 0.5 to 4.0 meq/g dry resin, particularly 0.8 to 2.0 meq/g dry resin. In order to provide such an ion exchange capacity, in the case of an ion exchange membrane made of a copolymer consisting of the polymerized units of (a) and (b) above, the polymerized units of (b) preferably contain 1 to 40 mol%,
In particular, 3 to 25 mol% is suitable. The cation exchange membrane used in the present invention does not necessarily need to be formed from one type of polymer, nor does it need to have only one type of ion exchange group. For example, a laminated membrane of two types of polymers with smaller ion exchange capacity on the cathode side, or an ion exchange membrane with a weakly acidic exchange group such as a carboxylic acid group on the cathode side and a strong acidic exchange group such as a sulfonic acid group on the anode side are also used. can. These ion-exchange membranes are manufactured by various conventionally known methods, and if necessary, these ion-exchange membranes are preferably made of cloth, net, or other woven fabric, non-woven fabric, or metal made of a fluorine-containing polymer such as polytetrafluoroethylene. It can be reinforced with mesh, porous material, etc. Further, the thickness of the ion exchange membrane of the present invention is preferably 20 to 500μ, preferably 50 to 500μ.
Forced to 400μ. When forming a porous layer as described above on the anode side or cathode side of these ion exchange membranes, or even on the membrane surfaces on both electrode sides, the membrane is coated with appropriate ions that do not cause decomposition of the ion exchange groups it has. When the exchange group is a carboxylic acid group, for example, it is preferably an acid or ester type, and when it is a sulfonic acid group, it is preferably an -SO ₂ F type. Either type of electrode can be used in the membranes of the invention. For example, porous electrodes such as perforated plates, mesh or expanded metal are used. As a porous electrode, the major axis is 1.0 to 10 mm, the minor axis is 0.5 to 10 mm, and the wire diameter is
Expanded metal with a pore size of 0.1 to 1.3 mm and a porosity of 30 to 90% is exemplified. Although a plurality of plate electrodes can be used, it is preferable to use a plurality of plate electrodes with different porosity, with the one with the smaller porosity being used on the side closer to the membrane. As the anode material, platinum group metals, their conductive oxides, or their conductive reduced oxides, etc. are usually used, while as the cathode, platinum group metals, their conductive oxides, iron group metals, etc. are used. Ru. In addition, platinum group metals include platinum, rhodium, ruthenium,
Examples include palladium and iridium, and iron group metals include iron, cobalt, nickel, Raney nickel, stabilized Raney nickel, stainless steel,
Alkali-etched stainless steel (Special Publication Showa 54-)
19229), Raney-Nitzkelmecki cathode (Japanese Patent Application Laid-Open No. 1982-112785), and Rodan-Nitzkelmecki cathode (Japanese Patent Application Laid-open No. 115676-1982). If a hollow electrode is used, it can be formed from the material itself forming the anode or cathode. However, when platinum group metals or conductive oxides thereof are used, it is preferable to coat the surface of an expanded valve metal such as titanium or tantalum with these substances. When arranging electrodes in the present invention, the electrodes may be arranged in contact with the ion exchange membrane or may be arranged at appropriate intervals. Rather than firmly pressing the electrode against the ion exchange membrane through the porous layer, the electrode is preferably gently pressed against the porous layer at, for example, 0 to 2.0 kg/cm ² . In addition, in the case where a porous layer is provided only on one surface of the anode side or the cathode side of the ion exchange membrane in the present invention, the electrode placed on the ion exchange membrane side where no porous layer is provided is also placed on the ion exchange membrane surface. They can be placed in contact or without contact. 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 an aqueous alkali chloride solution, materials resistant to aqueous alkali chloride solutions and chlorine are used in the anode chamber, such as valve metal and titanium, and in the case of the cathode chamber. Iron, stainless steel, or nickel, which are resistant to alkali hydroxide and hydrogen, are used. The process conditions for electrolyzing an aqueous alkali chloride solution in the present invention include the above-mentioned JP-A-54-
Known conditions such as those in Publication No. 112398 can be employed. For example, an aqueous alkali chloride solution of 2.5 to 5.0 normal (N) is preferably supplied to the anode chamber, and water or diluted alkali hydroxide is supplied to the cathode chamber, preferably at a temperature of 80°C to 120°C and a current density of 10 to 100A/ Electrolyzed at dm ² . In such a case, heavy metal ions such as calcium and magnesium in the aqueous alkali chloride solution cause deterioration of the ion exchange membrane, so it is preferable to keep them as small as possible. Furthermore, an acid such as hydrochloric acid can be added to the aqueous alkali chloride solution in order to prevent the generation of oxygen at the anode as much as possible. The above description has mainly explained the use of the membrane of the present invention using the electrolysis of aqueous alkali chloride solutions as an example, but it can be similarly applied to the electrolysis of water, halogen acids (hydrochloric acid, hydrobromic acid), and alkali carbonate. Of course. Next, the present invention will be explained by examples. Example 1 Graphite fiber with an average fiber length of 0.13 mm and an average single fiber diameter of 12.5 μm (trade name: Kurekachi Yotsupu, Kureha Chemical Industry Co., Ltd.)
), methyl cellulose (viscosity of 2% aqueous solution
1500CPS) 0.4 parts, water 19 parts, cyclohexanol
A mixture containing 0.3 part of cyclohexanone and 0.1 part of cyclohexanone was kneaded to obtain a paste. The paste was applied to the ion exchange capacity of the printing substrate using a Tetron screen with a mesh number of 110 and a thickness of 117 μm, a printing plate with a screen mask of 30 μm thick underneath, and a urethane rubber squeegee. is 1.44meq/g - dry resin, thickness
Polytetrafluoroethylene with 280μm
Screen printing was performed on the cathode side surface of an ion exchange membrane made of a copolymer of CF ₂ =CFO(CF ₂ ) ₃ COOCH ₃ . The resulting printed layer on the cathode side of the ion exchange membrane was dried in air to solidify the paste. On the other hand, on the anode side surface of the ion exchange membrane, a particle size of 2~
10 parts of 10 μm titanium oxide (rutile type) powder, modified PTFE particles with a particle size of 0.5 μm or less whose polytetrafluoroethylene surface is coated with a copolymer of polytetrafluoroethylene and CF ₂ = CFO (CF ₂ ) ₃ COOCH ₃ 1 part, methylcellulose (viscosity of 2% aqueous solution
1500CPS) 0.3 parts, water 14 parts, cyclohexanol
The paste obtained by kneading a mixture containing 0.2 part of cyclohexanone and 0.1 part of cyclohexanone was
75μm Tetron screen with thickness below
Printing was carried out in exactly the same manner as described above, except that a printing plate with a 30 μm screen mask was used, and then dried. Thereafter, the graphite fiber layer and the titanium oxide layer were pressed onto the ion exchange membrane under conditions of a temperature of 140° C. and a pressure of 30 Kg/cm ² . The amount of graphite fibers and titanium oxide attached to the membrane surface was 1.0 mg and 1.2 mg per 1 cm ² of the membrane surface, respectively. After this, it was heated to 90°C and immersed in a 25% by weight aqueous solution of caustic soda.
The ionic membrane was hydrolyzed by soaking for 16 hours. On the anode side of the ion membrane, an anode with a low chlorine overvoltage made of expanded titanium metal (minor axis 2.5 mm, major axis 5.0 mm) coated with a solid solution of ruthenium oxide, iridium oxide, and titanium oxide, and on the cathode side. SUS304 expanded metal (minor diameter 2.5
mm, major axis 5.0 mm) was etched in a 52% by weight aqueous solution of caustic soda at 150°C for 52 hours to have a low hydrogen overvoltage, and the cathode was brought into pressure contact with the cathode.
Supply a 5N aqueous sodium chloride solution to the anode chamber and water to the cathode chamber, and maintain the concentration of the sodium chloride aqueous solution in the anode chamber at 4N and the concentration of the caustic soda aqueous solution in the cathode chamber at 35% by weight at 90℃, 40A/ Electrolysis was carried out at dm ² and the following results were obtained. Cell voltage Current efficiency 3.23V 92% Comparative example 1 Ion exchange capacity 1.44meq/g - resin, thickness
Polytetrafluoroethylene with 280 μm
Using an ion exchange membrane made of a copolymer of CF ₂ = CFO (CF ₂ ) ₃ COOCH ₃ and without attaching a porous layer to the membrane surface, electrolysis was carried out in the same manner and under the same conditions as in Example 1. The results were obtained. Cell voltage Current efficiency 3.57V 94% Example 2 In Example 1, carbonaceous fibers with an average fiber length of 0.13mm and an average single fiber diameter of 14.5μm were used instead of graphite fibers, and the carbonaceous fibers were placed on the cathode side membrane surface of the ion membrane. Electrolysis was carried out in exactly the same manner as in Example 1, except that 0.9 mg/cm ² of was deposited on the membrane surface, and the following results were obtained. Cell voltage Current efficiency 3.24V 92% Example 3 In Example 1, instead of screen printing graphite fibers and attaching them to the ion exchange membrane,
Except for the fact that stainless steel fibers of 150 μm and 10 μm in thickness were crimped onto the cathode side membrane surface at a rate of 2 mg per 1 cm ² of membrane.
Electrolysis was carried out in exactly the same manner as in Example 1, and the following results were obtained. Cell voltage Current efficiency 3.25V 92% Example 4 In Example 1, instead of graphite fibers, alumina fibers with an average single fiber diameter of 3 μm were crushed to a length of 100 μm or less, and were applied to the cathode side membrane surface of the ion membrane. Electrolysis was carried out in exactly the same manner as in Example 1, except that 0.8 mg of the alumina fiber was attached per 1 cm ² of the membrane surface,
The following results were obtained. Cell voltage Current efficiency 3.24V 92% Example 5 In Example 1, instead of graphite fibers, zirconia fibers with an average single fiber diameter of 6 μm were crushed to a length of 100 μm or less, and were applied to the cathode side membrane surface of the ion membrane. Electrolysis was carried out in exactly the same manner as in Example 1, except that 1.1 mg of the zirconia fiber was attached per 1 cm ² of the membrane surface, and the following results were obtained. Cell voltage Current efficiency 3.24V 92% Examples 6 to 8 In Example 1, instead of titanium oxide, iron oxide was deposited on the membrane surface as a porous layer on the anode side at a rate of 0.3 mg/ ^cm2 , and the porous layer on the cathode side was Table 1 shows the results of electrolysis carried out in exactly the same manner as in Example 1, except that a membrane having fibers of the materials and shapes shown in Table 1 attached at a rate of 1.0 mg/cm ² was used.

【table】

【table】

Claims (1)

[Scope of Claims] 1. A cation exchange membrane having a gas- and liquid-permeable porous layer that does not function as an electrode on at least one surface of the membrane, the porous layer being electrically conductive or non-conductive. A cation exchange membrane for electrolysis characterized by being composed of microfibers. 2 Conductive or non-conductive microfibers with a diameter of 0.01
~50μ, length 0.1~1000μ Claim 1
membrane. 3 The gas and liquid permeable porous layer has a porosity of 10 to
99% and a thickness of 0.01 to 1000μ. 4 The conductive or non-conductive microfibers are carbon fibers,
4. A membrane according to claim 1, comprising fluoropolymer fibers or non-oxide ceramic fibers. 5. Claims 1 to 5 in which 0.001 to 50 mg of conductive or non-conductive microfibers are bound per cm ² of membrane surface.
Any one membrane of 4. 6. The membrane according to any one of claims 1 to 5, wherein the cation exchange group is a sulfonic acid group, a carboxylic acid group, or a phosphoric acid group. 7. The membrane according to any one of claims 1 to 6, wherein the electrolysis is of water or an aqueous solution of an acid, alkali, alkali halide, or alkali carbonate.