JPS6123876B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a novel cation exchange membrane for electrolysis for producing alkali hydroxide and chlorine by electrolyzing an aqueous alkali chloride solution. In electrolytic cells for producing alkali hydroxide and chlorine by electrolyzing aqueous alkali chloride solutions, the diaphragm method is becoming mainstream instead of the mercury method from the viewpoint of pollution. Furthermore, in recent years, electrolytic cells using ion exchange membranes have been attracting attention as an alternative to asbestos membranes in order to obtain highly purified and highly concentrated alkali hydroxide with high energy efficiency. On the other hand, energy conservation is becoming a top priority worldwide, and from this point of view it is desirable to lower the cell voltage as much as possible even in this type of technology. Recently, a so-called SPE (Selid Polymer Electrolyte) type electrolytic cell using a fluorine-containing cation exchange membrane and having gas and liquid permeable anode and cathode layers bonded to the membrane surface has been developed in an electrolytic cell using an ion exchange membrane. Electrolytic cells have been proposed. (Japanese Unexamined Patent Publication No. 54-112398) When such an electrolytic cell is used, the electrical resistance caused by the electrolyte and the bubbles based on generated hydrogen and chlorine gas, which were conventionally considered to be difficult to avoid in this type of electrolytic cell, can be reduced. Since it can be reduced as much as possible, it is an excellent means of electrolyzing at a lower voltage than conventional ones. The anode and cathode in this electrolytic cell 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 the electrode easily leaves the electrode, and the electrolyte It is made permeable to gases and liquids so that it can penetrate. Such porous electrodes usually consist of a porous body formed into a thin layer by uniformly mixing active particles as anodes or cathodes with a substance that binds them, preferably graphite or other conductive material. ing. 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. Alkali resistance is required in addition to conventional chlorine resistance, and special and expensive materials must be selected. In addition, when the electrode and ion exchange membrane are combined, gas is generated as a result of the electrode reaction, which causes phenomena such as swelling in the cation exchange membrane, deteriorating membrane performance over a long period of time. It turned out to be difficult to implement stably. The present inventor continued research on an electrolytic cell that does not have these disadvantages and has a cell voltage as low as possible, and found that the surface of the cation exchange membrane has gas and liquid permeability without electrode activity. It was discovered that an electrolytic cell in which an anode or a cathode is arranged through a porous layer of metal can electrolyze an aqueous alkali chloride solution at an unexpectedly small voltage. When an oxide or an oxide hydrogel is used and constructed by heating and pressing it onto the membrane surface, the porous layer can be made uniform and extremely thin, resulting in a cation exchange membrane that can perform electrolysis at a lower voltage. I found out that it can be done. Thus, the present invention provides a method for producing a cation exchange membrane for electrolysis in which a gas- and liquid-permeable porous layer having no electrode activity is bonded to the surface. A method for producing a cation exchange membrane for electrolysis, characterized by forming the porous layer on the surface of the membrane by heating and pressing. When such a cation exchange membrane of the present invention is used, the electrodes are placed through the porous layer and do not come into contact with the ion exchange membrane. Therefore, for example, great alkali resistance is not required for the anode, and the range of selection of the anode material is correspondingly wide. In addition, since the porous layer has no electrode activity,
Since no gas is generated at the interface between the porous layer and the membrane, there is no adverse effect on the membrane. On the other hand, even in an electrolytic cell configured as described above, the cell voltage is unexpectedly low, and is much lower than, for example, when the electrode is placed in direct contact with the ion exchange membrane without intervening a porous layer in the present invention. This can be said to be an unexpected effect since it can also be obtained in the present invention when the porous layer is formed from a substantially non-conductive material having no electrode activity. In the present invention, the gas- and liquid-permeable porous layer formed on the surface of the ion exchange membrane and having no electrode activity is composed of a metal hydroxide or oxide hydrogel. When such a hydrogel is used, a porous layer having a uniform thickness and a small thickness can be formed on the membrane surface, so that an electrolytic cell with a lower cell voltage can be obtained, which is extremely advantageous industrially. The metal hydroxides or oxides used to form such hydrogels include those that have a higher chlorine overvoltage or hydrogen overvoltage than the electrodes disposed through the porous layer formed by the metal hydroxides or oxides, such as those that are themselves non-conductive. hydroxides or oxides are selected.
Such hydroxides or oxides include periodic table group A metals such as tin and lead, periodic table group B metals such as titanium, zirconium, and hafnium, and periodic table group B metals such as niobium and tantalum. family,
Iron group metals such as iron, nickel, and cobalt, or aluminum are used, and titanium, zirconium, iron, and lead are particularly preferred. In forming hydrogels of these metal hydroxides or oxides, for example, an aqueous solution of the above-mentioned metal chlorides, nitrates, sulfates, etc. is precipitated with an alkali, ammonia, etc., so that the particle size is preferably 0.01. ~10μ hydroxide or oxide hydrogels are prepared. However, the method for preparing the hydrogel is not particularly limited, and any known method can be employed. The content of metal hydroxide or oxide in the hydrogel is preferably 0.5 in terms of forming a porous layer.
~60%, especially 2.0-40% is suitable. If the content is too high or too low, it becomes difficult to form a uniform and thin porous layer. When forming a porous layer on the membrane surface from a metal hydroxide or oxide hydrogel, a fluorine-containing polymeric binder, preferably polytetrafluoroethylene, is preferably used in the form of a suspension. The amount of the fluorine-containing polymer used is preferably 0.05 to 5 parts, particularly preferably 0.05 to 5 parts per 10 parts of metal hydroxide or oxide in the hydrogel.
Preferably it is 0.1 to 3 parts. Furthermore, when forming a porous layer, appropriate solvents and surfactants are added as necessary so that the hydrogel and binder can be mixed uniformly, and a conductive filler such as graphite is added. A hydrolyzable filler such as carboxymethyl cellulose or polyvinyl alcohol may be added. After thoroughly mixing these raw materials, either obtain a cake that forms a porous layer on the filter using a filtration method, or make the mixture into a paste and apply this directly to the surface of the ion exchange membrane using a screen printing method or the like. Alternatively, the paste is applied onto a membrane-like material such as aluminum foil that can be dissolved and removed later, and the film-like material is pressed against the ion-exchange membrane surface.
A porous layer is formed on the membrane surface. The porous layer formed on the ion exchange membrane surface is then preferably molded using a press molding machine.
It is heated and pressed onto the membrane surface at 80 to 220°C and 1 to 15 kg/cm ² so that it is partially embedded in the membrane surface. The layer thus formed on the membrane surface preferably has an average pore diameter of 0.01.
~1000μ, especially 0.1-500μ, and a porosity of 20-99%, especially 25-95%, and the raw material preferably has a porosity of 0.1-100μ, especially 1-50μ. The content of metal hydroxide or oxide in the porous layer thus formed is preferably 50-99%, particularly 60-96%. In the electrolytic cell using the cation exchange membrane manufactured by the present invention, the electrode disposed through the porous layer may be a porous electrode such as a porous plate, a mesh, or an expanded metal, or a porous electrode with electrode activity. Any electrode consisting of a gas- and liquid-permeable porous layer can be used. When using either a porous electrode or an electrode consisting of a porous layer, the material forming the anode or cathode is selected from a material with a small chlorine overvoltage or hydrogen overvoltage, respectively. That is, as the anode, a platinum group metal, its conductive oxide, or its conductive reduced oxide, etc. are used, while as the cathode, a platinum group metal, its conductive oxide, or an iron group metal, etc. are used. In addition, platinum group metals include platinum, rhodium,
Ruthenium, palladium, and iridium are exemplified, and iron group metals include iron, cobalt, nickel, Raney nickel, and stabilized Raney nickel. If a porous 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. In the present invention, when the anode or cathode is disposed through a porous layer having no electrode activity formed on the membrane surface, the electrode is preferably disposed in contact with the porous layer to reduce the cell voltage. effective for. However, these anodes or cathodes do not necessarily need to be placed in contact with the porous layer, and may be placed at appropriate intervals as the case requires. In addition, when only either the anode or the cathode is disposed via a porous layer having no electrode activity according to the present invention, the opposite electrode, the anode or the cathode, is the above-mentioned porous electrode or electrode. An active porous layer is placed directly on the anode or cathode side of the cation exchange membrane. In such a case, these electrodes may be provided in contact with the ion exchange membrane surface, or
They may be provided at intervals. However, when a porous layer having electrode activity is used, it is preferable to bring it into contact with the membrane surface, further bonding it, and embedding it. The ion exchange group 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 adopt
Examples of ion-exchange group-containing fluorine-containing polymers include copolymers of vinyl monomers such as tetrafluoroethylene and chlorotrifluoroethylene and perfluorinated vinyl monomers having ion-exchange groups such as sulfonic acid, carboxylic acid, and phosphoric acid groups. Consolidation is preferably used. Further, a film-like polymer of trifluorostyrene into which an ion exchange group such as a sulfonic acid group is introduced can also be used. Among these monomers, it is particularly preferable to use monomers that can form the following polymerized units (a) and (b), since highly pure caustic alkali can be obtained with relatively high current efficiency. . (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: -((CF ₂ -) _x A, -O-(CF ₂ -) _x A, x, y, z are all 1 to 10, and Z, Rf are -
It is a group selected from F or a perfluoroalkyl group having 1 to 10 carbon atoms. Also, A is −SO ₃ M, −
COOM, or -SO ₂ F, -CN, -COF or -COOR which can be converted into these groups by hydrolysis, M is hydrogen or an alkali metal, and R is a carbon number of 1 to
10 alkyl groups are shown. 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 preferably 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 only 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 a smaller ion exchange capacity on the cathode side than on the anode side, the cathode side has a weakly acidic exchange group such as a carboxylic acid group, and the anode side has a strong acidic exchange group such as a sulfonic acid group. Ion exchange membranes can also be used. 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. The porous layer on the anode and cathode side, which is preferably bonded to and formed on the surface of these ion exchange membranes,
In order to avoid separation of the ion-exchange groups in the ion-exchange membrane, the form of the ion-exchange group is determined as appropriate, for example, in the case of a carboxylic acid group, the ester type, and in the case of a sulfonic acid group, the -SO ₂ F type. Bonding is achieved by the action of pressure and heat. The conditions for electrolyzing an aqueous alkali chloride solution in an electrolytic cell using the cation exchange membrane of the present invention are as follows:
Known conditions such as those disclosed in the above-mentioned Japanese Patent Application Laid-open No. 112398/1988 can be employed. For example, an aqueous alkali chloride solution of 2.5 to 5 normal (N) is preferably supplied to the anode chamber, and water or diluted alkali hydroxide is supplied to the cathode chamber, preferably at a current density of 80°C to 120°C.
Electrolyzed at 10-100A/ ^dm2 . 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 electrolytic cell in which the cation exchange membrane of the present invention is used may be of either a monopolar type or a bipolar type as long as it has the above configuration. In addition, the materials that make up the electrolytic cell are
For the anode chamber, a material that is resistant to aqueous alkali chloride and chlorine, such as titanium, is used, and for the cathode chamber, a material that is resistant to high concentrations of alkali hydroxide and hydrogen, such as iron, stainless steel, or nickel, is used. Ru. Further, when a porous layer electrode is used in the present invention, a current collector for feeding power to the porous layer electrode is disposed outside the porous layer electrode. The current collector usually has a chlorine or hydrogen overpotential equal to or higher than the electrode. For example, the anode is made of noble metal, valve metal, etc., and the cathode is made of iron, nickel, or stainless steel net, mesh, or expanded metal. However, as a current collector, the same electrode used for the porous layer with no electrode activity is used, for example, in the case of the anode, an expanded metal made of valve metal coated with a noble metal alloy or its conductive oxide is used. can. The current collector is preferably brought into contact with the porous layer by pressing it against the porous layer. Example 1 5 parts of iron hydroxide hydrogel containing 4% by weight of iron hydroxide with a particle size of 1 μm or less, 1 part of an aqueous dispersion containing 20% by weight of polytetrafluoroethylene particles with a particle size of 0.5 μm or less, and 0.1 part of methylcellulose. After thoroughly mixing and kneading, add isopropyl alcohol 2
of the mixture was added and kneaded again to obtain a paste. The paste was mixed with tetrafluoroethylene and CF ₂ =
A cation exchange membrane (ion exchange capacity: 1.45 meq/g dry resin, thickness 220 μm) made of a copolymer of CFO(CF ₂ ) ₃ COOCH ₃ was screen printed on one side in a size of 20 cm×25 cm. After air-drying the ion membrane, the printed layer was thermocompression bonded to the ion membrane under conditions of a temperature of 165° C. and a pressure of 60 kg/cm ² . The porous layer obtained on the ion exchange membrane had a thickness of 10 μ, a porosity of 95%, and contained 0.2 mg/cm ² of iron hydroxide. Thereafter, the ion exchange membrane was immersed in a 25% by weight aqueous sodium hydroxide solution at 90° C. for 16 hours to hydrolyze and elute methylcellulose. After that, an anode made of titanium micro-expanded metal coated with ruthenium-iridium oxide was placed in direct contact with the porous layer, and a nickel micro-expanded metal cathode was placed in direct contact with the other side of the ion membrane. The saline solution in the anode chamber was maintained at a concentration of 4N, and water was supplied to the cathode chamber to maintain the caustic soda concentration in the catholyte at 35% by weight, while electrolysis was carried out at 90°C, and the following results were obtained. Current density (A/dm ² ) Cell voltage (V) 20 3.04 40 3.34 60 3.61 80 3.73 Example 2 In Example 1, a hydrogel containing 4% by weight of zirconium oxide was used instead of the iron hydroxide hydrogel, and the porous layer was An electrolytic cell was assembled in the same manner as in Example 1, except that it was crimped onto the side surface of the cathode of the ion exchange membrane, and a saline solution was electrolyzed in the same manner as in Example 1, and the following results were obtained. Current density (A/dm ² ) Cell voltage (V) 20 3.05 40 3.36 60 3.64 80 3.77 Examples 3 to 7 Iron hydroxide hydrogel of Example 1 (porous layer on the anode side) or zirconium oxide hydrogel of Example 2 ( An electrolytic cell was formed in the same manner as in Example 1 except that the hydrogel shown in Table 1 below was used instead of the cathode side porous layer), and the produced caustic soda Electrolysis of a saline solution was carried out in the same manner as in Example 1, except that the concentration of . The results are shown in Table 2.

【table】

[Table] Example 8 The paste in Example 1 was screen printed on the anode surface of an ion exchange membrane and air-dried. In such cases, tetrafluoroethylene may be used as a binder.
CF ₂ =CFO(CF ₂ ) ₃ Polytetrafluoroethylene (modified PTFE) with a particle size of 0.5 μ or less, which was partially copolymerized with COOCH ₃ , was used. Furthermore, on the cathode surface of the ion exchange membrane, 3 parts of so-called stabilized Raney nickel, which is obtained by dissolving and removing the aluminum of Raney nickel alloy with alkali and partially oxidizing it, and the above-mentioned modified
After thoroughly kneading 1.5 parts of an aqueous dispersion containing 20% by weight of PTFE, 0.1 part of methyl cellulose, and 3 parts of water, 3 parts of isopropyl alcohol was further added, and the paste prepared by kneading was screen printed.
The porous layer provided on each ion exchange membrane was press-bonded to the ion exchange membrane in the same manner as in Example 1. The stabilized Raney nickel porous layer has a thickness of 25μ, a porosity of 80%, and a stabilized Raney nickel of 5
Contained mg/ ^cm2 . Next, after further hydrolysis under the same conditions as in Example 1, an anode similar to that described in Example 1 was placed on the iron hydroxide side, and nickel expanded metal was brought into pressure contact with the stabilized Raney nickel side. Then, electrolysis was carried out under the same conditions as in Example 1, and the following results were obtained. Current density (A/dm ² ) Cell voltage (V) 20 2.94 40 3.24 60 3.52 80 3.25 Comparative example 1 Ion exchange membrane similar to that described in Example 1 without any porous layer on both sides. Hydrolysis and electrolysis were carried out in exactly the same manner and means as in Example 1, and the following results were obtained. Current density (A/dm ² ) Cell voltage (V) 20 3.04 40 3.51 60 3.94 80 4.19

Claims (1)

[Scope of Claims] 1. A method for producing a cation exchange membrane for electrolysis, which has a gas- and liquid-permeable porous layer with no electrode activity bonded to its surface, in which a metal hydroxide or oxide hydrogel is bonded to a cation-exchange membrane. A method for producing a cation exchange membrane for electrolysis, which comprises forming the porous layer on the surface of the exchange membrane by heating and pressing. 2 Metal hydroxides or oxides are on the periodic table-A
Claim 1, which is a hydroxide or oxide of group -B group, -B group, iron group, or aluminum group.
manufacturing method. 3 Porous layer has an average pore diameter of 0.01 to 2000μ, porosity
10-99% and a thickness of 0.1-100μ.