JPS6261673B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a porous electrode-ion exchange membrane assembly. Specifically, the present invention relates to a method for producing a porous electrode-ion exchange membrane assembly having excellent electrolysis performance for alkali metal halides by forming a thin layer of an ion exchange membrane on a porous electrode.

In recent years, ion-exchange membrane salt electrolysis, which requires less electrolytic power, has been developed and is being put into practical use. The important point in the development and improvement of this ion-exchange membrane electrolysis method is to reduce the cell voltage and bring it closer to the theoretical electrolysis voltage. Loss other than the theoretical electrolytic voltage includes solution resistance, solution resistance due to bubbles, hydrogen overvoltage, membrane resistance, membrane potential, etc. Among these, efforts are being made to reduce solution resistance as much as possible by reducing the distance between the electrodes, hydrogen overvoltage by improving cathode active materials, and membrane resistance by improving ion exchange membranes. There is. Furthermore, as a method of preventing an increase in solution resistance due to air bubbles, it is possible to integrate a normal ion exchange membrane and a normal mesh electrode, but in this case, the electrolytic voltage may increase for reasons that are not clear. Therefore, it is necessary to provide an appropriate distance between the ion exchange membrane and the electrode to minimize the influence of bubbles.

Furthermore, in order to improve the drawbacks of the ion exchange membrane method, an electrolysis method using a solid polymer electrolyte (abbreviated as SPE) has been proposed. In other words, in the SPE electrolysis method, since the electrode catalyst is bonded to the ion exchange membrane, gas generation due to the electrode reaction occurs from the surface of the electrode catalyst, and the solution resistance due to the solution resistance and the bubbles between the ion exchange membrane and the electrode. The increase can be removed.

As a method for manufacturing such an ion exchange membrane-electrode catalyst assembly, a mixture of catalytic active particles obtained by thermally decomposing a noble metal compound and perfluorinated carbon resin (abbreviated as PFC) particles is directly applied to an ion exchange membrane. A hot press embedding method is used. After sintering a mixture of catalytically active particles obtained by thermally decomposing a noble metal compound and PEC particles on aluminum foil, the aluminum foil is melted and removed and formed into a sheet. A method of bonding a sheet-like material onto an ion exchange membrane, a method of depositing metal on an ion exchange membrane by electroless plating, etc. have been proposed.

Even in the SPE electrolysis method, membrane resistance accounts for a large portion of power loss other than the theoretical electrolysis voltage, and it is necessary to minimize membrane resistance in order to reduce electrolysis power.

However, the above-mentioned conjugate is essentially a method of forming an electrode catalyst layer on an ion exchange membrane;
According to this method, the strength of the bonded body depends on the strength of the membrane, so in order to obtain a strength that can withstand industrial use, the membrane thickness must be at least 0.1 m/m, and in some cases, Reinforcement with PFC net is also necessary. Along with this, there has been a problem in that the membrane resistance inevitably increases to some extent.

The present inventors have conducted intensive research on a method similar to the SPE electrolysis method that lowers membrane resistance and electrolysis power, and as a result, they have achieved good current efficiency and are able to reduce salt contamination in an industrial manner. They discovered that the film thickness required to be negligible should be at least 10 μm or more, and found a method to make the strength of the bonded product industrially usable even in the case of such a film thickness, thereby providing the present invention. Ivy.

That is, in the present invention, when forming a thin film of an ion exchange membrane on one surface of a porous electrode, the pores of the porous electrode are sealed in advance with a soluble solid plugging material to form a substantially flat surface. A fine powder of ion exchange resin is present on the surface, or a suspension thereof, or a solution of ion exchange resin is applied, and if necessary, a thin layer of ion exchange membrane is formed by heating film formation or evaporation of the solvent. This is a method for producing a porous electrode-ion exchange membrane assembly, which is characterized in that the plugging material is then eluted and removed.

The porous electrode-ion-exchange membrane assembly obtained by the present invention has a membrane thickness less than half that of a commonly used ion-exchange membrane, and it is also possible to reduce the membrane thickness to one-tenth or less compared to conventional membranes. It is. Therefore, the membrane resistance is extremely low compared to conventional ion exchange membrane assemblies, and the electrolytic voltage can be reduced accordingly.
Furthermore, the membrane can be easily bonded to a porous electrode and exhibits good durability.

The present invention will be specifically explained below.

As the porous electrode used in the present invention, those used in common salt electrolysis using an ion exchange membrane method can be used without particular limitation. As the material, metals used for the cathode of common salt electrolysis using the ion exchange membrane method, such as nickel, iron, and stainless steel, or metals used for the anode, such as titanium, are suitably used. Also, known shapes can be used, but preferred are sintered bodies or net-like bodies of the above-mentioned fine metal powder, or structures in which these are lined with expanded metal or coarse-pored net-like bodies.

These shapes preferably have a porosity of 30 to 90%, particularly 50 to 80%, an electrode thickness of 0.05 to 2 m/m, particularly 0.1 to 1 m/m, and an average pore diameter of 0.1 to 100%.
μ, particularly preferably selected from the range of 0.1 to 30 μ.

In addition, various platings are applied to the electrode structure, such as platinum group metals such as platinum, iridium, ruthenium, palladium, and rhodium, and oxides of one or more of these metals, and catalyst components such as nickel and iron, depending on the purpose. It also makes a good electrode. As the plating means, well-known electrolytic plating, chemical plating, a method of applying a substance containing the above-mentioned substances or heat-convertible to them and then applying heat thereon, etc., may be employed depending on the purpose. In this way, an electrode with low hydrogen overvoltage or chlorine overvoltage in salt electrolysis can be obtained.

What is important in the present invention is the formation of a thin ion exchange membrane on the porous electrode surface and the means for this purpose. The thin film may be formed on one side of the porous electrode.

The ion exchange resin used to form the thin film of the ion exchange membrane of the present invention is not particularly limited as long as it has excellent durability, but generally contains sulfonic acid groups, carboxylic acid groups, sulfonic acid amide groups, etc. So-called perfluorocarbon-based cation exchange resins based on fluorocarbons having exchange groups are preferably used, and among them, those having exchange groups having sulfonic acid and carboxylic acid groups are preferably used for salt electrolysis. Ru. In addition, in order to form an ion exchange membrane, a fine powder of the ion exchange resin, for example, a powder of about 0.05 to 10μ, a suspension thereof, or a solution of the ion exchange resin is applied onto the sealed porous electrode. It is heated to remove the medium if necessary and melted to form a uniform film, or it is formed into a film by evaporating the solvent from the solution. In particular, in order to form an ion exchange membrane having carboxylic acid groups,
A thin film is formed by using a fine powder of an ion exchange resin having a carboxylic acid group, or by applying a fine powder of an ion exchange resin having a sulfonic acid group and its suspension, or a solution of the ion exchange resin to a porous electrode. After that, it may be converted into a carboxylic acid using a known method such as chemical treatment or ultraviolet irradiation treatment.

The purpose of the present invention is to lower the electrolytic voltage by reducing the membrane resistance, and for this purpose, the thickness of the ion exchange membrane to be formed is preferably 10μ to 100μ.
10~20μ is good.

The most important thing in the present invention is a means for forming a thin film, and as this means, the pores of the porous electrode are sealed in advance with a soluble solid plugging material to form a substantially flat plate image, and the pores are formed on the flat plate surface. After forming an ion exchange membrane in the presence of an ion exchange resin and forming a thin film of the ion exchange membrane by heating or evaporating a solvent as necessary, the plugging material is eluted and removed.

The soluble solid plugging material used in the present invention must be easy to seal and can be eluted and removed from the porous electrode after forming a thin film. It is desirable that the plugging material has a temperature higher than the forming temperature of the thin film of the ion exchange membrane used. Any known substance can be used without any particular restriction as long as it satisfies these conditions. For example, inorganic powders such as aluminum, sodium carbonate, and salt, fatty acid esters soluble in organic solvents such as glycol stearate, methyl stearate, glycol palmitate, methyl palmitate, methyl linoleate, and glycol linoleate, or sodium stearate and palmitin. There are water-soluble higher fatty acid salts such as sodium acid, sodium linoleate, and sodium oleate.
In particular, it is also preferable to use an inorganic powder as described above mixed with a higher fatty acid ester or salt. Also,
A known method may be employed for filling and clogging the porous electrode with the above-mentioned soluble solid plugging material. For example, a method of physically pushing the fine powder of the plugging material as described above into the porous electrode as it is, or a method of impregnating the pores of the porous electrode with a mixture of the plugging material and a solvent and then drying it. However, the point is that the purpose is achieved if the plugging material seals the pores of the porous resin and forms a substantially flat surface. The solvent at this time is water,
Alcohol etc. are common.

A thin film of an ion exchange membrane is formed using the above-mentioned ion exchange resin on the electrode having a substantially flat surface by the above method. At this time, fine powder of ion exchange resin and its suspension or solution of ion exchange resin are applied, and the medium used for this is generally water, butanol, isopropyl alcohol, methanol, ethanol, etc. The method of applying the suspension or solution containing the ion exchange resin is not particularly limited, and may be applied by any method such as brushing or spraying. The resulting film thickness is controlled by the suspension concentration and the number of times of coating and drying.

These can be easily learned by those skilled in the art through preliminary implementation. Generally speaking, suspensions or solutions have a low concentration, from a few percent to a few percent, and in some cases, a thickener such as glycol is used to adjust the viscosity to an appropriate level (e.g., about 5 to 50 cp). It is preferable to do so. Then remove the medium by drying,
The resin is heated to form a film. At this time, the conditions and method are not particularly limited as long as the temperature, pressure, etc. required for heating film formation are within a range that allows the ion exchange resin to melt and adhere to the porous electrode. For example, a common method is to melt the resin at a temperature of 250 to 350°C, press it at a pressure of 5 to 15 kg/cm ² , and then cool it to form a thin film layer.

Further, the evaporation of the solvent is also carried out by known means such as reduced pressure.

The thin film formed by the method described above allows the plugging material to be eluted and removed from the porous electrode. Methods for this purpose include eluting the plugging material in a solvent or using a solution that chemically reacts with the plugging material to remove it. As the solvent, water, dilute hydrochloric acid, dilute methanol sulfuric acid, ethyl ether, ethanol, butanol, and isopropyl alcohol are preferably used, but the solvent is not limited to these. There are no particular restrictions on the material as long as it does not reduce the performance of the porous electrode-ion exchange membrane assembly.
Selection of these solvents can be easily made by those skilled in the art as needed.

Porous electrode formed by the above method
The ion exchange membrane assembly can further reduce the electrolytic power by forming an electrode catalyst layer on the thin membrane, which is opposite to the integrated electrode. As the method for depositing the catalyst, any known method conventionally used in the production of SPE can be used without particular limitation.

Examples are shown below to specifically explain the present invention, but the present invention is not particularly limited thereto.

Example 1 A porous electrode made of a sintered body of fine nickel powder lined with a nickel mesh (porosity 70%, plate thickness 1 m/
After physically pushing 1μ aluminum powder onto the surface of the pore size (pore size: 1μ) to seal the pores, a 10% by weight aqueous suspension of fine powder of acid-type Nafion Powder 501 (manufactured by Dupont) was applied and dried. After repeating this process four times, hot pressing was carried out at 250° C. and 10 kg/cm ² for 10 minutes to form a Nafion thin film with a thickness of about 20 μm on the porous nickel plate. This material was irradiated with ultraviolet light for 30 minutes at 150° C. in a nitrogen monoxide atmosphere at atmospheric pressure to modify the sulfonic acid groups to carboxylic acid groups, and then the plugged aluminum was removed with 5% NaOH.

This porous electrode-ion exchange membrane assembly was assembled into an electrolytic cell separated into two chambers by the assembly so that the ion exchange membrane was on the anode side. as an anode
Using DSA (manufactured by Permeretsk), in the anode chamber
3.5N-NaCl (PH=2), 6N-NaOH was supplied to the bonded body side, and the current density was increased using porous nickel as a cathode.
Electrolysis was carried out at 30 A/dm ² and a temperature of 80°C.

As a result, the cell voltage was 2.80V and the current efficiency was 93~94.
It was %. The salt content in the obtained caustic soda was (30PPm) (calculated as 50% caustic soda).

Example 2 310 g/g was applied to the surface of the porous electrode similar to Example 1.
After applying a saline solution, the holes were dried, impregnated with salt, and sealed. Thereafter, a thin film of ion exchange membrane was formed on the surface of the porous electrode (film thickness: 18 μm) in the same manner as in Example 1 (however, ethanol was used as the medium). This porous electrode-ion exchange membrane assembly was immersed in a water tank to remove the sealed salt.

This conjugate was converted into carboxylic acid in the same manner as in Example 1, and then incorporated into an electrolytic cell and electrolyzed. The cell voltage was 2.8 V and the current efficiency was 93 to 94%.

Example 3 A solution of 1 g of H ₂ PtCl _{6.6H 2} O dissolved in 80 ml of butanol was applied to a porous nickel electrode, and thermally decomposed at 350°C in a nitrogen gas atmosphere. This was repeated several times to activate the porous nickel electrode. It became. The hydrogen generation overvoltage of this electrode was 0.1V. (80℃, 6N—
(NaOH, 30 A/dcm ² ) This activated electrode was treated in the same manner as in Example 1 to form a thin ion exchange membrane, and then electrolysis was performed in the same manner as in Example 1. As a result, the cell voltage
It was 2.70V and the current efficiency was 93%.

Example 4 A thin film of an ion exchange membrane was formed on a porous nickel electrode activated in the same manner as in Example 3 by the same method as in Example 1. After that, an IrCl ₄ -butanol solution was applied on the ion exchange membrane thin film of the porous nickel electrode and thermally decomposed in hydrogen at 140°C to form a thin layer of Ir. Electrolytic plating was applied. This three-layer laminate (Pt/Ir layer - ion exchange thin film - porous nickel plate) was incorporated into an SPE cell and an electrolytic test was conducted. The current collector is a titanium expanded metal plated with platinum on the anode side (long diameter 5m/
m, short axis 2 m/m) Ni expanded metal was used on the cathode side, 3.5N-NaCl solution was supplied on the anode side, and 6N-NaOH was supplied on the cathode side at 80℃, current density 30A/dm ²
When electrolyzed with a cell voltage of 2.60V, the current efficiency was 92%.

Example 5 A porous nickel electrode was activated in the same manner as in Example 3, and then sealed using a mixture of aluminum powder and Marcel soap (50:50 weight ratio).
Thereafter, a 10% IPA solution of Nafion 601 (manufactured by Dupont) was applied onto the electrode and dried under reduced pressure, and this was repeated several times to form a Nafion thin film with a thickness of about 10 μm on the porous nickel plate. Thereafter, the sulfonic acid groups were exchanged with carboxylic acid groups by irradiation with ultraviolet rays in a nitrogen monoxide atmosphere, and then treated in the same manner as in Example 4 to form a three-layer laminate (Pt/Ir layer - ion exchange membrane - porous Nickel plate) was formed. This three-layer laminate was assembled into an SPE cell with the Pt-Ir layer on the anode side and the porous nickel plate on the cathode side, and an electrolytic test was conducted. The current collector is a titanium expanded metal plated with platinum on the anode side (long axis 5 m/m, short axis 2 m/m).
m) Ni expanded metal with the same specifications is used on the cathode side. When 3.5N-NaCl was supplied to the anode side and 10N-NaOH was supplied to the cathode side and electrolysis was performed at 80°C and 30A/dm ² , the cell voltage was 2.60V and the current efficiency was 90%.

Example 6 The surface of a porous nickel electrode similar to that of Example 1 was coated with a melt of methyl palmitate at 80°C to seal the pores. Thereafter, a thin film of naphion was formed on a porous nickel plate in the same manner as in Example 5, and then washed with water.
I pulled out the sealed soap. Thereafter, it was treated in the same manner as in Example 4 and electrolyzed, resulting in a cell voltage of 2.6 V and a current efficiency of 92%.

Example 7 A 10 wt % solution of sodium stearate was brushed onto the surface of the same porous nickel electrode as in Example 1 several times to seal the pores. Thereafter, a thin film of naphion was formed on a porous nickel plate in the same manner as in Example 5, and then washed with water to remove the sealed pores of sodium stearate. After this, treatment was carried out in the same manner as in Example 4, and electrolysis was performed, resulting in a cell voltage of 2.6V and a current efficiency of 92%.
It was hot.

Claims (1)

[Scope of Claims] 1. When forming a thin film of an ion exchange membrane on at least one surface of a porous electrode, the pores of the porous electrode are sealed in advance with a soluble solid plugging material to form a substantially flat surface. Then, a fine powder of ion exchange resin is present on the flat plate surface, or a suspension thereof, or a solution of ion exchange resin is applied, and if necessary, the ion exchange membrane is thinned by heating or evaporation of the solvent. A method for producing a porous electrode-ion exchange membrane assembly, which comprises forming a layer and then eluting and removing a plugging material. 2. The method according to claim 1, wherein the porous electrode is made of a material selected from the metals consisting of nickel, iron, stainless steel, and titanium. 3. The method of claim 1, wherein the porous electrode is activated with a platinum group metal or an oxide thereof. 4. The method according to claim 1, wherein the porous electrode comprises a sintered body of fine metal powder, a fine-pore network, or a structure in which these are lined with either expanded metal or a coarse-pore network. 5. The method according to claim 1, using a porous electrode having a porosity of 30 to 90%, a plate thickness of 0.1 to 1 m/m, and an average pore diameter of 0.1 to 30 μm. 6. The method according to claim 1, wherein the ion exchange membrane has a thickness of 10μ to 100μ. 7. The method according to claim 1, wherein the plugging material is an inorganic powder, a fatty acid ester, or a water-soluble fatty acid salt. 8 Claim 7, in which the inorganic powder is one selected from aluminum, common salt, and sodium carbonate.
The method described in section. 9 Fatty acid ester is glycol stearate,
Methyl stearate, glycol palmitate,
The method according to claim 7, which is at least one selected from methyl palmitate, methyl linoleate, and glycol linoleate. 10. The method according to claim 7, wherein the water-soluble fatty acid salt is at least one selected from sodium stearate, sodium palmitate, sodium linoleate, and sodium oleate. 11. The method according to claim 7, wherein the plugging material is a mixture of an inorganic powder and a fatty acid ester or a soluble fatty acid salt. 12. The method according to claim 1, wherein the ion exchange resin is a perfluorocarbon resin.