JPS6045710B2 - electrolytic cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a novel method suitable for producing caustic alkali stably over a long period of time and with low power consumption, with no iron elution at all in the electrolysis of aqueous alkali chloride solutions using a diaphragm. This relates to electrolytic cells.

For example, a method for producing chlorine and caustic soda by electrolyzing a saline solution using a cation exchange membrane as a diaphragm is known.

This electrolysis method using a cation exchange membrane has attracted particular attention in recent years because the amount of salt mixed into the caustic soda produced at the cathode is extremely small, and there is no pollution problem compared to the mercury method or asbestos method. It has been. Cation exchange membranes have been developed and improved in order to increase the concentration and current efficiency of caustic soda obtained in the cathode chamber, and recently, caustic soda of 20 wt % or more can be obtained with a high current efficiency of 90% or more.

Cation exchange membranes based on barfluorocarbon polymers have been developed, and some are on the verge of commercialization.
On the other hand, in recent years, the importance of energy saving has been recognized worldwide, and from this point of view, it is strongly desired in this field to reduce the electrolytic power as much as possible, that is, to reduce the electric voltage as much as possible. Until now, for the purpose of reducing the electric sliding voltage, porous electrodes such as expanded metal, punch metal, and wire mesh have been used, and the composition of these electrodes themselves and the gap between the electrodes have been changed in order to make it easier for the generated gas to escape behind the electrode. Various methods have been proposed, such as controlling the distance, or specifying the composition of the cation exchange membrane and the type of exchange group. Among these, especially in the electrolysis of an aqueous alkali chloride solution in which the main cathode reaction is hydrogen generation reaction using a diaphragm, the iron cathode of the above-mentioned shape is mainly used at low cost, and
It is used because it exhibits a fairly low hydrogen overvoltage.

However, as mentioned above, with the development of cation exchange membrane salt electrolysis technology, further reduction in power consumption is desired from the viewpoint of energy saving, and Japanese Patent Application Laid-open Nos. 55-92295 and 1982-62148 etc. As can be seen, various efforts have been made to develop cathodes having hydrogen overpotentials lower than those of iron. Although these cathodes formed with metal coatings having a low hydrogen overvoltage can achieve their original purpose to a certain extent, it has become clear that they include the following serious problems. That is, instead of the conventional iron cathode, a cathode made of a base material made of iron or iron-based metal and coated with a metal having a low hydrogen overvoltage is installed in a cathode chamber whose inner surface is made of iron or iron-based metal. When used, a phenomenon is observed in which the amount of iron eluted increases dramatically in a short period of time.

This phenomenon tends to become more pronounced under severe electrolytic conditions such as high temperature and high alkali concentration. This elution of iron not only deteriorates the quality of the obtained caustic alkali and deteriorates the performance of diaphragms such as cation exchange membranes, but also causes corrosion of the inside of the cathode chamber, which is made of iron or iron-based metals, to progress to the electrolytic cell itself. This develops into a serious problem of shortening the lifespan of people.

As a means to prevent this elution of iron, it is conceivable to construct the cathode chamber with a metal such as nickel that has corrosion resistance against alkali. However, using metals resistant to alkali corrosion for all of the constituent metals of the cathode chamber would be expensive and impractical. Furthermore, in this case, the cathode base material must also be made of a metal that is resistant to alkali corrosion. This is because when using a cathode in which a substrate made of iron or iron-based metal is coated with a coating such as nickel that has a low hydrogen overvoltage by plating, etc., the cathode is attached to the cathode chamber by a method such as welding. Even if this is done carefully, the coating will be damaged and the iron matrix will be exposed, and iron will continue to dissolve from this exposed area. Therefore, the same reason applies to a method in which a coating having resistance to alkali corrosion is applied to the inner surface of the cathode chamber and the cathode made of iron or iron-based metal by a plating method, etc., and then the two are integrated by a method such as welding. There is a problem with this. Another possibility is to use a plastic electrolytic cell. However, this has problems in terms of processing and strength, and even if it could be adopted, it would not be a fundamental means of preventing iron elution.
As a result of various studies to solve these problems, the present inventors found that even if a cathode coated with a metal having a low hydrogen overvoltage is used, iron or iron-based The iron cathode and cathode chamber frame made of metal can be used as is, and no matter how complex the electrolytic cell structure is, it prevents iron from leaching, and it can be used stably over a long period of time and with low power consumption. They completed a manufacturable electrolytic cell.

That is, the present invention uses a diaphragm to separate an anode chamber and a cathode chamber,
In an electrolytic cell used to supply an aqueous alkali chloride solution to the anode chamber and produce chlorine from the anode chamber and hydrogen and caustic alkali from the cathode chamber, the inner surface of the cathode chamber, the cathode, and the surfaces of other cathode chamber members made of iron or iron-based metals are Everything is in an electrolytic cell in which nickel plating is applied from a nickel plating bath containing nickel salts, and then active nickel plating is applied using an activated nickel plating bath containing nickel salts and sulfur-containing compounds. The other cathode chamber members mentioned here are:
Refers to members present inside the cathode chamber, such as conductive rods, current collectors, and welded parts. When nickel plating is performed on a cathode base material made of iron or iron-based metal using a nickel plating bath in which a sulfur-containing compound, such as rodanium nickel, is dissolved,
It has long been known that the resulting coatings exhibit low hydrogen overpotentials.

However, when the surface of the coating thus obtained is carefully and deeply observed using a microscope, it is found that there are many cracks, and the coating itself lacks adhesion to the iron base. Therefore, if such an active coating is applied directly to the iron substrate, phenomena such as peeling or falling off of the coating are likely to occur, and even if it is in close contact with the substrate, the iron will continue to leach out through cracks. This creates a gap between the substrate and the coating, causing the coating to fall off. As a result, the iron base is exposed, and iron elution progresses from this portion, which accelerates the peeling and falling off of the active coating. For the purpose of improving the adhesion between a substrate made of iron or iron-based metal and activated nickel plating applied from an activated nickel plating bath containing tanned nickel, etc., a copper coating is applied to the iron or iron-based base material. A method has been proposed in which active nickel plating is then performed.

However, in the experience of the present inventors, it is difficult to say that copper itself has excellent corrosion resistance against alkalis.
Therefore, even if the adhesion itself is improved by applying activated nickel plating, corrosion of the copper progresses through cracks, and eventually the active film will fall off, compared to when activated nickel is applied directly to the iron base. It was confirmed that they are the same. As a result of our search to improve these problems, the present inventors discovered that nickel plating was performed from a nickel plating bath containing nickel salts, and active nickel plating was performed from an activated nickel plating bath containing nickel salts and sulfur-containing compounds. It has been found that there are some materials that have excellent adhesion.

The present invention was completed based on this knowledge. That is, after nickel plating is performed on an iron or iron-based metal substrate using a nickel plating bath that does not contain sulfur-containing compounds and contains nickel salts, it is then plated using an activated nickel plating bath that contains nickel salts and sulfur-containing compounds. Furthermore, by performing active nickel plating, it is possible to obtain an active coating that has extremely excellent adhesion to the iron substrate of the cathode chamber, cathode, etc. as a whole.

The composition of the nickel plating bath is as follows.

The nickel salt may be any soluble salt, and usually one or more of any water-soluble nickel salts such as nickel sulfate, nickel chloride, ammonium nickel sulfate, and nickel sulfamate are used.

The concentration of nickel salt is not particularly limited, but is usually 0.
It is used in a concentration range of 1 molar to 2.0 molar. In this case, if active nickel plating is performed in which the same type of nickel salt as the nickel salt used in the nickel plating bath is also used in the active nickel plating bath, the adhesion between the nickel plating and the active nickel plating will be even better. It is most effective in terms of adhesion when an active nickel plating bath is used in which not only the nickel salt used in nickel plating but also other components and their concentrations are made the same.
In the present invention, as a method for applying nickel plating to the iron substrate of the cathode chamber, cathode, etc. using a nickel plating bath containing nickel salt, both electroplating method and electroless plating method can be performed. Electrolytic plating is preferred. In particular, the best way to obtain a cathode and cathode chamber with a coating that is extremely adhesive, strong, and exhibits a stable and low hydrogen overvoltage over a long period of time is to This method involves applying electroless nickel plating to all parts surfaces, then electrolytic nickel plating, and finally active nickel plating. Therefore, it is also an effective method to apply the means of the present invention to an electrolytic cell assembled by electroless nickel plating of the cathode chamber, cathode, and other cathode chamber interior surfaces made of iron or iron-based metal in advance. One of the excellent features of the present invention is that after the cathode is installed in the cathode chamber, the entire surface of the cathode chamber, the cathode, and other cathode chamber components can be coated, so that no iron substrate is exposed. This means that there are no such cases.

As mentioned above, if the cathode chamber and the cathode are coated, and an attempt is made to integrate them by welding or other methods, the coating will be damaged, and the deterioration of activity and exposure of the iron base cannot be avoided. It is as follows. One of the more excellent features of the present invention is that active nickel plating is applied not only to the cathode but also to the inner surface of the cathode chamber, so that the electric voltage is further reduced.

That is, compared to the case where the active coating is applied only to the cathode, the area covered with the active coating is larger, so the effect is substantially the same as that of a reduction in current density, and the electric voltage is reduced. This is particularly noticeable when using a bipolar electrolytic cell. Of course, it is generally difficult to apply an active coating uniformly to cathode chambers, cathodes, and other cathode chamber components having complex shapes, but this is not a hindrance in the slightest in the present invention. do not have. This is because the area where current most easily flows is on the opposite anode side of the cathode, so the thickest active coating is applied to this area. When electrolyzing saline water, the area where the most current flows is the opposite anode surface of the cathode, so it can be said that it is more efficient to have the thickest active coating applied to this area. When applying nickel plating to an iron base, the thickness is 4
~100p is a good guess.

It is not necessary that the entire surface of the cathode, cathode chamber, and other cathode chamber members be plated to a uniform thickness, but it is sufficient that the thickness falls within this range. When electroless nickel plating is applied to an iron substrate and then nickel plating is performed, the appropriate thickness of the electroless nickel plating is 2 to 50 μm.

If it is thinner than this, the effect of preventing iron elution is small, and if it is thicker than this, it is uneconomical. The appropriate thickness of the nickel plating applied on the electroless nickel plate is 2 to 50 microns. If the thickness is less than 2μ, the adhesion to the active nickel plating is weak, and plating to a thickness of 50μ or more is uneconomical.

The thickness of the activated nickel plating on the nickel plating is preferably 5 μm or more and 100 μm or less. If the thickness is less than 5 μm, the effect of reducing the hydrogen overvoltage will be small, and plating to a thickness of 100 μm or more will increase the cost.

Sulfur-containing compounds used in activated nickel plating include sulfides such as thiocyanate, thiourea, ammonium sulfide,
Furthermore, there are compounds such as sulfites, bisulfites, dithionites, and thiocyanates and/or thioureas are particularly effective.

The concentration of these sulfur-containing compounds added to the plating bath is 0.01 molar or more and 1.5 molar or less,
Preferably, the concentration is limited to 0.05 molar or more and 0.5 molar or less. The reason for this is that at a concentration of 0.01 mol or less, the effect of reducing hydrogen overvoltage is insufficient, and at a concentration of 1.5 mol or more, the adhesion of the activated nickel plating to the nickel plating decreases. It is also possible to use separately prepared nickel plating baths containing nickel salts and activated nickel plating baths containing nickel salts and sulfur-containing compounds. After nickel plating is performed in a nickel plating bath containing a nickel salt, an active nickel plating bath prepared by dissolving a sulfur-containing compound in the used nickel plating bath can be used.

In the present invention, it goes without saying that any embodiment can be adopted as long as active nickel plating is performed in an active nickel plating bath containing a sulfur-containing compound after nickel plating.

In addition, the current density when performing nickel plating and active nickel plating by electroplating does not necessarily have to be the same and can be selected as appropriate, but is usually 0.1A/
It is carried out in the range of Dm2 or more and 10 A/Dm2 or less.

Although the ion exchange membrane method has been mainly mentioned so far, it goes without saying that the electrolytic cell of the present invention can also be applied to the diaphragm method for asbestos and the like. As described above, after applying nickel plating to the inside of the cathode chamber, the cathode, and all other surfaces of the cathode chamber components using a 24-layer bath containing nickel salts, nickel plating was applied using an activated nickel plating bath containing nickel salts and sulfur-containing compounds. By applying activated nickel plating, there is no exposed iron part, thus preventing iron elution.
Furthermore, it is possible to manufacture an electrolytic cell having a cathode chamber having an active coating and a cathode that stably maintains an extremely low hydrogen overvoltage over a long period of time.

That is, the present invention uses an extremely simple method to produce an electrolytic cell having an iron-based metal cathode chamber without any modification.
Even under harsh conditions of high temperature and high alkali concentration,
This is an effective electrolytic cell for producing caustic alkali stably for a long period of time and with extremely low power consumption, without increasing hydrogen overvoltage and without elution of iron into caustic alkali. Hereinafter, the present invention will be explained in detail with reference to Examples.
Example 1 After alkaline degreasing and pickling of the cathode chamber whose inner surface is made of iron, the cathode made of iron expanded metal, and all other surfaces of the cathode chamber members, the conditions shown in Table 2 are applied using the nickel plating bath shown in Table 1. Nickel plating was performed.

Table 1 Nickel plating bath composition Nickel sulfate 0.91m01/e Nickel chloride 0.19rr101/e Boric acid
0.4911101/l Table 2 Nickel plating conditions bath temperature
60℃ Current density 6A/Cathode projected area Dm2 Plating time 3 After confusion, Table 3
Active nickel plating was carried out under the conditions shown in Table 4 using the active nickel plating bath shown in Table 4.

Table 3 Nickel chloride 0.5m01/e Ammonium chloride 1.0rT101/e Thiourea
0.2rT101/e Table 4 Bath temperature
50℃ current density
1.5A/cathode projected area Dm2 plating time
The cathode chamber and cathode thus obtained for 3 hours were combined with an anode chamber having an anode made of titanium lath coated with ruthenium oxide via a perfluorosulfonic acid ion exchange membrane to form an electrolytic cell, and the electrolysis shown in Table 5 was carried out. Salt water was electrolyzed under the following conditions.

The results are shown in Table 6. Table 5 Cathode chamber NaOH concentration 32% temperature
80℃ current density
30A/Dm2 Comparative Example 1 An electrolytic cell is constructed by combining a cathode chamber and cathode whose inner surface is made of iron with an anode chamber having an anode made of titanium lath coated with ruthenium oxide via a perfluorosulfonic acid ion exchange membrane,
Salt water was electrolyzed under the electrolytic conditions shown in Table 5.

Comparative Example 2 The cathode chamber whose inner surface was made of iron, the cathode, and all other surfaces of the cathode chamber members were subjected to active nickel plating using the active nickel plating bath shown in Table 3 of Example 1 under the conditions shown in Table 4. did.

An electrolytic cell was constructed by combining the thus obtained cathode chamber and cathode with an anode chamber having an anode made of titanium lath coated with ruthenium oxide through a perfluorosulfonic acid ion exchange membrane, and under the electrolytic conditions shown in Table 5. I did electrolysis. The results are shown in Table 6. Comparative Example 3 Only the cathode made of expanded iron was plated with nickel using the nickel plating bath shown in Table 1 of Example 1 under the plating conditions shown in Table 2.

Then, using the activated nickel plating bath shown in Table 3,
Activated nickel plating was applied under the plating conditions shown in . The cathode thus obtained was attached by welding to a cathode whose inner surface was made of iron. This was then combined with an anode chamber having an anode made of ruthenium oxide coated on titanium glass via a perfluorosulfonic acid ion exchange membrane to form an electrolytic cell, and electrolysis of saline water was carried out under the electrolytic conditions shown in Table 5. .
The results are shown in Table 6. Example 2 A cathode chamber whose inner surface was made of iron and a cathode made of expanded iron metal were degreased with alkali, acid washed, and then treated under the conditions shown in Table 2 of Example 1 using the nickel plating bath shown in Table 1 of Example 1. Nickel plating was performed.

Next, using the activated nickel plating bath shown in Table 7, Table 4
Activated nickel plating was applied under the conditions shown in . Table 7 Nickel sulfate 0.46rT101/e
Nickel chloride 0.10m01/e Boric acid 0.49rT101/l Thiourea 0.20rT101/e The thus obtained cathode chamber and cathode were coated with ruthenium oxide on a titanium lath through a perfluorosulfonic acid ion exchange membrane. In combination with an anode chamber having an anode, an electrolytic cell was constructed, and saline solution was electrolyzed under the conditions shown in Table 5 of Example 1.

Table 8 shows the changes over time in the q-sliding voltage and the iron concentration in NaOH. Example 3 After alkali degreasing and pickling, a cathode chamber whose inner surface is made of iron and a cathode made of expanded iron 5 metal are prepared as shown in Table 1 of Example 1.
Using the nickel plating bath shown in Example 1, nickel plating was carried out under the conditions shown in Table 2.

Next, using the activated nickel plating bath shown in Table 9, Table 4
Active nickel metal θ-kiing was performed under the conditions shown in . Table 9 Nickel sulfate 0.91m01/l Nickel chloride 0.19rr101/' Boric acid 0.49rT101/e Thiourea 0.201T101/l The cathode chamber and cathode thus obtained were passed through a perfluorosulfonic acid ion exchange membrane. In combination with an anode chamber having an anode made of a titanium lath coated with ruthenium oxide, electrolysis of saline water was carried out under the conditions shown in Table 5.

Table 10 shows the changes over time in electric sliding voltage and iron concentration in NaOH.
Shown below. Example 4 After alkali degreasing and pickling, a cathode chamber whose inner surface was made of iron and a cathode made of iron expanded metal were subjected to electrolytic nickel plating at 90°C for 3 minutes using Kanisen Blue Schumer electroless nickel plating solution. .

Next, active nickel plating was carried out using the active nickel plating bath shown in Table 9 of Example 3 under the conditions shown in Table 4. An electrolytic cell was constructed in which the cathode chamber and cathode thus obtained were combined with an anode chamber having an anode made of titanium lath coated with ruthenium oxide through a perfluorosulfonic acid ion exchange membrane, and salt was added under the conditions shown in Table 5. Performed water electrolysis. Table 11 shows the changes over time in the electric sliding voltage and the iron concentration in NaOH. Table 11.

Example 5 A cathode chamber whose inner surface was made of iron and a cathode made of iron expanded metal were degreased with alkaline and washed with acid, and then plated at 90C for 2 hours using Kanisen Blue Schumer electroless nickel plating solution.
Performed electroless nickel plating.

Next, using the nickel plating bath shown in Table 1 of Example 1,
Nickel plating was performed under the conditions shown in Table 2. Thereafter, active nickel plating was performed using the active nickel plating bath shown in Table 9 of Example 3 under the conditions shown in Table 4. The cathode chamber and cathode thus obtained were combined with an anode chamber having an anode made of titanium lath coated with ruthenium oxide via a perfluorosulfonic acid ion exchange membrane to constitute an electrolytic cell, and the electrolytic cell was constructed as shown in Table 5 of Example 1. Electrolysis of saline water was carried out under the following conditions. Table 12 shows the changes over time in the electric sliding voltage and the iron concentration in NaOH.

712゜゛9゜ - Reference Example Using a flat iron plate of 30CTn x 50α, alkaline degreasing,
After pickling, three-powder electroless nickel plating was performed at 90° C. using Kanisen Blue Schumer electroless nickel plating solution.

Next, using the nickel plating bath shown in Table 1 of Example 1,
Nickel plating was performed under the conditions shown in Table 13. Table 1
3 Bath temperature 60℃ Current density 2A/Dm2 Plating time
After that, active nickel plating was performed using the active nickel plating bath shown in Table 9 of Example 3 under the conditions shown in Table 14.

Table 14 Bath temperature 60°C current density
0.5A/Dm2 plating time
Table 15 shows the adhesion test results by a 3 hour 90 degree bending test.

Reference Comparative Example 3 After alkaline degreasing and pickling, an iron flat plate of 30 cm x 50 CTn was subjected to active nickel plating using the active nickel plating bath shown in Table 9 of Example 3 under the conditions shown in Table 14.

Table 15 shows the adhesion test results by 90 degree bending test.

4 Table 15 Reference example No peeling even after 10 bending tests.

Reference Comparative Example Peeled off in two bending tests.

Claims (1)

[Claims] 1. In an electrolytic cell used to separate an anode chamber and a cathode chamber using a diaphragm and supply an aqueous alkali chloride solution to the anode chamber to obtain chlorine from the anode chamber and hydrogen and caustic alkali from the cathode chamber, iron or All surfaces of the cathode chamber, cathode, and other cathode chamber components made of iron-based metals are nickel-plated using a nickel plating bath containing nickel salts, and then in an activated nickel plating bath containing nickel salts and sulfur-containing compounds. An electrolytic cell made of activated nickel plating.