JPS586983A - Electrolytic cell - Google Patents

Abstract

PURPOSE:To prevent the elution of iron to caustic alkali by subjecting all of the inside surfaces of cathode chambers constituted of cathodes applied with metallic coatings having low hydrogen overvoltage and iron frames of cathode chambers and the surfaces of the other members in the cathode chamber nickel plating. CONSTITUTION:In the stage of segmenting an electrolytic cell to anode chambers and cathode chambers by the use of diaphragms and electrolyzing alkali chloride, the cathodes made by applying metallic coatings having low hydrogen overvoltage on the surfaces of iron or ferrous metallic base bodies are mounted in the cathode chambers constituted of iron or ferrous metallic cathode frames. The low hydrogen overvoltage coatings are formed by using an active nickel plating bath dissolved with, for example, nickel rhodanide. Nickel plating or electroless plating is applied on all of the inside surfaces of the cathode chambers constituted of such cathodes and cathode chamber frames and the surfaces of the other inside members of the cathode chambers. These are plated to about 5-35mu thick. It is possible to produce caustic alkali at less electric power consumption from aq. alkali chloride soln. stably for a long period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel electrolytic cell suitable for producing caustic alkali with no iron elution during electrolysis, stable IMJ over a long period of time, and low power consumption.

A method for producing chlorine and caustic soda by electrolyzing a saline solution using a cation exchange membrane as a diaphragm is known.
The electrolysis method using a ζO cation/exchange membrane has an extremely small amount of salt mixed into the caustic soda produced at the cathode, and there is no pollution problem compared to the mercury method or asbestos method, and it has become particularly popular in recent years. It has been attracting attention.

In order to increase the concentration and current efficiency of caustic soda obtained in the cathode chamber, cation exchange membranes have been developed and improved.
Cation exchange membranes based on par-70 carbon polymers that can be obtained with a high efficiency have been developed, and some are about to be commercialized. On the other hand, in recent years, the importance of energy conservation has become a global concern, and from this perspective, it is important to reduce electrolytic power as much as possible in this field.
It is strongly desired to reduce the battery voltage as much as possible.

Up until now, for the purpose of lowering the battery cell voltage, expanded metal,
Measures have been proposed, such as using porous electrodes such as punch metal or wire mesh, controlling the composition of these electrodes themselves and the distance between them, or specifying the composition of the cation exchange membrane and the type of exchange group. ing. Of these, an aqueous alkali chloride solution in which the main reaction is a hydrogen generation reaction using a diaphragm at the cathode.
In electrolysis, iron cathodes of the above-mentioned shape are used mainly because they are inexpensive and exhibit a fairly low hydrogen overvoltage. However, as mentioned above, with the development of cation-exchange membrane salt electrolysis technology, further reductions in power consumption are desired from the perspective of energy conservation.
No. 92295.

゛ As seen in Japanese Unexamined Patent Publication No. 56-62148, efforts are being made to develop cathodes that have a hydrogen overvoltage that is lower than that of iron. Although these metal-coated cathodes with a low hydrogen overvoltage can achieve their original purpose, it is clear that they include the following serious problems.

In other words, when a single electrode made of iron or an iron-based metal with a metal coating having a low hydrogen overvoltage applied to the surface of the base material is used instead of the conventional iron cathode, the amount of iron leached becomes extremely large in a short period of time. A phenomenon that adds to #' is recognized. This phenomenon tends to become more pronounced under severe electrolytic conditions such as high temperature and high alkali concentration.

This leaching of iron deteriorates the quality of the obtained caustic.

Not only does it cause performance deterioration of diaphragms such as cation exchange membranes, but it also causes corrosion of the inside of the fCC electrode, which is composed of iron or iron-based metals, and causes serious problems such as shortening the life of the electrolytic cell itself. . 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,
It is expensive and impractical to use anti-alkaline earth metals for all of the metals constituting the cathode chamber, so it is impossible to employ them in parallel. Furthermore, in this case the cathode
1.1.1 The base material must also be made of a metal that is resistant to alkali corrosion. This is because when using a single electrode made of iron or iron-based metal with a coating such as nickel that has a low hydrogen overvoltage applied by plating, etc., when attaching the electrode to the cathode chamber by a method such as welding, - Even if done carefully, the coating will be damaged and the iron substrate will be exposed.
This is because the elution of iron from this exposed portion progresses. 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 all at once, the inventors of the present invention have found that the iron cathode and cathode chamber frame made of iron or iron-based metals that have been used up to now can be used as they are, and that any complicated They have completed an electrolytic cell that can prevent iron from leaching out even with a simple electrolytic cell structure, and can produce caustic alkali stably over a long period of time with low power consumption.

That is, the present invention uses a diaphragm to separate an anode chamber and a cathode chamber, supplies an aqueous alkali chloride solution to the anode chamber, and performs electrolysis to obtain chlorine from the anode chamber and hydrogen and caustic alkali from the anode chamber. In the tank, an electrode made of a metal coating having a low hydrogen overvoltage on the surface of a substrate made of iron or iron-based metal is attached to a nine-cathode chamber made of iron or iron-based metal (one-electrode chamber frame), and then The electrode, the inner surface of the cathode chamber, and the surfaces of other cathode chamber members are all plated with nickel or electroless nickel in an electrolytic cell.

In the present invention, a known method may be suitably employed as a method for coating the surface of an iron or sapon-based metal substrate with a low hydrogen overvoltage, and is not particularly limited. A method of performing active nickel plating using an active nickel plating bath in which a sulfur-containing compound such as rhodan nickel is dissolved, a method of thermal spraying metal powder such as nickel, cobalt, platinum, etc.
Alternatively, a method may be used in which a liquid containing these metal powders is applied and then heated and sintered to cover the surface.

A particularly effective method is nickel salt α05~(19
A method of performing active nickel plating using an active nickel plating bath containing a molar concentration of thiocyanate groups and ammonium ions at a molar concentration at least t1 times the thiocyanate group concentration;
and nickel salt, the amount of sulfur in the compound is α01 mol ~ tO
The oxidation number of thiourea and/or sulfur in the molar concentration range is 5.
At least one of the following oxoacid salts is used in an active nickel plating bath containing ammonium ions at a molar concentration of at least 15 times the sulfur concentration in the sulfur compound.
, activated nickel plating, then 50-500℃
This method involves heat treatment.

What is unique about the present invention is that even if a gold coating with a low hydrogen overvoltage is applied by such a method and further nickel plating or electroless nickel plating is applied to the nine cathodes, the hydrogen overvoltage hardly increases. Another surprising fact is that the durability of the film is dramatically improved.

After installing a metal-coated cathode with a low hydrogen overvoltage in the cathode chamber, the inside surface of the anode chamber composed of the cathode chamber frame made of iron or iron-based metal, and all other surfaces of the cathode chamber members are removed. Either nickel plating or electroless nickel plating may be applied to the surface, but electroless nickel plating is preferable because it allows uniform plating over the entire surface. The thickness of the plating can be selected arbitrarily, but if it is too thin, the effect of preventing iron elution will be small, and if it is too thick, the cost will increase and the degree of hydrogen overvoltage of the active coated cathode will increase. , 5-35P is suitable.

The other cathode chamber members herein refer to members present in the cathode chamber, such as the conductive rod 8 current collector and the welded portion. It goes without saying that members using anti-alkaline earth metals such as nickel instead of iron-based metals do not need to be plated with nickel or electroless nickel if possible.

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 aqueous nickel salts such as nickel sulfate, nickel chloride, nickel ammonium sulfate, and nickel sulfaminate are used.

The concentration of nickel salt is not particularly limited, but is usually (11
It is used in a range of molar to 2-0 molar.

The present invention uses an extremely simple method that has not been adopted until now.
Without making any changes to the electrolytic cell made of iron-based metal, it is possible to elute iron into caustic alkali without increasing the hydrogen overvoltage under severe conditions of high temperature and high alkali concentration. This is an effective electrolytic cell that can produce caustic alkali with extremely low power consumption and is stable for a long period of time. In particular, when an active coated cathode is employed, the electrolytic cell becomes extremely practical and effective.

Examples are shown below, but Himi F! j4Vi is not limited to these.

Example 1 and Comparative Examples 1 and 2 Nickel chloride α5 was applied to the surface of expanded metal made of mild steel.
7 mol/l, ammonium chloride tO mol/j.

Using a bath in which thiourea α5 ek/l was dissolved, a 5 A/lk? was heated at 50°C with stirring. Activated nickel plating was carried out for 4 hours at a current density of . This was attached by welding to a conductive rod O#c in the head electrode chamber having a conductive rod as a negative pole.

After that, a portion K of the cathode chamber made of metal containing the cathode is removed.
)b Electroless plating of nickel was performed using Nisenbruschemer electroless nickel plating solution. The thickness of the electroless nickel plating was 20 tones. The cathode chamber is barfed through a sulfonic acid ion exchange membrane onto a titanium glass.
In combination with an anode chamber having an anode coated with ruthenium fII, an electrolytic cell is constructed, and a saline solution can be electrolyzed. The electrolysis conditions are shown in Table 1. Table 2 shows the change in cell voltage over time and the concentration of iron in caustic soda. - As Comparative Example 1, one electrode whose surface was activated in the same manner as in Example 1 was used as a conductive rod in the cathode chamber. The electrolysis cell was constructed by combining the anode chamber with an anode made of titanium lath coated with ruthenium oxide through a par 70 rosulfonic acid ion exchange membrane, which was attached by welding to the membrane. .

In addition, as a comparative example 2, a mild steel expanded metal without active coating was applied to the surface, and the above 2.
The results of electrolysis performed in the same manner as above are shown.

1st table anode chamber Na0Hll [32s Temperature 80℃ Current density 50A/lh! Table 2 Example 1 Battery voltage, CV') 555 A50 549 Iron concentration -) (Ll (Ll
(11 Comparative Example 1 Battery voltage (V) A48 !L63 A7
171 Iron concentration) 8 19 21 Comparison Ga 2 Battery voltage (V) 571 569 570
Iron concentration (r19m) 5 6 b
Example 2 and Comparative Example 5 An electrode whose surface was activated by plasma spraying nickel powder onto a mild steel expanded metal was attached by welding to a # conductive rod in an anode chamber having a conductive rod. The thickness of the sprayed coating was 1 (10 tones). Thereafter, electroless nickel plating was applied to the metal part of the anode chamber containing the anode using Kanisenbruschemer electroless nickel plating solution. The thickness of the plating was 10 mm.Next, the plate forming chamber was combined with an anode chamber having an anode made of titanium lath coated with ruthenium oxide through a 70p sulfonic acid ion exchange membrane to form an electrolytic cell. Water was electrolyzed. Table 3 shows changes in cell voltage over time and changes in iron concentration in caustic soda over time.

As Comparative Example 3, an anode whose surface was activated by applying pressure in the same manner as in Example 2 was attached to a conductive rod in a cathode chamber having a conductive rod using a 111 contact, and a titanium lath was applied to the anode through an ion exchange membrane. An electrolytic cell is configured in combination with an anode chamber having an anode coated with ruthenium oxide on top,
Electrolysis of salt water was performed.

The results are shown in Table 3.

Example 2 Cell voltage cf') 45B A51 151 Iron concentration (2) Gin (Ll α1 α1 Comparative example 5 Cell voltage (To) 553 569 570 Iron concentration $) 10 15 15 Patent applicant Toyo Soda Kogyo Co., Ltd.

Claims (1)

[Claims] 1) A diaphragm is used to separate the anode chamber and the anode chamber, and an alkali chloride aqueous solution is supplied to the anode chamber to produce chlorine from the anode chamber, hydrogen and caustic alkali from the cathode chamber. After attaching a polarization made of a metal coating with low hydrogen overvoltage on the surface of an iron or iron-based metal substrate to a cathode chamber composed of a polarization chamber frame made of iron or iron-based metal, An electrolytic cell in which the inner surface of the cathode chamber frame and the surfaces of other interior members of the cathode chamber are all nickel plated or electroless nickel plated.