JP3319880B2 - Anode for producing hypochlorite and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anode used for electrolytic oxidation of chloride ions and a method for producing the same, and more particularly to an anode suitable for producing hypochlorite by electrolysis and a method for producing the same.

[0002]

2. Description of the Related Art Anodes having a coating of a noble metal oxide for electrolytic oxidation of chloride ions to produce hypochlorite ions are well known. For example, MODERN CHLOR-
ALKALI TECHNOLOGY (KEVIN
WALL, ELLIS HORWOOD LIMIT
ED, 1986, P.E. 400) describes an electrode having an electrode coating composed of platinum plating, a mixture of platinum and iridium oxide, and a mixture of ruthenium oxide and titanium oxide. Japanese Patent Application Laid-Open No. 63-199887 describes an iridium oxide, and Japanese Patent Application Laid-Open No. 4-277081 describes an electrode having a coating of platinum and a palladium alloy. Further, JP-A-63-143277 discloses an electrode having a coating composed of an oxide of palladium, ruthenium and titanium and platinum.

When these conventional electrodes are used as anodes, the anode coating for producing hypochlorite ions from chloride ions has a low salt decomposition rate and contains low concentrations of hypochlorite ions. When a solution is prepared, a satisfactory current efficiency can be obtained. However, when a salt decomposition rate is high or when a solution containing hypochlorite ions having an effective chlorine concentration of 4% by weight or more is manufactured, the current efficiency is improved. It is low and cannot be industrially satisfactory.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an anode which has a high current efficiency even when the salt decomposition rate is increased and which has an effective chlorine concentration of 4% by weight or more with a high current efficiency. Is what you do.

[0005]

According to the present invention, there is provided an anode for producing hypochlorite having an electrode active coating formed on a conductive substrate, comprising 10 to 45% by weight of palladium oxide and 15 to 45% by weight.
45% by weight of ruthenium oxide, 10 to 40% by weight of titanium dioxide, 10 to 20% by weight of platinum, and 2 to 10% by weight of at least one metal selected from cobalt, lanthanum, cerium and yttrium. It has a coating containing an oxide, and, in a method for producing an anode for the production of hypochlorite having an electrode active coating formed on a conductive substrate, ruthenium, titanium, each compound of platinum A palladium oxide and an oxide of at least one metal selected from cobalt, lanthanum, cerium and yttrium are dispersed in the contained solution to form a slurry-like coating solution, which is coated on an electrode substrate, and an oxygen-containing atmosphere is formed. And a method for producing an anode for producing hypochlorite.

[0006] Further, the slurry-like coating solution comprises, as solid components, ruthenium chloride, chloroplatinic acid, butoxytitanium, together with palladium oxide and at least one metal oxide selected from cobalt, lanthanum, cerium and yttrium. And a method for producing an anode comprising a solution comprising butanol.

That is, the anode on which the electrode active film of the present invention is formed is made of cobalt, lanthanum, cerium in addition to the respective oxides and platinum of palladium, ruthenium and titanium conventionally used as the electrode active film for the anode. And oxides of at least one metal selected from yttrium.

The composition of the anodic coating of the present invention comprises 10 to 45% by weight of palladium oxide, 15 to 45% by weight of ruthenium oxide, 10 to 40% by weight of titanium dioxide, and 10 to 20% by weight of platinum. At least one of lanthanum, cerium oxide and yttrium oxide is 2-1
It is preferable to add 0% by weight.

When the mixing ratio of at least one of the respective oxides of cobalt, lanthanum, cerium and yttrium is less than 2% by weight or more than 10% by weight,
When the salt decomposition rate is high or the hypochlorite ion concentration is 4% by weight or more, the efficiency of chloride ion oxidation is reduced, which is not preferable.

When two or more oxides of cobalt, lanthanum, cerium and yttrium are used, the total content of the oxides may be within the above range.

The production of the anode of the present invention can be obtained by applying a slurry coating solution containing a solution containing a metal component together with a solid component of an oxide, followed by drying and firing in an oxygen-containing atmosphere. The solid component of the slurry-like coating solution contains an oxide of palladium and an oxide of at least one metal selected from cobalt, lanthanum, cerium, and yttrium, and includes ruthenium chloride, chloroplatinic acid, butoxytitanium, and the like as solution components. It is preferable that the metal component is dissolved in an organic solvent, and as the organic solvent,
Butanol can be used. Further, by using the slurry-like coating solution, an oxide added as a solid component to the slurry-like coating solution does not adversely affect the formation of the electrode active film, and an anode having excellent electrolytic characteristics can be obtained.

The particle size of the solid component used in the slurry coating solution is preferably 0.1 μm or more and less than 1 μm. When the particle size of the solid component is less than 0.1 μm, the effect of increasing the oxidation efficiency of chloride ions is reduced. Insufficient and small particle size requires special equipment for component preparation. On the other hand, if the particle size of the solid component is 1 μm or more, it is difficult to apply the solid component uniformly on the substrate surface, which is not preferable.

The oxides of cobalt, lanthanum, cerium, and yttrium used in the present invention include C
Those having a chemical formula of o ₂ O ₃ , Co ₃ O ₄ , La ₂ O ₃ , CeO ₂ , Y ₂ O ₃ are preferable. These oxides may be produced by any method, but those obtained by reacting an aqueous metal salt solution with an alkali and then dehydrating by heating are preferable. Further, it may be a single metal oxide, a eutectic oxide of two or more metals, or a mixture of two or more metal oxides.

It is desirable that the slurry-like coating liquid is appropriately stirred at the time of use so that the solid component is always suspended at a constant concentration. When the amount of the coating liquid is small, stirring with a magnet stirrer or a brush is sufficient, but when the amount of the coating liquid is large, stirring with a stirrer or a shaker is preferable.

The anode of the present invention is prepared by subjecting the electrode substrate to a pretreatment such as surface roughening by sandblasting or etching with an acid treatment, and then washing with water and drying to apply a slurry coating solution. It is preferable to use a brush, a brush, a roll, or the like for application. The substrate coated with the coating solution is dried at room temperature and further heated in an electric furnace.

The steps of applying, drying and heating and baking the slurry-like coating solution are repeated 5 to 10 times to form a film having a predetermined thickness. The firing can be performed by heating at 400 to 600 ° C. in an oxygen-containing atmosphere in an electric furnace for 5 to 30 minutes.

If the number of times the slurry-like coating solution is applied to the electrode substrate is small, the overvoltage is high or the anode activity is low, and if the number of coatings is large, the overvoltage is reduced and the anode activity is improved in proportion to the number. No, 5-10
Times are preferred.

The electrode active film of the anode obtained as described above is obtained by converting solid oxides of metals such as palladium, cobalt, lanthanum, cerium and yttrium into ruthenium oxide, titanium oxide and the like. It is fixed by a porous mixed matrix of platinum,
Further, since the solid component of the slurry-like coating liquid has no effect on the crystal structure of the porous mixed matrix, a film having high mechanical strength can be formed.

As the substrate of the anode of the present invention, a thin film-forming metal such as titanium or tantalum can be used, but titanium is most preferable.

The shape of the substrate of the anode may be any shape such as a bar, a cylinder, a plate, an expanded metal, a perforated plate, and a mat.

The anode obtained according to the present invention is obtained by electrolyzing salt water having a salt concentration of 25 to 320 g / l without a diaphragm to produce a sodium hypochlorite solution having an effective chlorine concentration of 0.1 to 80 g / l. Suitable for When obtaining a low concentration of hypochlorite, it is preferable to use a low-concentration saline solution, and when obtaining a high-concentration hypochlorite, it is preferable to use a high-concentration saline solution. The electrolysis is performed at a current density of 1 to 50 A / dm ² and a temperature of 5 to 40 ° C.
Can be done with

[0022]

In the anode of the present invention, a coating composed of oxides of palladium, ruthenium and titanium, and at least one oxide of platinum, cobalt, lanthanum, cerium and yttrium is formed on an electrode substrate as an electrode active material. When used for electrolysis of saline,
Even if the salt decomposition rate is increased, a decrease in current efficiency is small, and a high-concentration sodium hypochlorite solution having an effective chlorine concentration of 4% by weight or more can be obtained.

[0023]

The present invention will be described in more detail with reference to the following examples.

Example 1 A titanium plate having a length of 5 cm and a width of 5 cm was subjected to pretreatment such as surface roughening by sandblasting and etching with oxalic acid, and the pretreated titanium was added to ruthenium chloride, tetra-n-butoxytitanium and platinum chloride. In a solution containing an acid, along with palladium oxide particles, cobalt trioxide, lanthanum oxide,
An operation of preparing a slurry containing at least one oxide selected from cerium oxide and yttrium oxide, applying and drying the obtained slurry, and baking at 500 ° C. for 10 minutes in an electric furnace in an air-containing atmosphere is repeated four times. The sample was further coated and dried once, and then baked by heating in an electric furnace for 30 minutes in the same manner.
Twelve anodes were formed.

The obtained anode was evaluated by the following methods, and the results are shown in Table 1.

Height 30 mm, width 115 mm, height 80 mm
The anode of the present invention is attached to the
The current density is 40 A / dm ^{2 based on the} anode area at a distance between the electrodes of 2 mm using a 0 mm, 10 mm wide titanium plate as the cathode.
Then, the saline solution having a concentration of 250 g / liter was electrolyzed, and the average current efficiency when the effective chlorine concentration of the electrolytic solution became 4% by weight was obtained. The obtained current efficiency is shown in Table 1.

Comparative Example 1 An anode having the composition shown in Table 1 was produced in the same manner as in Example 1 except that no oxide of cobalt, lanthanum, cerium, or yttrium was used. And the results are shown in Table 1 as sample numbers 13 to 16.

[0028]

[Table 1]

Example 2 An anode manufactured in the same manner as in Example 1 was used at an electrolysis temperature of 23 to 25.
C, current density 20 A / dm ² , salt water concentration 28 g / l, and the effective chlorine concentration was 12,000.
The average current efficiency at the time of ppm was determined. The evaluation results are shown in Table 2 as sample numbers 17 to 28 together with the compositions of the electrodes.

Comparative Example 2 An anode having the composition shown in Table 1 was produced in the same manner as in Example 1 except that oxides of any of the metals cobalt, lanthanum, cerium and yttrium were not used.
The results are shown in Table 2 as sample numbers 29 to 32 together with the electrode composition.

[0031]

[Table 2]

Example 3 Under the same electrolysis conditions as in Example 1, the change over time in the electrolysis performance was measured. Sample No. 33 is Sample No. 2, 34 is 6 and 3
5 has the same composition as 8 and 36 has the same composition as 11. Table 3 shows the current efficiency.

Comparative Example 3 Using acetylacetonate of any metal of cobalt, lanthanum, cerium and yttrium, a coating solution in which only palladium oxide was in a slurry state and all others were in a liquid state was prepared. An anode having the same composition was prepared. Sample No. 37 is 33, 38 is 34, and 39 is 35
And 40 were adjusted to the same composition as 36.
Under the same electrolysis conditions as in Example 3, the change over time in electrolysis performance was measured, and the current efficiency is shown in Table 3.

[0034]

[Table 3]

[0035]

As described above, the anode of the present invention has a coating obtained by applying a slurry coating solution containing a solution containing a solid component of an oxide and a metal component and firing it. Since the oxidization efficiency is high and high-concentration hypochlorite ions can be generated with high current efficiency, it is possible to produce high-concentration hypochlorite with a lower power consumption unit than conventional anodes.

Continuation of front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C25B 1/00-15/08

Claims (2)

(57) [Claims] 1. An anode for producing hypochlorite having an electrode active coating formed on a conductive substrate, comprising 10 to 45% by weight.
Palladium oxide, 15 to 45% by weight ruthenium oxide, 10 to 40% by weight titanium dioxide, 10 to 20% by weight.
Characterized in that it has a coating containing an oxide of at least one metal selected from the group consisting of cobalt, lanthanum, cerium and yttrium together with 2% by weight of platinum together with 2% by weight of platinum. anode. 2. A method for producing an anode for producing hypochlorite having an electrode active film formed on a conductive substrate, the method comprising the steps of: adding palladium oxide and cobalt to a solution containing each compound of ruthenium, titanium and platinum; An oxide of at least one metal selected from the group consisting of lanthanum, cerium and yttrium is dispersed to form a slurry coating solution, which is coated on an electrode substrate and fired in an oxygen-containing atmosphere. Item 6. The method for producing an anode for producing hypochlorite according to Item 1.