JPH05179475A - Production of hypochlorite - Google Patents

Abstract

PURPOSE:To produce hypochlorite of high concentration with high efficiency by electrolyzing alkaline metal chloride in an anodic chamber of an ion- exchange membrane electrolyzer, adding anolyte to a cathodic chamber and reacting catholyte and chlorine generated in the anodic chamber. CONSTITUTION:An ion-exchange membrane electrolyzer 2 is divided into an anodic chamber 3 and a cathodic chamber 5 by an cation-exchange membrane 1. Water solution of alkaline metal chloride, such as salt water is fed to the anodic chamber 3 to perform electrolysis. The water solution of alkaline metal chloride with which the concentration in the anodic chamber 3 is lowered is added to the cathodic chamber 5 to keep the concentration of alkaline metal hydroxide in catholyte constant. Simultaneously the catholyte is taken out from the cathodic chamber to a reaction chamber 8. Here the catholyte consisting of alkaline water solution containing the hypochlorite and chlorine 9 generated in the anodic chamber 3 are reacted. Thereby hypochlorite, such as sodium hypochlorite is obtained in high concentration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing hypochlorite by electrolysis, and more particularly to a method for producing high concentration hypochlorite.

[0002]

2. Description of the Related Art Hypochlorites typified by sodium hypochlorite are used as bleaching agents and bactericides for treating sewage,
It is used in various fields from wastewater treatment to household kitchen or laundry. Hypochlorite can be produced by reacting chlorine with an alkali metal hydroxide obtained by electrolysis of an aqueous solution of an alkali metal chloride such as saline, or by using an alkali metal chloride without a diaphragm. It is carried out by a method of directly producing hypochlorite in the electrolytic cell by performing electrolysis in the electrolytic cell.

Since a method of reacting an alkali metal hydroxide with chlorine can obtain a high concentration of hypochlorite, this method is used when producing hypochlorite for the purpose of selling it. However, since an electrolytic facility for producing an alkali metal hydroxide and chlorine is required, it is carried out on a large scale in association with the production of sodium hydroxide or chlorine in an electrolytic plant such as a saline solution.

FIG. 2 shows a method of producing hypochlorite by reacting an aqueous sodium hydroxide solution obtained by electrolysis of sodium chloride with chlorine. An anode 22 is provided in the anode chamber 21, and a cathode 24 is provided in the cathode chamber 23.
Is provided, and the anode chamber and the cathode chamber are the cation exchange membrane 2
Saline solution was supplied to the anode chamber of the ion exchange membrane electrolytic cell 26 partitioned by 5, and the saline solution having a reduced concentration was taken out from the anode chamber 21, and dissolved chlorine was separated in the dechlorination tower 27. Later, in the salt adjusting step 26, the salt is dissolved and the saline is purified and circulated in the anode chamber.

On the other hand, water 29 is supplied to the cathode chamber 23 and circulates between it and the catholyte storage tank 30 while keeping the concentration of the sodium hydroxide aqueous solution of the catholyte constant. Then, the sodium hydroxide aqueous solution in the catholyte storage tank is reacted with chlorine 32 generated in the anode chamber of the electrolytic tank in the absorption tower 31 to produce the sodium hypochlorite aqueous solution.

Further, in the method of electrolyzing an aqueous solution of salt or the like in a diaphragmless electrolytic cell, the concentration of hypochlorite produced is relatively low, but it is a concentration that can be directly used for purification and sterilization of water. Since it can be produced and the production equipment is simpler than the electrolytic equipment for producing alkali hydroxide and chlorine, it is produced at a site requiring hypochlorite. Moreover, the electrolytic production of hypochlorite is
It is possible to adjust the current to be applied depending on the required amount of hypochlorite, and the characteristic feature is that all chlorine content effective for sterilization is dissolved in water. Therefore, even in the case where liquid chlorine storage facilities have been used so far to use gaseous chlorine or facilities that store concentrated hypochlorite, they do not need to be stored or transported. Hypochlorous acid is produced by electrolysis in Japan.

[0007]

The hypochlorite obtained by reacting the alkali metal hydroxide obtained in the ion exchange membrane electrolysis cell with chlorine can be obtained in high concentration. Its maintenance is complicated. Also, in the case of a method of electrolyzing an aqueous solution of alkali chloride such as common salt using a non-diaphragm electrolytic cell, the concentration of salt water supplied as an electrolytic solution should be 2% to 4%. is there. The higher the salt concentration, the higher the chlorine generation efficiency at the anode, but if salt water containing hypochlorous acid produced by electrolysis is used as is for water treatment, etc., if concentrated salt water is used, a high concentration of salt water will be obtained. Since it is not preferable to mix with the water to be treated, a salt concentration of seawater is usually used.

Hypochlorite is produced by the reaction between chlorine generated on the anode side and alkali generated on the cathode side. The hypochlorite salt is changed to chloric acid when electrolysis is further continued in the electrolytic cell. To do. Therefore, even if the residence time of the electrolytic solution is lengthened to produce a high concentration hypochlorite in a diaphragmless electrolytic cell, the amount of chlorate produced is increased, and the efficiency of hypochlorite production is increased. Will fall.

Therefore, in order to produce hypochlorite with high current efficiency, a plurality of electrolytic cells equipped with an anode and a cathode are placed through a partition plate without increasing the electrolysis rate in the unit electrolytic cell. Electrolyzers installed in multiple stages have been proposed (for example, Japanese Patent Publication No. 52-28104 and Japanese Patent Publication No. 61-44956).
issue).

However, the concentration of hypochlorous acid obtained by such a method is not sufficient, and there has been a demand for a method of electrolytically producing a highly efficient and high concentration hypochlorite salt.

[0011]

The method for producing hypochlorite by electrolysis according to the present invention is a method for producing an aqueous solution of an alkali metal chloride having a reduced concentration obtained in an anode chamber of an electrolytic cell partitioned by a cation exchange membrane as a cathode. This is a method of obtaining a high-concentration aqueous solution of hypochlorite by reacting an aqueous alkaline solution containing hypochlorite obtained in addition to the chamber with chlorine obtained in the anode chamber.

That is, the case of using a saline solution as an aqueous solution of an alkali metal chloride will be described. The saline solution is supplied to the anode chamber, and the saline solution whose concentration is lowered with the progress of electrolysis is supplied to the cathode chamber. Therefore, it is not necessary to perform the step of treating the returned saline solution having a reduced concentration, and since the returned saline solution having a reduced concentration in the anode chamber is added to the catholyte, water is added to adjust the concentration of the catholyte. It becomes unnecessary.

Furthermore, since the return saline is added to the catholyte, the chlorine dissolved in the anolyte can be effectively used for the production of hypochlorite. Further, the catholyte solution to which the return saline is added absorbs chlorine generated at the anode as it is to produce hypochlorite. As a result, it is possible to obtain a much higher concentration of hypochlorite compared to the hypochlorite obtained by direct electrolysis of saline, and the ion exchange membrane method electrolysis of salt produces chlorine and high concentrations of chlorine. In comparison with the method of producing a hypochlorite by reacting both with an aqueous solution of sodium hydroxide, the production process and production equipment are simpler, and the operation management of the production equipment is easier. It is easy to install at the place where the acid salt is consumed.

[0014]

[Function] The alkaline metal chloride aqueous solution is supplied to the anode chamber of the electrolytic cell using the cation exchange membrane to be electrolyzed, and the alkaline metal chloride aqueous solution having a reduced concentration in the anode chamber is supplied to the cathode chamber and the cathode A high concentration of hypochlorite can be produced by reacting the catholyte taken out from the chamber with chlorine generated in the anode chamber.

[0015]

The present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing one embodiment of the method for producing hypochlorite of the present invention.

In the anode chamber 3 of the ion-exchange membrane electrolytic cell 2 partitioned by the cation-exchange membrane 1, an anode in which a coating of an electrocatalytic substance containing an oxide of a platinum group metal is formed on a metal substrate such as titanium. 4 is provided, and the cathode chamber 5 is provided with a cathode 6 in which nickel, stainless steel, or a metal thereof is coated with a cathode active material that reduces hydrogen overvoltage. Electrolysis is performed while supplying the salt solution in which the salt is dissolved and purified in the salt solution adjusting step 7 to the anode chamber 3, and the salt solution having a reduced concentration is taken out from the anode chamber 3 and is supplied to the cathode chamber. While keeping the concentration of the aqueous sodium hydroxide solution in the chamber constant, the catholyte is reacted with chlorine 9 generated in the anode chamber in the reaction chamber 8 to produce sodium hypochlorite. In the reaction chamber, there is a storage tank 10 for the sodium hypochlorite aqueous solution in the lower part, and a mixed solution of sodium hypochlorite and sodium hydroxide is supplied from the upper part of the reaction chamber in the form of a shower by the circulation pump 11, and the anode chamber is used. It is reacted with the chlorine obtained in. It is necessary to cool the catholyte and chlorine supplied to the reaction chamber and the reaction chamber with cooling water or the like so that the generated hypochlorite is not decomposed.

Further, as the cation exchange membrane of the ion exchange membrane electrolytic cell used in the method of the present invention, a fluororesin cation exchange membrane can be used, but the concentration of the sodium hydroxide aqueous solution produced at the cathode is Since it is not necessary to make the concentration of the salt particularly high, it is possible to use a cation exchange membrane that does not adversely affect the electrolysis characteristics even if the saline solution supplied as the anolyte contains a relatively large amount of impurities. The water adjustment process can be simplified, and the operation of the electrolytic cell becomes easy.

Example 1 An electrode chamber unit having an anode (manufactured by Permelek Electrode Co., Ltd.) coated with an electrode catalyst material containing an oxide of a platinum group metal having a length of 400 mm and a width of 500 mm, and a nickel resin, and a fluororesin-based unit. Nafion 3 which is a cation exchange membrane
A bipolar electrode cell was assembled using four sheets of 24.

When a current of 400 amperes was passed through the electrolytic cell, the cell voltage was 14.2V. 300 g / l saline solution is supplied to the anode chamber at a flow rate of 12 liters / hour, 94 g / l return saline solution flowing out from the anode chamber is supplied to the cathode chamber, and the catholyte is taken out from the cathode chamber and reacted. Then, the catholyte was reacted with chlorine obtained in the anode chamber to obtain 13% by weight (158 g / l) of sodium hypochlorite aqueous solution at a flow rate of 11.4 liter / hour. The current efficiency for the production of hypochlorite was 85%.

[0020]

The alkali metal chloride aqueous solution is supplied to the anode chamber of the electrolytic cell using the cation exchange membrane for electrolysis,
An alkaline metal chloride aqueous solution with a reduced concentration in the anode chamber is supplied to the cathode chamber, and the catholyte taken out from the cathode chamber is reacted with chlorine generated in the anode chamber. The dechlorination step of No. 1 is unnecessary, and high-concentration hypochlorite can be easily produced at the place where hypochlorite is consumed.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an embodiment of the method of the present invention.

FIG. 2 is a diagram illustrating a conventional method for producing hypochlorite using an ion exchange membrane electrolytic cell.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Cation exchange membrane, 2 ... Ion exchange membrane electrolytic cell, 3 ... Anode chamber, 4 ... Anode, 5 ... Cathode chamber, 6 ... Cathode, 7 ... Saline adjustment process, 8 ... Reaction chamber, 9 ... Chlorine, 10 … Storage unit, 11…
Circulation pump, 21 ... Anode chamber, 22 ... Anode, 23 ... Cathode chamber, 24 ... Cathode, 25 ... Cation exchange membrane, 26 ... Ion exchange membrane electrolytic cell, 27 ... Dechlorination tower, 28 ... Saline solution adjusting step, 29 ... water, 30 ... catholyte storage tank, 31 ... absorption tower, 32
…chlorine

Claims (1)

[Claims] 1. An alkali metal chloride solution having a reduced concentration in the anode chamber is supplied by supplying an aqueous solution of an alkali metal chloride to the anode chamber of an ion exchange membrane electrolysis cell divided into an anode chamber and a cathode chamber by an ion exchange membrane for electrolysis. Substance aqueous solution is added to the cathode chamber,
A method for producing hypochlorite, characterized in that the concentration of alkali metal hydroxide in the catholyte is kept constant and the catholyte taken out from the cathode chamber is reacted with chlorine generated in the anode chamber.