JPH0529605B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for decomposing chlorate contained in saline water. More specifically, the present invention relates to a method for efficiently decomposing chlorate contained in recycled saline when saline is electrolyzed to produce caustic soda.

[Conventional technology and problems]

Currently, caustic soda is produced by electrolyzing salt water using the diaphragm method or the ion exchange membrane method, but in the anode chamber, chlorate is produced through side reactions such as Cl ₂ + 2NaOH → NaClO + NaCl + H ₂ O 3NaClO → NaClO ₃ + 2NaCl. is a byproduct. Therefore, in ion-exchange membrane electrolysis in which saline is used repeatedly, chlorate accumulates in the saline, resulting in adverse effects such as a decrease in the solubility of the saline and accelerated deterioration of the ion-exchange membrane.

Therefore, in order to reuse saline, it is necessary to reduce the concentration of sodium chlorate in the saline to a certain level or to remove it completely. For this reason, various methods have been implemented to partially discard saline water or to decompose chlorate.

Conventional decomposition methods include (1) adding a reducing agent and (2) adding a strong acid, but neither of them can be said to be a sufficient decomposition method.

That is, method (1) involves adding a reducing agent such as sodium sulfite, but it has the drawback that the _reducing agent is relatively expensive and the amount _used is _{large .} As shown in the reaction formula of SO ₄ + NaCl, SO ₄ ions are generated, and a secondary SO ₄ ion removal operation is required to promote deterioration of the anode and ion exchange membrane of the electrolytic cell.

In addition, method (2) is a method of decomposing chlorate using hydrochloric acid as a strong acid, as shown by the reaction formula, for example, NaClO ₃ +6HCl→3Cl ₂ +NaCl+3H ₂ O. However, if the pH of the salt water is around 1 or Since a sufficient decomposition rate cannot be obtained unless the acid is in the strong acid range, it is necessary to add 10 to 20 times the molar ratio of hydrochloric acid to the normally contained chlorate. For this reason, after decomposing the chlorate, it is necessary to add alkali to neutralize the excess hydrochloric acid, and in addition to the above equation, several percent of chlorine dioxide is usually produced as a by-product through the reaction of the following equation. do.

2NaCl ₃ +4HCl→2ClO ₂ +Cl ₂ +2NaCl+O _2Not only is this chlorine dioxide self-explosive, but if it is mixed into chlorine, it may cause a reaction failure in the chlorine-using equipment.

An object of the present invention is to provide a method for decomposing chlorate, which eliminates the drawbacks of the conventional methods, is simple and efficient in operation, and does not require secondary treatment.

[Means for solving problems]

That is, the present invention is a method for decomposing chlorate, which is characterized by bringing acidic or neutral saline containing chlorate into contact with carbon, and is represented by the reaction formula: 2NaClO ₃ +3C→3CO ₂ +2NaCl. As described above, this method uses carbon to decompose chlorate into carbon dioxide and salt.

The inventors further discovered that this reaction can be easily initiated by dissolving a small amount of chlorine in the system. i.e. produced by dissolved Cl ₂
NaClO and even HClO produced by hydrolysis
is initially adsorbed on carbon and further reacts to produce CO ₂ .

NaClO + HCl → HClO + NaCl Cl ₂ + H ₂ O → HClO + HCl 2HClO + C → CO ₂ + 2HCl Due to the HCl generated at this time, it is estimated that the pH value of the neutral liquid is 3 or less, and the reaction between chlorate and carbon occurs. was found to be accelerated and decomposed into carbon dioxide and salt with almost no side reactions.

The carbon used in the present invention may be activated carbon, charcoal, or the like, but activated carbon is particularly preferred, such as WA-4/8 mesh manufactured by Kyatara Kogyo Co., Ltd.

The saline solution may be neutral or acidic, but in consideration of the reaction rate, it is preferably PH3 or less, and the reaction will be further promoted if chlorine is dissolved therein. Furthermore, the temperature when bringing salt water into contact with carbon is 60° to 130°C,
Preferably, the contact time is 5 to 120 minutes. If the contact time is shorter than 5 minutes, the decomposition of the chlorate will be insufficient, and if it is longer than 120 minutes, no particular inconvenience will occur, but from economical considerations, 120 minutes or less is sufficient.

In addition, if the temperature is raised above 130° C., the reaction is further promoted, but a reaction tank with high pressure resistance is required, which causes disadvantages such as a large amount of energy being required for heating.

〔Example〕

The functions and effects of the present invention will be explained in more detail below using Examples and Comparative Examples.

Example 1 PH2.2 containing 21g/chlorate as _NaClO3
Add activated charcoal (Kiyatara Industries Co., Ltd. WA−) to 300 ml of saline solution.
After adding 150 ml of 4/8 mesh and maintaining the temperature at 85°C, changes in the concentration of chlorate were measured, and the results were as follows.

Time NaCl ₃ (g/) 0 21 After 1 hour 14.5 2 〃 10.5 5 〃 4 Example 2 PH2.3 containing 45 g/chlorate as NaClO ₃
Add activated charcoal (WA made by KITARA INDUSTRIAL CO., LTD.) to 300 ml of saline solution.
- 8/32 mesh) was added and heated and maintained at 103°C, and changes in chlorate concentration were measured, and the results were as follows.

Time NaClO ₃ (g/) 0 45 1 hour later 26 2 〃 16.5 5 〃 1.5 Example 3 Column (inner diameter 150 mm, height
1300 mm), a saline solution of pH 2.3 containing 30 g of chlorate as NaClO ₃ was continuously passed through the tube at 80° C. and at 30/h for 240 hours. The chlorate concentration in the effluent is
The average amount was 27 g/ _NaClO3 .

Example 4 Saline solution with pH 6.5 containing 45 g/chlorate as NaClO ₃ and 0.20 g/available chlorine as Cl ₂
300ml of activated carbon (WA-4/8 manufactured by KITARA INDUSTRIAL CO., LTD.)
When 150 ml of methane was added and maintained at 80°C, the chlorate concentration after 1 hour was 27 g/.

Example 5 PH2.6 with 37g/chlorate as _NaClO3
To 300 ml of saline solution, add activated charcoal (manufactured by Quitara Industries Co., Ltd.).
When 200ml of WA-4/8 mesh was added, the mixture was filled into a pressure-resistant container, and heated and maintained at 130°C under pressure, the chlorate concentration after 1 hour was 0.5 as _NaClO3 .
It was g/.

Comparative Example 1 PH2.1 containing 45g/chlorate as _NaClO3
When 300ml of saline solution was heated and maintained at 85℃, 3
The chlorate concentration after hours was 44.5g/ as _NaClO3 .
It was hot.

Comparative Example 2 PH8.1 containing 31g/chlorate as _NaClO3
To 300 ml of saline solution, add activated charcoal (manufactured by Quitara Industries Co., Ltd.).
When 150ml of WA-4/8 mesh was added and maintained at 90℃, the chlorate concentration after 3 hours was
It was 31g/as _NaClO3 .

Claims (1)

[Scope of Claims] 1. A method for decomposing chlorate, which comprises bringing acidic or neutral saline containing chlorate into contact with carbon. 2. The method according to claim 1, wherein the contact temperature is 60 to 130°C. 3. The method according to claim 1, wherein the carbon is one or more selected from activated carbon and charcoal. 4. The method according to claim 1, wherein the reaction is accelerated by the presence of chlorine.