JPS6287411A - Method of decomposing chlorate - Google Patents

Abstract

PURPOSE:To efficiently decompose a chlorate in a solution of salt, by optionally adding chlorine to a neutral or acidic solution of salt containing a chlorate and bringing the solution into contact with carbon. CONSTITUTION:Chlorine is optionally added to a neutral or acidic (preferably <=3 pH) containing a chlorate (e.g., NaClO3), which is brought into contact with carbon such as active carbon, charcoal, etc., and reacted at 60-130 deg.C for 5-120min, so that the chlorate in a circulating solution of salt in production of electrolytic caustic soda is efficiently decomposed.

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.
' 111g03 Na(JO-→NaCl0.-t
Chlorate is produced as a by-product due to side reactions such as 2 Na (7).Therefore, in ion-exchange membrane electrolysis where saline water is circulated, chlorate accumulates in the saline water, resulting in a decrease in the solubility of salt. Alternatively, adverse effects such as accelerated deterioration of the ion exchange membrane may occur.

Therefore, in order to reuse the saline solution, it is necessary to reduce the concentration of sodium chlorate in the saline solution 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.
None of these methods can be said to be sufficient decomposition methods.

In other words, method 0) involves adding a reducing agent such as sodium sulfite, but this method has the disadvantage that the reducing agent is relatively expensive and requires a large amount of use.
As shown in the reaction formula of 25Oa - 3 NazS (14+Na It becomes necessary.

In addition, the method (2) is, for example, NaCJOa + 611['J-→3C1g + N
a(J + As shown in the reaction formula of 31120, it is a method of decomposing chlorate using hydrochloric acid as a strong acid,
Sufficient decomposition rate cannot be obtained unless the salt water is in a strong acid range with a PU of about 1 or less, so it is necessary to add 10 to 20 times the molar ratio of hydrochloric acid to the normally contained chlorate. . Therefore, after decomposing the chlorate, it is necessary to add an alkali to neutralize the excess hydrochloric acid.'' In addition to the above equation, several percent of chlorine dioxide is usually produced as a by-product by the reaction of the following equation.

2NaCJ03+411('J)2CfOz +C
J! 2”2Naf”J +o.

This chlorine dioxide is self-explosive, and if mixed into chlorine, it may cause a reaction failure in the chlorine-using stage hiN.

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 Problem c] That is, the present invention is a method for decomposing chlorate, which is characterized by bringing an acidic or neutral saline solution containing chlorate into contact with carbon. -1〉3CO2+ 2 NaCl
As shown in the reaction formula, this is a method of decomposing chlorate into carbon dioxide and salt using carbon.

The inventors further discovered that by dissolving a small amount of chlorine in the system, the F, Rimoto reaction starts in the container. That is, Naα0 produced by dissolved α2 and further HCJO produced by hydrolysis are initially adsorbed on carbon and further react to produce CO.

NaCJO+ II(J->H(JO+Na(JCl
t +HtO-1 July 1 (JO+ Hα2] 1αO 1 G
-> COz + 211 (J) It is estimated that the pH value of the neutral liquid is 3 or less due to the H (j) generated at this time, and the reaction between chlorate and carbon is promoted, causing a It was found that it decomposed into carbon dioxide and salt without any 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 Mesosch manufactured by Catara Industries.

The brine may be neutral or acidic, but in consideration of the reaction rate, it is preferably p113 or less, and the reaction will be further promoted if chlorine is dissolved therein. Furthermore, the temperature when bringing the salt solution into contact with carbon is 60° to 130°C, and the contact time is 5 to 1
Preferably it is 20 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 disadvantage will occur, but from economical considerations, 120 minutes or less is sufficient.

Further, 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 I pH 2 with 21 g/Il chlorate as Naα03
, Activated carbon (Catarae) 1^- in 300mZ of saline solution of 2.
478 mesohydr) 150- was added and maintained at 85° C., and the change in chlorate concentration was measured, and the results were as follows.

Time NaαOz (g/N) After 1 hour 14.5 2 〃10.5 5〃4 Example 2 Activated carbon (Catar) was added to 300 ml of a saline solution of pH 2.3 containing 45 g/# of chlorate as Na CI Oz. Industrial ■ Manufacturing - 8/32 mesh) 150 - added to 103
The temperature was maintained at ℃, and the change in chlorate concentration was measured, and the results were as follows.

Time Naα (h (g/N) 1 hour later 26 2 〃16.5 5 〃1.5 Example 3 Column (inner diameter 150 mm, A 1,300-inch tall crane) was heated with a saline solution of pH 2.3 containing 30 g/It of chlorate as Naα03 at 80°C.
The solution was continuously passed for 240 hours at h. The chlorate concentration in the effluent is N a (j Oz, with an average of 27 g/jl
Met.

Example 4 N a (ρ11 containing 45 g/j! of chlorate as J 03 and 0.20 g/n of available chlorine as (J2)
6.5 300 ml of saline solution and activated charcoal (Catara L Industry ■
WA-4/Fl mesh) 150- was added and heated to 110°C.
When heating was maintained for 1 hour, the chlorate concentration was C2
It was 1 g/l.

Example 5 pH2 containing 37 g/e chlorate as NaC10x
200 mf of activated carbon (HA-4/8 mesh manufactured by Catara Kogyo ■) was added to 300 art of the saline solution prepared in 6. The acid salt concentration was 0.5 g/l as N a Q'03.

Comparative Example I When 300 liters of saline solution with a pH of 2.1 containing 45 g/l of chlorate in Na (JOz) was heated and maintained at 85°C, the chlorate concentration after 3 hours was Na('JO
i was 44.5 g/l.

Comparative Example 2 pl+ containing 31 g/# chlorate as Na (JO)
8. Add 150IIIL of activated carbon (HA-4/R mesh manufactured by Catara Kogyo ■) to 300℃ of the saline solution prepared at 90°C.
After 3 hours, the chlorate concentration was Na
It was 31g/71 as C1'Oz.

Claims (1)

[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.