JPH09308823A - Method for decomposing halogenated ethylene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for decomposing a halogenated ethylene effectively. SOLUTION: In the electrolysis of an aqueous solution containing electron carrying electrolyte in an electrolytic bath divided into an anodic side and a cathodic side by a diaphragm, a halogenated ethylene or its aqueous solution is introduced into the acidic anode side and/or the alkaline cathodic side and decomposed by the application of electrolytic voltage. By introducing the halogenated ethylene or its aqueous solution into a diaphragm electrolytic process, the halogenated ethylene can be decomposed efficiently and simply into harmless substances.

Description

Detailed Description of the Invention

(Field of Industrial Application) The present invention relates to a method of decomposing halogenated ethylene.

[0002]

2. Description of the Related Art Chlorinated organic compounds such as trichlorethylene and tetrachloroethylene, which are halogenated ethylene, are nonflammable liquids and have a high dissolution rate for dissolving substances. Therefore, they are used as degreasers and detergents. It has been heavily used and widely used. However, from the viewpoint of environmental pollution, these degreasers and the like are regulated objects in the Basic Law for Pollution Control, and at present, practical technologies to substitute them are not established.

On the other hand, various methods for collecting and removing used halogenated ethylene such as used trichlorethylene have been proposed in the past. For example, adsorption / activation with activated carbon or the like has been proposed.
A recovery method, a decomposition method by ultraviolet irradiation, an ozone decomposition method, an oxidative decomposition method using a specific oxidizing agent, and the like have been proposed (JP-A-63-190620, JP-A-229595).
3rd grade).

However, the above-mentioned treatment method is not always put to practical use because, for example, it requires a secondary treatment of the adsorption medium, the decomposition efficiency is insufficient, the treatment operation is complicated, and the treatment cost is high. Is not suitable.

The present inventors have unexpectedly discovered that halogenated ethylene such as trichlorethylene is decomposed extremely efficiently when it is subjected to predetermined electrolysis conditions, and the present invention is completed based on this finding. Came to.

[0006]

That is, according to the method of the present invention, electrolysis is performed by using an aqueous solution containing an electron carrier electrolyte in an electrolytic cell divided into an anode side and a cathode side by a diaphragm as an electrolytic solution. In carrying out, the halogenated ethylene or an aqueous solution thereof is introduced into the acidic anode side and / or the alkaline cathode side of the electrolytic cell, and decomposed under the application of an electrolytic voltage to decompose the halogenated ethylene. Depending on the treatment method, the halogenated ethylene is effectively decomposed.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, an aqueous solution containing an electron carrier electrolyte such as KNO ₃ is used as an electrolytic solution in an electrolytic cell divided into an anode side and a cathode side by a diaphragm. The specific configuration of the tank can be easily obtained by, for example, installing a cylindrical unglazed magnetic diaphragm (hereinafter referred to as unglazed cylinder) in the electrolytic cell.

When a predetermined voltage is applied with the inside of the bisque-fired cylinder in the electrolytic cell as the anode and the outside as the cathode, an electrolysis current flows, and the electrolysis of the electrolytic solution containing KNO ₃ causes nitric acid having a pH of about 0.8 to form nitric acid. It becomes strongly acidic and the cathode side becomes strongly alkaline of potassium hydroxide having a pH of about 13.2. When halogenated ethylene, such as trichlorethylene, is introduced into the anode side, the cathode side, or both sides of such an electrolytic cell, trichlorethylene turns into hypochlorous acid, chlorine gas and organic.
Decomposed into inorganic carbon compounds.

When the solution on the cathode side and the solution on the anode side are sampled at regular intervals and the concentration of trichlorethylene is measured, the amount of trichlorethylene is reduced with the passage of time of energization, and the progress of decomposition is confirmed. Hypochlorous acid was found in the anode chamber at the beginning of electrolysis, and chlorine ions and inorganic carbon were found on the anode and cathode sides after the electrolysis, and trichloroethylene was scarcely left.

It is considered that the trichlorethylene introduced into the electrolytic cell in the electrolytic treatment step is decomposed by the following reactions on the anode side and the cathode side.

On the anode side, trichlorethylene is oxidized by active oxygen generated as chlorine and exists as chlorine gas or chlorine ions, which further react with water.

Cl ₂ C = CClH + nO ₂ = Cl
^{_{2 + Cl - + CO 2 +}} CO 3 2 - Cl 2 + H 2 O = HClO + H + Cl - + 2H 2 O = 2HClO + 2H +

On the cathode side, the chlorine of trichloroethylene is replaced by active hydrogen to generate chlorine gas or chlorine ions, which further react with water to form hypochlorite ions.

Cl ₂ C = CClH + nH ₂ = 2C
^{_{H 4 + Cl 2 + Cl -}} Cl - + 2OH - = ClO - + H 2 O

Electrolyte Potassium Nitrate The potassium nitrate solution as an electrolytic solution shows no change after the electrolysis operation and maintains the concentration at the time of addition. The liquid volume inside the unglazed cylinder as an anode increases with time from the start of electrolysis. It is considered that this is because water accompanies the movement of nitrate ions from the outside to the anode.

The concentration of trichlorethylene decreases with time, but its decomposition rate increases with the increase of electrolysis voltage. Therefore, the applied voltage in this case is appropriately set according to the target processing amount and processing time.

Although the present invention has been described with reference to the decomposition of trichlorethylene, the method of the present invention can be similarly applied to other halogenated ethylene such as tetrachloroethylene having a relatively small molecular weight and having a double bond. Further, as the electron carrier electrolyte used as an electrolytic solution in the electrolysis operation, in addition to potassium nitrate, strong electrolytes such as potassium sulfate, sodium nitrate, sodium sulfate and the like can also be used. In addition to the unglazed cylinder, neutral, anionic or cation ion exchange resin fibers are used as the diaphragm.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention will be described below with reference to the drawings. FIG. 1 is a conceptual diagram showing the decomposition treatment method of halogenated ethylene of the present invention.

Example 1 A glass beaker (1) having a volume of 2000 cm ³ was filled with 25 pieces.
A bisque-fired cylinder (2) having a volume of 0 cm ³ was arranged, a platinum (Pt) electrode (3) was provided inside the bisque-fired cylinder (2), and a stainless steel (SUS) electrode (4) was provided outside. 1750 cm ³ of a 0.05 molar aqueous solution of potassium nitrate was filled as an electrolytic solution (5) into this electrolytic cell, and an aqueous solution of trichlorethylene (0.98
g / liter) 200 cm ³ is introduced, and the initial voltage is 1.5
Electrolysis was performed at V and current of 2.1A. The concentration of trichlorethylene after 2 hours is 0.03 mg /
It was lowered to 0.01 mg / liter per liter.

Example 2 In an electrolytic cell (1) having the same structure as in Example 1, 10 g of trichlorethylene was introduced into a bisque-fired cylinder (2), and electrolysis was performed at an initial voltage of 18 V and a current of 5.8 A. The concentration of trichlorethylene 10 hours after the start of electrolysis was 0.02 mg / l against the standard value of wastewater of 0.03 mg / l.
It had dropped to liters.

2 g of trichlorethylene under exactly the same conditions
When was introduced and electrolyzed, the concentration of trichlorethylene after 10 hours was 0.01 mg or less.

[0022]

According to the present invention, trichlorethylene or its aqueous solution can be decomposed very easily and with extremely high treatment efficiency by the diaphragm electrolysis method using an aqueous solution of a strong electrolyte having an electron carrier property as an electrolytic solution.

The apparatus used in this method may have a simple structure such as an electrolytic cell provided with a diaphragm such as a biscuit cylinder, and the electrolytic voltage may be set according to the treatment amount and the treatment time so as to be simple in a continuous or batch system. Processing can be performed by operation.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing an apparatus used for a decomposition treatment method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electrolytic tank (cathode side) 2 ... Unfired cylinder (anode side) 3 ... Platinum electrode (anode) 4 ... SUS electrode (cathode) 5 ... Electrolyte

Claims (3)

[Claims] 1. An anode side that exhibits acidity in the electrolytic cell when electrolysis is performed using an aqueous solution containing an electron carrier electrolyte as an electrolytic solution in an electrolytic cell divided into an anode side and a cathode side by a diaphragm. And / or a method for decomposing halogenated ethylene, characterized by introducing ethylene halide or an aqueous solution thereof on the side of the cathode exhibiting alkalinity and decomposing under the application of an electrolysis voltage. 2. The method for decomposing halogenated ethylene according to claim 1, wherein the diaphragm is selected from the group consisting of a bismuth magnetic diaphragm and a neutral, anionic or cationic synthetic fiber diaphragm. 3. The process for decomposing halogenated ethylene according to claim 1, wherein the halogenated ethylene is selected from low molecular weight halogenated ethylene having a double bond.