JP6061315B2 - Method and apparatus for dechlorination of chlorinated ethylenes - Google Patents

Description

  The present invention relates to a dechlorination method and a dechlorination apparatus for an object to be treated containing chlorinated ethylenes such as tetrachlorethylene waste liquid and factory wastewater generated in a nuclear facility.

  Tetrachlorethylene is used as a cleaning agent when checking asphalt solidification equipment in nuclear facilities. The generated tetrachlorethylene waste liquor contains impurities such as asphalt and insoluble solids containing radioactive materials incorporated into the asphalt, moisture, low boiling point solvents, etc., so the tetrachlorethylene waste liquor is subjected to normal industrial waste treatment. Not. Then, the processing method of the tetrachloroethylene waste liquid by which the tetrachloroethylene obtained by distilling the tetrachloroethylene waste liquid containing a radioactive substance, pure water, and iron composite particle | grains is mixed, and tetrachloroethylene is decomposed | disassembled was examined (for example, refer patent document 1). However, in the method described in Patent Document 1, since oxidation of iron composite particles and reduction of tetrachloroethylene occur as an equivalent reaction, an attempt to treat a large amount of tetrachloroethylene by this method alone requires a large amount of iron composite particles. Moreover, there was a problem that a large amount of iron oxide as waste was generated.

On the other hand, the electrolytic treatment of the organic compound-containing water is performed by an electrolytic device in which a cathode chamber having a cathode using conductive diamond and an anode chamber having an anode using conductive diamond are partitioned by an ion exchanger, A method for treating organic compound-containing water that circulates the organic compound-containing water between the cathode chamber and the anode chamber (see, for example, Patent Document 2), chlorine in an electrolytic cell divided into a carbon cloth cathode compartment and an anode compartment A method for dechlorination of chlorinated organic compounds (for example, see Non-Patent Document 1) has been studied.
However, in the method described in Patent Document 2, when a large amount of organochlorine compound is decomposed, as dechlorinated chlorine ions accumulate in the system, hypochlorite ions are generated at the anode, and next at the cathode. There was a problem that the reduction reaction of chlorite ion to chlorine ion became dominant and the decomposition of the organic chlorine compound was stagnant.
Further, in the method described in Non-Patent Document 1, a very high current density per volume (5.6 to 58 mA / mL for producing dechlorination with carbon cloth, a 500 mL capacity reaction vessel similar to the example of the present application is assumed. Then, 2800-29000 mA) was required, and there was a problem that it was not practical.

Furthermore, (i) a step of contacting functional water generated by electrolysis of water containing an electrolyte with a halogenated aliphatic hydrocarbon compound or an aromatic compound, and (ii) obtained by the step (i). And a method for decomposing a halogenated aliphatic hydrocarbon compound or an aromatic compound having a step of neutralizing a liquid to be produced (see, for example, Patent Document 3).
However, in the method described in Patent Document 3, the halogenated aliphatic hydrocarbon compound or the aromatic compound is configured to come into contact only with functional water generated at the anode under light irradiation. In the reductive dechlorination reaction, Oxidation reaction occurs. Therefore, there is a problem that harmful decomposition products such as dichloroacetic acid are generated, and there is a problem that it is necessary to incorporate a microbial treatment as a post-treatment. That is, an effective method for dechlorinating a large amount of an object containing a high concentration of chlorinated aliphatic hydrocarbon compound in a short time with a low current amount has been desired.

JP 2010-203930 A JP 2004-202283 A JP 2000-225336 A

S. M. Kulikov and 4 others, Electrochimica Acta, Volume 41, Issue 4, March 1996, Pages 527-531

In recent years, there has been a demand for a method of dechlorinating a large amount of an object to be treated containing a high concentration of chlorinated ethylenes in a short time, but such a dechlorination method has not been provided.
The problem to be solved by the present invention is to provide a method for dechlorinating a large amount of an object containing a high concentration of chlorinated ethylenes in a short time and an apparatus for carrying out the method.

  As a result of intensive investigations to solve the above problems, the inventors of the present invention have found that an object to be treated containing a high concentration of chlorinated ethylenes is in an electrolytic cell provided with a cathode (however, excluding a carbon electrode) and an anode. Thus, the present inventors have found that chlorinated ethylenes can be dechlorinated when brought into contact with only the cathode and subjected to an electrochemical dechlorination treatment.

In the method of dechlorinating chlorinated ethylenes of the present invention, an object to be treated containing chlorinated ethylenes is brought into contact only with the cathode in an electrolytic cell including a cathode (excluding a carbon electrode) and an anode, An electrochemical dechlorination treatment is performed at a pH of 7 to 12 to be treated, and the anode is separated from the cathode by a diaphragm, and is formed between the anode and the diaphragm during the electrochemical dechlorination treatment. The anolyte filling the anode compartment is cooled and circulated. A preferable material of the cathode is copper or a copper alloy. A more preferable material for the cathode is a Monel alloy.

The workpiece to be subjected to the electrochemical dechlorination treatment is preferably sucked from the lower end of the inclined portion formed at the lower part of the electrolytic cell and returned to the upper part of the electrolytic cell for circulation.
The object to be treated obtained by the electrochemical dechlorination treatment is preferably mixed with pure water and iron composite particles, and the dechlorination treatment is performed.

The dechlorination apparatus for chlorinated ethylenes of the present invention includes an electrolytic cell in which a cathode (excluding a carbon electrode) and an anode are separated by a diaphragm, chlorinated ethylenes, and has a pH of 7-12. A processing object circulation means is provided for sucking the prepared object to be processed from the lower end of the inclined part formed at the lower part of the cathode compartment including the cathode and returning it to the upper part of the cathode part.
The preferable treatment object circulation means is a centrifugal pump, and the preferable diaphragm is a cation exchange membrane.

  The dechlorination method for chlorinated ethylenes of the present invention and the dechlorination apparatus for chlorinated ethylenes of the present invention can dechlorinate a large amount of an object containing a high concentration of chlorinated ethylenes in a short time.

Schematic diagram of chlorinated ethylene dechlorination equipment

Hereinafter, the present invention will be described in detail with reference to the drawings showing preferred embodiments of the present invention.
FIG. 1 is a diagram showing an outline of a dechlorination apparatus for chlorinated ethylenes of the present invention. The electrolytic cell 1 includes a cathode 2 and an anode 3. The cathode 2 and the anode 3 are connected to a power source 4. The anode 3 is covered with a diaphragm, and the workpiece injected into the electrolytic cell 1 is in contact with the cathode 2 but not in contact with the anode 3. The anolyte filling the anode compartment formed between the anode 3 and the diaphragm is cooled by the heat exchanger 5 and sent to the anolyte tank 6 during electrolysis, and further separated from the anolyte tank 6 from the anode 3. Circulated to voids formed between the membranes.

The cathode 2 is made of a material such as copper, copper alloy, monel alloy (nickel-copper alloy), nickel, stainless steel, or iron. However, the material of the cathode 2 is not carbon. Preferred constituent materials of the cathode 2 are copper and a copper alloy, and a monel alloy is particularly preferably used.
The anode 3 is made of a material such as aluminum, titanium, a platinum group metal, or a platinum group coat metal. As the anode 3, for example, an iridium oxide-coated titanium electrode can be used.

Specific examples of the raw material of the membrane include cation exchange membranes; MF (microfilter) membranes having no functional groups, UF (ultrafilter) membranes, porous filter media such as ceramics; woven fabrics made of nylon, polyethylene, and polypropylene; Manila hemp; glass fiber; porous plastic film. As the diaphragm not having these functional groups, those having a pore diameter of 5 μm or less and not allowing gas to pass under non-pressurized conditions are preferable. Specific examples of the above-mentioned commercial products of the diaphragm include PE-10 membrane manufactured by Schweiz Seidengazefabrik, NY1-HD membrane manufactured by Flon Industry, and the like. A preferred raw material for the diaphragm is a cation exchange membrane.
The waste liquid containing chlorinated ethylenes that has been subjected to pretreatment such as filtration and distillation as needed is water, ethanol, methanol, acetonitrile, DMSO, etc. in which electrolytes such as anhydrous sodium sulfate and sodium chloride are dissolved. An object to be treated containing chlorinated ethylenes is obtained by being dispersed or dissolved in a polar solvent. The dispersion or dissolution of the waste liquid in the polar solvent may be performed before injection into the electrolytic cell 1 or may be performed in the electrolytic cell 1.

  An object to be treated containing chlorinated ethylenes is injected into the cathode compartment of the electrolytic cell 1, and after the anolyte is injected into the anode compartment, an electrochemical dechlorination treatment of the chlorinated ethylenes is performed. The anolyte is an electrolyte having the same composition as or different from the electrolyte used when preparing the object to be treated containing chlorinated ethylenes to be injected into the cathode compartment.

During electrolysis, pH of the treatment object is Ru 7-12 der. If the pH is too low, the hydrogen ion concentration in the object to be treated increases, and the reduction reaction of hydrogen ions on the surface of the cathode 2 (generation of hydrogen gas) becomes easy, and the cathode potential rises to reduce chlorinated ethylene. As a result of the difficulty of dechlorination, the decomposition rate of chlorinated ethylenes decreases or the chlorinated ethylenes do not decompose. When the diaphragm is a cation exchange membrane, if the pH is too high, the voltage during energization of the cation exchange membrane increases, the ion exchange capacity decreases, and the electrical resistance increases.

  During the electrolysis, the object to be processed in the electrolytic cell 1 can be stirred. The stirring means for the workpiece is not limited to a specific one. The workpiece can be sucked from the lower end of the inclined portion formed in the lower portion of the electrolytic cell 1 by the pump 7 which is the workpiece circulation means, and returned to the upper portion of the electrolytic cell 1 to be circulated and stirred. Specific examples of the pump 7 are a diaphragm pump and a spiral pump. A preferred pump 7 is a centrifugal pump.

  Specific examples of the chlorinated ethylenes to be dechlorinated by the chlorinated ethylene dechlorination method and dechlorination apparatus of the present invention are tetrachloroethylene, trichlorethylene, dichloroethylene, and vinyl chloride.

After the electrochemical dechlorination treatment, the object to be treated, pure water and iron composite particles are mixed, and dechlorination treatment of chlorinated ethylenes can be performed. The dechlorination treatment is performed by, for example, an apparatus shown by the decomposition tank unit 16 of FIG.
The series of operations may be batch or continuous.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. Various measurement methods are as follows.

(1) Measuring method of 1 to 4 chlorine substitution concentration of ethylene 5 mL sample solution collected from the cathode compartment is put into a vial, and immediately sealed with a butyl rubber stopper with a Teflon (registered trademark) liner and an aluminum seal, 30 Shake for more than a minute to equilibrate the gas-liquid chlorinated ethylene concentration. Next, 200 μL of a gas phase was collected with a gas tight syringe and used as a sample gas. A PID gas chromatograph (GC-311 manufactured by hnu) was used, and the sample gas was injected into the column (NBW-311 manufactured by hnu) at an inlet and detector temperature of 110 ° C. and a column temperature of 70 ° C. The 4-chlorine substitute concentration was measured.

(2) Chlorine ion concentration measuring method 10 mL of 1N nitric acid and 1 mL of 5 g / L silver nitrate solution are added to an appropriate amount of sample (0.1 mg or less as chloride ion) collected in a 100 mL stoppered measuring cylinder, and further Pure water was added to prepare a 100 mL solution, shaken well and left for 10 minutes. A part of the prepared solution was transferred to a 50 mm absorption cell, and the chlorine ion concentration was measured by a calibration curve method with a spectrophotometer (U-1800 manufactured by Hitachi, Ltd.) at a wavelength of 420 nm.

(3) Cathode potential measurement method The reference electrode (HC-151A manufactured by TOA / DKK) is immersed in the cathode compartment of the electrolytic cell, and the potential difference between the cathode and the reference electrode is a potentiostat HA-151A manufactured by Hokuto Denko Corporation. Measured by. The measured value was converted into a hydrogen standard electrode potential by the following formula.
Hydrogen standard electrode potential (VvsSHE) = Comparative electrode measured value (VvsAg / AgCl) + 0.199

Examples 1 and 2
The sodium hydroxide solution was added to 40 g / L anhydrous sodium sulfate solution in a 500 mL separable flask to adjust the pH to 12. In addition, in order to improve the measurement sensitivity of the chlorine ion concentration, anhydrous sodium sulfate solution was used as the electrolytic solution, but a 10 g / L sodium chloride solution can be used as the electrolytic solution.
Anode (DSE electrode manufactured by Permerek Electrode Co., Ltd.) placed in a cation exchange membrane (DuPont Co., Ltd. N424) molded in a bag shape and 30 mesh stainless steel wire mesh (manufactured by Fukuzawa Wire Mesh Co., Ltd.) Is placed in the separable flask, tetrachloroethylene or trichlorethylene is added to the cathode compartment so as to have an initial concentration of 7100 mg / L, and a low current of 0.15 A is applied by a DC power supply (LX018-2A manufactured by Takasago Seisakusho Co., Ltd.). The magnetic stirrer was set at a rotational speed of 230 mm / sec at a point where the rotational speed of the electrolyte in the separable flask was 3/4 of the inner circumference, and electrolysis was performed. The chlorine ion concentration in the workpiece was measured over time. Since chloride ions are generated by reductive dechlorination of tetrachlorethylene or trichlorethylene, the decomposition rate of tetrachloroethylene or trichlorethylene was calculated from the rate of increase of the chloride ion concentration. The results are shown in Table 1.

From this result, it was shown that this treatment method is effective for the decomposition of tetrachlorethylene and trichlorethylene.
In addition, as a result of measurement using PID gas chromatography, trace amounts of 1,1-dichloroethylene, t-1,2-dichloroethylene, and vinyl chloride monomers are generated as intermediate decomposition products of tetrachloroethylene and trichlorethylene, and these become ethylene over time. It was confirmed that this treatment method has wide applicability to chlorinated ethylenes in general because the phenomenon of degradation and decrease and disappearance was observed.

  From the analysis results of PID gas chromatography, trace amounts of 1,1-dichloroethylene, t-1,2-dichloroethylene and vinyl chloride are generated as intermediate decomposition products of the electrochemical decomposition reaction of tetrachloroethylene or trichlorethylene, and these are converted into ethylene. It was observed to change. Therefore, it was recognized that this dechlorination method can be applied to chlorinated ethylenes in general.

Examples 3 and 4 and Reference Examples 1 and 2
The apparatus used in Examples 1 and 2 was used, and tetrachlorethylene was added to anhydrous sodium sulfate solution to an initial concentration of 7100 mg / L, and electrochemical dechlorination treatment was performed. When the pH of the workpiece was 12, 7, 5, and 4, the chlorine ion concentration in the workpiece was measured, and the decomposition rate of chlorinated ethylene was calculated. The results are shown in Table 2.

From Table 2, the cathodic potential and the decomposition rate are not significantly changed in the range of pH 12 to 7, but when the pH is lowered to 5, the cathodic potential is increased and the decomposition rate is lowered, and when the pH is further lowered to 4. It was found that no decomposition occurred at all.
This is because the pH decreases and the hydrogen ion concentration in the electrolyte increases, which facilitates the reduction reaction of hydrogen ions (hydrogen gas generation) on the cathode surface, and the electrode potential increases to increase chlorinated ethylene. This is thought to be because the reductive dechlorination reaction of sucrose hardly occurs.
From this, the pH is controlled to 7 or more in the electrolytic treatment of the present invention.
Further, it was found that, when immersed in an electrolyte solution having a pH exceeding 12.5 for a long period of time, the voltage during energization inside and outside of the cation exchange membrane increases, that is, the ion exchange ability decreases and the electrical resistance increases. Therefore, the pH is controlled to 12 or less.

Examples 5-8
Except for changing the material of the cathode wire mesh, the same apparatus as that used in Examples 1 and 2 was used, and tetrachlorethylene was added to the anhydrous sodium sulfate solution so as to have an initial concentration of 7100 mg / L. Dechlorination treatment was carried out. The chlorine ion concentration in the workpiece was measured when the pH of the workpiece was 10 to 12, and the decomposition rate of chlorinated ethylene was calculated. The results are shown in Table 3.

From Table 3, compared with the stainless steel and nickel electrode, the Monel alloy electrode which is copper and a copper alloy showed the significantly high decomposition rate. The Monel alloy is an alloy of copper and nickel. Of these two components, copper has a high decomposition activity and nickel has a low decomposition activity. Therefore, it is considered that copper is an effective component for the electrolytic reduction treatment reaction. .
On the other hand, with the copper electrode being used repeatedly, the generation of patina was gradually observed, and the wire mesh wire diameter tended to become thinner, whereas the Monel alloy had a slightly blackened surface. Corrosion did not progress. This was thought to be due to the fact that copper is vulnerable to corrosion by chloride ions while Monel alloy has corrosion resistance to chloride ions.
From these findings, it can be said that it is desirable to use copper and a copper alloy as the material of the cathode, and it is more desirable to use a monel alloy.

Examples 9-12
A 2 L separable flask was used instead of the 500 mL separable flask, and the same apparatus as that used in Examples 1 and 2 was used except that the stirring means was changed as follows. It was added to anhydrous sodium sulfate solution to 7100 mg / L, and electrochemical dechlorination treatment was performed. The chlorine ion concentration in the workpiece was measured when the pH of the workpiece was 10 to 12, and the decomposition rate of chlorinated ethylene was calculated. The results are shown in Table 4.
(1) The rotational speed of the magnetic stirrer was set so that the rotational linear speed of the electrolyte in the 2 L separable flask was 140 mm / second at a point of 3/4 of the inner circumference (Example 9).
(2) The object to be treated was sucked by the diaphragm pump from the bottom of the 2L separable flask and returned to the top of the 2L separable flask and circulated (Example 10).
(3) The 2L separable flask is tilted to form a 20 degree gradient at the bottom thereof, and the workpiece is sucked from the bottom of the 2L separable flask by a diaphragm pump and the 2L separable flask. It was returned to the upper part of the flask and circulated (Example 11).
(4) The 2L separable flask is tilted to form a 20 degree gradient at the bottom thereof, and the object to be treated is sucked from the bottom of the 2L separable flask by a vortex pump and the 2L separable flask. Returned to the top and circulated (Example 12).

From Table 4, in the system of Examples 10 to 12, which employs circulating mixing that is easier to manufacture than the mechanical stirring of Example 9 in terms of apparatus, in the system in which the bottom surface of Example 10 is not inclined, tetrachloroethylene oil droplets appear. The phenomenon of staying at the bottom of the reactor was observed and mixing was not performed efficiently. As a result, the decomposition rate was less than ¼ that of the mechanical stirring system of Example 9.
On the other hand, in the systems of Examples 11 and 12 in which the bottom of the reactor is inclined and the electrolyte is extracted from the lowermost part, tetrachlorethylene oil droplets slide down the inclined surface and are sucked into the pump, Discharged circulation mixing was performed, and the decomposition rate was improved. In particular, in the system of Example 12 using a spiral pump, the phenomenon that the oil droplets of tetrachloroethylene were sheared by the swirling flow in the pump and dispersed in water occurred, and tetrachloroethylene was dispersed almost uniformly in water. As a result, the decomposition rate of the system of Example 12 increased to 1.5 times or more that of the system of Example 10.
From these findings, it is desirable for the stirring method of the present invention to suck the liquid from the lower part of the cathode compartment and return it to the cathode compartment again for liquid circulation. The liquid is preferably sucked from the lower part, and more preferably, the pump to be used is a spiral pump that generates a swirling flow.

Example 13
The same apparatus as that used in Example 12 was used, and tetrachlorethylene was added to anhydrous sodium sulfate solution to an initial concentration of 7100 mg / l to perform electrochemical dechlorination treatment. Tetrachlorethylene concentration was measured over time. The results are shown in Table 5.

  The tetrachlorethylene concentration decreased to 3000 mg / L in 48 hours and to 22 mg / L in 98 hours, but then the decomposition rate decreased, and 10 mg / L remained even after 194 hours (after 8 days). From this finding, it was shown that the low-concentration tetrachlorethylene treatment efficiency is low in the electrolytic reduction treatment of the present invention alone.

  After 194 hours from the start of dechlorination in Example 13, 670 mL of the object to be treated was collected from the 2 L separable flask and mixed with 1% by mass of iron composite particles (RNIP manufactured by Toda Kogyo Co., Ltd.) in water dispersion. After the total amount was 2 L, the mixture was slowly stirred (48 rpm) with a stirrer (manufactured by Shibata Kagaku), and the tetrachlorethylene concentration in the workpiece was measured over time. The results are shown in Table 6.

Trichlorethylene, dichloroethylene, and vinyl chloride were not detected in the object to be treated after 168 hours from the start of treatment with the iron composite particles. At this stage, the concentration of tetrachlorethylene in the object to be treated was below the wastewater standard value (0.1 mg / L).
In addition, since both the electrolytic treatment and the iron composite particle treatment are reduction treatments, the reducing atmosphere formed in the previous treatment does not adversely affect the subsequent treatment, and is advantageous as a combination.
From these results, it was found that a desirable effect of satisfying the wastewater standard value of tetrachloroethylene can be obtained by further mixing the treatment liquid subjected to electrolytic treatment with iron composite particles.

  The dechlorination method for chlorinated ethylenes and the dechlorination apparatus for chlorinated ethylenes of the present invention are suitable for inexpensive dechlorination of an object to be treated containing a high concentration of chlorinated ethylenes in a short time.

DESCRIPTION OF SYMBOLS 1 ... Electrolytic cell, 2 ... Cathode, 3 ... Anode, 4 ... Power supply, 5 ... Heat exchanger, 6 ... Anode liquid tank, 7 ... Pump

Claims (8)

An object to be treated containing chlorinated ethylenes is brought into contact only with the cathode in an electrolytic cell equipped with a cathode (excluding a carbon electrode) and an anode, and the pH of the object to be treated is 7 to 12 electrochemical. Dechlorination is carried out ,
The anode is separated from the cathode by a diaphragm, and during the electrochemical dechlorination treatment, the anolyte filled in the anode compartment formed between the anode and the diaphragm is cooled and circulated. Dechlorination method. The dechlorination method for chlorinated ethylenes according to claim 1 , wherein the material of the cathode is copper or a copper alloy. The method for dechlorination of chlorinated ethylenes according to claim 1 , wherein the material of the cathode is a Monel alloy. Article to be treated which are attached to the electrochemical dechlorination is circulated back to the electrolytic cell top while being sucked from the inclined portion the lower end which is formed in the lower portion of the electrolytic cell of claim 1-3 A method for dechlorination of chlorinated ethylenes according to any one of the above items. The chlorinated ethylene according to any one of claims 1 to 4 , wherein an object to be treated, pure water, and iron composite particles obtained by the electrochemical dechlorination treatment are mixed and subjected to dechlorination treatment. Dechlorination method. An electrolytic cell in which the cathode (except the carbon electrode) and the anode are separated by a diaphragm,
A processing object circulation means for sucking a processing object containing chlorinated ethylenes and having a pH adjusted to 7 to 12 from the lower end of the inclined part formed at the lower part of the cathode section including the cathode and returning it to the upper part of the cathode section ;
An anolyte filled in an anode compartment formed between the anode and the diaphragm;
A heat exchanger for cooling the anolyte,
An anolyte tank to which the anolyte cooled by the heat exchanger is sent,
A dechlorination apparatus for chlorinated ethylenes, comprising means for circulating the anolyte from the anolyte tank to the anode compartment .   The dechlorination apparatus for chlorinated ethylenes according to claim 7, wherein the treatment object circulation means is a centrifugal pump.   The dechlorination apparatus for chlorinated ethylenes according to claim 7 or 8, wherein the diaphragm is a cation exchange membrane.

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