JP2015160080A - Method and apparatus for dehalogenating organic halogen compound using conductive diamond electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for dehalogenating a large amount of the object to be processed that contains high concentration organic halogen compounds, to low concentration level in a short period of time.SOLUTION: An electrolysis tank includes: a cathode compartment provided with a cathode that contains conductive diamond; an anode compartment provided with an anode that does not contain conductive diamond; and a barrier membrane that separates the cathode compartment from the anode compartment. In the electrolysis tank, anolyte is circulated only to the anode compartment, and the object to be processed containing organic halogen compounds is circulated only to the cathode compartment and the object to be processed containing organic halogen compounds is contacted only with the cathode to carry out an electrochemical dehalogenation treatment.

Description

  The present invention relates to a dehalogenation method and a dehalogenation apparatus for an object to be treated containing an organic halogen compound such as an organic halogen solvent waste liquid generated in a nuclear facility or a factory effluent.

  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 that the tetrachlorethylene waste liquor is subjected to normal industrial waste treatment. It is not possible. Then, the processing method of the tetrachlorethylene waste liquid which mixes the tetrachloroethylene obtained by distilling the tetrachloroethylene waste liquid containing a radioactive substance, pure water, and iron composite particle, and decomposes | disassembles tetrachloroethylene is proposed (patent document 1). However, in the method described in Patent Document 1, since oxidation of iron composite particles and reduction of tetrachloroethylene occur as equivalent reactions, it is necessary to add a large amount of iron composite particles in order to treat a large amount of tetrachloroethylene, There was a problem that a large amount of iron oxide as waste was generated.

In order to solve this problem, electrochemical dechlorination treatment is performed by bringing the water to be treated containing high concentration of tetrachlorethylene into contact with only the cathode in an electrolytic cell having a cathode that is a Monel alloy and an anode that is an iridium oxide-coated titanium electrode. A method for treating tetrachlorethylene waste liquor that is dechlorinated by the above and reduced to ethylene and ethane has been proposed (Patent Document 2). However, in the method described in Patent Document 2, the treatment efficiency of low-concentration tetrachlorethylene is low, and the dechlorination reaction stops at about 10 mg / L (Patent Document 2 Example 14). Since the wastewater standard value for tetrachlorethylene is set at 0.1 mg / L by the Water Pollution Control Law, waste liquid containing about 10 mg / L of tetrachloroethylene cannot be drained as it is, and is further brought into contact with iron composite particles for tetrachlorethylene. It was necessary to apply a post-treatment to decompose the.
Moreover, when the stirring means by a normal stirrer is used, the decomposition rate of the high concentration tetrachlorethylene is about 48 mg / L · h (cited document 2 Example 9), which is more efficient than the method of Patent Document 1, There is a problem that it takes a long time to decompose a large amount of organochlorine compound.

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. At the same time, a method for treating organic compound-containing water (Patent Document 3) is proposed in which the organic compound-containing water is circulated between the cathode chamber and the anode chamber. However, the method disclosed in Patent Document 3 is difficult to reproduce in the following three points, which are contrary to the technical common knowledge of those skilled in the art regarding electrochemical reactions.
(1) Generation of chlorine gas According to Patent Document 3, when the organic chlorine compound-containing wastewater is treated, the water circulation of the wastewater is performed so as to flow from the cathode chamber to the anode chamber (paragraph 0039 and Example-2). However, in this method, chlorine ions are generated in the cathode chamber and flow into the anode chamber, so that chlorine gas is generated and returned to the electrolytic storage tank. Further, there is a description as to whether chlorine gas is generated by reduction around the cathode (paragraph 0040), but chlorine gas is generated by oxidation, and it is not correct to generate at the cathode. According to the apparatus configuration and example described in Patent Document 3, chlorine gas having toxicity and corrosivity is actually generated on the anode side.
(2) Decrease in decomposition efficiency due to oxidation-reduction ping-pong reaction of chloride ion Assuming that the water circulation method described in Example-2 of Patent Document 3 is incorrect, the method is changed so that the water circulation of the drainage flows from the anode chamber to the cathode chamber. In this case, chlorine gas generated at the anode is reduced at the cathode to become chlorine ions, so that the diffusion of chlorine gas in the electrolytic storage tank is avoided. However, if a large amount of organochlorine compound is decomposed using this modified circulation treatment process, the chlorine ions generated at the cathode flow into the electrolytic storage tank, the chlorine ion concentration of the waste water in the electrolytic storage tank rises, and at the anode Generation of hypochlorite ions, chlorate ions and chlorine gas from chlorine ions, and reduction reaction of these chlorinated oxidants to chlorine ions occur at the cathode. Since these reactions occur more easily electrochemically than the oxidation reaction of organochlorine compounds at the anode and the dechlorination reaction of organochlorine compounds at the cathode, only the oxidation-reduction ping-pong reaction of the above chloride ions becomes dominant. The decomposition efficiency of the target organochlorine compound is lowered, and the decomposition reaction is stagnant.
(3) Problem of corrosion of ion exchanger Even if any of the above methods (1) or (2) is used, if a diamond electrode is used for the anode, the ion exchanger is attacked due to its strong oxidizing power. As a result, the ion exchange capacity is lowered, and ions that should not originally permeate are transmitted. For example, chloride ions, which are anions, pass through the cation exchanger. If chlorine ions generated on the cathode side permeate the anode side, chlorine gas is generated as described above.
As described above, even if the method described in Patent Document 3 and improvements that can be normally made by those skilled in the art are added, the liquid is circulated using the diamond electrode for both the cathode and the anode as disclosed in Patent Document 3. The method cannot stably decompose organochlorine compounds.

Furthermore, a decomposition method using inorganic diamond at least as a cathode to reduce inorganic nitrate nitrogen to ammonia has been studied (see, for example, Patent Document 4 and Patent Document 5).
However, in the methods described in Patent Documents 4 and 5, the object to be reduced at the cathode is not an organic halogen compound but inorganic nitrate nitrogen, and no diaphragm is used. Therefore, the reaction solution contacts both the cathode and the anode, and when the organic halogen compound is treated by this method, not only the reductive dehalogenation reaction but also the oxidation reaction occurs simultaneously. Therefore, harmful decomposition products such as chlorine gas, bromine gas and dichloroacetic acid are generated.

  As described above, an effective method for safely dehalogenating a large amount of an object containing a high concentration of an organic halogen compound to a low concentration in a short time has not yet been provided.

JP 2010-203930 A JP 2013-039270 A JP 2004-202283 A JP 2004-321963 A JP 2010-270385 A

  An object of the present invention is to provide a method for safely dehalogenating a large amount of an object containing a high concentration of an organic halogen compound to a low concentration 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 contain a high concentration of an organic halogen compound in an electrolytic cell including a cathode using conductive diamond and an anode that is not conductive diamond. It was found that the organic halogen compound is dehalogenated to a low concentration in a short time by bringing the object to be treated into contact with the cathode only and subjecting it to an electrochemical dehalogenation treatment, thereby completing the present invention.

  According to the present invention, an anolyte is provided in an electrolytic cell comprising a cathode compartment including a cathode containing conductive diamond, an anode compartment containing an anode not containing conductive diamond, and a diaphragm separating the cathode compartment and the anode compartment. Is circulated only in the anode compartment, and an object to be treated containing an organic halogen compound (hereinafter also referred to as “object to be treated”) is circulated only in the cathode compartment and brought into contact with only the cathode to perform electrochemical desorption. Provided is a method for dehalogenating an organic halogen compound, characterized by performing a halogen treatment. In the present invention, an emulsifier may be added only to the cathode compartment.

  Further, according to the present invention, a cathode compartment including a cathode containing conductive diamond, an anode compartment containing an anode not containing conductive diamond, an electrolytic cell comprising a diaphragm separating the cathode compartment and the anode compartment, and an anolyte An organic halogen compound dehalogenation apparatus comprising: an anolyte circulation path that circulates only to the anode compartment; and a workpiece circulation path that circulates a treatment object containing the organic halogen compound only to the cathode compartment. .

  As for a cathode, it is desirable for all the surfaces which contact a to-be-processed object to be coat | covered with the conductive diamond. The substrate constituting the cathode is not limited, but niobium, polysilicon, tantalum, and titanium can be preferably used, and niobium is particularly preferable. The shape of the cathode is not limited, but in order to increase the contact area with the object to be processed, a corrugated flat plate, pleated folding, etc. are preferable, and punching metal, expanded metal, wire mesh, etc. are preferably used. Can do.

  The anode may be a commonly used electrode as long as it does not contain conductive diamond, and is particularly preferably an insoluble electrode. Although the base material which comprises an anode is not limited, Titanium, aluminum, and a platinum group metal can be used preferably. As the anode used in the present invention, an iridium oxide-coated titanium electrode whose surface is coated with a platinum group metal is particularly suitable.

  The diaphragm preferably has a pore size of 5 μm or less and does not transmit gas under non-pressurized conditions, such as a cation exchange membrane, an MF (microfilter) membrane having no functional group, a UF (ultrafilter) membrane, a ceramic, etc. Porous filter media; nylon, polyethylene, polypropylene woven fabric; Manila hemp; glass fiber; porous plastic film can be preferably used, and a cation exchange membrane is particularly suitable. Specific examples of commercially available diaphragms are PE-10 membranes from Schweiz Seidengazefabrik, NY1-HD membranes from Flon Industry, EDCORE from ASTOM, N424 from DuPont.

  The organic halogen compound dehalogenation method of the present invention and the organic halogen compound dehalogenation apparatus of the present invention can safely dehalogenate a large amount of an object containing a high concentration of an organic halogen compound to a low concentration in a short time. In particular, the corrosion of the diaphragm due to the generation and accumulation of halogen ions by electrolysis can be prevented, and the generation of halogen gas can be suppressed.

It is a schematic explanatory drawing which shows the structure of the dehalogenation apparatus of the organic halogen compound of this invention. It is a schematic explanatory drawing which shows the electrolytic cell of the dehalogenation apparatus of this invention used in Examples 1-4. It is a schematic explanatory drawing which shows the electrolytic cell of the conventional dehalogenation apparatus used in the comparative example 5. It is a schematic explanatory drawing which shows the electrolytic cell of the dehalogenation apparatus of this invention used in Example 5. FIG. It is a schematic explanatory drawing which shows the electrolytic cell of the conventional dehalogenation apparatus used in the comparative example 6.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic explanatory view showing the structure of the organohalogen compound dehalogenation apparatus of the present invention. The electrolytic cell 1 is divided into a cathode compartment including a cathode 2 and an anode compartment including an anode 3 by a diaphragm 4. The cathode 2 and the anode 3 are connected to a power source.

  The cathode compartment is provided with a workpiece inlet 11 for feeding a workpiece containing an organic halogen compound, and an electrolyte inlet 12 for feeding an electrolyte, and further contains the workpiece after electrolytic treatment. An outlet 14 for extracting the electrolyte from the cathode compartment and an inlet 15 for reintroducing the workpiece-containing electrolyte into the cathode compartment are provided, and a workpiece circulation path 16 connecting the outlet and the inlet is attached. . In order to drain the treated water after completion of the electrolytic treatment, a branch and a take-out port may be provided in the middle of the treatment object circulation path 16, or a treated water take-out port may be provided in the electrolytic cell 1. In the electrolytic cell 1 shown in FIG. 1, the bottom of the cathode compartment is inclined so that the outlet 14 of the workpiece-containing electrolytic solution is at the lowest position.

  The anode compartment is separated from the cathode compartment by the diaphragm 4, and the workpiece injected into the electrolytic cell 1 contacts only the cathode 2 and does not contact the anode 3. The anode compartment is provided with an inlet 18 for receiving the anolyte supplied from the anolyte tank 6 and an outlet 17 for extracting the anolyte from the anode compartment after being used for electrolysis. An anolyte circulation path 19 for sending the anolyte back to the anolyte tank 6 again and further from the anolyte tank 6 to the anode compartment is attached. The anolyte circulation path 19 includes the heat exchanger 5 that cools the anolyte extracted from the anolyte tank 6 and supplies the anolyte again to the anode compartment.

A method for dehalogenating an organic halogen compound using the apparatus shown in FIG. 1 will be described.
If necessary, an object to be processed containing an organic halogen compound subjected to pretreatment such as filtration and distillation is supplied through an object inlet 11 and an electrolytic solution is supplied through an electrolyte inlet 12 in an electrolytic cell. 1 into the cathode compartment. The electrolytic solution used for the cathode compartment is obtained by dispersing or dissolving an electrolyte such as anhydrous sodium sulfate or sodium chloride in a polar solvent such as water, ethanol, methanol, acetonitrile, or DMSO. Preparation of the electrolytic solution may be performed by dispersing or dissolving the electrolyte in a polar solvent in the electrolytic solution tank or the like before charging into the electrolytic cell 1, or by dispersing and dissolving the electrolyte and the polar solvent in the electrolytic cell 1. You may let them.
The anolyte is introduced from the anolyte tank 6 through the anolyte inlet 18 into the anode compartment in the electrolytic cell 1.

  An object to be treated containing an organic halogen compound is injected into the cathode compartment of the electrolytic cell 1, and after an anolyte is injected into the anode compartment, an electrochemical dehalogenation treatment of the organic halogen compound is performed. The anolyte may be an electrolyte having the same or different composition as the electrolyte injected into the cathode compartment. It is desirable that the anolyte does not contain halogen such as chlorine ions.

  During the electrolysis, the pH of the electrolytic solution containing the object to be processed is preferably 5 to 12.5, and more preferably 7 to 12. 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 the organic halogen compound by reductive desorption. As a result of the difficulty of the halogenation reaction, the decomposition rate of the organic halogen compound is reduced or the decomposition of the organic halogen compound does not occur. In the case where the diaphragm is a cation exchange membrane, if the pH of the electrolytic solution containing the object to be treated is too high, the energization voltage of the cation exchange membrane increases, the ion exchange capacity decreases, and the electrical resistance increases.

  During the electrolysis, the electrolytic solution containing the workpiece in the electrolytic cell 1 can be stirred. The stirring means is not limited, and general stirring means can be used. The electrolytic solution containing the object to be treated is sucked by the pump 7 from the outlet at the bottom of the electrolytic cell 1 (cathode compartment), returned to the inlet 15 at the upper part of the electrolytic cell 1 through the material circulation path 16 and circulated and stirred. obtain. Specific examples of the pump 7 are a diaphragm pump and a spiral pump. A preferred pump 7 is a centrifugal pump.

The electrolytic solution containing the workpiece that has been electrochemically dehalogenated in the electrolytic bath 1 is extracted from the outlet 14 at the bottom of the electrolytic bath 1, sent via the workpiece circulating path 16, and via the inlet 15. Then, it is again put into the cathode compartment in the electrolytic cell 1.
The anolyte used for the electrochemical dehalogenation treatment in the electrolytic cell 1 is extracted from the outlet 17 at the upper part of the electrolytic cell 1 and returned to the anolyte tank 6, and is again returned to the upper part of the electrolytic cell 1 through the anolyte circulation path 19. From the inlet 18 to the anode compartment. In FIG. 1, before putting into the anode compartment from the anolyte tank 6, the heat exchanger 5 cools the diaphragm to the operating temperature range, preferably 50 ° C. or less.

  Specific examples of the organic halogen compound to be dehalogenated by the organic halogen compound dehalogenation method and dehalogenation apparatus of the present invention include 1 to 4 halogen substituents of methane, 1 to 6 halogen substituents of ethane, and 1 to 4 of ethylene. Halogen-substituted, acetylene 1-2 halogen substituted, propane 1-8 halogen substituted, propylene 1-6 halogen substituted, allene (propadiene) 1-4 halogen substituted, allylene (methylacetylene) 1 1-4 halogen substituted products, 1-10 halogen substituted product of butane, 1-8 halogen substituted product of 1-, 2- or iso-butene, 1-6 halogen substituted product of 1,3-butadiene, 1-4 of acetic acid Halogen substituted products, 1-5 halogen substituted products of phenol, 1-10 halogen substituted products of biphenyl, and dioxins. Preferred organic halogen compounds are tetrachloroethylene, trichloroethylene, trifluoroacetic acid and bromoethane.

  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) Method for measuring the concentration of 1 to 4 halogen substituents of ethylene 5 mL of the sample solution collected from the cathode compartment is placed in a vial and immediately sealed with a butyl rubber stopper with a Teflon (registered trademark) liner and an aluminum seal for 30 minutes. Shake as described above to equilibrate the halogenated ethylene concentration in the gas and liquid. Next, a gas phase of 200 μL is collected with a gas tight syringe and used as a sample gas. Using a PID gas chromatograph (GC-311 manufactured by hnu), 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. 4 Measure the halogen substitution product concentration.

(2) Measuring method of halogen ion concentration Add 10 mL of 1N nitric acid and 1 mL of 5 g / L silver nitrate solution to an appropriate amount of sample (0.1 mg or less as halogen ion) collected in a 100 mL stoppered measuring cylinder, Add water to make a 100 mL solution, shake well and leave for 10 minutes. A part of the prepared solution is transferred to a 50 mm absorption cell, and the halogen ion concentration is 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 determined by Hokuto Denko's potentiostat HA-151A. Measure with The measured value is converted into a hydrogen standard electrode potential by the following formula.
Hydrogen standard electrode potential (VvsSHE) = Comparative electrode measured value (VvsAg / AgCl) + 0.199

[Example 1]
The test apparatus shown in FIG. 2 was used. 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 order to improve the measurement sensitivity of the halogen ion concentration, anhydrous sodium sulfate solution was used as the electrolytic solution, but a 10 g / L sodium chloride solution may be used as the electrolytic solution in practical use.
Anode 3 (DSE electrode manufactured by Permerek Electrode Co., Ltd.) placed in a cation-exchange membrane 4 (DuPont N424) formed into a bag shape, and niobium base diamond electrode 2 (manufactured by CONDIAS) as a cathode ) Was placed in the separable flask, and 40 g / L of anhydrous sodium sulfate solution was filled in the diaphragm bag as an anolyte. Tetrachlorethylene as an organic halogen compound was added to the cathode compartment to an initial concentration of 7100 mg / L, and a current of 1 A was applied using a DC power supply (LX018-2A manufactured by Takasago Seisakusho Co., Ltd.) The rotation speed of the magnetic stirrer was set so that the rotation linear velocity of the electrolyte solution was 230 mm / sec at a point of 3/4 of the inner circumference, and electrolysis was performed. The diamond electrode was coated on both sides with a diamond film, and all the surfaces in direct contact with the object to be treated were coated with diamond.

[Example 2]
The same procedure as in Example 1 was performed except that trichlorethylene was used as the organic halogen compound.

[Comparative Example 1]
The same procedure as in Example 1 was performed except that the cathode was changed to a Monel alloy wire mesh. A Monel alloy wire mesh having a surface area 4.5 times larger than the conductive diamond electrode used in Examples 1 and 2 was used.
The halogen ion concentration in the workpiece was measured over time. Since halogen ions are generated by reductive dehalogenation of tetrachloroethylene or trichloroethylene, the decomposition rate of tetrachloroethylene or trichlorethylene can be calculated from the increasing rate of the halogen 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. Since the phenomenon of decomposition and decrease and disappearance was observed, it was confirmed that this treatment method is widely applicable to all halogenated ethylenes.

  When the results of Comparative Example 1 and the results of Example 1 are compared, Example 1 using the diamond electrode of the present invention as the cathode is 1 in spite of the electrode area of the cathode being 1 / 4.5. It can be seen that the decomposition rate was 3 times faster.

  Moreover, the cathode potential at the time of the test of Example 1 reached −3.3 V, and it was shown that the cathode potential was overwhelmingly stronger than the cathode potential −1.2 V of Comparative Example 1. By generating such a strong reduction potential, it is considered that an efficient dehalogenation reaction of the organic halogen compound occurs.

[Example 3]
Using the apparatus shown in FIG. 2 in the same manner as in Example 1, tetrachloroethylene was added to an anhydrous sodium sulfate solution to an initial concentration of 7100 mg / L, and then emulsifier Riomix ML (manufactured by Lion Corporation) was added to 2500 mg / L. Then, electrochemical dehalogenation treatment was performed under the condition that the pH was adjusted to 12 with NaOH. When the tetrachlorethylene concentration became 150 mg / L or less and the liquid turbidity (oil droplets dispersed by the emulsifier) disappeared, tetrachlorethylene was added again to be about 7100 mg / L, and the operation for measuring the decomposition rate was repeated three times. It was. The results are shown in Table 2.

  From Table 2, it can be seen that in Example 3, the decomposition rate of tetrachloroethylene increased by about 2 times compared to Example 1 in which no emulsifier was added.

  Moreover, even if it adds tetrachloroethylene repeatedly and repeats a decomposition test, it turns out that the effect of an emulsifier continues and the decomposition rate does not fall. In ordinary electrolytic treatment, the emulsifier itself is decomposed by the oxidizing power of the anode and cannot be used repeatedly. However, under the conditions of the present invention, the emulsifier is brought into contact only with the cathode, so that the emulsifier can be used repeatedly.

[Example 4]
Using the apparatus shown in FIG. 2 in the same manner as in Example 1, electrochemical dehalogenation treatment was performed by adding tetrachloroethylene to an anhydrous sodium sulfate solution to an initial concentration of 120 mg / L. The halogen ion concentration was measured when the pH of the electrolytic solution containing the object to be processed in the cathode compartment was 10 to 12, and the decomposition rate of ethylene halide was calculated. The results are shown in Table 3.

[Comparative Example 2]
It carried out like Example 4 except having used the apparatus which changed the cathode into the Monel alloy metal mesh similarly to the comparative example 1, tetrachloroethylene concentration was measured, and the decomposition rate of the halogenated ethylene was published. The results are shown in Table 3.

From Table 3, it can be seen that in Example 4 using a diamond electrode as the cathode, the tetrachlorethylene concentration could be reduced to 0.01 mg / L within 48 hours.
On the other hand, in Comparative Example 2 using a Monel alloy for the cathode, a decrease in tetrachlorethylene concentration stagnated in the vicinity of 10 mg / L, and a phenomenon was observed that could not reach the drainage standard value of 0.1 mg / L.
From these results, it can be said that by using a diamond electrode as the material of the cathode, high concentration tetrachloroethylene can be efficiently decomposed to a low concentration and the drainage standard value can be satisfied.

[Comparative Example 3]
As in Example 1, the apparatus shown in FIG. 2 was used, and the cathode was changed to an electrode coated on one side with conductive diamond. A polysilicon base single-sided diamond electrode (made by CONDIAS) was used as the cathode, and the other test conditions were the same as in Example 1. The results are shown in Table 4.

  From Table 4, when an electrode whose surface is not coated with conductive diamond is used as a cathode, hydrogen gas is preferentially generated on the uncoated surface, and the cathode potential is only about -1.2V. It did not drop. As a result, compared with Example 1, the decomposition rate of tetrachloroethylene decreased to about 1/5. From this result, it can be said that, in the treatment method of the present invention, it is desirable that the cathode is coated with conductive diamond on all surfaces in contact with the object to be treated.

[Comparative Example 4]
The apparatus shown in FIG. 2 was used in the same manner as in Example 1, and both the cathode and the anode were changed to double-side coated diamond electrodes. The test was conducted in the same manner as in Example 1 except that a polysilicon base double-sided coated diamond electrode (manufactured by CONDIAS) was used as the cathode and anode. The results are shown in Table 5.

  The decomposition rate of tetrachlorethylene in Comparative Example 4 was similar to that in Example 1. However, when the operation of Comparative Example 4 was continued for 48 hours, the color of the cation exchange membrane (N424 manufactured by DuPont Co., Ltd.) molded and used as a diaphragm bag was decolorized from the initial dark brown color to become pale yellow, and the anode compartment (diaphragm) Chlorine ions entered the inside of the bag) and a strong chlorine odor was generated. This is thought to be due to the fact that the diaphragm was damaged by strong oxidizing power due to the use of a diamond electrode for the anode, and no longer served as a barrier against anions.

[Comparative Example 5]
The cation exchange membrane bag is removed from the apparatus shown in FIG. 2 and the apparatus (FIG. 3) in which both the anode and the cathode are in contact with the liquid to be treated is used. A test was conducted. The results are shown in Table 6.

  Table 6 shows the change in decomposition rate for each elapsed time from the start of the decomposition test. In Example 1, the degradation rate was approximately constant 60 mg organohalogen compound / L · h during operation for 24 hours, whereas in Comparative Example 5, the degradation rate was slow as 38 mg organohalogen compound / L · h from the beginning. Furthermore, there was a tendency for the decomposition rate to decrease with time. This is because chlorine ions generated at the cathode become hypochlorite at the anode because there is no diaphragm, and this causes a ping-pong reaction in which it becomes chlorine ions again at the cathode, resulting in reduced current efficiency of organic halogen decomposition. This is considered to cause a stagnation of the decomposition of the organic halogen compound.

[Example 5]
A tetrachlorethylene decomposition test was performed using the electrolytic test apparatus shown in FIG. The electrolytic cell shown in Fig. 4 has a DSE electrode (manufactured by Permerec Co., Ltd.) with a polysilicon base electrode (manufactured by CONDIAS) coated with conductive diamond on one side in contact with the electrolyte containing the object to be treated. Were placed opposite to each other as an anode, and a cation exchange membrane (N424 manufactured by DuPont Co., Ltd.) was arranged as a diaphragm 4 between both electrodes to separate the anode compartment and the cathode compartment. The cathode and the anode were configured such that only one side was in contact with the liquid, and the side and back surfaces were blocked from coming into contact with a Teflon (registered trademark) packing.
The object to be treated is mixed with the electrolytic solution in the mixing tank, supplied to the cathode compartment of the electrolytic tank through the inlet 15, extracted from the outlet 14 at the upper part of the cathode compartment, returned to the mixing tank, and fed again into the cathode compartment. Formed. A circulation path 19 for supplying the anolyte from the anolyte tank 6 to the anode compartment of the electrolytic cell, withdrawing it from the outlet 17 at the upper part of the anode compartment, returning it to the anolyte tank 6, and introducing it again into the anode compartment from the inlet 18 at the lower part of the electrolytic cell. Formed. The electrolytic solution and the anolyte were the same as in Example 1.

[Comparative Example 6]
A tetrachloroethylene decomposition test was conducted using the electrolytic test apparatus shown in FIG. The electrolytic cell shown in Fig. 5 is obtained by putting an object to be treated mixed with an electrolytic solution in a mixing vessel into the anode compartment, performing an electrolytic treatment, and then extracting from the upper portion of the anode compartment and feeding it from the lower portion of the cathode compartment. A circulation path is formed by extracting from the upper part of the cathode compartment and returning it to the mixing tank. In Comparative Example 6, the object to be processed flows from the anode compartment to the cathode compartment. As in Example 5, the cathode was a conductive diamond-coated polysilicon base electrode, and the anode was a DSE electrode. Table 7 shows the halogen decomposition rate calculated based on the tetrachlorethylene concentration measured at each elapsed time from the start of the decomposition test.

  In Example 5, the decomposition rate was almost constant 53 to 57 mg organic halogen compound / L · h during operation for 8 hours, whereas in Comparative Example 6, the decomposition rate was 35 mg organic halogen compound / L · h from the beginning. Slowly, the tendency for the decomposition rate to decrease with time was observed. This is because the liquid is circulated between the anode and the cathode, so that the chlorine ions generated at the cathode become hypochlorite at the anode, and the ping-pong reaction in which this becomes chlorine ions again at the cathode occurs preferentially to decompose the organic halogen. This is thought to be due to a decrease in current efficiency.

  The organic halogen compound dehalogenation method and the organic halogen compound dehalogenation apparatus of the present invention are suitable for dehalogenating an object to be treated containing a high concentration of an organic halogen compound to a low concentration in a short time.

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

Claims (8)

  In an electrolytic cell comprising a cathode compartment with a cathode containing conductive diamond, an anode compartment with an anode not containing conductive diamond, and a diaphragm separating the cathode compartment and the anode compartment, the anolyte is applied only to the anode compartment. Circulating, circulating an object to be treated containing an organic halogen compound only to the cathode compartment, bringing the object to be treated containing an organic halogen compound into contact with only the cathode, and performing an electrochemical dehalogenation treatment And a method for dehalogenation of an organic halogen compound.   2. The method for dehalogenating an organic halogen compound according to claim 1, wherein all surfaces of the cathode that are in direct contact with the object to be processed are coated with conductive diamond.   The method for dehalogenating an organic halogen compound according to claim 1, wherein the anode is titanium or surface-coated titanium.   The method for dehalogenating an organic halogen compound according to any one of claims 1 to 3, wherein an emulsifier is added to the object to be treated containing the organic halogen compound so as to contact only the cathode.   The method for dehalogenating an organic halogen compound according to any one of claims 1 to 4, wherein an object to be treated containing the organic halogen compound is extracted from the lower part of the electrolytic cell and returned to the upper part of the electrolytic cell and circulated. An electrolytic cell comprising a cathode compartment comprising a cathode comprising conductive diamond, an anode compartment comprising an anode not comprising conductive diamond, and a diaphragm separating the cathode compartment from the anode compartment;
An organic halogen compound dehalogenation apparatus comprising: a treatment object circulation path for circulating an object to be treated containing an organic halogen compound only to the cathode compartment; and an anolyte circulation path for circulating an anolyte only to the anode compartment.   The workpiece circulation path includes an outlet provided in the lower portion of the cathode compartment, an inlet provided in the upper portion of the cathode compartment, and a pipe for feeding the workpiece from the outlet to the inlet. Item 7. An apparatus for dehalogenating an organic halogen compound according to Item 6.   8. The organohalogen compound dehalogenation apparatus according to claim 6, wherein all surfaces of the cathode that are in direct contact with the object to be processed are coated with conductive diamond.