JP2006289231A - Method and system for decomposing and treating organic chlorine compound - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a system for effectively decomposing and treating organic chlorine compounds capable of decomposing byproducts decomposed such as chloroacetic acid, effectively utilizing chlorine formed by decomposition, and suppressing formation of an acidic waste solution. <P>SOLUTION: The method for decomposing and treating organic chlorine compounds in a gas form decomposable in the presence of a chlorine gas by light irradiation comprises: a mixed gas production process for producing a mixed gas containing the organic chlorine compound in a gas form and the chlorine gas; an organic chlorine compound decomposition process for decomposing the organic chlorine compounds by irradiating the mixed gas with light; a separation process for separating decomposed byproducts formed in the organic chlorine compound decomposition process from a gas formed in the organic chlorine compound decomposition process; an electrolysis process for decomposing the decomposed byproducts separated in the separation process by electrolysis; and a process for feeding a chlorine gas generated in the electrolysis process to the mixed gas production process. The system for the method for decomposing and treating organic chlorine compounds is disclosed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a decomposition method and apparatus for decomposing gaseous organic chlorine compounds such as chlorinated ethylene.

  A method for decomposing gas chlorinated organic compounds such as chlorinated ethylene such as trichlorethylene and chlorinated methane by mixing with chlorine gas and irradiating with light has been introduced in, for example, Patent Document 1.

  In such a process, decomposition by-products such as chloroacetic acids are generated by decomposition. Chloroacetic acids are strongly acidic, easily absorbed in water and highly soluble, so they are easily removed from the gas and concentrated to a high concentration in the liquid.

  On the other hand, there is an electrolysis method using a conductive diamond electrode as a method for decomposing a solute in a solution. For example, Patent Document 2 discloses a method of electrolyzing a solution solute using an anode containing conductive crystalline doped diamond.

Non-Patent Document 1 reports that a conductive diamond electrode doped with boron has a very wide potential window and operates stably even in a strong corrosive aqueous solution.
JP 2001-137697 A Japanese Patent Laid-Open No. 7-299467 Fujishima et al., “Electrochemistry”, Vol, 67 (1999) 389.

  In a method in which an organic chlorine compound such as trichloroethylene is decomposed by mixing with chlorine gas and irradiating with light, decomposition byproducts such as chloroacetic acids are generated by the decomposition. These chloroacetic acids have recently been established in water supply standards and are becoming a hot topic in terms of their impact on human health. Further, in the decomposition of the organic chlorine compound, hydrochloric acid is generated and an acidic waste liquid is generated.

  An object of the present invention is an efficient organochlorine compound that can decompose decomposition byproducts such as chloroacetic acids, can effectively use chlorine generated by decomposition, and can suppress the generation of acidic waste liquid. It is an object to provide a decomposition processing method and apparatus.

According to the present invention, there is provided a method for decomposing a gaseous organochlorine compound that can be decomposed by irradiating light in the presence of chlorine gas,
A mixed gas production process for producing a mixed gas containing the gaseous organochlorine compound and chlorine gas;
An organic chlorine compound decomposition step of decomposing the organic chlorine compound by irradiating the mixed gas with light;
A separation step of separating a decomposition by-product generated in the organic chlorine compound decomposition step from a gas obtained from the organic chlorine compound decomposition step;
An electrolysis process for electrolyzing the decomposition by-product separated in the separation process; and a process for supplying the chlorine gas generated in the electrolysis process to the mixed gas production process. A method is provided.

  Gaseous organic chlorine compounds that can be decomposed by irradiation with light in the presence of chlorine gas are trichloroethylene, tetrachloroethylene, cis-1,2-dichloroethylene, 1,1-dichloroethylene, and trans-1,2-dichloroethylene. It can be at least one selected from the group consisting of:

  The decomposition by-product may be chloroacetic acids.

  In the electrolysis step, a conductive diamond electrode is preferably used for the anode.

  In the electrolysis step, an acidic electrolyte solution containing hydrochloric acid can be used.

  In the separation step, the gas obtained from the organochlorine compound decomposition step is brought into contact with an absorbing solution, and an absorbing solution that has absorbed the decomposition by-product and a gas that has not been absorbed by the absorbing solution can be obtained.

  A step of supplying a part of the gas that has not been absorbed by the absorbing liquid to the mixed gas manufacturing step can be provided.

According to the present invention, there is provided a decomposition apparatus for gaseous organochlorine compounds that can be decomposed by irradiating light in the presence of chlorine gas,
A mixed gas production means for producing a mixed gas containing the gaseous organochlorine compound and chlorine gas;
Organochlorine compound decomposition means for decomposing the organochlorine compound by irradiating the mixed gas with light;
Separation means for separating a decomposition by-product generated in the organochlorine compound decomposing means from a gas obtained from the organochlorine compound decomposing means;
Decomposing organochlorine compounds having electrolysis means for electrolyzing decomposition by-products separated by the separation means; and transport means for supplying chlorine gas generated by the electrolysis means to the mixed gas production means A processing device is provided.

  According to the present invention, a novel organic chlorine compound decomposition method without decomposition byproducts, which can decompose organic chlorine compounds such as trichlorethylene and decompose decomposition byproducts such as chloroacetic acids, has been shown. Furthermore, by generating and reusing the chlorine produced by the decomposition of decomposition by-products in the decomposition of organic chlorine compounds, the generation of acidic waste liquid can be suppressed, and efficient use of organic chlorine compounds with reduced chemical consumption. A decomposition method and apparatus are provided.

  Examples of gaseous organochlorine compounds that can be decomposed by irradiating light in the presence of chlorine gas include, for example, trichloroethylene, tetrachloroethylene, cis-1,2-dichloroethylene, 1,1-dichloroethylene, trans-1,2- Examples include chlorinated ethylene such as dichloroethylene.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

  FIG. 1 is a process flow diagram for explaining one embodiment of the method for decomposing an organochlorine compound of the present invention.

  In FIG. 1, a gaseous organochlorine compound that can be decomposed by irradiating light in the presence of chlorine gas is introduced by the introduction means 1 and mixed with chlorine gas from the electrolysis means 12 at the junction 2. Thereafter, the organic chlorine compound decomposition means 3 is led. Actually, the gas containing the gaseous organic chlorine compound may be used as the gas to be processed, and the gas to be processed may be led to the junction 2. As for chlorine gas, a gas containing chlorine gas (chlorine-containing gas) may be led to the junction 2.

  Such a gas to be treated may be an exhaust gas from a factory using an organic chlorine compound, a painting process, or the like, or an exhaust gas generated when a wastewater or groundwater containing an organic chlorine compound is subjected to an aeration process. Alternatively, it may be vaporized from a solid or liquid organic chlorine compound-containing waste. Moreover, the suction gas from a contaminated ground may be sufficient. In any case, the gas introduced into the organic chlorine compound decomposition means 3 is in a state in which oxygen is contained in addition to the organic chlorine compound, that is, the gas to be treated is a mixed state of the organic chlorine compound with air. Alternatively, the organic chlorine compound is in a mixed state with a gas containing oxygen. When the gas to be treated is a suction gas from a contaminated ground or a factory exhaust gas that contains a large amount of a reducing substance, oxygen may be mixed separately. The amount of oxygen at this time is equal to or more than that of the organic chlorine compound to be decomposed, and is an amount obtained by adding an amount necessary to oxidize the inflowing reducing substance.

  The introduction of oxygen is not necessarily performed, but the introduction of oxygen can be performed by the oxygen introduction means 1a and the junction 2a.

  The oxygen introduction means 1a may be performed by connecting an oxygen cylinder, or may be performed by PSA (Pressure Swing Adsorption). PSA is a method of separating the target gas continuously by alternately repeating the pressurization and depressurization operations by utilizing the difference in adsorption characteristics of the adsorbent to the gas. The PSA used here removes oxygen from the air. It is something to take out. The oxygen introduced here is mixed with the previous gas to be processed at the junction 2a. There is no particular positional relationship between the merging point 2 and the merging point 2a, and the merging point 2a may be in front of the merging point 2.

  The organic chlorine compound decomposing means 3 includes a reaction vessel 3a for internally decomposing the organic chlorine compound and a light irradiation means 3b for irradiating the organic chlorine compound with light. The organochlorine compound is decomposed by irradiation with light in the reaction vessel 3a. The gas after the decomposition reaction passes through the duct 5 and is guided to the separation means 6.

  In the present invention, the decomposition by-product produced by the decomposition of the organic chlorine compound from the gas introduced to the separation means is separated by the separation means 6. The separated decomposition by-product is decomposed by the electrolysis means 12, and the generated chlorine gas is reused by the organic chlorine compound decomposition means 3.

  In the organochlorine compound decomposition means for irradiating light to a mixed gas containing chlorine gas and gaseous organochlorine compound, in the present invention, it is not necessary to irradiate with ultraviolet rays. Therefore, the light source used as the light irradiation means 3b is 300 nm to 500 nm. The wavelength within the range of 350 nm to 450 nm is more preferable.

  Here, an example of the organic chlorine compound decomposition means will be described in detail with reference to FIG. In FIG. 2, a cylindrical lamp 13 as a light irradiating means has the same shape as a straight tube fluorescent lamp in the form shown here. The lamp 13 is surrounded by a cylindrical reaction vessel 14 around the lamp 13, the gas introduced from the reaction vessel inlet 15 is retained inside the reaction vessel 14, and light irradiation is performed by the lamp 13. Thereafter, the gas is discharged from the reaction vessel outlet 16. Here, the reaction vessel 14 and the lamp 13 are integrated and have a sealed structure.

  The material of the reaction vessel is preferably a resin such as vinyl chloride, tetrafluoroethylene, polyethylene, or polypropylene, a corrosion-resistant metal such as hastelloy, glass, ceramic, or FRP from the viewpoint of preventing corrosion of the material constituting the vessel. Further, a stainless steel or steel material coated with the above resin material may be used. The surface in contact with the gas of the light irradiation means can be formed of glass, quartz or the like. As the light irradiation means, for example, a fluorescent lamp or a black light can be used. The size of the reaction vessel varies depending on the concentration of chlorine gas present during the reaction and the light irradiation intensity of the light irradiation means, but the gas residence time is preferably 20 seconds or more, and more preferably 40 seconds or more.

  Returning to FIG. 1 again, the description will be continued.

  The gas after the decomposition reaction by the organic chlorine compound decomposition means 3 includes surplus chlorine gas that is not consumed in the decomposition reaction, and mist of an acidic liquid of chloroacetic acid or the like generated by the decomposition of the organic chlorine compound or hydrochloric acid. .

  Here, chloroacetic acid refers to monochloroacetic acid, dichloroacetic acid, or trichloroacetic acid.

  In the separation means 6, the gas introduced from the organic chlorine compound decomposition means is brought into contact with the absorption liquid to obtain an absorption liquid that has absorbed decomposition by-products such as chloroacetic acids and a gas that has not been absorbed by the absorption liquid. Thus, the decomposition by-product can be separated from the gas obtained from the organic chlorine compound decomposition means. Alternatively, the separation may be performed by cooling the gas after the decomposition reaction and condensing and separating the decomposition by-products.

  As the absorbing solution, water, an aqueous hydrochloric acid solution or an aqueous alkaline solution can be used. As will be described later, it is desirable that the absorbing solution is acidic in the recovery of chlorine gas from the absorbing solution. Therefore, the absorbing solution is preferably water or an aqueous hydrochloric acid solution, and water is sufficient. This is because excess chlorine gas that has not been used for decomposition is absorbed in water at first and becomes an aqueous hydrochloric acid solution, and water becomes acidic due to absorption of chloroacetic acids.

  Since the solubility of chloroacetic acids in water is high, it can be absorbed in a large amount by an absorption liquid mainly composed of water. For example, the solubility of monochloroacetic acid in water is 6140 g / L (25 ° C.), and sodium trichloroacetate is 1200 g / L (25 ° C.). Other chloroacetic acids are also considered to have such a high solubility. Therefore, when treating a gas containing organochlorine compounds with a dilute organochlorine compound, chloroacetic acids can be absorbed in a small amount of absorption liquid and concentrated to a high concentration, and the electrolysis means in the subsequent stage can be miniaturized. The device can be miniaturized.

  When the absorbing solution is water at the initial stage, surplus chlorine is also absorbed in water, and the absorbing solution becomes a hydrochloric acid aqueous solution. Since absorption of chloroacetic acids is not greatly affected by pH, chloroacetic acids are absorbed regardless of whether the absorbing solution is water or a hydrochloric acid aqueous solution. That is, the absorbing solution may be one having a low pH such as a hydrochloric acid aqueous solution.

  In the method of absorbing chloroacetic acid in water, chlorine gas is hardly absorbed and discharged from the separating means 6 as the pH of the absorbing solution decreases. When an aqueous hydrochloric acid solution is used as the absorbing solution, chlorine gas is less likely to be absorbed at an early stage than when water is used as the absorbing solution. The processing gas discharged from the separating means 6 is guided to the chlorine gas absorbing means 8 by the duct 7, removed from the chlorine gas, and released to the atmosphere by the purified gas discharging means 9.

  As the chlorine gas absorbing means 8, a known technique capable of absorbing and removing chlorine gas can be used as appropriate. For example, an alkali scrubber may be used, or a water scrubber may be used. However, it is preferable to adjust by adding an alkali agent so long as the pH does not decrease. It is preferable to drain and replace with fresh water, or to control pH adjustment by adding an alkali agent.

  In the separation means 6, the absorbing liquid that has absorbed decomposition by-products (which may have absorbed chlorine gas) is stored in the tank 10. The tank 10 may be a part of the separation unit 6, and may be integrated with the separation unit 6 in particular. For example, when a scrubber is used as the separating means, the lower part of the scrubber can be used as the tank 10.

  When the separation is performed using the absorbing liquid, a part of the gas that has not been absorbed by the absorbing liquid (the gas discharged from the separating means) may be mixed with the mixed gas supplied to the organochlorine compound decomposing means. For example, the gas can be branched in the middle of the duct 7, and the branched gas can be merged with the junction 2. Thereby, the total amount of chlorine gas in the organochlorine compound decomposing means 3 can be increased without increasing the amount of electricity in the electrolyzing means 12.

  The purified gas discharge means 9 can be appropriately configured using a duct and a fan. The material of the duct and fan may be made of steel, but the mist from the scrubber etc. contains salt and alkali, so the resin is coated on the surface with resin such as PVC, stainless steel, or resin in consideration of corrosion. The product etc. are preferable.

  Here, an example of the structure of the scrubber as the separating means 6 will be described in detail with reference to FIG.

  The scrubber body 17 is a cylindrical tower and has a packed bed 18 formed by charging a filler. Examples of the filler used include Lahi Shilling, Berle Saddle, Interlock Saddle, Terrarette (trade name, manufactured by Nippon Steel Chemical Industries Co., Ltd.), Lahishi Super Ring (trade name, manufactured by Nippon Steel Chemical Industries Co., Ltd.), and the like. .

  Here, it is set as the structure which installs the distributor 19 in the upper part inside a scrubber main body, and is a position above the packed bed 18, and introduces water and flows down in the tower. The liquid is introduced into the distributor 19 from the introduction port 20 by piping. A gas outlet 21 is provided in the upper part of the scrubber, and a mist separator 22 is installed in the lower part. In addition, a filler fall prevention net 23 is laid so that the filler does not fall, and a water collection tank 24 is installed immediately below. Further, the water collection tank 24 is provided with a treated water outlet 25 and a gas inlet 26. Although not shown, by providing piping for connecting the treated water outlet 25 and the circulation pump suction port, and piping for connecting the circulation pump discharge port and the introduction port 20, the liquid in the water collection tank 24 is stored inside the scrubber. Circulate through. That is, the liquid pressurized by the circulation pump from the water collection tank 24 is sprinkled by the distributor 19, falls from the top to the bottom through the packed bed 18, and returns to the water collection tank 24. The gas from the gas inlet 26 moves from the bottom to the top inside the scrubber. At this time, the liquid comes into contact with the gas from the gas inlet 26 and absorbs the gas.

  Returning to FIG. 1 again, the description will be continued.

  The absorbing liquid in the separation means 6 is extracted from the tank 10 and processed by the electrolysis means 12.

  The transfer means 11 to the electrolysis means 12 can be formed using piping, a pump, a valve, etc. suitably. The liquid level of the tank 10 or the electrolysis means 12 may be automatically controlled by automatically operating a pump or a valve. Although the treatment by the electrolysis means 12 can be a continuous process, the introduction means 1 may be stopped and transferred, and the introduction means may be operated again after transfer to perform the electrolysis.

  As the electrolysis means 12, one using a tank in which two electrodes, one of which is an anode and the other is a cathode, can be used. The shape of the two electrodes may be any shape, and may be a plate-like or mesh-like plate, and may be the same tube shape or rod shape. Examples of the material include conductive diamond and lead. The two poles do not necessarily have to have the same shape and the same material, and the two poles may have different shapes, or the two poles may be made of different materials.

  FIG. 5 shows the results of a batch test of electrolysis of 20 L of an aqueous solution of dichloroacetic acid having a concentration of 3500 mg / L. The cathode material was titanium, and the anode was titanium, lead, or conductive diamond. The size of the electrode was 8 cm × 24 cm for both the cathode and anode, and 20 A was supplied from a DC power source. FIG. 6 shows the results of an attempt to electrolyze trichloroacetic acid at a concentration of 3500 mg / L under the same conditions.

  When the anode was a titanium electrode, dichloroacetic acid was not decomposed and even an increase in concentration was observed, but in all other cases, a tendency to be decomposed was observed. However, it can be seen that the conductive diamond electrode is rapidly decomposed and it is advantageous to use the conductive diamond electrode for the anode.

  Compared to conventional metal electrodes such as platinum, the conductive diamond electrode has an extremely wide potential window and can efficiently oxidatively decompose only organic compounds while suppressing generation of hydrogen and oxygen due to electrolysis of water. Furthermore, since the conductive diamond electrode is excellent in chemical stability, there is little concern about corrosion even in the treatment of a liquid in which hydrochloric acid or chloroacetic acid is concentrated at a high concentration.

  The conductive diamond electrode that can be used in the present invention is a metal material such as titanium, zirconium, niobium, tantalum, molybdenum, tungsten, carbon, silicon wafer, etc. as a base material, and deposits a diamond thin film on the surface of these base materials, Alternatively, it can be synthesized. Furthermore, it is also possible to use polycrystalline diamond deposited and synthesized in a plate shape or the like without using a substrate. As the diamond, a material doped with boron, boron or the like to impart desired conductivity can be used.

  In the present invention, a single container containing two electrodes is used as the electrolysis means 12, and a liquid (such as a chloroacetic acid solution) containing a decomposition byproduct as an electrolyte is introduced into the container to perform the electrolysis. be able to. In addition, electrolysis means having a two-chamber configuration by providing a container (reaction liquid retention chamber) separate from a container (electrolysis reaction chamber) containing two electrodes can be used.

  Here, an example of an electrolysis apparatus as electrolysis means will be described in detail with reference to FIG.

  Inside the electrolytic reaction tank 27, a conductive diamond plate is used as an anode 28, and a titanium plate or a stainless steel plate is used as a cathode 29, and these two plates are arranged facing each other. A DC power supply 30 is connected to the anode 28 and the cathode 29, a positive electrode of the power supply 30 is connected to the anode 28, and a negative electrode of the power supply 30 is connected to the cathode 29.

  The electrolytic reaction tank 27 is installed on the reaction liquid retention tank 31. The electrolytic reaction tank 27 has a hole in the upper side surface and is connected to the reaction liquid retention tank 31 below by a pipe 32. The reaction liquid retention tank 31 has a hole on the side or bottom and is connected to the suction side of the circulation pump 34 by a pipe 33, and one end of a pipe 35 is connected to the pump discharge side. There is a check valve (not shown), and the other end of the pipe 35 is connected to a hole at the bottom of the upper electrolytic reaction tank 27. The liquid containing the decomposition by-product is circulated through the lower reaction liquid retention tank 31 and the upper electrolytic reaction tank 27 by the circulation pump 34. Due to this circulation, a flow is generated inside the electrolytic reaction tank 27, and the chlorine gas etc. on the electrode surface is easily peeled off due to the flow also generated on the electrode surface, and the chlorine gas etc. is separated and efficient chlorine generation occurs. At least one of the electrolytic reaction tank 27 and the reaction liquid retention tank 31 has a hole for exhausting chlorine gas, and a pipe connected to this hole is connected to a pipe in front of the photoreaction tank. The generated chlorine is mixed with the gaseous organochlorine compound-containing gas to be treated. Here, holes 36 and 37 for exhausting chlorine gas are respectively provided in both, and the hole 37 is connected to the junction 2 in FIG.

  The liquid containing the decomposition by-product is supplied from the liquid supply hole 32a containing the decomposition by-product, but it may be supplied from the upper part of the electrolytic reaction tank.

  In the reaction liquid retention tank 31, gas blowing and liquid stirring may be performed by a blower. That is, a pipe 38 is connected to a suction side of a blower 39 through a hole 36 for exhausting chlorine gas, and a discharge side of the blower 39 passes through a hole 42 opened in the reaction liquid retention tank 31 by a pipe 41 and diffuses a pipe 43. Connected to. The air diffuser is a tubular tube having a large number of fine holes, which discharges gas from the holes to the liquid inside the reaction liquid retention tank, and may have a shape such as a diffuser plate. A gas containing chlorine generated in the electrolytic reaction tank 27 is passed to the reaction liquid retention tank 31, and after the liquid in the tank is stirred, the gaseous organic chlorine compound is discharged from the hole 37 for exhausting the chlorine gas. Used for disassembling. In order to balance the flow rate of the chlorine gas-containing gas generated in the electrolytic reaction tank 27 and the air volume of the blower 39, an air inlet 40 is provided in the pipe 38. A valve for adjusting the flow rate may be provided in the pipe 38, the pipe 41, the pipe from the air inlet 40 to the pipe 38, or the like. Alternatively, an air flow control mechanism such as an inverter may be provided in the blower 39, and the air flow of the blower 39 may be adjusted by the chlorine gas-containing gas generation flow rate.

  In the electrolytic reaction tank 27, a liquid containing a decomposition by-product such as a chloroacetic acid solution undergoes electrolysis and chlorine is generated. The chlorine concentration in the chlorine gas-containing gas discharged from the hole 37 varies depending on the pH of the solution.

  The liquid containing decomposition by-products such as a chloroacetic acid solution led to the electrolytic reaction tank 27 is an acidic liquid containing hydrochloric acid by absorbing chlorine in the separation means 6 in the previous stage. The decrease in pH also proceeds by electrolysis in The pH of the liquid containing the decomposition by-product is preferably 3 or less, more preferably about 1 from the viewpoint of promptly expelling chlorine generated by the decomposition from the electrolytic reaction tank 27 as chlorine gas. The presence of a liquid flow generated between the electrolytic reaction tank 27 and the reaction liquid retention tank 31 by the circulation pump 34 is also effective for promoting the removal of the gas generated in the electrolytic reaction tank 27.

  7 and 8 show the results of a batch test on chloroacetic acid decomposition and chlorine generation using an electrolysis apparatus using a conductive diamond electrode. In the experiment, using the apparatus of FIG. 4, the circulation pump flow rate is 5 L / min, the blower flow rate is 3 L / min, the blower pressure increase width is 0.1 MPa, the electrolytic reaction tank capacity is 3 L, the reaction liquid retention tank capacity is 7 L, the electrolytic reaction tank and the reaction liquid. The material of the retention tank was vinyl chloride. A net-like plate coated with conductive diamond was used for the anode, and the cathode material was a titanium flat plate. The external shape of the electrode was 8 cm × 24 cm for both the cathode and anode, and 20 A was supplied from the DC power source.

  In the test of FIG. 7, an aqueous solution in which tetrachloroethylene-containing air was irradiated with light in the presence of chlorine gas was absorbed into pure water and neutralized with caustic soda. This aqueous solution had a trichloroacetic acid concentration of 8200 mg / L and a pH of 7.3 due to neutralization. In the test of FIG. 8, by the same operation, the trichloroacetic acid concentration was 76000 mg / L, and the pH by neutralization was 5.5. Both prepared aqueous solutions are 20L. In both the tests of FIGS. 7 and 8, the trichloroacetic acid decomposition rate after 6 hours is around 70%, but the concentration of generated chlorine (the concentration of chlorine in the gas discharged from the holes 37) is as shown in FIG. In the test, it is several hundred volppm (volppm represents volume parts per million), whereas the test of FIG. 8 exceeds 15000 volppm after 2 hours. In the test of FIG. 8, the pH dropped to less than 2 in 1 hour after the start of decomposition. Although the pH of the liquid is the course of decomposition, it shows that a lower pH is more advantageous for removing chlorine from the liquid and generating chlorine gas. Almost no effect on the degradation of trichloroacetic acid by pH was observed.

  The chlorine-containing gas generated from the electrolysis means 12 is mixed with the organic chlorine compound-containing gas introduced from the introduction means 1 in FIG. 1 at the junction 2 and then introduced to the organic chlorine compound decomposition means 3 for decomposition treatment. Is done.

The decomposition treatment method of the present invention is a decomposition apparatus for gaseous organochlorine compounds that can be decomposed by irradiation with light in the presence of chlorine gas,
A mixed gas production means for producing a mixed gas containing the gaseous organochlorine compound and chlorine gas;
Organochlorine compound decomposition means for decomposing the organochlorine compound by irradiating the mixed gas with light;
Separation means for separating a decomposition by-product generated in the organochlorine compound decomposing means from a gas obtained from the organochlorine compound decomposing means;
Electrolysis means for electrolyzing the decomposition by-products separated by the separation means;
The chlorine gas generated by the electrolysis means can be suitably implemented by an organic chlorine compound decomposition treatment apparatus having a transfer means for supplying the mixed gas production means.

  As the mixed gas production means, the introduction means 1, the junction point 2, the line for introducing the chlorine-containing gas from the electrolysis means 12 to the junction point 2, the line for introducing the mixed gas from the junction point to the organic chlorine compound decomposition means 3 are appropriately ducted, etc. What is necessary is just to form using. The organochlorine compound decomposition means, separation means, electrolysis means, and transfer means are as described above.

  FIG. 9 shows the apparatus used in the example.

  Air containing 750 volppm of tetrachloroethylene was used as an organic chlorine compound-containing gas, which is a gas to be treated, and the air volume was 120 L / min.

  The tetrachloroethylene-containing air is introduced from a pipe as introduction means 1 and mixed with a chlorine-containing gas having a chlorine concentration of 5300 volppm and an air volume of 10 L / min at a junction 2 and then introduced to an organic chlorine compound decomposition means.

  Chlorine is generated from the electrolysis tank. Here, the apparatus of FIG. 4 was used for the electrolysis tank. Here, the anode 28 was an 8 cm × 24 cm × 0.1 cm conductive diamond mesh plate, the cathode 29 was a titanium plate of the same size, and the distance between the cathode and anode was set to 1 cm. The conductive diamond electrode used here was boron doped and a diamond thin film deposited and synthesized on a niobium base material by a microwave CVD method.

  The DC power source 30 connected to the anode 28 and the cathode 29 was a DC stabilized power source (trade name: PAS20-36) manufactured by Kikusui Electronics Co., Ltd., and the current value was 20A. The capacity of the electrolytic reaction tank 27 was 3 L, that of the reaction liquid retention tank 31 was 40 L, and the capacity of the circulation pump 34 was 5 L / min. The flow rate of the blower 39 was 10 L / min, and the pressure increase width was 0.1 MPa. A gas containing chlorine gas is exhausted from a chlorine gas exhaust hole in the electrolytic reaction chamber and the reaction liquid retention chamber, and a pipe 55 connected thereto is connected at a connection point 2 with the pipe 1 to form a tetrachloroethylene-containing gas (gas to be treated). ) And led to the reaction vessel 14.

  The generation method of the chlorine-containing gas includes an initial operation at the start of operation, a main operation, and a post-treatment operation.

  The initial operation is performed at the start of operation. In the initial operation, the transfer pump 54 was completely stopped, the valve 49b was closed, and the valves 49C and 49a were opened. The reaction liquid retention tank 31 was charged with 4.5 L of a 10% by mass hydrochloric acid solution and 500 mL of trichloroacetic acid, diluted with pure water to 10 L, and this was sent to the electrolytic reaction tank 27 by the circulation pump 34 and circulated. Further, in the reaction liquid retention tank 31, the blower 39 blows outside air from the valve 49 </ b> C and stirs the liquid.

  The initial operation was continued for 24 hours, and then the main operation was started. In this operation, the transfer pump 54 was operated, the valves 49b and 49a were adjusted and opened, and the valve 49C was completely closed. The operation of the transfer pump 54 is a quantitative liquid feeding.

  The organochlorine compound decomposition means is the same shape as in FIG. 2 and connected in series. The reaction vessel 14 is a cylindrical tube with an inner diameter of 200 mm × length of 1000 mm, and the material is vinyl chloride. The lamp 13 is a black light ( One product of Toshiba Lighting & Technology Co., Ltd., trade name: FHF32BLB) was placed in each reaction vessel. In both the initial operation and the main operation, the mixed gas of the tetrachloroethylene-containing gas (the gas to be treated) and the chlorine gas passes through the organochlorine compound decomposition means.

  The gas (including mist-like condensate) exiting the final reaction vessel is transferred to the separation means by the pipe 44.

  A scrubber made of pure water was used as the separation means. In the initial operation, the drain (liquid extracted from the water collection tank 24 by the transfer means 11) is operated without being discharged. However, when the main operation is started, the drain is quantitatively transferred to the electrolytic reaction tank 27 by the transfer pump 54 at 60 mL / h. Is done.

  The separating means has the same shape as that shown in FIG. 3, and the scrubber body 17 uses a cylindrical can having an inner diameter of 200 mm and a length of 1.5 m, and a filler (manufactured by Nippon Steel Chemical Co., Ltd., trade name: Terralet S). Filled layer was formed by filling type II). The capacity of the water collection tank 24 was 20 L, and 10 L of pure water was initially put in this water collection tank to make an internal circulating liquid. The internal circulating liquid circulates between the scrubber main body and the water collection tank by the circulation pump 46 and piping. In addition, pure water is replenished via a ball tap valve 45 in order to compensate for the decrease in liquid due to continuous draining, evaporation and scattering.

  Initially, trichloroacetic acid is mainly absorbed and concentrated in the internal circulating liquid, which is pure water. The trichloroacetic acid concentration after continuous operation for 24 hours was about 70,000 mg / L.

  Chlorine gas that has not been captured by the absorbing solution by the separating means is transferred to the alkali scrubber 50 using the sodium hydroxide aqueous solution as the absorbing solution by the fan 47 and the duct. Here, the alkali scrubber 50 has the same structure as the separation means of FIG. 3, and contains an aqueous sodium hydroxide solution (5 mass%) inside, and is adjusted by a pH meter (not shown) and sodium hydroxide addition means (not shown). The pH is controlled not to be 11 or less. Here, chlorine gas is absorbed, and the gas after chlorine removal is sucked by the fan 51 and the duct and released into the atmosphere.

  In both the initial operation and the main operation, the gas (including the mist-like condensate) exiting the reaction vessel 14 passes through the scrubber 17 and the alkali scrubber 50. However, there is a branch point 48 in the middle of the duct downstream of the fan 47, and after this operation, a part 10 L / min of the gas containing chlorine gas moves to the mixing point 53 through the pipe 52. The amount of movement of the gas containing the chlorine gas to be branched was adjusted by the opening degree of the valves 49a and 49b.

  Note that a hydrochloric acid injection device (not shown) was added to the reaction liquid retention tank 31 in consideration of the case where the chlorine gas concentration for performing the photodecomposition reaction suitably is insufficient. Not used for.

  In this example, the main operation was performed for 120 hours following the initial operation. The aqueous solution in the electrolysis tank at that time is about 20 L, the trichloroacetic acid concentration is about 80,000 mg / L, and the chlorine gas concentration generated from the electrolytic reaction tank (the chlorine concentration in the gas flowing through the pipe 55) is about 5300 volppm. there were.

  A post-processing operation was performed after the main operation.

  In the post-treatment operation, the introduction of the tetrachloroethylene-containing air was stopped, and 10 L of the aqueous solution in the electrolysis tank was first taken out and secured in a container (not shown), and the remaining 10 L of trichloroacetic acid aqueous solution was electrically charged with a conductive diamond electrode. Disassembled. The operating condition at this time is that the lamp 13 is turned off, the transfer pump 54 is completely stopped, the valve 49b is closed, and the valves 49C and 49a are opened. At this time, the fan 47 and the fan 51 were operated by adjusting the air volume. The operation in this state was performed for 8 hours, 10 L of pure water was added to the electrolysis tank and the operation was further performed for 8 hours, and 10 L of pure water was added again and the operation was continued for 8 hours to complete the post-processing operation.

  In the post-treatment operation, the trichloroacetic acid aqueous solution in the electrolysis tank is decomposed by the conductive diamond electrode, and the generated chlorine gas is absorbed by the alkali scrubber 50. The final trichloroacetic acid concentration in the electrolysis tank is 0.16 mg. / L. Since the aqueous solution in the electrolysis tank after the post-treatment operation has a concentration capable of draining, the pH was adjusted and drained.

  Thereafter, 10 L of the aqueous solution secured in the previous container was returned to the electrolysis tank, and the main operation could be started again without performing the initial operation.

  At this time, the trichloroacetic acid aqueous solution in the electrolysis tank is used and recycled in the main operation again. In addition, the amount of chlorine gas consumed in the previous main operation is 1.2 kg, and when converted to hydrochloric acid, the amount is 20 L or more of 20% by mass hydrochloric acid aqueous solution. That is, it is considered that 10 L / 120 h of waste liquid was recovered and the same amount of hydrochloric acid was saved.

  In this example, the concentration of tetrachlorethylene in the treated gas (the gas exhausted through the fan 51) was less than 1 volppm in both the initial operation and the main operation.

  The present invention can be suitably used for purifying soil and groundwater, for example.

It is a process flow figure for explaining one embodiment of a decomposition processing method of an organic chlorine compound of the present invention. It is the schematic which shows the structure of an example of an organochlorine compound decomposition | disassembly means. It is the schematic which shows the structure of the scrubber which is an example of an acidic liquid separation means. It is the schematic which shows the structure of the electrolyzer which is an example of an electrolysis means. It is a graph which shows the electrolysis batch test result of dichloroacetic acid aqueous solution. It is a graph which shows the electrolysis batch test result of trichloroacetic acid aqueous solution. It is a graph which shows the result of the batch test regarding the trichloroacetic acid decomposition | disassembly and chlorine generation by a conductive diamond electrode. It is a graph which shows the result of the batch test regarding trichloroacetic acid decomposition | disassembly and chlorine generation by a conductive diamond electrode. It is a process flow figure which shows the outline of the apparatus used for the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Introduction means 1a Oxygen introduction means 2 Junction point 2a Oxygen junction point 3 Organochlorine compound decomposition means 3a Reaction vessel 3b Light irradiation means 5 Duct 6 Separation means 7 Duct 8 Chlorine gas absorption means 9 Purified gas discharge means 10 Tank 11 Transfer means 12 Electrolysis means 13 Lamp 14 Reaction vessel 15 Reaction vessel inlet 16 Reaction vessel outlet 17 Scrubber body 18 Packing layer 19 Distributor 20 Inlet 21 Gas outlet 22 Mist separator 23 Filler fall prevention net 24 Water collecting tank 25 Treated water outlet 26 Gas inlet 27 Electrolytic reaction tank 28 Anode 29 Cathode 30 DC power supply 31 Reaction liquid retention tank 32 Pipe 32a Liquid supply hole 33 containing decomposition by-products 33 Pipe 34 Circulation pump 35 Pipe 36 Hole 37 for exhausting chlorine gas Hole 38 for exhausting chlorine gas Piping 39 Blower 40 Air inlet 41 Pipe 42 hole (for diffuser pipe connection)
43 Aeration pipe 44 Piping 45 Ball tap valve 46 Circulation pump 47 Fan 48 Branch point 49a Valve 49b Valve 49c Valve 50 Alkaline scrubber 51 Fan 52 Piping 53 Mixing point 54 Transfer pump 55 Piping

Claims (8)

A method for decomposing a gaseous organochlorine compound that can be decomposed by irradiating light in the presence of chlorine gas,
A mixed gas production process for producing a mixed gas containing the gaseous organochlorine compound and chlorine gas;
An organic chlorine compound decomposition step of decomposing the organic chlorine compound by irradiating the mixed gas with light;
A separation step of separating a decomposition by-product generated in the organic chlorine compound decomposition step from a gas obtained from the organic chlorine compound decomposition step;
An electrolysis process for electrolyzing the decomposition by-product separated in the separation process; and a process for supplying the chlorine gas generated in the electrolysis process to the mixed gas production process. Method.   Gaseous organic chlorine compounds that can be decomposed by irradiation with light in the presence of chlorine gas are trichloroethylene, tetrachloroethylene, cis-1,2-dichloroethylene, 1,1-dichloroethylene, and trans-1,2-dichloroethylene. The method according to claim 1, wherein the method is at least one selected from the group consisting of:   The method according to claim 1 or 2, wherein the decomposition by-product is chloroacetic acid.   The method according to claim 1, wherein a conductive diamond electrode is used for the anode in the electrolysis step.   The method according to any one of claims 1 to 4, wherein an acidic electrolyte solution containing hydrochloric acid is used in the electrolysis step.   In the separation step, the gas obtained from the organochlorine compound decomposition step is brought into contact with an absorption liquid to obtain an absorption liquid that has absorbed the decomposition by-products and a gas that has not been absorbed by the absorption liquid. The method according to any one of the above.   The method according to claim 6, further comprising supplying a part of the gas not absorbed by the absorbing liquid to the mixed gas manufacturing process. An apparatus for decomposing gaseous organochlorine compounds that can be decomposed by irradiating light in the presence of chlorine gas,
A mixed gas production means for producing a mixed gas containing the gaseous organochlorine compound and chlorine gas;
Organochlorine compound decomposition means for decomposing the organochlorine compound by irradiating the mixed gas with light;
Separation means for separating a decomposition by-product generated in the organochlorine compound decomposing means from a gas obtained from the organochlorine compound decomposing means;
Decomposing organochlorine compounds having electrolysis means for electrolyzing decomposition by-products separated by the separation means; and transport means for supplying chlorine gas generated by the electrolysis means to the mixed gas production means Processing equipment.

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