JP5743441B2 - Method for electrolysis of polychlorinated biphenyls - Google Patents

Description

  The present invention relates to an electrolysis method and an electrolysis apparatus for an organic chlorine compound, particularly polychlorinated biphenyl (hereinafter referred to as “PCB”).

  In recent years, cases of soil contamination due to harmful substances have become apparent with the redevelopment of factory sites. If soil is contaminated with harmful substances, it may adversely affect human health. For this reason, there are increasing concerns about soil contamination, and social demands for countermeasures are increasing.

  In addition to heavy metals and volatile organic compounds, organochlorine compounds are known as causative substances for soil contamination. For example, PCB is a substance that has been widely used as an insulating oil or a heat medium because of its insulating properties and chemical stability. However, its toxicity became apparent in light of the environmental pollution problem that occurred in the 1965s. Its manufacture and use was prohibited by the Ordinance of the Ministry of International Trade and Industry.

  However, an effective method for treating PCB has not been established, and its waste has been stored for more than 30 years, and has reached the present day. The “Stockholm Convention on Persistent Organic Pollutants (POPs Convention)” was adopted in 2001, and Japan has already ratified it, but it came into effect in May 2004 with over 50 countries ratified. Under this treaty, PCB is designated as one of nine prohibited substances for production and use, and appropriate disposal targets are set up to 2016. In Japan, the “PCB Waste Special Measures Law” was enacted, and it was stipulated that these PCBs be processed by 2016. Currently, the country is promoting the establishment of a regional wide-area treatment facility utilizing Japan Environmental Safety Corporation, and the commercialization of PCB waste treatment.

  On the other hand, PCB-contaminated soil, which is thought to exist in a wide range at a relatively low concentration, has a greater impact on the environment than stored PCB waste. The “Ministry of the Environment” formulated “Guidelines for the Structure and Maintenance of PCB-Contaminated Soil Remediation Facilities”. Currently, among existing technologies applicable to PCB-contaminated soil, the indirect heating separation method at 600 to 700 ° C by rotary kiln is the mainstream, but even with this method, on-site treatment is not possible from the viewpoint of consideration for the neighborhood. difficult. Therefore, an on-site processing technique under milder conditions is desired.

  For example, Patent Document 1 discloses a method of electrolyzing PCB separated from contaminated soil as a method of decomposing PCB at normal temperature and not causing secondary pollution such as exhaust gas.

JP 2006-130395 A

  Conventionally, a method for detoxifying an organic chlorine compound by electrolysis is known. However, in the conventional method in which a cylindrical electrolytic cell system is employed and an expensive metal such as palladium is used as the cathode material of the electrode, the initial cost and the operation cost are very high in consideration of scale-up to an actual scale.

  Therefore, an object of the present invention is to provide an inexpensive electrode material while maintaining the electrolysis efficiency of the organic chlorine compound.

  As a result of intensive studies by the present inventors to solve the above-mentioned problems, it was found that the use of stainless steel as the cathode material can reduce the initial cost and the operation cost while maintaining the electrolysis efficiency. .

That is, the present invention includes the following.
(1) An electrolysis apparatus for an organic chlorine compound comprising an anode, a cathode, and an electrolytic cell, wherein stainless steel is used as the cathode.
(2) The electrolysis apparatus according to (1), wherein the anode and the cathode are flat and both electrodes are arranged in parallel with an interval of 1.5 to 5 mm.

(3) The electrolysis apparatus according to (1) or (2), further including a separation device for separating the organic chlorine compound from the contaminated soil.
(4) The electrolyzer according to any one of (1) to (3), wherein the organic chlorine compound is polychlorinated biphenyl (PCB).

(5) A method of electrolyzing an organic chlorine compound using the electrolyzer according to any one of (1) to (4).
(6) The electrolysis method according to (5), wherein electrolysis is performed at a current density of 2800 A / m ² or more.

(7) The electrolysis method according to (5) or (6), wherein the organic chlorine compound is separated from the contaminated soil using a cleaning agent.
(8) The electrolysis method according to (7), wherein the cleaning agent is a nonionic surfactant or a mixture of a nonionic surfactant and cyclodextrin.

  According to the present invention, the organochlorine compound can be efficiently electrolyzed and the cost can be reduced.

The results of an electrolysis test using SUS304 as the cathode and the electrode spacing of 2 mm are shown. The relationship between a current density and PCB residual ratio is shown.

Hereinafter, the present invention will be described in detail.
1. Electrolytic device The organic chlorine compound electrolysis device according to the present invention comprises an anode, a cathode and an electrolytic cell, and uses stainless steel as the cathode.

  Representative examples of the “organochlorine compound” include PCB, but dioxins (for example, polychlorinated dibenzoparadoxine (PCDD), polychlorinated dibenzofuran (PCDF), etc.); organochlorine solvents (for example, tetrachloroethylene, Trichlorethylene, dichloroethylene, trichloroethane, carbon tetrachloride, dichloromethane, etc.); organochlorine pesticides (eg, DDT, BHC, aldrin, endrin, dieldrin, heptachlor, etc.) are also included.

  It is not necessary to use a special material for the “anode”, and those commonly used in the field to which the present invention belongs can be used. For example, platinum, titanium, lead, iron, copper, aluminum, indium, carbon, etc. can be mentioned. Preferably, titanium plated with platinum is used.

  Stainless steel is used for the “cathode” material. Examples of the stainless steel include austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, and ferrite-austenite stainless steel.

  As austenitic stainless steel, SUS304, SUS301, SUS301L, SUS630, SUS631, SUS302, SUS302B, SUSXM15J1, SUS303, SUS303Se, SUS304L, SUS304J1, SUS304J2, SUS305, SUS309S, SUS310S, US3S, 34 Can do.

  Examples of the ferritic stainless steel include SUS430, SUH409, SUH409L, SUH21, SUS410L, SUS430F, SUS430LX, SUS430J1L, SUS434, SUS436L, SUS444, SUS436J1L, SUSXM27, and SUS447J1.

  Examples of the martensitic stainless steel include SUS410, SUS410S, SUS410F2, SUS416, SUS420J1, SUS420J2, SUS420F, SUS420F2, and SUS431.

  Examples of the ferritic-austenitic stainless steel include SUS329J1, SUS329J3L, and SUS329J4L.

  In the present invention, the type of stainless steel used is not particularly limited, but it is preferable to use austenitic stainless steel, and it is particularly preferable to use SUS304 and SUS316 that are widely used in industry. By using stainless steel as the cathode material, the cost can be significantly reduced.

  It is not necessary to use a special electrolytic cell, and a general electrolytic cell made of glass or the like can be used.

  The shape of the anode and the cathode is a flat plate, and both electrodes are preferably arranged in parallel with an interval of 1.5 to 5 mm, particularly preferably in parallel with an interval of 1.8 to 3 mm. By reducing the distance between the electrodes, a large current can be obtained at a low voltage, and the operation cost can be reduced.

  The electrolysis apparatus of the present invention preferably further includes a stirrer and an ultrasonic generator. It is possible to promote the decomposition of the organic chlorine compound by electrolysis while stirring and / or generating ultrasonic waves.

  It is preferable that the electrolyzer of the present invention further includes a separation device for separating the organic chlorine compound from the contaminated soil. It is preferable that the separation device includes a container for storing an aqueous dispersion containing contaminated soil, a stirrer, and an ultrasonic generator. By generating ultrasonic waves in an aqueous dispersion containing contaminated soil, it is easy to separate the organic chlorine compounds adhering to the soil particles from the soil particles, and by further stirring, the soil particles and the organic chlorine compound can be separated. it can. By leaving the mixture for a predetermined time after stirring, the soil particles from which the organic chlorine compound has been separated are deposited in the container, and the sparingly soluble organic chlorine compound is suspended in the supernatant. The supernatant liquid can be sent out to the electrolytic cell by connecting the separator and the electrolytic cell.

  In addition, the treated water electrolyzed in the electrolytic cell can be returned to the separator and reused. For example, by installing a submersible pump or the like in the electrolytic cell, the treated water can be returned to the separator and reused.

  Furthermore, by installing a sand pump or the like in the separation device, the earth and sand from which the organic chlorine compound has been separated can be recovered, and this can be effectively used as backfill soil for construction.

2. Electrolysis Method The method for electrolyzing an organic chlorine compound in the present invention is characterized in that it is carried out in an electrolytic cell in which an anode and a cathode made of a stainless steel material are arranged.

  The shape of the anode and the cathode is a flat plate, and both electrodes are preferably arranged in parallel with an interval of 1.5 to 5 mm, particularly preferably in parallel with an interval of 1.8 to 3 mm. By reducing the distance between the electrodes, a large current can be obtained at a low voltage, and the operation cost can be reduced.

Although there is no restriction | limiting in particular in the current density which electrolyzes, in order to decompose | disassemble an organic chlorine compound efficiently, it is preferable to carry out at 2800 A / m < ² > or more, and it is especially preferable to carry out at 2800-3200 A / m < ² >.

  The decomposition of the organic chlorine compound can be promoted by electrolysis while stirring and / or generating ultrasonic waves.

  The electrolysis method of the present invention is suitable for decomposing low-concentration organochlorine compounds. For example, it is suitable for decomposing organochlorine compounds present in contaminated soil. The method for separating the organic chlorine compound from the contaminated soil is not particularly limited, but generally, a method of separating the organic chlorine compound from the soil particles by stirring the contaminated soil in water is adopted. In this case, an organic solvent may be added to water in order to increase the degree of separation. Examples of the organic solvent used for this purpose include n-hexane, isopropanol, and methanol. More preferably, a detergent can be added to the water. Examples of the cleaning agent include nonionic surfactants, and mixtures of nonionic surfactants and cyclodextrins.

  Nonionic surfactants include polyoxyethylene alkyl ethers (eg, polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether); glycerin fatty acid esters (eg, glycerol monoester) Sorbitan fatty acid esters (eg, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate, sorbitan trioleate); polyoxyethylene Sorbitan fatty acid ester (eg, polyoxyethylene sorbitan monococonut oil fatty acid ester, polyoxyethylene sorbitan monolaur Polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, etc .; polyoxyethylene fatty acid esters (eg, polyethylene glycol monolaurate, Polyethylene glycol monostearate, polyethylene glycol distearate, polyethylene glycol monooleate, etc.); polyoxyethylene derivatives (eg, polyoxyethylene distyrenated phenyl ether, polyoxyethylene polyoxypropylene glycol, etc.); polyoxyethylene sorbitol Fatty acid esters (eg, polyoxyethylene sorbitol tetraoleate); propylene glycol fatty acid Ester, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, sucrose fatty acid ester (sucrose stearate ester and sucrose palmitate ester), such as polyglycerol fatty acid esters. These surfactants may be used alone or in combination of two or more. The nonionic surfactant preferably used in the present invention is polyoxyethylene alkyl ether.

  Cyclodextrins include α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin. These cyclodextrins may be used alone or in combination of two or more. The cyclodextrin preferably used in the present invention is α-cyclodextrin.

  When the nonionic surfactant is used alone, it is preferably used at a concentration of 0.5 to 1.5%, particularly preferably 0.8 to 1.2%. Most preferably, it is used at a concentration of 0%.

  When the nonionic surfactant and cyclodextrin are used in combination, the concentration of the nonionic surfactant is preferably 0.3 to 0.7%, particularly preferably 0.5%. On the other hand, the concentration of cyclodextrin is preferably 0.1 to 0.3%, particularly preferably 0.2%.

  The electrolysis apparatus and electrolysis method of the present invention are preferably used for decomposing organochlorine compounds separated from contaminated soil. However, low-concentration organochlorine compounds contained in rivers and oceans, and capacitors, etc. It can also be used for the purpose of decomposing high-concentration organochlorine compounds contained in equipment.

EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, the technical scope of this invention is not limited by this.
1. Electrolysis test Table 1 shows the conditions of the electrolysis test.

  An electrolytic cell having a capacity of 3 L was used, and an anode obtained by subjecting a titanium plate to platinum plating was used. For the cathode, two types of SUS304 were compared with an alloy of palladium and silver, which is considered to have excellent hydrogen storage capacity, in consideration of cost.

  In the electrolysis test, a POE nonionic surfactant (polyoxyethylene alkyl ether) was dissolved in distilled water at a concentration of 1% and α-cyclodextrin was 0.2% to simulate a soil washing solution. , A POE-based nonionic surfactant (polyoxyethylene alkyl ether) dissolved in distilled water at a concentration of 0.5% was prepared, and KC-400-based condenser liquid was dispersed therein, and a PCB concentration of 200 mg / The initial density was adjusted using L as a guide. The voltage and current were kept constant, and the change in PCB concentration with time in the liquid phase in the electrolytic cell was measured.

2. Results The results of a test using SUS304 as the cathode are shown in FIG. Although there was a slight difference in the adjusted initial concentration, the concentration decreasing tendency was almost the same, and 90% or more of PCB decomposition was possible in the electrolysis time of 2 hours.

FIG. 2 shows the relationship between the current density and the PCB remaining rate after 120 minutes of electrolysis. Even when stainless steel was used as the cathode material, 90% or more of PCB could be decomposed by treatment for 2 hours by electrolysis by setting the current density to about 3000 A / m ² .

  The data with a low PCB removal rate with a palladium electrode was for a test case with an electrode spacing of the order of several centimeters, and the voltage increased according to the distance between the anode and the cathode, and as a result, a high current value could not be obtained. Table 2 shows typical conditions and results of the electrolysis test.

  Regardless of the electrode material, the smaller the electrode interval, the higher the current can be achieved at a lower voltage, and the stainless steel electrode with a 2 mm interval gave the best electrolysis efficiency.

  Table 3 shows the metal element concentration in the liquid phase of the electrolysis test using SUS304 as the cathode.

  A slight elution from the cathode into the liquid phase of iron, chromium and nickel was observed by electrolysis for 2 hours. However, it is about 1 mg / L, which is a level with no problem as durability of the electrode. As for chromium, hexavalent chromium was not detected, but the total chromium was about 0.8 mg / L.

  When SUS316 was used, the electrolysis performance was equivalent to that of SUS304, and the metal concentration after 2 h of T—Cr could be made less than 0.5 mg / L.

Claims (5)

A polychlorinated biphenyl (PCB) electrolysis apparatus comprising an anode, a cathode and an electrolytic cell,
The anode and the cathode are flat, and both electrodes are arranged in parallel with an interval of 1.5 to 5 mm,
Using stainless steel as the cathode,
2800 / ^{m 2} or more 3200A / ^{m 2} or less of the current density, and performing electrolysis at 60V voltage below than 20V, the electrolyzer. The electrolyzer according to claim 1, further comprising a separator for separating PCB from contaminated soil. Electrical decomposing the PCB using electrolysis apparatus according to claim 1 or 2. The electrolysis method according to claim 3 , wherein the PCB is separated from the contaminated soil using a cleaning agent. The electrolysis method according to claim 4 , wherein the cleaning agent is a nonionic surfactant or a mixture of a nonionic surfactant and cyclodextrin.

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