JP2007061706A - Polychlorinated biphenyl decomposition method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a decomposition method which can efficiently decompose organic chlorine compounds in an aqueous solution. <P>SOLUTION: The organic chlorine compounds (4-CBP) are captured by a hydrophilic host compound H with a hydrophilic field in the aqueous solution, and then decomposed by light irradiation. The hydrophilic host compound H is, for example, cyclodextrin or its derivative, and incorporates the organic chlorine compound as a guest compound to form a clathrate complex. An electron releasing group may be introduced into the cyclodextrin, or an electron donor may be added into the aqueous solution. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a decomposition method for decomposing an organic chlorine compound such as polychlorinated biphenyl (PCB), and relates to a novel decomposition method that enables decomposition in an aqueous solution.

  Many of the causative substances of environmental pollution in recent years have been used in a large quantity and for many purposes because of their convenience, and as a result, they have been released into the environment and spread widely. For example, surfactants and organic chlorine compounds are representative examples.

  Among these, organic chlorinated compounds such as polychlorinated biphenyl (PCB) are chemically stable, so they are not sufficiently decomposed and removed by natural purification power or ordinary wastewater treatment methods, etc. It remains in the middle and becomes an environmental pollutant.

  Under such circumstances, a method for decomposing the organochlorine compound has been studied in various fields. For example, a method for oxidative decomposition by burning in an incinerator has been proposed (for example, Patent Document 1). Etc.). Patent Document 1 discloses a method in which the combustion temperature in the furnace main body is completely burned at a decomposition temperature of 1400 ° C. or higher necessary for the oxidative decomposition of PCB. It is said that it can be oxidized and decomposed efficiently.

  However, when an organic chlorine compound is decomposed by combustion, chlorine is combined with oxygen to form dioxins, which may cause environmental destruction. Dioxins become more difficult to collect and are difficult to treat efficiently. In addition, if the decomposition by combustion is recovered in the form of, for example, waste oil, it can be treated by putting it in a furnace. For example, organochlorine compounds remaining in water or soil Not suitable for disassembling.

Therefore, the present inventor has developed a technique for decomposing an organic chlorine compound by light irradiation in the presence of an aliphatic amine in an organic solvent (see Non-Patent Document 1). In the invention described in Non-Patent Document 1, it was confirmed that 4-chlorobiphenyl (MCB) was decomposed into biphenyl and chlorine by irradiating light with a low-pressure mercury lamp in acetonitrile in the presence of triethylamine, for example. Yes.
JP-A-7-91638 Journal of The Chemical Society Chemical Communications p384 (1973)

  By the way, although the method of the said nonpatent literature 1 has the advantage that there is no generation | occurrence | production of dioxin compared with the decomposition | disassembly by the said combustion, and it can apply also about the organic chlorine compound in water and soil, an organic solvent A new problem arises because of the decomposition reaction. Specifically, acetonitrile used as the organic solvent is highly toxic, has health problems for workers, and its treatment becomes a problem.

  The present invention has been proposed in view of such problems of the prior art, and does not generate harmful substances such as dioxins, and can efficiently decompose organic chlorine compounds in water and soil. An object of the present invention is to provide a method for decomposing an organic chlorine compound that can be efficiently decomposed in an aqueous solution.

  The present inventor has conducted various studies over a long period of time in order to achieve the above-described object. As a result, it has been found that treatment in an aqueous solution becomes possible by incorporating an organic chlorine compound with a hydrophilic host compound having a hydrophobic field. The present invention has been completed on the basis of such findings, and in an aqueous solution, after capturing the organic chlorine compound with a hydrophilic host compound having a hydrophobic field, the organic chlorine compound is obtained by irradiating with light. It is characterized by decomposing.

  For example, cyclodextrin is a hydrophilic compound, but has a hydrophobic field at the center. When an organochlorine compound is allowed to act using such a compound as a hydrophilic host compound, the organochlorine compound is incorporated as a guest compound in the hydrophobic field to form an inclusion complex. This inclusion complex is dispersed in an aqueous solution due to the property (hydrophilicity) of the host compound. Therefore, when the clathrate complex dispersed in the aqueous solution is irradiated with light to decompose the organic chlorine compound, the organic chlorine compound is decomposed in the aqueous solution.

  According to the present invention, an organic chlorine compound can be decomposed in an aqueous solution. Therefore, it is not necessary to use an organic solvent for the decomposition treatment, and it is possible to solve the health problem of the worker, the problem of the treatment of the used organic solvent, and the like. Further, according to the present invention, since the organic chlorine compound is decomposed by light irradiation, the treatment can be performed without producing any harmful by-products such as dioxin. Furthermore, in the method of the present invention, an organic chlorine compound is incorporated into a hydrophilic host compound to concentrate it, and an efficient decomposition treatment can be realized. For example, in the treatment of organic chlorinated compounds in water or soil. Easy to apply.

  Hereinafter, an organic chlorine compound decomposition method to which the present invention is applied will be described in detail with reference to the drawings.

  FIG. 1 schematically shows the decomposition treatment method of the present invention. Here, 4-chlorobiphenyl (4-CBP) will be described as an example of the organic chlorine compound.

  The host compound H used here is a compound having a hydrophilic group such as a hydroxyl group. For example, the surrounding a is hydrophilic and the hollow central portion b functions as a hydrophobic field. When an organic chlorine compound (for example, the 4-CBP) is allowed to act on the host compound H in an aqueous solution, the 4-CBP is converted into a central portion b ( Incorporated into the hydrophobic field), for example, forms an inclusion complex HS. By the formation of the inclusion complex HS, the organochlorine compound (4-CBP) is collected and concentrated.

  As described above, the organic chlorine compound (4-CBP) is collected and concentrated by the host compound H in an aqueous solution, and then irradiated with light to decompose the organic chlorine compound (4-CBP). As light to irradiate, it is an ultraviolet-ray, for example. By irradiating with ultraviolet rays, as shown in FIG. 1C, 4-chlorobiphenyl is decomposed into chlorine and biphenyl (BP). In the decomposition, it was confirmed that not only biphenyl (BP) but also QBP in which two of them were combined was produced.

  The decomposition of the organic chlorine compound by the light irradiation can be performed in an arbitrary atmosphere such as air, but is preferably performed in an oxygen-free atmosphere (for example, an inert gas atmosphere). This is because the decomposition reaction by light irradiation is quenched by the presence of oxygen, and the reaction becomes slow.

  The above is the basic structure of the decomposition treatment method of the present invention, and by this, an organic chlorine compound such as polychlorinated biphenyl (PCB) can be efficiently decomposed. Moreover, since the decomposition treatment method is performed in an aqueous solution as described above, it is not necessary to use an organic solvent for the reaction.

  In the above-described decomposition treatment method, any compound can be used as the host compound H as long as it is a hydrophilic compound having a hydrophilic group and a compound having a hydrophobic field. Specific examples include cyclodextrin and derivatives thereof, chitosan and derivatives thereof, and the like.

  Cyclodextrin is a compound in which glucose is polymerized in a cyclic manner. Α-cyclodextrin having a polymerization degree of 6, β-cyclodextrin having a polymerization degree of 7, γ-cyclodextrin having a polymerization degree of 8, and the like are known. ing. Any of these can be used as the host compound H, but β-cyclodextrin is preferred in consideration of matching of the size of the hydrophobic field and the size of the organochlorine compound. By using β-cyclodextrin as the host compound H, the organic chlorine compound is smoothly collected and concentrated.

  Formula 1 shows the chemical formula of β-cyclodextrin. FIG. 2 schematically shows β-cyclodextrin. As described above, β-cyclodextrin is a polymer in which seven glucoses are cyclically polymerized, has a trapezoidally distorted cylindrical shape, and hydroxyl groups are arranged outward, so that the periphery is hydrophilic. . On the other hand, the inside of the ring is a hydrophobic environment and includes various molecules. In the decomposition treatment of the present invention, an inclusion complex HS is formed by taking an organic chlorine compound into this hydrophobic space. In addition, (beta) -cyclodextrin has the advantage that it is the most easily available among cyclodextrins, and is cheap.

  The host compound H is not limited to the cyclodextrin, and a compound having the same function can be used. For example, chitosan can be exemplified as such a compound. Chitosan is obtained by deacetylating chitin contained in crab shells and the like, and has a structure shown in Chemical Formula 2. Chitosan is also hydrophilic because it has a hydroxyl group and an amino group, and the cyclic portion constitutes a hydrophobic field.

  In the decomposition treatment, an organochlorine compound may be allowed to act on the host compound H in an aqueous solution. However, considering decomposition by subsequent light irradiation, it is effective that an electron donor coexists. By the presence of the electron donor, decomposition by light irradiation is promoted, and the decomposition reaction proceeds efficiently.

  In this case, the electron donor may coexist by introducing an electron donating group into the host compound, or may coexist by adding an electron donor to the aqueous solution. For example, in the former case, an electron donating group may be introduced into the aforementioned cyclodextrin. Examples of the electron donating group to be introduced include an amino group, a diethylamino group, an azide group, an amide group, and a group containing sulfur. On the other hand, when an electron donor is added to the aqueous solution, an aliphatic amine (for example, diethylamine or triethylamine) or ammonia may be added as the electron donor.

  When the decomposition treatment is performed by light irradiation, as described above, an organic chlorine compound (for example, 4-CBP) undergoes a photodechlorination reaction and is decomposed into chlorine and biphenyl. Even after the decomposition, a part of the biphenyl is a host. It remains in the hydrophobic field of the compound. In such a case, if the host compound is washed with an organic solvent after the decomposition reaction, it becomes possible to remove the biphenyl and reuse the host compound.

  At this time, as an organic solvent used for washing, a general-purpose organic solvent having low toxicity can be used. For example, hexane, petroleum-based solvent, or the like can be used. Of these, hexane is preferable from the viewpoints of washing efficiency, availability, handling, and low toxicity. In washing, for example, the organic solvent may be added to the aqueous solution after the decomposition treatment, shaken sufficiently, and then allowed to stand to remove the separated organic solvent. Since biphenyl included in the host compound is hydrophobic, it quickly migrates into the organic solvent and is removed from the host compound. The host compound from which biphenyl has been removed can be used over and over again.

  Hereinafter, specific examples to which the present invention is applied will be described based on experimental results.

Example 1
In this experiment, 4-chlorobiphenyl (4-CBP) was used as a model molecule of polychlorinated biphenyl (PCB). Then, β-cyclodextrin (β-CD) is used as a host compound, and these are mixed in an aqueous solution at β-CD: 4-CBP = 1: 1 to 1:20 (molar ratio), and at room temperature for 48 hours. Stirring to form an inclusion complex. The aqueous solution containing the inclusion complex is irradiated with light (ultraviolet light: wavelength 254 nm) for 24 hours using a low-pressure mercury lamp, and the product is analyzed by electron ionization mass spectrometry (EI-MS) and high performance liquid chromatography (HPLC). Quantification was performed. The results are shown in Table 1.

  As is apparent from Table 1, by incorporating 4-CBP using β-cyclodextrin as a host compound and performing ultraviolet irradiation, almost all 4-CBP is harmless biphenyl (BP), or QBP in which two biphenyls are bonded. Has been broken down.

Example 2
In this example, β-cyclodextrin was used as a host compound, triethylamine was added as an electron donor to the aqueous solution, and the others were attempted to decompose 4-CBP in the same manner as in Example 1. After light irradiation, the product was analyzed and quantified in the same manner as in Example 1. The results are shown in Table 2.

  As is apparent from Table 2, good results were also obtained in the photodecomposition reaction of 4-CBP using β-cyclodextrin in the presence of triethylamine as a reaction field, and most of 4-CBP was biphenyl (BP ) Or QBP.

Example 3
In this example, β-cyclodextrin was used as a host compound, diethylamine was added as an electron donor to the aqueous solution, and the others were attempted to decompose 4-CBP in the same manner as in Example 1. After light irradiation, the product was analyzed and quantified in the same manner as in Example 1. The results are shown in Table 3.

  As is apparent from Table 3, good results were also obtained in the photodecomposition reaction of 4-CBP using β-cyclodextrin in the presence of diethylamine as a reaction field, and most of 4-CBP was biphenyl (BP ) Or QBP.

Example 4
In this example, β-cyclodextrin was used as a host compound, and ammonia was added to an aqueous solution as an electron donor. Other than this, decomposition of 4-CBP was attempted in the same manner as in Example 1. After light irradiation, the product was analyzed and quantified in the same manner as in Example 1. The results are shown in Table 4.

  As is apparent from Table 4, good results were also obtained in the photodecomposition reaction of 4-CBP using β-cyclodextrin in the presence of ammonia as a reaction field, and most of 4-CBP was biphenyl (BP ) Or QBP.

  In Examples 2 to 4 to which an electron donor was added, some unreacted substances were observed, and it seemed that the decomposition efficiency was lowered, but this is because β-cyclodextrin is an additive. This is due to the inclusion of an electron donor, thereby reducing the inclusion ability for 4-CBP, and the degradation efficiency itself is improved more than when β-cyclodextrin is used.

Introducing an electron donating group into β-cyclodextrin As shown in FIG. 3, by replacing the primary hydroxyl group at the 6-position and the secondary hydroxyl group at the 3-position of the β-cyclodextrin with substituents R ₁ and R ₂ , respectively. Derivatives 1 to 5 were synthesized. Derivative 1 is unsubstituted β-cyclodextrin. For these β-cyclodextrin derivatives, the association constant with 4-CBP was determined by UV spectrum, and further fluorescence quenching experiments were performed to confirm the electron transfer of the amino group. Table 5 shows the association constant of each derivative.

  As shown in Table 5, the association constant of each derivative and 4-CBP was in the order of derivative 2> derivative 5> derivative 3> derivative 1> derivative 4. Therefore, among the derivatives, it can be said that the derivative 2 has the most excellent inclusion ability with respect to 4-CBP. As a result of the quenching experiment, 4-CBP was included and isolated in the derivative 1, and the fluorescence intensity increased. In the derivative 2, the fluorescence intensity tended to decrease. This can be said to suggest electron transfer between the amino group and 4-CBP.

Example 5
In this example, 6-amino-β-cyclodextrin (the derivative 2) was used as a host compound, and the other attempt was made to decompose 4-CBP in the same manner as in Example 1. After light irradiation, the product was analyzed and quantified in the same manner as in Example 1. The results are shown in Table 6. Moreover, the time change of the ratio of the product in the said photolysis reaction was investigated. The results are shown in FIG.

  As is apparent from Table 6, it can be seen that 4-CBP was almost completely decomposed by introducing an amino group into β-cyclodextrin. Further, as shown in FIG. 4, the decomposition proceeds in an extremely short time. When β-cyclodextrin having an amino group introduced is used as a host compound, the main product is QBP, and it is not an exaggeration to say that only QBP is generated. Therefore, when the time change in the photolysis reaction using β-cyclodextrin having an amino group introduced was followed using UV and HPLC, it was found that QBP was produced via BP in the production process of QBP.

Example 6
In this example, 6-azido-β-cyclodextrin (derivative 3) was used as the host compound, and the other attempt was made to decompose 4-CBP in the same manner as in Example 1. After light irradiation, the product was analyzed and quantified in the same manner as in Example 1. The results are shown in Table 7.

  As is clear from Table 7, even when an azide group was introduced, most of the 4-CBP was decomposed, but some unreacted products were observed, and when an amino group was introduced (Example 5). It can be seen that the effect is slightly higher.

Example 7
In this example, diethylamino-β-cyclodextrin (the derivative 4) was used as a host compound, and the other attempt was made to decompose 4-CBP in the same manner as in Example 1. After light irradiation, the product was analyzed and quantified in the same manner as in Example 1. The results are shown in Table 8.

  As is apparent from Table 8, when a diethylamino group was introduced, almost all of 4-CBP was decomposed as in Example 5, indicating that the decomposition efficiency was very excellent.

Example 8
In this example, 3-amino-β-cyclodextrin (the derivative 5) was used as a host compound, and the other attempt was made to decompose 4-CBP in the same manner as in Example 1. After light irradiation, the product was analyzed and quantified in the same manner as in Example 1. The results are shown in Table 9.

  As is apparent from Table 9, even when an amino group was introduced at the 3-position, almost all 4-CBP was decomposed as in Example 5, but when the proportion of 4-CBP was increased, it was slightly decomposed. A decrease in rate is seen.

It is a schematic diagram explaining the basic principle of this invention. It is a figure which shows typically the structure of (beta) -cyclodextrin. It is a schematic diagram which shows the example of introduction | transduction of the electron donating group to (beta) -cyclodextrin. It is a characteristic view which shows the time change of photolysis reaction at the time of using 6-amino- (beta) -cyclodextrin as a host compound.

Claims (10)

  A method for decomposing an organic chlorine compound, comprising: capturing an organic chlorine compound with a hydrophilic host compound having a hydrophobic field in an aqueous solution; and then decomposing the organic chlorine compound by light irradiation.   The method for decomposing an organochlorine compound according to claim 1, wherein the hydrophilic host compound is cyclodextrin or a derivative thereof, and an inclusion complex is formed using the organochlorine compound as a guest compound.   The method for decomposing an organochlorine compound according to claim 2, wherein the cyclodextrin is β-cyclodextrin.   The method for decomposing an organic chlorine compound according to any one of claims 1 to 3, wherein an electron donating substituent is introduced into the hydrophilic host compound.   5. The method for decomposing an organochlorine compound according to claim 4, wherein the electron-donating substituent is an amino group or an amide group.   The method for decomposing an organic chlorine compound according to any one of claims 1 to 3, wherein an electron donor is added to the aqueous solution.   The method for decomposing an organochlorine compound according to claim 6, wherein the electron donor is at least one selected from diethylamine, triethylamine, and ammonia.   The method for decomposing an organochlorine compound according to any one of claims 1 to 7, wherein the light irradiation is ultraviolet irradiation.   The organic chlorine compound decomposition treatment according to any one of claims 1 to 8, wherein after the decomposition of the organic chlorine compound by the light irradiation, the hydrophilic host compound is washed with an organic solvent and reused. Method.   The method for decomposing an organic chlorine compound according to claim 9, wherein the organic solvent is hexane.

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