JP2004167232A - Method for decomposing hardly decomposable halogenated organic compound - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of safely dehalogenating and detoxifying a large quantity of a hardly decomposable halogenated organic compound such as PCB (polychlorobiphenyls) in a short time and putting to practical use at a lower cost. <P>SOLUTION: This method for decomposing the hardly decomposable halogenated organic compound is to irradiate a microwave to the hardly decomposable halogenated organic compound such as the PCB in the presence of an alkaline compound, an inorganic catalyst and an organic hydrogen donor. For the alkaline compound, caustic soda, caustic potash, a sodium alkoxide, a potassium alkoxide, calcium hydroxide, or the like, is used. For the inorganic catalyst, a metal-carrying complex metal oxide, a carbon crystalline compound, a metal-carrying carbon compound, a metal oxide, or the like, is used. For the organic hydrogen donor, a heterocyclic compound, an amine compound, an alcoholic compound, a ketonic compound, a cycloaliphatic compound, or the like, is used. <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to a method for safely decomposing and removing hardly decomposable halogenated organic compounds such as polychlorinated biphenyl (hereinafter abbreviated as PCB).

  It is well known that in the process of using hydrocarbon oils in various technical fields, it is contaminated with halogenated organic compounds such as PCBs and it is difficult to detoxify them, but PCBs are extremely harmful to living organisms including the human body. Therefore, it was specified as a specific chemical substance in 1973, and its manufacture, import, and use were banned. However, after that, tens of thousands of tons of PCBs are left untreated without an appropriate disposal method being determined.

  Among the most hardly decomposable halogenated organic compounds, PCB which is the most hardly decomposable is chlorinated dibenzo-p-dioxin (PCDD) and dibenzofuran (PCDF) which are highly toxic dioxins when decomposed at high temperature (300 to 750 ° C). Since it is a by-product, it is technically difficult to safely decompose PCB, and various methods for safe and efficient decomposition of PCB have been studied for many years.

  For example, a method of decomposing harmful halogenated organic compounds by irradiating microwaves while blowing hydrogen gas into a reaction system in which a white metal catalyst supported on activated carbon is mixed with an aqueous solution of a halogenated aromatic compound (Japanese Patent Application Laid-Open 2001-19646) and a chemical extraction method in which 1,3-dimethyl-2-imidazolidinone (hereinafter, abbreviated as DMI) is heated with KOH as a solvent for a halogenated organic compound for a long time (JP-A-6-25691). Various dechlorination techniques or detoxification techniques such as those disclosed in Japanese Unexamined Patent Publications (KOKAI) are proposed.

JP 2001-19646 A (Claim 1, Paragraph No. 0009, etc.) JP-A-6-25691 (Claim 1, Claim 5, Paragraph No. 0004, Paragraph No. 0011, etc.)

  However, in the invention described in JP-A-2001-19646, it is necessary to supply hydrogen gas from the outside to a reaction system containing an aromatic chlorine compound, which is not preferable as a practical method. In addition, a 1% aqueous solution of p-chlorophenol is targeted as a halogenated aromatic compound, and there is no oil-based high-concentration detoxification technology yet. In addition, the solvent DMI used in the chemical extraction method described in JP-A-6-25691 is expensive at 2,000 yen / kg, and the reaction time of this chemical extraction method is as long as about 12 hours. Not suitable for processing.

  Various methods for decomposing hardly decomposable halogenated organic compounds have been studied in addition to the above methods.However, economical and practical techniques have not been established, and large-scale processing can be safely performed at low cost. There is a demand for the development of a method capable of decomposing in a short time.

  For volatile polyhalogenated organic compounds (VOCs) such as tetrachloroethylene and trichlorethylene, for which environmental standards for fluorocarbons, destructive substances of the ozone layer, water quality and wastewater have been newly established, combustion / pyrolysis / thermal plasma decomposition Method, supercritical method, catalyst method, reagent decomposition method, electrolytic reduction method, ultraviolet decomposition method and microbial decomposition method, and the former two methods have reached the practical research stage. However, for these halogenated organic compounds, development of a less expensive treatment method is desired.

  An object of the present invention is to provide a method which can detoxify a hardly decomposable halogenated organic compound such as PCB in a short time and safely in a large amount and detoxify it, and can be put to practical use at a lower cost.

  In order to solve the above problems, the present inventors have conducted intensive studies and found that a hardly decomposable halogenated organic compound is irradiated with microwaves in the presence of an alkali compound, an inorganic catalyst and an organic hydrogen donor, The present inventors have found that it can be detoxified by dehalogenation in a short time, and have reached the present invention.

  That is, the present invention provides a method for decomposing a hardly decomposable halogenated organic compound, which comprises irradiating a hardly decomposable halogenated organic compound with microwaves in the presence of an alkali compound, an inorganic catalyst, and an organic hydrogen donor. It provides a method.

  In the method for decomposing a hardly decomposable halogenated organic compound of the present invention, it is preferable that the hardly decomposable halogenated organic compound is polychlorinated biphenyl and its analogous compound.

  Further, in the method for decomposing a hardly decomposable halogenated organic compound of the present invention, the alkali compound is a mixture of at least one or two or more selected from the group consisting of caustic soda, caustic potash, sodium alkoxide, potassium alkoxide and calcium hydroxide. It is preferable that Further, the organic hydrogen donor is preferably a mixture of at least one or two or more selected from the group consisting of a heterocyclic compound, an amine compound, an alcohol compound, a ketone compound and an alicyclic compound. . Further, it is preferable that the inorganic catalyst is at least one or a mixture of two or more selected from the group consisting of a metal-supported composite metal oxide, a carbon crystal compound, a metal-supported carbon compound, and a metal oxide.

  In the method for decomposing a hardly decomposable halogenated organic compound of the present invention, it is particularly preferable that the hardly decomposable halogenated organic compound is polychlorobenzene.

  As described above, according to the method for decomposing hardly decomposable halogenated organic compounds of the present invention, halogenated organic compounds such as PCB and polychlorobenzene are decomposed in a short time. Therefore, oil containing a high concentration of halogenated aromatic compounds such as PCB and polychlorobenzene can be dechlorinated in a short period of time in the form of an oil-based oil. In comparison with, safe and mass processing is possible.

  Thus, on a practical scale, it is possible to detoxify hardly decomposable halogenated aromatic compounds such as PCB and polychlorobenzene in a short time and at low cost.

  In the method for decomposing a hardly decomposable halogenated organic compound according to the present invention, the hardly decomposable halogenated organic compound is decomposed by irradiating microwaves in the presence of an alkali compound, an inorganic catalyst and an organic hydrogen donor. It is characterized by the following. The alkali compound, the inorganic catalyst and the organic hydrogen donor are essential components in the present invention, and if any of them is missing, the halogenated organic compound cannot be dechlorinated in a short time.

  The hardly decomposable halogenated organic compound of the present invention includes polychlorinated biphenyl (PCB) and its related compounds, that is, PCB, monochlorobenzene (MCB), 1,2-dichlorobenzene (DCB), 1,2,4 Polychlorobenzene such as trichlorobenzene (TCB), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), polychloroterphenyl (PCT), pesticides (aldrin, dieldrin, p, p'-DDT) , P, p'-DDE), chlorofluorocarbons, halons, and volatile polyhalogenated organic compounds (VOC) such as tetrachloroethylene and trichloroethylene, which are substances that destroy the ozone layer.

  The hardly decomposable halogenated organic compounds described above may be used alone or in combination of two or more. These hardly decomposable halogenated organic compounds may be simple substances, or those dissolved in a solvent such as oil or various organic solvents, and the form is not particularly limited. Further, it may contain various substances used for taking out the hardly decomposable halogenated organic compound from a device (transformer, condenser, etc.) using the compound, for example, a detergent such as dodecane.

  Examples of the alkali compound used in the present invention include caustic soda, caustic potash, sodium alkoxide, potassium alkoxide, calcium hydroxide and the like. Among them, caustic soda and caustic potash are particularly preferable. The above alkali compounds can be used alone or in combination of two or more.

  The organic hydrogen donor used in the present invention means a compound capable of donating a hydrogen atom to a radical generated from a halogenated organic compound, and includes, for example, a heterocyclic compound, an amine compound, and an alcohol compound. Compounds, ketone compounds and alicyclic compounds. Among them, alcohol compounds, ketone compounds and alicyclic compounds are preferable, and alcohol compounds are particularly preferable. The organic hydrogen donors described above can be used alone or in any combination of two or more.

  Examples of the heterocyclic compound include 1,3-dimethyl-2-imidazolidinone (DMI).

  Examples of the amine compound include dimethylethylene diamine (hereinafter abbreviated as DED).

  Examples of the alcohol-based compound include linear or branched monohydric alcohols and polyhydric alcohols. The alcohol preferably has 1 to 12 carbon atoms, and more preferably 2 to 9 carbon atoms. The alcohol may be either aliphatic or aromatic, but is preferably an aliphatic alcohol. Specific examples of the alcohol compound include methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, aliphatic alcohols such as octanol, cyclopropanol, cyclobutanol, cyclopentanol, cyclohexanol, cycloheptanol, Examples thereof include alicyclic alcohols such as cyclooctanol, and polyhydric alcohols such as ethylene glycol, propylene glycol, and decalin diol.

  Examples of the ketone compound include methyl ethyl ketone, cyclohexanone, tricyclododecanone and the like.

  Examples of the alicyclic compound include tetralin and cyclohexane.

  The inorganic catalyst used in the present invention is not particularly limited as long as it can increase the dechlorination reaction rate of the halogenated organic compound. Inorganic catalysts have a long catalyst life and are stable even in the presence of alkali compounds, and therefore are more preferably used than organic catalysts. Preferred specific examples of the inorganic catalyst include, for example, a metal-supported composite metal oxide, a carbon crystal compound, a metal-supported carbon compound, and a metal oxide. Among them, a carbon crystal compound and a metal-supported carbon compound are preferable because of high stability in an alkaline atmosphere, and a metal-supported carbon compound is particularly preferable. The above-mentioned inorganic catalysts can be used alone or in combination of two or more.

  Examples of the metal-supported composite metal oxide include metal-supported zeolite, tobermorite, and asbestos.

  Examples of the carbon crystal compound include graphite, carbon nanotubes (both containing and not containing metal), fullerene and the like.

  As the metal-supported carbon compound, any carbon compound that supports a metal can be used without limitation. Examples of the supported metal include iron, silver, platinum, palladium, ruthenium, and rhodium. From the viewpoint of increasing the dechlorination efficiency, palladium, ruthenium, and platinum are preferred. Specific examples of the metal-supported carbon compound include, for example, Fe / C, Ag / C, Pt / C, Pd / C, Ru / C, Rh / C and the like. Regarding the metal-supported carbon compound, the amount of supported metal is 1 to 20 wt%, more preferably 5 to 10 wt%, and the particle diameter is desirably 75 to 300 μm, and more desirably 125 to 250 μm. If it is coarse, the reactivity is poor, and if it is fine, handling becomes difficult.

Examples of the metal oxide include NiO, Fe ₂ O ₃ , and Fe ₃ O ₄ .

  The microwave output is desirably in the range of 10 W to 20 kW. If it is less than 10 W, the amount of generated hydrogen is small. On the other hand, when the power exceeds 20 kW, the utilization rate of microwaves deteriorates. More preferably, a microwave in the range of 65 W to 5 kW is desirable.

  The microwave frequency is desirably 1 to 300 GHz. In a frequency range of less than 1 GHz or more than 300 GHz, the heating of the inorganic catalyst and the organic hydrogen donor becomes insufficient. More preferably, a frequency of 1 to 5 GHz is desirable.

  When irradiating microwaves, any of continuous irradiation and intermittent irradiation may be employed. The irradiation time and the irradiation stop time can be appropriately determined according to the halogenated organic compound, the organic hydrogen donor, the reaction catalyst and the like to be used for the reaction.

  The reaction time is desirably 0.01 to 300 minutes. When the reaction time is less than 0.01 minute, the decomposition reaction is insufficient, and when the reaction time is longer than 300 minutes, there is no practical meaning. More preferably, it is 5 minutes to 180 minutes.

  It is more preferable to carry out the reaction in an inert gas atmosphere, since undesirable side reactions do not occur.

  In the method for decomposing a hardly decomposable halogenated organic compound of the present invention, the molar ratio of alkali compound / organic hydrogen donor / halogenated organic compound (converted to a concentration of 100%) is based on the organic hydrogen donor. In addition, 0.001 to 5/10 / 0.000001 to 10 is desirable. If the molar ratio of the alkali compound is less than 0.001, the decomposition reaction of the halogenated organic compound does not proceed. When the molar ratio of the alkali compound exceeds 5, stirring and mixing becomes difficult. If the molar ratio of the halogenated organic compound is less than 0.000001, the reaction proceeds sufficiently, but has no practical significance. When the molar ratio of the halogenated organic compound exceeds 10, the dechlorination reaction becomes insufficient. The molar ratio of the three components is preferably from 0.1 to 3/10 / 0.1 to 5, and more preferably from 1 to 3/10 / 0.1 to 1.

  The amount of the inorganic catalyst to be added is preferably in the range of 0.00001 to 0.1 as a weight ratio to the total amount of the solution when the concentration of the halogenated organic compound is 100%. When the weight ratio is less than 0.00001, the amount of generated hydrogen decreases, and when the weight ratio exceeds 0.1, it becomes difficult to stir and mix the system in which the components of the present invention are mixed, and expensive inorganic systems that do not work effectively There is a catalyst, which is economically disadvantageous. It is more preferably in the range of 0.0001 to 0.01, and particularly preferably in the range of 0.001 to 0.002.

  According to the method for decomposing a halogenated organic compound of the present invention, the halogenated organic compound itself such as PCB is decomposed at a speed equal to or higher than that when hydrogen gas is blown into the reaction system from the outside. Although the mechanism is not clear, it is considered that an alkali metal radical provided from an alkali compound promotes a dehalogenation reaction of a halogenated organic compound such as PCB, and a hydrogen radical from a hydrogen donor enters therein.

  Next, the present invention will be specifically described with reference to examples, but the present invention is not limited to only the following examples. In the following examples, an experiment of the decomposition reaction was performed using 1,2,4-trichlorobenzene (TCB) as a PCB simulation liquid.

  FIG. 1 is a schematic diagram of a halogenated organic compound decomposing apparatus used in this example. The three-necked flask 2 is placed in the microwave generator 1, and two of the three-necked flasks are used as the nitrogen inlet 2 a and the insertion port 2 b of the thermometer 3, and the Liebig cooling pipe 4 is provided in the center port 2 c. To remove the reaction product out of the reaction system.

(Experimental method of Example 1 and Comparative Example 2)
The experiments from Example 1 to Comparative Example 2 investigated the influence of the presence or absence of an alkali compound and the presence or absence of a catalyst on the dechlorination reaction of TCB.

(Example 1)
As an alkaline compound, KOH flakes (95%) manufactured by Nippon Soda Co., Ltd. was ground in a mortar, and 3.43 g (0.061 mol) of the KOH flakes were added to a cyclo-gel manufactured by Wako Pure Chemical Industries, Ltd. to be used as an organic hydrogen donor. 30.59 g (0.306 mol) of hexanol, 50 mg of activated carbon (Pt / C: manufactured by Wako Pure Chemical Industries, Ltd.) having a particle diameter of 150 to 180 μm carrying 5 wt% of platinum as an inorganic catalyst, and 1 And 0.56 g (0.0031 mol) of 2,4-trichlorobenzene (manufactured by Wako Pure Chemical Industries, Ltd.) were introduced into a 200 ml three-necked flask 2.

  After introducing the mixture of each substance into the flask 2 and replacing the gas inside the flask 2 with nitrogen gas, the mixture was irradiated with a microwave having a frequency of 2.45 GHz and an irradiation energy of 325 W for 80 minutes while stirring the mixture with a magnetic stirrer. During the reaction, nitrogen gas was flowed at 50 ml / min. The microwave alternately repeated irradiation for 13.5 seconds and non-irradiation for 13.5 seconds. The above reaction times are the sum of these times.

  Since the Liebig condenser 4 was attached to the upper part of the three-necked flask 2, the cyclohexanol refluxed, and the internal temperature of the flask 2 was kept near its boiling point (160 ° C.).

(Comparative Example 1)
The reaction was carried out under the same conditions as in Example 1 except that the reaction time was 40 minutes without adding an alkali compound.

(Comparative Example 2)
The reaction was carried out under the same conditions as in Example 1 except that the reaction time was 40 minutes without adding the inorganic catalyst (Pt / C).

(Results of Example 1 and Comparative Example 2)
The solution before and after the reaction was applied to a gas chromatography mass spectrometer QP5050A manufactured by Shimadzu Corporation using a ULBON HR-20M (manufactured by Shimadzu GLC) as a capillary column (column temperature 80 ° C. → 220 ° C.). Dechlorination (decomposition rate) was confirmed by a change in the peak area of 2,4-trichlorobenzene (TCB).

  The amount of hydrogen generated during the reaction was analyzed by gas chromatography 13A manufactured by Shimadzu Corporation using a molecular sieve 5A (GL Science Co., Ltd.) as a capillary column (column temperature 100 ° C.). Table 1 shows the analysis results.

  From the results shown in Table 1, in Example 1, TCB was almost completely eliminated. At that time, 30% by volume of hydrogen gas was generated in the reaction product taken out of the reaction system. Therefore, it is considered that the hydrogen radical derived from cyclohexanol contributes to the dechlorination reaction.

  On the other hand, in Comparative Example 1, no hydrogen gas was generated during the reaction, and no decomposition of TCB occurred. From this, it was confirmed that the presence of an alkali compound was necessary for the decomposition reaction of TCB.

  In Comparative Example 2, no hydrogen gas was generated during the reaction, and the decomposition rate of TCB was 60%. From this, it was confirmed that the decomposition reaction rate of TCB was improved by the presence of the inorganic catalyst.

(Experimental method of Examples 2 to 7)
In the experiments from Example 2 to Example 7, the effects of the reaction time and the initial charge of TCB on the decomposition rate were investigated.

(Example 2)
The reaction was carried out under the same conditions as in Example 1 except that the reaction time was changed to 10 minutes.

(Example 3)
The reaction was carried out under the same conditions as in Example 1 except that the reaction time was 20 minutes.

(Example 4)
The reaction was carried out under the same conditions as in Example 1 except that the reaction time was 40 minutes.

(Example 5)
The reaction was carried out under the same conditions as in Example 1 except that the reaction time was 60 minutes.

(Example 6)
The reaction was carried out under the same conditions as in Example 1 except that the TCB amount was 1.11 g (0.0062 mol) and the reaction time was 40 minutes.

(Example 7)
The reaction was carried out under the same conditions as in Example 1 except that the TCB amount was 2.22 g (0.012 mol) and the reaction time was 40 minutes.

(Results of Examples 2 to 7)
Table 2 summarizes the analysis results of Examples 2 to 7. The results of Examples 2 to 5 were plotted together with the results of Example 1 in FIG. In addition, the results of Examples 6 and 7 were plotted in FIG.

  As shown in FIG. 2, 80% or more of TCB was decomposed in a reaction time of 10 minutes, and TCB disappeared almost completely in a reaction time of 80 minutes.

  Further, as can be seen in FIG. 3, even when the amount of TCB charged was 2.22 g, 70% or more was decomposed in 40 minutes.

(Experimental methods of Examples 8 to 31)
The experiments from Example 8 to Example 31 investigated the effects of the types of alkali compounds, organic hydrogen donors, and inorganic catalysts on the dechlorination reaction of TCB. The reaction was carried out under the same conditions as in Example 1 except for the molar ratio of each substance, the amount of catalyst added, and the like in the experiments from Example 8 to Example 31.

(Results of Examples 8 to 31)
Table 3 summarizes the evaluation results of Examples 8 to 31. In addition, evaluation of the dechlorination reaction was performed as follows.
：: good (decomposition rate is 65% or more)
Δ: insufficient (decomposition rate is 30% or more and less than 65%)
×: defective (decomposition rate is less than 30%)

  From the above examples of the present invention, it was found that TCB was effectively decomposed in the reaction system of this example.

BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic of the halogenated organic compound decomposition | disassembly experimental device by microwave used for this invention. It is a figure which shows the time change of the TCB decomposition rate from Example 1 to Example 5. It is a figure which shows the change of the decomposition rate by the TCB preparation amount of Example 4, Example 6, and Example 7.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Microwave generator 2 Three-necked flask 3 Thermometer 4 Liebig condenser

Claims (6)

A method for decomposing a hardly decomposable halogenated organic compound, comprising irradiating the hardly decomposable halogenated organic compound with microwaves in the presence of an alkali compound, an inorganic catalyst, and an organic hydrogen donor. 2. The method for decomposing a hardly decomposable halogenated organic compound according to claim 1, wherein the hardly decomposable halogenated organic compound is polychlorinated biphenyl and its analogous compound. 2. The hardly decomposable halogenated organic compound according to claim 1, wherein the alkali compound is at least one or a mixture of two or more selected from the group consisting of caustic soda, caustic potash, sodium alkoxide, potassium alkoxide and calcium hydroxide. How to decompose the compound. The organic hydrogen donor is a mixture of at least one or two or more selected from the group consisting of heterocyclic compounds, amine compounds, alcohol compounds, ketone compounds and alicyclic compounds. A method for decomposing a hardly decomposable halogenated organic compound according to claim 1. The inorganic catalyst is at least one selected from the group consisting of a metal-supported composite metal oxide, a carbon crystal compound, a metal-supported carbon compound, and a metal oxide, or a mixture of two or more thereof. For decomposing hardly decomposable halogenated organic compounds. The method for decomposing a hardly decomposable halogenated organic compound according to any one of claims 1 to 5, wherein the hardly decomposable halogenated organic compound is polychlorobenzene.

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