JP2007105059A - Method of decomposing dioxins - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of decomposing dioxins capable of decomposing dioxins under a mild condition and with a high decomposition rate. <P>SOLUTION: The method of decomposing dioxins is characterized by continuous or intermittent application of microwaves to at least one kind of catalyst selected from a carbon crystal compound and a compound carrying metal in a carrier while bringing a mixture liquid with a treated substance including dioxins, a hydrogen donor and an alkaline compound into contact with the catalyst, and heating of the mixture liquid to a temperature at the boiling point of the hydrogen donor or lower. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for decomposing dioxins, and more particularly to a method for decomposing dioxins capable of decomposing dioxins at a high decomposition rate under mild conditions.

  Dioxin (polychlorodibenzodioxin: PCDD), polychlorodibenzofuran (PCDF), and coplanar PCB (in the present invention, these three members are collectively referred to as “dioxins”) are the process of burning chlorine-containing organic compounds or It is produced as a by-product in the synthesis process of specific organic compounds containing chlorine. Dioxins have been regarded as a problem in recent years as one of the pollutants of the environment (air, soil, water, etc.) due to their strong toxicity.

  For this reason, as a measure against environmental pollution, processing for removing and collecting soil, combustion ash, etc. contaminated with dioxins is performed. In addition, dioxins contained in wastewater from various factories such as cleaning factories, leachate generated at waste landfill sites, and washing wastewater such as ash and soil are also being treated. As a countermeasure, it is necessary to decompose dioxins in polluted substances.

  Dioxins require a high temperature of 80 to 900 ° C. or higher for thermal decomposition, are thermally stable compounds, and are chemically stable compounds. For this reason, various decomposition methods have been studied in the past, but all require special reaction conditions or special chemicals.

  For example, Patent Document 1 discloses dioxins composed of specific nitrogen-containing sulfur-containing compounds (such as Na salt of trimercaptotriazine) as a method for decomposing fly ash discharged from an incinerator and dioxins contained in the incineration ash. There has been proposed a method in which a decomposing agent and dioxins are contacted at 200 ° C. to 300 ° C. for 3 to 60 minutes. However, this method is an excellent method in that dioxins can be decomposed by contacting them at a temperature lower than 300 ° C, but the decomposition rate of dioxins is low, and a high temperature treatment of 200 ° C or higher is required. Therefore, it is difficult to say that it is a mild decomposition treatment method.

  Patent Document 2 proposes a honeycomb-type cracking catalyst in which vanadium pentoxide and tungsten trioxide are supported on titanium oxide as a cracking catalyst for coplanar PCBs contained in exhaust gas from garbage incineration facilities and sludge incineration facilities. Has been. However, this catalyst is applied to the decomposition of dioxins in exhaust gas, and the required decomposition temperature is as high as 200 ° C.

  Patent Document 3 proposes a catalyst in which a noble metal such as platinum is supported on cerium oxide-zirconium oxide in which oxygen defects are introduced by reduction treatment. This catalyst has a contact temperature of 0 to 100 ° C. between the catalyst and the material to be treated, and is a catalyst capable of detoxifying dioxins efficiently at a sufficiently low treatment temperature. The toxicity equivalent of dioxins is as high as 0.097 (ng-TEQ / g).

JP 2001-247838 A JP 2002-136873 A JP 2002-306965 A

  The present invention has been made in view of the above-described conventional problems, and an object thereof is to provide a method for decomposing dioxins capable of decomposing dioxins under mild conditions and at a high decomposition rate.

  As a result of diligent investigations to solve the above problems, the present inventors have added a hydrogen donor and an alkali compound to an object to be treated containing dioxins to obtain a mixed solution, which is brought into contact with a specific catalyst. The present inventors have found that dioxins in the object to be treated can be rendered harmless under mild conditions by irradiating the catalyst with microwaves, and the present invention has been achieved.

That is, the present invention is as follows.
1) A mixed liquid obtained by mixing an object to be treated containing dioxins, a hydrogen donor, and an alkali compound is brought into contact with at least one catalyst selected from a carbon crystal compound and a metal-supported compound. A method for decomposing dioxins, wherein the catalyst is irradiated with microwaves continuously or intermittently and heated to a temperature below the boiling point of the hydrogen donor,
2) The method for decomposing dioxins according to 1) above, wherein the catalyst mixture is irradiated with microwaves while the mixed solution is circulated through the catalyst filler filled with the catalyst.
3) The hydrogen donor is at least one compound selected from the group consisting of a heterocyclic compound, an amine compound, an alcohol compound, a ketone compound and an alicyclic compound, as described in 1) or 2) above. Decomposition method of dioxins,
4) The method for decomposing dioxins according to 1) or 2), wherein the hydrogen donor is an alcohol compound having a boiling point of 100 ° C. or lower,
5) The method for decomposing dioxins according to any one of 1) to 4), wherein the alkali compound is at least one compound selected from the group consisting of caustic soda, caustic potash, sodium alkoxide, potassium alkoxide, and calcium hydroxide. ,
6) The method for decomposing dioxins according to any one of 1) to 5), wherein the catalyst is a palladium-supported carbon compound,
7) The method for decomposing dioxins according to any one of 1) to 6), wherein the dioxins are polychlorodibenzofuran (PCDF), and
8) The method for decomposing dioxins according to any one of 1) to 7), wherein the object to be treated is incinerated ash, soil, a hardly decomposable organic halogen compound, or oil / water containing them.

  According to the present invention, microwaves are irradiated to the catalyst while contacting the catalyst by a means such as circulating the mixture of the object to be processed, dioxins, hydrogen donor and alkali compound through the catalyst filling device, etc. By reacting at a low temperature, dioxins in the mixed solution can be decomposed at a high decomposition rate. In addition, dioxins can be decomposed under mild conditions without the need for a high-temperature and high-pressure reaction vessel and without supplying hydrogen and heat from the outside, so that the energy required for decomposition can be reduced and side reaction products can be produced. Very unlikely to generate.

  Further, by applying the method of the present invention to the decomposition of dioxins in polychlorinated biphenyls (PCB), PCBs can be decomposed at a high decomposition rate, and coexisting dioxins, particularly polychlorodibenzofuran (PCDF). ) Can be rendered harmless with a high decomposition rate.

  In the method for decomposing dioxins according to the present invention, a mixed liquid obtained by mixing an object to be treated containing dioxins, a hydrogen donor and an alkali compound is selected from a carbon crystal compound and a compound in which a metal is supported on a carrier. The catalyst is irradiated with microwaves continuously or intermittently while being brought into contact with at least one kind of catalyst, and heated to a temperature not higher than the boiling point of the hydrogen donor for reaction.

  Examples of the object to be treated containing dioxins include incinerated ash, soil, hard-to-decompose organic halogen compounds such as PCB, water / oil containing these, and the like, either solid or liquid. May be. Examples of the oil include an electrical insulating oil, a heat medium oil, a lubricating oil, and a mineral oil extracted from an organic halogen compound contained in a solid.

  Examples of the hydrogen donor used in the present invention include organic hydrogen donors such as heterocyclic compounds, amine compounds, alcohol compounds, ketone compounds, and alicyclic compounds. Among these compounds, alcohol compounds, ketone compounds, and alicyclic compounds are preferable from the viewpoint of safety. In particular, they are highly safe, can be obtained at low cost, are easily controlled in reaction, and are aromatic. Alcohol compounds are preferred from the viewpoint of high decomposition efficiency of the group halogen compounds. These hydrogen donors can be used alone or in any combination of two or more. Here, the “hydrogen donor” means a compound that can donate a hydrogen atom to a radical generated from a decomposition target compound.

  The alcohol compound may be either an aliphatic alcohol or an aromatic alcohol, and a monohydric alcohol or a polyhydric alcohol having a linear or branched chain can be used. The carbon number of the alcohol compound is preferably in the range of 1 to 12, more preferably in the range of 2 to 9, and still more preferably in the range of 3 to 6. Specific examples of the alcohol compound include, for example, methanol, ethanol, 1-propanol, 2-propanol, n-butanol, s-butanol, t-butanol, 1-pentanol, 2-pentanol, and 3-pentanol. 1-hexanol, 2-hexanol, 3-hexanol, 1-heptanol, 2-heptanol, 3-heptanol, 1-octanol, 2-octanol and other aliphatic alcohols, cyclopropyl alcohol, cyclobutyl alcohol, cyclopentyl alcohol, cyclohexyl Examples thereof include alicyclic alcohols such as alcohol, cycloheptyl alcohol and cyclooctyl alcohol, and polyhydric alcohols such as ethylene glycol, propylene glycol and decalin diol.

  Among alcohol compounds, alcohols having a boiling point of 100 ° C. or less are preferable, and examples thereof include methanol, ethanol, 1-propanol, 2-propanol, t-butanol and the like. These alcohol compounds are preferable because they are highly safe, can be obtained at low cost, can be easily controlled, and have high decomposition efficiency of dioxins. In addition, the use of alcohol having a relatively low boiling point is advantageous in that the decomposition efficiency can be increased while maintaining the reaction temperature low, and the production of side reaction products can be suppressed.

  Moreover, it is preferable from a viewpoint of handleability to select the said alcohol whose boiling point is higher than the reaction temperature mentioned later.

  The alkali compound used in the present invention can be used without limitation as long as it can promote the decomposition reaction of dioxins, but from the viewpoint of increasing the dechlorination efficiency, NaOH, KOH, sodium alkoxide, potassium alkoxide, Calcium hydroxide or the like is preferably used. Among these, NaOH or KOH is particularly preferable from the viewpoints of cost and handling properties. An alkali compound can be used individually or in combination of 2 or more types.

  The catalyst used in the present invention is at least one selected from a carbon crystal compound and a compound having a metal supported on a carrier, and can be used without limitation as long as it can promote the decomposition reaction of dioxins. The type is not particularly limited. An inorganic catalyst is preferable to an organic catalyst because it has a long catalyst life and is stable even in the presence of an alkali compound. The catalyst can be suitably used because it is considered to be highly safe in an alkaline atmosphere and exhibit high activity against microwaves, and a compound in which a metal is supported on a carrier is particularly preferable. Examples of the carrier include carbon such as activated carbon and graphite, metal oxides such as silica gel, alumina and zeolite, and composite metal oxides, resins such as polyethylene, polystyrene, polycarbonate, and polymethyl methacrylate. These catalysts can be used individually or in combination of 2 or more types.

  Here, examples of the carbon crystal compound include graphite, carbon nanotubes (both including and not including metal), fullerene, and the like.

The metal-supported oxide and metal-supported composite oxide can be used without limitation as long as they are metal-supported oxides and composite oxides. It is the same as the carbon compound. Specific examples of the metal-supported oxide include Pd / TiO ₂ (palladium-supported titanium dioxide). Specific examples of the metal-supported composite oxide include Pd / SiO ₂ .Al ₂ O ₃ (palladium-supported silica-alumina).

  Among the above catalysts, a metal-supported carbon compound in which a metal is supported on a carbon support is most preferred from the viewpoints of high microwave absorption, good decomposition efficiency, and high safety in an alkaline atmosphere.

  As said metal carrying | support carbon compound, if it is a carbon compound which carry | supported the metal, it can be used without a restriction | limiting, The metal carrying amount is 1-20 mass% with respect to the catalyst whole quantity, More preferably, it is 5-10 mass%. It is good to be. Examples of the supported metal include iron, silver, platinum, ruthenium, palladium, rhodium, and the like. From the viewpoint of increasing the dechlorination efficiency, palladium, ruthenium, and platinum are preferable, and palladium is more preferable. Specific examples of the metal-supported carbon compound include Pd / C (palladium-supported carbon compound), Ru / C (ruthenium-supported carbon compound), and Pt / C (platinum-supported carbon compound).

  The catalyst used in the present invention may be granular or honeycomb-shaped. In the case of granular, it is necessary to fix with a mesh or the like. When it exceeds 10 mm, the specific surface area is insufficient, and when it is less than 75 μm, the mesh is easily clogged. More preferably, it is 150 μm to 5 mm. The catalyst particles should have the same particle size as possible.

  In the method for decomposing dioxins of the present invention, when a mixed solution is obtained, an object to be treated containing dioxins, a hydrogen donor, and an alkali compound are mixed by a conventional method. If there are insoluble substances (solid, fine particles, etc.) in the mixed solution, there is a risk of clogging when circulating in the catalyst filling device. It is preferably introduced into the apparatus.

  In the above mixed solution, the mixing ratio (molar ratio) of alkali compound / hydrogen donor is preferably 0.005 to 0.1 / 1, more preferably 0.01 to 0.1 / 1. When the proportion of the hydrogen donor is too small, the decomposition reaction does not proceed. On the other hand, when the proportion of the hydrogen donor is too large, the decomposition reaction proceeds, but it has no practical meaning and is not economical. As the alkali compound and the hydrogen donor, those obtained by premixing both in advance and dissolving the alkali compound in the hydrogen donor can also be used.

  In addition, the alkali compound is preferably used in an amount equal to or greater than that of chlorine desorbed from the organic halogen compound in the mixed solution from the viewpoint of increasing the decomposition efficiency. The ratio (molar ratio) of the alkali compound / organic halogen compound is preferably 1.0 or more, more preferably 1.0 to 1.5. When the amount of the alkali compound is too small, the dechlorination reaction does not proceed. On the other hand, when the amount of the alkali compound is too large, stirring and mixing of the reaction system becomes difficult.

  The amount of the catalyst in the reaction system is preferably 0.005 to 0.2, more preferably 0.01 to 0.15, still more preferably 0.05 to 0 as a mass ratio with respect to the total mass of the mixed solution. .1 should be good. When the amount of catalyst is too small, the amount of hydrogen generation is small and decomposition is difficult to proceed. On the other hand, when the amount of catalyst is too large, the economy is poor. Furthermore, when a catalyst is added to the reaction system, stirring and mixing of the reaction system becomes difficult.

  When the mixed solution is brought into contact with the catalyst, a method of adding a predetermined amount of catalyst to the mixed solution and stirring, a method of circulating the mixed solution through a catalyst filling device filled with the catalyst, or the like can be employed. From the viewpoint that the mixed solution can be frequently contacted with the catalyst and the catalyst can be easily recovered after decomposition, a method in which the mixed solution is circulated through a catalyst filling device filled with the catalyst is preferable.

  The irradiation position of the microwave is not particularly limited as long as the catalyst in the reaction system is irradiated. However, the irradiation is directed toward the catalyst in the catalyst filling device from the viewpoint of promoting the decomposition by increasing the catalytic activity as much as possible. Is preferred.

  In the present invention, the output, frequency, and irradiation method of the microwave applied to the catalyst filling device are not particularly limited, and may be electrically controlled so that the reaction temperature can be maintained within a predetermined range. When the output is too low, the amount of hydrogen generation is reduced, and when the output is too high, the utilization rate of the microwave is deteriorated. Therefore, it is desirable to set the range of 10 W to 20 kW while being electrically controlled. The microwave frequency is preferably 1 to 300 GHz. In the frequency range below 1 GHz or above 300 GHz, the catalyst and the hydrogen donor are not sufficiently heated. Microwave irradiation may be either continuous irradiation or intermittent irradiation, but it is preferable to perform continuous irradiation while being electrically controlled. As the microwave device, a device using a microwave generator such as a magnetron, a microwave oscillator using a solid element, or the like can be used as appropriate.

  The irradiation time and the irradiation stop time can be appropriately determined according to the type of the object to be treated, the hydrogen donor, the reaction catalyst, or the like, and may be performed until the decomposition reaction sufficiently proceeds.

  The reaction atmosphere is more preferably carried out in an inert gas because undesirable side reactions do not occur. However, since it may be difficult to procure an inert gas depending on the processing environment of the object to be processed, the reaction can be performed in a natural atmosphere.

  The reaction temperature is not particularly limited as long as it is equal to or lower than the boiling point of the hydrogen donor to be used, but is preferably 50 to 200 ° C, and particularly preferably 10 to 80 ° C. When the reaction temperature is less than 10 ° C., the decomposition reaction becomes insufficient. On the other hand, when the temperature exceeds 80 ° C., the decomposition reaction proceeds sufficiently, but by-products are easily generated, and the economy is inferior. From the viewpoint of balancing the suppression of side reaction products and the decomposition rate of dioxins, the reaction is more preferably performed at 30 to 80 ° C. and at a temperature lower than the boiling point of the alcohol by 10 ° C. or more (preferably 20 ° C. or more). Is good.

  The catalyst used in the decomposition treatment of the present invention may be reused for the treatment of other objects to be treated after the regeneration treatment. The regeneration process of the catalyst may be performed by a known method. For example, the catalyst can be regenerated by washing the catalyst at 10 to 80 ° C. using an organic solvent such as acetone or a lower alcohol. There is no limitation on the washing time, and it may be appropriately determined according to the desorption status of the adsorbed organic halogen compound.

  According to the method for decomposing dioxins of the present invention, when the dioxins are decomposed at a speed equivalent to or faster than that when hydrogen gas is blown into the reaction system from the outside, and the object to be treated is PCB, the PCB itself Is decomposed and dechlorinated. Although the mechanism is not clear, it is considered that the alkali metal radical provided from the alkali compound promotes the decomposition reaction of dioxins, and the hydrogen radical from the hydrogen donor enters therein.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited only to a following example.

Example 1 (Decomposition test of dioxins contained in PCB)
Experiments were performed using a simple microwave reactor temperature control type ZMW-024 manufactured by Shikoku Keiki Kogyo Co., Ltd. Four of the five-necked flasks are used as a liquid phase supply port, return port, nitrogen introduction port, and sampling port to the column in the microwave reactor, and a Dimroth condenser is provided at the center port. The reaction product was taken out of the reaction system.

  PCB containing dioxins in the amount shown in Table 1 (KC-1000 manufactured by Kaneka Chemical Co., Ltd. (biphenyl pentachloride (KC-500) / mixture of 6/4 (mass ratio) of trichlorobenzene)) 1.5 ml Then, 2.45 g of KOH flakes and 150 ml of isopropyl alcohol manufactured by Wako Pure Chemical Industries, Ltd., which were mixed for 20 minutes with a 3000 rpm homomixer, were introduced into the above five-necked flask having an internal volume of 200 ml. After replacing the inside of the flask with nitrogen gas, the mixed solution in the flask was supplied to the column in the microwave reactor at 10 ml / min while the inside of the flask was stirred with a magnetic stirrer, and the inside of the apparatus was circulated. The column has a granular activated carbon (trade name: Diahop 008) and a catalyst (average particle diameter of 1) supporting 5% palladium (Pd). It was irradiated for 10 hours while electrically controlling microwaves with a frequency of 2.45 GHz and an output of 40-60 W so that the column surface was kept constant at 60 ° C. Nitrogen gas was also used during the reaction. At a flow rate of 50 ml / min.

(Measurement method of dioxins)
10 μl of the solution before and after the reaction was subjected to a gas chromatography mass spectrometer (GC / GC) manufactured by Hewlett-Packard Co. using BPX-DXN-1 (0.15 mmID) and BPX-DXN-2 (0.15 mmID) manufactured by SGE as columns. MS) Measured at a column temperature of 160 ° C. to 300 ° C. by applying to HP6800 series. To identify dioxins, create a standard chromatogram, compare the relative retention time of each appearing peak with respect to the internal standard, compare the peak area ratio and chromatogram pattern in the two monitor channels with the chromatogram obtained as a result of the measurement. I went. The dioxin concentration was determined from the peak area using a calibration curve prepared in advance.

  Table 1 shows the concentrations of dioxins and PCB in the treatment liquid before and after the decomposition treatment.

  As shown in Table 1, according to the method of the present invention, it was confirmed that dioxins (particularly polychlorodibenzofuran (PCDF)) can be rendered harmless under mild conditions. At the same time, PCB could be decomposed by 99.999% or more.

Claims (8)

While contacting a mixture containing a dioxin-containing material, a hydrogen donor, and an alkali compound with at least one catalyst selected from a carbon crystal compound and a metal-supported compound. A method for decomposing dioxins, wherein the catalyst is irradiated with microwaves continuously or intermittently and heated to a temperature below the boiling point of the hydrogen donor. 2. The method for decomposing dioxins according to claim 1, wherein the catalyst filling device is irradiated with microwaves while the mixed solution is circulated through the catalyst filling device filled with the catalyst. The dioxins according to claim 1 or 2, wherein the hydrogen donor is at least one compound selected from the group consisting of a heterocyclic compound, an amine compound, an alcohol compound, a ketone compound, and an alicyclic compound. Disassembly method. The method for decomposing dioxins according to claim 1 or 2, wherein the hydrogen donor is an alcohol compound having a boiling point of 100 ° C or lower. The method for decomposing dioxins according to any one of claims 1 to 4, wherein the alkali compound is at least one compound selected from the group consisting of caustic soda, caustic potash, sodium alkoxide, potassium alkoxide and calcium hydroxide. The method for decomposing dioxins according to any one of claims 1 to 5, wherein the catalyst is a palladium-supported carbon compound. The method for decomposing dioxins according to any one of claims 1 to 6, wherein the dioxins are polychlorodibenzofuran (PCDF). The method for decomposing dioxins according to any one of claims 1 to 7, wherein the object to be treated is incinerated ash, soil, a hardly decomposable organic halogen compound, or oil / water containing them.