JP2000342710A - Method of decomposing halogenated organic compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively decompose dioxins in soil by reacting a halogenated organic compound with one or more of amidine compounds seleted from a group consisting of guanidines, amino guanidines, guanylic ureas and their salts by heating. SOLUTION: When the soil around an incinerator, e.g. a garbage incinerator and the like is contaminated by halogenated organic compounds, e.g. polychlorodibenzo-p-dioxins, polychlorodibenzofuran and the like, the dioxins in soil should be decomposed. In such a case, the halogenated organic compound is decomposed and disposed by reacting the compound with one or more of amino acid compounds selected from a group consisting of guanidines, amino guanidines, guaniylic ureas and their salts by heating. It is recommended that amount of the amidine compounds to be added is 0.1-10 wt.% to the materials to be disposed, e.g. soils and the like at the dried, state in view of the dioxin's decomposing efficiency and disposal cost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for decomposing halogenated organic compounds, and relates to polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) contained in soil (hereinafter referred to as a combination thereof). (Hereinafter referred to as "dioxins").

[0002]

2. Description of the Related Art Incinerators, such as refuse incinerators, emit organic compounds such as phenol, benzene and acetylene, chlorinated aromatic compounds such as chlorophenol and chlorobenzene, and chlorinated alkyl compounds during combustion. Dioxin precursors are generated. When dioxin precursors coexist with fly ash, they become dioxins due to their catalytic action and are present in the fly ash. In addition, the generated dioxins may pollute the garbage incineration plant and the surrounding soil.

[0003] Conventionally, techniques for decomposing dioxins in soil include a method using supercritical water, a method using ozone and ultraviolet rays, a method using heating, a method using maitake, enoki mushroom or wood immortal fungus, and a method using a catalyst. Have been.

The following method has been proposed as a method for decomposing dioxins in fly ash. The dioxin-containing fly ash is placed in a reducing atmosphere such as nitrogen gas at 320 to 400 ° C. for 1 to 2 hours (for example, 320 ° C.
(2 hours at 340 ° C for 1 to 1.5 hours) (Hagenmeier process “ORGANOHALOG”
EN COMPOUUNDS Vo. 27 (1996) "
147-152). The dioxin-containing fly ash is heat-treated at 300 to 500 ° C. in the presence of a dioxin production inhibitor such as pyridine (Japanese Patent Laid-Open No. 4-241880).

[0005] However, all of the above conventional methods for decomposing dioxins in soil have problems in terms of decomposition efficiency, treatment operation, and the like. In particular, the method using ultraviolet light has an effect only on the surface irradiated with ultraviolet light. Therefore, the decomposition rate is poor, and the treatment with a catalyst is difficult. In addition, the heat treatment has a problem of resynthesis and evaporation of dioxins, and decomposition efficiency by fungi is poor.

On the other hand, the above-mentioned method for decomposing dioxins in fly ash has the disadvantage that the processing temperature is relatively high and the processing time is long, so that the required heating energy is large and the processing cost is high. . In particular, in the above-mentioned method, it is necessary to perform the treatment in a reducing atmosphere such as nitrogen gas, which increases the labor cost. Moreover, these methods also have a problem of resynthesis and evaporation of dioxins.

[0007] On the other hand, the applicant of the present invention has found that dioxins can be decomposed and removed in a short time even in a low-temperature region, which was considered not to decompose dioxins by the conventional method. As a possible method of decomposing dioxins, a method of decomposing dioxins by the action of a gaseous or liquid amine compound has been proposed (Japanese Patent Application No. 9-222,197).
-321357. Hereinafter, it is referred to as “first application”. ).

According to the method of the prior application, the chlorine of the dioxins reacts with the amino group (nitrogen atom) in the amine compound, so that the dioxins are usually not decomposed at a low temperature of less than 300 ° C. In the above, the dechlorination reaction of dioxins progresses rapidly, and it becomes possible to decompose and remove dioxins at a low temperature in a short time.

[0009]

However, the above-mentioned prior application method is not suitable for decomposing dioxins in soil for the following reasons.

That is, even when an amine compound is used, the reaction temperature is preferably higher from the viewpoint of the decomposition efficiency of dioxins, and it is practically desirable to carry out the treatment at a temperature of about 250 to 300 ° C. However, at this temperature, the amine compound vaporizes, and all or most of the amine compound is present in gaseous form. However, the gaseous amine compound and dioxins in the soil are sufficiently contacted to achieve high decomposition efficiency. It is difficult to get. It is conceivable to increase the contact efficiency between dioxins in soil and the amine compound by stirring and mixing the gaseous amine compound and the soil, but in this case, a high-pressure airtight container is required, and the processing equipment is complicated and In addition to being expensive, many amine compounds which do not contribute to the reaction are also present, so that the required usage increases. In addition, the soil contains stones, gravel, silt, clay, etc., and may also contain grasses, glass fragments, cans, nails, etc. It is very difficult to do. Also, from an economic perspective,
After the treatment, it is desired to recover and reuse the remaining amine compound. However, the recovery of the gaseous amine compound requires complicated operation and complicated equipment, which is practically difficult.

An object of the present invention is to solve the above-mentioned problems of the prior application, and to provide a method for decomposing a halogenated organic compound which can decompose dioxins in soil efficiently.

[0012]

According to the present invention, there is provided a method for decomposing a halogenated organic compound, wherein the halogenated organic compound is one or two or more selected from the group consisting of guanidine, aminoguanidine, guanylurea and salts thereof. The above-mentioned amidine compound is reacted under heating.

In the present invention, the amino groups of these amidine compounds react with halogens of halogenated organic compounds such as chlorine of dioxins to be dehalogenated, thereby decomposing the dioxins.

These amidine compounds are not vaporized at a reaction temperature effective for decomposing dioxins, but are added to and mixed with a solid (eg, powder), liquid, or solution to be treated, such as soil. Heat reaction can be easily performed.

[0015]

Embodiments of the present invention will be described below in detail.

The amidine compounds used in the present invention include guanidine (NH ₂ C (NH ₂ ) = NH), aminoguanidine (H ₂ NNHC (NH ₂ ) = NH), guanylurea (NH ₂ C (NHCONH ₂ ) = NH) and their acid salts. Of these, the acid salts of guanidine, aminoguanidine, and guanylurea are not particularly limited, and carbonate, hydrochloride, sulfate, nitrate, phosphate, acetate, And propionate.

One of these amidine compounds may be used alone, or two or more of them may be used in combination.

The amount of these amidine-based compounds is preferably about 0.1 to 10% by weight based on the air-dry weight of the object to be treated such as soil from the viewpoint of the decomposition efficiency of dioxins and the treatment cost.

As an addition form of the amidine compound, an aqueous solution is desirable, but a solution using a solvent other than water may be used.
In some cases, the powder may be added as it is. If the powder is added as it is, after adding it to the object to be treated such as soil,
What is necessary is just to become a dissolved state.

The higher the reaction temperature, the higher the decomposition rate and consequently the higher the decomposition rate.
Particularly, the temperature is preferably set to 250 to 350 ° C. When the reaction temperature is lower than 200 ° C., the progress of the reaction is slow and the decomposition rate is low. When the reaction temperature exceeds 400 ° C., heat energy increases, processing costs rise, and in addition, problems such as the evaporation of a halogenated organic compound such as dioxins to a gaseous phase occur.

The reaction time varies depending on the reaction temperature, the form of the object to be treated, the concentration of dioxins, and other conditions, but can be appropriately set within a range of 10 to 180 minutes in the usual case.

In order to carry out the present invention, an amidine compound may be added to an object to be treated containing a halogenated organic compound such as soil containing dioxins and heated to a predetermined temperature for a predetermined time. There is no particular limitation on the processing apparatus such as the mixing apparatus and the heating apparatus. (An amidine-based compound may be added to the heated object to be treated.)
At the time of the heating reaction, it is preferable to perform a little stirring and mixing in order to make the temperature of the treatment system uniform, but this stirring and mixing is not necessarily required.

When the amidine compound is added to the object to be treated, a small amount of water is preferably supplied in order to enhance the uniform dispersibility of the amidine compound in the object to be treated. It is convenient to add the system compound as an aqueous solution to the object to be treated and mix uniformly.

The heating can be performed using, for example, a rotary kiln. That is, for example, while introducing the mixture from one end of the rotary kiln and discharging the mixture from the other end, the temperature inside the kiln is gradually increased from one end to the other end, dried in the kiln, and then dried in the kiln. The reaction is carried out while passing through a zone at or above the temperature, and the halogenated organic compound is discharged in a sufficiently decomposed state.

The treated material discharged from the kiln is disposed of by landfill or the like. If the gas discharged from the kiln may contain volatile matter from the soil or a decomposition product of an amidine-based compound, the gas phase may be burned in a heavy oil burner, an electric furnace, etc., and then discharged. . Or you may wash and remove.

The method of the present invention can be carried out simply by adding an amidine-based compound to an object to be treated such as soil in advance, mixing and heating, and can be easily carried out by an extremely simple apparatus. .

In the present invention, the halogenated organic compound to be decomposed includes the above-mentioned PCDD or PCD.
F and other dioxins and dioxin-containing substances, polychlorinated biphenyls (PCB), pentachlorophenol, 2,4-dichlorophenoxyacetic acid, 2,4-
Environmental hormones such as dichlorophenol are exemplified.

The objects to be treated containing these halogenated organic compounds are not limited to soil at all, and include activated carbon, incinerated ash, incinerated fly ash, sediments for lakes and rivers, construction soil, bricks , Concrete, sludge, wood and the like.

[0029]

The present invention will be described more specifically with reference to comparative examples and examples.

Comparative Examples 1 to 3 Dioxin decomposition tests were carried out using dioxin-contaminated soil (air-dried, particle size 2 mm or less) as a sample. The results of measuring the dioxin concentration of this sample are as shown in Table 1.

20.0 g of this sample was placed in a porcelain crucible,
After placing in an electric furnace adjusted to the temperature shown in Table 1 for 60 minutes,
After standing to cool, the concentration of dioxins was measured, and the decomposition rate was determined. The results are shown in Table 1.

The method for measuring the concentration of dioxins and the method for calculating the toxic equivalent shown in Table 1 are described in "Provisional Manual for Soil Investigations Concerning Dioxins", January 1998 (Soil Pesticide Division, Water Quality Conservation Bureau, Environment Agency). Depending on the method. The decomposition rate is a percentage of the dioxin concentration or the toxic equivalent with respect to the dioxin concentration or the toxic equivalent of the sample.

Examples 1 to 6 In Comparative Example 1, an aqueous solution of the amidine compound shown in Table 1 was previously added to 20 g of the sample and mixed so that the amount of the amidine compound added to the soil was as shown in Table 1. In the same manner as in Comparative Example 1, it was placed in an electric furnace adjusted to the temperature shown in Table 1 for 60 minutes, and then allowed to stand for cooling to measure the concentration of dioxins and determine the decomposition rate. The results are shown in Table 1.

From Table 1, it can be seen that the higher the heating temperature, the higher the efficiency of decomposition of dioxins, and the addition of the amidine compound does not vaporize the amidine compound. It is clear that decomposition efficiency can be achieved.

[0035]

[Table 1]

[0036]

As described in detail above, according to the method for decomposing a halogenated organic compound of the present invention, a halogenated organic compound such as dioxins contained in soil or the like can be removed without complicated operation or complicated equipment. Easy and efficient disassembly,
The content concentration can be reduced to an extremely low concentration.

Claims (2)

[Claims] 1. A halogenated organic compound, guanidine,
A method for decomposing a halogenated organic compound, comprising reacting one or more amidine-based compounds selected from the group consisting of aminoguanidine, guanylurea, and an acid salt thereof with heating. 2. The method for decomposing a halogenated organic compound according to claim 1, wherein the halogenated organic compound is a dioxin or a dioxin-containing substance.