JPH0852454A - Method for decomposing aromatic halogen compounds - Google Patents

Abstract

(57) [Summary] [Objective] Reaction products are generally present in soil, and aromatic halogen compounds such as PCBs can be decomposed using chemicals that are harmless even if present, and contaminated soil can be used. Provide a way to convert to land. [Structure] A substance containing an organic substance is added to and mixed with a solid substance contaminated with an aromatic halogen compound.
The method of decomposing aromatic halogen compounds by heating to ℃ ~ 450 ℃, the substance containing the organic matter, humus, compost, starch or sucrose in powder form, sodium formate or potassium formate from To be elected.

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 aromatic halogen compounds, and more particularly to a method for decomposing aromatic halogen compounds such as PCB and dioxin contained in solid substances such as soil.

[0002]

2. Description of the Related Art PCBs are currently used in sludge accumulated in estuaries and sea areas where effluent from paper mills and chemical plants is currently flowing out.
, Dioxin, etc. are contained, and PCBs and dioxin are detected in fish through the process of bioconcentration, which is a problem. Such sludge is dredged from the seabed to be dehydrated, and then landfilled as it is or after being solidified with cement. The land where sludge including PCBs is reclaimed on land is only managed so that PCBs do not leak out and cannot be used for anything. Also, PCB
PC leaked from a transformer or condenser that used
There is also soil contaminated with B, and in this case as well, it is only managed so as not to leak to the environment, and decomposition treatment is not performed.

As a method for treating an aromatic halogen compound other than the method of solidifying soil with cement to contain harmful substances, a high temperature combustion method, a microbial decomposition method, a chemical decomposition method and the like have been studied. Although the high temperature combustion method has an example in the case of liquid PCB or the like, when it is applied to the soil, the soil is ashed and the soil quality is changed, and therefore, no experiment has been conducted on the soil. The microbial decomposition method has a problem that the processing time is extremely long, which is several decades. On the other hand, the chemical decomposition method is characterized in that it can be decomposed in a short time and at a relatively low temperature.

The following various methods are known as chemical decomposition methods. In U.S. Pat. Nos. 4,447,541 and 4,574,013, an alkali component and a sulfoxide catalyst [DMSO (dimethyl sulfoxide)] are disclosed.
A method of heating using a reagent mixture of and is shown.
This method uses an expensive sulfoxide catalyst, and has a problem that it produces an odorous compound when heated to a high temperature and decomposes into a flammable by-product under high temperature conditions. U.S. Pat. No. 4,400,552 discloses a decomposition method using a reagent composed of a reaction product of an alkali metal hydroxide with a polyglycol or a polyglycol monoalkyl ether and oxygen. Similarly, US Pat. No. 4,35
Nos. 1,718 and 4,353,793 disclose methods of treating with polyethylene glycol and an alkali metal hydroxide. Further, International Patent Application No. PCT / US91 / 01112 discloses a method in which carbon obtained by pyrolyzing a carbohydrate is used as a catalyst and a high boiling point hydrocarbon is treated as a hydrogen donor.

[0005]

When the soil is treated with a sulfoxide catalyst, polyethylene glycol or a high boiling point hydrocarbon as in the conventional treatment method described above, the chemicals used are all high boiling point liquids. Therefore, unreacted chemicals and sometimes reaction products remain in the treated soil. Although these chemicals are less toxic than PCBs, they do not exist in the surface soil in the natural world, and the soil remains contaminated, making it a natural choice for parks and residential land. The problem is too large to be used as an industrial site. In addition, since the chemicals are expensive, if the unreacted chemicals are to be collected, the apparatus becomes complicated and large in size, and in any case, an increase in running cost cannot be avoided. In the present invention, the reaction product is generally present in the soil, and even if it is present, a harmless substance is used to produce PCB.
It is an object of the present invention to provide a method capable of decomposing an aromatic halogen compound such as the above and converting contaminated soil into usable land.

[0006]

In order to solve the above-mentioned problems, in the present invention, a substance containing an organic substance is added to a solid substance such as soil or sludge containing an aromatic halogen compound to obtain 300- The heating is performed at 450 ° C., whereby the halogen atoms in the nascent stage generated when the organic substance is thermally decomposed can be dehalogenated to decompose the aromatic halogen compound. Next, the present invention will be described in detail. Examples of aromatic halogen compounds that can be decomposed in the present invention include PCB (polychlorobiphenyl), which is a harmful pollutant in soil and sludge, PCDD [commonly called dioxin (polychlorodibenzodioxin)], P
CDF [commonly known as furan (polychlorodibenzofuran)],
PCP (pentachlorophenol) and the like.

The organic substances which generate hydrogen by thermal decomposition are carbohydrate (cellulose) which is the main component of water, grass and paper and hydrocarbon which is the main component of plastics. For the purpose of dehalogenation only, all organic substances can be used,
Artificial materials such as plastics are not preferred for the treated soil to be safe and reusable land.
Humus or compost is most suitable because the treated soil is a substance containing organic matter that is not different from ordinary soil. Humus soil is the surface soil that contains a lot of organic matter, such as leaves that have rotten due to biodegradation. Compost is like artificially making humus, and agriculturally, straw or the like is used for compost, but other than that, there are compost using sewage sludge and garbage. Since it is difficult to secure a large amount of humus when actually treating contaminated soil, compost is the most suitable because it is easily available. Commercially available and readily available products include starch and sucrose. Of course, these also generate hydrogen by thermal decomposition, but since they are biodegradable, there is no problem if unreacted substances remain in the soil after treatment.

Also, sodium formate and potassium formate generate hydrogen by thermal decomposition, and both reaction products and unreacted substances are harmless and can be preferably used. Since the generation of hydrogen by these thermal decompositions is caused by heating in an oxygen-free state or a low oxygen concentration state, heating is preferably performed in an inert gas atmosphere, for example, a nitrogen gas atmosphere. When compost or starch is used as the organic substance, the reaction products are biphenyl (C ₁₂ H ₁₀ ), chlorine and hydrogen chloride, and carbon of the thermal decomposition product. Since biphenyl has a boiling point of 254 ° C, it vaporizes completely above 300 ° C and does not remain in soil. The evaporated biphenyl is collected by a combination of an absorption tower, a condenser, an activated carbon adsorption tower, etc., which is scraped with high boiling point oil. Chlorine and hydrogen chloride are emitted in gaseous form and do not remain in the soil. Chlorine and hydrogen chloride gas are removed by an exhaust gas treatment device such as a gas absorption tower using an alkaline aqueous solution. Carbon, a pyrolysis product, remains in the soil but is not a problematic component.

When a formate salt such as sodium formate is used, sodium oxalate is separately produced as a reaction product, and the sodium oxalate remains in the soil but is easily decomposed by microorganisms to become sodium carbonate. , Sodium carbonate is harmless, and it exists in general soil though there are some quantitative differences. In addition, when microorganisms decompose organic matter in soil, carboxyl groups such as oxalic acid are produced as an intermediate product, so that oxalate is also present in general soil. Even if another formate is heated, it decomposes to generate hydrogen. However, in the case of formate salts of heavy metals such as lead formate and nickel formate, heavy metals remain in the treated soil and are not suitable for the purpose of detoxifying the soil. Further, lead formate decomposes at 190 ° C. to generate hydrogen gas, but when the temperature is low, dechlorination reaction due to hydrogen radicals is unlikely to occur. On the other hand, sodium formate is most suitable because it decomposes at 300 ° C. or higher and can generate hydrogen at a temperature at which a dechlorination reaction occurs. Potassium formate has the same effect as sodium formate, and even if potassium carbonate remains in the soil, it is harmless, so that the object of the present invention is met.

The thermal decomposition temperature of cellulose is 240 to 400.
Although it is ℃, decomposition of PCB etc. occurs at 300 ℃ or more.
The decomposition product, biphenyl, also evaporates at temperatures above 300 ° C and does not remain in the soil. The higher the temperature, the faster the decomposition rate, but if the temperature becomes too high and falls within the temperature range of 460 to 500 ° C., a melt may be generated and the trouble of stopping the rotation of the mixer may occur. Moreover, when heated to 500 ° C. or higher, all organic substances in the soil are completely carbonized.
In order not to carbonize the organic matter more than necessary, it is preferably 450 ° C. or lower, and from the viewpoint of energy saving, it is 300 to 45 ° C.
It is optimum to heat in the range of 0 ° C. Water is not directly involved in the reaction in the present invention, but when water is mixed with soil and organic matter or sodium formate or potassium formate, it can be mixed evenly, and the inside of the pores can be impregnated with a reagent soaked in the pores. It is possible to react with PCB or the like adsorbed on.

[0011]

[Function] Organic substances in anoxic or low oxygen concentration state 30
It is a well known fact that when heated to 0 to 800 ° C., thermal decomposition occurs and combustible gases such as hydrogen gas, methane gas, carbon monoxide gas are generated. However, when the organic substance and the aromatic halogen compound coexist, if heated to 300 ° C. or higher, H ₂ in the nascent stage is generated before it becomes H ₂ (hydrogen gas).
It was found that (hydrogen atom) causes a substitution reaction with halogen, that is, a dehalogenation reaction. This dehalogenation reaction is called a radical reaction.

For example, in the case of PCB, as shown in the following formulas (1) and (2), it is dehalogenated and decomposed into biphenyl, hydrogen chloride and chlorine. _{C 12 H 4 Cl 6 + 6H} → C 12 H 10 + 3Cl 2 ··· (1) C 12 H 4 Cl 6 + 12H → C 12 H 10 + 6HCl ··· (2) In the case of using a formate salt, e.g., formic acid Heating sodium above 250 ° C decomposes it into hydrogen and sodium oxalate. ₂ NaHCO ₂ → H ₂ + Na ₂ C ₂ O ₄ (3) In a pure substance, hydrogen gas is generated according to the equation (3). However, coexist aromatic halogen compounds, and causes a substitution reaction, i.e. dehalogenation reaction of a halogen nascent H (hydrogen atom) before the H ₂ (hydrogen gas) at 300 ° C. or higher.

From the viewpoint of the dehalogenation reaction with hydrogen, it is also conceivable to carry out a hydrogenation reaction using hydrogen gas to effect dehalogenation. However, in the case of hydrogenation reaction, the reaction does not occur unless the catalyst is present and the pressure is raised. In the reaction of the present invention, an aromatic halogen compound which is a target substance for dehalogenation, an organic substance of a hydrogen generating source, Na formate or K
By mixing and heating, it is possible to generate a hydrogen atom in the immediate vicinity of the aromatic halogen compound to cause a radical reaction, and it is possible to process at atmospheric pressure without the need for a catalyst or high pressure. There is. Unlike the case of liquid, when supplying or discharging solid such as soil to the reactor, there is no suitable supply device under high pressure conditions, and it is a great advantage that it can be treated at atmospheric pressure.

[0014]

EXAMPLES The present invention will now be specifically described with reference to examples, but the present invention is not limited thereto. Example 1 FIG. 1 shows a schematic configuration diagram of a glass experimental apparatus used in Examples. In FIG. 1, reference numeral 1 is a heating reactor, which is heated by a mantle heater 2 and which contains a mixture of a sample soil or sludge with a reagent therein, and a thermocouple 4 measures the temperature. The steam generated in the reactor 1 is cooled in the condenser 5 through which the cooling water 8 passes, and the condensate 7 is collected in the condensate receiver 6. The gas that does not condense is discharged through the activated carbon trap 9.

Using the glass experimental apparatus shown in FIG. 1, P
A treatment experiment was conducted on a soil containing 2500 mg / kg of CB (KC-300) and 1000 mg / kg of PCP.
As a result of an experiment conducted by adding a compost prepared by using sewage sludge as a reagent, PCB and PCP were added to the soil and the condensate after the treatment.
Is no longer detected. The processing conditions and results are shown below. (Treatment conditions) Soil weight: 70 g (dry), Addition amount of compost made using sewage sludge: 20 g, Addition amount of water: 10 cm ³ , Heating time: 1 h, Heating temperature: 350 ° C.

The experimental results are shown in Table 1.

[Table 1] Note) ND = not detected

Example 2 Using the glass experimental apparatus shown in FIG. 1, a sludge treatment experiment was carried out containing PCDDS (total dioxin amount) of 430 μg / kg and PCDFS (total furan amount of 620 μg / kg). Sludge is dehydrated to a water content of 81%. As a result of an experiment in which sucrose was added, PCDDS and PCDFS were not detected in the soil and the condensate after the treatment. The processing conditions and results are shown below. (Treatment condition) Weight of sludge (water content of sludge 81%): 150 g (wet), sucrose (sucrose): 5 g, water addition amount: 0 cm ³ , heating time: 1 h, heating temperature: 400 ° C.

The experimental results are shown in Table 2.

[Table 2] Note) ND = not detected

Example 3 Using the glass experimental apparatus shown in FIG. 1, PCB (KC-3
00) 2500 mg / kg and PCP 1000 mg / kg
A soil treatment experiment containing kg was conducted. The processing conditions and results are shown below. (Treatment conditions) Soil weight: 70 g (dry), Reagent (sodium formate addition amount): 2 g, Water addition amount: 10 cm ³ , Heating time: 1 h

The experimental results are shown in Table 3.

[Table 3] Note) ND = not detected At 250 ° C, decomposition is insufficient and PCB and PCP remain in the condensate. At 300 ° C or higher, PCB and PCP in the condensate were no longer detected. PCB and PCP concentrations in soil decrease with increasing temperature.

Example 4 Using the glass experimental apparatus shown in FIG. 1, a sludge treatment experiment containing PCDDS (total dioxin amount) of 430 μg / kg and PCDFS (total furan amount of 620 μg / kg) was carried out. Sludge is dehydrated to a water content of 81%. The processing conditions and results are shown below. (Treatment conditions) Weight of sludge (water content of sludge 81%): 150 g (wet), reagent: amount of sodium formate added: 2 g, amount of water added: 0 cm ³ , heating time: 1 h

The experimental results are shown in Table 4.

[Table 4] Note) ND = not detected PCDDS and PCDFS in the condensate at 300 ° C
Was slightly present, but it became ND at 350 ° C or higher,
It is clear that the dehalogenation reaction has taken place.

Example 5 Using the glass experimental apparatus shown in FIG. 1, PCB (KC-3
00) 2500 mg / kg and PCP 1000 mg / kg
A soil treatment experiment containing kg was conducted. It was confirmed that biphenyl was present in the condensate, and it was found that the dehalogenation reaction had occurred. The processing conditions and results are shown below. (Treatment conditions) Soil weight: 70 g (dry), Reagent: Potassium formate addition amount: 5 g, Water addition amount: 20 cm ³ , Heating temperature: 350 ° C., Heating time: 1 h

The experimental results are shown in Table 5.

[Table 5] Note) ND = not detected

[0025]

In the prior art, there is a problem that the liquid chemicals used contaminate the soil even if harmful aromatic halogen compounds such as PCB can be decomposed. However, in the present invention, as in humus soil or compost. A substance that does not differ from the soil, a biodegradable substance such as starch and sucrose, or a compound such as sodium or potassium formate that retains only the substances normally contained in the soil after treatment is added to the soil. Since it can be treated by adding it, it has the effect of becoming safe and usable land after treatment. Also, starch and sucrose are cheap, but if compost made from sewage sludge or raw waste is used, it will be cheaper because the waste will be reused.

Since the dehalogenation reaction is a radical reaction, there is no need to use a catalyst or increase the pressure as in the hydrogenation reaction, and the treatment can be performed at atmospheric pressure. Therefore, there is an advantage that the device can be configured with a very simple one. An external heat paddle type mixing heater or a multi-screw type mixer is used as a decomposition reactor for PCBs, etc., and chemicals such as soil and compost are added at normal pressure with a screw feeder or rotary feeder. The powder feeder can be used, which greatly simplifies the system. When soil is contaminated with a liquid chemical as in the conventional technique, an operation such as solvent extraction is required to recover the chemical, and the system becomes very complicated.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an experimental device used in an example of the present invention.

[Explanation of symbols]

1: Heating reactor, 2: Mantle heater, 3: Sample (soil or sludge), 4: Thermocouple, 5: Condenser, 6: Condensate receiver, 7: Condensate, 8: Cooling water, 9: Activated carbon trap

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryuji Uchida 4-2-1 Motofujisawa, Fujisawa City, Kanagawa Prefecture EBARA Research Institute

Claims (3)

[Claims] 1. A substance containing an organic substance is added to and mixed with a solid substance contaminated with an aromatic halogen compound, and 3
A method for decomposing an aromatic halogen compound, which comprises heating to 00 ° C to 450 ° C. 2. The substance containing organic matter is humus,
The method for decomposing an aromatic halogen compound according to claim 1, which is one or more substances selected from compost, powdery starch or sucrose. 3. Sodium or potassium formate is added to a solid substance contaminated with an aromatic halogen compound,
A method for decomposing an aromatic halogen compound, which comprises mixing and heating to 300 ° C to 450 ° C.