JPH08168752A - Treatment of aromatic halogen compound contained in soil - Google Patents

Abstract

PURPOSE: To provide a treating method of safely and surely decomposing and removing aromatic halogen compounds contained in soil with simple equipment by using only chemicals harmless to the human body. CONSTITUTION: Soil contaminated with aromatic halogen compounds, as it is, or after hydrogencarbonate of alkali metal and water are added to and mixed with it, is heated to 250-400 deg.C. Gas contg. volatilizing aromatic halogen compounds is brought into contact with a catalyst in the presence of gaseous hydrogen at 200-400 deg.C to treat aromatic halogen compounds contained in soil. The catalyst is selected from Pt, Pd, Ru, Rh and Ni or oxides thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating an aromatic halogen compound, and more particularly to polychlorinated biphenyl (PC).
The present invention relates to a method for detoxifying soil contaminated with aromatic halogen compounds such as B).

[0002]

2. Description of the Related Art Recently, soil pollution due to outflow or disposal of waste oil containing harmful organic halogen compounds such as PCB has been
It is recognized on the site of a factory. If these are left as they are, not only will they hinder the effective use of land, but rainwater and seepage water will cause the release of harmful substances, and there is a risk of inducing groundwater pollution. Conventionally, thermal decomposition treatment, extraction treatment, solidification / stabilization treatment, chemical dechlorination treatment, biological treatment by microorganisms, etc. have been proposed as treatment methods for soil contaminated with PCBs and the like. The pyrolysis treatment heats the soil at a high temperature (800 ° C. or higher), and therefore has a problem that the soil quality changes.
In the extraction treatment, there is a problem that the extraction liquid containing PCB or the like requires a thermal decomposition or a post-treatment of a chemical treatment to complicate the process, and the biological treatment requires a long time to complete the decomposition. The solidification / stabilization treatment only encloses harmful substances with cement solidifying agents, etc., and there is no guarantee that the harmful substances will not leak to the environment permanently.

On the other hand, the chemical desalting method is characterized in that it decomposes PCB in a short time and at a relatively low temperature. As the main chemical treatment methods, a method using an alkali catalyst (KGME method), a method using polyethylene glycol (KPEG method), an alkaline reagent, a hydrogen donor such as paraffin oil, and a carbon catalyst are added to soil and mixed. A method of heat treatment (BCD method) has been proposed.
Among these conventional chemical treatment methods, in the KGME method and the KPEG method, since expensive chemicals are added to the soil, not only the running cost increases but also unreacted chemicals or by-products remain in the soil after the treatment. Therefore, there is a risk that these may cause new environmental pollution. Further, the BCD method has a problem that a hydrogen donor (donor oil) remains in the soil although it is inexpensive and uses a harmless chemical. Therefore, a process for efficiently recovering the added chemicals from the soil is required, and there is a problem that the device becomes complicated and becomes large in size.

[0004]

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, the present invention decomposes and removes aromatic halogen compounds contained in soil safely and reliably with a simple device by using only chemicals that are harmless to the human body. It is an object to provide a processing method that does.

[0005]

In order to solve the above problems, in the present invention, soil contaminated with an aromatic halogen compound is heated as it is to 250 to 400 ° C., or the alkali metal hydrogen carbonate is added to the soil. After adding salt and water and mixing, the soil is heated to 250 to 400 ° C., and the gas containing the volatile aromatic halogen compound is heated to 200 to 400 ° C.
This is a method for treating an aromatic halogen compound by bringing it into contact with a catalyst at 400 ° C. in the presence of hydrogen to decompose and remove the aromatic halogen compound. In the treatment method, as the catalyst, platinum, palladium, ruthenium,
At least one selected from the group consisting of rhodium, nickel and oxides thereof is used as a metal oxide such as alumina,
Those supported on a carrier such as silica gel or silica-alumina can be used. The amount of metal supported is not particularly limited,
It is preferably 0.1 to 10% by weight (wt%).

The decomposition in the presence of the catalyst is preferably carried out under the condition that the contact gas contains hydrogen at 1% (volume) or more. Normally, hydrogen gas is diluted with nitrogen gas before the catalyst layer is supplied, but 250 of organic substances originally contained in the soil is supplied.
Hydrogen gas generated by thermal decomposition at ˜400 ° C. can also be used. Further, it is also possible to previously add a substance containing organic matter such as corrosive soil or compost, or an organic matter such as starch or sucrose to the soil, and use hydrogen gas generated by thermal decomposition of these additives. By the hydrogen gas produced by these thermal decompositions,
When the hydrogen gas concentration exceeds 1%, it is not necessary to supply hydrogen gas from the upstream of the catalyst layer. These hydrogen gases do not remain in the soil and contaminate the soil unlike conventional oily hydrogen donors (paraffinic oil).

Next, the present invention will be described in detail. When soil containing an aromatic halogen compound is heated above the boiling point of the aromatic halogen compound, water in the soil and the aromatic halogen compound volatilize. Alkali metal hydrogen carbonate has the effect of promoting the desorption of aromatic halogen compounds in soil,
When the alkali metal hydrogen carbonate is added to the soil and heated in advance, the concentration in the soil after the treatment can be reduced to 1/15 or less at the same treatment temperature as compared with the case where the alkali metal hydrogen carbonate is not added. It is considered that this is because the aromatic halogen compound was dehalogenated in the soil and changed to an aromatic halogen compound having a lower boiling point. The dehalogenation rate and amount are
Depends on the nature of the soil (organic matter content, pH, etc.) and the amount of alkali metal hydrogen carbonate added. Organic matter content in soil is 5
wt% or more, the addition amount of alkali metal hydrogen carbonate is 3 to 6
wt% is preferred. As the alkali metal hydrogencarbonate used, sodium hydrogencarbonate and potassium hydrogencarbonate are preferable, but sodium hydrogencarbonate, which is cheaper and available in large quantities, is more preferable. Sodium carbonate produced by thermal decomposition of sodium hydrogencarbonate remains in the treated soil as shown in the following formula. ₂ NaHCO ₃ → Na ₂ CO ₃ + CO ₂ + H ₂ O

In the present invention, a catalyst layer in which a catalyst containing a noble metal supported on a metal oxide is filled with a catalyst layer is provided above a heater for heating the soil containing an aromatic halogen compound, whereby the catalyst volatilizes from the soil. Gaseous aromatic halogen compounds are reductively decomposed. The shape of the catalyst is not particularly limited, but in order to bring the catalyst and the gas into proper contact with each other, it is desirable that the catalyst is granulated into a spherical shape or a pellet shape, or a honeycomb shape. The catalyst layer is heated to 200 to 400 ° C,
The gaseous aromatic halogen compound volatilized from the soil reacts with hydrogen to be harmless while passing through the catalyst layer. The main products, in the case of PCBs, are biphenyl, hydrogen chloride and chlorine gas. When oxygen coexists in the reaction gas, hydrogen is consumed in the reaction that produces water, and the efficiency of dehalogenation decreases.Therefore, by replacing it with an inert gas such as nitrogen, coexisting oxygen should be at the lowest possible concentration. It is desirable to do.

[0009]

The function of the present invention will be described below with reference to PCB as an aromatic halogen compound. When PCB contained in soil is heated near the boiling point of PCB, it is thermally desorbed and released into the gas phase, and is supplied to the catalyst layer together with the added hydrogen gas. In this treatment method, platinum acts as a catalyst, palladium, ruthenium, rhodium, in the catalytically active species such as nickel, has an action to dissociate the H ₂ gas, H radicals from H ₂ gas on the catalyst (H ·) is To generate. H ₂ → 2H · (1) The H radical generated on the catalyst causes a substitution reaction with the Cl atom in PCB, and dechlorination proceeds. H ・ + C ₁₂ H _10-n Cl _n → C ₁₂ H _11-n Cl _n-1 + Cl ・ (2) This dechlorination reaction proceeds sequentially, and PCB passes through the low chlorinated compound to complete biphenyl. Dechlorinated and detoxified. The Cl radical combines with the H radical or the Cl radical to generate HCl or Cl ₂ .

[0010]

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 an experimental apparatus used in the method for treating an aromatic halogen compound of the present invention. In FIG. 1, 1 is a heating reactor containing soil, which is heated by a mantle heater 2 to a predetermined temperature. 3 is a catalyst packed bed, which can be heated by the heater 4, 6 and 7 are thermocouples for detecting the temperature inside 1, 3, 5 is a hydrogen inlet, and 9 is a ribbon heater. The condenser 8 is cooled by water 12, the condensate is put in the condensate receiver 10, and the non-condensate is exhausted through the activated carbon trap 11.

Next, using the glass experimental apparatus shown in FIG. 1, a soil treatment experiment containing PCB (KC-400) at a concentration of 3500 mg / kg was conducted under the following treatment conditions. Soil weight: 70 g (dry) Sodium hydrogen carbonate addition amount: 4.2 g Water addition amount: 30 cm ³ Catalyst weight: 10 g Catalyst layer temperature: 310 ° C. Soil heating temperature: 380 ° C. Heating time: 1 h Hydrogen concentration: 5% (nitrogen dilution) ) Space velocity (SV): 500h ^{-1 In the} catalyst layer (inner diameter 20 mm, length 40 mm), Pt is γ
-Alumina was filled with a pellet-shaped catalyst (diameter 3 mm, length 3 mm) supporting 0.5 wt%. After the treatment, 99.99% of the added PCB was removed from the soil, and P was added to the condensate.
No CB was detected.

Example 2 Using the glass experimental apparatus shown in FIG. 1, PCB (KC-
300) at a concentration of 2500 mg / kg, a soil treatment experiment was conducted under the following treatment conditions. Soil Weight: 70 g (dry) Water amount: 30 cm ³ catalyst weight: 10 g catalyst layer temperature: 320 ° C. Soil heating temperature: 335 ° C. The heating time: 1h hydrogen concentration: 5% (diluted with nitrogen) space velocity (SV): 500h ^{- One} catalyst layer (inner diameter 20 mm, length 40 mm) has Pd of γ
-Alumina was filled with a pellet-shaped catalyst (diameter 3 mm, length 3 mm) supporting 0.5 wt%. After the treatment, 99.8% of the added PCB was removed from the soil and PC was added to the condensate.
B was not detected.

Example 3 Using the glass experimental apparatus shown in FIG. 1, PCB (KC-
300) at a concentration of 2500 mg / kg, a soil treatment experiment was conducted under the following treatment conditions. Soil weight: 70 g (dry) Addition amount of sodium hydrogen carbonate: 4.2 g Water addition amount: 30 cm ³ Catalyst weight: 10 g Catalyst layer temperature: 320 ° C. Soil heating temperature: 335 ° C. Heating time: 1 h Hydrogen concentration: 5% (nitrogen dilution) ) Space velocity (SV): 500h ^-1 Pd is γ in the catalyst layer (inner diameter 20 mm, length 40 mm)
-Alumina was filled with a pellet-shaped catalyst (diameter 3 mm, length 3 mm) supporting 0.5 wt%. After the treatment, 99.99% of the added PCB was removed from the soil, and P was added to the condensate.
No CB was detected.

Example 4 Using the glass experimental apparatus shown in FIG. 1, PCB (KC-
300) at a concentration of 2500 mg / kg, a soil treatment experiment was conducted under the following treatment conditions. Soil weight: 70 g (dry) Potassium hydrogen carbonate addition amount: 4.2 g Water addition amount: 30 cm ³ Catalyst weight: 10 g Catalyst layer temperature: 320 ° C. Soil heating temperature: 335 ° C. Heating time: 1 h Hydrogen concentration: 5% (nitrogen dilution) ) Space velocity (SV): 500h ^-1 Pd is γ in the catalyst layer (inner diameter 20 mm, length 40 mm)
-Alumina was filled with a pellet-shaped catalyst (diameter 3 mm, length 3 mm) supporting 0.5 wt%. After the treatment, 99.99% of the added PCB was removed from the soil, and P was added to the condensate.
No CB was detected.

Example 5 Using the glass experimental apparatus shown in FIG. 1, PCB (KC-
300) at a concentration of 2500 mg / kg, a soil treatment experiment was conducted under the following treatment conditions. Soil weight: 70 g (dry) Sucrose added amount: 10 g Sodium hydrogen carbonate added amount: 4.2 g Water added amount: 30 cm ³ Catalyst weight: 10 g Catalyst layer temperature: 310 ° C. Soil heating temperature: 350 ° C. Heating time: 1 h Catalyst layer (Inner diameter 20 mm, length 40 mm)
-Alumina was filled with a pellet-shaped catalyst (diameter 3 mm, length 3 mm) supporting 0.5 wt%. After the treatment, 99.99% of the added PCB was removed from the soil, and P was added to the condensate.
No CB was detected.

[0016]

According to the conventional chemical treatment technique, even if the soil contaminated with aromatic halogen compounds such as PCB can be purified, expensive chemicals are added to the soil, so that not only the running cost is increased. There was a problem that unreacted chemicals and byproducts remained in the soil after the treatment. On the other hand, in the present invention, even if it is not added or added, since inexpensive sodium hydrogen carbonate is used, the running cost can be reduced, and the treated soil is produced by thermal decomposition of sodium hydrogen carbonate. Since only harmless sodium carbonate remains, the soil can be returned to the environment without problems after treatment. Further, in the present invention, aromatic halogen compounds such as PCB volatilized from the soil are decomposed by the catalyst layer provided in front of the condenser to be harmless, and the post-treatment of condensed water is not required, so that the apparatus can be made compact. It is possible to significantly reduce the processing cost while being removed. In the conventional example in which the catalyst is added to the soil, PC attached to the soil
The contact efficiency between the aromatic halogen compound such as B and the catalyst is low,
After the treatment, the catalyst and the reaction product remain in the soil, but when the catalyst is reacted with the catalyst in a gaseous state as in the present invention, the contact efficiency is high, and the effect that the catalyst and the reaction product do not remain in the soil is obtained. can get.

[Brief description of drawings]

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

[Explanation of symbols]

1: heating reactor, 2: mantle heater, 3: catalyst,
4: heater, 5: hydrogen inlet, 6: thermocouple, 7: thermocouple, 8: condenser, 9: ribbon heater, 10: condensate receiver, 11: activated carbon trap, 12: water,

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 23/44 ZAB A 23/46 ZAB A 23/755 B09B 3/00 ZAB B09C 1/02 1 / 08 B01J 23/74 321 A B09B 3/00 ZAB 304 K

Claims (5)

[Claims] 1. A soil contaminated with an aromatic halogen compound is heated to 250 to 400 ° C., and a gas containing the volatilized aromatic halogen compound is added in the presence of hydrogen gas to the gas.
A method for treating an aromatic halogen compound contained in soil, which comprises contacting with a catalyst at 00 to 400 ° C. 2. A soil contaminated with an aromatic halogen compound is added with an alkali metal hydrogen carbonate and water and mixed, and then the soil is heated to 250 to 400 ° C. to volatilize aromatics. A method for treating an aromatic halogen compound contained in soil, comprising bringing a gas containing a halogen compound into contact with a catalyst at 200 to 400 in the presence of hydrogen gas. 3. The method of treating an aromatic halogen compound contained in soil according to claim 2, wherein the alkali metal hydrogen carbonate is sodium hydrogen carbonate or potassium hydrogen carbonate. 4. The catalyst is characterized in that at least one selected from platinum, palladium, ruthenium, rhodium, nickel or oxides thereof is supported on a metal oxide carrier. Item 4. A method for treating an aromatic halogen compound contained in the soil according to item 1, 2 or 3. 5. The hydrogen gas has a concentration of 1 in the contact gas.
% (Capacity) or more exists, Claims 1-4 characterized by the above-mentioned.
The method for treating an aromatic halogen compound contained in the soil according to any one of 1.