JPH04279178A - Decomposition of organic halogen compound - Google Patents

Abstract

PURPOSE:To provide a method for decomposing an organic halogen compound, especially polychlorine aromatic compound by making the compound harmless through causing the compound to react with water vapor under plasma discharge. CONSTITUTION:The title method causes an organic halogen compound to react with water vapor under plasma discharge and decomposes the compound by dehydrogenation reaction through generation of hydrogen halide, reactional change of carbonaceous material into carbon dioxide, etc.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention relates to polychlorinated biphenyl (PCB), dichlorodiphenyltrichloroethane (D
Decomposes dangerous organic halogen compounds such as DT),
It concerns a method of rendering it harmless.

0002

BACKGROUND OF THE INVENTION It is well known that the disorderly disposal of various organic compounds containing halogen elements destroys the environment and poses a danger to public health. Polychlorinated biphenyls, trichlorophenoxyacetic acid, dichlorodiphenyltrichloroethane, etc. were once useful compounds, but due to their toxicity and accumulative properties, they have been found to be persistent environmental hazards, and safe and effective treatment methods have been developed. has come to be needed. Since the carbon-halogen bonds inherent in organic halogen compounds are extremely stable, they have a high resistance to biological decomposition, and cannot be effectively decomposed using general chemical decomposition. Depending on the known methods, such as catalytic hydrogenation dehalogenation, molten salt reaction, alkali metal reduction, and supercritical hydroxylation, only partial dehalogenation usually occurs, and expensive reagents and wide range of temperature control are required. ,
This method requires an inert atmosphere, complicated equipment, and consumes a large amount of energy.

[0003] The method of thermal decomposition is currently considered to be the closest to practical use, but the unburned hydrocarbons produced in the furnace during this process react with chlorides, oxygen, etc., producing highly toxic dioxins and It produces harmful intermediate products and is likely to cause secondary pollution. Therefore, the decomposition and removal rate of hydrocarbons is 99.9999.
% or more, it is necessary to set the heating conditions to a high temperature of 1,400° C. or higher and a residence time of 1.5 seconds or more. The improved electric reactor method, plasma arc method, rotary cylindrical furnace combustion method, etc. are expected to be pyrolysis methods that meet these conditions.

In the improved electric reactor method, PCBs, dioxins, etc. are decomposed by rapid electrical heating to about 2,200° C. using thermal radiation in the near-infrared region in a nitrogen atmosphere. The plasma arc method uses a plasma arc to spray a liquid substance into a gas stream ionized by plasma.
It decomposes in a microsecond order at a high temperature of 0°C. However, these methods require a huge amount of energy for decomposition, and are not suitable for large-scale processing because they require considerable cost to prevent corrosion damage to equipment due to hydrogen chloride generated at high temperatures. According to the rotary cylindrical furnace combustion method, the heat recovery efficiency is high, but there remains the problem of preventing damage to the equipment due to hydrogen chloride generated at high temperatures.Furthermore, since the combustion temperature is relatively low, it is difficult to recover even if the residence time is long. The drawback is that there is a large possibility of generation of dioxins due to incomplete combustion.

[0005]

[Problems to be Solved by the Invention] As mentioned above, conventional thermal decomposition methods require high temperatures to completely decompose carbonaceous substances containing organic halogen compounds.
This caused extremely low energy efficiency and damage to the equipment due to hydrogen halide. On the other hand, decomposition methods using chemical methods can decompose at relatively low temperatures, but they have drawbacks such as requiring expensive reagents, incomplete decomposition, and requiring a relatively long time for the reaction. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for rapidly dehalogenating and decomposing organic halogen compounds at relatively low temperatures, which has significant advantages over the conventional methods described above.

[0006]

[Means for Solving the Problems] In order to achieve the above object, in the present invention, an organic halogen compound is reacted with water vapor under plasma discharge, and a dehalogenation reaction is performed by producing hydrogen halide, and carbonaceous carbonate is produced. It is decomposed by gasification reaction etc.

[0007]

[Operation] Plasma discharge is preferably performed in a nitrogen stream, but it can also be applied in an air stream. Atmospheric gas temperature is several thousand degrees Celsius
Although it can be applied from a high temperature of , it is preferable to use it at around room temperature. Even if the atmospheric gas temperature is low, the temperature of the ions excited and produced by the plasma is high, at several 1,000 degrees Celsius, so that the ionized reaction gas causes a rapid decomposition reaction. As the plasma, low-frequency discharge plasma, high-frequency discharge plasma, microwave discharge plasma, etc. can be used, and among these, high-frequency discharge plasma is preferred because it does not require direct insertion of electrodes and has high plasma generation efficiency.

[0008] The organic halogen compound is sprayed into the gas stream together with water vapor. If spray injection is difficult, the same effect can be achieved by injecting it in the form of a powder, droplets, thin film, etc. It is necessary that the water vapor is in excess of the reaction equivalent; if this amount is small, secondary pollution is likely to occur due to intermediate harmful reaction products. The generated hydrogen halide is highly corrosive, but since the temperature is low, it has many corrosion-resistant materials that can be used industrially, and can be easily removed by passing it through an alkaline layer.

[0009]

[Example 1] Nitrogen was flowed at a flow rate of 2 to 5 l/min into a flow-through reaction test apparatus equipped with a plasma generator, and 13.
Plasma was generated using a high frequency of 56 MHz and 300 W. The temperature of the electrode portion at this time was room temperature to 100° C., and the residence time of nitrogen gas in the plasma was 1/10 second or less. The respective concentrations of water and PCB (tetrachloride) are 4
As a result of spraying and reacting with nitrogen as a carrier so that the concentration was 0,000 ppm and 2,000 ppm, no PCB was detected in the exit gas.
In addition to hydrogen halides, carbon dioxide gas and water were detected.

0010

[Example 2] Nitrogen was flowed at a flow rate of 2 to 5 l/min into a flow reaction test apparatus equipped with a plasma generator, and 13.
A high frequency electric field of 56 MHz and 300 W was applied between the electrodes to cause plasma discharge. At this time, the temperature of the electrode part is room temperature to 100℃, and the residence time of nitrogen gas in the plasma is 1
/10 seconds or less. Water and DDT (powder) at concentrations of 50,000 ppm and 2,000 ppm, respectively
As a result of spraying nitrogen as a carrier and injecting it into plasma and causing a reaction, no DDT was detected in the exit gas, but carbon dioxide gas, water, etc. were detected in addition to hydrogen chloride.

The method for decomposing organic halogen compounds according to the present invention can be used to decompose not only polychlorinated aromatic compounds such as PCB and DDT shown here, but also accumulative toxic substances such as dioxins and benzpyrenes, and fluorine-containing compounds. It goes without saying that it can be applied to a wide range of decompositions of harmful organic halogen compounds, such as decomposition of bromine-containing compounds.

0012

Effects of the Invention As described above, the present invention decomposes organic halogen compounds by reacting with water vapor under plasma discharge, and has the following effects and is widely used for environmental conservation, public health, and industrial purposes. Extremely effective. (1) At around room temperature, dangerous compounds such as PCBs and DDT that pose problems in waste disposal can be rapidly decomposed and rendered harmless. (2) Unlike the thermal decomposition method, there is no risk of secondary pollution caused by the formation of dioxins, and it can be completely decomposed. (3) Since the temperature is low, there is little energy loss, and damage to equipment due to generated hydrogen halide can be suppressed, and there is no problem in finding structural materials that can be used industrially, so it is easy to put into practical use.

Claims (1)

[Claims] 1. A method for decomposing organic halogen compounds, particularly polychlorinated aromatic compounds, which comprises reacting the organic halogen compounds with water vapor under plasma discharge.