JP2681034B2 - How to make CFCs harmless - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detoxifying chlorofluorocarbon.

[0002]

2. Description of the Related Art Freon has been used in large amounts in various refrigerants, foams, sprays, etc. because it is very stable and has little toxicity to the human body. However, since it has recently been discovered that CFCs destroy the ozone layer, their manufacture and use are being discontinued worldwide. For example, the Montreal Protocol stipulates that the production of CFCs should be stopped by the end of 1995. In addition, studies have been conducted to detoxify a large amount of CFCs produced so far, but since CFCs are extremely stable, a simple decomposition method has not been found, and a method for decomposing and detoxifying a large amount of CFCs easily and inexpensively has been proposed. Researchers all over the world are struggling with the development.

Recently, attention has been paid to a method of introducing CFCs together with fuel and air into a rotary kiln of a cement factory or a solid waste treatment factory and decomposing the CFCs in a flame formed by the fuel and air. In this method, it is presumed that CFCs that have come into contact with high-temperature flames in the rotary kiln are decomposed by thermal decomposition, reduction with fuel gas, high-temperature hydrolysis, and the like. This method has an advantage that a large amount of CFCs can be processed with a slight modification to existing equipment. However, in this method, since fuel, air, and CFC coexist in a high-temperature environment, there is a danger pointed out by Urano et al. That a highly toxic dioxin is produced in a minute amount [Resource environment measures, 30-7 P. 609 (19
94)].

The present inventors have conducted a search for a substance that reacts exothermically with Freon and found that silane reacts violently with Freon (Proceedings of the 32nd Combustion Symposium P.561; 1994). November). And
The present inventor has demonstrated that when a mixed gas of freon and silane is heated in a pressure vessel, an explosive reaction occurs instantly, and the freon is efficiently decomposed by this reaction (the above-mentioned announcement).
However, in this demonstration experiment, since CFCs are decomposed and rendered harmless by reacting CFCs and silane in a batch process in a pressure vessel, if this method is directly carried out as a CFC decomposition and detoxification method, the efficiency will be improved due to the batch system. In addition to this, a pressure vessel having high strength must be used, which is problematic in practical use.

[0005]

An object of the present invention is to provide a method for detoxifying chlorofluorocarbon that can be industrially advantageously carried out.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. That is, according to the present invention, the chlorofluorocarbon and the silane are subjected to a combustion reaction, the high temperature gas obtained in this combustion reaction step is cooled, and then contacted with alkaline water to cause the halide, chlorine and carbon contained in the gas. Is provided in the alkaline water, while at least a part of the gas components not captured in the alkaline water is circulated in the combustion reaction step.

The CFC used as a raw material in the present invention is CCl ₃ F (CFC-1), which is called a specific CFC.
1), CCl ₂ F ₂ (CFC-12), C ₂ Cl ₃ F ₃ (CFC-113), C ₂ Cl ₂ F ₄ (CFC-114), and C ₂ ClF ₅ (CFC-115), CClF ₃ (CFC-13) that destroys the ozone layer as well as CFCs
Etc. are collectively referred to as CFC. Also,
Fluorinated chlorinated hydrocarbons containing hydrogen atoms in the molecule collectively called HCFC, for example C ₂ H ₃ C called alternative CFC
Any of lower halogenated carbons and lower halogenated hydrocarbons including IFF ₂ (Freon-142b) and the like and containing fluorine and chlorine in the molecule can be used as the raw material to be treated in the present invention. Examples of the silane used in the present invention include monosilane and disilane.

The combustion reaction between chlorofluorocarbon and silane in the present invention explosively proceeds at high temperature, and the chlorofluorocarbon is almost completely decomposed in a short time. The main reactions of CFCs and silanes used in the present invention are shown in Table 1, and each reaction has a large amount of heat generation. The reaction products are slightly different depending on the type of chlorofluorocarbon. When the amount of silane is large, the amount of hydrogen generated is large, and when the amount of chlorofluorocarbon is large, the amount of chlorine generated is large. The calorific value in Table 1 is the calorific value per mol of silane.

[0009]

[Table 1]

When a Freon and a silane are subjected to a combustion reaction,
The proportion of CFC used is usually 20 to 90 vol%, preferably 50 to 80, based on the total amount of CFC and silane.
vol%. The specific usage ratio of this CFC should be determined according to the type of CFC. For example, CFC 11
In the case of, 40 to 80 vol%, preferably 45 to 6
0% by volume, and in the case of CFC 13 is 40 to 80
vol%, preferably 45 to 60 vol%, and in the case of CFC 113, it is 25 to 40 vol%, preferably 30 to 40 vol%. When reacting CFCs with silane, the reaction rate (decomposition rate) of CFCs should be kept at 98% or more, preferably in the range of 99 to 99.9%.
Further, nitrogen gas can be mixed as a diluent gas into the mixture of freon and silane. The mixing amount of the diluent gas is 50 to 90 vol%, preferably 60 to 80 vol% in the total gas mixture.

In the case of reacting CFC with silane, a conventionally known combustion burner is used as the reaction device. Freon and silane can be continuously reacted by supplying CFC and silane to the combustion burner, ejecting a mixed gas of both from the tip nozzle of the burner, and igniting the mixed gas.

Next, the present invention will be described in detail with reference to the drawings. FIG. 1 shows an example of a flow sheet for carrying out the method for detoxifying chlorofluorocarbon of the present invention. In this figure, 1
Is a gas mixer, 2 is a combustion furnace, 3 is a heat exchanger, 4 is a cooling device, 5 is an alkali cleaning device, and 6 is a dehumidifying device.

In FIG. 1, Freon and silane are supplied to the gas mixer 1 through lines 11 and 12, respectively, where they are mixed. Further, unreacted CFC from the dehumidifier 6 is supplied to this mixer through the line 28.
The mixed gas from the mixer 13 is supplied to the combustion furnace 2 through the line 13. In the combustion furnace 2, the mixed gas is
It is ejected from the tip of the burner into the furnace, where it reacts combustibly.

The high temperature gas produced in the combustion furnace 2 is discharged as exhaust gas from the inside of the furnace through the line 14, introduced into the heat exchanger 3, and cooled. In the heat exchanger 3, a cooling medium such as water or an organic liquid is introduced through the line 15 and the heated cooling medium is discharged through the line 16. The heat exchanger 3 can be a waste heat boiler, in which case water is used as the cooling medium and hot steam is discharged from the line 16. In this heat exchanger 3, the high temperature exhaust gas of 900 ° C. or higher discharged from the combustion furnace is cooled to 300 ° C. or lower, preferably 250 ° C. or lower. The cooled exhaust gas is introduced into the cooling device 4.

In the cooling device 4, the cooling water from the line 19 is sprayed in the form of fine droplets through the spray device a, and the exhaust gas introduced into the cooling device 4 comes into contact with the fine droplets of the cooling water. And then cooled further. Water having a pH of 7 to 10 or alkaline water is used as the cooling water.
The alkaline water can be obtained by adding an alkaline substance such as sodium hydroxide or calcium hydroxide to water. The exhaust gas after coming into contact with the cooling water is introduced into the alkali cleaning device 5 through the line 18.

In the alkaline cleaning device 5, the alkaline water AW is sent to the spray device b through the pump 20, the line 21 and the line 22, and is sprayed from there as fine droplets. In addition, alkaline water is replenished to this apparatus through a line 23. The exhaust gas introduced into the alkali cleaning device 5 contacts the alkaline water here.

The exhaust gas from the combustion furnace 2 is, as can be seen from the reaction formula shown in Table 1, silicon tetrafluoride (SiF ₄ ),
It is composed of halides such as hydrogen fluoride (HF) and hydrogen chloride (HCl), chlorine (Cl ₂ ), carbon, and unreacted CFCs. In the cooling device 4,
Some of these components are trapped in the cooling water and removed.
In this case, the substance removed is silicon tetrafluoride,
Examples thereof include halides such as hydrogen fluoride and hydrogen chloride, chlorine, carbon and the like. Silicon tetrafluoride is hydrolyzed to HSi
It becomes O ₃ and HF. The cooling water that has captured these substances is discharged through the line 19 '.

On the other hand, in the alkaline cleaning device 5, the remaining substances not captured and removed by the cooling water in the cooling device 4 are removed. That is, hydrogen fluoride, hydrogen chloride and chlorine all react with the alkaline water and are captured. In addition, the carbon in the exhaust gas, due to contact with alkaline water,
It is captured in alkaline water and suspended in alkaline water. The alkaline water that has captured the substances described above is discharged through the line 24.

As described above, all the harmful substances other than unreacted CFCs in the exhaust gas discharged from the combustion furnace 2 are removed from the exhaust gas. The gaseous substances in the alkali cleaning device 5 are discharged from the alkali cleaning device 5 through the line 25. This exhaust gas is composed of unreacted CFC, hydrogen, water vapor, and carrier gas when carrier gas is used. This exhaust gas can be released to the atmosphere after a simple defreon treatment, for example, contact treatment with an adsorbent that exhibits adsorption to freon, such as activated carbon, and then released into the atmosphere. Dehumidifier 6 filled with solid desiccants such as zeolite, zeolite, and lime
It is preferable that the gas is introduced into the gas mixer 1 to remove water in the exhaust gas, and then is circulated through the line 28 to the gas mixer 1.
In this case, if necessary, a part of the circulating gas may be supplied to the line 2
It is extracted through 7 and subjected to defluorocarbon treatment such as adsorbent treatment, and then released to the atmosphere.

In the flow sheet shown in FIG. 1, the gas mixer 3 and the dehumidifying device 6 can be omitted, and one of the heat exchanger 3 and the cooling device 4 can be omitted in some cases. Further, the alkali cleaning device may be a packed tower of a packing material such as Raschig ring. In the case of a packed tower, the exhaust gas comes into countercurrent contact with the flowing alkaline water, and the harmful substances in the exhaust gas are captured by the alkaline water and removed from the exhaust gas.

[0021]

EFFECTS OF THE INVENTION According to the present invention, since CFCs are decomposed by burning reaction with silane to decompose them, CFCs can be decomposed efficiently, and the exhaust gas from the combustion furnace heat-exchanges them. Thermal energy can be recovered. Furthermore, in the present invention, since the exhaust gas is brought into contact with the alkaline water, not only the halide and chlorine contained in the exhaust gas but also the carbon can be captured by the alkaline water. Furthermore, in the present invention, unreacted CFCs can be completely detoxified by circulating the CFCs for combustion reaction treatment without discharging CFCs out of the system.

[Brief description of the drawings]

FIG. 1 shows an example of a flow sheet for carrying out the method of the present invention.

[Explanation of symbols]

 1 Gas Mixer 2 Combustion Furnace 3 Heat Exchanger 4 Cooling Device 5 Alkaline Cleaning Device 6 Dehumidifying Device

Claims (1)

(57) [Claims] 1. A fluorocarbon and a silane are combusted to react with each other, and the high temperature gas obtained in this combustion reaction step is cooled, and then contacted with alkaline water to remove halides, chlorine and carbon contained in the gas from the alkali. A method for detoxifying chlorofluorocarbon, characterized in that it is trapped in water, while at least a part of a gas component not trapped in alkaline water is circulated in the combustion reaction step.