JP2001328950A - Method for decomposition of halide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for the decomposition of halides effective for efficiently decomposing various halide gases such as organic halides and inorganic halides to a harmless decomposition product. SOLUTION: An organic halide and/or inorganic halide is decomposed in a combustion flame containing an alkali metal compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to various halides such as organic halides containing fluorine, chlorine, bromine or hydrogen such as chlorofluorocarbon, perfluorocarbon and chlorocarbon, and inorganic halides such as NF ₃ and SF _6. The present invention relates to a halide decomposition method for efficiently decomposing and detoxifying a gas.

[0002]

2. Description of the Related Art Chlorofluorocarbon (CFC) is
It has low toxicity and is extremely useful for applications such as dry cleaning agents, solvents for various applications, foaming agents, and energy conversion working fluids such as refrigerants.On the other hand, chlorofluorocarbons released into the atmosphere emit ultraviolet rays from sunlight when they reach the stratosphere. And destruction of the ozone layer is a problem. For this reason, specific fluorocarbons, which are particularly destructive to ozone, have been totally abolished since 1996 due to the phased use regulations.

[0003] The behavior of chlorofluorocarbons in the atmosphere has been further extended to a major problem of global warming, and the problem of perfluorocarbons (PFCs) as well as chlorofluorocarbons has been pointed out as a substance. The consumption of perfluorocarbon is gradually increasing industrially for uses such as an etching agent and a dry cleaning agent in the semiconductor industry. The thermal emission characteristics of perfluorocarbons that cause the greenhouse effect are similar to those of chlorofluorocarbons, but less perfluorocarbons are used as chlorofluorocarbons because of their long lifetime in the atmosphere. That's why. Perfluorocarbons are very stable chemically and have the action of decomposing them in the atmosphere.
It is said that there is only ultraviolet light having a wavelength of 130 nm or less which is irradiated only in a very high layer of the atmosphere. It has been estimated that the lifetime of chlorofluorocarbons after being released into the atmosphere is several hundred years, while that of perfluorocarbons is estimated to be thousands to tens of thousands of years, and it is said that the effect on the greenhouse effect is large. ing.

[0004] Chlorofluorocarbons that, when released into the atmosphere, destroy the ozone layer, and perfluorocarbons that are not permanently destroyed but cause global warming, are therefore destroyed in the final stages of equipment that uses them. Is required.

As for the decomposition of chlorofluorocarbon and perfluorocarbon, at present, a method of burning and decomposing with a combustion gas such as propane or methane (combustion method), using a catalyst under a high steam pressure in a temperature range of 400 to 700 ° C. Contact and decomposition method (catalytic method), 50
Methods such as a method of decomposing by contacting an alkali or the like in a temperature range of 0 ° C. to 900 ° C. (thermochemical decomposition method) and a method of decomposing in high-frequency plasma (plasma method) are being studied.

However, both methods have drawbacks. Combustion method can easily obtain the high temperature required for decomposition, and can decompose a large volume of halide gas.
On the other hand, the burden on the environment due to the production of nitrogen oxides and carbon dioxide by combustion is large. In addition, since a higher combustion temperature is required for a hardly decomposable gas, a larger amount of fuel gas is required. Can decompose PFC and CFC at a relatively low temperature, but it requires replacement due to deterioration of the catalyst, and since many catalysts generate acidic substances, corrosion of the reactor by acid poses a problem. . The thermochemical decomposition method does not involve the production of an acid by immobilizing a halide, but the exchange of a reactant is indispensable. In the plasma method, it is difficult to decompose a large volume of gas at a time, and requires a lot of energy.

[0007]

Under these circumstances, one of the methods that are currently being industrially studied as a system for decomposing halides such as CFC and PFC is considered.
One is the combustion method. Due to the combustion method, many C
Although FC and PFC are decomposed, it is difficult to decompose substances having high chemical stability, such as CF ₄ , even by the combustion method. As a method of accelerating the decomposition, increasing the temperature of the combustion flame can be cited, and a method using a gas having a higher oxygen concentration than air as a supporting gas is adopted.
However, it is difficult to obtain a decomposition rate close to 100% for CF ₄ even in a combustion flame using oxygen as a combustion supporting agent. In general, when the combustion temperature is high, N ₂ used as a diluent gas of PFC and oxygen of the supporting gas react with each other, so that the generation rate of harmful nitrogen oxides such as N ₂ O is increased and the load on the environment is reduced. Becomes larger. In addition, in order to use a gas having an oxygen concentration higher than that of air as a combustion supporting agent, equipment for supplying oxygen, equipment for producing oxygen, and the like are required as additional equipment. For this reason, development of a method for decomposing PFCs such as CF ₄ and C ₂ F ₆ efficiently without imposing a burden on the environment has been desired.

[0008]

[Specific means for solving the problem]
As a result of intensive studies on a method for efficiently decomposing organic halides and / or inorganic halides by the combustion method, it was found that it is effective to add a decomposition aid to the combustion flame, and particularly to combust alkali metal compounds. The present inventors have found that it is effective to add as a decomposition aid in a flame, and have reached the present invention.

That is, the present invention is characterized in that an alkali metal compound coexists in a combustion flame to decompose an organic halide and / or an inorganic halide, and in particular, the alkali metal compound is an alkali metal hydroxide. And a method for decomposing a halide.

In the present invention, the organic halide is C
Cl_TwoF_Two, CCl_ThreeF, CCl_TwoFCClF_Two, CCIF_Two
CF_Three, CCIF_ThreeChromium consisting of carbon, chlorine, fluorine, etc.
Lofluorocarbon compound, CH_ThreeF, CH_TwoF_Two, CH
F_Three, C_TwoH_TwoF_Four, C_TwoH_FourF_TwoSuch as carbon, hydrogen, fluorine
Consisting of a hydrofluorocarbon compound, CF_Four, C_TwoF
₆, C_ThreeF₈, C_FourF_Ten, C_FiveF₁₂, C₆F₁₄, C_FiveF₈Etc charcoal
Perfluorocarbon compound consisting of nitrogen and fluorine, CC
l_Four, C_TwoCl₆And the like. Ma
In addition, the inorganic halide is NF_Three, SF₆Inorganic hood such as
Refers to compound gas. In the present invention, these compounds
Is N_Two, He or the like may be mixed.

The decomposition aid used in the present invention is preferably an alkali metal compound. Examples of the alkali metal compound include elements of Group Ia of the periodic table (Li, Na, K, Rb,
Hydroxides, oxides, hydrides, carbonates comprising Cs)
Chlorates, perchlorates, halides, sulfites, sulfates, persulfates, nitrites, nitrates, phosphates, organic acid salts, and the like. One or more of these compounds are combined. Can be used.

[0012] Among the alkali metal compounds, an alkali metal hydroxide is most desirable. The reason is that alkali hydroxides are highly reactive with halides even in combustion flames with low temperatures. Further, after the halide is decomposed, carbon dioxide gas, which is a greenhouse gas, is generated. The carbon dioxide gas and the hydroxide react with each other to reduce greenhouse gas emissions. Particularly, potassium hydroxide is most preferred.

Next, as a method of supplying a decomposition aid to the combustion gas, a powder of the decomposition aid is dispersed and mixed in advance with a fuel or a supporting agent and supplied, or the powder, an aqueous solution thereof, or an organic solvent is supplied. A method of spraying and spraying a dissolved or dispersed solution or the like can be used.

At a temperature of 900 ° C. or higher, most of the alkali metals have a vapor pressure on the order of KPa or higher. For example, when the temperature of each compound when showing a vapor pressure of 1.33 KPa is shown in parentheses following each chemical symbol, KF (1039 ° C.), KI (887 ° C.), K
OH (863 ° C), KBr (982 ° C), KCl (96
8 ° C), NaF (1240 ° C), NaI (903 ° C),
NaOH (897 ° C), NaCl (1017 ° C), Li
Br (888 ° C.), LiCl (932 ° C.), LiF (1
211 ° C.) and LiI (841 ° C.). Also, K ₂
CO ₃ has a dissociation pressure of 1.10 KPa at 1000 ° C. With respect to the compounds that evaporate in the flame, it is also effective to install a heat-resistant container containing the compound in the vicinity of or in the flame and to diffuse the decomposition aid vaporized by the heat of the flame into the flame. .

Further, the alkali metal hydroxide is
It melts even at a low melting point of 270-450 ° C. For these hydroxides, a container containing the compound is placed near the flame, the flame is preheated or the container is heated with a heater or the like to melt the decomposition aid, and the liquefied decomposition aid is added to the flame. It is also effective to use an implementation method that spreads the data.

In the present invention, there are no particular restrictions on the fuel and the supporting agent used.
Propane, natural gas, gaseous fuels such as CO, methanol,
Although liquid fuels such as gasoline, light oil, heavy oil, and kerosene can be used, hydrogen and methane are particularly desirable, and hydrogen is most desirable. For that reason, alkali metal hydroxides are known as strong carbon dioxide absorbents, and alkali metal hydroxides are added to combustion gases that generate a large amount of carbon dioxide, for example, combustion gases using LPG as fuel. This is because, when added, the hydroxide of the alkali metal becomes a carbonate, and in a low-temperature combustion flame such as an air flame, the reaction activity with the halide decreases.

In addition, air, oxygen, air having a high oxygen concentration, or other oxidizing gas can be used as the combustion supporting agent. In particular, when hydrogen is used as fuel, it is preferable to use air rather than oxygen. The advantage is that the combustion temperature can be lowered,
This is because generation of nitrogen oxides such as N ₂ O can be suppressed and special supply equipment is not required. The fuel and the supporting agent are mixed and ignited to obtain a combustion flame, but there is no particular limitation on the mixing ratio of the fuel and the supporting agent.
Premixed combustion or diffusion combustion may be used.

[0018]

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

Examples 1 to 27 The outline of the combustion test apparatus will be described. Gas burner for hydrogen gas as combustion device (inner diameter of outlet: 10 mm)
Was used. Fuel gas pipes, supporting gas pipes, and supply pipes for cracked gas were incorporated in the gas supply ports, and flow meters were installed in each of the pipes to control the gas flow rate. Also,
The outlet of the gas burner was fixed vertically upward, and a platinum plate was placed above the gas outlet to supply a decomposition aid.

Next, the test method will be described. First, the fuel gas and the supporting gas are supplied to the line to ignite the burner, and then the supply of the halide gas is started. After the supply of the decomposition aid is stabilized and the flame is sufficiently stabilized, the combustion gas is sampled. The sampling method is that a SUS sampling tube connected to a vacuum metal container is set at the top of the flame, the valve provided on the tube is opened, and the combustion gas is collected in the container. Analysis is performed by FT-IR and gas chromatography to determine the decomposition rate of the halide gas.

The test conditions and results are shown in Table 1. In addition,
The calculation of the decomposition rate of the halide was calculated by the following equation.

Decomposition rate (%) = (1− (amount of halide gas in combustion gas (flow rate)) / [amount of halide gas at burner inlet (flow rate)]) × 100 where halide gas in combustion gas The quantity (flow rate)
Combustion gas amount (flow rate) x halide gas concentration in combustion gas.

Comparative Examples 1 to 4 Using the same test apparatus as in the above-described examples, tests were conducted in the same manner as in the examples, without charging the reaction aid into platinum dishes. Table 1 shows the conditions and results of the test.

[0024]

[Table 1]

[0025]

According to the method of the present invention in which a decomposition aid is added to a combustion gas to burn and decompose a halide, the halide can be decomposed efficiently and the ozone layer destruction and global warming can be prevented. Become.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2E191 BA01 BA15 BC01 BD12 4H006 AA05 AC24 BA02 BA28 BA29 BA30 BA32 BA34 BA35 BA36 BA37 BC10 BE20 BE30 EA02

Claims (2)

[Claims] 1. A method for decomposing a halide, comprising decomposing an organic halide and / or an inorganic halide in the presence of an alkali metal compound in a combustion flame. 2. The method according to claim 1, wherein the alkali metal compound is an alkali metal hydroxide.