JP3216868B2 - Decomposition method of halide gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is, chlorofluorocarbons, perfluorocarbons, chlorocarbons such as fluorine, chlorine, or an organic halogen compound containing bromine, and various halide gas inorganic halogen compounds such as SF ₆ efficiently decomposed Regarding detoxifying methods.

[0002]

2. Description of the Related Art Chlorofluorocarbons (CFCs) have low toxicity and are extremely useful for applications such as dry cleaning agents, solvents for various uses, foaming agents, and energy conversion working fluids such as refrigerants, but chlorofluorocarbons released into the atmosphere are used. When the fluorocarbon reaches the stratosphere, it is decomposed by the ultraviolet rays of sunlight, and this destructs the ozone layer. Since then, an international plan has been in progress to abolish specific fluorocarbons, which are highly destructive to ozone, since 1996, because of their phased use restrictions.

[0003] The behavior of chlorofluorocarbons in the atmosphere is about to spread to the larger problem of global warming. At that time, as a base substance, chlorofluorocarbons and perfluorocarbons (PFC) are used.
Has also been pointed out. 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. It is said that perfluorocarbons are chemically very stable, and the only thing that has the action of decomposing them in the atmosphere is ultraviolet rays having a wavelength of 130 nm or less which are 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 which, when released into the atmosphere, destroy the ozone layer, perfluorocarbons which are not permanently destroyed but cause global warming, etc., are therefore destroyed at the final stage of equipment using them. It is demanded that it be lost.

The destruction of chlorofluorocarbons and perfluorocarbons has been conventionally carried out by the following four methods [Koichi Mizuno, Rust Prevention Management, 11, p. 7-13 (199
2), Kohei Urano, Review of Chemistry, No. 11, p144-1
58 (1991)] has been mainly studied or put into practical use. A method of decomposing by reacting in the presence of water in high-frequency plasma exceeding 10,000 ° C. This method has the disadvantage that the equipment becomes large and the investment amount increases. A method of hydrolyzing with high-temperature and high-pressure water exceeding the critical point. This method has the disadvantage that the equipment becomes large and the investment amount increases. A method in which chlorofluorocarbon and perfluorocarbon are circulated through a catalyst layer kept at a high temperature to decompose them. This method has the disadvantage that the catalyst deteriorates.
Direct decomposition by combustion gas or heat from heater. This method has a drawback that, for example, in the case of CF ₄ which is a perfluorocarbon, a high temperature of 1,000 to 1,200 ° C. is required and the material of the reactor is deteriorated.

[0006] Both methods have drawbacks,
Chlorocarbons in question as a source of contamination itself groundwater and soil, inorganic halogen compounds such as SF ₆ with a global warming effect like are also included, better degradation detoxification techniques such as halide gas is obtained ing.

[0007]

Meet the demands on THE INVENTION try to problem solving] Such techniques, the present invention is, chlorofluorocarbons, perfluorocarbons, chlorocarbons such as fluorine, chlorine or organohalogen compound containing bromine, inorganic halogen such as SF ₆ Provided is an improved method of thermally decomposing various halide gases such as compounds at a lower temperature using a more compact apparatus and detoxifying the gases, thereby preventing these halide gases and the like from being released into the atmosphere. I do.

[0008]

To solve the above problems, the present inventors have conducted various studies on novel auxiliaries, and as a result, have found that the oxides or hydroxides of alkaline earth compounds can be converted to water. The present inventors have found that a product obtained by adding potassium oxide is extremely useful for thermally decomposing and rendering harmless a halide gas and the like, and have accomplished the present invention.

That is, according to the present invention, an organic halide gas or SF ₆ gas is mixed with a potassium hydroxide content of 0.05%.
Contacting potassium hydroxide and an alkaline earth metal oxide or a mixture of alkaline earth metal hydroxides in a temperature range of 300 to 900 [deg.] C. in a range of from about 40% by weight to about 40% by weight. To provide a decomposition method.

[0010] halide gas of interest in the present invention, chlorofluorocarbons, perfluorocarbons, chlorocarbons such as fluorine, chlorine, or an organic halogen compound containing bromine, in various halide gas inorganic halogen compounds such as SF ₆ is there.

Although the method of the present invention is basically a pyrolysis method, it is characterized in that the temperature required for the decomposition is much lower than that of the conventional method. In addition, in the conventional thermal decomposition method and the catalytic decomposition method, since the decomposition product is still a harmful substance, it is necessary to add a separate detoxification step after the decomposition step, which hinders downsizing of the apparatus and cost reduction. However, on the other hand, the present invention solves both of these problems because thermal decomposition and detoxification proceed simultaneously.

It is known that an oxide or hydroxide of an alkaline earth compound which is a main component of a decomposition aid such as a halide gas in the present invention is effective as a decomposition aid even if it is simple. However, in simple terms, the temperature required for decomposition was high and the material of the device was damaged, so that it could not be said that it was a practical decomposition aid. The inventors of the present invention have made intensive studies on the improvement of the chemical composition based on alkaline earth compound oxides, and found that potassium hydroxide as a second component has an effect of lowering the decomposition temperature. The reaction mechanism of the mixture of potassium hydroxide and the oxide or hydroxide of the alkaline earth compound is not clear, but the reaction mechanism of decomposing the halide gas and the like at a low temperature is not clear. In this case, since almost no effect is recognized, the effect is specific to potassium hydroxide. On the other hand, as for the oxides or hydroxides of the alkaline earth compounds as the main components, any of calcium oxide, calcium hydroxide, magnesium oxide and magnesium hydroxide was found to have a combined effect with potassium hydroxide.

[0013] The compounding method of potassium hydroxide with an oxide or hydroxide of an alkaline earth compound is as follows: particles of hydroxide of an alkaline earth compound are immersed in an aqueous solution of potassium hydroxide, then the liquid is separated and dried. Further, in the case of calcium hydroxide, the use temperature is 580 ° C or higher, and in the case of magnesium hydroxide, the use temperature of 350 ° C or higher converts the hydroxide of the alkaline earth compound into an oxide. When used at a temperature below these dislocation temperatures, there is no difference in the effect even when used as a hydroxide. A mixture of an alkaline earth compound oxide or hydroxide and potassium hydroxide is formed into granules, if necessary. These are examples of the compounding method, but the method is not particularly limited,
What is necessary is just to employ | adopt suitably.

The content of potassium hydroxide in the mixture of the alkaline earth compound oxide or hydroxide and potassium hydroxide may be in the range of 0.05 to 40% by weight. If the content is lower than the lower limit, the effect cannot be expected. If the content is higher than the upper limit, molten potassium hydroxide (melting point 405 ° C.) separates from the oxide of the alkaline earth compound and flows down to the lower part of the reactor. Inconveniences, such as blockage of piping, occur. A more desirable range is 0.
1 to 20% by weight.

The gas-solid contact between the decomposing agent and the halide gas to be treated or the like may be performed according to a commonly used method, and an appropriate method such as a fixed bed or a moving bed can be selected. The temperature required for the reaction when the decomposing agent according to the present invention is used varies depending on the type of the compound contained in the gas to be treated. Perfluorocarbon is classified as a hardly decomposable compound among halide gases.
₄ is the most difficult to decompose and requires a high temperature of 1200 ° C. for mere thermal decomposition to completely decompose,
According to the method of the present invention, it can be completely decomposed at 900 ° C. Further, CCl ₄ is a compound that can be decomposed at a relatively low temperature, and can be completely decomposed at 400 ° C. according to the method of the present invention. Setting the optimum temperature is important to prevent too high a temperature setting from wasting thermal energy, or too low a temperature setting to prevent insufficient decomposition and release of undecomposed gas to the atmosphere. It is.

The heating of the reactor is generally carried out by an external means such as an electric heater. However, the method is not limited to this method and may be appropriately designed in consideration of various conditions.

[0017]

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 23, Comparative Examples 1 to 20 Ni tubes having an inner diameter of 22 mm and a length of 300 mm as reactors (alumina tubes having the same inner diameter and the same length in experiments where the temperature exceeds 900 ° C.) Was set vertically in an annular furnace equipped with a temperature control mechanism, and gas was flowed from the bottom to the top of the reactor at a flow rate of 1000 CC / min (gas volume is based on a standard state). A flow controller and a valve for diluting the halide gas with N ₂ and supplying it quantitatively were installed in the reactor inlet side pipe. A branch pipe was branched from the main exhaust line to a reactor outlet side pipe, and a sample for analysis was collected. Analysis was performed by gas chromatography and infrared absorption spectrophotometer.

The decomposition agent was prepared as follows. 2 parts by weight of a calcium hydroxide powder or a magnesium hydroxide powder was added to 1 part by weight of an aqueous solution of potassium hydroxide and mixed to form a paste, which was dried at 120 ° C. in an N ₂ atmosphere and solidified. This is crushed and sieved to a diameter of 2m
A granular agent of m to 3 mm was obtained. The concentration of the aqueous potassium hydroxide solution was determined so that the final ratio of potassium hydroxide to calcium hydroxide or magnesium hydroxide was a predetermined value.

In the comparative examples, calcium hydroxide or magnesium hydroxide was treated in the same manner as above using water or an aqueous solution of sodium hydroxide. Tables 1 to 3 show the composition of the treatment agent used for each run, the temperature of the reactor, and the concentration of the treatment gas on the inlet side and the outlet side 5 minutes after the start of the reaction. In both Examples and Comparative Examples, the decomposing agent prepared as described above was filled up to the upper end of the reactor.

When the temperature of the reactor is 580 ° C. or more for calcium hydroxide and 350 ° C. or more for magnesium hydroxide, the reaction is examined after the completion of the reaction. Except for those that were converted to halides, they were converted to calcium oxide in calcium hydroxide and to magnesium oxide in magnesium hydroxide. Therefore, the components of the treating agent are indicated as CaO and MgO in the table.

In Example 4, when the gas treatment was continued, the total number of equivalents of the treating agent charged (one molecule of CaO
= 2 equivalents, 1 molecule of MgO = 2 equivalents, 1 molecule of KOH =
1 equivalent, 1 molecule of NaOH = 1 equivalent) 100
When the cumulative number of equivalents of halogen contained in the supplied processing gas reaches 56 (calculated as F of one atom = 1 equivalent, Cl of one atom = 1 equivalent), C ₂ F _{6 is} contained in the outlet gas.
Was slightly detected. Further, when the cumulative equivalent number of the halogen reached 71, the C ₂ F ₆ concentration in the outlet gas became the same as the concentration in the inlet gas. Analysis of the reactor contents at this point showed that the chemicals near the gas inlet side were mostly CaF ₂ and KF, CaO and KOH were small, F was fixed in a safe form of solid, The usage efficiency was found to be high.

In the treatment of perfluorocarbons and chlorofluorocarbons having 2 or more C atoms in the molecule, no lower-order halogenated carbons were found in the outlet gas. And all Ru by the method of the present invention
In n, HF, HCl and CO were not contained in the outlet gas. Further, the decomposed carbon is discharged as CO ₂ or remains in the reactor in the state of carbon as it is.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

[0027]

As described above, according to the present invention, it is possible to decompose a halide gas or the like at a low temperature with high efficiency. Therefore, there is provided a method which is advantageous in terms of heat energy required for decomposition and the structure and material of the apparatus. Provided.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shinsuke Nakagawa 5253 Oki Obe, Ube City, Yamaguchi Prefecture Inside Central Glass Chemical Research Laboratory (56) References JP-A-63-80830 (JP, A) 5-137812 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 53/34-53/96 B01J 20/00-37/36

Claims (1)

(57) [Claims] 1. An organic halide gas or SF ₆ gas, potassium hydroxide and an alkaline earth metal oxide or alkaline earth metal water having a potassium hydroxide content in the range of 0.05 to 40% by weight. 30 with the mixture of oxides
A method for decomposing a halide gas, wherein the contact is performed in a temperature range of 0 to 900 ° C.