Reactive agent and process for decomposing fluorine...

Details Reactive agent and process for decomposing fluorine... Reactive agent and process for decomposing fluorine...

2001-09-21

2003-05-13

Bos, Steven (Department: 1754)

Hazardous or toxic waste destruction or containment

Containment

Solidification, vitrification, or cementation

C588S253000, C588S249000, C423S24000R

Reexamination Certificate

active

06563011

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a reactive agent and a process for decomposing and detoxifying various fluorine compounds such as chlorofluorocarbons (hereinafter simply referred to as “CFC”), hydrochlorofluorocarbons (hereinafter simply referred to as “HCFC”), perfluorocarbons (hereinafter simply referred to as “PFC”), hydrofluoro-carbons (hereinafter simply referred to as “HFC”), perfluoroethers (hereinafter simply referred to as “PFE”), hydrofluoroethers (hereinafter simply referred to as “HFE”) and sulfur fluoride, simultaneously with the compounds produced on using these fluorine compounds, for example, in an etching or cleaning step during the process of manufacturing a semiconductor device, such as HF, SiF
4
or COF
2
.
BACKGROUND OF THE INVENTION
Most of the above-described fluorine compounds are generally stable and harmless to the human body, therefore, their use is outspread in various fields. In recent years, the amount of HFC as a refrigerant of car air conditioner or the like and PFC for etching or as a cleaning gas in the process of manufacturing semiconductors is particularly increased. Furthermore, a large amount of sulfur hexafluoride is being used for capacitors, transformers and the like because of its excellent electrical insulating property. These fluorine compounds are a stable compound and in turn have a large global warming potential coefficient. If such a fluorine compound is released as it is into the global environment, there is a fear that its effect continues for a long period of time. In particular, SF
6
, CF
4
, C
2
F
6
and the like are a very stable gas and have a very long life in air. Therefore, on discharge after their use, these gases must be released after decomposition into a harmless substance having no effect on the global environment. As an alternate compound therefor, PFE and HFE are proposed but these also have the same global warming problem. Furthermore, the gas discharged after use in the process of manufacturing semiconductor devices contains gases such as HF, SiF
4
and COF
2
and these gases must also be released after decomposition into a safe substance together with the above-described compounds.
CFC heretofore used in a large amount as a refrigerant, detergent or the like, and HCFC as an alternate compound thereof cannot be released as it is and must be decomposed into a harmless substance because ozone layer destruction occurs as a serious environmental problem.
Conventionally, as a technique for decomposing such fluorine compounds, for example, (1) a combustion decomposition method of treating the compound together with a fuel (see, WO94/05399), (2) a thermal decomposition method using a reactive agent such as silica or zeolite (see, JP-A-7-116466 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)), and (3) a catalytic decomposition method using an alumina or the like (see, JP-A-10-286434) are known.
However, method (1) is disadvantageous in that generation of NO
x
must be controlled during the combustion or a large amount of diluting gas is necessary, causing a decrease in the decomposing ratio, and moreover, a secondary treatment of HF contained in the exhaust gas after the decomposition is necessary. Method (2) also has a problem in that a high temperature of 1,000° C. or more is necessary particularly for decomposing PFC (e.g., CF
4
, C
2
F
6
) at a sufficiently high rate and moreover, a separate secondary treatment of compounds such as SiF
4
contained in the exhaust gas after the decomposition is necessary. According to the method (3), decomposition may be performed at a relatively low temperature as compared with the methods (1) and (2), however, the following problems still remain. For decomposing PFC in an amount of 100%, the supply gas must be diluted with air or the like to reduce the PFC concentration in the gas. Furthermore, in order to bring out the catalytic action of alumina, it is necessary to allow a large amount of steam to be present together and thereby hydrolyze, for example, fluoride or the like accumulated on the alumina surface. Therefore, an anticorrosive material against HF generated by the high-temperature decomposition of fluoride on the alumina surface, and a secondary treatment of HF are necessary.
As such, a method for effectively decomposing fluorine compounds using an industrially advantageous process is heretofore not known and more improvements are demanded.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above-described problems and provide a reactive agent which can thermally decompose fluorine compounds at a relatively low temperature without adding water and which can fix the decomposition products (e.g., F, SO
x
) of the decomposed fluorine compound to the reactive agent.
Another object of the present invention is to provide a process for efficiently decomposing particularly PFC which is difficult to decompose.
As a result of extensive investigations to solve the above-described problems, the present inventors have found that these objects can be attained by a reactive agent for decomposing fluorine compounds, comprising alumina and an alkaline earth metal compound. Furthermore, the present inventors have found that in a process for decomposing fluorine compounds, comprising contacting a fluorine compound with the above-described reactive agent at a temperature of 200° C. or more, the fluorine compound can be thermally decomposed, the generated chlorine atoms, fluorine atoms and/or sulfur atoms can be fixed as a chloride, a fluoride and/or a sulfate of an alkaline earth metal in the reactive agent, and if desired, by adding a metal oxide to the reactive agent to incorporate oxygen into the fluorine compound, the carbon monoxide generated can be simultaneously oxidized and thereby detoxified. The present invention has been accomplished based on these findings. The present invention relates to a reactive agent and a process for decomposing fluorine compounds, described in (1) to (28) below:
(1) A reactive agent for decomposing fluorine compounds, comprising alumina and an alkaline earth metal compound;
(2) the reactive agent for decomposing fluorine compounds as described in (1) above, wherein the alumina has a specific surface area of 50 m
2
/g or more;
(3) the reactive agent for decomposing fluorine compounds as described in (1) or (2) above, wherein the alumina is pseudo boehmite alumina;
(4) the reactive agent for decomposing fluorine compounds as described in (1) or (2) above, wherein the alumina is obtained by baking pseudo boehmite alumina at a baking temperature of from h400 to 1,000° C.;
(5) the reactive agent for decomposing fluorine compounds as described in any one of (1) to (4) above, wherein the alkaline earth metal compound is a carbonate of magnesium, calcium, strontium or barium;
(6) the reactive agent for decomposing fluorine compounds as described in any one of (1) to (5) above, wherein the alumina and the alkaline earth metal compound present in the reactive agent each is in the form of a powder having a particle size of 100 &mgr;m or less;
(7) the reactive agent for decomposing fluorine compounds as described in any one of (1) to (6) above, wherein the alumina and the alkaline earth metal compound are present in the reactive agent at a mass ratio of from 1:9 to 1:1;
(8) the reactive agent for decomposing fluorine compounds as described in any one of (1) to (7) above, which contains at least one oxide of a metal selected from the group consisting of copper, tin, nickel, cobalt, chromium, molybdenum, tungsten and vanadium;
(9) the reactive agent for decomposing fluorine compounds as described in (8) above, wherein the content of the metal oxide is, in terms of a ratio to the total mass of the alumina and alkaline earth metal compound, from 1:99 to 5:95;
(10) the reactive agent for decomposing fluorine compounds as described in any one of (1) to (9), which has an alkali metal content of 0.1 mass % or less;
(11) the reactive agent for decomposing fluorine compounds as desc

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