JP2005185897A - Method for treating sulfur hexafluoride gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating sulfur hexafluoride gas to be used as an insulating medium of a gas insulation switchgear, or the like and a dry etching agent or a fluorinating agent of LSI (large scale integrated circuits). <P>SOLUTION: This method for treating exhaust gas, namely, bringing exhaust gas containing sulfur hexafluoride gas into contact with a treating agent to remove the sulfur hexafluoride gas from the exhaust gas comprises a preceding step to use catalyst-containing silicon oxide as the treating agent and produce silicon fluoride gas and sulfur oxide gas and a succeeding step to treat the gases produced at the preceding step by an alkali chemical-packed cylinder or a wet scrubber. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for treating sulfur hexafluoride gas used as an insulating medium such as a gas insulated switchgear, an LSI dry etching agent or a fluorinating agent.

Sulfur hexafluoride gas (SF ₆ ) is used in large quantities as an insulating medium for gas insulated switchgear and the like. In recent years, it has attracted attention as an LSI dry etching agent or fluorinating agent, and its demand is increasing year by year. When these sulfur hexafluoride gases are used, it is always necessary to remove them when exhausting the residual gas. In particular, sulfur hexafluoride gas has a high ozone depletion potential (ODP) and global warming potential (GWP), and has recently become a major international problem.

  Since these sulfur hexafluoride gases are extremely stable in the atmosphere and are only slightly soluble in water, they cannot be completely treated by conventional abatement techniques such as abatement equipment using an alkaline chemical or a wet scrubber. Moreover, in the detoxification technique by decomposition using combustion gas or heat, although the sulfur hexafluoride gas is decomposed, undecomposed components remain, or sulfur tetrafluoride gas that is difficult to remove is generated.

As a method for treating NF ₃ , the present applicant reacts various metals including Si and non-oxide compounds thereof with NF ₃ at 200 ° C. to 800 ° C., and collects the fluoride gas obtained. A method was proposed (Patent Document 1). However, in this reaction processing method, in order to obtain a required processing speed in the case of sulfur hexafluoride gas, the reaction temperature must be increased, and extra heat energy is required for the processing, which is required for the reactor. There was a problem that the quality of the material to be used was of a high quality. Further, it is disclosed that sulfur hexafluoride gas is decomposed by contacting molecular oxygen or water vapor in the presence of alumina (Al ₂ O ₃ ) (Patent Documents 2 and 3). incomplete.

The present invention has been made paying attention to such a point, and an object thereof is to provide a method for removing sulfur hexafluoride gas which does not cause a reduction in the processing speed.
Japanese Examined Patent Publication No. 63-48570 JP-A-10-192653 Japanese Patent Laid-Open No. 10-286434

  As a result of intensive investigations in view of such problems, the present inventors have used sulfur hexafluoride gas, which has low reactivity at room temperature and is difficult to perform detoxification, and silicon oxide containing a catalyst. The inventors have found that sulfur hexafluoride gas can be easily and inexpensively treated by generating sulfur gas and treating the silicon fluoride gas and sulfur oxide gas, and the present invention has been achieved.

  That is, the present invention provides an exhaust gas treatment method for removing sulfur hexafluoride gas from exhaust gas by contacting the exhaust gas containing sulfur hexafluoride gas with the treatment agent. The present invention provides a method for treating sulfur hexafluoride gas, characterized in that silicon fluoride gas and sulfur oxide gas are produced, and the produced gas is treated with an alkali chemical filling tube or a wet scrubber at a later stage.

  Hereinafter, the contents of the present invention will be described in detail.

Silicon oxide containing a catalyst used in the present invention generates silicon fluoride gas and sulfur oxide gas by reaction with sulfur hexafluoride gas. The silicon fluoride gas is SiF ₄ , SiOF ₂ , Si ₂ OF ₆ or the like, and mainly generates SiF ₄ . The sulfur oxide gas is SO ₂ , SOF ₂ , SO ₂ F _2, etc., and mainly generates SO ₂ .

Next, the catalyst to be included is Pt, Pd, Al ₂ O ₃ , Ga ₂ O ₃ , or ZnO. These catalysts can be contained alone or as a mixture of two or more. The amount of the catalyst is preferably in the range of 0.01 to 5% by weight with respect to silicon oxide. If it is less than 0.01% by weight, the effect of the catalyst is small and not preferable, and if it exceeds 5% by weight, the contact between silicon oxide and gas is small and silicon fluoride gas cannot be generated. The heating temperature of the treatment agent is preferably in the range of 100 to 1000 ° C. If it is less than 100 ° C., the reaction rate is low and sufficient reaction efficiency cannot be obtained, and if it exceeds 1000 ° C., the silicon oxide and the contained catalyst are softened or melted, and contact with the gas is not sufficient.

  Finally, the generated silicon fluoride gas and sulfur oxide gas are treated with conventional detoxification technologies such as an alkali detoxifying agent-filled cylinder using an alkali chemical such as calcium hydroxide and a wet scrubber using water in the subsequent stage. Is done. In the cylinder filled with an alkaline pesticide, the cylinder is filled with a pesticide formed in a granular or lump shape of about 2 to 5 mm mainly composed of calcium hydroxide. Detoxification treatment. In the cylinder, the gas component is solidified and processed by reaction equations such as equations (1) and (2). On the other hand, in the wet scrubber, water is sprayed from the upper part in the cylinder and dispersed, and the generated gas introduced from the lower part is detoxified by contact between the gas and water. In the cylinder, the gas component is liquefied or solidified by reaction equations such as equations (3) and (4).

SiF ₄ <Gas> + 2Ca (OH) ₂ <Solid>
→ SiO ₂ <solid> + 4CaF ₂ <solid> + O ₂ <gas> (1)
2SO ₂ <Gas> + 2Ca (OH) ₂ <Solid>
→ 2CaSO ₃ <solid> + H ₂ O <liquid> (2)
SiF ₄ <Gas> + 2H ₂ O <Liquid>
→ SiO ₂ <Solid> + 4HF <Liquid> (3)
SO ₂ <Gas> + H ₂ O <Solid>
→ H ₂ SO ₃ <Liquid> (4)

  As described in detail above, according to the method of the present invention, in the exhaust gas treatment method for removing sulfur hexafluoride gas from the exhaust gas by bringing the exhaust gas containing sulfur hexafluoride gas into contact with the treatment agent, the treatment is performed in the previous stage. By using silicon oxide containing a catalyst as an agent, silicon fluoride gas and sulfur oxide gas are produced, and the produced gas is treated at a later stage, whereby sulfur hexafluoride gas can be treated easily and inexpensively. .

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to such examples.

Examples 1-9, Comparative Examples 1-2
FIG. 1 shows a schematic diagram of an experimental flow for confirming the treatment of sulfur hexafluoride gas by the method of the present invention. A sample gas 1 containing exhaust gas to be treated is introduced into and contacted with a filling cylinder 2 filled with silicon oxide containing a catalyst. The filling cylinder 2 is heated by the heater 3 to heat the inside of the filling cylinder 2. A switching valve 4 is provided at the outlet of the filling cylinder, and the outlet gas is switched to the subsequent alkaline chemical filling cylinder 5 or the wet scrubber 6 for processing. In these, it becomes possible to process the silicon fluoride gas and sulfur oxide gas generated in the preceding stage. Further downstream of them, there is a switching valve 7 for switching between the gas that has passed through the former stage and the gas that has passed through the latter stage, and each gas is connected to a Fourier transform infrared absorption spectrometer (FT-IR) 8. You can check the processing status.

In Example 1, nitrogen gas containing SF ₆ = 1000 ppm was used as the gas to be processed, and SiO ₂ containing 0.1 wt% Pt was used as the processing agent. The filling tube heating temperature was 700 ° C. About 500 cm ^{3 of} this processing target gas was introduced per minute and contacted. The silicon fluoride gas and sulfur oxide gas generated by the reaction were treated with an alkali chemical filling device (alkali chemical used calcium oxide), and then confirmed with a Fourier transform infrared absorption spectrometer. As a result, SF ₆ was 5 ppm or less, which is the lower limit of detection, and it was confirmed that the treatment was good. In addition, it was confirmed that the silicon fluoride gas and sulfur oxide gas produced by the reaction were similarly treated well after being treated with a wet scrubber. As a result of quantitative analysis of the reaction product in the former stage using a Fourier transform infrared absorption spectrometer, SiF ₄ as silicon tetrafluoride and SO _{2 as} sulfur dioxide were found to be in accordance with a chemical reaction formula as shown in formula (5). It is thought that it was generated.

2SF ₆ + 3SiO ₂ → 3SiF ₄ + 2SO ₂ + O ₂ (5)

For comparison, the same gas treatment as in Example 1 was performed at 700 ° C. and 1000 ° C. using SiO ₂ not containing Pt. As a result, SF ₆ could not be completely removed as shown in Table 1.

Next, in the same manner as in Example 1, a nitrogen gas containing SF ₆ = 1000 ppm was used as the gas to be treated, and the catalyst was a single substance of Pt, Pd, Al ₂ O ₃ , Ga ₂ O ₃ , ZnO or A mixture was used. The catalyst concentration was 0.1% by weight. In the case of a mixture, all the components were adjusted to 0.1% by weight. The heating temperature of this filling cylinder was 500-650 degreeC. After processing the metal fluoride gas generated by the reaction with an alkali chemical filling device and a wet scrubber, the results were confirmed with a Fourier transform infrared absorption spectrometer. As a result, in any analysis method, the detection lower limit of SF ₆ was 5 ppm or less. It was confirmed that it was treated well. These conditions and results are shown in Table 1.

Examples 10-12
In the same manner as in Example 1, nitrogen gas containing SF ₆ = 1000 ppm was used as the gas to be treated, and Pt was used as the catalyst. The catalyst concentration was 0.01 wt%, 1 wt%, 5 wt%, and the heating temperature was 700 ° C. As a result, it was 5 ppm or less of the detection lower limit of SF ₆ , and it was confirmed that the treatment was good. These conditions and results are shown in Table 1.

It is the schematic of the experimental flow of a sulfur hexafluoride gas abatement process.

Explanation of symbols

1 ... Sample gas (sulfur hexafluoride + nitrogen)
2 ... Filling tube 3 of silicon oxide containing catalyst 3 ... Filling tube heater 4 ... Switching valve 5 ... Alkaline chemical filling device 6 ... Wet scrubber 7 ... Switching valve 8 ...・ Fourier transform infrared absorption spectrometer

Claims (3)

In a method for treating exhaust gas in which exhaust gas containing sulfur hexafluoride gas is contacted with a treatment agent to remove sulfur hexafluoride gas from the exhaust gas, silicon fluoride containing a catalyst is used as a treatment agent in the previous stage, and silicon fluoride is used. A method for treating sulfur hexafluoride gas, comprising generating gas and sulfur oxide gas and treating the silicon fluoride gas and sulfur oxide gas with an alkali chemical filling cylinder or a wet scrubber in a subsequent stage. _{Catalyst, Pt, Pd, Al 2 O} 3, Ga 2 O 3 treatment methods sulfur hexafluoride gas as claimed in claim 1 or characterized in that it is a one or a mixture of two or more consisting of ZnO,. The method for treating a sulfur hexafluoride gas according to any one of claims 1 to 2, wherein the pretreatment agent is heated to 100 to 1000 ° C.