KR100529748B1 - Method for Purifying Sulfur Hexafluoride - Google Patents

Abstract

The present invention provides a method for purifying sulfur hexafluoride in which a sulfur-containing hexafluoride containing impurities is contacted with a tablet comprising a carbonaceous solid and at least one compound selected from alkaline earth metal compounds, alkali metal aluminates or tetraalkylammonium salts. It is about. Purified SF ₆ of the present invention can be recycled as an insulating medium of the gas.

Description

Method for Purifying Sulfur Hexafluoride

The present invention relates to a method for purifying sulfur hexafluoride, and more particularly, to a method for purifying a recovered sulfur hexafluoride containing harmful impurities in contact with a purifying agent.

Sulfur hexafluoride (hereinafter referred to as SF ₆ ) has excellent electrical insulation as a gas, and thus demand for gas insulators such as breakers and transformers is gradually increasing. SF ₆ itself is chemically stable and nontoxic and corrosive.

However, when SF ₆ is used in equipment of a small substation, etc., a strong electric field such as corona discharge and arc is generated in the circuit breaker, resulting in decomposition into various impurities that degrade the operation of the equipment. Sulfur tetrafluoride (hereinafter referred to as SF ₄ ), sulfur difluoride (hereinafter referred to as SF ₂ ), and sulfur monofluoride (hereinafter referred to as S ₂ F ₂ ) are very reactive substances, When water is present, it reacts with water to react with hydrofluoride (hereinafter referred to as HF), sulfite gas (hereinafter referred to as SO ₂ ), thionyl fluoride (hereinafter referred to as SOF ₂ ), and sulfuryl fluoride (hereinafter referred to as SOF ₂ ). ₂ F ₂ ) and very small amounts of sulfur pentafluoride (hereinafter referred to as S ₂ F ₁₀ ). Use of SF ₆ gas contained in the impurity degrades the performance of the equipment used, for example, metal parts of the equipment will be corroded. Therefore, the SF ₆ gas contained in the impurities should be removed from the instrument and replaced in a timely manner.

SF ₆ gas is expensive and can not deny the effects of environmental pollution such as global warming, so recently, recycling of SF ₆ by recovery of used SF ₆ and removal of harmful impurities from the recovered SF ₆ as indicated above Several purification methods have been proposed to meet these demands. For example, (1) a dry method of contacting recovered SF ₆ gas with activated alumina and X-type synthetic zeolite (Japanese Patent Publication No. 47-6205), and (2) contacting an impure gas component with a conversion agent which is a solid agent. Wet method of contacting a solid product with a non-toxic gas absorbed by using a gas absorbent (Japanese Patent Laid-Open No. 60-54723), and (3) recovering SF ₆ gas in an alkali bath (aqueous calcium hydroxide solution). (4) contacting the recovered SF ₆ gas with a lithium-substituted macroreticular ion exchange resin (Hamano et al., SF ₆ Gas Recovering Apparatus in a High Electric Power Plant, 1996 Electric Society Conference) Japanese Patent Laid-Open No. 6-211506 and the like are known.

However, there are some problems in the above-mentioned document, for example, the method of (1) does not obtain sufficient adsorption effect on SO ₂ , SOF _2, SO ₂ F ₂ , S ₂ F _10, etc., and the method of (2) In calcium hydroxide reacts with impurities to produce hydrogen that must be adsorbed and removed. However, the hydrogen produced is combustible and the removal capacity is not sufficient in this method. The method of (3) is a wet method, so a large-scale device is required. In the method of (4), an expensive absorbent must be used, and since the method is wet, the gas will be contaminated with a large amount of water. Thus, these methods are uneconomical and unsuitable for industrialization.

In order to solve the above problems, the present invention is to provide a method for producing purified SF ₆ to remove simple and harmful impurities from SF ₆ containing impurities.

The present invention provides purification of SF ₆ by contacting SF ₆ containing impurities with a tablet comprising a carbonaceous solid and at least one compound selected from the group consisting of alkaline earth metal compounds, alkali metal aluminates or tetraalkylammonium salts. To provide a way.

The impurities of SF ₆ include at least one selected from the group consisting of SO ₂ , S ₂ F ₂ , SF ₂ , SF ₄ , S ₂ F ₁₀ , and SOF ₂ .

The alkaline earth metal compound refining agent is preferably selected from the group consisting of oxides, hydroxides, carbonates or nitrates of calcium, magnesium, barium and strontium.

The alkali metal aluminate tablets are preferably selected from the group consisting of lithium aluminate, sodium aluminate, potassium aluminate or cesium aluminate.

The tetraalkylammonium salt tablets are tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetramethylammonium carbonate, tetraethylammonium carbonate, tetramethylammonium chloride, tetraethylammonium chloride, tetramethylammonium aluminate Or tetraethylammonium aluminate.

Preferably, the carbonaceous solid tablet is selected from the group consisting of coke powder, coal, chartantan, charcoal, pitch, activated carbon or carbon black. The specific surface area of the tablet is preferably in the range of 80 m ² / g to 1000 m ² / g.

Moreover, it is preferable that the average pore diameter of the said refiner exists in the range of 7 GPa-1500 GPa.

The concentration of HF contained in SF ₆ purified by the above is preferably not more than 0.1 ppm by weight.

In the purification method of SF ₆ purified as described above, a dehydration step is preferably added, and in this dehydration step, zeolite is preferably used as the dehydrating agent. The concentration of water contained in the refining SF ₆ by the preferably is less than 50 ppm by weight.

The above-mentioned SF ₆ process containing impurities is first contacted with the tablet on the pellet composed of a carbonaceous solid and an alkaline earth metal compound and then to at least one of the tetraalkylammonium salts supported on the alkali metal aluminate and the carbonaceous solid. It is preferred to contact the configured tablets and then to apply a dehydration process to each of the contacting steps.

The SF ₆ purification method of the present invention is used in gas insulators such as gas circuit breakers (GCN), and SF ₆ (hereinafter referred to as "impurity SF ₆ ") that is decomposed by corona discharge or electric arc generated during interruption to generate harmful impurities. It is applied to the purification process such as regeneration and the removal of its harmful impurities.

Impurity SF ₆ after use in such gas insulators is generally HF, SF ₄ , SF ₂ , S ₂ F ₂ , SO ₂ , SOF ₂ , SO ₂ F ₂ , Corrosive and harmful impurities such as S ₂ F ₁₀ .

According to one embodiment of the purification method of the present invention, for example, a purification agent composed of at least one compound and a carbonaceous solid from the group consisting of an alkaline earth metal compound, an alkali metal aluminate or a tetraalkylammonium salt is charged into a reaction tube, and Impurity SF ₆ is passed through the reaction tube in a gas stream at room temperature. Accordingly, impurities in impurity SF ₆ are adsorbed by the refining agent and are substantially free of SF ₆ (hereinafter referred to as "purified SF ₆ "). Can be recovered simply and effectively.

In regenerating the obtained tablet SF ₆ to the above gas insulator, the water content of the tablet SF ₆ is preferably 50 ppm or less by weight. This can be achieved by adding to the dehydration step in the SF ₆ purification step, for example using zeolite as the dehydrating agent.

It will be described in detail for each component of the present invention.

The tablets used in the present invention consist of carbonaceous solids and at least one compound selected from the group consisting of alkaline earth metal compounds, alkali metal aluminates or tetraalkylammonium salts.

In general, the carbonaceous solids of the present invention are effective at adsorbing most of the impurities resulting from the decomposition of SF ₆ but the impure SF ₆ contains a significant amount of HF which causes the adsorptive capacity of the carbonaceous solids to be lowered. According to the present invention, all harmful impurities in impurity SF ₆ can be effectively removed by contact with a carbonaceous solid combined with at least one compound selected from the group consisting of alkaline earth metal compounds, alkali metal aluminates or tetraalkyl ammonium salts. Can be. The inventors do not intend to be bound by a particular theory, but one or more compounds selected from the group consisting of alkaline earth metal compounds, alkali metal aluminates or tetraalkylammonium salts remarkably effectively remove significant amounts of HF, and Together, it is generally believed that the purifying agent of the present invention facilitates the effective removal of harmful impurities of impurity SF ₆ .

In any case, a tablet comprising one or more compounds selected from the group consisting of carbonaceous solids and alkaline earth metal compounds, alkali metal aluminates or tetraalkylammonium salts may be used to purify harmful SF from impurities SF ₆ with selective removal of harmful impurities. We found that we get ₆ .

The alkaline earth metal compound is composed of an oxide of calcium, magnesium, barium or strontium, hydroxide, carbonate, nitrate, and the like, which may be used alone or in combination of two or more thereof. Of these, calcium oxide, calcium hydroxide, calcium carbonate and calcium nitrate are preferred, and more particularly quicklime, slaked lime or limestone are preferred because they are inexpensive and easy to handle.

The alkali metal aluminate is composed of lithium aluminate, sodium aluminate, potassium aluminate or cesium aluminate, and these may be used alone or in combination of two or more thereof. Among these, sodium aluminate and potassium aluminate are preferable because they can be easily obtained. But sodium aluminate is most preferred.

The tetraalkylammonium salts may be tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetramethylammonium carbonate, tetraethylammonium carbonate, tetramethylammonium chloride, tetraethylammonium chloride, tetramethylammonium aluminate or Tetraethylammonium aluminate, which may be used alone or in combination of two or more. Among these, tetramethylammonium hydroxide, tetramethylammonium carbonate, tetramethylammonium chloride or tetramethylammonium aluminate is preferable because it can be easily obtained. However, tetramethylammonium carbonate is most preferred. Tetramethylammonium carbonate and tetramethylammonium aluminate can be prepared by reaction of tetramethylammonium hydroxide with a carbonate gas or aluminum hydroxide.

The carbonaceous solid is composed of coke, coal, chartan, charcoal, pitch, activated carbon or carbon black, and may be used alone or in combination of two or more thereof. The carbonaceous carbon is in the form of powder, fine grains or pellets. The fine phase is spherical or crushed or in the form of a powder. The carbonaceous solid is preferably in the range of 100 m ² / g to 2500 m ² / g, but more preferably in the range of 500 m ² / g to 2000 m ² / g. Particularly preferred carbonaceous solids are powdered chartan and activated carbon in fine grain form.

The tablet can be prepared by various methods. For example, activated carbon or the like can be immersed in an aqueous solution such as sodium aluminate as a carbonaceous solid to obtain a supported tablet. As another method, for example, a mixture of slaked lime powder and tarthan powder may be mixed in a predetermined ratio, mixed with water, molded into pellets for easy handling, and dried to obtain pellet-type tablets.

When the tablet is supported, for example, the amount of alkali metal aluminate and / or tetraalkylammonium salt supported on the carbonaceous solid is in the range of 1 to 30 g per 100 ml of activated carbon when the activated carbon is used as the carbonaceous solid. desirable. If the supported formulation is 1 g / ml or less, the purification effect is not sufficient, and if it is 30 g / 100 ml or more, the carbonaceous solid is filled with micropores and the purification effect is also reduced. The carrier preferably has a pore diameter in the range of 7 to 300 mm 3. In general, supported formulations are preferred because they have a large specific surface area for the role of such supported formulations.

In the case where the tablet is in the form of pellets, for example, the mixing ratio of the alkaline earth metal compound and the carbonaceous solid depends on the special composition, but preferably equal to or more than the carbonaceous solid.

The tablets, whether supported or pelletized, should be sufficiently dried. Drying is preferably carried out using an inert gas such as nitrogen, helium or argon as a drying gas.

The specific surface area of the tablet is preferably in the range of 80 m ² / g to 1000 m ² / g, particularly preferably in the range of 100 m ² / g to 700 m ² / g. Moreover, the range of 7-1500 mm <3> is preferable and, as for the average pore diameter of the said refiner, the range of 7 kPa-1100 kPa is especially preferable. Leaving this range, the purification effect is lowered. In preparing the tablet, the specific surface area and average pore diameter of the tablet can be adjusted according to the selection of the material, the blending ratio, the production method, and the conditions.

In the case where the tablet is supported, the specific surface area is preferably in the range of 300 m ² / g to 800 m ² / g, particularly preferably in the range of 400 m ² / g to 600 m ² / g. Moreover, the pore diameter of the said tablet is preferably in the range of 4 kPa to 200 kPa, more preferably in the range of 8 kPa to 100 kPa.

After each dehydration step, impure SF ₆ is preferably treated with pelletized tablets followed by supported tablets. Because pelletized tablets can remove significant amounts of HF without deterioration, supported tablets are deteriorated by HF while more effectively removing other impurities in impure SF ₆ .

In order to purify impure SF ₆ with a tablet, impure SF ₆ may be brought into contact with the tablet. The impurity concentration in impurity SF ₆ which must be subjected to the purification process should be 2.0% or less by weight. If the concentration of impurities is higher than the above amount, a large amount of purification agent is required and the purification time is longer.

When contacted with a purifying agent, impure SF ₆ is in the form of a gas or a liquid, but contacting with gaseous impurity SF ₆ is preferred. As the contact method, any method such as a fluidized bed method or a mobile bed method may be used, as well as a fixed bed method generally used for fluid-solid contact. However, the stationary phase system is preferred. In the case of using the gas-solid contacting method, the pressure in the contacting process does not need to be particularly limited, but from an economic point of view, the range of atmospheric pressure to 2 MPa is preferable. Moreover, although the temperature of a contact process does not need to specifically limit, For example, it is good to select in the range of -40-100 degreeC. If there is no special situation, it is preferable to keep the contact temperature at room temperature from an economical point of view.

As described above, in the contact process with the purification agent, impure SF ₆ can be purified, for example, to a level of 0.1 wt ppm or less (as measured by halogen ion analysis or ion chromatography) as the HF concentration. Under the above purification conditions, the amount of S ions is SO ^- as 0.1-ppm or less (measured by ion chromatography). Other harmful impurities such as SO ₂ , SF ₂ , SF ₄ , SO ₂ F ₂ and SOF ₂ are also below the limit detected by gas chromatography or (GC) or gas chromatography / mass spectrometry (GC / MAS) (0.1 ppm by weight). It can be set as follows).

In order to regenerate the purified SF ₆ obtained in the above contact process as a gas insulating medium, water, which is one factor of SF ₆ decomposition, must be sufficiently removed. Therefore, in the SF ₆ refining method of the present invention, it is preferable to add a dehydration step to thoroughly control the water content. This dehydration step is preferably carried out by gas-solid contact using, for example, a synthetic zeolite or the like as the dehydrating agent after the above-mentioned contact step. Suitable dehydrating agents used in this dehydration step are synthetic zeolites, and in particular, a suitable particle size range may be selected and used from generally known molecular sieves known as Molecular Sieves.

In the gas-solid contact dehydration process using molecular sieves, the preferred reaction pressure is in the range of atmospheric pressure to 2 MPa, and the preferred reaction temperature is in the range of -40 to 100 ° C. . In this dehydration step, the water content in the refined SF ₆ is 50 ppm or less by weight, and particularly preferably, the water content limit is 10 ppm or less by weight.

According to the present invention, SF ₆ containing an impurity is contacted with a carbonaceous solid with a purifying agent containing at least one selected from the group consisting of alkali earth metal compounds, alkali metal aluminates or tetraalkylammonium salts. Therefore, harmful impurities in impurity SF ₆ can be removed simply and effectively without the need for a large-scale device. In addition, in the purification step of the present invention, a dehydration step may be added to reduce the water which is one factor of SF ₆ decomposition, thereby regenerating the purified SF ₆ as a gas insulation medium.

The following examples illustrate the invention in more detail.

Example

Impurity SF ₆ sample

For the test, the following impure SF ₆ was prepared.

(Impurity SF ₆ sample No 1)

SF ₆ is charged with a gas densitization tester to a charging pressure of about 0.5 MPa (sodium denko company, purity: 99.999%, halogen ions: 1 ppm by weight or less), and the gas insulation test is repeated. A vacuum dried and cooled cylinder container was taken and determined as impure SF ₆ sample No. 1.

The obtained impurity SF ₆ sample No 1 was analyzed by gas chromatography using various detectors such as an electron trap detector (GC / ECD), a flame photodetector, a thermal conductivity detector, and gas chromatography / mass spectrometry (GC / MS). Halogen ion analysis (ion chromatography) and water content analysis were also adopted (modified oscillator method).

The results are expressed in ppm based on the weight of (the amount of one component compared to the total amount of the components other than the H ₂ O. In the case of H ₂ O, H ₂ O by weight / total weight).

Component Analysis Value (Unit: Weight ppm)

(Impurity SF ₆ sample No 2)

To prepare a sample of Impurity SF ₆ Sample No 2, commercially available sulfa tetrafluoride (SF ₄ ) and sulfa pentafluoride (S ₂ F ₁₀ ) were added to the above impurity SF ₆ sample No 1.

The analysis results of impurity SF ₆ sample No 2 are as follows. Analysis of S ₂ F ₁₀ was determined by electron trap detector gas chromatography (GC / ECD).

Component Analysis Value (Unit: Weight ppm)

Preparation of Tablets

Three tablets were prepared.

Preparation of Tablets

(Tablet No 1)

100 ml of granular activated carbon (specific surface area: 1200 m ² / g, particle size: 0.5 to 2 mm) was immersed in 40 ml of 25% aqueous sodium aluminate solution and stirred for 1 hour. It takes the impregnated activated carbon (a NaAlO _2/100 ml loading of 10g on activated carbon), this - after filtering the impregnated carbon a to the stainless tube to dry for 3 hours at a temperature of 200 ℃ under nitrogen gas sodium containing no water-aluminate Refining agent No1 was called.

The specific surface area of the tablet No 1 was about 570 m ² / g, and the average pore size was about 14 mm ³ .

(Tablet No 2)

In 40 ml of 25% aqueous tetramethylammonium hydroxide solution, 100 ml of granular activated carbon (specific surface area: 1200 m ² / g, particle diameter: 0.5 to 2 mm) was immersed and stirred for 1 hour. After filtration, the supported carbon was dried for 5 hours at a temperature of 50 ° C. under a nitrogen gas in a stainless tube, thereby containing no water and containing tetramethylammonium hydroxide-supported activated carbon [10 g of (CH ₃ ) ₄ NOH / 100 ml] was obtained as Purifier No 2.

The specific surface area of tablet No2 was about 560 m <^2> / g, and the average pore diameter was about 13 mm <3>.

(Tablet No 3)

Charcoal particles having a particle size of 250 μm or less and calcined lime having a particle size of 250 μm or less are mixed at a weight ratio of 1: 3, and granulated by adding water mixed in a Henschel mixer, followed by granulation at 110 ° C. for 4 hours. It was dried and dehydrogenated by heat treatment at 800 ° C. for 8 hours under nitrogen atmosphere. The resulting fired product was pelletized to a size of 2 to 4 mm. This was called Purifier No3.

Purifier No 3 was mainly composed of carbon (C) and calcium oxide (CaO), and the specific surface area was about 120 m ² / g, and the average pore size was about 1000 mm ³ .

Purification Experiment

(Example 1)

A 75 ml SUS cylinder was charged with 40 ml of the above No 1 tablet and fed the impure SF ₆ sample No 1 at a rate of 12 Nl / hr at room temperature.

The gas was taken out from the exit of the cylinder, and then subjected to gas chromatography and halogen ion analysis. Halogen ion analysis was performed by suctioning the gas of the outlet taken from ultrapure water for a predetermined time, and the ultrapure water was analyzed by ion chromatography.

The analysis results are as follows.

Component analysis value (unit: weight ppm,-: display below measurement limit)

The above results indicate that the purification agent No 1 effectively removed the harmful impurities in the impure SF ₆ sample No 1.

(Example 2)

A 75 ml volume of SUS cylinder was charged with 40 ml of the above No 2 tablet and fed with impure SF ₆ sample No 1 at a rate of 20 Nl / hr at room temperature.

Gas was collected from the outlet of the cylinder, and then gas chromatography and halogen ion analysis were performed as in Example 1.

The analysis results are as follows.

Component analysis value (unit: weight ppm,-: display below measurement limit)

From the above results, it was found that the purification agent No 2 effectively removed the harmful impurities in the impure SF ₆ sample No 1.

(Example 3)

An experiment was conducted to remove moisture from the outlet gas sample obtained in Example 2.

A 75 ml SUS cylinder was charged with 60 ml of commercial zeolite (Molecular Siber 3, manufactured by Union Shoa Co., Ltd.), and the outlet gas sample obtained in Example 2 was introduced therein and the cylinder was discharged. The moisture content of the gas was analyzed. The moisture content was 5 ppm or less by weight.

It is shown that the water removal in the sample by the method of Example 3 is very effective.

(Example 4)

Two 75 ml capacity SUS cylinders were connected.

A first 75 ml capacity SUS cylinder was charged with 40 ml of tablet No 3 and a second cylinder was filled with 40 ml of tablet No 1. Impurity SF ₆ sample NO 1 was fed from the first cylinder to the second cylinder at a rate of 20 Nl / hr at room temperature. Gas was taken from the outlet of the second cylinder and gas analysis and halogen ion analysis were performed in the same manner as in Example 1.

The analysis results are as follows.

Component analysis value (unit: weight ppm,-: display below measurement limit)

The above results show that the combination of the purification agents No 1 and NO 3 is effective for the removal of perfluorocarbons (CF ₄ , C ₂ F ₆ ) as well as the removal of harmful impurities.

(Example 5)

A 75 ml SUS cylinder was charged with 40 ml of the above No. 1 tablet and fed with impure SF ₆ sample NO 2 at a rate of 12 Nl / hr at room temperature.

Gas was extracted from the outlet of the cylinder, and gas chromatography and halogen ion analysis were performed in the same manner as in Example 1. S ₂ F ₁₀ was analyzed by electron capture detection gas chromatography (GC / ECD).

The analysis results are as follows.

Component analysis value (unit: weight ppm,-: display below measurement limit)

The above results indicate that the purification agent No 1 effectively removed not only the SF ₄ and S ₂ F ₁₀ in the impure SF ₆ sample No 2 but also harmful impurities.

The method for purifying sulfur hexafluoride of the present invention comprises contacting a sulfur-containing hexafluoride containing impurities with a purifying agent comprising a carbonaceous solid and at least one compound selected from alkaline earth metal compounds, alkali metal aluminates or tetraalkylammonium salts. In the present invention, in the present invention, harmful impurities can be removed simply and effectively without requiring a large-scale apparatus. In addition, the purification method of the present invention can remove water, which is one factor of SF ₆ decomposition, by attaching a dehydration process, and recycle purified SF ₆ as an insulating medium of gas.

Claims (13)

Impurity SF comprising contacting a sulfur containing hexafluoride (SF ₆ ) containing impurities with a purifier consisting of a carbonaceous solid and at least one compound selected from alkaline earth metal compounds, alkali metal aluminates and tetraalkylammonium salts. _6, the purification method. The method of claim 1, wherein the impurity contained in SF ₆ is at least one selected from the group consisting of HF, SO ₂ , S ₂ F ₂ , SF ₂ , SF ₄ , S ₂ F ₁₀ , SOF _2, and SO ₂ F ₂ . Method for purifying impurities SF ₆ characterized in that. The impurity SF according to claim 1, wherein the alkaline earth metal compound as a refining agent is selected from the group consisting of oxides, hydroxides, carbonates and nitrates of calcium, magnesium, barium and strontium. _6, the purification method. The method for purifying impure SF ₆ according to claim 1, wherein the alkali metal aluminate as a refining agent is selected from the group consisting of lithium aluminate, sodium aluminate, potassium aluminate and cesium aluminate. The method of claim 1, wherein the tetraalkylammonium salt as a purification agent is tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetramethylammonium carbonate, tetraethylammonium carbonate, tetramethylammonium chloride, tetraethylammonium A process for purifying impure SF ₆ , characterized in that it is selected from the group consisting of chloride, tetramethylammonium aluminate and tetraethylammonium aluminate. The method of claim 1, wherein the purification of the carbonaceous solid is coke, carbon char, coal, pitch, charcoal of SF ₆ impurity is characterized, at least one kinds selected from the group consisting of activated carbon, and carbon black. The method of claim 1 wherein the purifying agent is in the method for purifying impure SF ₆ characterized in having a specific surface area of ^{80 m 2 / g ~ 1000 m} 2 / g range. The method for purifying impure SF ₆ according to claim 1, wherein the refining agent has an average pore diameter in the range of 7 kPa to 1500 kPa. The method for purifying impure SF ₆ according to claim 1, wherein the HF concentration in the obtained purified SF ₆ is 0.1 ppm or less by weight. The method for purifying impure SF ₆ according to claim 1, wherein a dehydration step is added. The method for purifying impure SF ₆ according to claim 10, wherein zeolite is used as a dehydrating agent in the dehydration process. 11. The method of claim 10, wherein the purification of the resulting moisture content of the refined SF ₆ is not 50 ppm or less by weight impurities characterized in SF _6. The method of claim 1, wherein the SF ₆ containing impurities is first brought into contact with the pellet-type refining agent consisting of a carbonaceous solid and an alkaline earth metal compound, and then alkali metal aluminate and tetra supported on the carbonaceous solid. A method for purifying impurity SF ₆ , characterized by contact with at least one purifying agent selected from alkylammonium salts, and after each contacting step, a dehydration step is added.