JP3727551B2 - Method and apparatus for separating and recovering perfluoro compound gas - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for separating and recovering perfluoro compound gases such as CF ₄ , C ₂ F ₆ , C ₃ F ₈ , C ₄ F ₁₀ , SF ₆ , and NF ₃ used in semiconductor manufacturing and the like.
[0002]
[Prior art]
In semiconductor manufacturing and the like, perfluoro compound gases such as CF ₄ , C ₂ F ₆ , C ₃ F ₈ , C ₄ F ₁₀ , SF ₆ , and NF ₃ are used in processes such as etching and cleaning.
Further, in a gas-insulated electrical apparatus such as a gas-insulated switchgear, a perfluoro compound gas may be used as an electrical insulation gas.
It has been pointed out that perfluoro compound gases can be harmful to the global environment (for example, greenhouse gases).
For this reason, the perfluoro compound gas contained in the gas discharged from the semiconductor manufacturing process is separated and recovered and reused.
Japanese Patent Application Laid-Open Nos. 9-103633 and 10-128034 describe a method for separating and recovering perfluoro compound gas in exhaust gas by membrane separation using an organic polymer (polysulfone or the like) membrane. ing.
[0003]
[Problems to be solved by the invention]
However, in the separation and recovery method using the organic polymer membrane, the perfluoro compound gas recovery rate may be insufficient.
For this reason, a separation and recovery method using a carbon membrane having an excellent perfluoro compound gas separation performance has been proposed.
For example, Japanese Patent Application Laid-Open No. 2000-185212 discloses a method for separating and recovering a perfluoro compound gas from a gas mixture using a carbon film obtained by carbonizing an organic polymer film by heat treatment.
However, when a carbon membrane is used, the gas permeation amount is likely to fluctuate and the perfluoro compound gas recovery rate may be reduced.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a separation and recovery method and apparatus that can more efficiently separate and recover perfluoro compound gas.
[0004]
[Means for Solving the Problems]
The present inventor has found that the variation in the gas permeation amount that occurs when using a carbon membrane is caused by the deterioration of the permeation characteristics of the carbon membrane due to moisture in the gas, and has completed the present invention based on this finding. .
The method for separating and recovering a perfluoro compound gas according to the present invention comprises supplying a gas mixture containing a perfluoro compound gas to a carbon membrane separation means having a carbon membrane obtained by heat-treating an organic polymer membrane. It is characterized in that water in the mixture is removed and the water content is -40 ° C. or less in terms of dew point .
As a result, the moisture concentration in the gas mixture can be lowered, the gas permeation characteristics of the carbon membrane can be prevented from deteriorating due to the adhesion of water, and the gas permeation flow rate in the carbon membrane separation means can be kept high.
Therefore, the perfluoro compound gas in the gas mixture can be separated and recovered efficiently.
As a method of removing moisture in the gas mixture, it is preferable to use at least one of membrane separation, adsorption separation, and condensation separation.
Prior to supplying the gas mixture to the carbon membrane separation means, it is preferable to remove the reactive fluorine-based gas composed of any of HF, F ₂ , WF ₆ , SiF ₄ , and BF _{3 in} the gas mixture.
[0005]
The perfluoro compound gas separation and recovery apparatus of the present invention is a carbon membrane that separates and recovers a perfluoro compound gas in a gas mixture containing a perfluoro compound gas using a carbon membrane obtained by heat-treating an organic polymer membrane. Separation means is provided, and moisture removal means is provided upstream of the carbon membrane separation means to remove moisture in the gas mixture so that the moisture content is -40 ° C. or less at the dew point .
It is preferable that the moisture removing means can remove moisture in the gas mixture by at least one of membrane separation, adsorption separation, and condensation separation.
In the present invention, the reactive fluorine-based gas removing means for removing the reactive fluorine-based gas composed of any of HF, F ₂ , WF ₆ , SiF ₄ , and BF ₃ in the gas mixture on the upstream side of the carbon membrane separation means. Is preferably provided.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a first embodiment of the perfluoro compound gas separation and recovery apparatus of the present invention.
The separation / recovery device 1 shown here passes through a compression unit 2 that compresses a gas mixture containing a perfluoro compound gas, a moisture removal means 3 that removes moisture in the gas mixture that has passed through the compression unit 2, and a moisture removal means 3. And a membrane separation unit 4 for recovering perfluoro compound gas in the gas mixture.
[0007]
The compression unit 2 includes a storage tank 5 that stores the gas mixture, and a compressor 6 that compresses the gas mixture from the storage tank 5.
[0008]
In the separation and recovery apparatus 1 of the present embodiment, the moisture removing means 3 is configured to reduce the amount of moisture in the gas mixture to −40 ° C. or less at the dew point, which includes removing moisture in the gas mixture by membrane separation. What can be used can be used.
Specifically, those using a separation membrane that transmits moisture and does not transmit perfluoro compound gas are preferable. Examples of the separation membrane include those made of an organic polymer material made of polyimide, polysulfone, or the like.
[0009]
As the moisture removing means 3, a device capable of removing moisture in the gas mixture by adsorption separation can be used.
Specifically, a case in which a moisture adsorption layer made of a moisture adsorbent such as silica, alumina gel, or molecular sieve is provided in the outer cylinder can be exemplified.
[0010]
As the moisture removing means 3, a device capable of removing moisture in the gas mixture by condensation separation can be used.
Specifically, it is preferable to include a cooling means for cooling the gas mixture and a water separation means for separating the water condensed or solidified by cooling from the gas component.
[0011]
The moisture removing means 3 can be configured to remove moisture in the gas mixture by two or more of the membrane separation, adsorption separation, and condensation separation.
[0012]
The membrane separation unit 4 includes first and second carbon membrane separation units (carbon membrane separation means) 7 and 8 that separate and recover the perfluoro compound gas in the gas mixture that has passed through the water removal means 3.
[0013]
The first and second carbon membrane separators 7 and 8 include carbon membranes obtained by carbonizing an organic polymer membrane made of an organic polymer material such as polyimide, polypyrrolone, or polyacrylonitrile by heat treatment. .
Specifically, this carbon film is obtained by heat-treating the organic polymer film at 500 to 900 ° C. in an inert gas (nitrogen or the like) atmosphere to at least partially carbonize it.
The shape of the carbon membrane of the carbon membrane separators 7 and 8 can be hollow fiber, tubular, spiral, or the like. The carbon membrane separation units 7 and 8 may employ an internal pressure type structure that allows gas to permeate from the inside to the outside of the carbon membrane, such as a hollow fiber shape or a tube, or an external pressure type that allows gas to permeate from the outside to the inside of the carbon membrane. A structure may be adopted.
[0014]
Next, the first embodiment of the separation and recovery method of the present invention will be described by taking as an example the case where the separation and recovery apparatus 1 shown in FIG. 1 is used.
Examples of the gas mixture that is the target of the separation and recovery method of the present embodiment include a gas mixture that is discharged from a semiconductor manufacturing process and the like and contains a perfluoro compound gas.
For example, a mixed gas of perfluoro compound gas (CF ₄ , C ₂ F ₆ , C ₃ F ₈ , C ₄ F ₁₀ , SF ₆ , NF ₃ etc.) and an inert gas (nitrogen gas etc.) can be exemplified.
This gas mixture is introduced into the storage tank 5 through the conduit 11. At this time, the atmosphere can also be introduced into the storage tank 5 through the pipe 12.
[0015]
Next, the gas mixture in the storage tank 5 is introduced into the compressor 6 through the pipe line 13, compressed in the compressor 6, and then introduced into the moisture removing means 3 through the pipe line 14. The moisture removing means 3 removes moisture in the gas mixture by membrane separation, adsorption separation, condensation separation or the like.
The In water removal is such that the dew point of the gas mixture is -40 ℃ or less (preferably -60 ° C. or less).
If this dew point exceeds this range, the permeate flow rate fluctuates in the carbon membrane separation units 7 and 8 and the recovery rate of the perfluoro compound gas tends to decrease.
[0016]
The gas mixture from which moisture has been removed by the moisture removing means 3 is introduced into the first carbon membrane separation unit 7 through the conduit 15.
In the first carbon membrane separation unit 7, most of the inert gas (nitrogen gas or the like) in the gas mixture permeates the carbon membrane.
Part of the permeated gas is returned to the storage tank 5 through the pipe line 16, and the remaining part is discharged out of the system through the pipe line 17 branched from the pipe line 16.
On the other hand, since the perfluoro compound gas in the gas mixture hardly permeates the carbon membrane, most of the perfluoro compound gas does not permeate the carbon membrane and is sent to the second carbon membrane separator 8 through the pipe 18 as a concentrated gas.
[0017]
In the second carbon membrane separation unit 8, the inert gas remaining in the concentrated gas permeates the carbon membrane and is returned to the storage tank 5 from the pipeline 19 as a permeated gas.
The perfluoro compound gas in the concentrated gas is recovered through the pipe line 20.
Thus, in the membrane separation unit 4, the perfluoro compound gas in the gas mixture is separated and recovered by membrane separation in the carbon membrane separation units 7 and 8.
[0018]
In the separation and recovery method of the present embodiment, the moisture in the gas mixture is removed by the moisture removing means 3 before the gas mixture is supplied to the carbon membrane separators 7 and 8, so that the gas mixture is supplied to the carbon membrane separators 7 and 8. The moisture concentration of the gas mixture can be lowered.
For this reason, in the carbon membrane separation parts 7 and 8, it can prevent that the gas permeation characteristic of a carbon membrane deteriorates by adhesion of water, and can maintain a high gas permeation | transmission flow rate.
Therefore, the perfluoro compound gas in the gas mixture can be separated and recovered efficiently.
[0019]
Some exhaust gases discharged from semiconductor manufacturing processes include reactive fluorine-based gases in addition to perfluoro compound gases, inert gases, and the like . Here, the reactive fluorine-based gas is one or a mixture of two or more of HF, F ₂ , WF ₆ , SiF ₄ , and BF ₃ .
Since the reactive fluorine-based gas has high reactivity, it can cause deterioration of the carbon membranes of the carbon membrane separation units 7 and 8.
For this reason, it is preferable to remove reactive fluorine-type gas as shown below.
[0020]
FIG. 2 shows a second embodiment of the separation and recovery apparatus of the present invention. The separation and recovery apparatus 21 shown here absorbs a reactive fluorine-based gas between the compressor 6 and the water removal means 3. An absorption cylinder (reactive fluorine-based gas removing means) 22 provided with a reactive fluorine-based gas absorbent to be removed is provided.
As the absorbent used in the absorption cylinder 22, a calcium hydroxide-containing treatment agent (for example, soda lime) can be used.
[0021]
In order to separate and recover the perfluoro compound gas in the gas mixture using the separation and recovery device 21, the gas mixture containing the perfluoro compound gas is introduced into the absorption cylinder 22 through the storage tank 5 and the compressor 6.
In the absorption cylinder 22, the reactive fluorine-based gas in the gas mixture is absorbed and removed by the absorbent.
The gas mixture that has passed through the absorption cylinder 22 is introduced into the moisture removing means 3, where moisture in the gas mixture is removed.
The gas mixture that has passed through the moisture removing means 3 is introduced into the membrane separation unit 4, where the perfluoro compound gas in the gas mixture is concentrated and recovered by membrane separation in the carbon membrane separation units 7, 8. .
[0022]
In this separation and recovery method, the reactive fluorine-based gas in the gas mixture is removed by the absorption cylinder 22 before the gas mixture is supplied to the carbon membrane separation units 7 and 8, and therefore the carbon membrane separation unit using the reactive fluorine-based gas. 7 and 8 can be prevented beforehand.
Therefore, the permeation performance of the carbon membrane separators 7 and 8 can be maintained over a long period of time.
[0023]
Further, since the reactive fluorine-based gas in the gas mixture is removed by the absorption cylinder 22 before the gas mixture is supplied to the moisture removing means 3, the moisture removing means 3 is deteriorated by the reactive fluorine-based gas and the moisture removing performance is improved. It can be prevented in advance.
[0024]
FIG. 3 shows a third embodiment of the separation and recovery apparatus of the present invention. The separation and recovery apparatus 31 shown here includes a water removal means 3 for removing moisture in the gas mixture, and a gas that has passed through the moisture removal means 3. A compression unit 2 that compresses the mixture, and a membrane separation unit 4 that recovers perfluoro compound gas in the gas mixture that has passed through the compression unit 2, and a reactive fluorine-based gas upstream of the moisture removing means 3. An absorption cylinder (reactive fluorine-based gas removing means) 32 is provided for removing water.
As the absorption cylinder 32, the same structure as the absorption cylinder 22 can be used.
[0025]
In order to use this separation and recovery device 31, the reactive fluorine-based gas in the gas mixture is removed by the absorption cylinder 32, and then moisture is removed by the moisture removing means 3.
The gas mixture from which the reactive fluorine compound and moisture have been removed is compressed by the compression unit 2 and then introduced into the membrane separation unit 4 to separate and recover the perfluoro compound gas in the gas mixture by membrane separation.
[0026]
According to this method, since the reactive fluorine-based gas in the gas mixture is removed by the absorption cylinder 32, it is possible to prevent the performance of the water removing means 3 and the membrane separation unit 4 from being deteriorated.
[0027]
【Example】
Hereinafter, the separation and recovery method of the present invention will be described with reference to specific examples.
(Example)
The following tests were conducted using the separation and recovery apparatus 1 shown in FIG.
As the water removal means 3, the one provided with a water adsorbent layer made of molecular sieve in the outer cylinder was used.
In this embodiment, a mixture of nitrogen and CF ₄ is used as the gas mixture. Nitrogen and CF ₄ were supplied at the following flow rates. Water was added to this gas mixture so that the dew point was -20 ° C.
Nitrogen: 45L / min
CF ₄ : 90 mL / min
This gas mixture was introduced into the moisture removing means 3 through the storage tank 5 and the compressor 6 to remove moisture in the gas mixture. This resulted in a dew point of the gas mixture of −63 ° C.
The gas mixture that passed through the moisture removing means 3 was introduced into the first carbon membrane separation unit 7, about 70% of the permeate gas was returned to the storage tank 5, and the concentrated gas was introduced into the second carbon membrane separation unit 8. The concentrated gas that passed through the second carbon membrane separation unit 8 was recovered from the pipe line 20.
The inflow pressure of the gas mixture in the carbon membrane separation units 7 and 8 at the start of the test was set to 0.8 MPa and 0.7 MPa, respectively.
FIG. 4 shows changes with time in the flow rate of the permeating gas in the first carbon membrane separation unit 7.
[0028]
(Comparative example)
As shown in FIG. 5, a perfluoro compound gas recovery test was performed under the same conditions as in Example 1 using the same separation and recovery apparatus 41 as that used in Example except that the water removal means 3 was not provided. It was.
The time-dependent change of the flow rate of the permeate gas in the first carbon membrane separation unit 7 is also shown in FIG.
[0029]
From FIG. 4, in the comparative example in which the moisture removal of the gas mixture is not performed, the permeate flow rate in the first carbon membrane separation unit 7 is decreased, whereas in the example in which the water removal is performed, the permeate flow rate is maintained and good for a long time. It can be seen that safe driving has become possible.
[0030]
【The invention's effect】
As described above, in the separation and recovery method of the present invention, moisture in the gas mixture is removed prior to supplying the gas mixture to the carbon membrane separation means, so the moisture concentration of the gas mixture supplied to the carbon membrane separation means Can be lowered.
For this reason, in the carbon membrane separation means, it is possible to prevent the gas permeation characteristics of the carbon membrane from deteriorating due to the adhesion of water, and to keep the gas permeation flow rate high.
Therefore, the perfluoro compound gas in the gas mixture can be separated and recovered efficiently.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a first embodiment of a perfluoro compound gas separation and recovery apparatus according to the present invention.
FIG. 2 is a configuration diagram showing a second embodiment of the separation and recovery device of the present invention.
FIG. 3 is a configuration diagram showing a third embodiment of the separation and recovery device of the present invention.
FIG. 4 is a graph showing test results.
FIG. 5 is a configuration diagram showing an example of a separation and recovery device.
[Explanation of symbols]
1, 21, 31, 41 ... separation and recovery device, 3 ... moisture removal means, 7,8 ... carbon membrane separation part (carbon membrane separation means), 22,32 ... absorption cylinder (reactivity) Fluorine gas removal means)

Claims (6)

A gas mixture containing a perfluoro compound gas is supplied to a carbon membrane separation means having a carbon membrane obtained by heat treating an organic polymer membrane, and the perfluoro compound gas in the gas mixture is separated using this carbon membrane. A method of collecting,
Prior to supplying the gas mixture to the carbon membrane separation means, the water content in the gas mixture is removed, and the water content is reduced to -40 ° C. or less at the dew point .  2. The method for separating and recovering perfluoro compound gas according to claim 1, wherein at least one of membrane separation, adsorption separation, and condensation separation is used as a method for removing moisture in the gas mixture. The reactive fluorine-based gas composed of any one of HF, F ₂ , WF ₆ , SiF ₄ , and BF _{3 in} the gas mixture is removed prior to supplying the gas mixture to the carbon membrane separation means. 3. A method for separating and recovering perfluoro compound gas according to 1 or 2. A separation and recovery device comprising a carbon membrane separation means for separating and recovering a perfluoro compound gas in a gas mixture containing a perfluoro compound gas using a carbon membrane obtained by heat treating an organic polymer membrane ,
An apparatus for separating and recovering a perfluoro compound gas, characterized in that water removal means is provided upstream of the carbon membrane separation means to remove moisture in the gas mixture and to bring the amount of water to -40 ° C. or less at the dew point. .  5. The separation of perfluoro compound gas according to claim 4, wherein the moisture removing means is capable of removing moisture in the gas mixture by at least one of membrane separation, adsorption separation, and condensation separation. Recovery device. Reactive fluorine-based gas removing means for removing a reactive fluorine-based gas composed of any one of HF, F ₂ , WF ₆ , SiF ₄ , and BF ₃ in the gas mixture is provided on the upstream side of the carbon membrane separation means. The apparatus for separating and recovering perfluoro compound gas according to claim 4 or 5.

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