JP4998929B2 - Gas purification method - Google Patents

Description

  The present invention relates to a gas purification method, and more particularly, to a gas purification method for purifying carbon dioxide gas for semiconductor production using a carbon film having a molecular sieving action.

  At present, it is desirable that the gas used in the semiconductor field is an ultra-high purity gas having a higher impurity volume concentration of ppb-ppb level than that of a high purity gas having an impurity volume concentration of ppb-ppm level. ing.

  Carbon dioxide gas for semiconductors is widely used for cleaning silicon wafers, removing residual photoresist, and recently supercritical applications.

  Gas purification techniques include metal catalyst and adsorbent purification methods, rectification (liquefaction purification) and solidification purification methods, and separation membrane purification methods. As an example of purifying impurities in carbon dioxide, carbon monoxide is converted to carbon dioxide and removed with a platinum or palladium catalyst, nitrogen oxides are converted to nitrogen and water, and water is removed with an adsorbent. The liquefaction is purified to remove nitrogen and the like (see, for example, Patent Document 1 and Patent Document 2), and hydrocarbons other than methane are converted to carbon dioxide and removed with a platinum-based or palladium-based catalyst (for example, Patent Document 1). 3 (see Patent Document 4), an organic substance is converted into carbon dioxide and water with a titanium oxide catalyst, and finally liquefied and purified to remove nitrogen or the like (see, for example, Patent Document 5). (See, for example, Patent Document 6 and Patent Document 7), carbon dioxide is solidified and low-boiling impurities are exhausted (for example, refer to Patent Document 8). Such as away (for example, see Patent Document 9) and the like.

  Although it is not a direct gas purification technology, low-purity carbon dioxide exhaust gas from liquefaction purification is introduced into a separation membrane that can selectively pass carbon dioxide, and carbon dioxide is recovered efficiently. Examples include producing high-purity carbon dioxide (see, for example, Patent Document 10).

JP 2007-22906 A Japanese Patent Laid-Open No. 10-13010 JP 61-127613 A Japanese Patent No. 3927332 JP 2004-196556 A JP 2006-502957 A Japanese Patent No. 3522785 JP 2002-13696 A JP-A-6-269648 JP 2004-323263 A

  However, the inventions exemplified in Patent Documents 1 to 4, 6, and 7 are purification methods using a metal catalyst as a purification technique, and heating requires several hundred degrees of heating and uses a lot of energy. It is not an economically advantageous method.

  The invention exemplified in Patent Document 5 is a purification method using a photocatalyst as a purification technique, and the purification requires irradiation with ultraviolet rays, and a separate facility for irradiating ultraviolet rays is required.

  The invention exemplified in Patent Document 8 is a purification method by solidifying carbon dioxide as a purification technique and exhausting gas phase, and the purification requires cooling of −150 to −196 ° C. Because it is used, it is not an economically advantageous method.

  The inventions exemplified in Patent Document 9 are all capable of being purified when the impurity volume concentration contained in the gas to be purified is from ppm to% level and the impurity volume concentration is from ppt to ppb level. Not shown. Conventional gas used as a semiconductor material requires an impurity volume concentration of ppb-ppm level, but now, an impurity volume concentration of ppp-ppb level is required.

  The invention exemplified in Patent Document 10 is used for recovering carbon dioxide, and does not purify carbon dioxide.

  Then, an object of this invention is to provide the gas purification method which refine | purifies highly pure carbon dioxide gas to ultra-high purity with a further high purity by simple methods without operation, such as heating and cooling.

To solve this problem,
Such invention in claim 1, a gas purification method for purifying using a carbon membrane having a molecular sieving action to be purified gas, wherein the purified gas is a carbon dioxide containing 10ppm or less impurities, the carbon The gas purification method is characterized in that the membrane is formed from polyphenylene oxide as a raw material .

The invention according to claim 2, wherein comprises impurities methane or ethane, the carbon film Ri hollow fiber or tubular der, it is characterized by using a container which is separated by the resin wall for fixing a bundle of the carbon film The gas purification method according to claim 1.

According to the present invention, by purifying high-purity carbon dioxide gas using a carbon film having a molecular sieving action, it is possible to remove impurities in the order of ppm contained therein and to achieve ultra-high purity.
In addition, since the carbon membrane is superior in separation performance compared to existing organic polymer membranes, it is possible to efficiently purify a gas containing impurities of 10 ppm or less. Further, by forming the carbon membrane into a hollow fiber shape, the membrane module can be designed more compactly than the flat membrane shape and the spiral wound shape.

It is a schematic sectional drawing which shows an example of the carbon membrane module in this invention. It is AA 'sectional drawing in the carbon membrane module shown in FIG. It is a schematic sectional drawing which shows an example of a carbon membrane module in case the sweep gas supply port in this invention is provided in the carbon membrane module one end surface. It is a schematic sectional drawing which shows an example of the carbon membrane module in which the sweep gas supply port in this invention was provided in the carbon membrane module peripheral surface.

  Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 to 4.

One embodiment of the carbon membrane module 1 used in the gas purification method of the present invention is shown in FIGS.
In FIG. 1, reference numeral 1 denotes a carbon membrane module. The carbon membrane module 1 is generally composed of a sealed container 6 and a carbon membrane unit 2 provided in the sealed container 6.

  The sealed container 6 has a hollow cylindrical shape, and is provided with a permeate gas discharge port 4 at one end and an unpermeate gas discharge port 5 at the other end. Further, a gas supply port 3 is provided on the peripheral surface of the sealed container 6.

The carbon membrane unit 2 is composed of a plurality of hollow fiber carbon membranes 2a... And a resin wall 7 that binds and fixes these hollow fiber carbon membranes 2a. The resin wall 7 is hermetically fixed to the inner wall of the sealed container 6 using an adhesive or the like.
FIG. 2 is a cross-sectional view taken along the line AA ′ in the carbon membrane module shown in FIG. 1 and illustrates the surface structure of the resin wall 7 in the sealed container 6. In the resin wall 7, openings of hollow fiber-like carbon membranes 2a ... are formed.

  The inside of the sealed container 6 is divided into a first space 9 and a second space 10 by a resin wall 7, and the first space 9 is a space on the side where a bundle of hollow fiber-like carbon membranes 2a ... The second space 10 is a space on the opposite side to the side where the bundle of hollow fiber-like carbon membranes 2a.

  One end of the hollow fiber-like carbon membrane 2a... Is fixed to the resin wall 7 and opened, and the other end is closed. In the portion where the hollow fiber-like carbon membrane 2a is fixed by the resin wall 7, the opening of the hollow fiber-like carbon membrane 2a ... communicates with the second space 10, whereby the first space 9 And the second space 10 communicate with each other through the carbon membrane unit 2.

The hollow fiber-like carbon membrane 2a ... is produced by sintering after producing an organic polymer membrane. For example, an organic polymer such as polyimide is dissolved in an arbitrary solvent to prepare a film forming stock solution. In addition, a solvent which is mixed with the solvent of the film forming stock solution but is insoluble in polyimide is prepared.
Next, the film-forming stock solution is extruded from the circumferential annular port of the hollow fiber spinning nozzle having a double-pipe structure, and the solvent is simultaneously extruded into the coagulating liquid from the central circular port of the spinning nozzle to form a hollow fiber shape. Manufacturing organic polymer membranes. Next, the obtained organic polymer film is carbonized after being infusibilized to form a carbon film.

  The carbon membrane is used by selecting an optimal form such as a carbon membrane coated only on a porous support and a carbon membrane coated on a gas separation membrane other than the carbon membrane. Examples of the porous support include ceramic materials such as alumina, silica, zirconia, magnesia, and zeolite, and metal filters. Application to the support has effects such as an increase in mechanical strength and simplification of carbon film production.

  The organic polymer used as the raw material for the carbon film includes polyimide (aromatic polyimide), polyphenylene oxide (PPO), polyamide (aromatic polyamide), polypropylene, polyfurfuryl alcohol, polyvinylidene chloride (PVDC), phenol resin, Examples thereof include cellulose, lignin, polyetherimide, and cellulose acetate.

  Among the carbon film materials described above, polyimide (aromatic polyimide), cellulose acetate, and polyphenylene oxide (PPO) can be easily formed into a hollow fiber carbon film. Polyimide (aromatic polyimide) and polyphenylene oxide (PPO) have particularly high separation performance. Furthermore, polyphenylene oxide (PPO) is less expensive than polyimide (aromatic polyimide).

Next, a gas purification method using the carbon membrane module 1 shown in FIG. 1 will be described.
Here, the molecular sieving action is an action in which a gas having a small molecular diameter is separated from a gas having a large molecular diameter, depending on the molecular diameter of the gas and the pore diameter of the separation membrane.

  In general, gas separation membranes have a separation factor of 10 to 1000. Therefore, in order to purify into an ultra high purity gas having an impurity volume concentration of ppt-ppb level, a high purity gas having an impurity volume concentration of 10 ppm or less is supplied as a gas to be purified. However, even when a gas having an impurity volume concentration of 10 ppm or more is supplied, the gas separation membrane generally has a separation factor of 10 to 1000, and thus is effective as a purification method. In addition, although the lower limit of the impurity volume concentration of the high purity gas is not particularly set, the impurity volume concentration that requires ultra-high purity purification can be exemplified by about 300 ppb.

The carbon dioxide gas to be purified may be contaminated with impurities during gas production or cylinder replacement. At the time of gas production, nitrogen, oxygen, argon, or moisture as atmospheric components, and in the case of carbon dioxide derived from petroleum refining, hydrogen, methane, and ethane may be mixed into the product gas. Atmosphere components and moisture may be mixed when replacing the cylinder.
Among these, hydrogen, oxygen, nitrogen, argon, and moisture that are easily removed by the adsorbent, which are components lower in boiling point than carbon dioxide, are easily removed in the purification process to high purity, but methane and ethane are Since it has a relatively high boiling point and is an inert component, it tends to remain even in a high-purity purification process.
In the method of the present invention, it is possible to convert high-purity carbon dioxide to ultra-high-purity carbon dioxide by removing these components for the time being.

For example, when carbon dioxide contains methane and ethane as impurity gases, the molecular diameter of carbon dioxide is 0.33 nm, and the molecular diameter of methane and ethane is 0.38 nm. It may be between the molecular diameter of methane and the molecular diameter of methane.
Carbon dioxide containing methane and ethane is continuously supplied from the gas supply port 3 of the carbon membrane module 1 and flows into the first space 9. The carbon dioxide selectively permeating through the hollow fiber-like carbon membrane 2a ... from the first space 9 flows into the second space 10 through the inside of the hollow fiber-like carbon membrane 2a ... 4 is derived.
Methane and ethane that have not permeated the hollow fiber carbon membrane 2a... From the first space 9 are discharged from the non-permeated gas discharge port 5. As a result, the methane and ethane concentrations in carbon dioxide are reduced.
As for oxygen, nitrogen, and argon, oxygen is 0.346 nm, nitrogen is 0.364 nm, argon is 0.34 nm, and its molecular diameter is larger than that of carbon dioxide, so the concentration of these components on the transmission side is low.
The pore diameter of the carbon film can be adjusted by changing the firing temperature during carbonization.

  When the purification is performed, the carbon membrane module 1 is maintained at a constant temperature in a temperature range of −20 ° C. to 120 ° C. Although the permeation | transmission flow rate of a carbon membrane can be increased if the temperature to hold | maintain is high, there exists an economical advantage by using at normal temperature.

The pressure of the gas supplied to the carbon membrane module 1 is normally maintained at about 0.5 MPaG, but can be set to 1 MPaG or more if a support is used. As the pressure of the supplied gas is higher, the amount of purification treatment can be increased.
Further, if the permeate gas discharge port 4 is connected to a vacuum facility or the like, the pressure on the permeate side is lowered, and the purification efficiency can be further increased. In the case of the present invention, the high purity gas filled in a container such as a cylinder is adjusted to a predetermined pressure with a decompressor and supplied to the carbon membrane module 1 without using a pressurizer or the like. It is possible to purify to ultra high purity gas.

  In addition, when refining high purity gas to ultra high purity gas, the carbon membrane module 1 may be used in a plurality of stages in series. Further, the ultra-high purity gas purified by the carbon membrane module 1 may be returned to the carbon membrane module 1 and circulated again.

FIG. 3 shows another embodiment of the carbon membrane module 1 used in the gas purification method of the present invention. The difference in configuration from the carbon membrane module 1 shown in FIG. 1 is that the gas supply port 3 and the non-permeate gas discharge port 5 are provided on the peripheral surface of the sealed container 6, and both ends of the carbon membrane unit 2 are made of resin. It is fixed by the wall 7, and the inside of the sealed container 6 is separated by the resin wall 7 into three spaces of the first space 11, the second space 12, and the third space 13.
By providing a sweep gas supply port 8 at one end of the sealed container 6 and supplying the sweep gas as a sweep gas from the permeation side of the carbon film, that is, the sweep gas supply port 8, it is possible to promote the permeation of impurities. it can. As the sweep gas, ultra high purity carbon dioxide that does not contain methane or ethane or is sufficiently reduced is used from the gas supply port 3.

  FIG. 4 shows another embodiment of the carbon membrane module 1 used in the gas purification method of the present invention. 3 is different from the carbon membrane module 1 shown in FIG. 3 in that the gas supply port 3 is provided not on the peripheral surface of the closed vessel 6 but on the end surface in the longitudinal direction of the closed vessel 6 and the sweep gas supply port 8 is provided on the peripheral surface. It is being done.

  In addition, by using an adsorbent, a catalyst, etc. in the front | former stage or back | latter stage of the carbon membrane module 1, the gas component difficult to isolate | separate with a carbon membrane can be isolate | separated and refine | purified. For example, since moisture having a molecular diameter smaller than that of carbon dioxide permeates the carbon film in the same manner as carbon dioxide, molecular sieves or the like are installed as a dehumidifier before the carbon film. As a result, carbon dioxide gas containing impurities from which only water has been removed can be used as the gas to be purified, and methane, ethane, and the like can be separated.

  Hereinafter, the present invention will be described in more detail with reference examples and examples. However, the present invention is not limited to the following examples.

Example 1 Purification of Carbon Dioxide Gas Containing Impurities Using Carbon Film In Example 1, a gas containing high-concentration impurities was purified using the carbon membrane module shown in FIG.
The specifications of the carbon membrane module were as follows. Hollow fiber carbon membrane tube outer diameter: 0.375 mm, hollow fiber carbon membrane tube length: 122 mm, number of hollow fiber carbon membrane tubes: 37, total surface area of hollow fiber carbon membrane tubes: 53.152 cm ² . The hollow fiber carbon membrane was produced by forming an organic polymer membrane using polyphenylene oxide (PPO) as a raw material and carbonizing it.

  The carbon membrane module was maintained at 30 ° C., and the pressure of the supply gas was set to 0.45 MPaG by installing a back pressure regulator at the non-permeate gas outlet.

(A) Carbon dioxide 459.0 sccm containing methane and ethane as impurities was supplied to the carbon membrane module, and volume concentrations of methane and ethane in the permeate gas were measured.
(B) 6.4 sccm of carbon dioxide containing methane and ethane as impurities was supplied to the carbon membrane module, and the volume concentrations of methane and ethane in the permeate gas were measured.

The gas concentration (GC-FID) equipped with a flame ionization detector was used for volume concentration measurement. The recovery rate indicates the ratio of the flow rate of the permeating gas to the supply gas. The measurement results are shown in Table 1.

  From Table 1, the permeate gas flow rate is about 5 sccm in both cases (a) and (b), and the volume concentration of the impurity gas is 1/50 to 1/100 for methane and ethane. It was possible to reduce to 1/1000.

Comparative Example 1 Purification of Carbon Dioxide Gas Containing Impurities Using Organic Polymer Membrane In Comparative Example 1, a gas containing low-concentration impurities was purified using an organic polymer membrane module.
This organic polymer membrane module was the same type as the carbon membrane module shown in FIG. 1 except that an organic polymer membrane was used instead of the carbon membrane.
The specifications of the organic polymer membrane module were as follows. Hollow fiber organic polymer membrane tube outer diameter: 0.658 mm, hollow fiber organic polymer membrane tube length: 123 mm, number of hollow fiber organic polymer membrane tubes: 37, hollow fiber organic polymer membrane tube total surface area: 81. 07 cm ² . The hollow fiber organic polymer membrane was manufactured by forming an organic polymer membrane using polyphenylene oxide (PPO) as a raw material.

  The organic polymer membrane module was maintained at 30 ° C., and the pressure of the supply gas was set to 0.45 MPaG by installing a back pressure regulator at the non-permeate gas outlet.

(A) Carbon dioxide (577.9 sccm) containing methane and ethane as impurities was supplied to the organic polymer membrane module, and volume concentrations of methane and ethane in the permeate gas were measured.
(B) Carbon dioxide (10.7 sccm) containing methane and ethane as impurities was supplied to the organic polymer membrane module, and volume concentrations of methane and ethane in the permeate gas were measured.

For the measurement of volume concentration, gas chromatography (GC-FID) equipped with a flame ionization detector was used. The recovery rate indicates the ratio of the flow rate of the permeating gas to the supply gas. The measurement results are shown in Table 2.

  From Table 2, the permeate gas flow rate is about 7.5 sccm in any of the cases (a) to (d), and the volume concentration of the impurity gas should be 1/4 to 1/12 for methane or ethane. For example, it could be reduced to 1/6 to 1/16 or less. However, at the same recovery rate, the performance of the carbon film is inferior.

(Comparative Example 2) Purification of carbon dioxide gas containing impurities by porous adsorbent In Comparative Example 2, a gas containing low-concentration impurities was purified using a packed column packed with molecular sieves having a pore diameter of 0.3 nm. . The specifications of the packed column were as follows. Column inner diameter: 10.2 mm, column length: 100 mm, and molecular sieve packing: 4.1 g.
Use molecular sieves that are packed in a column and then heat treated at 200 ° C for 1 hour and 350 ° C for 2 hours with nitrogen flowing at 1 liter / min and returned to room temperature over 10 hours. did.

  The packed column was maintained at 30 ° C., and the pressure of the supply gas was set to 0.30 MPaG by installing a back pressure regulator at the packed column outlet.

  Carbon dioxide containing 500.0 sccm of methane and ethane as impurities was supplied to the packed column, and the volume concentration of methane and ethane in the packed column outlet was measured.

For the measurement of volume concentration, gas chromatography (GC-FID) equipped with a flame ionization detector was used. Table 3 shows the measurement results.

  From Table 3, the volume concentrations of methane and ethane at the outlet of the packed column were almost the same as or slightly increased from the feed gas. The cause of the increase may be that carbon dioxide was methanated by molecular sieves, but impurities could not be removed anyway.

(Comparative Example 3) Purification of carbon dioxide gas containing impurities by metal catalyst In Comparative Example 3, a gas containing low concentration impurities was purified using a packed column packed with an alumina catalyst carrying a nickel catalyst. The specifications of the packed column were as follows. Column inner diameter: 10.2 mm, column length: 100 mm, and alumina catalyst loading: 5.8 g. The alumina catalyst was used after it was packed in a column and heated at 180 ° C. for 3 hours while flowing nitrogen at 1 liter / min and returned to room temperature over 10 hours.

The packed column was maintained at 30 ° C., and the pressure of the supply gas was set to 0.30 MPaG by installing a back pressure regulator at the packed column outlet.

  Carbon dioxide containing 500.0 sccm of methane and ethane as impurities was supplied to the packed column, and the volume concentration of methane and ethane in the packed column outlet was measured.

For the measurement of volume concentration, gas chromatography (GC-FID) equipped with a flame ionization detector was used. Table 4 shows the measurement results.

  From Table 4, the volume concentrations of methane and ethane at the outlet of the packed column were almost the same as or slightly increased from the feed gas. The cause of the increase may be that carbon dioxide was methanated by molecular sieves, but impurities could not be removed anyway.

(Comparative Example 4) Purification of carbon dioxide gas containing impurities by metal catalyst In Comparative Example 4, a gas containing low concentration impurities was purified using a packed column packed with an alumina catalyst supporting a nickel catalyst. This alumina catalyst was the same as Comparative Example 3 except that oxygen was added during the heat treatment. The specifications of the packed column were as follows. Column inner diameter: 10.2 mm, column length: 100 mm, and alumina catalyst loading: 5.8 g. After the alumina catalyst is packed in the column, it is heated at 180 ° C. for 3 hours while flowing nitrogen at a rate of 1 liter / min and oxygen at a rate of 0.01 liter / min. I used something.

  The packed column was maintained at 30 ° C., and the pressure of the supply gas was set to 0.30 MPaG by installing a back pressure regulator at the packed column outlet.

  Carbon dioxide containing 500.0 sccm of methane and ethane as impurities was supplied to the packed column, and the volume concentration of methane and ethane in the packed column outlet was measured.

表５より、充填カラム出口のメタン、エタンの体積濃度は、供給ガスとほぼ同程度もしくは若干増加した。増加した原因としては、二酸化炭素がモレキュラーシーブスによってメタン化された可能性が考えられるが、どちらにしても不純物の除去はできていない。 For the measurement of volume concentration, gas chromatography (GC-FID) equipped with a flame ionization detector was used. Table 5 shows the measurement results.

From Table 5, the volume concentrations of methane and ethane at the outlet of the packed column were almost the same as or slightly increased from the feed gas. The cause of the increase may be that carbon dioxide was methanated by molecular sieves, but impurities could not be removed anyway.

  The present invention can be applied to a recovery apparatus that recovers used carbon dioxide gas and uses it again as an ultra-high purity semiconductor material gas, or an apparatus or facility for manufacturing or filling ultra-high purity carbon dioxide gas. In addition, the amount of energy used is small compared to catalyst purification that requires rectification and heating, and adsorption purification that requires cooling, and it is an economical and environmentally friendly method.

  DESCRIPTION OF SYMBOLS 1 ... Carbon membrane module, 2 ... Carbon membrane unit, 2a ... Hollow fiber-like carbon membrane, 3 ... Gas supply port, 4 ... Permeate gas discharge port, 5 ... Non-permeate gas discharge port, 6 ... Sealed container, 7 ... Resin wall, 8 ... Sweep gas supply port, 9 ... 1st space, 10 ... 2nd space, 11 ... 1st space, 12 ... 2nd space, 13 ... 3rd space

Claims (2)

A gas purification method for purifying a gas to be purified using a carbon membrane having a molecular sieving action,
The gas to be purified is carbon dioxide containing impurities of 10 ppm or less,
A gas purification method , wherein the carbon film is formed using polyphenylene oxide as a raw material . The impurities include methane or ethane;
Wherein Ri carbon film hollow fiber or tubular der,
The gas purification method according to claim 1, wherein a container separated by a resin wall for bundling and fixing the carbon membrane is used .

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