JPH0446173B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention is directed to a gas separation membrane (hollow fiber, spiral membrane, flat membrane, etc.) made of aromatic polyimide having a specific high performance permselectivity. Water vapor is selectively removed from various mixed gases containing water vapor (e.g., air, natural gas, associated gas during crude oil extraction, fermentation gas, etc.) using gas separation equipment, and the mixed gas The present invention provides a method for drying. [Description of Prior Art] Conventionally, glycol absorption method, molecular sieve adsorption method, etc. have been generally adopted as methods for dehumidifying hydrocarbon gas such as natural gas. However, all of these methods require fairly large equipment, high equipment costs, and sufficient land for factory construction, making them difficult to use for offshore gas extraction where space is limited. It was not suitable, and there were also problems in terms of complexity of operation, operational safety, and difficulty in maintenance. In contrast to the above-mentioned absorption or adsorption methods, a gas separation module containing a built-in gas separation membrane has recently been developed as a method that can be made into a small, lightweight device, easy to maintain, and highly safe. Several methods have been proposed for dehumidifying or drying mixed gas. Methods for dehumidifying a mixed gas using such a gas separation membrane include, for example: (a) pressurizing a mixed gas containing water vapor to an extremely high pressure and supplying it to a gas separation device;
By significantly reducing the pressure on the permeate side of the gas separation membrane (see JP-A-54-152679), the pressure difference of water vapor between the supply side and the permeate side of the gas separation membrane is increased, and the mixed gas (b) The permeability of the main component of the supplied gas (for example, methane gas in natural gas) is relatively high, and the selective permeability of water vapor to methane gas (PH ₂
A method of dehumidifying mixed gas using a gas separation membrane with O/PCH ₄ ) of 200 to 400
193835), and (c) a method of dehumidifying the mixed gas by supplying a large amount of purge gas to the permeation side of the gas separation membrane to lower the partial pressure of the permeated water vapor (see Japanese Patent Laid-Open No. 50-2674). (see Publication No. 1), etc. are known. However, in the above-mentioned known method (a), in the area where the concentration of water vapor is high on the gas permeation side of the gas separation membrane (near the permeate gas outlet), water vapor is removed from the mixed gas at a sufficiently high removal rate. In addition, with method (b) described above, it is difficult to produce a gas separation membrane with gas separation performance compatible with this method. Alternatively, the method (c) described above has the disadvantage of consuming a considerable amount of purge gas. He had it. [Requirements and effects of the present invention] As a result of intensive research into a practical dehumidification method that eliminates the drawbacks of the above-mentioned "mixed gas dehumidification method using a gas separation membrane," the inventors found that water vapor It has a built-in gas separation membrane (hollow fiber membrane or spiral gas separation membrane) made of aromatic polyimide that has sufficiently high permeability (speed) and extremely high selective permeability of water vapor relative to other gas components. A gas separation device is used to flow a mixed gas along the gas supply side of the gas separation membrane while passing a small amount of externally supplied dry gas along the gas permeation side of the gas separation membrane of the gas separation device. The inventors have discovered that by selectively permeating water vapor in a mixed gas through a gas separation membrane, the mixed gas can be effectively dehumidified or dried, and the present invention has been completed. That is, this invention provides a permeated gas outlet and a dry gas supply port that communicate with the gas permeation side of the gas separation membrane, and a mixed gas supply port and non-permeated gas exhaust that communicate with the gas supply side of the gas separation membrane. The gas permeation rate ratio of water vapor and methane (PH ₂ O/
A gas separation membrane made of aromatic polyimide with a permselectivity of 200 or higher expressed by PCH ₄ A dry gas of 10% by volume or less with respect to the mixed gas is supplied from the dry gas supply port to flow along the gas supply side of the gas separation membrane. The present invention relates to a method for dehumidifying a mixed gas, which comprises removing water vapor from the mixed gas that has passed through the gas separation membrane while flowing along the permeation side. The method of this invention uses a gas separation membrane made of aromatic polyimide that has excellent water vapor permselectivity, and dehumidifies a mixed gas while flowing dry gas through the gas permeation side of the gas separation membrane. (a) The gas separation membrane built into the gas separation device can be used effectively, and the membrane area of the gas separation membrane layered inside the entire gas separation device can be reduced. (b) It is possible to use relatively low-pressure raw material gas, and mixing can be achieved without increasing the differential pressure between the raw material gas supply side and the gas permeation side. (c) Sufficient dehumidification can be performed even if the amount of drying gas (purge gas) supplied from the outside and distributed to the gas permeation side is relatively small compared to the supplied gas. I can,
This has the advantage of reducing waste of drying gas. In addition, the aromatic polyimide gas separation membrane used in the method of this invention has extremely excellent properties such as durability, heat resistance, chemical resistance, and moisture resistance. Another advantage is that dehumidification can be carried out stably over a long period of time. [Detailed explanation of each requirement of the present invention] Hereinafter, each requirement of the present invention will be explained in more detail with reference to the drawings. The gas separation device used in this invention is, for example,
As shown in FIG. 1, a gas separation device 1 includes a specific gas separation membrane 2 (such as a polyimide hollow fiber or a spiral membrane although not shown) built into a sealed container 7. The gas separation membrane has a permselectivity (gas separation performance) shown by the "ratio of gas permeation rates of water vapor and methane (PH ₂ O/PCH ₄ )" measured by the gas permeation test method described below. Any gas separation membrane (for example, hollow fiber membrane, spiral membrane, flat membrane, etc.) made of aromatic polyimide with a molecular weight of 200 or more, preferably 400 or more, and more preferably about 500 to 50,000 may be used. The gas separation membrane has a water vapor permeation rate (PH ₂ O; according to the gas permeation test method described below) at 25°C of about 1×10 ^-5 cm ³ /cm ² ·sec·cmHg or more, particularly 1×
It is preferably about 10 ⁻⁴ to 5×10 ⁻² cm ³ /cm ² ·sec·cmHg. In the gas separation membrane, if the permselectivity (PH ₂ O/PCH ₄ ) is less than 200, it is not suitable because dehumidification of the mixed gas will not be carried out sufficiently effectively. In addition, the sealed container has an "exhaust port 5 for permeated gas (water vapor, etc.) that has passed through the gas separation membrane" and a "supply port 6 for drying gas (purge gas)" that communicate with the gas permeation side of the gas separation membrane 2. ”, as well as a sealed container (for example, a cylindrical container, etc. ). In the gas separation device described above, both ends of the gas separation membrane (such as a bundle of hollow fibers) 2 are formed by solidifying a suitable thermosetting resin such as an elastomer resin, an acrylate resin, an epoxy resin, or a phenol resin. The gas separation membrane element is formed by being bound together by disc-shaped resin walls 8 and 8', and
In this element, each hollow fiber passes through the resin wall, and the holes inside the hollow fibers are opened toward the outside of the resin wall. It is sufficient that the portion 8' is hermetically fixed to the inner wall of the sealed container 7 using an adhesive or the like if necessary. The aromatic polyimide gas separation membrane described above is an aromatic polyimide membrane obtained by polymerizing (and imidizing) an acid component such as an aromatic tetracarboxylic acid or its acid dianhydride, and an aromatic diamine component. Gas separation membranes with an asymmetric structure (membranes that have an integral homogeneous layer and a porous layer) formed by a wet membrane forming method using a coagulating liquid using a solution of polyamic acid (or aromatic polymide), or It is a composite separation membrane manufactured by forming a thin homogeneous layer on the surface of a porous membrane made of an appropriate material using an aromatic polyimide solution, etc., and has sufficient gas separation performance for water vapor as described above. Separation membranes can be mentioned. The above-mentioned aromatic polyimide is particularly characterized by "-S-,
20 to 100 mol%, preferably 40 to 100 mol% of aromatic diamine containing a divalent group of -SO _{2 -}
A material obtained by polymerizing and imidizing an aromatic diamine component and an aromatic tetracarboxylic acid component in approximately equimolar amounts by mole % is extremely suitable in terms of high water vapor transmission rate. Examples of the aromatic diamine include diamino-dibenzothiophene or a derivative thereof, diamino-diphenylene sulfone or a derivative thereof, diamino-diphenyl sulfide or a derivative thereof, diamino-diphenyl sulfone or a derivative thereof, diamino-diphenylene sulfone or a derivative thereof, diamino-diphenylene sulfone or a derivative thereof, -Thioxanthene or its derivatives, etc. can be mentioned. In particular, as diamino-dibenzothiophene or its derivative, the general formula Diamino-dibenzothiophenes represented by or general formula Examples include diamino-diphenylene sulfones represented by: However, in the above general formula, R and R' include hydrogen, a carbon hydrogen substituent having 1 to 6 carbon atoms (alkyl group, alkylene group, aryl group, etc.), an alkoxy group having 1 to 6 carbon atoms, etc. For example, a methyl group,
Ethyl group, propyl group, etc. are suitable. The aforementioned diamino-dibenzothiophenes include 3,7-diamino-2,8-dimethyl-dibenzothiophene, 3,7-diamino-2,6-dimethyl-dibenzothiophene, and 2,8-diamino-3 ,7-dimethyl-dibenzothiophene, 3,
Examples of the diamino-diphenylene sulfones include 7-diamino-2,8-diethyl-dibenzothiophene and the like.
7-diamino-2,8-dimethyl-diphenylene sulfone, 3,7-diamino-2,8-diethyl-diphenylene sulfone, 3,7-diamino-
2,8-dipropyl-diphenylene sulfone,
Examples include 2,8-diamino-3,7-dimethyl-diphenylene sulfone and 3,7-diamino-2,8-dimethoxy-diphenylene sulfone. Furthermore, the diphenyl sulfide or its derivatives include 4,4'-diamino-diphenyl sulfone, 3,3'-diamino-diphenyl sulfone, 3,5-diamino-diphenyl sulfone,
Diamino-diphenyl sulfones such as 3,4'-diamino-diphenyl sulfone, and 4,
4'-diamino-diphenyl sulfide, 3,3'-
Diamino-diphenyl sulfides such as diamino-diphenyl sulfide, 3,5-diamino-diphenyl sulfide, and 3,4'-diamino-diphenyl sulfide can be mentioned; As the diamino-thioxanthene or its derivative, 3,7-diamino-thioxanthene-5,
5-dioxide, 2,8-diamino-thioxanthene-5,5-dioxide, 3,7-diamino-
Thioxanthone-5,5-dioxide, 2,8-
Diamino-thioxanthone-5,5-dioxide, 3,7-diamino-phenoxatin-5,5
-dioxide, 2,8-diamino-phenoxatin-5,5-dioxide, 2,7-diamino-thianthrene, 2,8-diamino-thianthrene,
Examples include 3,7-diamino-10-methyl-phenothiazine-5,5-dioxide. Furthermore, as the aromatic diamine, bis[(p
-aminophenoxy)phenyl]sulfide, bis[(p-aminophenoxy)phenyl]sulfone, and the like can also be mentioned. As the aromatic diamine component, the above-mentioned “-S
Other aromatic diamines can be used together with aromatic diamines that incorporate a divalent group of 4,4'-, or _-SO2- , such as 4,4'- Diamino-diphenyl ether, 3,3'-dimethyl-4,4'-diamino-diphenyl ether, 3,3'-diethoxy-4,4'-
Diphenyl ether compounds such as diamino-diphenyl ether and 3,3'-diamino-diphenyl ether; diphenylmethane compounds such as 4,4'-diamino-diphenylmethane and 3,3'-diamino-diphenylmethane; 4,4 Benzophenone compounds such as '-diamino-benzophenone and 3,3'-diamino-benzophenone, 2,2-bis(3-aminophenyl)propane, 2,2-bis(4-aminophenyl)propane, 2,2-bis[ 2,2-bis(phenyl)propane compounds such as 4-(4'-aminophenoxy)phenyl]propane, as well as o-, m-, p-phenylenediamine, 3,5-diaminobenzoic acid, 2,6- Diaminopyridine, o-tolidine, etc. can be mentioned. The aromatic tetracarboxylic acid components used in the production of the aromatic polyimide include 3,3',
4,4'-biphenyltetracarboxylic acid, or 2,3,3',4'-biphenyltetracarboxylic acid,
Or their dianhydrides, or biphenyltetracarboxylic acids such as lower alcohol esters thereof, 3,3',4,4'-benzophenonetetracarboxylic acid, or 2,3,3',4'- Benzophenonetetracarboxylic acids, such as benzophenonetetracarboxylic acid, their dianhydrides, or lower alcohol esters thereof; and pyromellitic acids, such as pyromellitic acid, its dianhydrides, or its esters. be able to. In particular, in this invention, an aromatic polyimide obtained from an aromatic tetracarboxylic acid component containing 50 to 100 mol%, especially 80 to 100% of biphenyltetracarboxylic acids, and the above-mentioned aromatic diamine component is used. Since it has excellent solubility in organic solvents such as phenolic compounds, gas separation membranes made of such aromatic polyimides can be used to prepare stable dope liquids for film formation, film formation properties, etc. This is preferable from the viewpoint of film formation. The gas separation polyimide membrane used in this invention is
An organic solvent solution such as aromatic polyamic acid (polyimide precursor) obtained from the above-mentioned aromatic diamine component and aromatic tetracarboxylic acid component or an organic solvent-soluble aromatic polyimide is used as a dope liquid for film formation. The dry film forming method involves a drying process in which the dope is used to form a thin film of the dope, the solvent is removed from the dope, and the film is solidified, or the thin film of the dope is brought into contact with the coagulating liquid. A wet film forming method is used to form a film by coagulating it, and it can be formed into a flat film shape or a hollow fiber shape to produce polyimide separation membranes with various structures. For example, the method for producing the gas separation polyimide membrane used in the present invention includes the above-mentioned aromatic diamine component consisting of the aromatic diamine (which may contain other aromatic diamines) and the above-mentioned biphenyltetracarboxylic acid. An aromatic tetracarboxylic acid component mainly containing acids is polymerized and imidized in one step in approximately equimolar amounts in an organic solvent of a phenolic compound at a temperature of about 140°C or higher to produce an aromatic polyimide, A solution of the aromatic polyimide (concentration: about 3 to 30
wt%) as dope liquid, about 30-150
A thin film (flat film or hollow fiber) of dope liquid is formed by coating, casting, or extruding into a hollow fiber shape on a substrate at a temperature of °C, and then the thin film is immersed in a coagulation liquid to form a coagulation film. Then, the solvent, coagulation liquid, etc. are evaporated and removed from the coagulated membrane, and finally, it is sufficiently dried and heat-treated at a temperature of 150 to 400℃, especially 170 to 350℃, to form an asymmetric gas separation membrane made of aromatic polyimide. A method for forming a film can be mentioned. In the method of this invention, a gas separation device incorporating the aforementioned aromatic polyimide gas separation membrane is used, and as shown in FIG. 1, a mixed gas containing water vapor is passed through the gas separation device 1. The mixed gas is continuously supplied from the mixed gas supply port 3 and allowed to flow along the gas supply side of the gas separation membrane 2, while the proportion of the mixed gas is 10% by volume or less, preferably 0.5 to 8% by volume. A certain amount of dry gas is supplied from the dry gas supply port 6, and while flowing along the gas permeation side of the gas separation membrane, water vapor components of the mixed gas that has passed through the gas separation membrane 2 are converted into the dry gas. On the other hand, the mixed gas that has not passed through the gas separation membrane (non-permeable gas) is discharged from the non-permeable gas outlet 4, thereby dehumidifying the mixed gas. It dries. In this invention, the mixed gas has a water vapor content close to a saturated state at the temperature and pressure during dehumidification (e.g., a saturated content of water vapor in the mixed gas that is the raw material gas at the temperature during the dehumidification operation). It is sufficient that it is contained in a mixed gas mainly composed of hydrocarbons, natural gas, petroleum gas, etc., at a content rate of at least 70% or more of its saturated content rate. In this invention, if the amount of drying gas supplied is too large compared to the amount of mixed gas supplied as raw material gas, the efficiency of removing water vapor from the mixed gas will not improve, and only the consumption of drying gas will increase. This is not appropriate because the amount increases unnecessarily, and if the amount of drying gas supplied becomes too small, it is not preferable because the water vapor itself will not be removed sufficiently. In this invention, the supply amount of the drying gas is such that the ratio is about 0.5 to 8% by volume with respect to the supply amount of the raw material gas (mixed gas), and at the same time,
The drying gas is supplied at an appropriate gas velocity (preferably 0.1 to 10
m/sec, particularly preferably at a gas velocity of the order of 0.5 to 8 m/sec). In this invention, the drying gas refers to a mixed gas having the same composition as the raw material gas, in which the water vapor content is approximately 300 ppm or less, particularly 200 ppm or less, and furthermore, approximately 1 to 100 ppm, or nitrogen gas or argon gas. , neon gas or other inert gas. Therefore, in some cases, as shown in Figure 2, a portion of the non-permeable gas from which water vapor has been removed may be passed through a branch line to supply dry gas. It may be passed through the line and supplied as a dry gas to the permeate gas side of the gas separation membrane. In this invention, the pressure of the mixed gas supplied to the gas separation device is adjusted to remove water vapor by the amount of drying gas supplied to the permeate gas side of the gas separation membrane or the pressure when the permeate gas is discharged. However, in this invention, when the pressure at the time of exhausting the permeated gas is near atmospheric pressure, the pressure is about 5 kg/cm ² or more,
In particular, it is preferably about 10 to 100 Kg/cm ² in order to increase the water vapor removal rate. In addition, the amount of the mixed gas supplied is such that the ratio of supply to the effective area of the gas separation membrane (relative to the effective membrane area of the hollow fiber) is approximately 0.05 to 100 ^{cm 3} /cm ² ·sec, particularly 0.1 to 10 cm ³ It is preferable that the supply amount be about 1/cm ² ·sec. [Example] In this invention, the gas permeation test was carried out using a gas separation device as shown in Fig. 1, with a built-in gas separation membrane (hollow fiber) made of each aromatic polyimide.
A mixed gas containing water vapor is supplied to the gas separation device at a supply pressure of approximately 6 to 52 kg/cm ² G and a temperature of 25°C, and gas separation is performed while supplying dry gas to the inside of the hollow fiber. The composition of each gas mixture that permeated the separation membrane and the amount of permeation of each component (water vapor analysis was performed using a DuPont Model 303 hygrometer, and analysis of other gases was performed using gas chromatography). It measures the water vapor permeation rate of gas separation membranes. Examples 1 to 3 Hollow fibers A made of aromatic polyimide were prepared. The hollow fiber A is an aromatic fiber formed from 100 parts by weight of biphenyltetracarboxylic dianhydride, 80 parts by weight of a diamino-dimethyl-diphenylene sulfone isomer mixture and 20 parts by weight of 2,6-diaminopyridine. Made of polyimide, effective length: 5.6cm, outer diameter: 305μ, inner diameter: 90μ, and water vapor transmission rate at measurement temperature of 25℃: 6.5×10 ^-4
cm ³ /cm ²・sec・cmHg). One of the hollow fibers A (effective membrane area: 0.54cm ² )
However, by using a gas separation device whose both ends are sealed with epoxy resin and built into a sealed container of the same type as shown in Figure 1, the gas shown in Table 1 is connected to the mixed gas supply port of the gas separation device. A mixed gas containing water vapor and mainly composed of methane shown in Table 1 was supplied at a pressure of 52 kg/cm ² G, a temperature of about 25°C, and a gas flow rate shown in Table 1. ), and on the other hand, dry argon gas (dry gas) containing only about 10 ppm or less of water vapor is supplied from the dry gas supply port of the gas separation device at the flow rate shown in Table 1, and the hollow fibers are While flowing along the inner surface (gas permeation side) of the internal hole of the gas separation membrane, the permeated gas containing water vapor, etc. that has permeated the gas separation membrane is recovered from the permeated gas outlet at approximately normal pressure, and the gas separation membrane is The non-permeate gas (dehumidified gas) that did not permeate was recovered from the non-permeate gas outlet of the gas separation device. The aromatic polyimide hollow fiber A used in Examples 1 to 3 above has a separation degree (PH ₂ O / PCH ₄ ) of about 460, which indicates permselectivity, as calculated from the results of each of those Examples. It was hot. The compositions and flow rates of the permeate gas and non-permeate gas were measured, and the results are shown in Table 1. Comparative Example 1 Water vapor was removed from the mixed gas in the same manner as in Example 1, except that no drying gas was supplied. The results are shown in Table 1. Examples 4-5 Hollow fibers B made of aromatic polyimide were prepared. The hollow fiber B contains 90 parts by weight of biphenyltetracarboxylic dianhydride and 10 parts by weight of pyromellitic dianhydride, 90 parts by weight of a diamino-dimethyl-diphenylenesulfone isomer mixture and 4,4'-diaminodiphenyl dianhydride. Made of aromatic polyimide formed from 10 parts by weight of enyl ether, effective length: 5.15cm, outer diameter: 434μ, inner diameter: 190μ,
And water vapor transmission rate at measurement temperature 25℃: 7.4×10 ^-4
cm ³ /cm ²・sec・cmHg). One of the hollow fibers B (effective membrane area: 0.70cm ² )
However, by using a gas separation device whose both ends are sealed with epoxy resin and built into a sealed container of the same type as shown in Figure 1, the gas shown in Table 1 is connected to the mixed gas supply port of the gas separation device. A mixed gas containing water vapor as shown in Table 1 and containing methane as its main component is supplied at a gas flow rate shown in Table 1, and dry argon gas (dry gas) is supplied as shown in Table 1 from the dry gas supply port of the gas separation device. The permeated gas was recovered at normal pressure from the passed gas outlet in the same manner as in Example 1, except that the gas was supplied at a flow rate, and the non-permeated gas (dehumidified gas) was recovered from the non-permeated gas outlet of the gas separation device. Recovered. The aromatic polyimide hollow fiber B used in Examples 4 and 5 above had a separation degree (PH ₂ O/PCH ₄ ) of about 2000, which indicates permselectivity. The compositions and flow rates of the permeate gas and non-permeate gas were measured, and the results are shown in Table 1. Comparative Example 2 Water vapor was removed from the mixed gas in the same manner as in Example 4, except that no drying gas was supplied. The results are shown in Table 1. Examples 6-7 A gas separation device incorporating hollow fibers B' of the same shape and material as in Example 4 was used, except that the effective length of the hollow fibers was 11.0 cm and the effective membrane area was 1.50 ^cm2 . In addition, a mixed gas having the water vapor content shown in Table 1 is used as the raw material gas, the supply amount of the mixed gas is changed as shown in Table 1, and the supply pressure of the mixed gas is set to 6 kg/cm. ^2G and the amount of drying gas supplied was changed in the same manner as in Example 4 to remove water vapor from the mixed gas. The results are shown in Table 1. Comparative Example 3 Water vapor was removed from the mixed gas in the same manner as in Example 6, except that no drying gas was supplied. The results are shown in Table 1. Examples 8 to 10 Hollow fibers C made of aromatic polyimide were prepared. The hollow fiber C is an aromatic polyimide formed from 100 parts by weight of biphenyltetracarboxylic dianhydride, 80 parts by weight of a diamino-dimethyl-diphenylene sulfone isomer mixture, and 20 parts by weight of 2,6-diaminopyridine. Effective length: approx. 25.3cm, outer diameter: 454μ, inner diameter:
230μ, and water vapor transmission rate at a measurement temperature of 25℃: 5.6×10 ^-4
cm ³ /cm ³・sec・cmHg). A bundle of 30 hollow fibers C (effective membrane area;
108 cm ² ), both ends of which are tightly sealed with epoxy resin, and a gas separation device built in a sealed container of the same type as shown in Figure 1 is used, and the mixed gas supply port of the gas separation device is used. A mixed gas containing water vapor and mainly composed of methane as shown in Table 1 was supplied at the gas flow rate shown in Table 1, the supply pressure of the mixed gas was set to 50 kg/cm ² G, and dry argon was added. The permeate gas was recovered at normal pressure from the permeate gas outlet in the same manner as in Example 1, except that the gas (dry gas) was supplied from the dry gas supply port of the gas separation device at the flow rate shown in Table 1. Non-permeate gas (dehumidified gas) was recovered from the non-permeate gas outlet of the gas separator. The aromatic polyimide hollow fibers C used in Examples 8 to 10 above had a separation degree (PH ₂ O/PCH ₄ ) of about 670, which indicates permselectivity. The compositions and flow rates of the permeate gas and non-permeate gas were measured, and the results are shown in Table 1. Comparative Example 4 Water vapor was removed from the mixed gas in the same manner as in Example 8, except that no drying gas was supplied. The results are shown in Table 1. Examples 11-12 Hollow fibers D made of aromatic polyimide were prepared. The hollow fiber D is made of an aromatic polyimide formed from 100 parts by weight of biphenyltetracarboxylic dianhydride and 100 parts by weight of a diamino-dimethyl-diphenylene sulfone isomer mixture, and has an effective length of about 4.1 cm, outer diameter: 220μ, inner diameter: 130μ,
And water vapor transmission rate at measurement temperature 25℃: 5.0×10 ^-4
cm ³ /・sec・cmHg). A bundle of six hollow fibers D (effective membrane area;
1.70 cm ² ), both ends of which are tightly sealed with epoxy resin, and a gas separation device built in a sealed container of the same type as shown in Figure 1 is used, and a device as shown in Figure 2 is used. A mixed gas containing water vapor and mainly composed of methane shown in Table 1 is supplied to the mixed gas supply port of the gas separation device at a gas flow rate shown in Table 1, and the mixed gas is The supply pressure was set to 10 kg/cm ² G, and as shown in Fig. 2, the non-permeable gas partially branched from the non-permeable gas line was supplied as dry gas via the circulation line from the dry gas supply port of the gas separation device. In the same manner as in Example 1, except that the gas was supplied at the flow rate shown in Table 1, the permeated gas was recovered from the permeated gas outlet at normal pressure, and the non-permeated gas (dehumidified gas) was collected from the non-permeated gas in the gas separation device. Collected from gas outlet. The hollow fiber D made of aromatic polyimide used in Examples 11 and 12 above had a degree of separation (PH ₂ O/PCH ₄ ) indicating permselectivity of about 1300. The compositions and flow rates of the permeate gas and non-permeate gas were measured, and the results are shown in Table 1. Comparative Example 5 Water vapor was removed from the mixed gas in the same manner as in Example 11, except that no drying gas was supplied. The results are shown in Table 1. 【table】

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of a gas separation apparatus used in the method of the present invention. FIG. 2 is a flow diagram when a part of the non-permeable gas (dehumidified gas) coming out of the non-permeable gas outlet of the gas separation device is recirculated and used as drying gas in the method of the present invention. The outline is shown below. 1... Gas separation device, 2... Hollow fiber, 3... Raw material gas supply port (mixed gas supply port), 4... Non-permeable gas discharge port, 5... Permeated gas discharge port, 6... Dry gas supply Mouth, 7... Sealed container, 8... Resin wall.

Claims (1)

[Claims] 1. A permeated gas outlet and a dry gas supply port that communicate with the gas permeation side of the gas separation membrane, and a mixed gas supply port and non-permeation gas that communicate with the gas supply side of the gas separation membrane. The gas permeation rate ratio of water vapor and methane (PH ₂
Using a gas separation device with a built-in aromatic polyimide gas separation membrane having a permselectivity expressed by O/PCH ₄ ) of 200 or more, a mixed gas containing water vapor is transferred to the gas separation device. A mixed gas is supplied from the dry gas supply port and allowed to flow along the gas supply side of the gas separation membrane, while a dry gas of 10% by volume or less with respect to the mixed gas is supplied from the dry gas supply port, and the gas separation membrane A method for dehumidifying a mixed gas, comprising removing water vapor from the mixed gas that has passed through the gas separation membrane while flowing the mixed gas along the gas permeation side of the gas.