JP2018171570A - Gas separation membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an asymmetric gas separation membrane which has a large gas permeation speed and has mechanical properties enough to satisfy a practical level.SOLUTION: A gas separation membrane has an asymmetric structure formed of a skin layer (separation layer) and a porous layer (support layer), has a water vapor permeation rate (P') of 350×10cm(STP)/cmsec cmHg or more, has a permeation rate ratio of water vapor to nitrogen (P'/P') of 500 or more, has a tensile breaking elongation in a hollow fiber membrane of 25% or more, and has breaking elongation of the hollow fiber membrane after subjected to hot water treatment in hot water at 150°C for 22 hours of 40% or more before the hot water treatment. The gas separation membrane is a gas separation membrane formed of polyimide, and in a step by a dry-wet phase conversion method using a polyimide solution containing polyimide and a solvent containing a phenol-based solvent and aliphatic alcohol, spinning is preformed.SELECTED DRAWING: None

Description

  The present invention is a gas separation membrane having an asymmetric structure composed of a skin layer and a porous layer, which has a high membrane permeation rate of the membrane permeation component, and has a mechanical property exceeding a practical level as a hollow fiber gas separation membrane. The present invention relates to a gas separation membrane having excellent hydrolysis resistance against water and a method for producing the same. Furthermore, the present invention relates to a gas separation method using the gas separation membrane, particularly to a dehumidification method.

  Gas separation membranes are used in various gas separation processes. Many of these are gas separation membranes formed of a glassy polymer with high gas selective permeability. In general, a gas separation membrane formed of a glassy polymer has a high gas selective permeability (separation degree), but has a disadvantage that a gas permeability coefficient (permeation rate) is small. For this reason, many gas separation membranes formed of glassy polymers have an asymmetric structure composed of a porous layer (support layer) and a thin skin layer (separation layer), that is, a separation layer that generates gas permeation resistance. The structure is made thin so that the gas permeation rate does not become too small.

  The gas separation membrane is suitably used as a hollow fiber gas separation membrane module. A hollow fiber gas separation membrane module usually has a hollow fiber membrane bundle consisting of a number of hollow fiber membranes in a container having at least a mixed gas inlet, a permeate gas outlet, and an unpermeated gas outlet. Contained and stored. In the hollow fiber gas separation membrane module, the mixed gas is supplied to a space in contact with the inside or outside of the hollow fiber membrane, and a specific component (membrane permeable component) in the mixed gas is selectively selected while flowing in contact with the hollow fiber membrane. Gas separation is performed by collecting the gas that has passed through the membrane and collected from the permeate gas discharge port and from which the specific component (membrane permeation component) has been removed, from the non-permeate gas discharge port.

  In a film having an asymmetric structure, the rate-determining process of the permeation rate at which the membrane permeation component permeates the membrane is usually the process of permeation through the skin layer. Since the permeation resistance in the process of permeating through the porous layer is relatively small, the effect of the membrane permeation component on the permeation rate through the membrane is practically negligible.

  However, when the permeation rate of the membrane permeation component through the membrane is extremely high, the permeation rate at which the membrane permeation component permeates the membrane permeates the porous layer as well as the process of the membrane permeation component permeation through the skin layer. The process is also affected in practice. In particular, when the membrane permeation component is water vapor, the permeation rate at which water vapor permeates through the membrane is extremely large (several hundred to several thousand times) compared to other inorganic gases. Is affected by the permeation resistance of the porous layer, which is practically not negligible. For this reason, development of the high performance dehumidification film | membrane which enlarged the permeation | transmission rate which water vapor | steam permeate | transmits a film | membrane was calculated | required.

  On the other hand, simply increasing the porosity of the porous layer in the asymmetric membrane and reducing the permeation resistance when the membrane permeation component permeates the membrane, thereby increasing the permeation rate at which the membrane permeation component permeates the membrane. Practical high-performance gas separation membrane that has both improved permeation rate and practical mechanical strength because the permeation rate can be increased, but the supporting function of the membrane that the porous layer should play, ie mechanical strength is reduced. It was difficult to get. There is also an attempt to improve the mechanical strength by selecting a high-strength material, but the high-strength material generally has a problem that the gas permeability coefficient is smaller.

  In Patent Document 1, the gas permeation resistance when the membrane permeation component of the porous layer permeates the membrane is reduced by forming an asymmetric membrane with a mixture of two or more types of polymers including at least one type of polyimide. In addition, a gas separation membrane capable of maintaining the mechanical strength of the membrane at a practical level or higher is described.

JP 2002-17211 A

  However, even in the invention described in Patent Document 1, the water vapor transmission rate is not sufficient, and further improvement has been demanded.

  Preferred embodiments of the present invention are as follows.

1. It has an asymmetric structure composed of a skin layer (separation layer) and a porous layer (support layer), and has a water vapor transmission rate (P ′ _H2O ) of 350 × 10 ⁻⁵ cm ³ (STP) / cm ² · sec · cmHg or more, the permeation rate ratio of water vapor and nitrogen ( _P′H2O / _P′N2 ) is 500 or more, the tensile elongation at break in the hollow fiber membrane is 25% or more, and in hot water at 150 ° C. A gas separation membrane wherein the breaking elongation of the hollow fiber membrane after 22 hours of hydrothermal treatment is maintained at 40% or more before the hydrothermal treatment.

2. ^2. The gas separation membrane according to 1 above, wherein the breaking strength at the hollow fiber membrane is 2.3 kgf / mm ² or more.

3. 3. The gas separation membrane according to 1 or 2 above, which is composed of polyimide.

4). The polyimide has the following general formula (1):

〔式（１）中、Ｂはテトラカルボン酸成分に起因する４価のユニットであり、Ａはジアミン成分に起因する２価のユニットである。〕
で表され、前記テトラカルボン酸成分が、３，３’，４，４’−ビフェニルテトラカルボン酸二無水物を含む、上記３に記載のガス分離膜。

[In Formula (1), B is a tetravalent unit resulting from a tetracarboxylic acid component, and A is a divalent unit resulting from a diamine component. ]
The gas separation membrane according to 3 above, wherein the tetracarboxylic acid component contains 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride.

5. 5. The gas separation membrane according to 4 above, wherein the tetracarboxylic acid component further comprises 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride.

6). 6. The gas separation membrane according to 4 or 5 above, wherein the diamine component contains diaminodiphenyl ethers.

7). The method for producing a gas separation membrane according to any one of 3 to 6,
A method for producing a gas separation membrane, comprising a step of performing a dry-wet phase conversion method using a polyimide solution containing polyimide and a solvent containing a phenol-based solvent and an aliphatic alcohol.

8). A method for separating water vapor from a mixed gas containing water vapor, using the gas separation membrane according to any one of 1 to 6 above.

  The asymmetric gas separation membrane of the present invention has a high gas permeation rate and mechanical properties sufficient for practical use. For this reason, when the gas separation membrane of the present invention is used, it is possible to provide a high-performance hollow fiber gas separation membrane module having a large gas separation speed, high efficiency and compactness, and high efficiency gas separation can be realized. In particular, when water vapor is removed (dehumidified) from a mixed gas containing water vapor, dehumidification can be performed with extremely high efficiency.

One aspect of the gas separation membrane of this embodiment has an asymmetric structure composed of a skin layer (separation layer) and a porous layer (support layer), and has a water vapor transmission rate (P ′ _H2O ) of 350 × 10 ^{−. 5} cm ³ (STP) / cm ² · sec · cm Hg or more, water vapor and nitrogen permeation rate ratio (P ′ _{H 2 O} / P ′ _{N 2} ) is 500 or more, and the elongation at break in the hollow fiber membrane is 25%. As described above, the breaking elongation of the hollow fiber membrane after the hot water treatment in hot water at 150 ° C. for 22 hours is maintained at 40% or more before the hot water treatment. The gas separation membrane of this embodiment has a high permeation rate, retains mechanical properties at a practical level or more when made into a hollow fiber membrane, and has excellent hydrolysis resistance to water. Details will be described below.

  The gas separation membrane of the present invention has an extremely thin dense layer (preferably having a thickness of 0.001 to 5 μm) mainly responsible for gas separation performance and a relatively thick porous layer (preferably having a thickness of 10 to 10 μm) that supports the dense layer. 2000 μm). Since the gas separation membrane has the advantage of having a wide effective surface area and high pressure resistance, it is preferable to form an asymmetric hollow fiber membrane. The asymmetric hollow fiber membrane has an inner diameter of about 10 to 3000 μm and an outer diameter of about 30 to 7000 μm. It is more preferable that

The gas separation membrane of the present invention has a high water vapor transmission rate. Specifically, the gas separation membrane preferably has a water vapor transmission rate (P ′ _H2O ) of 350 × 10 ⁻⁵ cm ³ (STP) / cm ² · sec · cmHg or more, and 370 × 10 ⁻⁵ cm. ³ (STP) / cm ² · sec · cmHg or more is more preferable. Although an upper limit is not specifically limited, Usually, it is 1000 * 10 < ^-5 > cm < ³ > (STP) / cm < ² > * sec * cmHg or less. In the present specification, “STP” means 0 ° C. and 1 atm, and is an abbreviation of “Standard Temperature and Pressure”.

The gas separation membrane of the present invention has high gas permselectivity (separation degree), and the water vapor and nitrogen permeation rate ratio (P ′ _{H 2 O} / P ′ _{N 2} ) is preferably 500 or more, more preferably 1000 or more. Is more preferable. The upper limit of the transmission rate ratio is not particularly limited, but is usually 100,000 or less. In this specification, the water vapor transmission rate (P ′ _H20 ) of the membrane and the water vapor / nitrogen transmission rate ratio (P ′ _{H 2 O} / P ′ _{N 2} ) are those at 35 ° C.

In the present invention, the mechanical strength of the gas separation membrane is represented by the breaking strength or breaking elongation in a tensile test when the membrane is a hollow fiber. These are values measured at a temperature of 23 ° C. using a tensile tester at an effective length of the sample of 20 mm and a tensile speed of 10 mm / min. The breaking strength is a value obtained by dividing the tensile stress of the hollow fiber membrane by the membrane cross-sectional area of the hollow fiber [unit: kgf / mm ² ], and the breaking elongation is the tensile length of the original hollow fiber L ₀ 100 × (L−L ₀ ) / L ₀ [unit:%] where L is the length at break.

  The gas separation membrane preferably has a breaking elongation of 25% or more when the hollow fiber membrane is formed, more preferably 30% or more, still more preferably 40% or more, and 60% or more. More preferably, the upper limit is not limited, but it is usually 1000% or less.

The gas separation membrane preferably has a breaking strength when a hollow fiber membrane is formed of 2.3 kgf / mm ² or more, more preferably 2.5 kgf / mm ² or more, and 3.0 kgf / mm ^2. More preferably, the upper limit is not limited, but it is usually 100 kgf / mm ² or less.

If the breaking strength or breaking elongation when the gas separation membrane is a hollow fiber membrane is within the above range, the mechanical strength is high and it can be handled easily without breakage or breakage. (Assembly and processing into a gas separation membrane module) can be performed. Furthermore, a gas separation membrane module using such a hollow fiber membrane having mechanical strength is particularly useful because it has excellent pressure resistance and durability. Also, the hollow fiber membrane in the separation membrane module is deformed continuously or intermittently depending on the flow rate, flow velocity, pressure, temperature, and fluctuations of the gas supplied and flowing inside and outside the hollow fiber. Although subjected to stress, the hollow fiber membrane composed of the gas separation membrane of the present invention has a breaking elongation of 25% or more, and preferably has a breaking strength of 2.3 kgf / mm ² or more. Fracture is unlikely to occur.

  Furthermore, the gas separation membrane of the present invention is excellent in water resistance and hot water resistance. The water resistance and hot water resistance of the gas separation membrane are determined by the retention rate of elongation at break in a tensile test after performing a hydrothermal treatment for 22 hours in hot water at a temperature of 150 ° C. using a hollow fiber membrane as the gas separation membrane (100 × Represented by the breaking elongation after hot water treatment / breaking elongation before hot water treatment [unit:%]).

  In the present invention, the gas separation membrane is a hollow fiber membrane, and the retention rate of the elongation at break after hydrothermal treatment for 22 hours in hot water at a temperature of 150 ° C. is preferably 40% or more, and 60% The above is more preferable.

  The material constituting the gas separation membrane of the present invention is not particularly limited, and examples thereof include polyimide, polyamide, polyethersulfone, polyamideimide, polyetherimide, and polycarbonate. Of these, the gas separation membrane is preferably made of polyimide.

  As a preferred embodiment of the polyimide constituting the gas separation membrane of the present invention, an aromatic polyimide represented by the repeating unit of the following general formula (1) will be described, but the present invention is not limited thereto.

  In the above formula (1), B is a tetravalent unit derived from the tetracarboxylic acid component, and A is a divalent unit derived from the diamine component. The units constituting the aromatic polyimide represented by the general formula (1) will be described in detail below.

  Unit B is a tetravalent unit derived from a tetracarboxylic acid component, and unit B1 having a diphenylhexafluoropropane structure represented by the following formula (B1) and unit B2 having a biphenyl structure represented by the following formula (B2) It is preferably at least one unit selected from For example, unit B preferably comprises 10 to 70 mol%, more preferably 20 to 60 mol% of unit B1, and preferably 90 to 30 mol%, more preferably 80 to 40 mol% of unit B2, In particular, it is preferably composed of the unit B1 and the unit B2. If the diphenylhexafluoropropane structure is less than 10 mol% and the biphenyl structure exceeds 90 mol%, the gas permeation performance of the resulting polyimide may be reduced, making it difficult to obtain a high performance gas separation membrane. On the other hand, if the diphenylhexafluoropropane structure exceeds 70 mol% and the biphenyl structure is less than 30 mol%, the mechanical strength of the resulting polyimide may be reduced.

  The unit B can also include a tetravalent unit based on a phenyl structure represented by the following formula (B3). The tetravalent unit based on the phenyl structure represented by the formula (B3) is preferably from 0 to 30 mol%, preferably from 10 to 20 mol%, based on the total amount of the unit B.

  Further, the unit B may include a tetravalent unit B4 derived from other tetracarboxylic acids other than the units B1, B2, and B3.

  Unit A is a divalent unit derived from a diamine component, and preferably contains at least one selected from unit A1 represented by the following formula (A1) and unit A2 represented by the following formula (A2).

式（Ａ２）中、Ａｒは、下記化学式（Ａｒ１）〜化学式（Ａｒ６）で示される残基の群から選ばれる１種以上の２価の残基である。

In the formula (A2), Ar is one or more divalent residues selected from the group of residues represented by the following chemical formulas (Ar1) to (Ar6).

  As one aspect of the present invention, when the unit A has the unit A1 represented by the formula (A1) and / or the unit A2 represented by the formula (A2), the unit A1 and the unit A1 The total of unit A2 is preferably 90 to 100 mol%.

  In one embodiment of the present invention, the unit A1 is preferably 50 mol% or more, more preferably 70 mol% or more, and more preferably 90 mol% or more based on the total unit amount of the unit A. Preferably, it may be 100 mol%.

  Next, the monomer component which can introduce | transduce each said unit of an aromatic polyimide is demonstrated.

  A tetracarboxylic acid component is a component which can introduce | transduce the tetravalent residue B into the polyimide which consists of a repeating unit shown by General formula (1).

  The unit consisting of the diphenylhexafluoropropane structure represented by the formula (B1) can be obtained by using (hexafluoroisopropylidene) diphthalic acid, its dianhydride, or its esterified product as the tetracarboxylic acid component. Examples of the (hexafluoroisopropylidene) diphthalic acids include 4,4 ′-(hexafluoroisopropylidene) diphthalic acid, 3,3 ′-(hexafluoroisopropylidene) diphthalic acid, and 3,4 ′-(hexafluoroisopropylidene). ) Diphthalic acid, their dianhydrides, or their esterified compounds can be preferably used, but 4,4 ′-(hexafluoroisopropylidene) diphthalic acid, its dianhydrides, or its esterified compounds are preferred. 4,4 ′-(hexafluoroisopropylidene) diphthalic dianhydride is more preferable.

  The unit consisting of the biphenyl structure represented by the formula (B2) can be obtained by using biphenyltetracarboxylic acid such as biphenyltetracarboxylic acid, its dianhydride, or esterified product thereof as the tetracarboxylic acid component. Examples of the biphenyltetracarboxylic acids include 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 2,3,3 ′, 4′-biphenyltetracarboxylic acid, and 2,2 ′, 3,3′-biphenyltetracarboxylic acid. Carboxylic acids, their dianhydrides, or esterified products thereof can be suitably used, but 3,3 ′, 4,4′-biphenyltetracarboxylic acid, its dianhydrides, or esterified products thereof are preferable, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride is more preferred.

  The tetravalent unit based on the phenyl structure represented by the formula (B3) can be obtained by using pyromellitic acids such as pyromellitic acid and its acid anhydride. These pyromellitic acids are suitable for enhancing the mechanical properties. However, if the amount is too large, the polymer solution at the time of film formation is solidified and it becomes difficult to form a hollow fiber. There is a case.

  The other tetracarboxylic acid component that gives the unit B4 is a tetracarboxylic acid other than the compounds shown above, and a compound that does not impair the effects of the present invention and can further improve the performance is selected. Examples thereof include diphenyl ether tetracarboxylic acids, benzophenone tetracarboxylic acids, diphenyl sulfone tetracarboxylic acids, naphthalene tetracarboxylic acids, diphenylmethane tetracarboxylic acids, diphenylpropane tetracarboxylic acids, and the like.

  A diamine component is a component which can introduce | transduce the bivalent residue A into the polyimide which consists of a repeating unit shown by General formula (1).

  The following are mentioned as a diamine component. Examples of the aromatic diamine component for introducing the residue A1 include 4,4′-diaminodiphenyl ether (44DADE), 3,4′-diaminodiphenyl ether (34DADE), 2,4′-diaminodiphenyl ether (24DADE), 3, Examples thereof include diaminodiphenyl ethers such as 3′-diaminodiphenyl ether (33DADE), 2,3′-diaminodiphenyl ether (23DADE), and 2,2′-diaminodiphenyl ether (22DADE). Among these, 4,4'-diaminodiphenyl ether (44DADE) and 3,4'-diaminodiphenyl ether (34DADE) are particularly preferable.

  Examples of the diamine component for introducing the residue A2 include bis (aminophenoxy) benzenes having an Ar group represented by the chemical formula (Ar1) and bis (aminophenoxy) biphenyls having an Ar group represented by the chemical formula (Ar2). Bis [(aminophenoxy) phenyl] propane having an Ar group represented by the chemical formula (Ar3), bis [(aminophenoxy) phenyl] hexafluoropropane having an Ar group represented by the chemical formula (Ar4), chemical formula (Ar5 Bis [(aminophenoxy) phenyl] sulfone having an Ar group represented by (II) and bis (aminophenoxy) naphthalene having an Ar group represented by the chemical formula (Ar6).

  Examples of bis (aminophenoxy) benzenes having an Ar group represented by the chemical formula (Ar1) include 1,4-bis (4-aminophenoxy) benzene (TPEQ), 1,3-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene and the like can be mentioned, among which 1,4-bis (4-aminophenoxy) benzene (TPEQ) is particularly preferable.

  Examples of the bis (aminophenoxy) biphenyl having an Ar group represented by the chemical formula (Ar2) include 4,4′-bis (4-aminophenoxy) biphenyl, 4,4′-bis (3-aminophenoxy) biphenyl, and the like. Among them, 4,4′-bis (4-aminophenoxy) biphenyl is particularly preferable.

  Examples of bis [(aminophenoxy) phenyl] propanes having an Ar group represented by the chemical formula (Ar3) include 2,2-bis (4-aminophenoxy (4-phenyl)) propane and 2,2-bis (3- Aminophenoxy (4-phenyl)) propane, 2,2-bis (4-aminophenoxy (3-phenyl)) propane, 2,2-bis (3-aminophenoxy (3-phenyl)) propane and the like, Among these, 2,2-bis (4-aminophenoxy (4-phenyl)) propane is particularly preferable.

  Examples of the bis [(aminophenoxy) phenyl] hexafluoropropane having an Ar group represented by the chemical formula (Ar4) include 2,2-bis (4-aminophenoxy (4-phenyl)) hexafluoropropane, 2,2- Bis (3-aminophenoxy (4-phenyl)) hexafluoropropane, 2,2-bis (4-aminophenoxy (3-phenyl)) hexafluoropropane, 2,2-bis (3-aminophenoxy (3-phenyl) )) Hexafluoropropane and the like, among which 2,2-bis (4-aminophenoxy (4-phenyl)) hexafluoropropane is particularly preferable.

  Examples of bis [(aminophenoxy) phenyl] sulfones having an Ar group represented by the chemical formula (Ar5) include bis [4- (4-aminophenoxy) phenyl] sulfone and bis [4- (3-aminophenoxy) phenyl]. A sulfone etc. are mentioned, Among them, bis [4- (4-aminophenoxy) phenyl] sulfone is particularly preferable.

  Examples of bis (aminophenoxy) naphthalene having an Ar group represented by the chemical formula (Ar6) include 1,4-bis (4-aminophenoxy) naphthalene, 1,4-bis (3-aminophenoxy) naphthalene, 1,3 -Bis (4-aminophenoxy) naphthalene can be mentioned. Among these, 1,4-bis (4-aminophenoxy) naphthalene is preferable.

  As a preferred embodiment of the present invention, the polyimide constituting the gas separation membrane is 40% by mole or more of 3,3 ′, 4,4′-biphenyltetracarboxylic, based on the total unit amount of unit B in formula (1). 60 mol% or more, more preferably 80 mol% or more of the unit based on 4,4′-diaminodiphenyl ether, with respect to the total unit amount of unit A, It is preferably contained in an amount of not less than wt% (may be 100 wt%).

  As a further preferred embodiment of the present invention, the polyimide constituting the gas separation membrane is represented by the following formula (1), wherein 40 mol% or more of the unit B is 3,3 ′, 4,4′-biphenyltetra Units based on carboxylic dianhydride, 10 mol% or more being units based on 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride, and all units of unit A It is preferable to contain 60% by weight or more (or 100% by weight) of polyimide which is a unit based on 4,4′-diaminodiphenyl ether with 50% by mole or more, more preferably 80% by mole or more based on the amount. .

  One type of polyimide may be used or two or more types may be used in combination.

<Preparation of polyimide solution>
As an embodiment of the polymer solution preparation method of the present invention, a polyimide solution preparation method will be described. The polyimide solution is prepared by adding a tetracarboxylic acid component and a diamine component in an organic polar solvent at a predetermined composition ratio, causing a polymerization reaction at a low temperature of about room temperature to produce polyamic acid, and then heating to imidize by heating. Alternatively, a two-stage method of chemical imidization by adding pyridine or the like, or a tetracarboxylic acid component and a diamine component are added at a predetermined composition ratio in an organic polar solvent, and a high temperature of about 100 to 250 ° C., preferably about 130 to 200 ° C. Is preferably carried out by a one-stage method in which a polymerization imidization reaction is carried out. When the imidization reaction is carried out by heating, it is preferred to carry out while removing water or alcohol that is eliminated. The amount of the tetracarboxylic acid component and diamine component used in the organic polar solvent is such that the polyimide solid content concentration in the solvent is about 5 to 50% by weight, preferably 5 to 40% by weight.

  Examples of the organic polar solvent include phenols such as phenol, cresol and xylenol, catechol having two hydroxyl groups directly in the benzene ring, catechol such as resorcin, 3-chlorophenol, 4-chlorophenol (described later). The same as parachlorophenol), phenolic solvents composed of halogenated phenols such as 3-bromophenol, 4-bromophenol, 2-chloro-5-hydroxytoluene; or N-methyl-2-pyrrolidone, 1,3 An amide solvent composed of amides such as dimethyl-2-imidazolidinone, N, N-dimethylformamide, N, N-diethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide; or a mixture thereof A solvent etc. can be mentioned suitably. Of these, amide solvents and phenol solvents are preferred, phenol solvents are more preferred, halogenated phenols are more preferred, and 4-chlorophenol is particularly preferred.

  The polyimide solution obtained by polymerization imidization can be directly used for spinning as described later. Also, for example, the obtained polyimide solution is poured into a solvent insoluble in polyimide, and the polyimide is precipitated and isolated, and then again dissolved in an organic polar solvent so as to have a predetermined concentration to obtain an aromatic polyimide solution. It can also be prepared and used for spinning.

<Method for producing gas separation membrane>
The asymmetric gas separation membrane of the present invention can be suitably obtained by a dry / wet phase conversion method using a polymer solution. The dry-wet phase change method is a known method for forming a film while bringing a polymer solution into contact with a coagulation liquid to cause phase change. In the dry-wet phase conversion method, the solvent on the surface of the polymer solution in the form of a film is evaporated to form a thin dense layer (separation layer), and then the coagulation liquid (compatible with the solvent of the polymer solution and the polymer is insoluble). This is a phase change method in which a porous layer (support layer) is formed by forming micropores by using a phase separation phenomenon that occurs in a solvent, and proposed by Loeb et al. (For example, US Pat. No. 3,133,132) It is a thing.

  The polymer contained in the polymer solution is not particularly limited, but preferably contains the above-described polyimide, more preferably contains 50% by weight or more of polyimide with respect to the total amount of the polymer, more preferably contains 70% by weight or more, and 100% by weight. %.

  In the present invention, the solvent of the polymer solution used in the dry / wet phase conversion method preferably includes a solvent capable of dissolving the polymer and an aliphatic alcohol. When the polymer solution contains an aliphatic alcohol, a gas separation membrane having a high permeation rate of a membrane permeation component (for example, water vapor), sufficiently high mechanical strength when made into a hollow fiber membrane, and high hot water resistance is obtained. be able to.

  The solvent capable of dissolving the polymer is preferably an organic polar solvent, and may be an organic polar solvent used when a polymer is synthesized by polymerizing monomers. As one embodiment of the present invention, when the polymer is polyimide, the organic polar solvent may be any one that can dissolve polyimide, and examples thereof include organic polar solvents used for the preparation of the polyimide solution described above.

  The aliphatic alcohol contained as the solvent of the polymer solution preferably has a boiling point of 60 ° C. or higher, more preferably 70 ° C. or higher, more preferably 120 ° C. or higher, and 150 ° C. or higher. Is more preferable, and 200 ° C. or higher is particularly preferable. The aliphatic alcohol may be a monohydric aliphatic alcohol or a dihydric or higher aliphatic polyhydric alcohol, preferably an aliphatic polyhydric alcohol, and more preferably a trihydric or higher polyhydric alcohol. .

  The monovalent aliphatic alcohol as the solvent of the polymer solution is preferably acyclic, and may be linear or branched, and has, for example, 1 to 7 carbon atoms. Although it does not specifically limit as monovalent | monohydric aliphatic alcohol, For example, propanols, such as methanol, ethanol, 1-propanol, and isopropanol, Butanols, such as 1-butanol, 2-butanol, and isobutanol, amyl alcohol, isoamyl alcohol Pentanols such as 2-pentanol, 3-pentanol, 2-methyl-1-butanol, isopentyl alcohol and neopentyl alcohol, hexanols such as 1-hexanol, 2-hexanol and 3-hexanol, 1- Examples include heptanols such as heptanol, 2-heptanol, 3-heptanol and 4-heptanol. Of these, ethanol is preferred.

  The aliphatic polyhydric alcohol as the solvent of the polymer solution is preferably acyclic, and may be linear or branched, and the carbon number is, for example, preferably 2 to 10, More preferably, it is 3-8. The aliphatic polyhydric alcohol means a divalent or higher alcohol, and is preferably a trivalent or higher alcohol. Examples of the aliphatic polyhydric alcohol include, but are not limited to, ethylene glycol, diethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1, 7-heptanediol, 1,8-octanediol, 1,2-, 1,3- or 2,3-butanediol, 2-methyl-1,4-butanediol, neopentyl glycol, 2,2-dimethyl- 1,3-propanediol, 2-methyl-1,5-pentanediol, 3-methyl-1,5-pentanediol, 2-methyl-1,6-hexanediol, 3-methyl-1,6-hexanediol 2-methyl-1,7-heptanediol, 3-methyl-1,7-heptanediol and 4-methyl-1,7-heptane Divalent aliphatic alcoholic solvent such as all, glycerin, trivalent or higher alcohol solvents such as diglycerin. Among these, when glycerin is used, it is easy to form a uniform porous layer, and a hollow fiber membrane excellent in mechanical strength and hot water resistance can be obtained.

  An aliphatic alcohol may be used individually by 1 type, or may use 2 or more types together.

  The content of the aliphatic alcohol in the polymer solution is preferably 5 to 30% by weight, more preferably 5 to 20% by weight, based on the total weight of the polymer solution. When the content of the aliphatic alcohol is within this range, the hollow fiber obtained has excellent permeability and mechanical properties. Moreover, when using a polymer solution for the below-mentioned spinning process, 10-20 weight% of solid content concentration of a polymer solution is preferable on film forming. Further, the solution viscosity (rotational viscosity) of the polymer solution is preferably 50 to 15000 poise at the discharge temperature in the spinning process, and in particular, when it is 100 to 10,000 poise, a shape after discharge such as a hollow fiber shape can be stably obtained. Therefore, it is preferable.

  The aliphatic alcohol may be mixed in a solution in which the polymer is dissolved, or the isolated polymer, the organic polar solvent, and the aliphatic alcohol may be mixed at the same time. During mixing, the polymer may be heated so as to dissolve in the organic polar solvent.

  As a preferred embodiment of the method for producing a gas separation membrane of the present invention, it is preferable to use a polymer solution containing a polymer and a mixed solvent of a halogenated phenol and an aliphatic alcohol, and a dry / wet phase conversion method. As a more preferred embodiment, it is preferable to form a gas separation membrane by a dry / wet phase conversion method using a polymer solution containing polyimide, parachlorophenol, and glycerin.

  As one aspect of the present invention, a method for producing a hollow fiber membrane by a dry / wet phase conversion method using a polymer solution will be described below.

  The method for producing a hollow fiber membrane usually includes a spinning step (spinning dope discharging step), a coagulation step, a washing step, a drying step, and a heat treatment step. Each of these processes is a process in which it is essential to continuously process the hollow fiber while continuously feeding / withdrawing the hollow fiber, and even if batch processing is performed while being wound around a bobbin or the like, or continuously There are processes that may be processed.

  First, in the spinning process (spinning dope discharging process), the spinning nozzle used for discharging the spinning dope liquid only needs to push the spinning dope liquid into the hollow fiber-like body, such as a tube-in-orifice type nozzle. Is preferred. Usually, the temperature range of the polymer solution (preferably polyimide solution) at the time of extrusion depends on the polymer contained in the dope solution, the type of the solvent, the viscosity, etc., for example, preferably about 20 ° C. to 150 ° C., more preferably 30 ° C. ~ 120 ° C. Further, spinning is performed while supplying a gas or a liquid into the hollow fiber-like body extruded from the nozzle.

  In the coagulation process that continues from the spinning process, the hollow fiber discharged from the nozzle is once extruded into the atmosphere or an inert gas atmosphere such as nitrogen, etc., and then guided to the coagulation bath and immersed in the coagulation liquid. . The coagulating liquid is preferably one that does not substantially dissolve the polymer component and is compatible with the solvent of the polymer component. Although not particularly limited, water, lower alcohols such as methanol, ethanol and propyl alcohol, ketones having a lower alkyl group such as acetone, diethyl ketone and methyl ethyl ketone, or mixtures thereof are preferably used. It is done. Moreover, when the polymer solution is a polyimide solution and the solvent of the polyimide solution is an amide solvent, an aqueous solution of an amide solvent is also preferable.

  In the coagulation process, the polymer solution discharged from the nozzle into a hollow fiber shape is immersed in a primary coagulation liquid that coagulates to such an extent that the shape can be maintained, wound around a guide roll, etc., and then subjected to secondary coagulation for complete solidification. It is preferable to immerse in a liquid. The primary coagulating liquid and the secondary coagulating liquid may be the same coagulating liquid or different coagulating liquids. In addition, it is possible to efficiently extract the solvent in the polyimide solution by increasing the number of coagulation liquid tanks.

  The spinning step and the coagulating step are preferably continuous processing steps in which the hollow fibers are continuously processed while the hollow fibers are continuously fed / taken off.

  In the next washing step, washing is carried out with a washing solvent such as ethanol, if necessary, and then a substitution solvent such as an aliphatic hydrocarbon such as isopentane, n-hexane, isooctane, n-heptane is used on the outer and inner sides of the hollow fiber. Replace the coagulation liquid and / or washing solvent.

  In the next drying step, the hollow fiber containing the substitution solvent is dried at an appropriate temperature. In the heat treatment step, preferably, the asymmetric gas separation hollow fiber membrane is obtained by performing heat treatment at a temperature lower than the softening point or secondary transition point of the polymer such as polyimide used.

  The washing, drying, and heat treatment steps may be a continuous treatment step in which the hollow fibers are continuously processed while continuously feeding / drawing the hollow fibers, or may be batch-treated while being wound around a bobbin or the like.

  The asymmetric gas separation membrane which is the hollow fiber membrane of the present invention can be suitably used in a modular form. The hollow fiber membrane preferably has an inner diameter of about 30 to 500 μm. A normal gas separation membrane module, for example, bundles about 100 to 1,000,000 (preferably 100 to 200,000) hollow fiber membranes having an appropriate length, and both ends of the hollow fiber bundle are connected to at least one end of the hollow fiber. Is fixed with a tube plate made of a thermosetting resin or the like so that the hollow fiber membrane element made of the obtained hollow fiber bundle and the tube plate is at least mixed gas introduction port It is obtained by storing and mounting in a container having a permeate gas discharge port and a non-permeate gas discharge port so that the space leading to the inside of the hollow fiber membrane and the space leading to the outside of the hollow fiber membrane are isolated. The tube sheet is hermetically attached to the container with an O-ring or an adhesive. In such a gas separation membrane module, a mixed gas is supplied from a mixed gas inlet to a space in contact with the inside or outside of the hollow fiber membrane, and specific components in the mixed gas are selectively selected while flowing in contact with the hollow fiber membrane. Gas separation is performed by allowing the permeate gas to permeate the membrane and the non-permeate gas that has not permeated the membrane to be discharged from the non-permeate gas exhaust port.

  The asymmetric gas separation membrane of the present invention can separate and recover various gas species with a high degree of separation (permeation rate ratio). However, it is excellent in water resistance and hot water resistance, so it is particularly used for separating water vapor. Is preferred. When water vapor is separated using the gas separation membrane of the present invention, that is, when dehumidification is performed, a mixed gas containing water vapor is supplied to the gas separation membrane module to a space in contact with the inside or outside of the hollow fiber membrane. Water vapor can be selectively permeated to the permeate side of the membrane, and a dehumidified gas as an unpermeated gas can be obtained very efficiently. Further, for example, a carrier gas may be allowed to flow in a direction countercurrent to the supplied mixed gas in the space on the permeate gas side to facilitate recovery of the permeate gas. In this case, a non-permeate gas may be used as the carrier gas. Good.

  Since the gas separation membrane of the present invention has a very high water vapor transmission rate, dehumidification and / or humidification can be performed extremely efficiently and suitably. When dehumidification is performed, water vapor is selectively transmitted to the gas separation membrane module including the gas separation membrane of the present invention by supplying the mixed gas containing water vapor to a space in contact with the inside or outside of the hollow fiber membrane. A gas that permeates to the side and is dehumidified as a non-permeating gas can be obtained very efficiently. In particular, it is more efficient and dehumidifying to supply a mixed gas containing water vapor to the inside of the hollow fiber membrane and introduce the dried carrier gas into the space outside the hollow fiber membrane so as to counter flow with the mixed gas. In addition, it is preferable to recycle and use a part of the dehumidified gas obtained on the non-permeating side of the gas separation membrane as a carrier gas as a simple carrier gas introduction method. When humidifying, supply a mixed gas containing a larger amount of water vapor (high water vapor partial pressure) to the space in contact with the inside or outside of the hollow fiber membrane, and a smaller amount of water vapor into the space on the opposite side of the hollow fiber membrane. By supplying a gas containing (low water vapor partial pressure), the water vapor selectively permeates the membrane, and the gas containing a smaller amount of water vapor can be easily humidified. In particular, a mixed gas containing a larger amount of water vapor and a gas containing a smaller amount of water vapor are desirable because it is highly efficient to supply the mixed gas so as to counter flow across the hollow fiber membrane.

  Furthermore, by using the gas separation membrane of the present invention, it is possible to suitably perform dehumidification and / or humidification of the supply gas for the fuel cell. A polymer electrolyte fuel cell generally includes a power generation element in which both sides of a solid polymer electrolyte membrane having hydrogen ion conductivity are sandwiched by carbon electrodes carrying a platinum catalyst, and a fuel gas such as hydrogen or A separator having a flow distribution function for supplying an oxidizing gas such as oxygen or discharging exhaust gas from an electrode, and a current collector disposed on the outside thereof are laminated. In this battery, when the solid polymer electrolyte membrane is dried, the ionic conductivity is lowered, and the solid polymer electrolyte membrane and the electrode are poorly contacted to cause a sudden drop in output. It is important to control to maintain a constant humidity. For this reason, it is necessary to humidify the supply gas (fuel gas and / or oxidizing gas) (dehumidification instead of humidification if there is too much water). It has already been proposed to use a separation membrane as a method for humidifying the supply gas. JP-A-3-269958 discloses the use of a porous film made of tetrafluoroethylene resin. JP-A-8-273687 and JP-A-8-315838 disclose that the permeation membrane area per unit area is increased by using a hollow fiber-like porous membrane and the humidification performance is improved. However, these humidifying membranes have a problem that the humidifying performance is not sufficient, and that when water and the membrane are in contact with each other for a long time, water oozes out to the supply gas side of the membrane fuel cell and droplets are generated. there were. Further, in fuel cells for automobiles and the like, a method of selectively permeating moisture in the exhaust gas of the fuel cell through the separation membrane and recycling it to the supply gas of the fuel cell has been studied. In the membrane, there is a problem that components other than moisture in the exhaust gas of the fuel cell are mixed into the supply gas of the fuel cell.

  When the gas separation membrane of the present invention is used for a fuel cell, the hot water resistance around 100 ° C. at which the polymer electrolyte fuel cell is operated is very good. Furthermore, since the gas separation membrane of the present invention has an asymmetric structure composed of a skin layer (separation layer) and a porous layer (support layer), when used in a fuel cell for a long time, Inconvenience that water oozes out to the membrane surface on the supply gas side and droplets are generated, and problems such as mixing of components other than moisture in the exhaust gas of the fuel cell into the supply gas of the fuel cell are unlikely to occur. Further, when the gas separation membrane is made of polyimide, it is excellent in heat resistance and chemical resistance required when used for fuel cells.

  Next, the production and characteristics of the hollow fiber gas separation membrane in the present invention will be specifically described with reference to examples. In addition, this invention is not limited to an Example.

  Each measuring method in an Example is as follows.

(Measurement method of water vapor permeability of hollow fiber membrane)
Using about 10 hollow fiber membranes, a stainless steel pipe, and an epoxy resin adhesive, an element for evaluating permeation performance having an effective length of 80 mm was prepared, and this was attached to a stainless steel container to form a pencil module. . A fixed amount of nitrogen gas containing saturated steam at 15 ° C. was supplied to the inside of the hollow fiber of the pencil module at a pressure of 5 kgfG / cm ² , and the dry gas obtained from the outlet side of the membrane was used as the product gas. 20% of the product gas having a low water vapor concentration was further supplied to the permeation side in order to make the permeation side of the membrane atmospheric pressure and to obtain a sufficient partial pressure difference of water vapor between the membrane supply side and the non-permeation side. The dew point of the supply gas and product gas was detected with a specular dew point meter to determine the water vapor partial pressure. From the measured amount of water vapor (water vapor partial pressure), the amount of supplied gas, and the effective membrane area, the water vapor transmission rate (P ′ _{H 2 O} ) of the membrane was calculated. These measurements were performed at 35 ° C.

(Measurement method of nitrogen gas permeation performance of hollow fiber membrane)
Using about 10 hollow fiber membranes, a stainless steel pipe, and an epoxy resin adhesive, an element for evaluating permeation performance having an effective length of 80 mm was prepared, and this was attached to a stainless steel container to form a pencil module. . A nitrogen pure gas of 5 kgfG / cm ² was supplied thereto and the permeation flow rate was measured. The permeation rate of nitrogen gas was calculated from the measured amount of permeated nitrogen gas, supply pressure, and effective membrane area. These measurements were performed at 35 ° C.

(Measurement of tensile strength and tensile elongation of hollow fiber membrane)
Using a tensile tester, measurement was performed at a temperature of 23 ° C., an effective length of 20 mm, and a tensile speed of 10 mm / min.

(Measurement of hydrolysis resistance of hollow fiber membrane)
The hollow fiber membrane was immersed in water in a sealed container and heated in an oven at 150 ° C. for 22 hours. After cooling the container, the hollow fiber was taken out, dried at 100 ° C. for 30 minutes to remove moisture, and the elongation at break was measured by a tensile test. The breaking elongation retention was obtained by dividing the breaking elongation after the hot water treatment by the breaking treatment before the hot water treatment, and this was used as an index of hydrolysis resistance.

<Example 1>
(Preparation of polyimide solution)
14.3 g of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (hereinafter referred to as s-BPDA) and 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (Hereinafter referred to as 6FDA) 9.2 g and 4,4-diamino-diphenyl ether (hereinafter 44DADE) 14.0 g together with 184 g of solvent parachlorophenol (hereinafter PCP) in a separable flask at a polymerization temperature of 190 ° C. Polymerization was performed for 6 hours to obtain a polyimide solution having a polymer concentration of 16% by weight. 22 g of glycerin was added to the obtained polyimide solution and stirred at 190 ° C. for 1 hour to finally obtain a polyimide solution having a solution viscosity at 100 ° C. of 2000 poise and a polymer concentration of 14.5% by weight.

(Method for producing asymmetric hollow fiber membrane)
The obtained polyimide solution is filtered through a 400 mesh wire mesh, and then discharged from a hollow fiber spinning nozzle (circular opening outer diameter 1000 μm, circular opening slit width 200 μm, core opening outer diameter 600 μm), and discharged hollow The filamentous body was passed through a nitrogen atmosphere and then dipped in a coagulation liquid consisting of a 75 wt% ethanol aqueous solution at 0 ° C. to obtain a wet thread. This was immersed in ethanol at 50 ° C. for 2 hours to complete the solvent removal treatment, and further washed by immersion in 70 ° C. isooctane for 3 hours to replace the solvent, followed by drying at 100 ° C. for 30 minutes, and then at 250 ° C. Heat treatment was performed for 30 minutes. The obtained hollow fiber membranes all had an outer diameter of 320 μm, an inner diameter of 200 μm, and a film thickness of 60 μm.

  The obtained hollow fiber membrane was measured for gas permeation performance, mechanical properties, and hydrolysis resistance by the methods described above. The results are shown in Table 1.

<Examples 2-7, Comparative Examples 1-5>
A polyimide hollow fiber was obtained in the same manner as in Example 1 except that the polyimide composition, glycerin concentration, and solid content concentration of the polymer solution were as shown in Table 1. In Example 3 and Comparative Example 2, two different polyimides (component A and component B) were mixed at a weight ratio of 7: 3. In Comparative Examples 4 and 5, the hollow fiber membranes listed in Table 1 were used. The gas permeation performance, mechanical properties, and hydrolysis resistance of each hollow fiber membrane were measured by the above methods. The results are shown in Table 1.

<Example 8>
A polyimide hollow fiber was obtained in the same manner as in Example 1 except that ethanol was used instead of glycerin, and the polyimide composition, ethanol concentration, and solid content polymer concentration of the polymer solution were as shown in Table 1. The obtained hollow fiber membrane was measured for gas permeation performance, mechanical properties, and hydrolysis resistance by the methods described above. The results are shown in Table 1.

  The gas separation membrane of the present invention is an asymmetric membrane with a further improved gas permeation rate, and has a practical level of mechanical strength and hydrolysis resistance. For this reason, if the gas separation membrane of the present invention is used, a more efficient and more compact high-performance hollow fiber gas separation membrane module with improved gas separation speed can be provided, and highly efficient gas separation can be realized. The gas separation membrane of the present invention can be preferably obtained by forming a polymer solution using a mixture of a halogenated phenol and an aliphatic alcohol as a solvent by a dry-wet phase conversion method.

  In particular, the gas separation membrane of the present invention can perform dehumidification with extremely high efficiency when water vapor is removed (dehumidified) from a mixed gas containing water vapor.

Claims (8)

It has an asymmetric structure composed of a skin layer (separation layer) and a porous layer (support layer), and has a water vapor transmission rate (P ′ _H2O ) of 350 × 10 ⁻⁵ cm ³ (STP) / cm ² · sec · cmHg or more, the permeation rate ratio of water vapor and nitrogen ( _P′H2O / _P′N2 ) is 500 or more, the tensile elongation at break in the hollow fiber membrane is 25% or more, and in hot water at 150 ° C. A gas separation membrane wherein the breaking elongation of the hollow fiber membrane after 22 hours of hydrothermal treatment is maintained at 40% or more before the hydrothermal treatment. The gas separation membrane according to claim 1, wherein the breaking strength at the hollow fiber membrane is 2.3 kgf / mm ² or more.   The gas separation membrane according to claim 1 or 2, comprising a polyimide. The polyimide has the following general formula (1):

[In Formula (1), B is a tetravalent unit resulting from a tetracarboxylic acid component, and A is a divalent unit resulting from a diamine component. ]
The gas separation membrane according to claim 3, wherein the tetracarboxylic acid component comprises 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride.   The gas separation membrane according to claim 4, wherein the tetracarboxylic acid component further comprises 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride.   The gas separation membrane according to claim 4 or 5, wherein the diamine component contains diaminodiphenyl ethers. It is a manufacturing method of the gas separation membrane according to any one of claims 3 to 6,
A method for producing a gas separation membrane, comprising a step of performing a dry-wet phase conversion method using a polyimide solution containing polyimide and a solvent containing a phenol-based solvent and an aliphatic alcohol.   The method to isolate | separate water vapor | steam from the mixed gas containing water vapor | steam using the gas separation membrane of any one of Claims 1-6.