JP6866730B2 - Gas separation membrane - Google Patents

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 a membrane permeation component and has mechanical properties equal to or higher than a practical level as a hollow fiber gas separation membrane. The present invention relates to a gas separation membrane which has excellent hydrolysis resistance to water and a method for producing the same. Furthermore, the present invention relates to a gas separation method using the gas separation membrane, particularly a dehumidification method.

Gas separation membranes are used in various gas separation steps. Many of these are gas separation membranes made of glassy polymers with high gas selective permeability. Generally, a gas separation membrane made 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, most gas separation membranes made of glassy polymer have an asymmetric structure composed of a porous layer (support layer) and a thin skin layer (separation layer), that is, a separation layer that causes gas permeation resistance. It has a structure that is thin so that the gas permeation rate does not become too low.

The gas separation membrane is preferably used as a hollow fiber gas separation membrane module. A hollow fiber gas separation membrane module usually has a hollow fiber membrane bundle composed of a large number of hollow fiber membranes in a container having at least a mixed gas introduction port, a permeated gas discharge port, and an unpermeated gas discharge port. Consists of storage. In the hollow fiber gas separation membrane module, the mixed gas is supplied to the space in contact with the inside or outside of the hollow fiber membrane, and a specific component (membrane permeation component) in the mixed gas is selectively selected while flowing in contact with the hollow fiber membrane. Gas separation is performed by recovering the gas that has permeated the membrane and is recovered from the outlet of the permeated gas and from which the specific component (membrane permeation component) has been removed from the outlet of the non-permeated gas.

In a membrane with an asymmetric structure, the rate-determining process of the permeation rate of the permeation component permeating the membrane is usually the process of permeating the skin layer. Since the permeation resistance of the process of permeating the porous layer is relatively small, the influence of the permeation component of the membrane on the permeation rate of permeating the membrane is often negligible in practice.

However, when the permeation rate of the membrane-permeable component through the membrane is extremely high, the permeation rate of the membrane-permeable component permeating the membrane is not only the process of the membrane-permeating component permeating the skin layer but also permeating the porous layer. The process also has a practically non-negligible effect. In particular, when the membrane permeation component is water vapor, the permeation rate of water vapor permeating the membrane is extremely high (up to hundreds to thousands times) compared to other inorganic gases, so the permeation rate of water vapor permeating the membrane. Is affected by the permeation resistance of the porous layer in a practically non-negligible manner. Therefore, there has been a demand for the development of a high-performance dehumidifying membrane in which the permeation rate at which water vapor permeates the membrane is increased.

On the other hand, in an asymmetric membrane, if the porosity of the porous layer is simply increased to reduce the permeation resistance when the membrane permeation component permeates the membrane, the permeation rate of the membrane permeation component permeating the membrane is increased. Although the permeation rate can be increased, the support function of the membrane that the porous layer should have, that is, the mechanical strength is reduced, so that a practical high-performance gas separation film having both an improved permeation rate and a practical level of mechanical strength is achieved. It was difficult to obtain. There are also attempts to improve the mechanical strength by selecting a high-strength material, but there is a problem that the high-strength material generally has a smaller gas permeability coefficient.

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

Japanese Unexamined Patent Publication No. 2002-172311

However, even in the invention described in Patent Document 1, the permeation rate of water vapor is not sufficient, and further improvement is required.

Preferred embodiments of the present invention are as follows.

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

2. The gas separation membrane according to 1 above, wherein the breaking strength of 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 the formula (1), B is a tetravalent unit caused by the tetracarboxylic acid component, and A is a divalent unit caused by the diamine component. ]
3. The gas separation membrane according to 3 above, wherein the tetracarboxylic acid component contains 3,3', 4,4'-biphenyltetracarboxylic dianhydride.

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

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 above.
A method for producing a gas separation membrane, which comprises a step of performing a dry-wet phase conversion method using a polyimide solution containing polyimide and a solvent containing a phenolic 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. Therefore, by using the gas separation membrane of the present invention, it is possible to provide a high-performance hollow fiber gas separation membrane module having a high gas separation speed, high efficiency, and more compactness, and high efficiency gas separation can be realized. In particular, when removing (dehumidifying) water vapor from a mixed gas containing water vapor, dehumidification can be performed with extremely high efficiency.

One aspect of the gas separation membrane of the present embodiment has an asymmetric structure composed of a skin layer (separation layer) and a porous layer (support layer), and has a water vapor permeation rate ( _P'H2O ) of 350 × 10 ^{−. 5} cm ³ (STP) / cm ² · sec · cm Hg or more, the water vapor to nitrogen permeation rate ratio ( _P'H2O / _P'N2 ) is 500 or more, and the elongation at break in the hollow yarn film is 25%. As described above, the breaking elongation of the hollow yarn film 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 the present embodiment has a high permeation rate, retains the mechanical properties of a hollow fiber membrane at a practical level or higher, and has excellent hydrolysis resistance to water. Hereinafter, a detailed description will be given.

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

The gas separation membrane of the present invention has a high water vapor permeation rate. Specifically, the gas separation membrane preferably has a water vapor permeation rate ( _P'H2O ) of 350 × ^10-5 cm ³ (STP) / cm ² · sec · cm Hg or more, preferably 370 × 10 ^-5 cm. ^{3 (STP)} / cm and more preferably 2 · sec · cmHg or more. The upper limit is not particularly limited, but is usually 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 for "Standard Temperature and Pressure".

The gas separation membrane of the present invention has high gas selective permeability (separation degree), and the permeation rate ratio of water vapor to nitrogen ( _P'H2O / _P'N2 ) is preferably 500 or more, preferably 1000 or more. Is more preferable. The upper limit of the permeation rate ratio is not particularly limited, but is usually 100,000 or less. In the present specification, the water vapor permeation rate ( _P'H20 ) of the membrane and the water vapor to nitrogen permeation rate ratio ( _P'H2O / _P'N2 ) are 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 the 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. Breaking strength hollow fiber membrane tensile at break stress divided by Makudan area of the hollow fiber values [unit: kgf / mm ^2] a and, breaking elongation of the original length of the hollow fiber L _0, tensile It is a value [unit:%] _{of 100 × (LL 0} ) / L ₀ when the length at break is L.

In the gas separation membrane, the elongation at break when the hollow fiber membrane is formed is preferably 25% or more, more preferably 30% or more, further preferably 40% or more, and 60% or more. Is more preferable, and the upper limit is not limited, but is usually 1000% or less.

Gas separation membranes, breaking strength at the time of forming the hollow fiber membrane is preferably at 2.3 kgf / mm ² or more, more preferably 2.5 kgf / mm ² or more, 3.0 kgf / mm ² The above is more preferable, and the upper limit is not limited, but is usually 100 kgf / mm ² or less.

When 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 easily handled without breaking or breaking, so that it is industrially modularized. (Assembly and processing to a gas separation membrane module) can be performed. Further, a gas separation membrane module using a hollow fiber membrane having such mechanical strength is particularly useful because it has excellent pressure resistance and durability. Further, the hollow fiber membrane in the separation membrane module is continuously or intermittently deformed by the flow rate, flow velocity, pressure, temperature of the supplied gas flowing inside or outside the hollow fiber and the fluctuation thereof. Although subjected to stress, the hollow fiber membrane composed of the gas separation membrane of the present invention is broken or damaged due to a ^{breaking elongation of 25% or more, preferably a breaking strength of 2.3 kgf / mm 2 or more.} Hard to break.

Further, the gas separation membrane of the present invention is excellent in water resistance and heat resistance. Regarding the water resistance and heat resistance of the gas separation membrane, the retention rate of elongation at break (100) in the tensile test after the gas separation membrane was made into a hollow fiber membrane and treated with hot water for 22 hours in hot water at a temperature of 150 ° C. × 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 elongation at break after hot water treatment in hot water at a temperature of 150 ° C. for 22 hours is preferably 40% or more, preferably 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, polyether sulfone, 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, the 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 caused by the tetracarboxylic acid component, and A is a divalent unit caused by the diamine component. The unit 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 is a unit B1 having a diphenylhexafluoropropane structure represented by the following formula (B1) and a 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 comprises preferably 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, substantially. It is preferably composed of unit B1 and unit B2. If the diphenylhexafluoropropane structure is less than 10 mol% and the biphenyl structure exceeds 90 mol%, the gas permeation performance of the obtained polyimide may deteriorate, 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 obtained polyimide may decrease.

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

The unit A is a divalent unit derived from the diamine component, and preferably contains at least one selected from the unit A1 represented by the following formula (A1) and the 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 / or the unit A1 and / or the unit A1 and / or the unit A2 are represented by the formula (A2). The total of units A2 is preferably 90-100 mol%.

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

Next, the monomer component into which each of the units of the aromatic polyimide can be introduced will be described.

The tetracarboxylic acid component is a component capable of introducing a tetravalent residue B into a polyimide composed of a repeating unit represented by the general formula (1).

The unit having a diphenylhexafluoropropane structure represented by the formula (B1) can be obtained by using (hexafluoroisopropyridene) diphthalic acid, a dianhydride thereof, or an esterified product thereof as a tetracarboxylic acid component. Examples of the (hexafluoroisopropyridene) diphthalic acids include 4,4′- (hexafluoroisopropyridene) diphthalic acid, 3,3′- (hexafluoroisopropyridene) diphthalic acid, and 3,4′- (hexafluoroisopropyridene). ) Diphthalic acids, their dianhydrides, or esters thereof can be preferably used, especially 4,4'-(hexafluoroisopropyridene) diphthalic acids, their dianhydrides, or esters thereof. , 4,4'-(hexafluoroisopropyridene) diphthalic acid dianhydride is more preferable.

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

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 mechanical properties, but if the amount is too large, the polymer solution during film formation becomes unstable and it becomes difficult to form hollow fibers. In some cases.

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 in some cases is selected. For example, diphenylether tetracarboxylic acids, benzophenone tetracarboxylic acids, diphenylsulfonetetracarboxylic acids, naphthalenetetracarboxylic acids, diphenylmethanetetracarboxylic acids, diphenylpropanetetracarboxylic acids and the like can be mentioned.

The diamine component is a component capable of introducing a divalent residue A into a polyimide composed of a repeating unit represented by the general formula (1).

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

As the diamine component for introducing the residue A2, 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) ), And bis [(aminophenoxy) phenyl] sulfones having an Ar group represented by (), and bis (aminophenoxy) naphthalenes having an Ar group represented by the chemical formula (Ar6).

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

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

Examples of bis [(aminophenoxy) phenyl] propane 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 can be mentioned. Among them, 2,2-bis (4-aminophenoxy (4-phenyl)) propane is particularly preferable.

Bis [(aminophenoxy) phenyl] hexafluoropropanes having an Ar group represented by the chemical formula (Ar4) include 2,2-bis (4-aminophenoxy (4-phenyl)) hexafluoropropane and 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, and among them, 2,2-bis (4-aminophenoxy (4-phenyl)) hexafluoropropane is particularly preferable.

Examples of the bis [(aminophenoxy) phenyl] sulfone having an Ar group represented by the chemical formula (Ar5) include bis [4- (4-aminophenoxy) phenyl] sulfone and bis [4- (3-aminophenoxy) phenyl]. Sulfones and the like can be mentioned, and among them, bis [4- (4-aminophenoxy) phenyl] sulfone is particularly preferable.

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

As a preferred embodiment of the present invention, the polyimide constituting the gas separation membrane in the formula (1) contains 3,3', 4,4'-biphenyltetracarboxylic in an amount of 40 mol% or more based on the total amount of the unit B. Polyimide, which is a unit based on an acid dianhydride and whose unit is based on 4,4'-diaminodiphenyl ether in an amount of 50 mol% or more, more preferably 80 mol% or more, based on the total amount of the unit A. It is preferably contained in an amount of% by weight or more (which may be 100% by weight).

As a more preferable aspect of the present invention, the polyimide constituting the gas separation membrane in the formula (1) contains 3,3', 4,4'-biphenyltetra in an amount of 40 mol% or more based on the total amount of the unit B. A unit based on a carboxylic dianhydride, in which 10 mol% or more is a unit based on 2,2'-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride, and all units of the unit A. It is preferable to contain 60% by weight or more (may be 100% by weight) of polyimide, which is a unit based on 4,4'-diaminodiphenyl ether in which 50 mol% or more, more preferably 80 mol% or more is based on the amount. ..

Only one type of polyimide may be used, or two or more types of polyimide may be used in combination.

<Preparation of polyimide solution>
As one aspect of the method for preparing the polymer solution of the present invention, the method for preparing the polyimide solution will be described. To prepare the polyimide solution, add a tetracarboxylic acid component and a diamine component in an organic polar solvent at a predetermined composition ratio, polymerize at a low temperature of about room temperature to produce polyamic acid, and then heat to imidize by heating. Alternatively, a two-step method of chemically imidizing by adding pyridine or the like, or adding a tetracarboxylic acid component and a diamine component in an organic polar solvent at a predetermined composition ratio, and a high temperature of 100 to 250 ° C., preferably about 130 to 200 ° C. It is preferably carried out by a one-step method in which the polymerization imidization reaction is carried out in. When the imidization reaction is carried out by heating, it is preferable to carry out the imidization reaction while removing the desorbed water or alcohol. The amount of the tetracarboxylic dian component and the diamine component used with respect to the organic polar solvent is preferably such that the solid content concentration of the polyimide 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, catechols having two hydroxyl groups directly on the benzene ring, catechols such as resorcin, 3-chlorophenol and 4-chlorophenol (described later). (Same as parachlorophenol), a phenolic solvent consisting of halogenated phenols such as 3-bromphenol, 4-bromphenol, 2-chloro-5-hydroxytoluene; or N-methyl-2-pyrrolidone, 1,3 An amide-based solvent consisting of amides such as -dimethyl-2-imidazolidinone, N, N-dimethylformamide, N, N-diethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide; or a mixture thereof. Phenol and the like can be preferably mentioned. Of these, amide-based solvents and phenol-based solvents are preferable, phenol-based solvents are more preferable, halogenated phenols are even more preferable, and 4-chlorophenol is particularly preferable.

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

<Manufacturing method of 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 transition method is a known method for forming a film while contacting a polymer solution with a coagulating liquid to perform a phase transition. In the dry-wet phase conversion method, the solvent on the surface of the film-shaped polymer solution 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). It is a phase conversion method in which micropores are formed to form a porous layer (support layer) by immersing in a solvent (solvent) and utilizing the phase separation phenomenon that occurs at that time, and proposed by Loeb et al. (For example, US Pat. No. 3,133,132). It was done.

The polymer contained in the polymer solution is not particularly limited, but preferably contains the above-mentioned polyimide, more preferably 50% by weight or more, more preferably 70% by weight or more, and 100% by weight, based on the total amount of the polymer. May be%.

In the present invention, it is preferable that the solvent of the polymer solution used in the dry-wet phase conversion method contains a solvent capable of dissolving the polymer and an aliphatic alcohol. Since 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 formed into a hollow fiber membrane, and high heat resistance is obtained. be able to.

The solvent capable of dissolving the polymer is preferably an organic polar solvent, and may be the organic polar solvent used when synthesizing the polymer by polymerizing the monomer. As one aspect of the present invention, when the polymer is polyimide, the organic polar solvent may be any one capable of dissolving the polyimide, and the organic polar solvent used for preparing the above-mentioned polyimide solution can be exemplified.

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

The monovalent aliphatic alcohol as the solvent of the polymer solution is preferably an acyclic alcohol, and may be linear or branched, and has, for example, 1 to 7 carbon atoms. The monovalent aliphatic alcohol is not particularly limited, and for example, propanols such as methanol, ethanol, 1-propanol and isopropanol, butanols such as 1-butanol, 2-butanol and isobutanol, amyl alcohol and isoamyl alcohol. , 2-Pentanol, 3-Pentanol, 2-Methyl-1-butanol, Isopentyl Alcohol, Neopentyl Alcohol and other Pentanols, 1-Hexanol, 2-Hexanol, 3-Hexanol and the like, 1- Examples thereof 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, may be linear or branched, and has, for example, preferably 2 to 10 carbon atoms. More preferably, the number is 3 to 8. The aliphatic polyhydric alcohol means a divalent or higher alcohol, and is preferably a trihydric or higher alcohol. The aliphatic polyhydric alcohol is not particularly limited, but for example, 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, 4-Methyl-1,7-Heptanediol and other dihydric aliphatic alcohol solvents, glycerin, diglycerin and the like 3 Examples include alcohol solvents having a valence or higher. Of these, when glycerin is used, a uniform porous layer can be easily formed, and a hollow fiber membrane having excellent mechanical strength and heat resistance can be obtained.

One type of aliphatic alcohol may be used alone, or two or more types may be used in combination.

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 the range, the permeation performance and mechanical properties of the obtained hollow fiber are excellent. When the polymer solution is used in the spinning step described later, the solid content concentration of the polymer solution is preferably 10 to 20% by weight in terms of film formation. Further, the solution viscosity (rotational viscosity) of the polymer solution is preferably 50 to 15,000 poise at the discharge temperature in the spinning process, and particularly when it is 100 to 10,000 poise, a shape such as a hollow thread after discharge can be stably obtained. Therefore, it is preferable.

The fatty alcohol may be mixed with the solution in which the polymer is dissolved, or the isolated polymer, the organic protic solvent and the fatty alcohol may be mixed at the same time. Upon mixing, the polymer may be heated to dissolve in an organic polar solvent.

As a preferable aspect 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 by a dry-wet phase conversion method. As a more preferable aspect, 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 discharge step), a solidification step, a washing step, a drying step, and a heat treatment step. Each of these steps includes a step in which it is essential to continuously process the hollow fiber while continuously sending / taking out the hollow fiber, and a batch process in which the hollow fiber is wound around a bobbin or the like, or continuously. There are steps that may be processed.

First, in the spinning process (spinning dope discharge process), the spinning nozzle used for discharging the spinning dope liquid may be any one that extrudes the spinning dope liquid into a hollow filament, such as a tube-in orifice type nozzle. Is preferable. Usually, the temperature range of the polymer solution (preferably polyimide solution) at the time of extrusion depends on the polymer contained in the doping solution, the type of solvent, the viscosity and the like, but for example, it is preferably about 20 ° C. to 150 ° C., more preferably 30 ° C. ~ 120 ° C. In addition, spinning is performed while supplying gas or liquid to the inside of the hollow filament that is extruded from the nozzle.

In the coagulation step continuous from the spinning step, the hollow filaments discharged from the nozzle are once extruded into the atmosphere or an atmosphere of an inert gas such as nitrogen, and subsequently led to a coagulation bath and immersed in the coagulation liquid. .. The coagulation 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. Be done. When the polymer solution is a polyimide solution and the solvent of the polyimide solution is an amide-based solvent, an aqueous solution of the amide-based solvent is also preferable.

In the coagulation step, the polymer solution discharged from the nozzle into a hollow thread shape is immersed in a primary coagulation liquid that coagulates to the extent that the shape can be maintained, wound up on a guide roll or the like, and then secondary coagulation for complete coagulation. It is preferable to immerse in a liquid. The primary coagulation liquid and the secondary coagulation liquid may be the same coagulation liquid or separate coagulation liquids. It is also possible to efficiently extract the solvent in the polyimide solution by increasing the number of coagulation liquid tanks.

The spinning step and the solidifying step are preferably continuous processing steps in which the hollow fibers are continuously processed while continuously sending / taking out the hollow fibers.

In the next washing step, if necessary, washing with a washing solvent such as ethanol is performed, and then an aliphatic hydrocarbon such as isopentane, n-hexane, isooctane, n-heptane, etc. is used to wash the outside and inside of the hollow yarn. Substitute the coagulating solution and / or washing solvent of.

In the next drying step, the hollow fiber containing the substitution solvent is dried at an appropriate temperature. Then, in the heat treatment step, preferably, the heat treatment is performed at a temperature lower than the softening point or the secondary transition point of the polymer such as polyimide used to obtain an asymmetric gas-separated hollow fiber membrane.

The washing / drying / heat treatment step may be a continuous treatment step in which the hollow fibers are continuously processed while continuously sending / taking out the hollow fibers, or may be batch processed in a state of 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 modularized and preferably used. The inner diameter of the hollow fiber membrane is preferably about 30 to 500 μm. In a normal gas separation membrane module, for example, about 100 to 1,000,000 hollow fiber membranes (preferably 100 to 200,000) of an appropriate length are bundled, and both ends of the hollow fiber bundle are attached to at least one end of the hollow fiber. The hollow fiber membrane element made of the obtained hollow fiber bundle and the tube plate is attached to at least the mixed gas introduction port by fixing with a tube plate made of a thermosetting resin or the like so as to maintain the open state. It is obtained by storing and attaching the space leading to the inside of the hollow fiber membrane and the space leading to the outside of the hollow fiber membrane in a container provided with a permeated gas discharge port and a non-permeated gas discharge port so as to be isolated from each other. The tube plate is hermetically attached to the container with an O-ring or an adhesive. In such a gas separation membrane module, the mixed gas is supplied from the mixed gas introduction port to the space in contact with the inside or the outside of the hollow fiber membrane, and while the mixed gas flows in contact with the hollow fiber membrane, specific components in the mixed gas are selectively selected. Gas separation is performed by discharging the permeated gas that has permeated the membrane from the permeated gas discharge port and the non-permeated gas that has not permeated the membrane from the non-permeated gas discharge 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), but is particularly used for separating water vapor because it is excellent in water resistance and heat resistance. Is preferable. When separating water vapor using the gas separation membrane of the present invention, that is, when dehumidifying, the gas separation membrane module is supplied with a mixed gas containing water vapor to a space in contact with the inside or outside of the hollow fiber membrane. , Water vapor is selectively permeated to the permeation side of the membrane, and a dehumidified gas as an unpermeated gas can be obtained extremely efficiently. Further, the carrier gas may be allowed to flow in the space on the permeated gas side in the direction of countercurrent with the supplied mixed gas, for example, to promote the recovery of the permeated gas. Good.

Since the gas separation membrane of the present invention has an extremely high water vapor permeation rate, dehumidification and / or humidification can be performed extremely efficiently and preferably. When dehumidifying, the gas separation membrane module provided with the gas separation membrane of the present invention is supplied with a mixed gas containing water vapor to a space in contact with the inside or outside of the hollow fiber membrane, thereby selectively permeating the membrane. A gas that permeates to the side and is dehumidified as a non-permeated gas can be obtained extremely efficiently. In particular, it is more efficient and dehumidifying by supplying the mixed gas containing water vapor to the inside of the hollow fiber membrane and introducing the dried carrier gas into the space outside the hollow fiber membrane so as to be countercurrent with the mixed gas. Further, it is preferable as a simple method for introducing the carrier gas that a part of the dehumidified gas obtained on the non-permeable side of the gas separation membrane is recycled and used as the carrier gas. When humidifying, a mixed gas containing a larger amount of water vapor (high partial pressure of water vapor) is supplied to the space in contact with the inside or the outside of the hollow thread film, and a smaller amount of water vapor is supplied to the space on the opposite side of the hollow thread film. By supplying the gas containing (the partial pressure of water vapor is low), the water vapor selectively permeates the film, and the gas containing a smaller amount of water vapor can be easily humidified. In particular, it is desirable to supply a mixed gas containing a larger amount of water vapor and a gas containing a smaller amount of water vapor so as to form a countercurrent with the hollow fiber membrane sandwiched therein, because it is highly efficient.

Further, by using the gas separation membrane of the present invention, dehumidification and / or humidification of the supply gas for the fuel cell can be preferably performed. In general, a polymer electrolyte fuel cell is a power generation element in which both sides of a hydrogen ion conductive solid polymer electrolyte membrane are sandwiched between carbon electrodes carrying a platinum catalyst and laminated, and a fuel gas such as hydrogen or fuel gas such as hydrogen is provided on each of the electrodes. It is configured by stacking a separator having a distribution function for supplying an oxidizing gas such as oxygen and discharging the exhaust gas from the electrode, and a current collector arranged on the outside thereof. In this battery, when the solid polymer electrolyte membrane dries, the ionic conductivity decreases and the contact between the solid polymer electrolyte membrane and the electrode deteriorates, causing a sharp decrease in output. Therefore, the solid polymer electrolyte membrane becomes It is important to control to maintain a constant humidity. Therefore, it is necessary to humidify the supply gas (fuel gas and / or oxidizing gas) (if there is too much water, dehumidify instead of humidifying). It has already been proposed to use a separation membrane as a method for humidifying the supplied gas. Japanese Unexamined Patent Publication No. 3-269598 discloses that a porous membrane made of a tetrafluoroethylene resin is used. It is disclosed in JP-A-8-273687 and JP-A-8-315838 that the permeation membrane area per unit area is increased and the humidification performance is enhanced by using the hollow filamentous porous membrane. However, there is a problem that the humidification performance is not sufficient with these humidifying membranes, and that if the membrane is in contact with water for a long time, water seeps out to the supply gas side of the fuel cell of the membrane and droplets are generated. there were. Further, in fuel cells for automobiles and the like, a method of selectively permeating water in the exhaust gas of the fuel cell by a separation film and recycling it into the supply gas of the fuel cell for use has been studied. In the quality film, there is also a problem that components other than water 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 heat resistance around 100 ° C. in which the polymer electrolyte fuel cell is operated is also extremely good. Further, since the gas separation film of the present invention has an asymmetric structure composed of a skin layer (separation layer) and a porous layer (support layer), the gas separation film of the fuel cell can be used for a long time. The inconvenience that water seeps out to the film surface on the supply gas side and droplets are generated, and the problem that components other than water in the exhaust gas of the fuel cell are mixed 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 it is used for a fuel cell.

Next, the production of the hollow fiber gas separation membrane and its characteristics in the present invention will be specifically described with reference to Examples. The present invention is not limited to the examples.

Each measurement method in the examples is as follows.

(Measuring method of water vapor permeation performance of hollow fiber membrane)
Using about 10 hollow fiber membranes, a stainless steel pipe, and an epoxy resin adhesive, an element for evaluation of permeation performance with an effective length of 80 mm was created, and this was mounted on a stainless steel container to form a pencil module. .. A constant amount of nitrogen gas containing saturated water vapor 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 a product gas. Atmospheric pressure was set on the permeation side of the membrane, and 20% of the product gas having a low water vapor concentration was further supplied to the permeation side in order to obtain a sufficient partial pressure difference of water vapor between the supply side and the non-permeation side of the membrane. The dew points of the supply gas and product gas were detected with a mirror-type dew point meter, and the partial pressure of water vapor was determined. _{The water vapor permeation rate (P'H2O} ) of the membrane was calculated from the measured amount of water vapor (partial pressure of water vapor), the amount of supplied gas, and the effective film area. These measurements were performed at 35 ° C.

(Measuring 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 evaluation of permeation performance with an effective length of 80 mm was created, and this was mounted on a stainless steel container to form a pencil module. .. A pure nitrogen 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 breaking strength and tensile breaking elongation of hollow fiber membrane)
Using a tensile tester, the measurement was performed at a temperature of 23 ° C. with 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 closed container and heated in an oven at 150 ° C. for 22 hours. After cooling the container, the hollow fiber was taken out and dried at 100 ° C. for 30 minutes to remove water, and then the elongation at break was measured by a tensile test. By dividing the breaking elongation after the hot water treatment by the breaking treatment before the hot water treatment, the breaking elongation retention rate was obtained, 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, s-BPDA) and 2,2'-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (Hereinafter, 6FDA) 9.2 g and 4,4-diamino-diphenyl ether (hereinafter, 44DADE) 14.0 g, together with 184 g of the solvent parachlorophenol (hereinafter, PCP), were polymerized in a separable flask at a polymerization temperature of 190 ° C. The polymerization was carried out for 6 hours to obtain a polyimide solution having a polymer concentration of 16% by weight. By adding 22 g of glycerin to the obtained polyimide solution and stirring at 190 ° C. for 1 hour, a polyimide solution having a solution viscosity at 100 ° C. of 2000 poisons and a polymer concentration of 14.5% by weight was finally obtained.

(Manufacturing method of asymmetric hollow fiber membrane)
The obtained polyimide solution was 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). After passing the filamentous material through a nitrogen atmosphere, it was immersed in a coagulating solution consisting of a 75 wt% ethanol aqueous solution at 0 ° C. to obtain a wet yarn. This is immersed in ethanol at 50 ° C. for 2 hours to complete the desolvation treatment, further immersed in isooctane at 70 ° C. for 3 hours to replace the solvent, dried at 100 ° C. for 30 minutes, and then at 250 ° C. The heat treatment was performed for 30 minutes. All of the obtained hollow fiber membranes had an outer diameter of 320 μm, an inner diameter of 200 μm, and a film thickness of 60 μm.

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

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

The gas separation membrane of the present invention is an asymmetric membrane having a higher gas permeation rate, and has practical level mechanical strength and hydrolysis resistance. Therefore, by using the gas separation membrane of the present invention, it is possible to provide a higher-efficiency and more compact high-performance hollow fiber gas separation membrane module having an improved gas separation rate, and it is possible to realize high-efficiency gas separation. Further, the gas separation membrane of the present invention can be preferably obtained by forming a polymer solution using a mixture of 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 removing (dehumidifying) water vapor from a mixed gas containing water vapor.

Claims (4)

It has an asymmetric structure composed of a skin layer (separation layer) and a porous layer (support layer), and has a water vapor permeation rate ( _P'H2O ) of 350 × ^10-5 cm ³ (STP) / cm ² · sec ·. and a cmHg or more on ^{408 × 10 -5 cm 3 (STP} ) / cm 2 · sec · cmHg or less, transmission speed ratio of steam and nitrogen _{(P 'H2O / P' N2} ) is 500 or more on the 2200 or less, the hollow tensile elongation at break of the yarn layer is not more than 119% on 25% or more, 40% or more elongation at break before hot water treatment of the hollow fiber membrane after treatment 22 hours hydrothermally hot water at 0.99 ° C. Holds above 87% ,
The following general formula (1):

[In the formula (1), B is a tetravalent unit caused by the tetracarboxylic acid component, and A is a divalent unit caused by the diamine component. ]
Consists of polyimide represented by
The tetracarboxylic acid component comprises 3,3', 4,4'-biphenyltetracarboxylic dianhydride and 2,2'-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride.
A gas separation membrane in which the diamine component contains diaminodiphenyl ethers. The gas separation membrane according to claim 1, wherein the breaking strength of the hollow fiber membrane is 2.3 kgf / mm ^{2 or more.} The method for producing a gas separation membrane according to claim 1 or 2.
A method for producing a gas separation membrane, which comprises a step of performing a dry-wet phase conversion method using a polyimide solution containing polyimide and a solvent containing a phenolic solvent and an aliphatic alcohol. A method for separating water vapor from a mixed gas containing water vapor using the gas separation membrane according to claim 1 or 2.