JP2019076866A - Gas separation membrane - Google Patents

Abstract

To provide an asymmetric gas separation membrane having high gas permeation speed and selective gas permeability sufficient for practical levels.SOLUTION: A gas separation membrane is made of polyimide and has an asymmetric structure formed of a skin layer (a separation layer) and a porous layer (a supporting layer), and has a water vapor permeation speed (P') of 400×10cm(STP)/cmsec cmHg or higher, and a permeation speed ratio (P'/P') for water vapor and nitrogen of 100 or greater.EFFECT: The asymmetric gas separation membrane can remove (dehumidify) water vapor from mixed gas containing water vapor with high efficiency since it has high gas permeation speed and high selective permeability of water vapor.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, wherein the membrane permeation rate of the membrane permeation component is high, and the selective permeation of gas above practical level as a hollow fiber gas separation membrane TECHNICAL FIELD The present invention relates to a gas separation membrane having conductivity, 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 glassy polymers with high gas selective permeability. In general, a gas separation membrane formed of a glassy polymer has high gas selective permeability (separation degree) but has a disadvantage that the gas permeation coefficient (permeation rate) is small. For this reason, most of the gas separation membranes formed 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 generates gas permeation resistance. It has a structure to make it thin so that the gas permeation rate does not become too low.

  The gas separation membrane is suitably used as a hollow fiber gas separation membrane module. In a hollow fiber gas separation membrane module, a hollow fiber membrane bundle usually comprising a large number of hollow fiber membranes is provided in a container having at least a mixed gas inlet, a permeated gas outlet, and an unpermeated gas outlet. Housed and configured. In the hollow fiber gas separation membrane module, the mixed gas is supplied to a space in contact with the inside or the 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. The gas is separated by recovering the gas which has been permeated through the membrane and recovered from the outlet of the permeate gas and from which the specific component (membrane permeated component) has been removed from the outlet of the non-permeate gas.

  In a membrane with an asymmetric structure, the rate-limiting process of permeation rate at which the membrane permeation component permeates through the membrane is usually a process of permeation through the skin layer. Since the process of permeation through the porous layer has a relatively low permeation resistance, the effect on the permeation rate of the membrane permeation component through the membrane can often be practically ignored.

  However, when the permeation rate of the membrane-permeable component through the membrane is extremely high, the permeation rate of the membrane-permeable component is not only the process of membrane-permeable component passing through the skin layer but also the porous layer. Depending on the process, it can not be ignored in practice. In particular, when the membrane-permeable component is water vapor, the transmission rate of water vapor through the membrane is extremely high (reaches several hundred times to several thousand times) as compared to other inorganic gases, so the transmission rate of water vapor permeating the membrane Is practically not negligible due to the permeation resistance of the porous layer. For this reason, development of a high performance dehumidifying membrane in which the permeation rate at which water vapor permeates through the membrane is increased has been required.

  On the other hand, in an asymmetric membrane, the porosity of the porous layer is simply increased to reduce the permeation resistance when the membrane permeation component permeates the membrane, thereby increasing the permeation rate of the membrane permeation component through the membrane, A practical high performance gas separation membrane having both an improved permeation rate and a practical level of mechanical strength since the permeation rate can be increased but the support function of the membrane to be borne by the porous layer, that is, the mechanical strength decreases. It was difficult to get Although there have been attempts to improve mechanical strength by selecting a high strength material (for example, polyimide), high strength materials generally have a problem that the gas permeation coefficient is smaller.

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

Japanese Patent Application Laid-Open No. 2002-172311

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

  The preferred embodiments of the present invention are as follows.

1. Composed of polyimide,
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 400 × 10 ^-5 cm ³ (STP) / cm ² · sec · A gas separation membrane having a cmHg or more and a water vapor / nitrogen permeation rate ratio ( _P'H2O / _P'N2 ) of 100 or more.

2. The gas separation membrane according to the above 1, wherein the polyimide contains a repeating unit represented by 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、下記式（Ｂ１）および下記式（Ｂ２）で示される構造を含み、Ａはジアミン成分に起因する２価のユニットであり、下記式（Ａ１）及び下記式（Ａ２）で示される構造を含む。〕

[In formula (1), B is a tetravalent unit derived from a tetracarboxylic acid component, includes a structure represented by the following formula (B1) and the following formula (B2), and A is a bivalent derived from a diamine component] And a structure represented by the following formula (A1) and the following formula (A2). ]

（式（Ａ１）中、ＲおよびＲ’は、互いに独立に、水素原子または有機基である。）

(In formula (A1), R and R ′ are, independently of each other, a hydrogen atom or an organic group.)

（式（Ａ２）中、Ｘは塩素原子又は臭素原子でｎは１〜３である。）

(In the formula (A2), X is a chlorine atom or a bromine atom and n is 1 to 3.)

3. In the above formula (1), B is further represented by the following formula (B3):

で示される構造を含む、上記２に記載のガス分離膜。

3. The gas separation membrane according to 2 above, which comprises a structure represented by

4. It is a manufacturing method of the gas separation membrane in any one of said 1-3, Comprising:
A method for producing a gas separation membrane, comprising the step of performing a dry / wet phase conversion method using a polyimide solution containing a polyimide and a solvent containing a phenolic solvent and an aliphatic alcohol.

5. A method for separating water vapor from a mixed gas containing water vapor using the gas separation membrane according to any one of the above 1 to 3.

  The asymmetric gas separation membrane of the present invention has a high gas permeation rate, and has a gas selective permeability sufficient for practical use. For this reason, when the gas separation membrane of the present invention is used, it is possible to provide a more efficient and more compact high performance hollow fiber separation membrane module with high gas separation speed, and highly efficient gas separation can be realized. In particular, when steam is removed (dehumidified) from a mixed gas containing steam, the dehumidification can be performed extremely efficiently.

One aspect of the gas separation membrane of the present embodiment is composed of polyimide and 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 ) Is 400 × 10 ⁻⁵ cm ³ (STP) / cm ² · sec · cmHg or more, and the transmission rate ratio of water vapor to nitrogen (P ′ _{H 2 O} / P ′ _{N 2} ) is 100 or more. The gas separation membrane of the present embodiment has a very high gas permeation rate. The details will be described below.

  The gas separation membrane of the present invention is mainly composed of a very thin dense layer (preferably 0.001 to 5 μm in thickness) responsible for gas separation performance and a relatively thick porous layer (preferably 10 to 10 nm in thickness) supporting the dense layer. And an asymmetric structure having It is preferable to form an asymmetric hollow fiber membrane because the gas separation membrane has an advantage that the effective surface area is large and the pressure resistance is high, 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. 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 ′ _{H 2 O} ) of 400 × 10 ⁻⁵ cm ³ (STP) / cm ² · sec · cmHg or more, 450 × 10 ⁻⁵ cm More preferably, it is ³ (STP) / cm ² · sec · cmHg or more. 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, which is an abbreviation of “Standard Temperature and Pressure”.

The gas separation membrane of the present invention has high selective gas permeability (separation degree) and preferably has a water vapor / nitrogen permeation rate ratio (P ' _H2O / P' _N2 ) of 100 or more, and 250 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 the present specification, the water vapor transmission rate ( _P'H20 ) of the membrane and the water vapor / nitrogen transmission rate ratio ( _P'H2O / _P'N2 ) are those at 35 ° C.

  The gas separation membrane of the present invention is composed of polyimide, but other polymers may be included as materials, as long as the effects of the present invention can be obtained. The other polymer is not particularly limited, and examples thereof include polyimide, polyamide, polyether sulfone, polyamide imide, polyether imide, polycarbonate and the like.

  Although the aromatic polyimide containing the repeating unit shown by following General formula (1) as a preferable one aspect | mode of the polyimide which comprises the gas separation membrane of this invention is demonstrated, this invention is not limited to this.

  In the said General formula (1), B is a tetravalent unit originating in a tetracarboxylic-acid component, A is a bivalent unit originating in a diamine component. The unit which comprises the aromatic polyimide represented by General formula (1) is explained in full detail below.

  The unit B is a tetravalent unit derived from a tetracarboxylic acid component, preferably a unit B1 based on a diphenylhexafluoropropane structure represented by the following formula (B1), a biphenyl structure represented by the following formula (B2) It contains at least one unit selected from the group consisting of unit B2 and unit B3 based on a phenyl structure represented by the following formula (B3), more preferably at least unit B1 and unit B2, further preferably, a unit B1, unit B2, and unit B3.

  The content of each unit contained in unit B is not particularly limited. The content of the unit B1 is preferably 10 to 70 mol%, more preferably 20 to 60 mol%, based on the total amount of units B. The content of the unit B2 is preferably 10 to 80 mol%, more preferably 20 to 70 mol%, based on the total amount of units B. The content of the unit B3 may be 0 mol%, preferably 5 to 20 mol%, more preferably 10 to 20 mol% with respect to the total unit amount of the unit B. Preferably, unit B substantially consists of unit B1 and unit B2, or unit B1, unit B2 and unit B3, and of all units constituting unit B, the sum of unit B1, unit B2 and unit B3 The content is preferably 80 mol% or more, preferably 90 mol% or more, and may be 100 mol%.

  When there are too few units B1 having a diphenylhexafluoropropane structure and too many units B2 having a biphenyl structure, the gas permeation performance of the resulting polyimide is lowered, making it difficult to obtain a high performance gas separation membrane There is. On the other hand, when there are too many units B1 and there are too few units B2, the mechanical strength of the polyimide obtained may fall.

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

  The unit A in the general formula (1) is a divalent unit derived from a diamine component, and preferably comprises a unit A1 represented by the following formula (A1) and a unit A2 represented by the following formula (A2) It contains at least one selected from the group, and more preferably includes unit A1 and unit A2.

（式（Ａ１）中、ＲおよびＲ’は、互いに独立に、水素原子または有機基である。）

(In formula (A1), R and R ′ are, independently of each other, a hydrogen atom or an organic group.)

（式（Ａ２）中、Ｘは塩素原子又は臭素原子でｎは１〜３である。）

(In the formula (A2), X is a chlorine atom or a bromine atom and n is 1 to 3.)

  In formula (A1), R and R ′ are, independently of one another, a hydrogen atom or an organic group, and as the organic group, for example, an alkyl group such as a methyl group, an ethyl group or a propyl group is preferable.

  In formula (A2), a plurality of X's are each independently a chlorine atom or a bromine atom, preferably a chlorine atom. In formula (A2), plural n's are each independently 1 to 3 and preferably 2. The unit A2 is preferably a unit represented by the following formula (A2-1).

  The content of each unit contained in unit A is not particularly limited. For example, the content of the unit A1 is preferably 30 to 70 mol%, more preferably 30 to 60 mol%, with respect to the total amount of the unit A. Although the gas permeability is improved by including the unit A1, if the content is too large, the degree of separation may decrease. The content of the unit A2 is preferably 30 to 70 mol%, more preferably 30 to 60 mol%, based on the total amount of the unit A. By including the unit A2, the degree of gas separation is improved, but if the amount is too large, the polymer may become insoluble and film formation may become difficult. The unit A preferably consists essentially of the unit A1 and the unit A2, and the total content of the unit A1 and the unit A2 is preferably 80 mol% or more of all the units constituting the unit A, and it is 90 mol % Or more is preferable, and 100 mol% may be sufficient.

  As a preferred aspect of this embodiment, in the polyimide composed of the repeating unit represented by the general formula (1), the unit B includes the unit B1 and the unit B2, and the unit A includes the unit A1 and the unit A2. As a more preferable aspect of this embodiment, the unit B includes the unit B1, the unit B2, and the unit B3, and the unit A includes the unit A1 and the unit A2.

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

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

  (Hexafluoroisopropylidene) diphthalic acid, a dianhydride thereof, or an ester thereof is used as a tetracarboxylic acid component capable of introducing a unit having a diphenylhexafluoropropane structure represented by the general formula (B1) Obtained by 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 products can be suitably used, but in particular, 4,4 '-(hexafluoroisopropylidene) diphthalic acid, its dianhydride, or its esterified product is preferable. More preferred is 4,4 '-(hexafluoroisopropylidene) diphthalic dianhydride.

  By using a biphenyltetracarboxylic acid such as biphenyltetracarboxylic acid, its dianhydride, or its esterified product as a tetracarboxylic acid component capable of introducing a unit having a biphenyl structure represented by the above general formula (B2) can get. Examples of the biphenyl tetracarboxylic acids include 3,3 ′, 4,4′-biphenyl tetracarboxylic acid, 2,3,3 ′, 4′-biphenyl tetracarboxylic acid, and 2,2 ′, 3,3′-biphenyl tetra Although carboxylic acids, their dianhydrides, or their esterified products can be suitably used, 3,3 ′, 4,4′-biphenyltetracarboxylic acid, their dianhydrides, or their esterified products are preferable, More preferred is 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride.

  As a tetracarboxylic acid component capable of introducing a tetravalent unit based on a phenyl structure represented by the above general formula (B3), pyromellitic acids such as pyromellitic acid and its acid anhydride can be used. The pyromellitic acids are suitable for enhancing the mechanical properties, but when the amount is too large, the polymer solution during film formation coagulates and becomes unstable and it becomes difficult to form a hollow fiber There is a case.

  The other tetracarboxylic acid component giving the unit B4 is a tetracarboxylic acid other than the compounds shown above, and a compound is selected which does not impair the effect of the present invention and in some cases can further improve the performance. For example, diphenyl ether tetracarboxylic acids, benzophenone tetracarboxylic acids, diphenyl sulfone tetracarboxylic acids, naphthalene tetracarboxylic acids, diphenylmethane tetracarboxylic acids, diphenyl propane tetracarboxylic acids and the like can be mentioned.

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

  The bivalent unit based on the diphenylene sulfone structure shown by Formula (A1) originates in a diamine component.

  As a diamine component capable of introducing a divalent unit of the formula (A1), 3,7-diamino-2,8-dimethyl-diphenylene sulfone (dimethyl-3,7-diamino-dibenzothiophene-5,5-, 5 Diaminodiphenylene sulfones such as 3,7-diamino-2,8-diethyl-diphenylene sulfone, 3,7-diamino-2,6-dimethyl-diphenylene sulfone, etc. may also be mentioned. .

  2,2 ′, 5,5′-tetrachlorobenzidine, 3,3 ′, 5,5′-tetrachlorobenzidine as a diamine component capable of introducing a divalent unit based on the biphenyl structure of the formula (A2) 3,3'-dichlorobenzidine, 2,2'-dichlorobenzidine, 2,2 ', 3,3', 5,5'-hexachlorobenzidine, 2,2 ', 5,5'-tetrabromobenzidine, 3 Benzidines such as 3,3 ′, 5,5′-tetrabromobenzidine, 3,3′-dibromobenzidine, 2,2′-dibromobenzidine, 2,2 ′, 3,3 ′, 5,5′-hexachlorobenzidine Are preferred, and 2,2 ', 5,5'-tetrachlorobenzidine is preferred.

  In the present embodiment, the ratio of the number of repeating units represented by the formula (1) is preferably 80 mol% or more, and may be 100 mol% with respect to the total number of repeating units.

  The polyimide may be used alone or in combination of two or more.

Preparation of Polyimide Solution
The preparation method of the polyimide solution used for manufacture of the gas separation membrane of this invention is demonstrated. The polyimide solution is prepared by adding a tetracarboxylic acid component and a diamine component at a predetermined composition ratio in an organic polar solvent, causing a polymerization reaction at a low temperature around room temperature to form a polyamic acid, and then heating to make it heat imidize Or a two-step method of chemical imidization by adding pyridine or the like, or by adding a tetracarboxylic acid component and a diamine component in a predetermined composition ratio to an organic polar solvent, preferably 100 to 250 ° C., more preferably 130 to 200 It is suitably carried out by a one-stage method in which the polymerization and imidization reaction is carried out at a high temperature of about. When the imidization reaction is carried out by heating, it is preferable to carry out while removing water or alcohol to be eliminated. The amount of the tetracarboxylic acid component and the diamine component used relative to the organic polar solvent is suitably 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. The mixing ratio of the tetracarboxylic acid component to the diamine component is, for example, about equimolar, preferably the molar ratio of the diamine component to the tetracarboxylic acid component [the number of moles of the diamine component / the number of moles of the tetracarboxylic acid component] is preferably 0. It is preferably from 0.90 to 1.10, more preferably from 0.95 to 1.05.

  Examples of organic polar solvents include phenols such as phenol, cresol and xylenol, catechols having two hydroxyl groups directly on the benzene ring, catechols such as resorcin, 3-chlorophenol, 4-chlorophenol (described later) Phenolic solvents such as parachlorophenol), 3-bromophenol, 4-bromophenol, halogenated phenols such as 2-chloro-5-hydroxytoluene, etc .; or N-methyl-2-pyrrolidone, 1, 3 -Amide-based solvents comprising amides such as dimethyl-2-imidazolidinone, N, N-dimethylformamide, N, N-diethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide, or mixtures thereof A solvent etc. can be mentioned suitably. Among these, amide solvents and phenol solvents are preferable, phenol solvents are more preferable, halogenated phenols are more preferable, and 4-chlorophenol is particularly preferable.

  The polyimide solution obtained by the polymerization and imidization can also be used directly for spinning as described later. Also, for example, the obtained polyimide solution is put into a solvent insoluble in polyimide to precipitate the polyimide, and after isolation, the polyimide solution is 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 of 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 polyimide solution. The dry-wet phase conversion method is a known method in which a polyimide solution is brought into contact with a coagulating solution to form a film while converting the phase. In the dry-wet phase conversion method, the solvent on the surface of the polyimide solution in the form of a film is evaporated to form a thin dense layer (separating layer), and then the coagulation liquid (compatible with the solvent of the polyimide solution) and the polyimide is insoluble And a method of forming a porous layer (supporting layer) by forming fine pores by immersion in a solvent) and the phase separation phenomenon occurring at that time, and proposed by Loeb et al. (Eg, US Pat. No. 3,133,132) It is

  The polyimide solution may contain other polymers, but preferably contains at least 50% by weight, more preferably at least 70% by weight, still more preferably at least 90% by weight, 100% by weight, based on the total amount of the polymer. It may be

  In the present invention, the solvent of the polyimide solution used in the dry-wet phase conversion method preferably contains a solvent capable of dissolving the polyimide and an aliphatic alcohol. When the polyimide solution contains an aliphatic alcohol, it is possible to obtain a gas separation membrane having a high permeation rate of a membrane-permeable component (for example, water vapor) and an excellent gas selective permeability. In addition, since the polyimide solution contains an aliphatic alcohol, it is possible to obtain a gas separation membrane having a sufficiently high mechanical strength when made into a hollow fiber membrane and a high thermal water resistance.

  The solvent capable of dissolving the polyimide is preferably an organic polar solvent, and may be the organic polar solvent used when polymerizing monomers to synthesize a polymer. As one aspect of the present invention, an organic polar solvent used for preparation of the above-mentioned polyimide solution can be exemplified.

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

  The monovalent aliphatic alcohol as a solvent for the polyimide solution is preferably acyclic and may be linear or branched, and has, for example, 1 to 7 carbon atoms. The monovalent aliphatic alcohol is not particularly limited, and examples thereof include 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, pentanols such as neopentyl alcohol, 1-hexanol, 2-hexanol, hexanols such as 3-hexanol, 1- Heptanols, such as heptanol, 2-heptanol, 3-heptanol, 4-heptanol, etc. are mentioned. Of these, ethanol is preferred.

  The aliphatic polyhydric alcohol as a solvent for the polyimide solution is preferably acyclic, and may be linear or branched, and the number of carbon atoms is, for example, preferably 2 to 10, More preferably, it is 3-8. The aliphatic polyhydric alcohol means a dihydric or higher alcohol and is preferably a trihydric or higher alcohol. The aliphatic polyhydric alcohol is not particularly limited. For example, ethylene glycol, diethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 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, using glycerin makes it easy to form a uniform porous layer, has a high gas permeation rate, and can obtain a hollow fiber membrane having gas selectivity sufficient for practical use.

  The aliphatic alcohol may be used alone or in combination of two or more.

  The content of the aliphatic alcohol in the polyimide solution is preferably 2 to 30% by weight, preferably 3 to 30% by weight, more preferably 5 to 20% by weight, based on the total weight of the polyimide solution. When the content of the aliphatic alcohol is in the above range, the permeation performance and mechanical properties of the obtained hollow fiber are excellent. Moreover, when using a polymer solution for the below-mentioned spinning process, 10 to 20 weight% of solid content concentration of a polymer solution is preferable on film forming. The solution viscosity (rotational viscosity) of the polymer solution is preferably 50 to 15,000 poise at the ejection temperature in the spinning step, and in particular 100 to 10,000 poise, it is possible to stably obtain the shape after ejection such as hollow fiber. So preferred.

  The aliphatic alcohol may be mixed in the solution in which the polyimide is dissolved, or the isolated polyimide, the organic polar solvent and the aliphatic alcohol may be mixed simultaneously. At the time of mixing, the polyimide 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 according to the present invention, a dry / wet phase conversion method is preferred using a polyimide and a polyimide solution containing a mixed solvent of a halogenated phenol and an aliphatic alcohol. As a more preferable 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 dry / wet phase conversion method using a polyimide solution will be described below.

  The method for producing a hollow fiber membrane usually includes a spinning process (spinning dope discharge process), a coagulation process, a washing process, a drying process and a heat treatment process. In each of these steps, it is necessary to continuously process the hollow fiber while continuously feeding out and taking up the hollow fiber, and batch processing in a state of being wound around a bobbin or the like, or continuously. There are steps that may be processed.

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

  In the coagulation process continuous from the spinning process, the hollow fiber discharged from the nozzle is temporarily pushed out into the atmosphere or in an inert gas atmosphere such as nitrogen, and then, it is led to the coagulation bath and immersed in the coagulation liquid. . The coagulation liquid is preferably one which does not substantially dissolve the polyimide component and is compatible with the solvent of the polyimide 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, methyl ethyl ketone and the like, or mixtures thereof are preferably used. Be When the solvent of the polyimide solution is an amide solvent, an aqueous solution of an amide solvent is also preferable.

  In the coagulation step, the polyimide solution discharged in the form of a hollow fiber from the nozzle is immersed in a primary coagulation solution that solidifies to the extent that the shape can be maintained, taken up on a guide roll or the like, and then secondary coagulation for complete solidification. It is preferable to immerse in liquid. The primary coagulating liquid and the secondary coagulating liquid may be the same coagulating liquid, or may be separate coagulating liquids. In addition, it is also possible to efficiently extract the solvent in the polyimide solution by increasing the number of coagulation liquid baths.

  The spinning step and the coagulation step are preferably continuous processing steps in which the hollow fiber is continuously processed while the hollow fiber is continuously sent out / taken off.

  In the next washing step, if necessary, washing with a washing solvent such as ethanol, and then using a substitution solvent such as aliphatic hydrocarbons such as isopentane, n-hexane, isooctane, n-heptane, etc. Replace the coagulation solution and / or the washing solvent of

  In the next drying step, the hollow fiber containing the displacement solvent is dried at an appropriate temperature. Then, in the heat treatment step, the asymmetric gas separated hollow fiber membrane is obtained by heat treatment preferably at a temperature lower than the softening point or secondary transition point of the used polyimide.

  The washing, drying, and heat treatment steps may be a continuous treatment step in which hollow fibers are continuously treated while feeding and taking off the hollow fibers continuously, or batch treatment may be performed 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 suitably used as a module. The inner diameter of the hollow fiber membrane is preferably about 30 to 500 μm. A typical gas separation membrane module bundles, for example, about 100 to 100,000,000 hollow fiber membranes (preferably 100 to 200000) of an appropriate length, and both ends of the hollow fiber bundle are at least one end of the hollow fiber. The hollow fiber membrane element comprising the hollow fiber bundle and the tube sheet obtained by fixing the tube with a tube sheet made of a thermosetting resin or the like is held in a state of holding the open state. It is obtained by storing and attaching the space communicating with the inside of the hollow fiber membrane and the space communicating with the outside of the hollow fiber membrane in a container provided with the permeate gas outlet and the non-permeate gas outlet. The tube sheet is sealingly attached to the container by an O-ring or an adhesive. In such a gas separation membrane module, the mixed gas is supplied from the mixed gas inlet to the space in contact with the inside or the outside of the hollow fiber membrane, and the specific component in the mixed gas is selectively selected while flowing in contact with the hollow fiber membrane. The gas separation is performed by discharging the non-permeated gas that has permeated through the membrane and the permeated gas has not permeated through the membrane from the permeate gas outlet.

  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 hot water resistance. Is preferred. When water vapor is separated using the gas separation membrane of the present invention, that is, when dehumidification is performed, mixed gas containing water vapor is supplied to the above-mentioned gas separation membrane module to a space in contact with the inside or the outside of the hollow fiber membrane. Water vapor can be selectively transmitted to the permeation side of the membrane, and a dehumidified gas can be obtained extremely efficiently as a non-permeated gas. Alternatively, the carrier gas may be flowed in the direction opposite to the mixed gas supplied, for example, in the space on the permeating gas side to promote the recovery of the permeating 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 dehumidifying, water vapor is selectively permeated through the gas separation membrane module provided with the gas separation membrane of the present invention by supplying mixed gas containing water vapor to a space in contact with the inside or outside of the hollow fiber membrane. It is possible to very efficiently obtain the dehumidified gas as the non-permeate gas which permeates to the side. In particular, it is more efficient to dehumidify 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 in countercurrent with the mixed gas. It is preferable because it can be used. Furthermore, it is preferable to recycle and use a part of the dehumidified gas obtained on the non-permeate side of the gas separation membrane as a carrier gas as a simple method for introducing a carrier gas. When humidifying, mixed gas containing a larger amount of water vapor (high water vapor partial pressure) is supplied to the space in contact with the inside or outside of the hollow fiber membrane, and a smaller amount of water vapor is supplied to the space on the opposite side of the hollow fiber membrane. By supplying the contained gas (low water vapor partial pressure), the water vapor can selectively permeate the membrane to easily humidify the gas containing a smaller amount of water vapor. In particular, it is desirable that the mixed gas containing a larger amount of water vapor and the gas containing a smaller amount of water vapor be supplied countercurrently across the hollow fiber membrane, as it is highly efficient.

  Furthermore, by using the gas separation membrane of the present invention, dehumidification and / or humidification of the supplied gas for the fuel cell can be suitably performed. In general, a polymer electrolyte fuel cell comprises a power generation element in which a hydrogen ion conductive solid polymer electrolyte membrane is laminated on both sides by a carbon electrode carrying a platinum catalyst, and fuel gas such as hydrogen or the like at each electrode. It is configured by laminating a separator having a distribution function for supplying an oxidizing gas such as oxygen or discharging an exhaust gas from an electrode, and a current collector disposed outside the separator. In this battery, when the solid polymer electrolyte membrane is dried, the ion conductivity decreases, and a contact failure between the solid polymer electrolyte membrane and the electrode occurs to cause a sharp drop in the output, so the solid polymer electrolyte membrane is It is important to control to maintain a constant humidity. For this reason, it is necessary to humidify the supplied gas (fuel gas and / or oxidizing gas) (if the water content is too much, dehumidify instead of humidification). It has already been proposed to use a separation membrane as a method of humidifying the supplied gas. The use of a porous membrane made of tetrafluoroethylene resin is disclosed in Japanese Patent Application Laid-Open No. 3-269958. JP-A-8-273687 and JP-A-8-315838 disclose that the permeation membrane area per unit area can be increased by using a hollow fiber-like porous membrane to enhance the humidification performance. However, these humidifying membranes have the problem that the humidifying performance is not sufficient, and the problem is that when the membrane is in contact with water for a long time, water leaks to the supply gas side of the membrane fuel cell to generate droplets. there were. Furthermore, in fuel cells for automobiles and the like, a method has been studied in which water in the exhaust gas of the fuel cell is selectively permeated through the separation membrane and recycled to the gas supplied to the fuel cell. In the case of the porous membrane, there is also a problem that components other than the moisture in the exhaust gas of the fuel cell are mixed into the supply gas of the fuel cell.

  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), the gas supplied from the fuel cell when used for a long time in the fuel cell It is hard to produce the problem that water leaks to the film surface of the side and a droplet is generated, and the problem that components other than the moisture in the exhaust gas of the fuel cell are mixed in the gas supplied to the fuel cell. When the gas separation membrane is made of polyimide, it is also excellent in heat resistance, chemical resistance and the like required when used for fuel cells.

  Next, the production of the hollow fiber gas separation membrane in the present invention and the characteristics thereof will be specifically described by way of examples. The present invention is not limited to the examples.

  Each measuring method in an Example is as follows.

(Method of measuring water vapor transmission performance of hollow fiber membrane)
Using approximately 10 hollow fiber membranes, a stainless steel pipe, and an epoxy resin adhesive, an element for permeation performance evaluation with an effective length of 80 mm was prepared, and this was mounted on a stainless steel container to form a pencil module . A fixed amount of nitrogen gas containing saturated steam at 15 ° C. was supplied at a pressure of 5 kgfG / cm ² to the inside of the hollow fiber of this pencil module, and the dry gas obtained from the outlet side of the membrane was used as the product gas. The permeation side of the membrane was atmospheric pressure, and in order to obtain a sufficient partial pressure difference of water vapor on the supply side and the non-permeation side of the membrane, 20% of the product gas with a low water vapor concentration was further supplied to the permeation side. The dew point of the supplied gas and the product gas was detected by a mirror dew point meter to determine the water vapor partial pressure. The water vapor transmission rate (P ' _H2O ) of the membrane was calculated from the measured amount of water vapor (water vapor partial pressure), the amount of supplied gas and the effective membrane area. In addition, these measurements were performed at 35 degreeC.

(Method of measuring nitrogen gas permeation performance of hollow fiber membrane)
Using approximately 10 hollow fiber membranes, a stainless steel pipe, and an epoxy resin adhesive, an element for permeation performance evaluation with an effective length of 80 mm was prepared, and this was mounted on a stainless steel container to form a pencil module . It was supplied with 5 kg fG / cm ² of pure nitrogen gas to measure the permeation flow rate. The permeation rate of nitrogen gas was calculated from the measured amount of permeation nitrogen gas, supply pressure and effective membrane area. In addition, these measurements were performed at 35 degreeC.

Example 1
(Preparation of polyimide solution)
45 mol% of 3,3 ′, 4,4′-biphenyltetracarboxylic acid dianhydride (hereinafter s-BPDA) and 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride The following 6FDA) 40 mol%, benzene-1,2,4,5-tetracarboxylic acid dianhydride (hereinafter PMDA) 15 mol%, 3,7-diamino-2,8-dimethyldibenzothiophene 5,5 A polymerization temperature of 190 in a separable flask together with 50 mol% of dioxide (hereinafter TSN) and 50 mol% 2,2'5,5'-tetrachlorobenzidine (hereinafter TCB) together with parachlorophenol (hereinafter PCP) as a solvent Polymerization was carried out for 12 hours at .degree. C. to obtain a polyimide solution having a polymer concentration of 18% by weight. Glycerin was added to the obtained polyimide solution to 5 wt% with respect to the total amount of the polymer solution. By stirring at 190 ° C. for 1 hour, a polyimide solution having a solution viscosity of 2000 poise at 100 ° C. and a polymer concentration of 17% by weight was finally obtained. The solution viscosity of the polyimide solution was measured at a temperature of 100 ° C. using a rotational viscometer (the shear rate of the rotor is 1.75 sec ⁻¹ ).

(Method for producing asymmetric hollow fiber membrane)
The resulting polyimide solution is filtered through a 400 mesh wire mesh, and then discharged from a hollow fiber spinning nozzle (round opening outer diameter 1000 μm, circular opening slit width 200 μm, core opening outer diameter 600 μm) and discharged hollow The filament was passed through a nitrogen atmosphere and then immersed in a coagulating solution consisting of a 75% by weight aqueous ethanol 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, and then it is dipped and washed in isooctane at 70 ° C. for 3 hours to replace the solvent, dried at 100 ° C. for 30 minutes, and then at 250 ° C. Heat treatment was performed for 30 minutes. The obtained hollow fiber membranes were all having an outer diameter of 330 μm, an inner diameter of 210 μm, and a film thickness of 60 μm.

  The gas permeation performance of the obtained hollow fiber membrane was measured by the above-mentioned method. The results are shown in Table 1.

Example 2, Comparative Examples 1 to 3
In Example 2 and Comparative Example 1, polyimide hollow fibers were obtained in the same manner as in Example 1 except that the composition of the polyimide, the concentration of glycerin, and the solid content concentration of the polymer solution were as shown in Table 1. In Comparative Examples 2 and 3, the hollow fiber membranes described in Table 1 were used. The gas permeation performance of each hollow fiber membrane was measured by the method 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 gas selective permeability sufficient for practical use. Therefore, by using the gas separation membrane of the present invention, it is possible to provide a highly efficient and compact high performance hollow fiber gas separation membrane module having an improved gas separation rate, and to realize high efficiency gas separation. Further, the gas separation membrane of the present invention can be obtained preferably 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, in the case of removing (dehumidifying) water vapor from a mixed gas containing water vapor, the gas separation membrane of the present invention can perform dehumidification with extremely high efficiency.

Claims (5)

Composed of polyimide,
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 400 × 10 ^-5 cm ³ (STP) / cm ² · sec · A gas separation membrane having a cmHg or more and a water vapor / nitrogen permeation rate ratio ( _P'H2O / _P'N2 ) of 100 or more. The gas separation membrane according to claim 1, wherein the polyimide contains a repeating unit represented by the following general formula (1).

[In formula (1), B is a tetravalent unit derived from a tetracarboxylic acid component, includes a structure represented by the following formula (B1) and the following formula (B2), and A is a bivalent derived from a diamine component] And a structure represented by the following formula (A1) and the following formula (A2). ]

(In formula (A1), R and R ′ are, independently of each other, a hydrogen atom or an organic group.)

(In the formula (A2), X is a chlorine atom or a bromine atom and n is 1 to 3.) B in the formula (1) is further represented by the following formula (B3):

The gas separation membrane according to claim 2, comprising a structure represented by The method for producing a gas separation membrane according to any one of claims 1 to 3, wherein
A method for producing a gas separation membrane, comprising the step of performing a dry / wet phase conversion method using a polyimide solution containing a 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 any one of claims 1 to 3.