JPH09897A - Fluorine-containing polyimide type gas separating membrane, and its manufacture and module thereof - Google Patents

Abstract

PURPOSE: To provide homogeneousness, a high permeating flux and a high separation coefficient in a large member area by specifying the membrane area of a separating membrane, the thickness of the skin layer, the permeating velocity of CO2 gas and the separation coefficient of CO2 /methane in a fluorine- containing polyimide type gas separating membrane. CONSTITUTION: A gas-separating membrane 3 comprises at least a sponge layer 2 composed of fluorine-containing polyimide resin having three or more fluorine atoms and two or more ether linkage sites, and a skin layer 1 formed on the surface thereof, and has a membrane area of 0.5m<2> or more. The average thickness of the skin layer 1 is within the range of 1-100nm, the permeating velocity of CO2 gas is within the range of 0.01-50Nm<3> /m<2> /h/atm and the separation coefficient of CO2 /methane is within the range of 2-60. A fluorine-containing polyimide type gas separating membrane having a high permeating flux and separation coefficient is obtained, wherein homogeneousness in a large membrane area is realized and defects such as pin holes and the like do not exist, and a gas- separating membrane having a high gas permeating flux and meeting cost requirements is realized by employing a simple manufacturing method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluorine-containing polyimide gas separation membrane which is homogeneous over a wide area and has a high permeation flux and a separation coefficient α, and a method for producing the same. More specifically, it relates to the production of a fluorine-containing polyimide gas separation membrane for gas separation by a wet phase inversion method using a specific solvent, and more specifically to specific components such as hydrogen, methane, carbonic acid from an industrial mixed gas. The present invention relates to the production of an asymmetric fluorine-containing polyimide gas separation membrane used in the form of an asymmetric membrane or a composite membrane used for separating and concentrating gas, oxygen, nitrogen, water vapor, organic vapor, ions and the like.

[0002]

2. Description of the Related Art Polyimide is known as a membrane separation material having excellent heat resistance and chemical resistance because it has a high glass transition temperature and a rigid molecular chain structure. Separation membranes using various polyimides are known. Is being considered. For example, US Pat. No. 4,378,400 and US Pat. No. 4,959,151.
An aromatic polyimide using biphenyltetracarboxylic dianhydride is disclosed in JP-A-5-7749, US Pat. No. 3,822,202, and US Pat. No. 3,8993.
09, US Pat. No. 4,532,041, US Pat. No. 4,645,824, US Pat. No. 4,705,540.
U.S. Pat. No. 4,717,393, U.S. Pat. No. 4,717,394, U.S. Pat. No. 4,838,900, U.S. Pat. No. 4,897,092, U.S. Pat.
32982, U.S. Pat. No. 4,929,405,
U.S. Pat. No. 4,981,497, U.S. Pat. No. 5,042.
992 and the like disclose fluorine-containing aromatic polyimides.

Further, a polyimide system using an aliphatic or alicyclic tetracarboxylic acid dianhydride is also disclosed in US Pat. No. 4,964,887 and US Pat. No. 4,988,371.

Considering that the separation membrane has practical mechanical strength, thinning and asymmetrical membranes are also being studied.
In consideration of having a high-performance separation membrane, thinning or asymmetrical membrane is also being studied. When a polymer having a high-performance separation coefficient is formed as a thin film on a suitable porous support membrane, the thickness of the thin film is preferably 0.1 μm in order to increase the gas permeation rate to a practical degree. The film thickness should be as follows. Forming such an ultra-thin film by coating was not suitable for industrial practice. Further, although asymmetric film formation is also described in the above publication, it is difficult to industrially form a film having a required film thickness of 0.1 μm or less without pinholes. U.S. Pat. No. 4,929,405 discloses controlling the film thickness of a fluorine-containing aromatic polyimide-based homogeneous film to a required thin film of 400 .ANG. It has no practical mechanical strength because it has no membrane layer. Therefore, film formation on an industrial scale is difficult.

In order to form a pinhole-free asymmetric film, post-treatment (Japanese Patent Application Laid-Open Nos. 5-049882 and 5-1998).
No. 146651) and pretreatment (JP-A-5-184887).
No.), improvement of manufacturing process (US Pat. No. 4,902,422, US Pat. No. 5,085,676, US Pat. No. 51.
Japanese Patent No. 65963) is disclosed.

[0006]

However, the above-mentioned conventional methods have problems that the number of working steps is increased and complicated, the cost is high, and stable film formation on an industrial level is difficult.
That is, when a polyimide separation membrane is manufactured at a practical industrial level and an efficient separation operation is performed, none of the above-mentioned conventional techniques is satisfactory. Specifically, firstly, a pinhole is formed during film formation, and the pinhole reduces the performance of the separation membrane, resulting in dispersion and instability, which makes it impossible to perform an efficient separation operation. Secondly, in order to compensate the first drawback, the film forming process is complicated and the cost is high. Thirdly, it is difficult to control the film-forming conditions to make the film-forming conditions strict so as to reduce pinholes as much as possible, and as a result, a film having a stable balance of separation performance and permeation cannot be manufactured.

In order to solve the above-mentioned conventional problems, the present invention is a fluorine-containing polyimide gas separation membrane which is homogeneous in a wide membrane area, has no defects such as pinholes, and has a high permeation flux and a separation coefficient α. Another object of the present invention is to provide a production method for obtaining a gas separation membrane which has a high gas permeation flux and is practically satisfactory in terms of cost by a simple membrane production method.

[0008]

[Means for Solving the Problems]
Therefore, the fluorine-containing polyimide gas separation membrane of the present invention is
At least 3 fluorine atoms and at least 2 ethers
Fluorine-containing polyimide resin having a bonding site
Membrane having at least a Ponzi layer and a skin layer on the surface thereof
Area 0.5m²The above gas separation membrane, wherein the skin is
The average thickness of the layers is in the range 1-100 nm₂Moth
Permeation rate of 0.01 to 50 Nm^Three/ M ²/ H / at
range of m, CO₂/ Methane separation coefficient α is in the range of 2-60
It is characterized by being surrounded.

In the above structure, it is preferable that the gas separation membrane is at least one separation membrane formed on the surface of the tube-shaped, hollow fiber-shaped, and gas-permeable support.
This is because such a separation membrane is practically useful as a module.

Next, the first method for producing a fluorine-containing polyimide-based gas separation membrane of the present invention is a gas separation device having at least a sponge layer made of a solvent-soluble fluorine-containing polyimide-based resin and a skin layer on the surface thereof. A method for producing a film, comprising: a fluorine-containing polyimide resin having at least 3 fluorine atoms and at least 2 ether bond sites in a repeating molecular structural unit constituting a polyimide resin layer; A solution consisting of an organic solvent (A) having a moment of moment of 3.0 D or less is extruded into a tube shape or coated on an appropriate support, and then the above-mentioned fluorine-containing polyimide resin is not dissolved, but the above organic solvent (A ) Is immersed in a solvent (B) having compatibility with the above) to remove the solvent.

Next, the second method for producing a fluorine-containing polyimide gas separation membrane of the present invention is a gas separation method comprising at least a sponge layer made of a solvent-soluble fluorine-containing polyimide resin and a skin layer on the surface thereof. A method for producing a film, comprising a fluorine-containing polyimide resin having at least 3 fluorine atoms and at least 2 ether bond sites in a repeating molecular structural unit constituting a polyimide resin layer,
A solution of an organic solvent (C) containing an organic solvent having at least one ether bond in a molecular structural unit as a main component is extruded into a tube shape or coated on an appropriate support, and then the above-mentioned fluorine-containing polyimide resin. Solvent (B) which does not dissolve but is compatible with the above organic solvent (A)
It is characterized by being immersed in the solvent to remove the solvent.

Next, the fluorine-containing polyimide gas separation membrane module of the present invention comprises a sponge layer composed of a fluorine-containing polyimide resin having at least 3 fluorine atoms and at least 2 ether bond sites, and a skin layer on the surface thereof. A module using at least a gas separation membrane having a membrane area of 0.5 m ² or more, wherein the skin layer has an average thickness of 1 to 100 nm and a CO ₂ gas permeation rate of 0.01 to 50 Nm. Range of ³ / m ² / h / atm,
The CO ₂ / methane separation coefficient α is in the range of 2 to 60.

In the module, a tubular shape,
It is preferably at least one formed in the shape of a hollow fiber and on the surface of the gas permeable support. This is because these modules are practically easy to use.

In the above constitution, it is preferable that at least one --CF ₃ group is contained in the repeating molecular structural unit constituting the fluorine-containing polyimide resin. This is because such resins also have high gas separation ability.

Further, in the above constitution, it is preferable that the fluorine-containing polyimide resin substantially contains the repeating unit represented by the above formula (Formula 1) as a main component. This is because such resins also have high gas separation ability.

Further, in the above constitution, it is preferable that the fluorine-containing polyimide resin substantially contains a repeating unit represented by the following formula (Formula 2) or the following formula (Formula 3) as a main component. This is because such resins also have high gas separation ability.

Further, in the above constitution, the organic solvent (A)
It is preferable that the dielectric constant is less than 10 and the dipole moment is less than 3.0D. Such a solvent has a property that it is difficult to be compatibilized with water, for example, but it will be compatibilized with time. Therefore, the polyimide resin is dissolved in the organic solvent (A) and cast-formed into, for example, a film, and then desolvated in water. When the solvent is used, the solvent is gradually removed, so that the skin layer and the sponge layer inside can be in a homogeneous state.

In the above constitution, the organic solvent (A)
Alternatively, the main component of (C) is preferably at least one liquid selected from diethylene glycol dimethyl ether, diethylene glycol diethyl ether and a mixed solvent thereof. Similarly to the above, when the solvent is removed in water, the solvent is gradually removed, so that the skin layer and the internal sponge layer are in a homogeneous state.

Further, in the above constitution, it is preferable that the solvent (B) is at least one liquid selected from water, alcohols and a mixture thereof. Similarly to the above, when the solvent is removed in the liquid, the solvent is gradually removed, so that the skin layer and the internal sponge layer are in a homogeneous state.

Further, in the above constitution, it is preferable to further form a protective film of an elastomer polymer on the fluorine-containing polyimide gas separation film. Further, it is possible to prevent pinhole defects and the like.

In the above construction, it is preferable that the thin film of the elastomer polymer is a film obtained by crosslinking a crosslinkable silicone resin. Similarly, it is possible to prevent pinhole defects and the like.

In the gas separation membrane of the present invention,
It is preferable that the sponge layer has no void portion having a diameter of more than 1 μm. This is because if the sponge layer is also homogeneous, the defects are reduced.

[0023]

According to the above-mentioned configuration of the present invention, at least 3
A film area of 0.5 including at least a sponge layer composed of a fluorine-containing polyimide resin having at least two fluorine atoms and at least two ether bond sites and a skin layer at the surface thereof.
m ² or more gas separation membrane, wherein the skin layer has an average thickness in the range of 1 to 100 nm and a CO ₂ gas permeation rate of 0.01 to 50 Nm ³ / m ² / h / atm.
Since the CO ₂ / methane separation coefficient α is in the range of 2 to 60, it is homogeneous in a wide membrane area, has no defects such as pinholes, and has a high permeation flux and a separation coefficient α. It is possible to realize a separation membrane and a gas separation membrane which has a high gas permeation flux by a simple membrane formation method and which is practically satisfactory in terms of cost.

Next, according to the first constitution of the method of the present invention, there is provided a method for producing a gas separation membrane comprising at least a sponge layer made of a solvent-soluble fluorine-containing polyimide resin and a skin layer on the surface thereof. And a fluorine-containing polyimide resin having at least three fluorine atoms and at least two ether bond sites in a repeating molecular structural unit constituting the polyimide resin layer, a dielectric constant of 30 or less, and a dipole moment of 3.0D. A solution consisting of the following organic solvent (A) is extruded into a tube shape or coated on an appropriate support, and then the above-mentioned fluorine-containing polyimide resin is not dissolved, but it is compatible with the above-mentioned organic solvent (A). By dipping it in the solvent (B) to remove the solvent, it has a high gas permeation flux with a simple film-forming method and is practically satisfactory in terms of cost. Film efficiently reasonably be manufactured.

Next, according to the second aspect of the method of the present invention, there is provided a method for producing a gas separation membrane having at least a sponge layer made of a solvent-soluble fluorine-containing polyimide resin and a skin layer on the surface thereof. And a fluorine-containing polyimide resin having at least three fluorine atoms and at least two ether bond sites in a repeating molecular structural unit constituting the polyimide resin layer, and an organic solvent having at least one ether bond in the molecular structural unit. A solution containing an organic solvent (C) containing as a main component is extruded in a tube shape or coated on an appropriate support, and then the above-mentioned fluorine-containing polyimide resin is not dissolved but is compatible with the above-mentioned organic solvent (A). It is highly practical in terms of cost because it has a high gas permeation flux by a simple film-forming method by being immersed in a solvent (B) having The possible gas separating membrane effectively rationally be produced.

Next, according to the fluorine-containing polyimide gas separation membrane module of the present invention, a sponge layer made of a fluorine-containing polyimide resin having at least 3 fluorine atoms and at least 2 ether bond sites and a skin layer on the surface thereof. A module using a gas separation membrane having a membrane area of 0.5 m ² or more including at least, wherein the skin layer has an average thickness in the range of 1 to 100 nm, and a CO ₂ gas permeation rate of 0.01. ~ 50 Nm ³ / m ² / h / atm range and CO ₂ / methane separation coefficient α in the range of 2 to 60, so that it is homogeneous in a wide membrane area, has no defects such as pinholes, and has high permeability. A fluorine-containing polyimide gas separation membrane having a flux and a separation coefficient α can be obtained, and a gas separation membrane module that can be practically satisfied in terms of cost can be realized.

[0027]

The present invention will be described more specifically with reference to the following examples. The present invention, by using a fluorine-containing polyimide having a specific structure and a specific solvent for the preparation of the dope, the thickness of the homogeneous skin layer by the wet phase inversion film formation method to a certain value or less, and the separation performance is significantly reduced. The present invention has been accomplished by finding a method for producing an asymmetric film that does not form pinholes over a wide range.

That is, the method for producing a fluorine-containing polyimide-based gas separation membrane of the present invention comprises fluorine having at least three fluorine atoms and at least two ether bond sites in the repeating molecular structural unit constituting the polyimide resin layer. A solution comprising a containing polyimide resin and an organic solvent (A) having a dielectric constant of 30 or less and a dipole moment of 3.0D or less, or an organic solvent having at least one ether bond in a molecular structural unit as a main component. A solution consisting of the organic solvent (C) is extruded into a tube shape or coated on an appropriate support, and then the above-mentioned fluorine-containing polyimide resin is not dissolved, but a solvent (B) compatible with the above organic solvent (A). ) Is soaked in.

The fluorine-containing polyimide resin layer used in the present invention is a layer that contributes to gas separation performance, and has at least 3 fluorine atoms and at least 2 ether bond sites in the repeating molecular structural unit that constitutes the polyimide. Although it is made of a fluorine-containing polyimide resin, it preferably has at least one —CF ₃ group in the repeating molecular structure constituting the polyimide resin layer. Furthermore, the fluorine content in the fluorine-containing polyimide thin film is 6 to 12
The number (the number of fluorine atoms in the repeating molecular structural unit) is preferable in order to obtain a separation membrane having substantially stable and high quality. Further, if the number exceeds 12, the practicality decreases.

The fluorine-containing polyimide resin used in the present invention preferably contains a repeating molecular structural unit represented by the above formula (Formula 1) as a main component. Examples of the tetravalent organic group having at least three fluorine atoms include A _{1 to} A _n.
Is not particularly limited as long as the proton of at least one tetravalent organic group is replaced with a fluorine atom or a group containing a fluorine atom, and more preferably at least one organic group of A _{1 to} A _n. One in which one proton is replaced with one —CF ₃ group is used, and for example, a tetravalent organic group represented by the following formula (Formula 4) is preferably used.

[0031]

Embedded image

The divalent organic group having at least two ether bond sites is at least one of R ₁ to
It is not particularly limited as long as it has at least two ether bond sites in a part of at least one divalent organic group of R _n , but more preferably it is represented by the following formula (Formula 5) or (Formula 6). The divalent organic group is preferably used.

[0033]

Embedded image

[0034]

[Chemical 6]

Further, the fluorine-containing polyimide resin used in the present invention has substantially the following formula (formula 7) or (formula 8).
It is more preferable that the repeating unit represented by

[0036]

[Chemical 7]

[0037]

Embedded image

Further, even if all of the imide ring moieties in the above formula (Formula 7) or (Formula 8) partially remain in the amic acid state, their abundance ratio is 30% or less, that is, There is no problem if the imidization ratio is 70% or more. The abundance ratio is a value obtained by quantifying and calculating the amount of residual —COOH with respect to all imide ring moieties using ¹ H-NMR. If the abundance ratio exceeds 30%, the affinity between the organic solvent (A) and the solvent (B) (-C
(Due to an increase in OOH) causes pinhole formation, and the separation performance of the original fluorine-containing polyimide gas separation membrane deteriorates.

The fluorine-containing polyimide resin used in the present invention may be used alone, but may also be used as a mixture of two or more kinds. Further, 50 mol% or less may be a copolymer with a polymer other than the fluorine-containing polyimide resin, such as polysulfone or polyaceterphone, or a mixture thereof.

The fluorine-containing polyimide resin used in the present invention can be obtained by using a tetracarboxylic dianhydride and a diamine component by a known polymerization method as described in, for example, US Pat. No. 3,959,350. For example, polyamic acid is polymerized in a polar solvent at a temperature of about 80 ° C. or lower, preferably 0 to 60 ° C., using tetracarboxylic dianhydride and diamine compound in approximately equimolar amounts. The polar solvent used here is not particularly limited, but N-methylpyrrolidone, pyridine, dimethylacetamide, dimethylformamide, dimethylsulfoxide, tetramethylurea,
Phenol, cresol and the like are preferably used.

A solution of the obtained polyamic acid in a polar solvent was added to a third solution of trimethylamine, triethylami, pyridine or the like.
An imidization promoter such as a primary amine compound, acetic anhydride, thionyl chloride, or carbodiimide is added, and the mixture is stirred at a temperature of 5 to 150 ° C. to imidize so that the imidization ratio becomes 70% or more. When carrying out the imidization reaction, 100 to 40 of the polyamic acid solution was added without adding an imidization accelerator.
It may be imidized by heating at 0 ° C., preferably 120 to 300 ° C.

After the imidization reaction, in order to remove the polar solvent and the imidization accelerator during the polymerization, the polyimide purified by dropping in a large amount of a solution of acetone, alcohol, water or the like is dried and then used in the present invention. It is re-dissolved in an organic solvent (A) having a re-ratio of 30 or less and a dipole moment of 3.0 D or less and used as a dope for film formation.

When the imidization reaction is carried out without adding an imidization accelerator, a polyamic acid powder or a polyamic acid solution obtained by dropping the polyamic acid solution into a large amount of a solution of acetone, alcohol or the like. The solid of the polyamic acid obtained by evaporating the solvent from (from which a precipitating agent or the like may be added during evaporation to form a polyamic acid powder, which may be separated by filtration) is imidized by heating at 100 to 400 ° C. The organic solvent (A) having a reductive rate of 30 or less and a dipole moment of 3.0D or less used in
It is re-dissolved in an organic solvent (C) whose main component is an organic solvent having at least one ether bond in a molecular structural unit and used as a dope for film formation.

The dielectric constant used in the present invention is 30 or less,
Use of an organic solvent (A) having a dipole moment of 3.0D or less or an organic solvent (C) containing as a main component an organic solvent having at least one ether bond in a molecular structural unit as a solvent during synthesis. You can also At this time, high separation membrane performance can be obtained without performing the step of removing the imidization accelerator, which is suitable for reducing the dope preparation step.

The dielectric constant used in the present invention is 30 or less,
Dope for film formation by re-dissolving in an organic solvent (A) having a dipole moment of 3.0 D or less or an organic solvent (C) containing an organic solvent having at least one ether bond in a molecular structural unit as a main component. The concentration of the polyimide solution in the case of preparing is 3 to 40% by weight, preferably 10 to 30% by weight. Moreover, when adjusting the dope for film formation, you may add a swelling agent, a dispersing agent, a thickener, etc. as needed.

The organic solvent (A) used in the present invention has a dielectric constant of 30 or less and a dipole moment of 3.0D or less, and the dielectric constant is more preferably 10 or less. Since the organic solvent (A) used in the present invention has a small polarity, its affinity with the solvent used as the coagulating liquid, that is, the solvent (C) becomes weak. Therefore, the rate of leaching of the dope solvent into the solvent used as the coagulating liquid is sufficiently lower than that of the skin layer formed during wet phase inversion film formation. Can be formed on a dynamic scale.

The organic solvent (A) used in the present invention is not particularly limited as long as the above conditions are satisfied, but diethylene glycol dimethyl ether (having a dielectric constant of 5.9).
7, the dipole moment is preferably 1.97D, and other examples include 1,2-dimethoxyethane (dielectric constant: 5.50, dipole moment: 1.79D). These may be used alone or as a mixture of two or more solvents. Further, in order to adjust the solubility of the fluorine-containing polyimide used and the viscosity of the dope, the aprotic ratio exceeds 30% and / or the dipole moment exceeds 3.0D within a range not exceeding 30% by weight. A solvent may be added. If the above aprotic solvent is added,
The organic solvent (A) particularly preferably used in the present invention is an organic solvent containing 60% by weight or more and 100% by weight or less of diethylene glycol dimethyl ether, although it is appropriately selected depending on the solvent used. For example, a mixed solution of 67 wt% diethyl glycol dimethyl ether and 33 wt% N-methylpyrrolidone (NMP) is exemplified.

N, which has been conventionally used as a dope solvent
-Methyl-2-pyrrolidone (dielectric constant 32.0 (25
℃), dipole moment is 4.00D (30 ℃)),
N, N-dimethylacetamide (dielectric constant: 37.8
(25 ° C), dipole moment is 3.72D), N, N
-Dimethylformad (dielectric constant is 36.7 (25
℃), dipole moment is 3.86D (25 ° C)), dimethyl sulfoxide (dielectric constant is 48.9 (20 ° C),
If an aprotic polar solvent with a dipole moment of 4.30D) is used, the dielectric constant is 32 or more, the dipole moment is 3.7D or more, and the solvent used as the coagulating liquid, for example, water has a strong affinity. it is conceivable that. Due to the strength of this affinity, the dope solvent is leached into the solvent used as the coagulating liquid at a faster rate than in the formation of the skin layer at the time of wet phase conversion film formation. A pinhole is formed in the. Furthermore, in the case of the aprotic polar solvent that has been conventionally used, during the wet phase conversion film formation, the dope for film formation is cast or spun on a gas permeable support, and then left at a predetermined temperature for a predetermined time. However, a part of the solvent is evaporated, but since the affinity with water is too strong, it absorbs moisture in the air, and the surface becomes cloudy to promote pinhole formation.

The organic solvent (C) used in the present invention is not particularly limited as long as it is an organic solvent containing an organic solvent having at least one ether bond in the molecular structural unit as a main component, and diethylene glycol dimethyl ether. , Diethylene glycol diethyl ether, diethylene glycol cibutyl ether, triethylene glycol diethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-sibutoxyethane and the like. Preferably, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, or a mixed solvent thereof is used. These may be used alone or as a mixture of two or more solvents. Further, in order to adjust the solubility of the fluorine-containing polyimide used and the viscosity of the dope, an aprotic solvent having no ether bond in the molecular structural unit may be added within a range not exceeding 30% by weight.

The wet phase conversion film forming method using the above dope will be described below. The method of forming the gas separation membrane and the form of the membrane in the present invention are not particularly limited, but the coagulating liquid or solvent (B ), A tubular (including hollow fiber) or flat membrane-shaped asymmetric membrane can be obtained.

In the case of a flat film, a dope is coated on a gas permeable support by a method such as casting or dipping, and immersed in a coagulating liquid, that is, a solvent (B) to obtain an asymmetric film in a composite form. Is also suitable in terms of increasing mechanical strength. Examples of suitable supports used in the present invention include a glass plate having a smooth surface and the following gas-permeable supports. Examples of the gas-permeable support include organic, inorganic, and metal porous materials having a smooth surface, woven cloth, non-woven cloth, and the like. The dope and the coating thickness on these gas-permeable supports are 25 to 400 μm, preferably 30 to 400 μm.
200 μm.

The dope using the organic solvent (A) used in the present invention is formed into a film at a temperature range of -80 to 80 ° C, preferably -20 to 40 ° C. As long as it does not dissolve the fluorine-containing polyimide resin used as the coagulant used when the organic solvent (A) is removed by immersion, that is, the solvent (B), it is compatible with the organic solvent (A), Although not limited, water, alcohols such as methanol, ethanol and isopropyl alcohol, and a mixed solution thereof are used, and water is particularly preferably used. The temperature of the coagulating liquid when the organic solvent (A) is removed by immersion, that is, the temperature of the solvent (B) is not particularly limited, but is preferably 0 to 50 ° C.

Under the above conditions, an asymmetric membrane is formed.
Therefore, the film area is 0.5m²Above average thickness of the skin layer
Can form a separation film in the range of 1 to 100 nm. S
The thickness of the Kin layer is almost constant, providing a wide range of separation performance.
A gas separation membrane that does not have pinholes that greatly reduce
It can be manufactured. As a result, the membrane area is large
Even if you create a tool, for example, CO₂The permeation flux of gas
0.1-50 Nm^Three/ ²/ Hr. / Atm range, CO
₂/ Methanol separation coefficient α in the range of 2-60
Can be created.

In the gas separation membrane obtained in the present invention, it is preferable that the surface of the fluorine-containing polyimide thin film is further coated with an elastomer polymer. Forming and laminating a thin film of an elastomer polymer is suitable for blocking defects on the surface of the gas separation membrane and at the same time preventing the surface from being scratched. The elastomeric polymer refers to a polymer having a flexible film-forming ability, and specific examples thereof include polypropylene, polyvinyl chloride, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, polyptadiene, polyisoprene. , Chloroprene rubber, poly (4-methyl-pentene-1), ptadiene-
Styrene copolymers, isoprene-isobutylene copolymers, homopolymers or copolymers of ethylenic monomers or conjugated diene monomers such as polyisobutylene, etc., in addition to the above monomer components, acrylic Ronitrile,
A copolymer containing a monomer component having a functional group such as (meth) acrylic acid ester and (meth) acrylic acid,
Alternatively, there may be mentioned a copolymer having both a soft segment and a hard segment, such as polyether polyol, polyurethane polyether, polyurethane polyester or polyamide polyether. Further, in addition to the above, an epoxy resin, an ethyl cellulose, a butoxy resin, or the like that is cured by a linear long-chain curing agent can be used as the elastomer polymer in the present invention.

In the present invention, a crosslinkable silicone resin is particularly preferably used as the elastomer polymer.
Such a crosslinkable silicone resin is a silicone resin which is soluble in an organic solvent before crosslinking, but becomes insoluble in an organic solvent after crosslinking.
The film can be formed according to the method described in Japanese Patent No. 705.

The form of the element using the above gas separation membrane is not particularly limited, and it is a hollow fiber type element when it is extruded into a tubular shape, and it is, for example, a spiral type or a flat membrane type when it is applied on an appropriate support. It can be modularized as a tubular element.

Next, description will be made with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a flat membrane type separation membrane 10 coated on a support according to an embodiment of the present invention. In FIG. 1, 3 is a fluorine-containing polyimide resin layer, which is a skin layer 1 and a sponge layer 2.
It is formed with. The polyimide resin layer 3 is formed on the surface of the gas permeable support 4 which is a polyester nonwoven fabric having a thickness of about 100 μm. FIG. 2 is a traced enlarged SEM photograph of the skin layer 1 and the sponge layer 2 of FIG. The thickness L ₁ of the skin layer 1 is about 40 nm, the thickness L ₂ of the shows only partially in Figure 2 the sponge layer 2 was approximately 30 [mu] m. In FIG. 2, the white portion indicates the polyimide resin portion and the black portion indicates the shadow due to the void.

Next, FIGS. 3A and 3B are reduced views of FIG. 2 and show that the sponge layer 2 is relatively uniform both in the thickness direction and in the surface direction. FIG. 4A is a traced cross-sectional SEM photograph of a gas separation membrane made of a conventional fluorine-containing polyimide resin layer, and FIG. 4B is FIG.
It is an enlarged view of the A section of (a). This asymmetric membrane is formed by using N-methylpyrrolidone (NMP) as a solvent and removing the solvent in water. In FIG. 4A, 21
Is a skin layer, 22 is a sponge layer, 23 is a finger void portion (cylindrical void) formed in the sponge layer in the vertical direction, and 24 is a finger void portion formed in the lateral direction (depth direction). Compared with FIG. 3 (a) of an embodiment of the present invention, which is an enlarged view of the same magnification, the asymmetric membrane of the prior art has a large finger void portion with a diameter of about 10 μm. The product of the present invention does not have this and has a uniform sponge layer.

In the present invention, a module equipped with the obtained element is brought into contact with a mixed gas mainly containing carbon dioxide and methane such as natural gas to selectively permeate carbon dioxide to concentrate methane. It is suitable for use.

The present invention is described below with reference to examples, but the present invention is not limited to these examples. (Example 1) A fluorine-containing polyimide having a repeating unit represented by the above formula (Formula 7) was synthesized by the following method in a solvent of diethylene glycol dimethyl ether. Screw [4
-(4-Aminophenoxy) phenyl] proban 0.7
Under a nitrogen atmosphere, 5,5'-2,2,2-trifluoro-1- (trifluoromethyl) ethylidene-was dissolved in a solution prepared by dissolving 5 mol of 1842 g of diethylene glycol dimethyl ether as the organic solvent (A) or (C). Bis-1,3-isobenzofurandione (6FDA) 0.7
5 mol was added, and the mixture was brought to room temperature and stirred for 8 hours to carry out polymerization to obtain a polyamic acid.

Then, 406 g of diethylene glycol dimethyl ether was added to make the solution uniform, and then 2.25 mol of the imidizing agent viridine and 2. acetic anhydride.
25 mol was added, and the mixture was stirred at room temperature for 12 hours to carry out an imidization reaction. After the reaction, the obtained solution was used as a film-forming solution, filtered, and allowed to stand to be sufficiently defoamed to prepare.

The above film-forming solution was heated to 25 ° C. and an applicator was used to form a polyester nonwoven fabric having a width of 1 m, a length of 15 m, a thickness of about 200 μm and a basis weight of 85 g / m ² and a thickness of 200.
It was cast at a thickness of μm and immersed in water at 25 ° C. as a coagulating liquid for 5 minutes and in water at 20 ° C. for 1 hour. The film obtained is 60
It was dried at ° C. Thus, the asymmetric film as shown in FIGS. The obtained separation membrane was assembled into a cylindrical module (effective membrane area 1.4 m ² ) and the permeation rate and separation performance were measured. The measurement was carried out using the pure gases (CO ₂ , CH ₄ ,
N ₂ ), and the pressure was reduced to 1 × 10 ^-2 torr on the permeation side. The measurement temperature is 25 ° C. The results are shown in Table 1.

[0063]

[Table 1]

Example 2 On the surface of the gas separation membrane obtained in Example 1, a crosslinkable silicone resin solution which is an elastomeric polymer (GE Silicones RTV615 Hexane 3) was used.
wt% solution) was applied and heat-treated at 110 ° C. for 15 minutes to form a thin film of an elastomer polymer, which was laminated. Then, the measurement was performed under the same conditions as in Example 1. Table 2 shows the results.

[0065]

[Table 2]

(Comparative Example 1) The procedure of Example 1 was followed except that the diamine component was changed to 4,4'-oxydianiline having only one ether bond. Since it was insoluble in the solvent corresponding to the organic solvent (A) or (C), the film could not be formed.

(Example 3) Of the separation membrane obtained in Example 1, a module having a width of 0.33 m and a length of 2.0 m was assembled into a cylindrical module (effective area 0.54 m ² ), the permeation rate and the separation performance. Was measured. The results are shown in Table 3.

[0068]

[Table 3]

As is clear from Table 3, the effective area is 0.54
It was confirmed that the module of m ² also has practically sufficient permeation rate and separation performance.

[0070]

As described above, according to the present invention, at least a sponge layer made of a fluorine-containing polyimide resin having at least 3 fluorine atoms and at least 2 ether bond sites and a skin layer on the surface thereof are provided. A gas separation membrane having a membrane area of 0.5 m ² or more, wherein the skin layer has an average thickness of 1 to 100 nm and a CO ₂ gas permeation rate of 0.01 to 50 Nm ³ / m ² / h / atm
And the separation coefficient α of CO ₂ / methane is in the range of 2 to 60, it is homogeneous over a wide membrane area, has no defects such as pinholes, and has a high permeation flux and a separation coefficient α. It is possible to realize a polyimide-based gas separation membrane and a gas separation membrane having a high gas permeation flux by a simple membrane-forming method and being practically satisfactory in terms of cost.

Next, according to the first method of the present invention, there is provided a method for producing a gas separation membrane comprising at least a sponge layer composed of a solvent-soluble fluorine-containing polyimide resin and a skin layer on the surface thereof. , A fluorine-containing polyimide resin having at least three fluorine atoms and at least two ether bond sites in a repeating molecular structural unit constituting the polyimide resin layer, and a dielectric constant of 30 or less and a dipole moment of 3.0D or less. A solvent consisting of the organic solvent (A) is extruded into a tube shape or coated on an appropriate support, and then the above-mentioned fluorine-containing polyimide resin is not dissolved, but a solvent compatible with the above organic solvent (A). (B)
By immersing it in the solvent and removing the solvent, it is possible to efficiently and rationally manufacture a gas separation membrane having a high gas permeation flux and practically satisfying the cost in a simple membrane forming method.

Next, according to the second method of the present invention, there is provided a gas separation membrane comprising at least a sponge layer made of a solvent-soluble fluorine-containing polyimide resin and a skin layer on the surface thereof. A fluorine-containing polyimide resin having at least three fluorine atoms and at least two ether bond sites in a repeating molecular structural unit constituting the polyimide resin layer, and an organic solvent having at least one ether bond in the molecular structural unit. A solution containing the organic solvent (C) as a main component is extruded in a tube shape or coated on an appropriate support and then the above-mentioned fluorine-containing polyimide resin is not dissolved, but it is compatible with the above-mentioned organic solvent (A). By dipping it in the solvent (B) that it has and removing the solvent, it has a high gas permeation flux with a simple film-forming method, and is practically satisfactory in terms of cost. The gas separation membrane efficiently reasonably be produced that.

Next, according to the fluorine-containing polyimide gas separation membrane module of the present invention, a sponge layer made of a fluorine-containing polyimide resin having at least 3 fluorine atoms and at least 2 ether bond sites and a skin layer on the surface layer thereof. A module using a gas separation membrane having a membrane area of 0.5 m ² or more including at least, wherein the skin layer has an average thickness in the range of 1 to 100 nm, and a CO ₂ gas permeation rate of 0.01. ~ 50 Nm ³ / m ² / h / atm range and CO ₂ / methane separation coefficient α in the range of 2 to 60, so that it is homogeneous in a wide membrane area, has no defects such as pinholes, and has high permeability. A fluorine-containing polyimide gas separation membrane having a flux and a separation coefficient α can be obtained, and a gas separation membrane module that can be practically satisfied in terms of cost can be realized.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a flat membrane type separation membrane coated on a support according to an embodiment of the present invention.

FIG. 2 is a trace diagram of an enlarged cross-sectional SEM photograph of FIG.

3A and 3B are reduced views of FIG.

4A is a traced SEM photograph of a cross section of a gas separation membrane made of a fluorine-containing polyimide resin layer according to the prior art, and FIG. 4B is an enlarged view of part A of FIG. 4A.

[Explanation of symbols]

 1 Skin Layer 2 Sponge Layer 3 Fluorine-Containing Polyimide Resin Layer 4 Gas Permeable Support 10 Flat Membrane Gas Separation Membrane 21 Skin Layer 22 Sponge Layer 23, 24 Finger Void (Cylindrical Void)

Claims (15)

[Claims] 1. A gas separation having a membrane area of 0.5 m ² or more, which is provided with at least a sponge layer made of a fluorine-containing polyimide resin having at least 3 fluorine atoms and at least 2 ether bond sites and a skin layer on the surface thereof. The membrane has an average thickness of 1 to 100 nm and a CO ₂ gas permeation rate of 0.01 to 50 Nm ^3.
/ M ² / h / atm, CO ₂ / methane separation coefficient α is in the range of 2 to 60, a fluorine-containing polyimide-based gas separation membrane. 2. The gas separation membrane has a tubular shape, a hollow fiber shape,
The fluorine-containing polyimide gas separation membrane according to claim 1, which is at least one separation membrane formed on the surface of the gas-permeable support. 3. A method for producing a gas separation membrane comprising at least a sponge layer made of a solvent-soluble fluorine-containing polyimide-based resin and a skin layer on the surface thereof, which comprises a repeating molecular structural unit constituting the polyimide resin layer. And a solution containing a fluorine-containing polyimide resin having at least three fluorine atoms and at least two ether bond sites and an organic solvent (A) having a dielectric constant of 30 or less and a dipole moment of 3.0D or less, It is extruded into a tube shape or coated on an appropriate support, and then the fluorine-containing polyimide resin is not dissolved, but it is immersed in a solvent (B) compatible with the organic solvent (A) to remove the solvent. A method for producing a fluorine-containing polyimide gas separation membrane, comprising: 4. A method for producing a gas separation membrane, which comprises at least a sponge layer made of a solvent-soluble fluorine-containing polyimide-based resin and a skin layer as a surface layer of the sponge layer, which comprises a repeating molecular structural unit constituting the polyimide resin layer. A solution containing a fluorine-containing polyimide resin having at least three fluorine atoms and at least two ether bond sites, and an organic solvent (C) containing an organic solvent having at least one ether bond in the molecular structural unit as a main component Is extruded into a tube shape or coated on an appropriate support, and then the fluorine-containing polyimide resin is not dissolved but is immersed in a solvent (B) having compatibility with the organic solvent (A) to remove the solvent. A method for producing a fluorine-containing polyimide gas separation membrane, comprising: 5. Gas separation having a membrane area of 0.5 m ² or more, comprising at least a sponge layer made of a fluorine-containing polyimide resin having at least 3 fluorine atoms and at least 2 ether bond sites and a skin layer on the surface thereof. A module using a membrane, wherein the skin layer has an average thickness of 1
To 100 nm, the CO ₂ gas permeation rate is 0.01 to 50 Nm ³ / m ² / h / atm, CO
A fluorine-containing polyimide-based gas separation membrane module having a ₂ / methane separation coefficient α in the range of 2 to 60. 6. The module has a tubular shape, a hollow fiber shape,
The fluorine-containing polyimide-based gas separation membrane module according to claim 5, which is at least one formed on the surface of the gas permeable support. 7. The method for producing a fluorine-containing polyimide-based gas separation membrane according to claim 3 or 4, wherein at least one —CF ₃ group is contained in the repeating molecular structural unit constituting the fluorine-containing polyimide resin. 8. The fluorine-containing polyimide-based gas separation membrane according to claim 1, 3, 4 or 5, wherein the fluorine-containing polyimide resin substantially contains a repeating unit represented by the following formula (Formula 1) as a main component. The manufacturing method and module. (However,
A _{1 to} A _n represent a tetravalent organic group consisting of an aromatic, alicyclic or aliphatic hydrocarbon group, R _{1 to} R _n are a divalent aromatic, alicyclic or aliphatic hydrocarbon group, Alternatively, these hydrocarbon groups represent a divalent organic group bonded by a divalent organic bonding group, and at least one organic group among A _{1 to} A _n is an organic group having three or more fluorine atoms. , R _{1 to} R _n
At least one of the organic groups has at least two ether bond sites. ) [Chemical 1] 9. The fluorine according to claim 1, 3, 4 or 5, wherein the fluorine-containing polyimide resin essentially contains a repeating unit represented by the following formula (Formula 2) or the following formula (Formula 3). Containing polyimide gas separation membrane, its manufacturing method and module. Embedded image Embedded image 10. The method for producing a fluorine-containing polyimide gas separation membrane according to claim 3, wherein the organic solvent (A) has a dielectric constant of 10 or less and a dipole moment of 3.0D or less. 11. The fluorine-containing polyimide according to claim 3, wherein the organic solvent (A) or (C) contains at least one liquid selected from diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and a mixed solvent thereof as a main component. Method for producing a gas separation membrane. 12. The method for producing a fluorine-containing polyimide gas separation membrane according to claim 3, wherein the solvent (B) is at least one liquid selected from water, alcohols and a mixture thereof. 13. The fluorine-containing polyimide-based gas separation membrane according to claim 1, 3, 4 or 5, further comprising a protective film of an elastomer polymer formed on the fluorine-containing polyimide-based gas separation membrane. . 14. The fluorine-containing polyimide gas separation membrane according to claim 13, and the method for producing the same, wherein the thin film of the elastomer polymer is a film obtained by crosslinking a crosslinkable silicone resin. 15. The fluorine-containing polyimide-based gas separation membrane according to claim 1, wherein the sponge layer has no void portion having a diameter of more than 1 μm.