JPH08173778A - Manufacture of fluorine containing polyimide gas separating membrane - Google Patents

Abstract

PURPOSE: To provide a method for obtaining a fluorine containing polyimide gas separating membrane wherein high gas permeable flux is provided by a simple membrane making method, and it can be practically satisfied from the standpoint of cost. CONSTITUTION: A fluorine containing polyimide resin containing at least 3 fluorine atoms in a repeated molecular structural unit composing a polyimide resin layer, and an organic solvent (A) of at most 30 dielectric constant and at most 3.0D dipole moment are tubularly extruded or applied onto suitable based material. Then, it is dipped in solvent (B) which does not dissolve the fluorine containing polyimide resin and has compatibility with the organic solvent (B).

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-based gas separation membrane for gas separation, and more specifically to specific components such as hydrogen, methane, carbon dioxide, oxygen, water vapor and ions from an industrial mixed gas. The present invention relates to a method for producing a fluorine-containing polyimide-based separation membrane used in the form of an asymmetric membrane or a composite membrane used for separating and concentrating 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, in U.S. Pat. No. 4,378,400 and U.S. Pat. No. 4,959,151, aromatic polyimides using biphenyltetracarboxylic dianhydride are disclosed in JP-A-5-7749, U.S. Pat. No. 3,822,202, and U.S. Pat. Publication, U.S. Patent No. 4532041
U.S. Pat.No. 4,645,824, U.S. Pat.
No. 0, U.S. Pat.No. 4,717,393, U.S. Pat.
394, U.S. Pat.No. 4,838,900, U.S. Pat.
97092, U.S. Pat.No. 4932982, U.S. Pat.
4929405, U.S. Pat. No. 4,981,497, U.S. Pat. No. 5,042,992, etc. disclose fluorine-containing aromatic polyimides.

A polyimide system using an aliphatic or alicyclic tetracarboxylic dianhydride is also disclosed in US Pat.
It is disclosed in Japanese Patent No. 4964887 and US Pat. No. 4,988,371.

Further, thinning and asymmetrical thinning have been studied in consideration of practicality. U.S. Pat.No. 4,929,405 discloses controlling the film thickness of a fluorine-containing aromatic polyimide-based homogeneous film to a thin film of 400 Å or less by a water surface expansion method, but it has no supporting film layer and is practically mechanical. It has no strength. Therefore, it is difficult to form a film on an industrial scale or to form a module.

Asymmetrization is effective as a method for giving practical mechanical strength to the separation membrane. For example U.S. Patent No. 4
240914, U.S. Pat.No. 4358378, U.S. Pat.
4385084, U.S. Pat. No. 4,410,568 and the like disclose aliphatic polyimide asymmetric membranes. In addition, US patent
3925211, U.S. Pat.No. 4,113,628, U.S. Pat.No. 4,378,324, U.S. Pat.No. 4440643, U.S. Pat.
No. 4460526, U.S. Pat.No. 4474662, U.S. Pat.No. 4485056, U.S. Pat.No. 4512893, U.S. Pat.
4532041, U.S. Pat.No. 4,908,134, JP-A-4-22
No. 7831 discloses asymmetric film formation of an aromatic polyimide and a precursor polyamic acid. U.S. Pat. No. 47055 also relates to asymmetric membranes of fluorine-containing aromatic polyimide.
40, U.S. Pat.No. 4,717,394, U.S. Pat.No. 508
5676, US Pat. No. 5,178,940 and the like.

As a method for producing these Loeb-type asymmetric membranes, a wet phase inversion method is used, but it is hard to say that it is a method capable of producing an asymmetric membrane that does not form pinholes that greatly deteriorate the separation performance. Among the above-disclosed publications, the asymmetric membrane described in U.S. Pat.No. 4,717,394 discloses high separation and permeation performance, but the separation is due to the method for producing an asymmetric membrane having no gas permeable support. Since the mechanical strength of the film is weak and it cannot be handled practically, and a post-treatment step with alcohol is required, it is difficult to form the film on an industrial level.

In order to form a pinhole-free asymmetric film, post-treatment (Japanese Patent Laid-Open No. 049882/1993, No. 5-146651)
Etc.), pretreatment (JP-A-5-184887, etc.), improvement of film forming process (US Pat. No. 4902422, US Pat. No. 5085676).
And U.S. Pat. No. 5,165,963). However, these 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.

[0008]

When the polyimide separation membrane is manufactured at a practical industrial level, the above-mentioned conventional techniques are not 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. Secondly, in order to make up for the first drawback, the process of film formation becomes complicated and the cost becomes high. Thirdly, it is difficult to control the film-forming conditions because the film-forming conditions are made strict and the pinholes are made as small as possible, and as a result, it is impossible to manufacture a film having stable separation performance and permeation performance in good balance.

The present invention has been made in order to solve these problems, and it is a gas separation membrane which has a high gas permeation flux and is practically satisfactory in terms of cost by a simpler membrane forming method. The present invention has been accomplished by finding a method for obtaining the above.

[0010]

Means for Solving the Problems That is, according to the present invention, by using a specific solvent for preparing a dope, the thickness of the homogeneous skin layer is set to a certain value or less by the wet phase conversion film forming method, and the separation performance is improved. The present invention has been accomplished by finding a method capable of forming an asymmetric film that does not form a pinhole that greatly reduces in a wide range.

That is, the method for producing a fluorine-containing polyimide-based gas separation membrane of the present invention comprises a fluorine-containing polyimide resin having at least 3 fluorine atoms in the repeating molecular structural unit constituting the polyimide resin layer and a molecular structural unit. An organic solvent (A) having at least two ether bonds,
The composition is such that it 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 is immersed in a solvent (B) compatible with the above organic solvent (A).

Alternatively, as another configuration, the method for producing a fluorine-containing polyimide gas separation membrane of the present invention comprises a fluorine-containing polyimide resin having at least three fluorine atoms in repeating molecular structural units constituting a polyimide resin layer. , An organic solvent (C) having a dielectric constant of 30 or less and a dipole moment of 3.0D or less is extruded in a tube shape or coated on an appropriate support, and then the above-mentioned fluorine-containing polyimide resin is not dissolved, It is configured to be immersed in a solvent (B) having compatibility with the organic solvent (C).

The polyimide resin layer used in the present invention is a layer that contributes to gas separation performance, and is composed of a fluorine-containing polyimide resin having at least 3 fluorine atoms in the repeating molecular structural unit constituting the polyimide. it is preferred that at least one -CF ₃ group in repeating molecular units constituting the polyimide resin layer. Furthermore, the fluorine content in the fluorine-containing polyimide thin film is 6
The number is preferably from 12 to 12 (the number of fluorine atoms in the repeating molecular structural unit) in order to obtain a gas composite separation membrane having substantially stable and high quality. On the other hand, when the number exceeds 12, the raw material cost becomes high and the practicality is lowered.

The fluorine-containing polyimide resin used in the present invention has a general formula:

[0015]

Embedded image

(However, A ₁ and A _{2 in} [Chemical Formula 3] are aromatic,
A tetravalent organic group consisting of an alicyclic or aliphatic hydrocarbon group is shown, wherein R ₁ and R ₂ are divalent aromatic, alicyclic or aliphatic hydrocarbon groups, or these hydrocarbon groups are divalent. A divalent organic group bonded by an organic bonding group is shown, and A ₁ , A ₂ ,
At least one of R ₁ and R ₂ is an organic group having 3 or more fluorine atoms. In addition, m and n follow the following formula. It is preferable that the main component is a repeating molecular structural unit represented by m + n = 1,0 ≦ m ≦ 1,0 ≦ n ≦ 1). The tetravalent organic group having at least three fluorine atoms is not particularly limited as long as the proton of the tetravalent organic group of A ₁ or A ₂ is replaced with a fluorine atom or a group containing a fluorine atom. , And more preferably at least one of the tetravalent organic groups of A ₁ or A _2.
One in which one proton is replaced by one —CF ₃ group is used.

[0017]

[Chemical 4]

A tetravalent organic group represented by and the like are preferably used. The divalent organic group having at least three fluorine atoms is not particularly limited as long as the proton of the divalent organic group of R ₁ or R ₂ is replaced with a fluorine atom or a group containing a fluorine atom. And more preferably at least one of divalent organic groups represented by R ₁ or R _2.
Those One proton is changed every one of -CF ₃ groups is used. Specifically, the formula [Formula 5]

[0019]

Embedded image

A divalent organic group represented by: is preferably used.

Further, the fluorine-containing polyimide resin used in the present invention has substantially the following formula:

[0022]

[Chemical 6]

It is more preferable that the repeating unit represented by In addition, even if all of the imide ring moieties in the formula [Chemical Formula 6] partially remain in the state of the amic acid, the abundance ratio is 30% or less, that is, the imidization ratio is 70% or more. If there is no problem. Furthermore p
The value is preferably in the range of 50 ≦ p ≦ 500. In addition, the abundance ratio is the residual —CO for all imide ring sites.
It is a value obtained by quantifying the amount of OH using ¹ H-NMR and calculating it. If the abundance ratio exceeds 30%, the ratio between the organic solvent (A) and the solvent (B) or the organic solvent
Affinity between (C) and solvent (B) (due to increase of -COOH)
Therefore, it causes formation of pinholes, and the original separation performance of the fluorine-containing polyimide-based 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, if it is 50 mol% or less, it may be a copolymer with a polymer such as polysulfone or polyether sulfone other than the fluorine-containing polyimide resin, or a mixture thereof.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The fluorine-containing polyimide resin used in the present invention is a known polymerization method using a tetracarboxylic dianhydride and a diamine component, for example, as described in US Pat. No. 3,959,350. Can be obtained at. For example, the tetracarboxylic dianhydride and the diamine compound are used in approximately equimolar amounts, and the polyamic acid is polymerized by stirring in a polar solvent at a temperature of about 80 ° C. or lower, preferably 0 to 60 ° C. 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.

By using the organic solvent (A) used in the present invention as a polar solvent for polymerizing the above polyamic acid, the production process can be carried out as a dope solvent without being replaced with a dope solvent after the polymerization. Therefore, it is preferably used. That is, an organic solvent having at least two ether bonds in the molecular structural unit, which is a dope solvent
Examples of (A) include 1,2-dimethoxyethane, 1,2
-Diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, triethylene glycol dimethyl ether and the like are preferably used as a solvent for polymerization. Besides being used alone, they are also used as a mixed solvent of two or more kinds.

A tertiary amine compound such as trimethylamine, triethylamine and pyridine, and an imidization promoter such as acetic anhydride, thionyl chloride and carbodiimide are added to the obtained polar solvent solution of polyamic acid at a temperature of 5 to 150 ° C. Stir to imidize so that the imidization ratio becomes 70% or more. When performing the imidization reaction, 100 to 4 of the polyamic acid solution was added without adding an imidization accelerator.
It may be imidized by heating at 00 ° C, preferably 120 to 300 ° C.

After the imidization reaction, in order to remove the polar solvent and the imidization accelerator during the polymerization, a polyimide purified by dropping into a large amount of a solution of acetone, alcohol, water or the like in the molecular structural unit used in the present invention is used. Is redissolved in an organic solvent (A) having at least two ether bonds and used as a dope for film formation. That is, when polymerization is carried out using the above-mentioned organic solvent (A) used in the present invention, the dope adjusting step is shortened, so that it can be used as a film forming dope without removing the imidization accelerator.

Alternatively, after the imidization reaction, in order to remove the polar solvent and imidization promoter during the polymerization, a polyimide purified by dropping into a large amount of a solution of acetone, alcohol or water is used in the present invention. It can also be used as a dope for film formation by re-dissolving in an organic solvent (C) having a dipole moment of 3.0 D or less and a dipole moment of 30 D or less.

When the imidization reaction is carried out without adding an imidization accelerator, a polyamic acid powder or a polyamic acid solution obtained by dropping a 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 (which may be filtered during the evaporation to form a polyamic acid powder by adding a precipitating agent and the like) may be imidized by heating at 100 to 400 ° C. It is re-dissolved in the organic solvent (A) or the organic solvent (C) used in 1. and used as a dope for film formation.

When the film-forming dope is prepared by re-dissolving in the organic solvent (A) having at least two ether bonds in the molecular structural unit used in the present invention, the concentration of the polyimide solution is 3 to 40% by weight, It is 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 is as described in the above-mentioned specific examples. Among them, in particular,
Diethylene glycol dimethyl ether and diethylene glycol diethyl ether are preferably used, and most preferably used as a mixed solvent containing two kinds of diethylene glycol dimethyl ether and diethylene glycol diethyl ether.

Further, in order to adjust the solubility of the fluorine-containing polyimide used and the viscosity of the dope, aprotic compounds such as N-methyl-2-pyrrolidone (NMP), N, N-dimethylacetamide and N, N-dimethylformamide are used. A solvent may be added. The aprotic solvent is appropriately selected depending on the solvent used, but in the present invention, it is preferably used in an amount of about 40% by weight or less.

The dielectric constant used in the present invention is 30 or less,
When adjusting the dope for film formation by re-dissolving in the organic solvent (C) having a dipole moment of 3.0 D or less, the concentration of the polyimide solution 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 (C) used in the present invention has a dielectric constant of 30 or less and a dipole moment of 3.0 D or less, and the dielectric constant is more preferably 10 or less.
Since the organic solvent (C) used in the present invention has a small polarity, it has a weak affinity with the solvent used as the coagulating liquid, that is, the solvent (B). Therefore, the rate of leaching of the dope solvent into the solvent used as the coagulating liquid is sufficiently slower than the formation of the skin layer at the time of wet phase conversion film formation, so that pinholes are not formed in a wide range of homogeneous skin layers and industrial Can be formed on a dynamic scale.

When the dipole moment used in the present invention is μ (vector), the charge (or magnetic charge) q _1, q
_2, ..., q _n (scalar) are locations r _1, r _2, ...,
When it is in r _n (vector), it is represented by μ = Σq _i × r _i . Further, when the macroscopic electric field E (vector) inside the substance is given with the permittivity ε (scalar) used in the present invention, if the electric flux density d (vector) is determined, the amount given by d = εE It is called the dielectric constant of a substance.

The organic solvent (C) used in the present invention is not particularly limited as long as the above conditions are satisfied, but diethylene glycol dimethyl ether (dielectric constant: 5.97,
The dipole moment is preferably 1.97D),
2-dimethoxyethane (dielectric constant 5.50, dipole moment 1.79D) and the like. Besides being used alone, they are also used as a mixed solvent of two or more kinds.

Further, in order to adjust the solubility of the fluorine-containing polyimide used and the viscosity of the dope, the dielectric constant exceeds 30 and / or the dipole moment exceeds 3.0 D within a range not exceeding 30% by weight. An aprotic solvent may be added. The amount in which the aprotic solvent may be added is
The organic solvent (C) which is particularly preferably used in the present invention is 60% by weight or more of diethylene glycol dimethyl ether, although it is appropriately selected depending on the solvent used.
It is an organic solvent containing less than 00% by weight. For example, 67% by weight
33% by weight of diethylene glycol dimethyl ether
A mixed solution of N-methylpyrrolidone (NMP) is exemplified.

The wet phase conversion film forming method using the above dope will be described below. The film forming method and the film form of the gas separation membrane in the present invention are not particularly limited, but the coagulating liquid, that is, the solvent used in the present invention, such as the extrusion method of the organic solvent (A) or the organic solvent (C) dope, the casting method, etc. By immersing in (B), an asymmetric membrane such as a tubular shape (including hollow fiber shape) or a flat membrane shape can be obtained.

In the case of a flat membrane, 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 membrane in the form of a composite membrane. 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 metallic porous materials having a smooth surface, woven cloth, non-woven cloth, and the like. The dope on the gas permeable support and the coating thickness are 25 to 400 μm, preferably 30 to 2
It is 00 μm.

The dope using the organic solvent (A) or the organic solvent (C) used in the present invention is formed into a film at a temperature range of -30 to 80 ° C, preferably -20 to 40 ° C.

Although the fluorine-containing polyimide resin used is not dissolved as the coagulating liquid, that is, the solvent (B) used when the organic solvent (A) or the organic solvent (C) is removed by immersion,
It is not limited as long as it is compatible with the organic solvent (A) or the organic solvent (C), but water, alcohols such as methanol, ethanol, isopropyl alcohol and a mixed solution thereof are used, and particularly water is used. It is preferably used. The temperature of the coagulation liquid, that is, the solvent (B) when the organic solvent (A) or the organic solvent (C) is removed by immersion is not particularly limited, but it is preferably 0 to 50 ° C.

By forming an asymmetric membrane under the above conditions, it is possible to produce a gas separation membrane having a uniform skin layer thickness of about 1000 Å or less, which is almost constant, and which does not have pinholes which greatly deteriorate the separation performance over a wide range. .

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 elastomer 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, polybutadiene and polyisoprene. Ethylene monomer or conjugated diene monomer alone such as chloroprene rubber, poly (4-methyl-pentene-1), butadiene-styrene copolymer, isoprene-isobutylene copolymer, or polyisobutylene Polymers and copolymers, further copolymers containing a monomer component having a functional group such as acrylonitrile, (meth) acrylic acid ester, (meth) acrylic acid, etc. in addition to the above monomer components, Or polyether polyol, polyurethane polyether, polyurethane polyester or It can be mentioned a copolymer having both a so-called soft and hard segments, such as Li amide polyether. Further, in addition to the above, epoxy resin, ethyl cellulose, butoxy resin, etc., which are cured by a linear and long chain curing agent can also 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 that is soluble in an organic solvent before crosslinking, but becomes a resin insoluble in an organic solvent after crosslinking, for example, the method described in JP-A-59-225705. The film can be formed according to

[0046]

[Function] N-methyl-2-pyrrolidone (dielectric constant: 32.0 (25 ° C), dipole moment: 4.00 D (30 ° C)), N, N-dimethylacetamide (dielectric constant: Is 37.8 (25 ℃) and the dipole moment is 3.72
D), N, N-dimethylformamide (dielectric constant 36.7 (25
℃), dipole moment 3.86D (25 ℃)), dimethylsulfoxide (dielectric constant 48.9 (20 ℃), dipole moment 4.30D), etc. The dipole moment is 3.7 D or more, and it is considered that the dipole moment has a strong affinity with the solvent used as the coagulating liquid, for example, water. 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.

Further, in the case of the aprotic polar solvent which has been conventionally used, during the wet phase inversion film formation, the dope for film formation is cast or spun on the gas permeable support and then at a predetermined temperature. Although it is left to stand for a predetermined period of time to evaporate a part of the solvent, it absorbs moisture in the air due to its too strong affinity with water, and the surface becomes cloudy to promote pinhole formation.

However, the organic solvent (A), which is the dope solvent used in the present invention, has a high solubility for the fluorine-containing polyimide resin and has a weak affinity with the solvent used as the coagulating liquid due to the influence of the ether bond. . Therefore, since the speed of the dope solvent leaching into the solvent used as the coagulating liquid is sufficiently smaller than that of the skin layer during wet phase inversion film formation, pinholes are not formed in a wide range of homogeneous skin layers, and industrial Can be formed on a dynamic scale.

The organic solvent (C), which is the dope solvent used in the present invention, has a high solubility of the fluorine-containing polyimide resin, a dielectric constant of 30 or less, and a dipole moment of 3.0D or less. As a result, the affinity with the solvent used as the coagulation liquid becomes weak. Therefore, since the speed of the dope solvent leaching into the solvent used as the coagulating liquid is sufficiently smaller than that of the skin layer during wet phase inversion film formation, pinholes are not formed in a wide range of homogeneous skin layers, and industrial Can be formed on a dynamic scale.

[0050]

The present invention will be described below with reference to examples.
The present invention is not limited to these examples.

Example 1 A fluorine-containing polyimide having a repeating unit represented by the formula [Chemical Formula 6] was synthesized by the following method. 2,2-bis (4-aminophenyl) hexafluoropropane (BAAF) was added to 7.7 parts diethylene glycol dimethyl ether (DEGDME) 5
In a solution dissolved in 6.9 parts, under nitrogen atmosphere, 5,5'-2,2,2
-Trifluoro-1- (trifluoromethyl) ethylidene-bis-1,3-isobenzofurandione (6FD
A) 10.3 parts was added, and the mixture was stirred at room temperature for 8 hours for synthesis to obtain a polyamic acid.

After this, 12.6 parts of diethylene glycol diethyl ether (DEGDEE) was added, and after the solution became uniform, 5.5 parts of pyridine, which is an imidization accelerator, and 7.0 parts of acetic anhydride were added, and the mixture was allowed to stand at room temperature. The mixture was stirred for 12 hours to carry out imidization reaction. After the reaction, the obtained solution was filtered as a dope without refining, and allowed to stand to be sufficiently defoamed and adjusted. The dope was cast at a thickness of 130 μm on a polyester non-woven fabric using an applicator at 0 ° C., and immersed in water at 47 ° C. as a solvent (B) as a coagulating liquid for 1 hour. Then, it was dried with hot air at 60 ° C. to obtain a gas separation membrane which was an asymmetric membrane. The permeation performance of the obtained gas separation membrane was evaluated, and the results are shown in Table 1. Note that p in the formula [Chemical Formula 6] was p = 435 when calculated based on the weight average molecular weight.

[0053]

[Table 1]

Example 2 After obtaining the polyamic acid in Example 1, DEGD was used.
The place where EE12.6 parts were added was changed to 17.4 parts, and as a result,
The number of parts of the fluorine-containing polyimide serving as the repeating unit represented by the formula [Chemical Formula 6] was changed from 18 parts to 17 parts, and the other conditions were the same as in Example 1. The results are shown in Table 1.

Example 3 In Example 1, the solvent used in synthesizing the polyamic acid was DEG.
The same procedure as in Example 1 was carried out except that 56.9 parts of DME was replaced with a mixed solvent of DEGDME and DEGDEE (34.7 parts and 22.2 parts). The results are shown in Table 1.

Examples 4 to 6 The surfaces of the gas separation membranes obtained in Examples 1 to 3 before drying were crosslinked silicone resin solutions (GE) which were elastomeric polymers.
A 3 wt% solution of RTV615 from Silicones in hexane) was applied and heat-treated at 110 ° C. for 5 minutes to form a thin film of an elastomer polymer, which was then laminated. The permeation performance of the obtained gas separation membrane was evaluated, and the results are shown in Table 1.

Comparative Example 1 To a solution prepared by dissolving 7.7 parts of BAAF in 56.9 parts of DEGDME was added 10.3 parts of 6FDA under a nitrogen atmosphere, and the mixture was stirred at room temperature for 8 hours. After this, 12.6 parts of DEGDME was added to make the solution uniform, and then 5.5 parts of pyridine, which is an imidization promoter, and 7.0 parts of acetic anhydride were added, and the mixture was allowed to stand at room temperature for 12 hours.
After stirring for an hour, an imidization reaction was performed. After the reaction, the obtained solution was filtered as a dope solution without being purified, and allowed to stand still for sufficient defoaming to be adjusted. After the dope solution was heated to 0 ° C., it was cast on a polyester non-woven fabric with an applicator to a thickness of 130 μm and immersed in water at 47 ° C. as a solvent (B) as a coagulating liquid for 1 hour. Then, it was dried with hot air at 60 ° C. to obtain a gas separation membrane which was an asymmetric membrane. The permeation performance of the obtained gas separation membrane was evaluated, and the results are shown in Table 1.

Comparative Example 2 The surface of the gas separation membrane before drying obtained in Comparative Example 1 was crosslinked silicone resin solution (GE Sil) which was an elastomer polymer.
3% by weight of RTV615 of icones in hexane)
By heat treatment at 10 ° C. for 5 minutes, a thin film of the elastomer polymer was formed and laminated. The permeation performance of the obtained gas separation membrane was evaluated, and the results are shown in Table 1.

As the organic solvent (C) used in the following examples, diethylene glycol dimethyl ether or a mixed solution containing diethylene glycol dimethyl ether was used. The dielectric constant of diethylene glycol dimethyl ether was 5.97 and the dipole moment was 1.97D.

Example 7 A fluorine-containing polyimide having a repeating unit represented by the formula [Chemical Formula 6] was synthesized by the following method. 5,5'-2,2,2-Trifluoro-1- (trifluoromethyl) ethylidene-bis-1,3-isobenzofurandione (6FDA) 0.1 mol
And 2,2-bis (4-aminophenyl) hexafluoropropane (BAAF) 0.1 mol with N-methyl-2-pyrrolidone (N
MP) solution was reacted for 4 hours to obtain a polyamic acid.

After this, 0.3 mol of pyridine and 0.3 mol of acetic anhydride
Was added and the imidization reaction was carried out for 15 hours. After the reaction, NMP was further added to dilute it to 8% by weight, and the NMP solution was added dropwise to an excess amount of water and purified to obtain a fluorine-containing polyimide having a repeating unit represented by the formula [Chemical Formula 5] as a structural unit. Obtained. Regarding the physical properties of the obtained fluorine-containing polyimide, the glass transition temperature was 301 ° C. and the weight average molecular weight was 159,000.

18 parts by weight of a fluorine-containing polyimide having a repeating unit represented by the formula [Chemical Formula 6] as a structural unit was diluted,
82 parts by weight of diethylene glycol dimethyl ether was added as an organic solvent (C), and the mixture was stirred at 100 ° C. for 6 hours and dissolved. After that, the dope was filtered by allowing it to stand still to sufficiently defoam. The dope was cast on a polyester nonwoven fabric with a width of 20 cm and a thickness of 300 μm using an applicator, and immersed in water at 5 ° C. for 1 hour as a solvent (B) which was a coagulating liquid. Then, it was washed with water and air-dried at room temperature to obtain a gas separation membrane which was an asymmetric membrane. The permeation performance of the obtained gas separation membrane was evaluated, and the results are shown in Table 2.

[0063]

[Table 2]

Example 8 Example 6 was repeated except that the temperature of water of the solvent (B) as a coagulating liquid was adjusted to 20 ° C., the solution was washed with water, and then dehydration treatment and solvent substitution treatment were performed with ethanol and hexane for 1 hour. In the same manner as above, the permeation performance of the obtained gas separation membrane was evaluated, and the results are shown in Table 2.

Example 9 The same as Example 7 except that the solvent (B) as a coagulating liquid was changed to methanol at 22 ° C., washed with water, and then dehydrated and solvent-replaced with ethanol and hexane for 1 hour. Then, the permeation performance of the obtained gas separation membrane was evaluated, and the results are shown in Table 2.

Example 10 16 parts by weight of a fluorine-containing polyimide having a repeating unit represented by the formula [Chem. 6] as a structural unit was used as an organic solvent (C), and 74 parts by weight of diethylene glycol dimethyl ether and NM were used.
A mixed solution of 10 parts by weight of P was added and dissolved. After that, the dope was filtered by allowing it to stand still to sufficiently defoam. Width of dope on polyester non-woven fabric using applicator 20
cm, thickness 300 μm, cast, coagulating solvent
As (B), it was immersed in water at 22 ° C. for 1 hour. The permeation performance of the obtained gas separation membrane was evaluated in the same manner as in Example 7 except that the dehydration treatment and the solvent substitution treatment were performed with ethanol and hexane for 1 hour, and the results are shown in Table 2.

Example 11 The surface of the gas separation membrane obtained in Example 10 was treated with a crosslinkable silicone resin solution (GE Silicones) which is an elastomer polymer.
RTV615 of hexane 3wt% solution), 110 ℃
A thin film of an elastomeric polymer was formed by heat-treating for 30 minutes and laminated. The permeation performance of the obtained gas separation membrane was evaluated, and the results are shown in Table 1.

Example 12 The gas separation membrane thus obtained was evaluated for permeation performance in the same manner as in Example 11 except that the solvent (B) as a coagulating liquid was changed to a 10% ethanol aqueous solution at 22 ° C., and the results are shown in Table 1. Shown in.

Example 13 16 parts by weight of a fluorine-containing polyimide having a repeating unit represented by the formula [Chemical Formula 6] as a structural unit was used as an organic solvent (C) in an amount of 64 parts by weight of diethylene glycol dimethyl ether and NM.
A mixed solution of 20 parts by weight of P was added and dissolved. After that, the dope was filtered by allowing it to stand still to sufficiently defoam. Width of dope on polyester non-woven fabric using applicator 20
cm, thickness 300 μm, cast, coagulating solvent
As (B), it was immersed in water at 22 ° C. for 1 hour. After dehydration treatment and solvent substitution treatment with ethanol and hexane for 1 hour, the mixture was air-dried to obtain a gas separation membrane which is an asymmetric membrane. On the surface of the obtained gas separation membrane, a crosslinkable silicone resin solution which is an elastomer polymer (GE Silicones RTV615 hexane
3 wt% solution) was applied and heat-treated at 110 ° C. for 15 minutes to form a thin film of the elastomer polymer, which was laminated. The permeation performance of the obtained gas separation membrane was evaluated, and the results are shown in Table 2. The permeation performance was evaluated and the results are shown in Table 2.

Example 14 8 parts by weight of a fluorine-containing polyimide having a repeating unit represented by the formula [Chemical Formula 6] as a structural unit, and a formula [Chemical Formula 7]

[0071]

[Chemical 7]

Using 10 parts by weight of a fluorine-containing polyimide having a repeating unit represented by the structural unit as an organic solvent (C), 55 parts by weight of diethylene glycol dimethyl ether and N
A mixed solution of 27 parts by weight of MP was added and dissolved. After that, the dope was filtered by allowing it to stand still to sufficiently defoam. Width of dope on polyester non-woven fabric using applicator 2
A solvent that is a coagulating liquid cast with a thickness of 0 cm and a thickness of 300 μm
As (B), it was immersed in water at 5 ° C. for 1 hour. Then, it was washed with water and dried with hot air at 130 ° C. to obtain a gas separation membrane as an asymmetric membrane. The permeation performance of the obtained gas separation membrane was evaluated, and the results are shown in Table 2. Note that p in the formula [Formula 7] was p = 310 when calculated based on the weight average molecular weight.

Test Example 1 The permeation performance of the gas separation membrane obtained in Example 8 was evaluated using various gases, and the results are shown in Table 3.

[0074]

[Table 3]

Comparative Example 3 The gas separation membrane thus obtained was evaluated for permeation performance in the same manner as in Example 7 except that the dope prepared by changing the organic solvent (C) from diethylene glycol dimethyl ether to NMP was used. It shows in Table 2. The carbon dioxide / methane gas separation coefficient (α) of the obtained gas separation membrane was as low as 0.6, and the presence of pinholes was recognized in the homogeneous skin layer.

[0076]

INDUSTRIAL APPLICABILITY According to the present invention, by using a specific solvent for producing a dope, the thickness of the homogeneous skin layer is set to a certain value or less by the wet phase conversion film forming method, and the separation performance is greatly reduced over a wide range. Since it is a method that can form a fluorine-containing polyimide resin-based asymmetric film that does not form pinholes, it has high gas permeability and gas selectivity, and is a gas that is practically satisfactory in terms of resistance and cost. A separation membrane can be obtained.

Claims (10)

[Claims] 1. A fluorine-containing polyimide resin having at least three fluorine atoms in a repeating molecular structural unit constituting a polyimide resin layer, and an organic solvent (A) having at least two ether bonds in the molecular structural unit. Characterized in that it is extruded into a tube shape or coated on an appropriate support and then immersed in a solvent (B) which is compatible with the organic solvent (A) but does not dissolve the fluorine-containing polyimide resin. A method for producing a fluorine-containing polyimide-based gas separation membrane. 2. A fluorine-containing polyimide resin having at least 3 fluorine atoms in repeating molecular structural units constituting a polyimide resin layer, and an organic solvent having a dielectric constant of 30 or less and a dipole moment of 3.0 D or less ( C) is extruded in a tube shape or coated on an appropriate support, and then immersed in a solvent (B) which does not dissolve the fluorine-containing polyimide resin but is compatible with the organic solvent (C). A method for producing a fluorine-containing polyimide gas separation membrane, comprising: 3. The method for producing a fluorine-containing polyimide-based gas separation membrane according to claim 1, wherein the repeating molecular structural unit constituting the fluorine-containing polyimide resin has at least one --CF ₃ group. 4. A fluorine-containing polyimide resin is substantially [Chemical Formula 1] (However, A ₁ and A _{2 in} [Chemical Formula 1] represent a tetravalent organic group consisting of an aromatic, alicyclic or aliphatic hydrocarbon group, and R ₁
And R ₂ represent a divalent aromatic, alicyclic or aliphatic hydrocarbon group, or a divalent organic group in which these hydrocarbon groups are bonded by a divalent organic bonding group, A ₁ , A ₂ , At least one of R ₁ and R ₂ is an organic group having 3 or more fluorine atoms. In addition, m and n follow the following formula. m + n
The method for producing a fluorine-containing polyimide-based gas separation membrane according to claim 1, 2 or 3, wherein the main component is a repeating unit represented by the formula: 1,0≤m≤1,0≤n≤1). . 5. A fluorine-containing polyimide resin is substantially [Chemical Formula 2] The method for producing a fluorine-containing polyimide-based gas separation membrane according to claim 1, 2 or 3, wherein the repeating unit represented by the formula is a main component. 6. The organic solvent (A) is a mixed solvent containing two kinds of diethylene glycol dimethyl ether and diethylene glycol diethyl ether.
Alternatively, the method for producing a fluorine-containing polyimide-based gas separation membrane according to Item 3. 7. The method for producing a fluorine-containing polyimide gas separation membrane according to claim 2, wherein the organic solvent (C) has a dielectric constant of 10 or less and a dipole moment of 3.0 D or less. 8. The method for producing a fluorine-containing polyimide gas separation membrane according to claim 1, 2 or 3, wherein the solvent (B) is water, alcohols or a mixture thereof. 9. The method for producing a fluorine-containing polyimide gas separation membrane according to claim 1, 2 or 3, wherein a thin film of an elastomer polymer is formed on the fluorine-containing polyimide gas separation membrane. 10. The method for producing a fluorine-containing polyimide gas separation membrane according to claim 9, wherein the thin film of the elastomer polymer is formed by crosslinking a crosslinkable silicone resin.