JP2018001118A - Gas separation membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas separation membrane having high plasticity resistance against carbon dioxide and gas separation performance durable in practical use, a production method of the gas separation membrane, a separation method of a gas mixture, a gas separation membrane module using the same and a gas separation device.SOLUTION: A gas separation membrane containing the baked substance of a polyimide resin obtained by heat-treating the polyimide resin having an HFIP group (hexafluoro isopropanol group) at least in a condensed polycyclic aromatic hydrocarbon skeleton at 200-400°C and a separation method of a gas mixture separating carbon dioxide or at least methane from the gas mixture containing at least carbon dioxide and methane using the gas separation membrane are provided.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a gas separation membrane, a method for producing the same, a method for separating a gas mixture, a gas separation membrane module using the same, and a gas separation device.

  The use of methane, one of the important energy resources, is increasing year by year due to industrial development and population growth. Therefore, an efficient and low-cost method is required for the process of purifying methane from natural gas containing methane as a main component.

  Natural gas is a gas mixture containing methane as a main component, but also contains many kinds of gases as subcomponents. Carbon dioxide, which is an example of this, is an acid gas and is one of the causes of corrosion in pipelines. Therefore, a process for separating carbon dioxide from natural gas is required before supplying natural gas to the pipeline. In the conventional separation / purification process, a chemical absorption method is employed. While this method purifies high purity methane, it is expensive to maintain and operate.

  Therefore, in the current separation / purification process, a part of the conventional process is replaced with a separation process using a gas separation membrane. The separation process using a gas separation membrane can use the pressure generated by the flow of natural gas (in the pipe) as the driving force for separating the gas, and is therefore less expensive than the chemical absorption method. Separation method. As the material of the gas separation membrane, a polymer membrane such as a cellulose acetate membrane or a polyimide membrane is employed. However, when these polymer membranes are exposed to carbon dioxide contained in natural gas under high pressure, the polymer membranes may be plasticized. Since the plasticized polymer membrane expands excessively, there is a problem that the gas permeability coefficient is increased and the gas selectivity is lowered due to an increase in the gas diffusion coefficient, and high-purity methane cannot be obtained. is there.

  As described in Non-Patent Document 1, the cellulose acetate film is recognized to be plasticized under carbon dioxide exposure of 10 atm (1.0 MPa) or more. On the other hand, the polyimide film generally has higher plastic resistance than the cellulose acetate film, but in practice, further improvement in plastic resistance has been desired. For example, Non-Patent Document 2 and Non-Patent Document 3 disclose that a polyimide resin into which a cross-linked structure is introduced is used, and a film obtained therefrom has good plastic resistance. However, a gas separation membrane obtained from a polyimide resin introduced with a crosslinked structure may have a reduced gas permeability coefficient and a reduced natural gas throughput with a reduction in free volume in the polymer.

  On the other hand, as gas separation membranes having excellent gas separation performance, Patent Document 1, Patent Document 2 and Patent Document 3 use a polyimide resin having a hexafluoroisopropanol group (hereinafter sometimes referred to as HFIP group) as a raw material. A gas separation membrane was disclosed. Patent Documents 4 and 5 disclose that a polyimide resin having an HFIP group can be obtained by thermal imidization of a polyamic acid having an HFIP group. However, detailed information on plastic resistance to carbon dioxide has not been revealed.

JP 2013-10096 A JP 2014-128787 A JP 2014-128788 A JP 2007-119503 A JP 2007-119504 A

Journal of Membrane Science, Vol 47, 301-332, 1989 Journal of Membrane Science, Vol 225, 77-90, 2003 Macromolecules, Vol 40, 583-589, 2007.

  The present invention relates to a gas separation membrane having a high plastic resistance to carbon dioxide and having a gas separation performance that can withstand practical use, a method for producing a gas separation membrane, a method for separating a gas mixture, a gas separation membrane module using the same, and a gas An object is to provide a separation device.

  In order to achieve the above object, the inventors of the present invention have made extensive studies by paying attention to a polyimide having an HFIP group in a condensed polycyclic aromatic hydrocarbon skeleton among polyimides having an HFIP group. As a result, a gas separation membrane comprising a fired product obtained by heat-treating a polyimide having a HFIP group on a condensed polycyclic aromatic hydrocarbon skeleton has excellent plastic resistance to carbon dioxide in an environment exposed to high-pressure carbon dioxide. And has been found to have gas separation performance that can withstand practical use, and the present invention has been completed.

（一般式（１）中、Ｒ^１は一般式（２）で表される２価の有機基であり、Ｒ^２は脂環、芳香環およびアルキレン基からなる群より選ばれる少なくとも一種を含有する４価の有機基である。）

（一般式（２）中、ａおよびｂは、それぞれ独立に０〜２の整数であり、１≦ａ＋ｂ≦４である。）
［発明２］
前記Ｒ^１が、以下のいずれかの２価の有機基である、発明１に記載の気体分離膜。

［発明３］
前記Ｒ^２が、以下のいずれかの４価の有機基である、発明１または２に記載の気体分離膜。

［発明４］
前記ポリイミド樹脂が、一般式（３）で表される繰り返し単位をさらに有する、発明１〜３のいずれかに記載の気体分離膜。

（一般式（３）中、Ｒ^３は一般式（４）で表される２価の有機基または一般式（５）で表される２価の有機基であり、Ｒ^４は脂環、芳香環およびアルキレン基からなる群より選ばれる少なくとも一種を含有する４価の有機基である。）

（一般式（４）中、Ｒ^５は単結合、酸素原子、硫黄原子、ＣＯ、ＣＨ_２、ＣＨ_２ＣＨ_２、ＳＯ、ＳＯ_２、Ｃ（ＣＨ_３）_２、Ｃ（ＣＨ_３）（ＣＨ_２ＣＨ_３）、ＮＨＣＯ、Ｃ（ＣＦ_３）_２、芳香環または脂環であり、Ｒ^６およびＲ^７はそれぞれ独立に水素原子、アルキル基またはフルオロアルキル基であり、ｃおよびｄは、それぞれ独立に０〜２の整数であり、１≦ｃ＋ｄ≦４である。）

（一般式（５）中、Ｒ^８は水素原子、アルキル基またはフルオロアルキル基であり、ｅは１〜４の整数である。）
［発明５］
前記Ｒ^３が、以下のいずれかの２価の有機基である、発明４に記載の気体分離膜。

［発明６］
前記Ｒ^４が、以下のいずれかの４価の有機基である、発明４または５に記載の気体分離膜。

［発明７］
前記ポリイミド樹脂の質量平均分子量が、２００００以上、５０００００以下である、発明１〜６のいずれかに記載の気体分離膜。
［発明８］
前記焼成体が、前記ポリイミド樹脂の２００〜４００℃での加熱処理体である、発明１〜７のいずれかに記載の気体分離膜。
［発明９］
発明１乃至８の何れか一項に記載の気体分離膜を用いて、二酸化炭素及びメタンを少なくとも含むガス混合物から二酸化炭素を分離する、ガス混合物の分離方法。
［発明１０］
発明１乃至８の何れかに記載の気体分離膜を用いて、二酸化炭素及びメタンを少なくとも含むガス混合物からメタンを分離する、ガス混合物の分離方法。
［発明１１］
発明１乃至８の何れかに記載の気体分離膜を含む気体分離膜モジュール。
［発明１２］
発明１１に記載の気体分離膜モジュールを少なくとも備える気体分離装置。
［発明１３］
一般式（１）で表される繰り返し単位を有するポリイミド樹脂。

（一般式（１）中、Ｒ^１は一般式（２）で表される２価の有機基であり、Ｒ^２は脂環、芳香環およびアルキレン基からなる群より選ばれる少なくとも一種を含有する４価の有機基である。）

（一般式（２）中、ａおよびｂは、それぞれ独立に０〜２の整数であり、１≦ａ＋ｂ≦４である。）
［発明１４］
前記Ｒ^１が、以下のいずれかの２価の有機基である、発明１３に記載のポリイミド樹脂。

［発明１５］
前記Ｒ^２が、以下のいずれかの４価の有機基である、発明１３または１４に記載のポリイミド樹脂。

［発明１６］
質量平均分子量が、２００００以上、５０００００以下である、発明１３〜１５のいずれかに記載の気体分離膜。 The present invention includes the following inventions.
[Invention 1]
A gas separation membrane comprising at least a fired body of a polyimide resin having a repeating unit represented by the general formula (1).

(In General Formula (1), R ¹ is a divalent organic group represented by General Formula (2), and R ² contains at least one selected from the group consisting of an alicyclic ring, an aromatic ring and an alkylene group. (It is a tetravalent organic group.)

(In general formula (2), a and b are each independently an integer of 0 to 2, and 1 ≦ a + b ≦ 4.)
[Invention 2]
The gas separation membrane according to invention 1, wherein R ¹ is any ^one of the following divalent organic groups.

[Invention 3]
The gas separation membrane according to invention 1 or 2, wherein R ² is any of the following tetravalent organic groups.

[Invention 4]
The gas separation membrane according to any one of inventions 1 to 3, wherein the polyimide resin further has a repeating unit represented by the general formula (3).

(In the general formula (3), R ³ is a divalent organic group represented by formula (4) a divalent organic group or a group represented by formula represented (5), R ⁴ is an alicyclic, aromatic A tetravalent organic group containing at least one selected from the group consisting of a ring and an alkylene group.)

(In the general formula (4), R ⁵ is a single bond, an oxygen atom, a sulfur atom, CO, CH ₂ , CH ₂ CH ₂ , SO, SO ₂ , C (CH ₃ ) ₂ , C (CH ₃ ) (CH ₂ CH ₃ ), NHCO, C (CF ₃ ) ₂ , an aromatic ring or an alicyclic ring, R ⁶ and R ⁷ are each independently a hydrogen atom, an alkyl group or a fluoroalkyl group, and c and d are each independently (It is an integer of 0 to 2, and 1 ≦ c + d ≦ 4.)

(In General Formula (5), R ⁸ is a hydrogen atom, an alkyl group or a fluoroalkyl group, and e is an integer of 1 to 4.)
[Invention 5]
The gas separation membrane according to invention 4, wherein R ³ is any one of the following divalent organic groups.

[Invention 6]
The gas separation membrane according to invention 4 or 5, wherein R ⁴ is any of the following tetravalent organic groups.

[Invention 7]
The gas separation membrane according to any one of Inventions 1 to 6, wherein the polyimide resin has a mass average molecular weight of 20,000 or more and 500,000 or less.
[Invention 8]
The gas separation membrane according to any one of inventions 1 to 7, wherein the fired body is a heat-treated body of the polyimide resin at 200 to 400 ° C.
[Invention 9]
A method for separating a gas mixture, wherein the gas separation membrane according to any one of inventions 1 to 8 is used to separate carbon dioxide from a gas mixture containing at least carbon dioxide and methane.
[Invention 10]
A gas mixture separation method, wherein methane is separated from a gas mixture containing at least carbon dioxide and methane, using the gas separation membrane according to any one of inventions 1 to 8.
[Invention 11]
A gas separation membrane module comprising the gas separation membrane according to any one of inventions 1 to 8.
[Invention 12]
A gas separation device comprising at least the gas separation membrane module according to the eleventh aspect.
[Invention 13]
A polyimide resin having a repeating unit represented by the general formula (1).

(In General Formula (1), R ¹ is a divalent organic group represented by General Formula (2), and R ² contains at least one selected from the group consisting of an alicyclic ring, an aromatic ring and an alkylene group. (It is a tetravalent organic group.)

(In general formula (2), a and b are each independently an integer of 0 to 2, and 1 ≦ a + b ≦ 4.)
[Invention 14]
The polyimide resin according to Invention 13, wherein R ¹ is any ^one of the following divalent organic groups.

[Invention 15]
The polyimide resin according to Invention 13 or 14, wherein R ² is any of the following tetravalent organic groups.

[Invention 16]
The gas separation membrane according to any one of Inventions 13 to 15, wherein the mass average molecular weight is 20,000 or more and 500,000 or less.

  The gas separation membrane of the present invention can provide a gas separation membrane having a high plastic resistance to carbon dioxide and having a gas separation performance that can be practically used, and a method for producing the same. Moreover, the gas separation membrane of the present invention can provide a gas separation method including a gas mixture separation method, a gas separation membrane module, and a gas separation membrane module.

2 is a plot of carbon dioxide supply pressure and permeation coefficient in the plastic resistance test of the gas separation membrane obtained in Example 1. FIG. 4 is a plot of carbon dioxide supply pressure and permeation coefficient in the plastic resistance test of the gas separation membrane obtained in Example 2. FIG. 6 is a plot diagram of carbon dioxide supply pressure and permeation coefficient in a plastic resistance test of a gas separation membrane obtained in Comparative Example 5. FIG. 6 is a plot of carbon dioxide supply pressure and permeation coefficient in a plastic resistance test of a gas separation membrane obtained in Comparative Example 6. FIG. 10 is a plot diagram of carbon dioxide supply pressure and permeation coefficient in a plastic resistance test of a gas separation membrane obtained in Comparative Example 7. FIG.

  Configurations and combinations thereof in the following embodiments are examples, and additions, omissions, substitutions, and other modifications of the configurations can be made without departing from the spirit of the present invention. Further, the present invention is not limited by the embodiments, and is limited only by the scope of the claims.

<1. Gas separation membrane>
The gas separation membrane of the present invention is a gas separation membrane for efficiently separating a specific gas from a gas mixture. The kind of gas contained in this gas mixture is not specifically limited, Only 2 types or more than 2 types may be included.

  Examples of the gas include hydrogen, helium, carbon monoxide, carbon dioxide, hydrogen sulfide, oxygen, nitrogen, ammonia, sulfur oxide (SOx), nitrogen oxide (NOx), hydrocarbon, unsaturated hydrocarbon, Examples include perfluoro compounds. Here, examples of the hydrocarbon include methane, ethane, and propane. Examples of the unsaturated hydrocarbon include ethylene and propylene. Examples of the perfluoro compound include tetrafluoroethane. Can be mentioned.

  The combination of these gases is not particularly limited, but preferably contains at least carbon dioxide and hydrocarbons, and particularly preferably contains at least carbon dioxide and methane.

  The gas separation membrane of the present invention is excellent in gas separation selectivity, particularly carbon dioxide permeability, and exhibits excellent performance as a carbon dioxide / hydrocarbon, particularly carbon dioxide / methane separation membrane.

  A gas separation membrane according to an embodiment of the present invention is a gas separation membrane for separating carbon dioxide from a gas mixture containing at least carbon dioxide and methane.

  A gas separation membrane according to another embodiment of the present invention is a gas separation membrane for separating methane from a gas mixture containing at least carbon dioxide and methane.

  A glassy polymer film having a glass transition temperature, such as a polyimide resin, generally has a low carbon dioxide permeability coefficient as the supply pressure increases. When the supply pressure is further increased, the glassy polymer membrane is plasticized by carbon dioxide, so that the carbon dioxide permeability coefficient increases as the supply pressure increases. Accordingly, the supply pressure of carbon dioxide when the carbon dioxide permeability coefficient is minimized refers to the pressure at which plasticization of the glassy polymer film starts. Therefore, in this specification, the supply pressure to the gas separation membrane when the permeability coefficient of carbon dioxide is minimized is defined as “plasticization start pressure”.

  The gas separation membrane of the present invention includes at least a fired body of a polyimide resin having a repeating unit represented by the general formula (1) (hereinafter sometimes referred to as “polyimide resin (1)”). The gas separation membrane of the present invention may contain other various resins in addition to the fired body of the polyimide resin (1), or may be made of a fired body of the polyimide resin (1). The gas separation membrane of the present invention is preferably made of a fired body of polyimide resin (1).

  Moreover, in the gas separation membrane of this invention, the content rate of the polyimide resin (1) with respect to this baked body whole quantity is not specifically limited. The content is preferably 90% by mass or more, and particularly preferably composed only of a fired body obtained by heat-treating only the polyimide resin (1).

  The fired body of the polyimide resin (1) can be obtained by heat-treating (baking) the polyimide resin (1). The temperature of this heat treatment is not particularly limited. It is usually 180 ° C. or higher and 400 ° C. or lower, preferably 200 ° C. or higher and 325 ° C. or lower, more preferably 250 ° C. or higher and 320 ° C. or lower. If the temperature of the heat treatment is 250 ° C. or higher, a gas separation membrane having excellent plastic resistance to carbon dioxide can be obtained, and if it is 400 ° C. or lower, the thermal decomposition of the polyimide resin (1) hardly occurs and is sufficient. A gas separation membrane having a high mechanical strength can be obtained. In addition, the fired body of the polyimide resin (1) obtained by performing the heat treatment at the above temperature has a denser molecular chain than the fired body obtained by performing the heat treatment at a temperature lower than the above temperature. Packing facilitates intermolecular charge transfer and is considered to have a more stable structure.

  The time for the heat treatment is not particularly limited. Usually 30 minutes to 24 hours, preferably 1 to 12 hours.

  The gas separation membrane of the present invention may be a symmetric membrane comprising a dense layer or an asymmetric membrane comprising a dense layer and a porous layer. In the case of an asymmetric membrane, the dense layer has a different permeation rate depending on the gas species and serves to separate the gas mixture, while the porous layer serves as a support for maintaining the membrane shape. It becomes possible. The shape of the asymmetric membrane is not particularly limited, and may be, for example, a flat membrane shape or a hollow fiber membrane shape.

  In the case of a symmetric film, the film thickness is not particularly limited. The thickness is preferably 5 μm or more and 1 mm or less, and particularly preferably 10 μm or more and 100 μm or less. If it is 5 μm or more, film formation is easy and difficult to break, and if it is 1 mm or less, the target gas is easy to permeate.

  In the case of an asymmetric film, the thickness of the dense layer in the asymmetric film is not particularly limited. The thickness is preferably from 10 nm to 10 μm, particularly preferably from 30 nm to 1 μm. If it is 10 nm or more, film formation is easy, and if it is 10 μm or less, the target gas is easy to permeate. Further, the thickness of the porous layer in the asymmetric membrane is not particularly limited. In the case of a flat film, it is preferably 5 μm or more and 2 mm or less, and particularly preferably 10 μm or more and 500 μm or less. If it is 5 μm or more, film formation is easy, and if it is 2 mm or less, the target gas is easy to permeate. In the case of a hollow fiber membrane, it is preferable that the outer side is a dense layer and the inner side is a porous layer. The film thickness is not particularly limited, and the inner diameter is preferably 10 μm or more and 4 mm or less, particularly 20 μm or more and 1 mm or less. The outer diameter is preferably from 30 μm to 8 mm, particularly preferably from 50 μm to 1.5 mm. If the inner diameter is 10 μm or more and the outer diameter is 30 μm or more, it is easy to produce a hollow fiber membrane, and if the inner diameter is 1 mm or less and the outer diameter is 8 mm or less, a hollow fiber membrane-like gas separation membrane suitable for practical use is obtained.

[Polyimide resin (1)]
The polyimide resin (1) has at least a repeating unit represented by the following general formula (1).

In general formula (1), R ¹ is a divalent organic group represented by general formula (2), and R ² contains at least one selected from the group consisting of an alicyclic ring, an aromatic ring and an alkylene group. It is a tetravalent organic group.

  In the general formula (2), a and b are each independently an integer of 0 to 2, and 1 ≦ a + b ≦ 4.

In the general formula (1), the tetravalent organic group according to R ² is not particularly limited as long as it contains at least one selected from the group consisting of an alicyclic ring, an aromatic ring and an alkylene group. This tetravalent organic group may contain a fluorine atom, a chlorine atom, an oxygen atom, a sulfur atom or a nitrogen atom in the structure. In addition, when the structure has a hydrogen atom, part or all of the hydrogen atom may be substituted with an alkyl group, a fluoroalkyl group, a carboxyl group, a hydroxy group, or a cyano group.

The tetravalent organic group according to R ² is particularly preferably any of the following.

The polyimide resin (1) is not particularly limited as long as it has at least the repeating unit represented by the general formula (1). Among these, those having any of the following repeating units are preferable.

Among these, the polyimide resin (1) is particularly preferably one represented by any of the following repeating units.

Among these, the polyimide resin (1) is more preferably one represented by any of the following repeating units.

  The repeating unit represented by the general formula (1) may be regularly arranged in the polyimide (1) or may be present at random.

  The weight average molecular weight (Mw) of the polyimide resin (1) is preferably 20000 or more and 500000 or less, particularly preferably 30000 or more and 200000 or less. If it is 20000 or more, a tough film can be obtained, and if it is 500000 or less, it is suitable for film formation. Here, the mass average molecular weight is a value obtained by measuring with gel permeation chromatography (abbreviation: GPC) and converting with a standard polystyrene calibration curve.

The polyimide resin (1) may further have a repeating unit represented by the following general formula (3).

In general formula (3), R ³ is a divalent organic group represented by the following general formula (4) or a divalent organic group represented by the following general formula (5), and R ⁴ is an alicyclic ring, It is a tetravalent organic group containing at least one selected from the group consisting of an aromatic ring and an alkylene group.

In the general formula (4), R ⁵ is a single bond, an oxygen atom, a sulfur atom, CO, CH ₂ , CH ₂ CH ₂ , SO, SO ₂ , C (CH ₃ ) ₂ , C (CH ₃ ) (CH ₂ CH ₃ ), NHCO, C (CF ₃ ) ₂ , aromatic ring or alicyclic ring.
R ⁶ and R ⁷ are each independently a hydrogen atom, an alkyl group or a fluoroalkyl group.
c and d are each independently an integer of 0 to 2, and satisfy 1 ≦ c + d ≦ 4.

In the general formula (5), R ⁸ is a hydrogen atom, an alkyl group or a fluoroalkyl group. e is an integer of 1-4.

In the general formula (4), examples of the aromatic ring according to R ⁵ include divalent organic groups represented by the following structures.

In the general formula (4), examples of the alicyclic ring according to R ⁵ include divalent organic groups represented by the following structures.

In general formula (4), examples of the alkyl group according to R ⁶ and R ⁷ include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, and a tert-butyl group. A fluoroalkyl group Examples thereof include a trifluoromethyl group, a pentafluoroethyl group, a heptafluoro-n-propyl group, and a heptafluoroisopropyl group.

In general formula (5), examples of the alkyl group according to R ⁸ include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, and a tert-butyl group. As the fluoroalkyl group, Examples thereof include a trifluoromethyl group, a pentafluoroethyl group, a heptafluoro-n-propyl group, and a heptafluoroisopropyl group.

In general formula (3), the tetravalent organic group according to R ⁴ is not particularly limited as long as it contains at least one selected from the group consisting of an alicyclic ring, an aromatic ring and an alkylene group. This tetravalent organic group may contain a fluorine atom, a chlorine atom, an oxygen atom, a sulfur atom or a nitrogen atom in the structure. In addition, when the structure has a hydrogen atom, part or all of the hydrogen atom may be substituted with an alkyl group, a fluoroalkyl group, a carboxyl group, a hydroxy group, or a cyano group.
Further, in the general formula (3), tetravalent organic group according to R ⁴ in general formula (1) may be the same as R ² in.

In general formula (3), the tetravalent organic group according to R ⁴ is particularly preferably any of the following.

When the polyimide resin (1) further has a repeating unit represented by the general formula (3), the repeating unit represented by the general formula (3) is preferably any one of the following repeating units.

Especially, it is especially preferable that the repeating unit represented by the general formula (3) is any one of the following repeating units.

  When the polyimide resin (1) further has a repeating unit represented by the above general formula (3), the number of repeating units represented by the above general formula (1) in the polyimide resin (1) and the above general formula (3) The ratio of the number of repeating units represented by) is not particularly limited. From the viewpoint of plastic resistance to carbon dioxide, the number of repeating units represented by the general formula (1) / the number of repeating units represented by the general formula (3) is preferably 0.02 or more. .05 or more is particularly preferable.

[Production method of polyimide resin (1)]
As an example of a method for producing the polyimide resin (1), an essential raw material is a naphthalenediamine having an HFIP group represented by the following general formula (6) and a tetracarboxylic dianhydride represented by the following general formula (7). And a method of obtaining a polyimide resin (1) by polycondensation in an organic solvent to obtain a polyamic acid, and then dehydrating and ring-closing the polyamic acid to imidize. In these methods, if necessary, other diamines, other tetracarboxylic dianhydrides, or both may be added to the essential raw materials.

  In general formula (6), a and b are synonymous with a and b in general formula (2), respectively. A and b in the general formula (2) are derived from a and b in the naphthalenediamine represented by the general formula (6), respectively.

In the general formula (7), ^{R 2} has the same meaning as ^{R 2} in the general formula (1). R ² in the general formula (1) is derived from R ² in the tetracarboxylic dianhydride represented by the general formula (7).

  As the other diamine, various diamine compounds can be used.

When manufacturing the polyimide resin (1) further having the repeating unit represented by the general formula (3), a diamine represented by the following general formula (8) or a diamine represented by the following general formula (9) Is used.

In the general formula ^{(8), R 5, R} 6, R 7, c and d are the general formula ^{(4) R 5, R 6} , respectively ^R 7, c and d in the same meaning. R ⁵ , R ⁶ , R ⁷ , c and d in the general formula (4) are derived from R ⁵ , R ⁶ , R ⁷ , c and d in the diamine represented by the general formula (8), respectively.

In the general formula (9), ^{R 8} and e are each and ^{R 8} and e in the general formula (5) interchangeably. R ⁸ and e in the general formula (5) are derived from R ⁸ and e in the tetracarboxylic dianhydride represented by the general formula (9), respectively.

  As said other tetracarboxylic dianhydride, various tetracarboxylic dianhydrides can be used.

  The organic solvent used in the polycondensation reaction is not particularly limited as long as it does not inhibit the reaction. Examples thereof include amide solvents, aromatic solvents, halogen solvents, lactones, alcohols, glycol ethers, and the like. These may be used alone or in combination of two or more.

  Examples of the amide solvent include N, N-dimethylformamide, N, N-dimethylacetamide, hexamethylphosphoric triamide, N-methyl-2-pyrrolidone and the like.

  Examples of the aromatic solvent include benzene, anisole, diphenyl ether, nitrobenzene, and benzonitrile.

  Examples of the halogen solvent include chloroform, dichloromethane, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, and the like.

  Examples of the lactones include γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, and α-methyl-γ-butyrolactone.

  Examples of the alcohols include n-butyl alcohol.

  Examples of the glycol ethers include 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol and the like.

  The reaction temperature in the condensation polymerization reaction is usually -20 to 80 ° C. In general, the polycondensation reaction between diamine and tetracarboxylic dianhydride is a one-to-one reaction expressed as a molar ratio. Therefore, in the polycondensation reaction, “the naphthalenediamine and the other It is preferable that the abundance ratio of “diamine” and “the tetracarboxylic dianhydride and the other tetracarboxylic dianhydride” is represented in a molar ratio of 1: 1.

  The polyimide resin (1) can be obtained by further dehydrating and ring-closing the polyamic acid obtained by the condensation polymerization reaction. This dehydration cyclization reaction is performed under conditions such as a heating method and a chemical method that promote cyclization. The heating method imidizes the polyamic acid immediately after polycondensation by heating at a high temperature of 150 to 250 ° C., and the chemical method consists of 2 moles each of a base such as pyridine or triethylamine and acetic anhydride at 0 to 50 ° C. with respect to the starting diamine. The polyimide resin (1) solution can be obtained by imidizing by adding an equivalent amount or more and less than 10 equivalents. The obtained polyimide resin (1) solution may be used as it is for the production of a gas separation membrane, which will be described later, or may be concentrated or diluted, or the polyimide resin (1 ) May be obtained.

  In addition to the method described above, the method for producing the polyimide resin (1) includes naphthalenediamine having an HFIP group represented by the general formula (6) and tetracarboxylic dianhydride represented by the general formula (7). A method of obtaining polyimide resin (1) by using materials as essential raw materials and melting them at 150 ° C. or higher can also be mentioned.

<2. Manufacturing method of gas separation membrane>
The gas separation membrane according to the present invention is obtained by heat-treating at least the polyimide resin (1). At this time, other resin may be heat-treated together with the polyimide resin (1), or the heat-treated polyimide resin (1) and other resin may be combined.

  When heat-treating the polyimide resin (1), the polyimide resin (1) is preferably handled as a solution dissolved in an organic solvent in order to obtain various shapes and film thicknesses. When using it as a solution, apply it on a substrate such as glass, silicon wafer, metal, metal oxide, ceramics, resin, etc. by a commonly used method such as spin coating, spray coating, flow coating, impregnation coating, brush coating, etc. Can do.

  The type of the organic solvent is not particularly limited as long as the polyimide resin (1) is dissolved and volatilizes at the heat treatment temperature or lower. For example, an organic solvent used in the condensation polymerization reaction can be used. Moreover, the organic solvent of patent document 2 can also be used besides the said organic solvent.

  Moreover, the density | concentration of the polyimide resin (1) in this solution is although it does not specifically limit, 5 mass% or more and 50 mass% or less are preferable, Most preferably, they are 10 mass% or more and 40 mass% or less.

  In addition, the polyamic acid is applied onto a substrate and heated at the above heat treatment temperature to advance the dehydration ring-closure reaction to convert it into the polyimide resin (1), and the gas separation membrane of the present invention. You can also.

  Furthermore, the gas separation membrane of the present invention can also be produced by heat-treating a polyimide resin (1) precursor polyamic acid solution or a polyimide resin (1) solution obtained by dehydrating and ring-closing the polyimide resin (1) solution into a desired membrane shape. can do. At this time, this solution may be a solution obtained by pouring the polyamic acid or polyimide resin (1) into a poor solvent, precipitating, collecting, and drying, and then re-dissolving in an organic solvent.

  When producing a symmetrical membrane as the gas separation membrane of the present invention, when using the polyamic acid solution of the aforementioned polyimide resin (1) precursor, for example, a spin coater or applicator is used on a substrate such as a glass substrate. After wet coating using, heat treatment is performed in a dry gas such as air, nitrogen or argon to obtain a fired body through evaporation of the organic solvent and the cyclization dehydration reaction, and then firing from the base material. It is obtained by peeling the body. When using a solution of the polyimide resin (1), for example, after applying it to a base material such as a glass substrate or a PTFE (polytetrafluoroethylene) substrate using a spin coater or an applicator, air, nitrogen, argon or the like A heat treatment is performed in a dry gas to obtain a fired body through evaporation of the organic solvent, and then peeled from the substrate.

  When producing an asymmetric membrane as the gas separation membrane of the present invention, a coagulation liquid using a poor solvent that is compatible with the organic solvent of the polyimide solution but does not dissolve the polyimide from the discharge port by placing the polyimide solution in a pressure vessel There is a method in which a solvent existing in the vicinity of the surface of the polyimide film is evaporated in the air and a dense layer is formed on the surface side, and then a fine porous layer is formed on the bath side. .

  As such a coagulating liquid, water or an aqueous coagulating liquid that is a mixed solution of water and an organic solvent is preferably used. The composition of this mixed solution is not particularly limited. It is preferable to contain 30% by mass or more and 90% by mass or less, and preferably 40% by mass or more and 80% by mass or less of water based on the total mass of the mixed solution. Examples of the organic solvent used here include alcohol solvents such as methanol, ethanol and isopropanol, and ketone solvents such as acetone, methyl ethyl ketone, diethyl ketone and diethyl ketone.

<3. Separation method of gas mixture>
The gas mixture separation method of the present invention is a method for separating a specific gas from a gas mixture.

  In the gas mixture separation method of the present invention, the components of the raw material gas mixture are not particularly limited. For example, hydrogen, helium, carbon monoxide, carbon dioxide, hydrogen sulfide, oxygen, nitrogen, ammonia, sulfur oxide (SOx), nitrogen oxide (NOx), hydrocarbon, unsaturated hydrocarbon, perfluoro compound and the like. Here, examples of the hydrocarbon include methane, ethane, and propane, examples of the unsaturated hydrocarbon include propylene, and examples of the perfluoro compound include tetrafluoroethane. .

  Especially, it is preferable that the main components of a gas mixture are a carbon dioxide and methane. That is, the proportion of carbon dioxide and methane in the gas mixture is preferably 5 to 50%, more preferably 10 to 40% as the proportion of carbon dioxide. When the gas mixture is in the presence of an acidic gas such as carbon dioxide, the separation method of the gas mixture using the gas separation membrane of the present invention exhibits particularly excellent performance, and more excellent performance in the separation of carbon dioxide and methane. Demonstrate.

The gas separation performance of the gas separation membrane of the present invention is not particularly limited. Regarding the gas permeability coefficient, particularly the CO ₂ permeability coefficient and the CH ₄ permeability coefficient, the CO ₂ permeability coefficient is preferably 10 barr or more, particularly preferably 20 barr or more, under conditions of 150 kPa and 35 ° C., 30 More preferred is Barrer or higher. Further, under the conditions of 150 kPa and 35 ° C., the gas selectivity (particularly CO ₂ / CH ₄ selectivity) is preferably 30 or more, and particularly preferably 35 or more.

Among them, as for the gas permeability coefficient, the CO ₂ permeability coefficient is 10 barr or more, preferably 20 barr or more, and the gas selectivity (especially CO ₂ / CH ₄ selectivity) is 30 or more, preferably Is more preferably 35 or more, because it is a gas separation membrane that simultaneously satisfies high permeability and high selectivity.

<4. Gas separation membrane module and gas separation device>
The gas separation membrane of the present invention can be a gas separation membrane module. Moreover, it can be set as the apparatus which has a means for carrying out the separation collection | recovery or separation refinement | purification of gas using the gas separation membrane or gas separation membrane module of this invention.

  The gas separation membrane of the present invention can be suitably used in a modular form. Examples of the module include a spiral type, a hollow fiber membrane type, a pleat type, a tubular type, a plate & frame type, and the like. The gas separation membrane of the present invention may be applied to a gas separation / recovery device as a membrane / absorption hybrid method used in combination with an absorbing solution as described in JP-A-2007-297605, for example.

  Hereinafter, the present invention will be described more specifically based on examples, but the present invention is not limited to these examples.

[Example 1] Gas separation membrane comprising a fired product of polyimide (A) heated at 250 ° C A three-necked flask with a capacity of 500 mL equipped with a nitrogen introduction tube and a stirring blade was charged with HFIP-NDA (3.1 g) shown in the following reaction formula. 6 mmol), HFIP-MDA (30.0 g, 56 mmol), BPDA (18.4 g, 62 mmol), dimethylacetamide (hereinafter sometimes referred to as DMAc) (100 g), and stirred at 20 ° C. in a nitrogen atmosphere. Then, the following reaction was performed. Pyridine (19.8 g, 250 mmol) and acetic anhydride (25.6 g, 250 mmol) were sequentially added to the resulting reaction solution, and the mixture was further stirred for 24 hours to perform imidization. Thereafter, DMAc (50 g) was added to dilute the reaction solution after imidization, and pressure filtration was performed to prepare a DMAc solution of polyimide (A) in the reaction formula.

Gel permeation chromatography (hereinafter sometimes referred to as GPC) of polyimide DMAc solution, manufactured by Tosoh Corporation, model name: HLC-8320GPC, column: TSKgel SuperHZM-H, solvent: tetrahydrofuran (hereinafter referred to as THF) The measurement results of the molecular weight in ()) were Mw = 51300 and Mw / Mn = 2.3.

  The gas separation membrane made of the fired body of the polyimide (A) was prepared by applying the DMAc solution of the polyimide (A) to a glass substrate.

A DMAc solution of polyimide (A) is dropped on a glass substrate, and the spin coater is used to increase the rotation speed to 600 rpm over 10 seconds. Then, the rotation is maintained at 600 rpm for 10 seconds, and the polyimide (A) DMAc solution is added. And uniformly coated on a glass substrate. After drying for 30 minutes at a temperature of 180 ° C. in a nitrogen atmosphere, the solvent was removed, and after heat treatment at 300 ° C. for 2 hours, the polyimide (A) was removed by cooling and peeling the polyimide film from the glass substrate. A gas separation membrane made of a fired body obtained by heat treatment at 250 ° C. was obtained.
When the film thickness was measured with a film thickness meter (manufactured by Nikon Corporation, model name: DIGIMICRO MH-15), it was 40 μm.

[Example 2] Gas separation membrane comprising a fired product of polyimide (A) heated at 300 ° C The same operation as in Example 1 was performed to prepare a DMAc solution of polyimide (A). A DMAc solution of polyimide (A) is dropped on a glass substrate, and the spin coater is used to increase the rotation speed to 600 rpm over 10 seconds. Then, the rotation is maintained at 600 rpm for 10 seconds, and the polyimide (A) DMAc solution is added. And uniformly coated on a glass substrate. After drying for 30 minutes at a temperature of 180 ° C. in a nitrogen atmosphere, the solvent was removed, and after heat treatment at 300 ° C. for 2 hours, the polyimide (A) was removed by cooling and peeling the polyimide film from the glass substrate. A gas separation membrane made of a fired body obtained by heat treatment at 300 ° C. was obtained.

[Example 3] In a 500 mL three-necked flask equipped with a gas separation membrane nitrogen inlet tube made of a fired body of polyimide (B) by heating at 250 ° C and a stirring blade, HFIP-NDA (18.4 g, 38 mmol), HFIP-MDA (20.0 g, 38 mmol), BTDA (24.2 g, 75 mmol), and DMAc (132 g) were added, and the mixture was stirred at 20 ° C. in a nitrogen atmosphere to carry out the following reaction. Pyridine (9.0 g, 114 mmol) and acetic anhydride (11.7 g, 114 mmol) were sequentially added to the resulting reaction solution, and the mixture was further stirred for 24 hours to perform imidization. Then, the DMAc solution of the polyimide (B) in reaction formula was prepared by carrying out pressure filtration.
The measurement results of the molecular weight by GPC of the DMAc solution of polyimide (B) were Mw = 25000 and Mw / Mn = 2.5.

  A DMAc solution of polyimide (B) is dropped on a glass substrate, and the spin speed is increased to 500 rpm over 10 seconds using a spin coater, and then held at a rotation speed of 500 rpm for 10 seconds. And uniformly coated on a glass substrate. In a nitrogen atmosphere, the solvent is removed by drying for 30 minutes at a temperature of 180 ° C., and after heat treatment at 250 ° C. for 2 hours, the polyimide film is removed by cooling and peeling the polyimide film from the glass substrate. A gas separation membrane made of a fired body obtained by heat treatment at 250 ° C. was obtained.

[Example 4] Gas separation membrane comprising a fired product of polyimide (C) heated at 250 ° C A three-neck flask having a capacity of 500 mL equipped with a nitrogen introduction tube and a stirring blade was charged with HFIP-NDA (30.0 g, 61 mmol), BTDA (19.7 g, 61 mmol), and DMAc (103 g) were added, and the mixture was stirred at 20 ° C. in a nitrogen atmosphere to carry out the following reaction. Pyridine (10.2 g, 129 mmol) and acetic anhydride (13.1 g, 129 mmol) were sequentially added to the resulting reaction solution, and the mixture was further stirred for 24 hours to perform imidization. Thereafter, a DMAc solution of polyimide (C) in the reaction formula was prepared by filtration under pressure.
The measurement results of the molecular weight by GPC of the DMAc solution of polyimide (C) were Mw = 26200 and Mw / Mn = 2.1.

  A DMAc solution of polyimide (C) is dropped on a glass substrate, and the spin coater is used to raise the rotation speed to 450 rpm over 10 seconds, and then held at the rotation speed of 450 rpm for 10 seconds. And uniformly coated on a glass substrate. After drying for 30 minutes at a temperature of 180 ° C. in a nitrogen atmosphere, the solvent was removed, and after heat treatment at 250 ° C. for 2 hours, the polyimide (C) was removed by cooling and peeling the polyimide film from the glass substrate. A gas separation membrane made of a fired body obtained by heat treatment at 250 ° C. was obtained.

[Comparative Example 1] A gas separation membrane made of a fired body of polyimide (P1) heated at 300 ° C In a 500 mL three-necked flask equipped with a nitrogen introducing tube and a stirring blade, HFIP-MDA (58. 3 g, 110 mmol), BPDA (32.4 g, 110 mmol), and DMAc (220 g) were added, and the mixture was stirred at 20 ° C. in a nitrogen atmosphere to carry out the following reaction. Pyridine (34.8 g, 440 mmol) and acetic anhydride (44.9 g, 440 mmol) were sequentially added to the resulting reaction solution, and the mixture was further stirred for 24 hours to perform imidization. Then, the DMAc solution of the polyimide (P1) shown in the following reaction formula was produced by carrying out pressure filtration.
The measurement results of the molecular weight by GPC of the DMAc solution of polyimide (P1) were Mw = 95200 and Mw / Mn = 1.9.

  The gas separation membrane made of the fired body of the polyimide (P1) was prepared by applying the DMAc solution of the polyimide (P1) to a glass substrate.

A DMAc solution of polyimide (P1) is hung on a glass substrate, and the rotation speed is increased to 300 rpm over 10 seconds using a spin coater, and then held at a rotation speed of 300 rpm for 10 seconds. And uniformly coated on a glass substrate. In a nitrogen atmosphere, the solvent is removed by drying at 180 ° C. for 30 minutes, and after heat treatment at 300 ° C. for 2 hours, the polyimide (P1) is removed by cooling and peeling the polyimide film from the glass substrate. A gas separation membrane made of a fired body obtained by heat treatment at 300 ° C. was obtained.
When the film thickness was measured with the film thickness meter, the film thickness was 80 μm.

[Comparative Example 2] Gas separation membrane comprising a fired product of polyimide (P1) heated at 250 ° C The same operation as in Comparative Example 1 was performed to prepare a DMAc solution of polyimide (P1). A DMAc solution of polyimide (P1) is hung on a glass substrate, and the rotation speed is increased to 300 rpm over 10 seconds using a spin coater, and then held at a rotation speed of 300 rpm for 10 seconds. And uniformly coated on a glass substrate. After drying for 30 minutes at a temperature of 180 ° C. in a nitrogen atmosphere, the solvent is removed, and after heat treatment at 200 ° C. for 2 hours, the polyimide (P1) is removed by cooling and peeling the polyimide film from the glass substrate. A gas separation membrane made of a fired body obtained by heat treatment at 250 ° C. was obtained.
When the film thickness was measured with the film thickness meter, the film thickness was 80 μm.

[Comparative Example 3] Gas separation membrane composed of a fired product of polyimide (P1) heated at 200 ° C The same operation as in Comparative Example 1 was performed to prepare a DMAc solution of polyimide (P1). A DMAc solution of polyimide (P1) is hung on a glass substrate, and the rotation speed is increased to 300 rpm over 10 seconds using a spin coater, and then held at a rotation speed of 300 rpm for 10 seconds. And uniformly coated on a glass substrate. After drying for 30 minutes at a temperature of 180 ° C. in a nitrogen atmosphere, the solvent is removed, and after heat treatment at 200 ° C. for 2 hours, the polyimide (P1) is removed by cooling and peeling the polyimide film from the glass substrate. A gas separation membrane made of a fired body obtained by heat treatment at 200 ° C. was obtained.
When the film thickness was measured with the film thickness meter, the film thickness was 80 μm.

[Comparative Example 4] A gas separation membrane made of a fired product of Matrimid 5218 heated at 200 ° C A 3-neck flask refers to a specific polyimide polymer sold under the Matrimid (registered trademark) trademark of Matrimid 5218 (manufactured by Huntsman Advanced Materials) (Hereinafter, it may be referred to as Matrimid.) (0.6 g) and THF (16 g) were added, and the mixture was stirred at room temperature for 48 hours to prepare a Matrimid solution in THF. Matrimid THF solution was placed in a circular PTFE dish having a diameter of 10 cm, held in a glove bag filled with vapor of THF for 48 hours, and the solvent was removed and dried to obtain a Matrimid membrane. This membrane was heat-treated at 200 ° C. for 2 hours in a nitrogen atmosphere, and then cooled to obtain a gas separation membrane made of a fired body obtained by heat-treating Matrimid at 200 ° C.
When the film thickness was measured with the film thickness meter, the film thickness was 82 μm.

[Comparative Example 5] Gas separation membrane composed of a fired body of polyimide (P2) heated at 250 ° C A three-neck flask with a capacity of 500 mL equipped with a nitrogen introduction tube and a stirring blade was charged with mTB (23.4 g, 110 mmol) shown in the following reaction formula ), 6FDA (48.9 g, 110 mmol) and DMAc (220 g) were added, and the mixture was stirred at 20 ° C. in a nitrogen atmosphere to carry out the following reaction. To the resulting reaction solution, pyridine (34.8 g, 440 mmol) and acetic anhydride (44.9 g, 440 mmol) were sequentially added, and the mixture was further stirred for 24 hours to perform imidization. Then, the DMAc solution of the polyimide (P2) shown by the following reaction formula was produced by carrying out pressure filtration.
The measurement results of the molecular weight by GPC of the DMAc solution of polyimide (P2) in the following reaction formula were Mw = 86000 and Mw / Mn = 1.7.

The gas separation membrane made of the fired body of polyimide (P2) was prepared by applying the DMAc solution of polyimide (P2) to a glass substrate.
A DMAc solution of polyimide (P2) is dropped on a glass substrate, and the spin rate is increased to 500 rpm over 10 seconds using a spin coater. Then, the DMAc solution of polyimide (P2) is held at a rotation speed of 500 rpm for 10 seconds. And uniformly coated on a glass substrate. In a nitrogen atmosphere, the solvent is removed by drying for 30 minutes at a temperature of 180 ° C., and after heat treatment at 250 ° C. for 2 hours, the polyimide film (P2) is removed by cooling and peeling the polyimide film from the glass substrate. A gas separation membrane made of a fired body obtained by heat treatment at 250 ° C. was obtained.
When the film thickness was measured with the film thickness meter, the film thickness was 74 μm.

[Comparative Example 6] A gas separation membrane made of a fired body of polyimide (P3) heated at 250 ° C In a 500 mL three-necked flask equipped with a nitrogen inlet tube and a stirring blade, HFIP-MDA (58. 3 g, 110 mmol), 6FDA (48.9 g, 110 mmol), and DMAc (220 g) were added, and the mixture was stirred at 20 ° C. in a nitrogen atmosphere to carry out the following reaction. Pyridine (34.8 g, 440 mmol) and acetic anhydride (44.9 g, 440 mmol) were sequentially added to the resulting reaction solution, and the mixture was further stirred for 24 hours to perform imidization. Then, the DMAc solution of the polyimide (H) shown in the following reaction formula was produced by carrying out pressure filtration.
The measurement results of the molecular weight by GPC of the DMAc solution of polyimide (H) in the following reaction formula were Mw = 60000 and Mw / Mn = 2.0.

The gas separation membrane made of the fired body of the polyimide (P3) was prepared by applying the DMAc solution of the polyimide (P3) to a glass substrate.
A DMAc solution of polyimide (H) is hung on a glass substrate, and the spin coater is used to increase the rotation speed to 150 rpm over 10 seconds. Then, the rotation is maintained at 150 rpm for 10 seconds, and the polyimide (P3) DMAc solution is added. And uniformly coated on a glass substrate. In a nitrogen atmosphere, the solvent is removed by drying at a temperature of 180 ° C. for 30 minutes, and after heat treatment at 250 ° C. for 2 hours, the polyimide (P3) is removed by cooling and peeling the polyimide film from the glass substrate. A gas separation membrane made of a fired body obtained by heat treatment at 250 ° C. was obtained.
When the film thickness was measured with the film thickness meter, the film thickness was 74 μm.

[Comparative Example 7] A gas separation membrane made of a fired body of polyimide (P4) heated at 250 ° C. In a 500 mL three-necked flask equipped with a nitrogen introduction tube and a stirring blade, HFIP-MDA (40. 0 g, 75 mmol), BTDA (24.3 g, 75 mmol) and DMAc (137 g) shown in the following reaction formula were added, and the mixture was stirred at 20 ° C. in a nitrogen atmosphere to carry out the following reaction. Pyridine (12.5 g, 158 mmol) and acetic anhydride (16.2 g, 158 mmol) were sequentially added to the resulting reaction solution, and the mixture was further stirred for 24 hours to perform imidization. Then, the DMAc solution of the polyimide (G) shown in the following reaction formula was produced by carrying out pressure filtration.
The measurement result of the molecular weight by GPC of the DMAc solution of polyimide (G) was Mw = 172000 and Mw / Mn = 2.0.

The gas separation membrane made of the fired body of polyimide (P4) was prepared by applying the DMAc solution of polyimide (P4) to a glass substrate.
A DMAc solution of polyimide (P4) is hung on a glass substrate, and the spin speed is increased to 300 rpm over 10 seconds using a spin coater. Then, the DMAc solution of polyimide (P4) is held at a rotation speed of 300 rpm for 10 seconds. And uniformly coated on a glass substrate. After drying for 30 minutes at a temperature of 180 ° C. in a nitrogen atmosphere, the solvent is removed, and after heat treatment at 250 ° C. for 2 hours, the polyimide (P4) is removed by cooling and peeling the polyimide film from the glass substrate. A gas separation membrane made of a fired body obtained by heat treatment at 250 ° C. was obtained.
When the film thickness was measured with the film thickness meter, the film thickness was 80 μm.

Table 1 shows the methane permeability coefficient, carbon dioxide permeability coefficient, and gas selectivity (CO ₂ / CH ₄ ) in the gas separation membranes obtained in the above Examples and Comparative Examples.

[Test Example 2] Measurement of plasticization start pressure <Evaluation of plastic resistance to carbon dioxide>
In the obtained gas separation membrane, non-patent document Ind. Eng. Chem. According to the method described in Res, Vol 42, 6389-6395, 2003, the carbon dioxide permeability coefficient at each carbon dioxide supply pressure was measured. Specifically, a gas separation membrane having a membrane area of 3.14 cm ² is placed in a stainless steel cell, and the gas supply pressure is in the range of 0.15 MPa to 4.3 MPa at a temperature of 25 ° C. The supply pressure was increased in order, and the carbon dioxide permeability coefficient at that time was measured. The supply pressure at the lowest permeation coefficient among the obtained permeation coefficients was defined as the plasticizing start pressure. The plastic resistance of each gas separation membrane was evaluated by comparing the plasticization start pressure of each gas separation membrane.

1 to 5 show plots of carbon dioxide supply pressure and permeation coefficient in the gas separation membranes obtained in Examples 1 and 2 and Comparative Examples 5 to 7, and Table 2 shows the respective plasticization start pressures.

As shown in Table 2, the gas separation membrane made of the fired body of polyimide having the HFIP group of Example 1 and the condensed polycyclic aromatic hydrocarbon was obtained from the fired body of polyimide having no HFIP group of Comparative Example 5. Compared with the gas separation membrane, the plasticizing start pressure was large and the plastic resistance was excellent.
Further, the gas separation membrane made of the fired product of polyimide having the HFIP group and the condensed polycyclic aromatic hydrocarbon of Example 1 has the HFIP group of Comparative Examples 2 and 6, but the condensed polycyclic aromatic hydrocarbon. Compared to a gas separation membrane made of a fired body of polyimide that does not have a plasticity, the plasticization start pressure was large and the plastic resistance was excellent.
Furthermore, as shown in Example 1 and Example 2, even in a fired body made of the same polyimide (A) as a raw material, in Example 2 where the firing temperature is 300 ° C., the firing temperature is 250 ° C. The plastic resistance more excellent than Example 1 was shown.

Moreover, as shown in Table 1, the gas separation membrane comprising a fired product of polyimide having HFIP groups and condensed polycyclic aromatic hydrocarbons of Examples 1 and 2 has excellent gas permeation performance and gas selectivity. showed that.

Claims (16)

A gas separation membrane comprising at least a fired body of a polyimide resin having a repeating unit represented by the general formula (1).

(In General Formula (1), R ¹ is a divalent organic group represented by General Formula (2), and R ² contains at least one selected from the group consisting of an alicyclic ring, an aromatic ring and an alkylene group. (It is a tetravalent organic group.)

(In general formula (2), a and b are each independently an integer of 0 to 2, and 1 ≦ a + b ≦ 4.) The gas separation membrane according to claim 1, wherein R ¹ is any ^one of the following divalent organic groups.

The gas separation membrane according to claim 1 or 2, wherein R ² is any one of the following tetravalent organic groups.

The gas separation membrane according to any one of claims 1 to 3, wherein the polyimide resin further has a repeating unit represented by the general formula (3).

(In the general formula (3), R ³ is a divalent organic group represented by formula (4) a divalent organic group or a group represented by formula represented (5), R ⁴ is an alicyclic, aromatic A tetravalent organic group containing at least one selected from the group consisting of a ring and an alkylene group.)

(In the general formula (4), R ⁵ is a single bond, an oxygen atom, a sulfur atom, CO, CH ₂ , CH ₂ CH ₂ , SO, SO ₂ , C (CH ₃ ) ₂ , C (CH ₃ ) (CH ₂ CH ₃ ), NHCO, C (CF ₃ ) ₂ , an aromatic ring or an alicyclic ring, R ⁶ and R ⁷ are each independently a hydrogen atom, an alkyl group or a fluoroalkyl group, and c and d are each independently (It is an integer of 0 to 2, and 1 ≦ c + d ≦ 4.)

(In General Formula (5), R ⁸ is a hydrogen atom, an alkyl group or a fluoroalkyl group, and e is an integer of 1 to 4.) The gas separation membrane according to claim 4, wherein R ³ is any one of the following divalent organic groups.

The gas separation membrane according to claim 4 or 5, wherein R ⁴ is any one of the following tetravalent organic groups.

  The gas separation membrane according to any one of claims 1 to 6, wherein the polyimide resin has a mass average molecular weight of 20,000 or more and 500,000 or less. The gas separation membrane according to any one of claims 1 to 7, wherein the fired body is a heat-treated body of the polyimide resin at 200 to 400 ° C.   A method for separating a gas mixture, wherein the gas separation membrane according to any one of claims 1 to 8 is used to separate carbon dioxide from a gas mixture containing at least carbon dioxide and methane.   A method for separating a gas mixture, wherein the gas separation membrane according to any one of claims 1 to 8 is used to separate methane from a gas mixture containing at least carbon dioxide and methane.   A gas separation membrane module comprising the gas separation membrane according to any one of claims 1 to 8.   A gas separation device comprising at least the gas separation membrane module according to claim 11. A polyimide resin having a repeating unit represented by the general formula (1).

(In General Formula (1), R ¹ is a divalent organic group represented by General Formula (2), and R ² contains at least one selected from the group consisting of an alicyclic ring, an aromatic ring and an alkylene group. (It is a tetravalent organic group.)

(In general formula (2), a and b are each independently an integer of 0 to 2, and 1 ≦ a + b ≦ 4.) The polyimide resin according to claim 13, wherein R ¹ is any ^one of the following divalent organic groups.

The polyimide resin according to claim 13 or 14, wherein R ² is any one of the following tetravalent organic groups.

The gas separation membrane according to any one of claims 13 to 15, wherein the mass average molecular weight is 20,000 or more and 500,000 or less.

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