WO2018131697A1 - Gas separation membrane - Google Patents

Abstract

This gas separation membrane contains a polyimide which has a repeating unit represented by formula (1). This gas separation membrane has excellent gas separation performance in a separation temperature range of from 35°C to 70°C (inclusive), and exhibits particularly excellent separation performance for CO₂ and CH₄. Formula (1) (In formula (1), R¹ represents a divalent organic group represented by formula (2).) Formula (2) (In formula (2), R² represents a hydrogen atom, an alkyl group or a fluoroalkyl group; and a represents an integer of 1-2.)

Description

Gas separation membrane

The present invention relates to a gas separation membrane, a gas separation method using the same, and a gas separation apparatus.

Conventionally, a chemical absorption method in which an acidic gas is adsorbed to amines or the like has been used as a method for removing and purifying an acidic gas such as carbon dioxide (CO ₂ ) from natural gas containing methane (CH ₄ ). The chemical absorption method is a method in which high-purity methane is efficiently obtained by adsorbing an acidic gas to an amine. However, refining natural gas using the chemical absorption method requires a large gas separation device for the amount of purification, which requires construction costs, and costs for reusing the amine used as the absorbent in the purification process. There are problems such as taking.

Compared with the chemical absorption method, the gas separation method using a gas separation membrane can use a small gas separation device for the gas throughput, and is advantageous for offshore plants of natural gas with a limited installation area. When separating the natural gas, the pressure of the natural gas at the time of sampling can be used as the driving force for passing the gas separation membrane.

In a natural gas separation and purification process using a gas separation membrane, a polymer such as polyimide is used as a material for the gas separation membrane. For example, the polyimide membrane exhibits excellent separation performance of carbon dioxide and methane at room temperature (about 20 ° C.). However, the separation and purification of natural gas is generally performed continuously with the sampling gas, and is generally performed in the vicinity of 50 ° C., which is a higher temperature range. When a polyimide membrane is used, the selectivity between carbon dioxide and methane decreases near 50 ° C., and high-purity methane tends not to be obtained. For example, Non-Patent Document 1 describes that the separation selectivity between carbon dioxide and methane by a polyimide membrane decreases as the temperature increases.

Natural gas is a fossil fuel containing a light hydrocarbon gas as a combustible gas. Specific examples of the hydrocarbon gas contained include methane, ethane, propane, butane, and pentane. Natural gas contains nonflammable gases such as nitrogen, oxygen, carbon dioxide, water vapor, hydrogen sulfide gas, sulfurous acid gas, or sulfur oxide gas in addition to hydrocarbon gases. It is preferable to remove the flammable gas and separate and purify the combustible gas.

Generally, a gas separation membrane has a relationship in which gas separation selectivity and permeability at the time of gas separation are opposite to each other. Therefore, a polymer membrane having high permeability is inferior in separation selectivity. However, particularly in the high temperature range, a gas separation membrane having high gas permeability and excellent gas separation selectivity is required, and development of a polymer material having excellent gas separation performance compared to conventional polyimide membranes has been demanded. I'm in a hurry.

Patent Document 1 has a phenylenediamine skeleton, and at least one hydrogen atom on the phenylenediamine is a hexafluoroisopropanol group (2-hydroxy-1,1,1,3,3,3-hexafluoroisopropyl group; A fluorine-containing polymerizable monomer substituted with —C (CF ₃ ) ₂ OH (hereinafter sometimes referred to as HFIP group) and a polyimide which is a polymer compound using the same are disclosed. Patent Documents 2 to 5 disclose gas separation membranes having a polyimide structure containing HFIP groups.

Patent Document 6 discloses a methane separation method capable of separating and purifying methane from biogas containing a high concentration of carbon dioxide with high efficiency, a methane separation device using the same, and a methane utilization system, and a gas separation membrane module Is used.

JP 2007-119504 A JP 2013-10096 A JP 2014-128787 A JP 2014-128788 A JP 2016-137484 A JP 2007-297605 A

Journal of Membrane Science, Vo47, 203-215, 1989

At a temperature of 50 ° C., the permeability coefficient of carbon dioxide when separating natural gas is 10 Barrer or more, and the permeability coefficient ratio between carbon dioxide and methane (CO ₂ permeability coefficient P _CO2 / CH ₄ permeability coefficient P _CH4 ) exceeds 40 A gas separation membrane having gas separation performance is not disclosed in the prior art.

An object of the present invention is to provide a gas separation membrane having excellent gas separation performance, a gas separation method using the same, and a gas separation device. Specifically, a gas separation membrane excellent in removing carbon dioxide from natural gas and obtaining a gas containing high-concentration methane in a high temperature range of 35 ° C. or higher and 70 ° C. or lower, and gas using the same An object of the present invention is to provide a separation method and a gas separation apparatus. In particular, the permeability coefficient P _CO2 of carbon dioxide when a gas containing carbon dioxide and methane is separated at a separation temperature of 50 ° C. is 10 Barrer or more, and the permeability coefficient ratio of carbon dioxide and methane (CO ₂ permeability coefficient P An object of the present invention is to provide a gas separation membrane having a gas separation performance with a _{CO 2} / CH ₄ permeability coefficient P _CH4 ) exceeding 40.

As a result of intensive studies by the present inventors, among polyimides having an HFIP group, a diamine having an HFIP group in a phenylenediamine skeleton and 4,4′-diphenylsulfonetetracarboxylic dianhydride (hereinafter referred to as DSDA). Is used for the gas separation membrane, and at a temperature of 50 ° C., the carbon dioxide has a permeability coefficient P _CO2 of 10 Barrer or more when the gas containing carbon dioxide and methane is separated. It was found that a gas separation performance exceeding 40 (CO ₂ permeability coefficient P _CO2 / CH ₄ permeability coefficient P _CH4 ) ratio of 40 and _methane was obtained. Further, the present inventors have found that the gas separation membrane of the polyimide has a different permeability coefficient ratio between oxygen and nitrogen and can concentrate oxygen or nitrogen in a gas containing oxygen and nitrogen. Based on these findings, the present invention has been completed. 1 Barrer = 1 × 10 ⁻¹⁰ cm ³ (STP) · cm / sec · cm ² · cmHg.

That is, the present invention includes the following inventions 1 to 17.

（式（１）中、Ｒ¹は式（２）で表される２価の有機基である。）

（式（２）中、Ｒ²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、aは１～２の整数である。） [Invention 1]
A gas separation membrane comprising a polyimide having a repeating unit represented by formula (1).

(In formula (1), R ¹ is a divalent organic group represented by formula (2).)

(In the formula (2), R ² is a hydrogen atom, an alkyl group or a fluoroalkyl group, and a is an integer of 1 to 2)

（式（３）中、Ｒ¹は前記式（１）のＲ¹と同義である。Ｒ³は、以下の式で表されるいずれかの４価の有機基である。）

[Invention 2]
The gas separation membrane according to Invention 1, wherein the polyimide further comprises a polyimide containing a repeating unit represented by the formula (3).

(In the formula (3), R ¹ is .R ³ R ¹ as synonymous of the formula (1) is any tetravalent organic group represented by the following equation.)

[Invention 3]
The gas separation membrane of Invention 1 or Invention 2, wherein R ¹ is any ^one of the following divalent organic groups.

[Invention 4]
The gas separation membrane according to inventions 1 to 3, wherein the polyimide has a weight average molecular weight of 20,000 or more and 500,000 or less.

[Invention 5]
The gas separation membrane according to any one of inventions 1 to 4, wherein the polyimide heated at 50 ° C. or more and 400 ° C. or less is used.

[Invention 6]
The gas separation membrane of inventions 1 to 5, wherein the gas to be separated is a gas containing at least carbon dioxide and methane.

[Invention 7]
The gas separation membrane of invention 6 wherein the permeability coefficient of carbon dioxide at 50 ° C. and 150 kPa is 10 Barrer or more, and the permeability coefficient ratio (P _CO2 / P _CH4 ) between carbon dioxide and methane is 40 or more.

[Invention 8]
The gas separation membrane of invention 6 or invention 7, wherein the gas containing carbon dioxide and methane is natural gas.

[Invention 9]
A gas separation method for separating methane from a gas containing carbon dioxide and methane using the gas separation membranes of the inventions 6 to 8.

[Invention 10]
A gas separation method for separating carbon dioxide from a gas containing carbon dioxide and methane using the gas separation membranes of the inventions 6 to 8.

[Invention 11]
The gas separation method of Invention 9 or Invention 10, wherein gas separation is performed at 35 ° C. or more and 70 ° C. or less.

[Invention 12]
A gas separation membrane module having the gas separation membrane of inventions 1 to 8.

[Invention 13]
A gas separation device having the gas separation membrane of the inventions 1 to 8.

[Invention 14]
The gas separation membrane of inventions 1 to 5, wherein the gas to be separated is a gas containing at least oxygen and nitrogen.

[Invention 15]
The gas separation membrane of the invention 14 whose gas containing oxygen and nitrogen is air.

[Invention 16]
A gas separation method for separating oxygen from a gas containing oxygen and nitrogen using the gas separation membranes of the inventions 14 to 15.

[Invention 17]
A gas separation method for separating nitrogen from a gas containing oxygen and nitrogen using the gas separation membranes of the inventions 14 to 15.

According to the present invention, a gas separation membrane having excellent gas separation performance at a separation temperature of 35 ° C. or higher and 70 ° C. or lower, a gas separation method and a gas separation apparatus using the same are obtained. The gas separation performance is such that the permeability coefficient of carbon dioxide when separating gas containing carbon dioxide and methane is 10 Barrer or higher and the permeability coefficient ratio of carbon dioxide and methane (CO ₂ permeability) (Coefficient / CH ₄ permeability coefficient) exceeds 40, and it is excellent in removing carbon dioxide from natural gas and obtaining a gas containing a high concentration of methane.

CO ₂ permeability coefficient and CO ₂ / CH ₄ permeability coefficient ratio (CO ₂ permeability coefficient / CH ₄ ) measured in the gas permeability performance test (50 ° C. test ambient temperature) of the gas separation membranes obtained in the examples and comparative examples. It is a graph showing the relationship of a transmission coefficient.

Each configuration in the following embodiment and a combination thereof are examples of the embodiment of the present invention, and addition, omission, replacement, and other modifications of the configuration 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.

The gas separation membrane of the present invention contains polyimide.

When using a gas separation membrane to separate carbon dioxide or methane from a gas containing carbon dioxide and methane, the larger the carbon dioxide permeability coefficient of the gas separation membrane, the better the gas throughput per unit time. The larger the methane permeability coefficient ratio (CO ₂ permeability coefficient / CH ₄ permeability coefficient), the better the separation selectivity between carbon dioxide and methane.

In gas separation membranes, gas permeability is the solubility indicating how much gas dissolves into the membrane (hereinafter sometimes referred to as the solubility coefficient) and how fast the gas moves through the membrane (hereinafter referred to as the diffusion coefficient). The permeability coefficient is expressed as the product of the solubility coefficient and the diffusion coefficient.

In the gas separation membrane, the temperature dependence of the CO ₂ solubility coefficient and the CO ₂ diffusion coefficient cancel each other, and as a result, it is presumed that the temperature dependence of the CO ₂ permeability coefficient is low. In addition, the phenylenediamine-derived skeleton having an HFIP group in the polyimide used for the gas separation membrane increases the free volume in the polyimide, thereby activating the permeation of CH ₄ with a large dynamic molecular size into the membrane. As a result, the temperature dependence of CH ₄ is lowered, and the gas separation membrane has a free volume that is optimal for the selection of carbon dioxide and methane, resulting in a high carbon dioxide and methane permeability coefficient ratio. It is assumed that (CO ₂ permeability coefficient / CH ₄ permeability coefficient) is expressed. Therefore, it is presumed that a gas separation performance with a carbon dioxide permeability coefficient of 10 Barrer or more and a carbon dioxide and methane permeability coefficient ratio exceeding 40 was obtained in a high temperature range of 50 ° C.

1. Polyimide The polyimide contained in the gas separation membrane of the present invention will be described.

（式（１）中、Ｒ¹は式（２）で表される２価の有機基である。）

（式（２）中、Ｒ²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、aは１～２の整数である。） [Polyimide having a repeating unit represented by the formula (1)]
The polyimide which the gas separation membrane of this invention contains has a repeating unit represented by General formula (1). Hereinafter, the repeating unit represented by formula (1) may be referred to as repeating unit (1), and the polyimide having the repeating unit represented by formula (1) may be referred to as polyimide (1).

(In formula (1), R ¹ is a divalent organic group represented by formula (2).)

(In the formula (2), R ² is a hydrogen atom, an alkyl group or a fluoroalkyl group, and a is an integer of 1 to 2)

R ¹ is a divalent organic group, and may have not only a linear structure but also an alicyclic, unsaturated, aromatic, or polycyclic structure with a carbon atom, or a heterocyclic structure. , Hydrogen atom, fluorine atom, chlorine atom, oxygen atom, sulfur atom or nitrogen atom may be contained. Further, some or all of the hydrogen atoms may be substituted with an alkyl group, a fluoroalkyl group, a carboxyl group, a hydroxy group, or a cyano group.

R ¹ is preferably any one of the following divalent organic groups.

The polyimide (1) used for the gas separation membrane of the present invention is preferably a polyimide (1) having any one of the following repeating units.

Particularly preferred among these is polyimide (1) having the following repeating units.

The repeating unit (1) may be regularly arranged in the polyimide (1) or may be irregularly arranged.

[Polyimide having a repeating unit represented by the formula (3)]
The polyimide (1) contained in the gas separation membrane of the present invention may further have a repeating unit represented by the formula (3). Hereinafter, the repeating unit represented by the general formula (3) may be referred to as a repeating unit (3).

R ¹ is a divalent organic group, and may have not only a linear structure but also an alicyclic, unsaturated, aromatic, or polycyclic structure with a carbon atom, or a heterocyclic structure. , Hydrogen atom, fluorine atom, chlorine atom, oxygen atom, sulfur atom or nitrogen atom may be contained. Further, some or all of the hydrogen atoms may be substituted with an alkyl group, a fluoroalkyl group, a carboxyl group, a hydroxy group, or a cyano group.

R ¹ is preferably any one of the following organic groups.

R ³ is any tetravalent organic group represented by the following formula.

R ³ is preferably any organic group represented by the following formula.

The polyimide (1) used for the gas separation membrane of the present invention is preferably a polyimide having any of the following repeating units (3) in addition to the repeating unit (1).

Particularly preferred among these is polyimide (1) having the following repeating unit (3).

In the case where the polyimide (1) has a repeating unit (3) in addition to the repeating unit (1), the abundance ratio of the repeating unit (1) and the repeating unit (3) is not particularly limited. When the polyimide (1) having the unit (1) and the repeating unit (3) is used as the gas separation membrane of the present invention, in order to obtain the desired separation performance of carbon dioxide and methane, the repeating unit (1) The presence is preferably 0.05 or more, more preferably 0.1 or more, and further preferably 0.5 or more, with 1 as the repeating unit (3). That is, repeating unit (1): repeating unit (3) = 0.05: 1 to 1: 0.

[Weight average molecular weight of polyimide]
The weight average molecular weight (Mw) of the polyimide (1) contained in the gas separation membrane of the present invention is preferably from 20,000 to 500,000, particularly preferably from 30,000 to 200,000. If it is 20000 or more, a tough gas separation membrane can be obtained, and if it is 500,000 or less, it can be formed. Here, the weight average molecular weight is a value obtained by measuring by gel permeation chromatography (GPC) and converting to polystyrene using a standard polystyrene calibration curve.

2. Manufacturing method of polyimide The manufacturing method of the polyimide (1) which the gas separation membrane of this invention contains is demonstrated.

（式（４）中、ａおよびＲ²は式（２）のａおよびＲ²とそれぞれ同義である。式（２）中のａおよびＲ²は、式（４）で表されるフェニレンジアミン中のａおよびｂにそれぞれ由来する。）

Polyimide (1) can be obtained by reacting phenylenediamine represented by formula (4) with tetracarboxylic dianhydride represented by formula (5).

(In the formula (4), a and R ² are each synonymous with a and R ² of formula (2). A and R ² in formula (2) during phenylenediamine represented by the formula (4) Derived from a and b.)

Specifically, the following method for producing polyimide (A) or (B) can be shown.
(A): phenylenediamine represented by formula (4) and tetracarboxylic dianhydride represented by formula (5) are subjected to condensation polymerization in an organic solvent to obtain a polyamic acid, and then the polyamic acid is dehydrated. The manufacturing method of the polyimide which obtains a polyimide (1) by making it ring-close and imidize.
(B): In the presence of a phenylenediamine having an HFIP group represented by the formula (4) and a tetracarboxylic dianhydride represented by the formula (5), the polyimide is heated, melted and reacted at 150 ° C. or higher. The manufacturing method of the polyimide which obtains (1).

In the polyimide production method of (A) or (B), a diamine other than that represented by formula (4) or a tetra other than that represented by formula (5) may be used as necessary to adjust the properties of the resulting polyimide. Carboxylic dianhydride, or both, may be added.

(A) The polyimide production method will be described.

As shown below, the polyimide production method (A) is obtained by polycondensing a phenylenediamine represented by the formula (4) and a tetracarboxylic dianhydride represented by the formula (5) in an organic solvent. In this method, an acid is obtained, and then the polyamic acid is dehydrated and cyclized and imidized to obtain polyimide (1).

The organic solvent to be used may be one that does not inhibit the polycondensation reaction for obtaining a polyamic acid from the phenylenediamine represented by the formula (4) and the tetracarboxylic dianhydride represented by the formula (5). Examples of such organic solvents include amide solvents, aromatic solvents, halogen solvents, lactone solvents, alcohol solvents, and glycol ether solvents. These organic solvents may be used alone or in combination of two or more.

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

Specific examples of the aromatic solvent include benzene, anisole, diphenyl ether, nitrobenzene, benzonitrile, and p-chlorophenol. Specific examples of the halogen solvent include chloroform, dichloromethane, 1,2-dichloroethane, and 1,1,2,2-tetrachloroethane.

Specific examples of the lactone solvent include γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, and α-methyl-γ-butyrolactone.

Specific examples of the alcohol solvent include n-butyl alcohol.

Specific examples of glycol ether solvents include 2-methoxyethanol, 2-ethoxyethanol, and 2-butoxyethanol.

The reaction temperature in the polycondensation reaction for obtaining a polyamic acid from the phenylenediamine represented by the formula (4) and the tetracarboxylic dianhydride represented by the formula (5) is usually −20 ° C. or higher and 80 ° C. or lower. Since the polycondensation reaction between diamine and tetracarboxylic dianhydride is a one-to-one reaction expressed in molar ratio, in the polycondensation reaction, the phenylenediamine represented by formula (4) and formula (5) It is preferable that the abundance ratio of the tetracarboxylic dianhydride represented by the formula is represented as a molar ratio of 1: 1.

The polyimide (1) is obtained by further dehydrating and ring-closing the polyamic acid obtained by the polymerization reaction to imidize.

Dehydration ring closure is a method in which the polyamic acid immediately after condensation polymerization is heated to 100 ° C. or higher and 350 ° C. or lower, or 0 ° C. or higher and 50 ° C. or lower, pyridine, triethylamine, etc. The base and acetic anhydride of each are imidized by adding 2 molar equivalents or more and 10 equivalents or less, and the polyimide (1) solution can be obtained. The obtained polyimide (1) solution may be directly used for the production of a gas separation membrane described later, or may be concentrated or diluted, or an organic solvent or the like is removed from the polyimide (1) solution. Thus, polyimide (1) itself may be obtained.

3. Gas Separation Membrane The gas separation membrane of the present invention is particularly excellent in carbon dioxide permeability and excellent in separation of a mixed gas containing carbon dioxide and hydrocarbons, particularly a mixed gas containing carbon dioxide and methane. A gas separation membrane according to an embodiment of the present invention is a gas separation membrane for separating carbon dioxide or methane from a gas containing at least carbon dioxide and methane. Further, the gas separation membrane of the present invention is excellent in separation of oxygen and nitrogen, and is useful as a gas separation membrane for separating oxygen from a gas (for example, air) containing oxygen and nitrogen.

The gas separation membrane of the present invention contains at least polyimide (1). In the gas separation membrane of the present invention, the content of the polyimide (1) is preferably 40% by mass or more, more preferably 80% by mass or more, and particularly preferably only the polyimide (1).

In order to adjust film physical properties, various polymer compounds other than polyimide (1) may be contained as components. Examples of such a polymer compound include acrylic resins, silicone resins, polyurethane resins, polyamide resins, polyimide resins, polyamideimide resins, polyester resins, epoxy resins, phenol resins, bismaleimide resins, polycarbonate resins, polyvinyl butyral resins, polyvinyl resins. Formal resin, vinyl resin, rubber, wax, shellac and other natural resins can be used. Also. Two or more of these may be used in combination.

The temperature when heating (baking) the polyimide (1) contained in the gas separation membrane of the present invention is preferably 50 ° C. or higher and 400 ° C. or lower, more preferably 100 ° C. or higher and 325 ° C. or lower. In particular, it is preferably 150 ° C. or higher and 320 ° C. or lower. When the heating temperature is lower than 50 ° C., it is difficult to obtain a dense separation layer as a gas separation membrane. When the heating temperature is higher than 400 ° C., there is a concern about thermal decomposition of polyimide (1), and it is used as a gas separation membrane. It is difficult to obtain a sufficient mechanical strength.

The heating time is preferably 30 minutes or longer and 24 hours or shorter, more preferably 1 hour or longer and 12 hours or shorter.

4). Performance gas permeability coefficient of the gas separation membrane, especially CO ₂ permeability coefficient under the conditions of 150 kPa, 50 ° C., CO ₂ permeability coefficient is preferably 10 barrels (Barrer) above. Under the conditions of 150 kPa and 50 ° C., the permeability coefficient ratio between carbon dioxide and methane (CO ₂ permeability coefficient / CH ₄ permeability coefficient) is preferably 40 or more, particularly preferably 42 or more, and further preferably 45 or more.

Above all, under conditions of 150 kPa and 50 ° C., the gas permeability coefficient is a CO ₂ permeability coefficient of 10 barr or more, and the permeability coefficient ratio between carbon dioxide and methane (CO ₂ permeability coefficient / CH ₄ permeability coefficient). Is more preferably 45 or more, because it is a gas separation membrane that satisfies both high permeability and very excellent gas selectivity at the same time, and is particularly preferable.

The gas separation performance of the gas separation membrane of the present invention is that the CO ₂ permeability coefficient is 10 barrels or more at 50 ° C., and the permeability coefficient ratio (CO ₂ permeability coefficient / CH ₄ permeability coefficient) between carbon dioxide and methane is 40 or more. It is.

As described in the examples, when the gas separation membrane of the present invention is used, the CO ₂ permeability coefficient is 10 Barrer or more under the conditions of 150 kPa and 50 ° C., and the permeability coefficient ratio (CO 2) between carbon dioxide and methane. ₍₂ permeability coefficient / CH ₄ permeability coefficient) of 40 or more can be obtained, and high carbon dioxide permeability and gas selectivity can be satisfied simultaneously.

5). Shape of Gas Separation Membrane 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 can serve as a support for maintaining the membrane shape. Become. The shape of the asymmetric membrane may be, for example, a flat membrane shape or a hollow fiber membrane shape.

In the case of a symmetric film, the thickness is preferably 500 nm or more and 1 mm or less, more preferably 10 μm or more and 100 μm or less. If it is thinner than 500 nm, the film formation is not easy and it is easy to break, and if it is thicker than 1 mm, the gas hardly penetrates.

When the asymmetric film is formed into a flat film, the thickness of the dense layer is preferably 10 nm or more and 10 μm or less, and more preferably 30 nm or more and 1 μm or less. If it is thinner than 10 nm, the film formation is not easy and it is easy to break, and if it is thicker than 10 μm, the gas hardly penetrates. The layer thickness of the porous layer is preferably 5 μm or more and 2 mm or less, more preferably 10 μm or more and 500 μm or less. If it is thinner than 5 μm, it is not easy to form a film and it is easy to break.

When the asymmetric membrane is a hollow fiber membrane, the outer side is preferably a dense layer and the inner side is preferably a porous layer, and the inner diameter is preferably 10 μm or more and 4 mm or less, more preferably 20 μm or more. The outer diameter, which is 1 mm or less, is preferably 30 μm or more and 8 mm or less, and more preferably 50 μm or more and 1.5 mm or less. When the inner diameter is less than 10 μm and the outer diameter is less than 30 μm, it is difficult to produce a hollow fiber membrane, and when the inner diameter is less than 1 mm and the outer diameter is less than 8 mm, it is not suitable for practical use as a hollow fiber membrane-shaped gas separation membrane.

6). Method for Producing Gas Separation Membrane The gas separation membrane of the present invention is a solution in which polyimide (1) is dissolved in an organic solvent, and is usually used for spin coating, spray coating, flow coating, impregnation coating, brush coating, etc. on a substrate. After coating by the method, it can be produced by forming or forming the film as it is.

The kind of organic solvent should just be what melt | dissolves a polyimide (1) and volatilizes below a heating temperature, Preferably, the kind of organic solvent shown by the manufacturing method of the polyimide (1) of (A) is used. Can do. Moreover, you may use the solution of the said polyimide (1) used with the manufacturing method of the polyimide of (A). The obtained gas separation membrane is preferably heated at a temperature of 50 ° C. or more and 400 ° C. or less after film formation or at the time of molding.

Moreover, the solution of the polyamic acid obtained by the manufacturing method of the polyimide (1) of (A) is applied on a substrate, and the organic solvent is volatilized by heating at a heating temperature of 50 ° C. or more and 400 ° C. or less. At the same time, the dehydration ring-closure reaction is allowed to proceed to form a polyimide (1) membrane, which can be used as the gas separation membrane of the present invention.

The concentration of the polyimide (1) or the polyamic acid that is a precursor thereof in the solution is preferably 5% by mass or more and 50% by mass or less, and more preferably 10% by mass or more and 40% by mass or less. . The solution to be applied is a solution of polyimide (1) or polyamic acid poured into a poor solvent to precipitate, collect and dry the polyimide (1) polyamic acid, and then re-dissolved in an organic solvent. It may be used.

In manufacturing a gas separation membrane, the substrate on which the polyimide (1) solution or the polyamic acid solution that is a precursor thereof is applied includes glass, silicon wafer, metal, metal oxide, ceramics, or resin. Can do.

When producing a symmetrical membrane as the gas separation membrane of the present invention, when using the above-mentioned polyamic acid solution, for example, after wet application to a substrate such as a glass substrate using a spin coater or applicator, air, By heating in a dry gas such as nitrogen or argon, the fired body is obtained through evaporation of the organic solvent and the cyclization dehydration reaction, and then the fired body is peeled off from the substrate. When using a solution of polyimide (1), for example, after applying it to a substrate such as a glass substrate or PTFE (polytetrafluoroethylene) substrate using a spin coater or an applicator, a dry gas such as air, nitrogen, or argon It is obtained by peeling from the base material after obtaining a fired body by evaporating the organic solvent by heating in.

When producing the gas separation membrane of the present invention, as a method for obtaining an asymmetric membrane, specifically, a solution of polyimide (1) is placed in a pressure vessel and is compatible with an organic solvent in the solution from its discharge port. The polyimide is discharged into a bath filled with a poor solvent that does not dissolve, and the solvent present in the vicinity of the surface of the obtained polyimide film is evaporated in the air to form a dense layer on the surface side. A method of forming the porous layer can be exemplified.

In this case, water or a mixed solution of water and an organic solvent is preferably used as the poor solvent. The composition of this mixed solution is such that when a mixed solution of water and an organic solvent is used, water is 30% by mass or more and 90% by mass or less, preferably 40% by mass or more and 80% by mass with respect to the total mass of the mixed solution % Or less is preferably included. Examples of the organic solvent include alcohol solvents and ketone solvents.

Specific examples of the alcohol solvent include methanol, ethanol, and isopropanol. Examples of the ketone solvent include acetone, methyl ethyl ketone, diethyl ketone, and diethyl ketone.

When producing a composite membrane as the gas separation membrane of the present invention, a coating liquid containing polyimide (1) is applied on a porous support (porous support) to form a gas separation layer. Is preferred. Although content of the polyimide (1) in a coating liquid is not specifically limited, It is preferable that it is 0.1 to 30 mass%, and it is especially 0.3 to 10 mass% especially. preferable. If the content of the polyimide (1) is too low, it is not preferable because it penetrates into the porous region when a film is formed on the support and a defect occurs on the surface of the separation layer. On the other hand, if the content is too high, the porous portion is filled at a high concentration, the separation layer is also thickened, and the permeability may be lowered. By adjusting the molecular weight, structure, and solution viscosity of the polyimide (1), the composite film can be appropriately produced. When manufacturing the composite membrane, another layer such as a siloxane compound may be present between the polyimide (1) and the porous support layer in order to smooth the surface of the support layer.

Examples of porous support materials include polyolefin resins such as polyethylene and polypropylene, fluorine-containing resins such as polytetrafluoroethylene, polyvinyl fluoride, and polyvinylidene fluoride, polystyrene, cellulose acetate, polyurethane, polyacrylonitrile, polyphenylene oxide, and polysulfone. And various resins such as polyethersulfone, polyimide, polyamide, and polyamideimide.

7). Gas Separation Method The gas separation method of the present invention uses a gas separation membrane containing the polyimide (1) of the present invention. This is a method for separating a specific kind of gas from a gas containing at least two kinds of gases.

The gas separation method of the present invention exhibits particularly excellent performance when the gas contains an acidic gas such as carbon dioxide. The gas separation method of the present invention is preferably used for separation of a gas containing carbon dioxide and hydrocarbons, particularly a gas containing carbon dioxide and methane, because the gas separation membrane of the present invention is particularly excellent in carbon dioxide permeability. In particular, carbon dioxide or methane can be suitably separated with good selectivity from a gas containing carbon dioxide and methane.

When the gas separation method of the present invention is used, a CO ₂ permeability coefficient of 10 barrels or more is obtained at 50 ° C., and a permeability coefficient ratio (CO ₂ permeability coefficient / CH ₄ permeability coefficient) between carbon dioxide and methane is 40 or more. can get.

As described in the examples, when the gas separation method of the present invention is used, a CO ₂ permeability coefficient of 10 barr or more and a permeability coefficient ratio of carbon dioxide and methane (150 bar, 50 ° C.) CO ₂ permeability coefficient / CH ₄ permeability coefficient) of 40 or more can be obtained, and high carbon dioxide permeability and gas selectivity can be satisfied at the same time.

It is preferable to separate a gas containing carbon dioxide and methane, particularly natural gas, at 35 ° C. or higher and 70 ° C. or lower. More preferably, it is 40 degreeC or more and 60 degrees C or less. More preferably, it is 45 degreeC or more and 55 degrees C or less.

[gas]
Although the gas which the gas separation membrane of this invention isolate | separates is not specifically limited, It is a gas containing 2 or more types of gas, Preferably it is a gas containing a carbon dioxide and a hydrocarbon, Especially, a carbon dioxide and methane are included. It is a gas. The abundance ratio of carbon dioxide with respect to the total amount of gas including carbon dioxide and methane is preferably 1% or more and 80% or less, more preferably 5% or more and 60% or less, and more preferably expressed in mass%. Is 7% or more and 50% or less.

The type of gas other than carbon dioxide and methane is not particularly limited, but other than hydrogen, helium, carbon monoxide, hydrogen sulfide, oxygen, nitrogen, ammonia, sulfur oxide (SOx), nitrogen oxide (NOx), and methane And hydrocarbons, unsaturated hydrocarbons, perfluoro compounds and the like. Here, as hydrocarbons other than methane, ethane, propane, butane or pentane can be exemplified, and as unsaturated hydrocarbons, ethylene and propylene can be exemplified. Tetrafluoroethane can be raised as the perfluoro compound.

Specific examples of the gas to be separated by the gas separation membrane of the present invention include natural gas, which is effective for separating and purifying hydrocarbons, which are combustible gas components, by separating incombustible gas contained in natural gas. Can be used.

Specific examples of the gas separated by the gas separation membrane of the present invention include biogas, and methane, which is a low-permeability gas, is preferably used for separation and purification from biogas containing methane and carbon dioxide. Can do.

Specific examples of the gas to be separated by the gas separation membrane of the present invention include a mixed gas obtained by an oil recovery enhancement method (EOR). From a mixed gas containing methane and carbon dioxide, a low permeability gas can be used. Certain methane can be suitably used for separation and purification. Further, the separated and recovered carbon dioxide can be used as a drop for EOR gas.

8). Gas Separation Device The gas separation membrane of the present invention can be used in a gas separation device as a means for separating and recovering or purifying gas.

The gas separation membrane of the present invention can be suitably used as a gas separation membrane module by being housed in a housing. Examples of the gas separation membrane module include a spiral type, a hollow fiber membrane type, a pleat type, a tubular type, and a plate & frame type.

Further, the gas separation membrane of the present invention may be used as a gas separation membrane module, for example, in a gas separation / recovery device by a membrane / absorption hybrid method used in combination with an absorbing solution described in Patent Document 6.

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

　ポリイミド（Ａ）のＤＭＡｃ溶液のゲル・パーミエーション・クロマトグラフィ（ＧＰＣ）による分子量の測定結果は、Ｍｗ＝７１０００、Ｍｗ／Ｍｎ＝３．０であった。なお、ＧＰＣには、東ソー株式会社製、機種名：ＨＬＣ－８３２０ＧＰＣ、カラム：ＴＳＫｇｅｌ ＳｕｐｅｒＨＺＭ－Ｈを用い、展開溶媒にはテトラヒドロフラン（ＴＨＦ）を用いた。Ｍｗは重量平均分子量、Ｍｎは数平均分子量である。 [Example 1]
[Production of gas separation membrane made of polyimide (A)]
<Preparation of polyimide (A)>
20.0 g (73 mmol) of HFIP-pPD and 26.1 g (73 mmol) of DSDA represented by the following formula were added to a 500-mL three-necked flask equipped with a nitrogen introduction tube and a stirring blade, and dimethylacetamide (73 mmol) as a solvent was further added. After adding 85 g of DMAc), the mixture was stirred at room temperature (20 ° C.) under a nitrogen atmosphere to obtain a reaction solution. To the obtained reaction solution, 12.1 g (153 mmol) of pyridine and 15.6 g (153 mmol) of acetic anhydride were sequentially added, and the mixture was further stirred for 24 hours to perform imidization. Thereafter, DMAc (58 g) was added to dilute the reaction solution after imidization, followed by pressure filtration to prepare a DMAc solution of polyimide (A) represented by the following formula.

The measurement result of the molecular weight by the gel permeation chromatography (GPC) of the DMAc solution of polyimide (A) was Mw = 71000 and Mw / Mn = 3.0. For GPC, Tosoh Corporation model name: HLC-8320GPC, column: TSKgel SuperHZM-H was used, and tetrahydrofuran (THF) was used as a developing solvent. Mw is a weight average molecular weight and Mn is a number average molecular weight.

<Production of gas separation membrane>
The prepared DMAc solution of polyimide (A) is hung on a glass substrate, and the rotation speed is increased to 1000 rpm over 10 seconds using a spin coater, and then the rotation is maintained for 10 seconds, uniformly on the glass substrate. Applied. Drying at 180 ° C. for 30 minutes in a nitrogen atmosphere to remove the solvent, heating at 250 ° C. for 2 hours, cooling, and peeling the polyimide film from the glass substrate to separate the gas from the polyimide (A) A membrane was obtained. When measured with a film thickness meter, the film thickness was 38 μm. As the film thickness meter, model name: DIGIMICRO MH-15 manufactured by Nikon Corporation was used.

　実施例1と同じ機器を用いて同様に測定したポリイミド（Ｂ）の分子量は、Ｍｗ＝８６６００、Ｍｗ／Ｍｎ＝２．７であった。 [Example 2]
[Production of gas separation membrane made of polyimide (B)]
<Preparation of polyimide (B)>
In a 500 mL three-necked flask equipped with a nitrogen introduction tube and a stirring blade, 20.0 g (73 mmol) of HFIP-pPD represented by the following formula, 13.1 g (36.5 mmol) of DSDA, and 16.2 g of 6FDA ( 36.5 mmol), and 98 g of DMAc was added as a solvent, followed by stirring at room temperature under a nitrogen atmosphere to obtain a reaction solution. To the obtained reaction solution, 12.1 g (153 mmol) of pyridine and 15.6 g (153 mmol) of acetic anhydride were sequentially added, and the mixture was further stirred for 24 hours to perform imidization. Then, the DMAc solution of the polyimide (B) shown to the following formula | equation was prepared by carrying out pressure filtration.

The molecular weight of the polyimide (B) measured similarly using the same apparatus as Example 1 was Mw = 86600 and Mw / Mn = 2.7.

<Production of gas separation membrane>
The prepared DMAc solution of polyimide (B) is hung on a glass substrate, and the rotation speed is increased to 400 rpm over 10 seconds using a spin coater. Then, the rotation is maintained for 10 seconds, and uniformly on the glass substrate. Applied. In a nitrogen atmosphere, the solvent is removed by drying at 180 ° C. for 30 minutes, and after heating at 250 ° C. for 2 hours, the gas separation membrane is formed of the polyimide (B) by cooling and peeling the polyimide membrane from the glass substrate. Got. When measured with the same film thickness meter as used in Example 1, the film thickness was 41 μm.

　実施例1と同じ機器を用いて同様に測定したポリイミド（Ｃ）の分子量は、Ｍｗ＝５５１００、Ｍｗ／Ｍｎ＝２．８であった。 [Example 3]
[Production of gas separation membrane made of polyimide (C)]
<Preparation of polyimide (C)>
In a 500 mL three-necked flask equipped with a nitrogen introduction tube and a stirring blade, 20.0 g (73 mmol) of HFIP-pPD represented by the following formula, 13.1 g (36.5 mmol) of DSDA, and 10.7 g of BPDA ( 36.5 mmol), and 81 g of DMAc was added as a solvent, followed by stirring at room temperature under a nitrogen atmosphere to obtain a reaction solution. To the obtained reaction solution, 12.1 g (153 mmol) of pyridine and 15.6 g (153 mmol) of acetic anhydride were sequentially added, and the mixture was further stirred for 24 hours to perform imidization. Thereafter, a DMAc solution of polyimide (C) represented by the following formula was prepared by filtration under pressure.

The molecular weight of polyimide (C) measured in the same manner using the same equipment as in Example 1 was Mw = 55100 and Mw / Mn = 2.8.

<Production of gas separation membrane>
The prepared DMAc solution of polyimide (C) is hung on a glass substrate, and the rotation speed is increased to 1100 rpm over 10 seconds using a spin coater. Then, the rotation is maintained for 10 seconds, and uniformly on the glass substrate. Applied. In a nitrogen atmosphere, the solvent is removed by drying at 180 ° C. for 30 minutes, and after heating at 250 ° C. for 2 hours, the gas separation membrane is made of the polyimide (C) by cooling and peeling the polyimide membrane from the glass substrate. Got. When measured with the same film thickness meter as used in Example 1, the film thickness was 57 μm.

　実施例1と同じ機器を用いて同様に測定したポリイミド（Ｐ１）の分子量は、Ｍｗ＝６３６００、Ｍｗ／Ｍｎ＝２．１であった。 [Comparative Example 1]
[Production of gas separation membrane made of polyimide (P1)]
<Preparation of polyimide (P1)>
30.0 g (151 mmol) of MDA represented by the following formula and 67.2 g (151 mmol) of 6FDA were added to a 500 mL three-necked flask equipped with a nitrogen introduction tube and a stirring blade, and 277 g of DMAc was added as a solvent. The reaction solution was obtained by stirring at room temperature under an atmosphere. To the obtained reaction solution, 47.9 g (605 mmol) of pyridine and 67.8 g (605 mmol) of acetic anhydride were added in this order, and the mixture was further stirred for 24 hours to perform imidization. Thereafter, a DMAc solution of polyimide (P1) represented by the following formula was prepared by filtration under pressure.

The molecular weight of polyimide (P1) measured in the same manner using the same equipment as in Example 1 was Mw = 63600 and Mw / Mn = 2.1.

<Production of gas separation membrane>
The prepared DMAc solution of polyimide (P1) is dropped on a glass substrate, and the spin coater is used to increase the rotation speed to 700 rpm over 10 seconds. Then, the rotation is maintained for 10 seconds and uniformly on the glass substrate. Applied. Drying at 180 ° C. for 30 minutes in a nitrogen atmosphere to remove the solvent, heating at 250 ° C. for 2 hours, cooling, and peeling the polyimide membrane from the glass substrate, thereby forming a gas separation membrane comprising the polyimide (P1) Got. When measured with the same film thickness meter as used in Example 1, the film thickness was 35 μm.

　実施例1と同じ機器を用いて同様に測定したポリイミド（Ｐ２）の分子量は、Ｍｗ＝１０６０００、Ｍｗ／Ｍｎ＝２．２であった。 [Comparative Example 2]
[Production of gas separation membrane made of polyimide (P2)]
<Preparation of polyimide (P2)>
After adding 10.0 g (92 mmol) of pPD shown in the following formula and 41.1 g (92 mmol) of 6FDA to a 500 mL three-neck flask equipped with a nitrogen introduction tube and a stirring blade, and adding 100 g of DMAc as a solvent, The reaction solution was obtained by stirring at 20 ° C. in an atmosphere. To the obtained reaction solution, 15.4 g (194 mmol) of pyridine and 19.8 g (194 mmol) of acetic anhydride were added in this order, and the mixture was further stirred for 24 hours for imidization. Then, the DMAc solution of the polyimide (P2) shown below was prepared by carrying out pressure filtration.

The molecular weight of polyimide (P2) measured in the same manner using the same equipment as in Example 1 was Mw = 106000 and Mw / Mn = 2.2.

<Production of gas separation membrane>
The prepared DMAc solution of polyimide (P2) is dropped on a glass substrate, and the rotation speed is increased to 1000 rpm over 10 seconds using a spin coater. Then, the rotation is maintained for 10 seconds, and uniformly on the glass substrate. Applied. Drying at 180 ° C. for 30 minutes in a nitrogen atmosphere to remove the solvent, heating at 250 ° C. for 2 hours, cooling, and peeling the polyimide membrane from the glass substrate to form a gas separation membrane made of the polyimide (P2) Got. When the film thickness was measured with the same film thickness meter used in Example 1, the film thickness was 41 μm when measured with the film thickness meter.

　実施例1と同じ機器を用いて同様に測定したポリイミド（Ｐ３）の分子量は、Ｍｗ＝９１０００、Ｍｗ／Ｍｎ＝３．２であった。 [Comparative Example 3]
[Production of gas separation membrane made of polyimide (P3)]
<Preparation of polyimide (P3)>
After adding 30.0 g (56 mmol) of HFIP-MDA and 20.2 g (56 mmol) of DSDA, and 100 g of DMAc as a solvent, to a 500 mL three-necked flask equipped with a nitrogen introduction tube and a stirring blade The mixture was stirred at room temperature under a nitrogen atmosphere to obtain a reaction solution. To the obtained reaction solution, 9.4 g (118 mmol) of pyridine and 12.1 g (118 mmol) of acetic anhydride were added in this order, and the mixture was further stirred for 24 hours to perform imidization. Then, the DMAc solution of the polyimide (P3) shown below was prepared by carrying out pressure filtration.

The molecular weight of polyimide (P3) measured in the same manner using the same equipment as in Example 1 was Mw = 91000 and Mw / Mn = 3.2.

<Production of gas separation membrane>
The prepared DMAc solution of polyimide (P3) is dropped on a glass substrate, and the spin coater is used to increase the rotation speed to 700 rpm over 10 seconds. Then, the rotation is maintained for 10 seconds, and uniformly on the glass substrate. Applied. Drying at 180 ° C. for 30 minutes in a nitrogen atmosphere to remove the solvent, heating at 300 ° C. for 2 hours, cooling, and peeling the polyimide membrane from the glass substrate, thereby forming a gas separation membrane made of the polyimide (P3) Got. When measured with the same film thickness meter used in Example 1, the film thickness was 43 μm.

　実施例1と同じ機器を用いて同様に測定したポリイミド（Ｐ４）の分子量は、Ｍｗ＝６７６００、Ｍｗ／Ｍｎ＝２．３であった。 [Comparative Example 4]
[Gas separation membrane made of polyimide (P4)]
<Preparation of polyimide (P4)>
To a 500 mL three-necked flask equipped with a nitrogen introduction tube and a stirring blade, 12.5 g (23.5 mmol) of HFIP-ODA and 8.4 g (23.5 mmol) of DSDA represented by the following formula were added, and DMAc was used as a solvent. After adding 31 g, the mixture was stirred at room temperature under a nitrogen atmosphere to obtain a reaction solution. To the resulting reaction solution, 3.9 g (49 mmol) of pyridine and 5.0 g (49 mmol) of acetic anhydride were added in this order, and the mixture was further stirred for 24 hours for imidization. Then, the DMAc solution of the polyimide (P4) shown in the following reaction formula was prepared by carrying out pressure filtration.

The molecular weight of the polyimide (P4) measured in the same manner using the same equipment as in Example 1 was Mw = 67600 and Mw / Mn = 2.3.

<Production of gas separation membrane>
The prepared DMAc solution of polyimide (P4) is hung on a glass substrate, and the spin coater is used to increase the rotation speed to 300 rpm over 10 seconds. Then, the rotation is maintained for 10 seconds and uniformly on the glass substrate. Applied. After removing the solvent by drying at 180 ° C. for 30 minutes in a nitrogen atmosphere, heating at 250 ° C. for 2 hours, cooling, and peeling the polyimide membrane from the glass substrate, the gas separation membrane comprising the polyimide (P4) Got. As a result of performing the gas separation performance test described below, the obtained gas separation membrane had the same CO ₂ permeability coefficient and CH ₄ permeability coefficient, and did not exhibit gas separation selectivity.

　実施例1と同じ機器を用いて同様に測定したポリイミド（Ｐ５）の分子量は、Ｍｗ＝７２０００、Ｍｗ／Ｍｎ＝３．１であった。 [Comparative Example 5]
[Production of gas separation membrane made of polyimide (P5)]
<Preparation of polyimide (P5)>
To a 500 mL three-necked flask equipped with a nitrogen inlet tube and a stirring blade, 29.3 g (55 mmol) of HFIP-ODA and 16.2 g (55 mmol) of BPDA shown below were added, and 100 g of DMAc was added as a solvent. And stirred at room temperature to obtain a reaction solution. To the obtained reaction solution, 17.9 g (220 mmol) of pyridine and 22.5 g (220 mmol) of acetic anhydride were added in this order, and the mixture was further stirred for 24 hours for imidization. Then, the DMAc solution of the polyimide (P5) shown in the following reaction formula was prepared by carrying out pressure filtration.

The molecular weight of polyimide (P5) measured in the same manner using the same equipment as in Example 1 was Mw = 72000 and Mw / Mn = 3.1.

<Production of gas separation membrane>
The prepared DMAc solution of polyimide (P5) is dropped on a glass substrate, and the spin coater is used to increase the rotation speed to 450 rpm over 10 seconds. Then, the rotation is maintained for 10 seconds and uniformly applied onto the glass substrate. did. In a nitrogen atmosphere, the solvent is removed by drying at 180 ° C. for 30 minutes, and after heating at 250 ° C. for 2 hours, the gas separation membrane is made of the polyimide (P5) by cooling and peeling the polyimide membrane from the glass substrate. Got. When the film thickness was measured with the same film thickness meter used in Example 1, the film thickness was 66 μm.

　実施例1と同じ機器を用いて同様に測定したポリイミド（Ｐ６）の分子量は、Ｍｗ＝７７５００、Ｍｗ／Ｍｎ＝２．６であった。 [Comparative Example 6]
[Production of gas separation membrane made of polyimide (P6)]
<Preparation of polyimide (P6)>
After adding 18.0 g (66 mmol) of HFIP-pPD and 21.1 g (66 mmol) of BTDA and 60 g of DMAc as a solvent to a 500 mL three-necked flask equipped with a nitrogen introduction tube and a stirring blade, A stirred reaction solution was obtained at room temperature under a nitrogen atmosphere. To the obtained reaction solution, 20.8 g (263 mmol) of pyridine and 26.8 g (263 mmol) of acetic anhydride were added in this order, and the mixture was further stirred for 24 hours to perform imidization. Then, the DMAc solution of the polyimide (P6) shown below was prepared by carrying out pressure filtration.

The molecular weight of the polyimide (P6) measured in the same manner using the same equipment as in Example 1 was Mw = 77500 and Mw / Mn = 2.6.

<Production of gas separation membrane>
The prepared DMAc solution of polyimide (P6) is dropped on a glass substrate, and the rotation speed is increased to 300 rpm over 10 seconds using a spin coater. Then, the rotation is maintained for 10 seconds, and uniformly on the glass substrate. Applied. In a nitrogen atmosphere, the solvent is removed by drying at 180 ° C. for 30 minutes, and after heating at 250 ° C. for 2 hours, the gas separation membrane is made of the polyimide (P6) by cooling and peeling the polyimide membrane from the glass substrate. Got. When measured with the same film thickness meter used in Example 1, the film thickness was 50 μm.

　実施例1と同じ機器を用いて同様に測定したポリイミド（Ｐ７）の分子量は、Ｍｗ＝８５９００、Ｍｗ／Ｍｎ＝３．３であった。 [Comparative Example 7]
[Production of gas separation membrane made of polyimide (P7)]
<Preparation of polyimide (P7)>
After adding 20.0 g (73 mmol) of HFIP-pPD and 22.6 g (73 mmol) of HFPA and 100 g of DMAc as a solvent to a 500 mL three-necked flask equipped with a nitrogen introduction tube and a stirring blade, a nitrogen atmosphere was added. Under stirring at room temperature, a reaction solution was obtained. To the obtained reaction solution, 12.1 g (153 mmol) of pyridine and 15.6 g (153 mmol) of acetic anhydride were sequentially added, and the mixture was further stirred for 24 hours to perform imidization. Then, the DMAc solution of the polyimide (P7) shown below was prepared by carrying out pressure filtration.

The molecular weight of polyimide (P7) measured in the same manner using the same equipment as in Example 1 was Mw = 85900 and Mw / Mn = 3.3.

<Production of gas separation membrane>
The prepared DMAc solution of polyimide (P7) is hung on a glass substrate, and the spin coater is used to increase the rotation speed to 700 rpm over 10 seconds. Then, the rotation is maintained for 10 seconds and uniformly on the glass substrate. Applied. Drying at 180 ° C. for 30 minutes in a nitrogen atmosphere to remove the solvent, heating at 250 ° C. for 2 hours, cooling, and peeling the polyimide membrane from the glass substrate to form a gas separation membrane made of the polyimide (P7) Got. When the film thickness was measured with the same film thickness meter as used in Example 1, the film thickness was 63 μm.

[Evaluation of gas separation performance]
The gas permeation coefficient of the gas separation membranes prepared in Examples 1 to 3 and Comparative Examples 1 to 7 was measured in accordance with JIS K 7126-1: 2006 “Plastics-Film and Sheet—Gas Permeability Test Method”. did. In this measurement, a differential pressure type gas permeability measuring device (model GTR-30AS manufactured by GTR Tech Co., Ltd.) was used. Specifically, a stainless steel cell membrane area 3.14 cm ² or more, arranged 15.2 cm ² or less of a gas separation membrane, 35 ° C., 0.15 MPa at 50 ° C. or 70 ° C., the supply pressure of methane As a result, the permeability coefficient of methane was measured. Next, carbon dioxide was used instead of methane, and the carbon dioxide permeability coefficient was measured in the same manner. From the measured permeability coefficient of methane and carbon dioxide, the ratio of permeability coefficient between methane and carbon dioxide (CO ₂ permeability coefficient / CH ₄ permeability coefficient) was calculated. The permeability coefficient ratio is an indicator of gas selectivity.

Table 1 shows the methane permeability coefficient, the carbon dioxide permeability coefficient, and the permeability coefficient measured at 35 ° C., 50 ° C. or 70 ° C. using the gas separation membranes prepared in Examples 1 to 3 and Comparative Examples 1 to 7 above. The ratio (CO ₂ permeability coefficient / CH ₄ permeability coefficient) is shown.

The gas separation performance of the gas separation membrane is greater for the gas of methane and carbon dioxide, the greater the permeability coefficient of carbon dioxide, the better the gas throughput per unit time, and the greater the permeability coefficient ratio, the greater the ratio of methane and carbon dioxide. Excellent separation performance.

As shown in Table 1, the gas separation membrane of the present invention containing the HFIP group and the polyimide having the structure derived from phenylenediamine or the structure derived from DSDA prepared in Examples 1 to 3 was compared with Comparative Example 1 and Comparative Example 1. Compared with the gas separation membrane prepared in Example 2 and containing a polyimide having no structure derived from HFIP groups and DSDA, the permeation coefficient ratio is large and the separation performance of methane and carbon dioxide is excellent in a 50 ° C. measurement environment. It was.

Further, the gas separation membranes prepared in Examples 1 to 3 and including the polyimide having the structure derived from HFIP group and phenylenediamine and the structure derived from DSDA have the structures derived from HFIP group and DSDA in Comparative Examples 3 and 4. Compared with a gas separation membrane containing polyimide having no structure derived from phenylenediamine, the permeability coefficient ratio was large at 35 ° C. and 50 ° C., and the separation performance of methane and carbon dioxide was excellent.

In addition, the gas separation membranes prepared in Examples 1 to 3 have a HFIP group of Comparative Example 5 and are 35% more than the gas separation membrane containing polyimide not having a structure derived from DSDA and a structure derived from phenylenediamine. At ℃ and 50 ℃, the permeability coefficient ratio was large, and the separation performance of methane and carbon dioxide was excellent.

The gas separation membranes prepared in Examples 1 to 3 are gas separations containing polyimide prepared in Comparative Example 6 or Comparative Example 7 having a structure derived from HFIP groups and phenylenediamine and not having a structure derived from DSDA. Compared with the membrane, the permeability coefficient ratio was large at 35 ° C. and 50 ° C., and the separation performance of methane and carbon dioxide was excellent.

In addition, the gas separation membrane prepared in Example 1 is compared with the gas separation membrane prepared in Comparative Example 3, which includes a polyimide having a structure derived from HFIP group and DSDA and not having a structure derived from phenylenediamine. At 70 ° C., the permeability coefficient ratio was large and the separation performance of methane and carbon dioxide was excellent.

The gas separation membrane of the present invention containing the polyimide having both the structure derived from HFIP group and phenylenediamine and the structure derived from DSDA prepared in Examples 1 to 3 is used when carbon dioxide is separated from natural gas by a gas separation membrane. In the temperature range of 35 ° C. to 70 ° C. that is practically used, the carbon dioxide removal ability is superior to that of the conventional gas separation membrane, and high-purity methane can be obtained without loss of methane in the separation process.

[Evaluation of gas separation performance for oxygen (0 ₂ ) and nitrogen (N ₂ ) mixed gas]
The gas permeability coefficient of the gas separation membranes prepared in Examples 1 to 3 and Comparative Examples 5 to 7 was measured according to JIS K 7126-1: 2006 “Plastics-Film and Sheet—Gas Permeability Test Method”. did. In this measurement, a differential pressure type gas permeability measuring device (model GTR-30AS manufactured by GTR Tech Co., Ltd.) was used. Specifically, membrane area 3.14 cm ² or more in a stainless steel cell, place the 15.2 cm ² or less of a gas separation membrane, at 35 ° C. or 50 ° C., the oxygen gas (0 ₂₎ supply pressure 0. The permeability coefficient of oxygen gas (0 ₂ ) was measured at 15 MPa. Next, nitrogen gas (N ₂ ) was used instead of oxygen gas (0 ₂ ), and the permeability coefficient of nitrogen gas (N ₂ ) was measured in the same manner. From the measured permeability coefficients of oxygen gas (0 ₂ ) and nitrogen gas (N ₂ ), the permeability coefficient ratio of nitrogen gas (N ₂ and oxygen gas (0 ₂ )) (nitrogen gas (N ₂ ) / oxygen gas (0 ₂₎ ) Transmission coefficient). The permeability coefficient ratio is an indicator of gas selectivity.

Table 2 shows the oxygen permeability coefficient, nitrogen permeability coefficient, and permeability coefficient ratio (O ₂₎ measured at 35 ° C. or 50 ° C. using the gas separation membranes prepared in Examples 1 to 3 and Comparative Examples 5 to 7 above. Transmission coefficient / N ₂ transmission coefficient).

If the gas separation membrane of the present invention is used, the oxygen concentration of air can be increased and a gas having a high oxygen concentration can be obtained.

Claims (17)

A gas separation membrane comprising a polyimide having a repeating unit represented by formula (1).

(In formula (1), R ¹ is a divalent organic group represented by formula (2).)

(In the formula (2), R ² is a hydrogen atom, an alkyl group or a fluoroalkyl group, and a is an integer of 1 to 2) The gas separation membrane according to claim 1, wherein the polyimide is a polyimide containing a repeating unit represented by the formula (3).

(In the formula (3), R ¹ is .R ³ R ¹ as synonymous of the formula (1) is any tetravalent organic group represented by the following equation.)

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

The gas separation membrane according to any one of claims 1 to 3, wherein the polyimide has a weight 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 4, wherein the polyimide heated at 50 ° C or higher and 400 ° C or lower is used. The gas separation membrane according to any one of claims 1 to 5, wherein the gas to be separated is a gas containing at least carbon dioxide and methane. The gas separation membrane according to claim 6, wherein the permeability coefficient of carbon dioxide at 50 ° C. and 150 kPa is 10 Barrer or more, and the permeability coefficient ratio (P _CO2 / P _CH4 ) between carbon dioxide and methane is 40 or more. The gas separation membrane according to claim 6 or 7, wherein the gas containing carbon dioxide and methane is natural gas. The gas separation method which isolate | separates methane from the gas containing a carbon dioxide and methane using the gas separation membrane of any one of Claim 6 thru | or 8. A gas separation method for separating carbon dioxide from a gas containing carbon dioxide and methane using the gas separation membrane according to any one of claims 6 to 8. The gas separation method according to claim 9 or 10, wherein gas separation is performed at 35 ° C or higher and 70 ° C or lower. A gas separation membrane module comprising the gas separation membrane according to any one of claims 1 to 8. A gas separation device comprising the gas separation membrane according to any one of claims 1 to 8. The gas separation membrane according to any one of claims 1 to 5, wherein the gas to be separated is a gas containing at least oxygen and nitrogen. The gas separation membrane according to claim 14, wherein the gas containing oxygen and nitrogen is air. A gas separation method for separating oxygen from a gas containing oxygen and nitrogen by using the gas separation membrane according to claim 14. A gas separation method for separating nitrogen from a gas containing oxygen and nitrogen using the gas separation membrane according to claim 14 or 15.

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