JP2015186804A - Method for manufacturing nitrogen-enriched air from hot gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for more conveniently and efficiently manufacturing nitrogen-enriched air to be used for explosion-proof of an aircraft or the like.SOLUTION: A method manufactures nitrogen-enriched air by supplying air of high temperature of 150°C or more to an air separation membrane module.

Description

  The present invention relates to a method for producing nitrogen-enriched air using an air separation membrane module that has high separation performance even at high temperatures and can maintain it for a long time.

  Some aircraft use an onboard inert gas generating system (OBIGGS) as one method of explosion-proofing a fuel tank. The oxygen concentration in the gas phase region in the fuel tank needs to be lower than a predetermined concentration in order to prevent the risk of explosion. Therefore, OBIGGS produces nitrogen-enriched air having a high nitrogen concentration by separating oxygen from the air, and supplies this to the fuel tank.

  OBIGGS produces nitrogen-enriched air, for example, with an air separation membrane module. The air separation membrane usually has a higher processing volume as the gas supplied is higher in pressure and temperature, so that the extracted gas of the engine and the surrounding air are compressed by a compressor or the like before being supplied to the air separation membrane module. . This compressed gas is usually 149-260 ° C.

  Conventional air separation membrane modules operate efficiently at about 82 ° C. to about 93 ° C., and cannot be used at such high temperatures because the separation performance is significantly reduced. Therefore, in general, the compressed gas is supplied to the air separation membrane module after being cooled to the temperature by using a heat exchanger or mixing with low-temperature air (Patent Document). 1).

JP 2010-142801 A

  An object of the present invention is to provide a method for producing nitrogen-enriched air by supplying high-temperature compressed air of 150 ° C. or higher to an air separation membrane module.

  The present invention relates to the following matters.

1. A method for producing nitrogen-enriched air from air using an air separation membrane module,
A method comprising supplying air at 150 ° C. or higher to an air separation membrane module.

2. The air separation membrane module is
At the start of use, the oxygen gas permeation rate ( _P′O2 ) at 175 ° C. is 20 × 10 ⁻⁵ cm ³ (STP) / cm ² · sec · cmHg or more, and the oxygen gas permeation rate and nitrogen gas at 175 ° C. The ratio to the transmission rate ( _P'O2 / _P'N2 ) is 1.8 or more, and
175 ° C. In 140 hours P _'O2 and P' _O2 / P when using _'N2 is, the use start before the P' that holds each 90% _O2 and P _'O2 / P' _N2 2. The method according to 1 above, which is characterized.

3. 3. The method according to 1 or 2 above, wherein the air separation membrane in the air separation membrane module is made of a material that does not exhibit a glass transition temperature below 225 ° C.

4). 4. The method according to any one of 1 to 3 above, wherein the air separation membrane exhibits a shape retention of 95% or more when placed at 175 ° C. for 2 hours.

5. An aircraft explosion-proof method, wherein nitrogen-enriched air is produced by the production method according to any one of 1 to 4 above and supplied to an aircraft fuel tank.

  According to the method of the present invention, high-temperature air, for example, 150 ° C. or higher, can be supplied to the air separation membrane module to obtain nitrogen-enriched air with an increased nitrogen concentration. The present invention is characterized by the use of an air separation membrane that has a high oxygen gas permeation rate and separation performance between oxygen and nitrogen at a high temperature and that can maintain the performance even when used at a high temperature for a long time. The present invention is suitable for an explosion-proof system for an aircraft fuel tank, for example. If this invention is used in this explosion-proof system, when supplying air to an air separation membrane module, the heat exchanger etc. for cooling high temperature air can be reduced in weight. In addition, since the air separation membrane has a higher permeation speed as the supplied air is higher in temperature, the method of the present invention that can process high-temperature air is efficient and requires a small membrane area. Therefore, the equipment in the aircraft can be simplified and reduced in weight.

The measurement result of Example 1 and Comparative Example 2 is shown. The measurement result of Example 1 and Example 2 is shown.

  The present invention is a method for generating nitrogen-enriched air from air using an air separation membrane module, characterized in that high-temperature air of 150 ° C. or higher is supplied to the air separation membrane module. In the present invention, unless otherwise specified, “high temperature” means 150 ° C. or higher, preferably 175 ° C. or higher, more preferably 200 ° C. or higher.

  In the air separation membrane module, for example, about 100 to 1,000,000 hollow fiber membranes of appropriate length are bundled, and at both ends of the hollow fiber bundle, at least one end of the hollow fiber is in an open state. The hollow fiber membrane element consisting of a hollow fiber bundle and a tube sheet obtained by fixing with a tube plate made of a thermosetting resin or the like, at least an air supply port, a permeate gas discharge port, and a non-permeate gas discharge port In a container provided with a space that communicates with the inside of the hollow fiber membrane and a space that communicates with the outside of the hollow fiber membrane. In such an air separation membrane module, air is supplied from the air supply port to a space in contact with the inside or outside of the hollow fiber membrane, and oxygen in the air selectively permeates the membrane while flowing in contact with the hollow fiber membrane. Permeate gas (oxygen-enriched air) is discharged from the permeate gas outlet, and non-permeate gas (nitrogen-enriched air) that has not permeated through the membrane is discharged from the non-permeate gas outlet, whereby gas separation is performed. .

  The air separation membrane used in the present invention is not particularly limited. For example, an extremely thin dense layer (preferably having a thickness of 0.001 to 5 μm) mainly responsible for air separation performance and a relatively thick thickness supporting the dense layer. Examples include an asymmetric air separation membrane having an asymmetric structure composed of a porous layer (preferably having a thickness of 10 to 2000 μm). A hollow fiber membrane having an inner diameter of 10 to 3000 μm and an outer diameter of about 30 to 7000 μm is preferable.

  The air separation membrane used in the present invention preferably has the following characteristics at high temperatures.

The air separation membrane used in the present invention preferably has a high oxygen gas permeation rate at a high temperature. For example, the oxygen transmission rate ( _P′O2 ) at 175 ° C. is 20 × 10 ⁻⁵ cm ³ (STP) / cm ² · sec · cmHg or more, preferably 25 × 10 ⁻⁵ cm ³ (STP) / cm ^2. It is at least sec · cmHg, more preferably at least 30 × 10 ⁻⁵ cm ³ (STP) / cm ² · sec · cmHg. Furthermore, the air separation membrane used in the present invention preferably has high separation performance even at high temperatures. For example, at 175 ° C., the ratio of the oxygen gas transmission rate and the nitrogen gas transmission rate ( _{P′O 2} / P ′ _N2 ) is 1.8 or more, preferably 2.0 or more, more preferably 2.5 or more. Note that the ratio of transmission speeds is usually larger at low temperatures. When the permeation rate ratio, that is, the separation performance is high, the recovery rate of the target nitrogen-enriched air becomes high.

In addition, the air separation membrane used in the present invention is preferably such that the oxygen gas permeation rate and membrane separation performance do not greatly deteriorate even when used for a long time at high temperatures. For example, when used at 175 ° C. for 140 hours, the oxygen transmission rate (P ′ _O2 ) and the ratio of the oxygen gas transmission rate to the nitrogen gas transmission rate (P ′ _O2 / P ′ _N2 ) It is preferably 75% or more of each of ' _O2 and _P'O2 / _P'N2 , more preferably 80% or more, and further preferably 90% or more.

  Furthermore, the shape of the air separation membrane used in the present invention is preferably maintained to such an extent that its function is not impaired even at high temperatures. For example, the glass transition temperature (Tg) of the material constituting the air separation membrane is preferably higher than 225 ° C. (that is, not shown below 225 ° C.), more preferably 250 ° C. or higher, more preferably 300 ° C. or higher (glass It is preferable that the transition temperature cannot be measured. Furthermore, it is preferable that the shape is maintained for a long time at a high temperature, and the shape retention when it is placed at 175 ° C. for 2 hours is preferably 95% or more, and more preferably 99% or more. Here, in the present invention, the shape retention rate refers to the ratio of the yarn length after heat treatment at 175 ° C. for 2 hours, gradually reduced to the original length before heat treatment.

  Examples of a material having a glass transition temperature higher than 225 ° C. and preferable for the separation membrane used in the present invention include polyimide, polyethersulfone, polyamide, polyetheretherketone, and particularly preferably polyimide.

  The material for forming the asymmetric gas separation hollow fiber membrane of the present invention (hereinafter also simply referred to as a hollow fiber membrane) is not particularly limited, but is suitable for an air separation membrane and has a glass transition temperature of 225 ° C. An example of a higher polyimide composition will be described. The polyimide having the following composition is an aromatic polyimide represented by the repeating unit of the following general formula (1), and the glass transition temperature is usually 250 ° C. or higher, preferably 300 ° C. or higher (including those in which the glass transition temperature cannot be measured). It is.

  In the above formula, B is a tetravalent unit due to the tetracarboxylic acid component, and A is a divalent unit due to the diamine component. The units constituting the aromatic polyimide will be described in detail below.

  Unit B is a tetravalent unit derived from a tetracarboxylic acid component, and is a unit B1 having a diphenylhexafluoropropane structure represented by the following general formula (B1) of 10 to 70 mol%, preferably 20 to 60 mol%. 90 to 30 mol%, preferably 80 to 40 mol% of the unit B2 having the biphenyl structure represented by the following general formula (B2), and substantially consisting of the unit B1 and the unit B2. If the diphenylhexafluoropropane structure is less than 10 mol% and the biphenyl structure exceeds 90 mol%, the gas separation performance of the resulting polyimide is lowered, making it difficult to obtain a high performance gas separation membrane. On the other hand, if the diphenylhexafluoropropane structure exceeds 70 mol% and the biphenyl structure is less than 30 mol%, the mechanical strength of the resulting polyimide may be reduced.

  The unit B can also include a tetravalent unit based on a phenyl structure represented by the following formula (B3). The tetravalent unit based on the phenyl structure represented by the formula (B3) is 0 to 30 mol%, preferably 10 to 20 mol%.

  Further, the unit B can include a tetravalent unit B4 derived from other tetracarboxylic acids other than the units B1, B2, and B3.

  Unit A is a divalent unit derived from the diamine component, unit A1 selected from the group consisting of the following general formulas (A1a), (A1b) and (A1c), and the following general formulas (A2a) and (A2b) A unit A2 selected from the group consisting of: Furthermore, the unit A can include a divalent unit A3 resulting from other diamine components other than the units A1 and A2.

  The unit A1a is a divalent unit based on the biphenyl structure represented by the formula (A1a), and the units A1b and A1c are hexafluoro-substituted structures represented by the formulas (A1b) and (A1c), more specifically 2 It has a unit of structure having one trifluoromethyl group.

（式中、Ｘは塩素原子または臭素原子で、ｎは１〜３である。）

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

（式中、ｒは０または１であり、フェニル環はＯＨ基により置換されていてもよい。）

(In the formula, r is 0 or 1, and the phenyl ring may be substituted with an OH group.)

（式中、ＹはＯまたは単結合を示す。）

(In the formula, Y represents O or a single bond.)

  When the unit A1 has a unit represented by the formula (A1a), 30 to 70 mol%, preferably 30 to 60 mol% is suitable for the unit A. These benzidines contribute to the improvement of the degree of separation, but if the amount is too large, the polymer becomes insoluble and film formation becomes difficult, and if the amount is too small, the degree of separation decreases, which is not preferable.

  When the unit A1 has a unit represented by the formula (A1b) and / or the formula (A1c), these are contained in the unit A in an amount of 10 to 50 mol%, preferably 20 to 40 mol%.

  Unit A2 is selected from the group consisting of sulfur-containing heterocyclic structures, specifically, units represented by the following general formulas (A2a) and (A2b).

（式中、Ｒ及びＲ’は水素原子又は有機基であり、ｎは０、１又は２である。）

(In the formula, R and R ′ are a hydrogen atom or an organic group, and n is 0, 1 or 2.)

（式中、Ｒ及びＲ’は水素原子又は有機基であり、Ｘは−ＣＨ_２−又は−ＣＯ−である。）

(In the formula, R and R ′ are a hydrogen atom or an organic group, and X is —CH ₂ — or —CO—.)

  Unit A2 is contained in unit A in an amount of 90 to 30 mol%, preferably 90 to 40 mol%, more preferably 90 to 50 mol%, still more preferably 80 to 60 mol%.

  Unit A3 can be contained in unit A in an amount of 50 mol% or less, preferably 40 mol% or less, more preferably 20 mol% or less.

  Next, the monomer component which comprises each said unit of an aromatic polyimide is demonstrated.

  The unit having a diphenylhexafluoropropane structure represented by the general formula (B1) can be obtained by using (hexafluoroisopropylidene) diphthalic acid, a dianhydride thereof, or an esterified product thereof as a tetracarboxylic acid component. Examples of the (hexafluoroisopropylidene) diphthalic acids include 4,4 ′-(hexafluoroisopropylidene) diphthalic acid, 3,3 ′-(hexafluoroisopropylidene) diphthalic acid, and 3,4 ′-(hexafluoroisopropylidene). ) Diphthalic acid, dianhydrides thereof, or esterified products thereof can be preferably used, but 4,4 ′-(hexafluoroisopropylidene) diphthalic acid, dianhydrides thereof, or esterified products thereof are particularly preferable. It is.

  The unit having a biphenyl structure represented by the general formula (B2) can be obtained by using biphenyltetracarboxylic acids such as biphenyltetracarboxylic acid, dianhydrides thereof, or esterified products thereof as a tetracarboxylic acid component. Examples of the biphenyltetracarboxylic acids include 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 2,3,3 ′, 4′-biphenyltetracarboxylic acid, and 2,2 ′, 3,3′-biphenyltetracarboxylic acid. Carboxylic acids, dianhydrides thereof, or esterified products thereof can be preferably used, but 3,3 ′, 4,4′-biphenyltetracarboxylic acid, dianhydrides thereof, or esterified products thereof are particularly preferable. It is.

  A 4-mer unit based on the phenyl structure represented by the general formula (B3) can be obtained by using pyromellitic acids such as pyromellitic acid and its acid anhydride. These pyromellitic acids are suitable for enhancing the mechanical properties. However, if the amount is too large, the polymer solution at the time of film formation is solidified and it becomes difficult to form a hollow fiber. .

  The other tetracarboxylic acid component that gives the unit B4 is a tetracarboxylic acid other than the compounds shown above, and a compound that does not impair the effects of the present invention and can further improve performance is selected. Examples thereof include diphenyl ether tetracarboxylic acids, benzophenone tetracarboxylic acids, diphenyl sulfone tetracarboxylic acids, naphthalene tetracarboxylic acids, diphenylmethane tetracarboxylic acids, diphenylpropane tetracarboxylic acids, and the like.

  The divalent unit based on the biphenyl structure represented by the general formula (A1a) can be obtained by using halogen-substituted benzidines represented by the general formula (A1a-M) as the diamine component.

（式中、Ｘは塩素原子または臭素原子で、ｎ＝１〜３である。）

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

  Examples of halogen-substituted benzidines include dichlorobenzidine (diaminodichlorobiphenyl), tetrachlorobenzidine (diaminotetrachlorobiphenyl), hexachlorobenzidine, tetrabromobenzidine, dibromobenzidine, hexabromobenzidine and the like. . Examples of the dichlorobenzidines include 3,3'-dichlorobenzidine (DCB), and examples of the tetrachlorobenzidines include 2,2 ', 5,5'-tetrachlorobenzidine (TCB).

  The divalent unit represented by the general formula (A1b) is obtained by using hexafluoro-substituted compounds represented by the general formula (A1b-M) as the diamine component.

（式中、ｒは０または１であり、フェニル環はＯＨ基により置換されていてもよい。）

（Ａ１ｂ−Ｍ）で示されるヘキサフルオロ置換化合物類の好ましい化合物は、一般式（Ａ１ｂ−Ｍ１）〜（Ａ１ｂ−Ｍ３）：

(In the formula, r is 0 or 1, and the phenyl ring may be substituted with an OH group.)

Preferred compounds of the hexafluoro-substituted compounds represented by (A1b-M) are general formulas (A1b-M1) to (A1b-M3):

で表される。

It is represented by

  Examples of the bis [(aminophenoxy) phenyl] hexafluoropropanes represented by the general formula (A1b-M1) include 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, 2,2 -Bis [4- (3-aminophenoxy) phenyl] hexafluoropropane can be mentioned. Examples of the bis (aminophenyl) hexafluoropropanes represented by the general formula (A1b-M2) include 2,2-bis (4-aminophenyl) hexafluoropropane. Examples of the hydroxyl group-substituted bis (aminophenyl) hexafluoropropanes represented by the general formula (A1b-M3) include 2,2-bis (3-amino-4-hydroxy) hexafluoropropane.

  Moreover, the bivalent unit shown by general formula (A1c) is obtained by using the hexafluoro substituted compounds shown by general formula (A1c-M) as a diamine component.

（式中、ＹはＯまたは単結合を示す。）

一般式（Ａ１ｃ−Ｍ）で表されるジアミン化合物類としては、例えば、２，２’−ビス（トリフルオロメチル）−４，４’−ジアミノジフェニルエーテル、２，２’−ビス（トリフルオロメチル）−４，４’−ジアミノビフェニル等を挙げることができる。

(In the formula, Y represents O or a single bond.)

Examples of the diamine compounds represented by the general formula (A1c-M) include 2,2′-bis (trifluoromethyl) -4,4′-diaminodiphenyl ether and 2,2′-bis (trifluoromethyl). Examples include -4,4'-diaminobiphenyl.

  Moreover, the unit which consists of a structure shown by the said general formula (A2a) or the said general formula (A2b) is a fragrance shown by the following general formula (A2a-M) and general formula (A2b-M) as a diamine component, respectively. It is obtained by using a group diamine.

（式中、Ｒ及びＲ’は水素原子又は有機基であり、ｎは０、１又は２である。）

(In the formula, R and R ′ are a hydrogen atom or an organic group, and n is 0, 1 or 2.)

（式中、Ｒ及びＲ’は水素原子又は有機基であり、Ｘは−ＣＨ_２−又は−ＣＯ−である。）

(In the formula, R and R ′ are a hydrogen atom or an organic group, and X is —CH ₂ — or —CO—.)

  Examples of the aromatic diamine represented by the general formula (A2a-M) include diaminodibenzothiophenes represented by the following general formula (A2a-M1) in which n in the general formula (A2a-M) is 0, or a general formula ( Preferred examples include diaminodibenzothiophene = 5,5-dioxides represented by the following general formula (A2a-M2) in which n of A2a-M) is 2.

（式中、Ｒ及びＲ’は水素原子又は有機基である。）

(In the formula, R and R ′ are a hydrogen atom or an organic group.)

（式中、Ｒ及びＲ’は水素原子又は有機基である。）

(In the formula, R and R ′ are a hydrogen atom or an organic group.)

  Examples of the diaminodibenzothiophenes (general formula (A2a-M1)) include 3,7-diamino-2,8-dimethyldibenzothiophene, 3,7-diamino-2,6-dimethyldibenzothiophene, and 3,7. -Diamino-4,6-dimethyldibenzothiophene, 2,8-diamino-3,7-dimethyldibenzothiophene, 3,7-diamino-2,8-diethyldibenzothiophene, 3,7-diamino-2,6-diethyl Dibenzothiophene, 3,7-diamino-4,6-diethyldibenzothiophene, 3,7-diamino-2,8-dipropyldibenzothiophene, 3,7-diamino-2,6-dipropyldibenzothiophene, 3,7 -Diamino-4,6-dipropyldibenzothiophene, 3,7-diamino-2,8-dimethoxydibenzo Thiophene, 3,7-diamino-2,6-dimethoxy dibenzothiophene, and the like 3,7-diamino-4,6-dimethoxy-dibenzothiophene.

  Examples of the diaminodibenzothiophene = 5,5-dioxides (general formula (A2a-M2)) include 3,7-diamino-2,8-dimethyldibenzothiophene = 5,5-dioxide and 3,7-diamino. -2,6-dimethyldibenzothiophene = 5,5-dioxide, 3,7-diamino-4,6-dimethyldibenzothiophene = 5,5-dioxide, 2,8-diamino-3,7-dimethyldibenzothiophene = 5 , 5-dioxide, 3,7-diamino-2,8-diethyldibenzothiophene = 5,5-dioxide, 3,7-diamino-2,6-diethyldibenzothiophene = 5,5-dioxide, 3,7-diamino -4,6-diethyldibenzothiophene = 5,5-dioxide, 3,7-diamino-2,8-dipropyldibenzothiophene = 5,5-dioxide, 3,7-diamino-2,6-dipropyldibenzothiophene = 5,5-dioxide, 3,7-diamino-4,6-dipropyldibenzothiophene = 5,5-dioxide, 3 , 7-diamino-2,8-dimethoxydibenzothiophene = 5,5-dioxide, 3,7-diamino-2,6-dimethoxydibenzothiophene = 5,5-dioxide, 3,7-diamino-4,6-dimethoxy And dibenzothiophene = 5,5-dioxide.

In the general formula (A2b-M), examples of the diaminothioxanthene-10,10-diones in which X is —CH ₂ — include, for example, 3,6-diaminothioxanthene-10,10-dione, 2,7 -Diaminothioxanthene-10,10-dione, 3,6-diamino-2,7-dimethylthioxanthene-10,10-dione, 3,6-diamino-2,8-diethyl-thioxanthene-10,10- Examples include dione, 3,6-diamino-2,8-dipropylthioxanthene-10,10-dione, 3,6-diamino-2,8-dimethoxythioxanthene-10,10-dione, and the like.

  Examples of the diaminothioxanthene-9,10,10-trione in the general formula (A2b-M) where X is —CO— include, for example, 3,6-diamino-thioxanthene-9,10,10-trione. 2,7-diamino-thioxanthene-9,10,10-trione and the like.

  The other diamine component that gives the unit A3 is a diamine compound other than the compounds shown above, and a compound that does not impair the effects of the present invention and can further improve performance is selected.

For example, diaminodiphenyl sulfones such as 3,3′-diaminodiphenyl sulfone, 3,4′-diaminodiphenyl sulfone, 4,4′-diaminodiphenyl sulfone, 4,4′-diamino-3,3′-dimethyldiphenyl sulfone ;
4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl ether, 3,3′-dimethyl-4,4′-diaminodiphenyl ether, 3,3′-diethoxy-4,4 ′ -Diaminodiphenyl ethers such as diaminodiphenyl ether;
Diaminodiphenylmethanes such as 4,4′-diaminodiphenylmethane, 3,3′-diaminodiphenylmethane;
2,2-bis (aminophenyl) propanes such as 2,2-bis (3-aminophenyl) propane and 2,2-bis (4-aminophenyl) propane;
2,2-bis (aminophenoxyphenyl) propanes such as 2,2-bis [4- (4-aminophenoxy) phenyl] propane and 2,2-bis [4- (3-aminophenoxy) phenyl] propane;
Diaminobenzophenones such as 4,4′-diaminobenzophenone and 3,3′-diaminobenzophenone;
Diaminobenzoic acids such as 3,5-diaminobenzoic acid;
Phenylenediamines such as 1,3-phenylenediamine and 1,4-phenylenediamine;
Dichlorodiaminodiphenyl ethers such as 2,2′-dichloro-4,4′-diaminodiphenyl ether;
Toluidines such as orthotolidine and metatolidine;
Dihydroxydiaminobiphenyls such as 2,2′-dihydroxy-4,4′-diaminobiphenyl;
Etc.

  Among these, diaminodiphenyl sulfones, diaminodiphenyl ethers, diaminobenzoic acids, dichlorodiaminodiphenyl ethers, and dihydroxydiaminobiphenyls are preferable.

  In the present invention, when the aromatic polyimide represented by the repeating unit of the general formula (1) is used for the asymmetric air separation membrane, for example, the tetracarboxylic acid component is 4,4 ′-(hexa) as the carboxylic acid that gives the unit B1. Fluoroisopropylidene-bis (phthalic anhydride), 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride as carboxylic acid to give unit B2, pyromellitic dianhydride as carboxylic acid to give unit B3, As the diamine component, 2,2 ′, 5,5′-tetrachlorobenzidine is used as a diamine that gives unit A1, and 3,7-diamino-dimethyldibenzothiophene = 5,5-dioxide is used as a diamine that gives unit A2. In the present invention, 3,7-diamino-dimethyldibenzothi Phen = 5,5-dioxide is an isomer 3,7-diamino-2, which is mainly composed of 3,7-diamino-2,8-dimethyldibenzothiophene = 5,5-dioxide and has different methyl group positions. It means a mixture containing 6-dimethyldibenzothiophene = 5,5-dioxide and 3,7-diamino-4,6-dimethyldibenzothiophene = 5,5-dioxide.

  The aromatic polyimide solution is prepared by adding a tetracarboxylic acid component and a diamine component in an organic polar solvent at a predetermined composition ratio, causing a polymerization reaction at a low temperature of about room temperature to produce a polyamic acid, and then heating to form a heated imide. Or a chemical imidization by adding pyridine or the like, or a tetracarboxylic acid component and a diamine component are added in a predetermined composition ratio in an organic polar solvent, and 100 to 250 ° C., preferably 130 to 200 ° C. It is suitably carried out by a one-stage method in which a polymerization imidization reaction is performed at a high temperature. When the imidization reaction is carried out by heating, it is preferred to carry out while removing water or alcohol that is eliminated. The amount of the tetracarboxylic acid component and diamine component used in the organic polar solvent is such that the concentration of the polyimide in the solvent is about 5 to 50% by weight, preferably 5 to 40% by weight.

  The aromatic polyimide solution obtained by polymerization imidization can be directly used for spinning as it is. In addition, for example, the obtained aromatic polyimide solution is put into a solvent insoluble in aromatic polyimide to precipitate and isolate the aromatic polyimide, and then dissolved again in an organic polar solvent to a predetermined concentration. It is also possible to prepare an aromatic polyimide solution and use it for spinning.

  The aromatic polyimide solution used for spinning preferably has a polyimide concentration of 5 to 40% by weight, more preferably 8 to 25% by weight, and the solution viscosity (rotational viscosity) is preferably 100 to 15000 poise at 100 ° C. It is preferably 200 to 10,000 poise, particularly 300 to 5000 poise. If the solution viscosity is less than 100 poise, a homogeneous film (film) may be obtained, but it is difficult to obtain an asymmetric film having high mechanical strength. On the other hand, if it exceeds 15000 poise, it is difficult to push out from the spinning nozzle, so it is difficult to obtain an asymmetric hollow fiber membrane having the desired shape.

  The organic polar solvent is not limited as long as the aromatic polyimide obtained can be suitably dissolved. For example, phenols such as phenol, cresol, and xylenol, and two hydroxyl groups directly on the benzene ring. Catechol, catechols such as resorcin, halogens such as 3-chlorophenol, 4-chlorophenol (same as parachlorophenol described later), 3-bromophenol, 4-bromophenol, 2-chloro-5-hydroxytoluene Phenolic solvents comprising fluorinated phenols, or N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, N, N-dimethylformamide, N, N-diethylformamide, N, N-dimethyl Amiamide such as acetamide, N, N-diethylacetamide Amide solvents consisting class, or a mixed solvent thereof and the like can be preferably exemplified.

  The hollow fiber membrane used in the present invention can be suitably obtained by spinning by a dry / wet method (dry wet spinning method) using the aromatic polyimide solution or the like. In the dry-wet method, the solvent on the surface of the polymer solution in the form of a hollow fiber is evaporated to form a thin dense layer (separation layer), and further, the coagulation liquid (compatible with the solvent of the polymer solution and the polymer is insoluble). This is a method (phase conversion method) in which a porous layer (support layer) is formed by forming micropores by using a phase separation phenomenon that occurs in the solvent), and proposed by Loeb et al. 3133132).

  The dry-wet spinning method is a method of forming a hollow fiber membrane by a dry-wet method using a spinning nozzle, and is described in, for example, JP-A-61-133106 and JP-A-3-267130.

  The production method usually includes a spinning process (spinning dope discharging process), a coagulation process, a washing process, a drying process, and a heat treatment process.

  First, in the spinning process (spinning dope discharging process), the spinning nozzle used for discharging the spinning dope liquid only needs to push the spinning dope liquid into the hollow fiber-like body, such as a tube-in-orifice type nozzle. Is preferred. Usually, the temperature range of the aromatic polyimide solution during extrusion is preferably about 20 ° C to 150 ° C, particularly 30 ° C to 120 ° C. A suitable temperature range varies depending on the type of solvent and viscosity of the dope. Further, spinning is performed while supplying a gas or a liquid into the hollow fiber-like body extruded from the nozzle.

  In the coagulation process that continues from the spinning process, the hollow fiber discharged from the nozzle is once extruded into the atmosphere or an inert gas atmosphere such as nitrogen, etc., and then guided to the coagulation bath and immersed in the coagulation liquid. . The coagulation liquid preferably does not substantially dissolve the aromatic polyimide component and is compatible with the solvent of the aromatic polyimide solution. Although not particularly limited, water, lower alcohols such as methanol, ethanol and propyl alcohol, ketones having a lower alkyl group such as acetone, diethyl ketone and methyl ethyl ketone, or mixtures thereof are preferably used. It is done. Moreover, when the solvent of the aromatic polyimide solution is an amide solvent, an aqueous solution of an amide solvent is also preferable.

  In the next washing step, washing is carried out with a washing solvent such as ethanol, if necessary, and then a substitution solvent such as an aliphatic hydrocarbon such as isopentane, n-hexane, isooctane, n-heptane is used on the outer and inner sides of the hollow fiber. Replace the coagulation liquid and / or washing solvent.

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

  Next, the present invention will be further described with reference to examples. In addition, this invention is not limited to a following example.

<Measuring method of glass transition temperature (Tg) of hollow fiber membrane>
The glass transition temperature (Tg) is measured according to the method for measuring the extrapolated glass transition start temperature of JIS K7121, using a Shimadzu DSC50 apparatus, a sample amount of 2 mg, from room temperature to 400 ° C. under a nitrogen atmosphere gas at 10 ° C./min. It carried out in.

<Method for measuring shape retention rate of hollow fiber membrane>
In the measurement of the shape retention rate, the length before and after heat treatment in which a hollow fiber having a length of 200 mm was held in a hot air thermostat at 175 ° C. for 2 hours was measured. The ratio of the length after the heat treatment to the original length before the heat treatment was defined as the shape retention rate.

<Measurement method of solution viscosity>
The solution viscosity of the polyimide solution was measured at a temperature of 100 ° C. using a rotational viscometer (shear rate of rotor: 1.75 sec ⁻¹ ).

<Production Example 1>
In a separable flask equipped with a stirrer and a nitrogen gas inlet tube, 200 mmol of 4,4 ′-(hexafluoroisopropylidene) -bis (phthalic anhydride) and 3,3 ′, 4,4′-biphenyltetra 225 mmol of carboxylic dianhydride, 75 mmol of pyromellitic dianhydride, 250 mmol of 2,2 ′, 5,5′-tetrachlorobenzidine, 3,7-diamino-dimethyldibenzothiophene = 5,5- 250 mmol of dioxide was added together with 1882 g of 4-chlorophenol as a solvent, and a polymerization imidization reaction was carried out with stirring at a reaction temperature of 190 ° C. for 20 hours while flowing nitrogen gas through the flask. The polyimide concentration was 17% by weight. An aromatic polyimide solution was prepared. The solution viscosity at 100 ° C. of this aromatic polyimide solution was 1940 poise.

  The prepared aromatic polyimide solution is filtered through a 400-mesh wire mesh, and this is used as a dope solution by using a spinning device equipped with a hollow fiber spinning nozzle (circular opening outer diameter 1000 μm). A dope solution is discharged from a circular opening having a circular opening slit width of 200 μm and a core opening outer diameter of 400 μm, and at the same time, nitrogen gas is discharged from the core opening to form a hollow fiber-like body in a nitrogen atmosphere. After passing through, it was immersed in a coagulation liquid to be solidified, and taken up by a take-up roll to obtain a wet hollow fiber membrane. Next, this hollow fiber membrane was dried and further subjected to a heat treatment at 250 ° C. for 30 minutes to obtain a hollow fiber membrane 1.

  The obtained hollow fiber membrane 1 generally had an outer diameter of 410 μm and an inner diameter of 280 μm. A yarn bundle element was formed from the hollow fiber membranes, and then a gas separation membrane module was formed from the yarn bundle elements of the respective hollow fiber membranes.

  Hereinafter, in Examples 1 and 2, the air separation membrane module 1 using the hollow fiber membrane 1 manufactured as described above is used. In Comparative Examples 1 and 2, the air separation membrane module 2 using the following hollow fiber membrane 2 is used. Alternatively, an air separation membrane module 3 using a hollow fiber membrane 3 was used.

  Table 1 shows the characteristics and the like of each hollow fiber membrane. Glass transition temperature and shape retention were measured by the above methods.

  Table 2 shows the specifications of each air separation membrane module.

<Example 1>
Air at 175 ° C. is supplied to the air separation membrane module 1 at a pressure of 0.2 MPaG, and the air supply amount is adjusted so that the oxygen gas concentration in the non-permeate gas, that is, nitrogen-enriched air is 12%. I drove continuously. At each elapsed time from the start of operation, the flow rate of the produced nitrogen-enriched air was measured. The measurement results are shown in FIG. Further, from the measurement results, the oxygen permeation rate ( _P′O2 ) of the air separation membrane after the lapse of 0 hours, 140 hours, and 2069 hours from the start of operation, and the ratio of the oxygen gas permeation rate and the nitrogen gas permeation rate indicating the separation performance ( _P'O2 / _P'N2 ) was calculated. The results are shown in Table 3.

At the time of starting operation (0 hour), _P′O2 is 35.4 × 10 ⁻⁵ cm ³ (STP) / cm ² · sec · cmHg, and the nitrogen-enriched air obtained from the air separation membrane module 1 The flow rate of was 0.748 Nm ³ / h. At 140 hours after the start of operation, _P′O2 was 33.4 × 10 ⁻⁵ cm ³ (STP) / cm ² · sec · cmHg, which was only a 5.6% decrease from the start of operation. P _'O2 after 2069 hours passed after the start of operation is ^{31.4 × 10 -5 cm 3 (STP} ) / cm 2 · sec · cmHg, was reduced by 11% from the start of operation. The flow rate of nitrogen-enriched air obtained from the air separation membrane module 1 after 2069 hours from the start of operation was 0.65 Nm ³ / h, which was only 13% lower than that at the start of operation. From this result, it can be seen that the air separation membrane module 1 maintains the gas separation membrane performance even when operated at 175 ° C. for 2000 hours.

<Comparative Example 1>
The same measurement as in Example 1 was attempted using the air separation membrane module 2, but the hollow fiber membrane contracted severely at 175 ° C., and it was impossible to obtain nitrogen-enriched air. In the air separation membrane module 2 maintained at 175 ° C., hollow crushing, thread breakage, tube sheet distortion, and the like were observed.

<Comparative Example 2>
The operation was performed under the same conditions as in Example 1 except that the air separation membrane module 3 was used, and the flow rate of nitrogen-enriched air at each elapsed time was measured. The measurement results are shown in FIG. P _'O2 in the time of starting the ^{operation, 19.3 × 10 -5 cm 3 (} STP) / cm is 2 · sec · cmHg, the flow rate of nitrogen-enriched air obtained from the air separation membrane module, 0. It was 625 Nm ³ / h. In 140 hours after after the start of operation, P _'O2 of the separation membrane decreases ^{11.3 × 10 -5 cm 3 (STP} ) / cm 41% of 2 · sec · cmHg and used at the start, the air separation membrane module The flow rate of nitrogen-enriched air obtained from No. 1 was 0.419 Nm ³ / h, a decrease of 35% from the start of use.

<Example 2>
The measurement was performed in the same manner as in Example 1 except that the air supply amount was adjusted so that the oxygen gas concentration in the produced nitrogen-enriched air was 5%. The measurement results are shown in FIG. The flow rate of nitrogen-enriched air at the start of operation was 0.18 Nm ³ / h. The flow rate of nitrogen-enriched air after 2069 hours from the start of operation is 0.15 Nm ³ / h, which is only a 16% decrease. From this result, it is understood that the air separation membrane module 1 maintains the gas separation membrane ability even after 2000 hours at 175 ° C. as in Example 1.

  According to the present invention, high-temperature air, for example, air at 150 ° C. or higher can be supplied to the air separation membrane module to obtain nitrogen-enriched air with an increased nitrogen concentration. The method of the present invention can be used, for example, in an aircraft fuel tank explosion-proof system.

Claims (5)

A method for producing nitrogen-enriched air from air using an air separation membrane module,
A method comprising supplying air at 150 ° C. or higher to an air separation membrane module. The air separation membrane module is
At the start of use, the oxygen gas permeation rate ( _P′O2 ) at 175 ° C. is 20 × 10 ⁻⁵ cm ³ (STP) / cm ² · sec · cmHg or more, and the oxygen gas permeation rate and nitrogen gas at 175 ° C. The ratio to the transmission rate ( _P'O2 / _P'N2 ) is 1.8 or more, and
175 ° C. In 140 hours P _'O2 and P' _O2 / P when using _'N2 is, the use start before the P' that holds each 90% _O2 and P _'O2 / P' _N2 The method of claim 1, characterized in that   The method according to claim 1 or 2, wherein the air separation membrane in the air separation membrane module is made of a material that does not exhibit a glass transition temperature below 225 ° C.   The method according to claim 1, wherein the air separation membrane exhibits a shape retention of 95% or more when placed at 175 ° C. for 2 hours.   An aircraft explosion-proof method, wherein nitrogen-enriched air is produced by the production method according to claim 1 and supplied to an aircraft fuel tank.

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