JP3462652B2 - Gas separation membrane and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention has excellent heat resistance, chemical stability, and mechanical properties, and is suitable for separating acidic gas such as carbon dioxide gas and sulfurous acid gas from combustion exhaust gas, and gas separation performance and separation performance. And a method for producing the same.

[0002]

2. Description of the Related Art The principle of gas separation by a membrane is that the permeation rate is determined by the product of the gas solubility coefficient in the membrane and the diffusion coefficient of the gas in the membrane, and the gas can be separated by the difference in the permeation rate depending on the type of gas. . Conventionally, a great number of polymer membranes have been studied as gas separation membranes. Among them, when the size of gas molecules such as hydrogen and methane are different, the polyimide membrane with dense packing and small free volume has the highest separation performance and is already in practical use. . But CO ₂ /
Separation of gases having similar molecular sizes such as N ₂ and CO ₂ / CH ₄ has a too low permeation rate, and therefore various studies have been conducted. In one direction, a method of introducing a bulky group or forming a copolymer has been investigated, and it is disclosed in JP-A-63-111921.
2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane acid anhydride (6FDA) and 3,4,3 ', 4'-benzophenonetetracarboxylic dianhydride (BTDA) as trimethyl. There is a polyimide film copolymerized with phenylenediamine (TrMPD), and a cardo type polyimide film having an extremely bulky fluorene group has also been investigated, and although improved permeability was obtained,
Separation factor 30-50, Transmission rate 10-100 Barre
At r, the practicability was still low.

In the other direction, there is a so-called carrier film impregnated with a liquid having a high affinity for carbon dioxide, and a separation coefficient of 1000 or more is obtained as an initial value, but it is not durable and is not practical. Further, attempts have been made to introduce a functional group having an affinity for carbon dioxide into the polymer membrane itself to enhance the selective permeability of carbon dioxide. JP-A-6-71
Japanese Patent Publication No. 148 describes that a copolymerized polyimide membrane of a diamine having a polyether segment exhibits a relatively high CO ₂ / N ₂ separability, and chitosan and amino, which are natural polymers containing amino groups. Glassy polymer membranes obtained by polymerizing a group-containing monomer have also been studied, but all of them have low permeability and are not practical.

[0004]

SUMMARY OF THE INVENTION In view of the above-mentioned conventional state of the art, the present invention is CO ₂ / N ₂ , CO ₂ / CH ₄ , SO ₂
Gas separation membrane having high permeation rate and separation coefficient even for gases with similar molecular size such as / air, H ₂ S / air, and having unprecedented high permeability and separability of acid gas, and method for producing the same The purpose is to do.

[0005]

[Means for Solving the Problems] As a means for solving the above problems, the present invention is based on a polymer having an aromatic polyimide skeleton having excellent mechanical properties and thermal properties, in which the benzene ring has a molecular arrangement. Suppresses high-density packing of
Selective separation of acidic gas by adopting a structure that has one or more alkyl groups that give a large free volume and gas permeability, and further introduces an amino group having an affinity for acidic gas into this alkyl group. By using a polymer having improved performance for a separation membrane material, a separation membrane having a high permeability and separation property of an acid gas such as carbon dioxide gas, which has never been obtained, is obtained.

Since ordinary aromatic polyimides are densely packed with polymer chains, they are insoluble in organic solvents and it is difficult to introduce functional groups such as halogen atoms and amino groups in a controlled manner. Polyimides having one or more alkyl groups in the ring become sparsely filled with polymer chains, so that they become soluble in a solvent and can be chemically modified by introducing various functional groups. In the case of a separation membrane, it is possible to improve the balance between permeability and separability and achieve the target. Therefore, as a result of various studies on a method of introducing an amino group as a functional group in order to impart selective separability to acidic gas represented by carbon dioxide, the present invention has been accomplished.

That is, the present invention includes the following configurations (1) to (4). (1) An aromatic polyimide having a repeating unit represented by the general formula (A) as a basic skeleton, wherein a part or all of hydrogen atoms of an alkyl group in the general formula (A) are substituted with an amine compound residue. A gas separation membrane comprising an amine-modified polyimide.

[Chemical 2] In the formula (A), X and Y have the following meanings. X: aromatic tetracarboxylic acid compound residue Y: aromatic diamine compound residue having at least one alkyl group as a substituent

(2) An aromatic polyimide having a repeating unit represented by the general formula (A) as a basic skeleton, wherein some or all of the hydrogen atoms of the alkyl group in the general formula (A) are amine compound residues. The gas separation membrane is characterized in that it is substituted with, and a part or all of the amine compound residue is composed of an amine-modified polyimide forming a crosslinked structure with another basic skeleton.

(3) A brominating agent is caused to act on a polyamic acid which is a precursor of an aromatic polyimide having a repeating unit represented by the general formula (A) as a basic skeleton to introduce bromine into a part of an alkyl group, The obtained brominated polyamic acid is imidized, or a brominating agent is caused to act on an aromatic polyimide having a repeating unit represented by the general formula (A) as a basic skeleton to introduce bromine into a part of an alkyl group. The obtained brominated polyimide is reacted with an amine compound to give a compound of the general formula (A)
An amine-modified polyimide in which some of the hydrogen atoms of the alkyl groups in the are substituted with an amine compound residue, and a film is formed at the stage of the brominated polyamic acid, the polyimide before bromination, the brominated polyimide, or the amine-modified polyimide. A method for producing a gas separation membrane, comprising:

(4) In the method for producing a gas separation membrane according to the above (3), a film is produced in the form of an amine-modified polyimide in which a part of bromine remains, and the amine compound is further reacted to crosslink the gas. Method for manufacturing separation membrane.

[0011]

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, the aromatic polyimide having the repeating unit represented by the general formula (A) is represented by the aromatic tetracarboxylic acid anhydride represented by the general formula (B) and the general formula (C). It is synthesized from an aromatic diamine compound having at least one alkyl group. Note that an aromatic tetracarboxylic acid ester compound can be used instead of the aromatic tetracarboxylic acid anhydride.

[Chemical 3] In formulas (B) and (C), X and Y have the same meanings as described above. The degree of polymerization (the number of repeating units) of the aromatic polyimide in the present invention is 40 or more, preferably 60 or more.

As an example of the aromatic tetracarboxylic acid anhydride of the general formula (B) which is a constituent element of the aromatic polyimide according to the present invention, 3,4,3 ', 4'-biphenyltetracarboxylic acid anhydride ( BPDA), wholly aromatic compounds such as 1,2,4,5-benzenetetracarboxylic dianhydride (PM); 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane acid anhydride A diphenylalkane compound such as (6FDA); a diphenylsulfone such as an acid anhydride of bis (3,4-dicarboxyphenyl) sulfone; 3,4,3 ′, 4′-benzophenonetetracarboxylic dianhydride (BTDA) A) diphenyl ketones; bis (dicarboxyphenyl) ether acid anhydrides and the like diphenyl ethers. Among these, BPDA and 6FDA are preferable. These aromatic tetracarboxylic acid anhydrides may be used alone or in combination of two or more, and may have a substituent.

The aromatic diamine compound having at least one alkyl group of the general formula (C), which is another constituent element of the aromatic polyimide according to the present invention, has one or more benzene rings, An aromatic diamine compound having an alkyl group such as a methyl group, an ethyl group or an isopropyl group or an alkyl ether group or alkylketone group thereof, preferably 2 to 4 on the benzene ring thereof is used. Further, a functional group such as a halogen atom, an OH group or a CN group may be substituted on these alkyl groups. As the aromatic diamine compound having an alkyl group of the general formula (C), a polyaromatic ring such as a naphthalene ring or anthracene ring, a pyridine ring, a pyrazine ring, a quinoline ring or a benzothiazole ring is used instead of the benzene ring. And the like, and may have two benzene rings bonded directly or with an alkylene group, an ether group or a sulfone group.

Specifically, for example, 2,4,6-trimethyl-1,3-phenylenediamine (TrMPD), 2,
3,5,6-Tetramethyl-1,4-phenylenediamine (TeMPD), 2,5-dimethyl-1,4-phenylenediamine (DMPD), 3,5,3 ', 5'-tetramethylbenzidine, 2 , 6,2 ', 6'-Tetramethylbenzidine, 2,2'-Dimethylbenzidine, 3,
3'-dimethylbenzidine, 4,4'-diamino-3,
Examples thereof include 3'-diethyldiphenylethane, 4,4'-diamino-3,5,3 ', 5'-tetraethyldiphenylethane and the like. These alkyl-substituted aromatic diamine compounds may be used alone or in combination of two or more kinds, or may be used in combination with other aromatic diamine compounds having no alkyl substituent.

Introduction of an amine compound residue into an alkyl group bonded as a side chain to a benzene ring in an aromatic polyimide obtained from the aromatic tetracarboxylic acid compound and an aromatic diamine compound having at least one alkyl group. There are several possible methods, but the method that can be safely and reliably controlled is to first substitute some of the hydrogen atoms of the alkyl group with bromine at the stage of the amidic acid of the polyimide or its precursor, and then add an amine compound thereto. This is a method of reacting to perform dehydrobromination.

That is, first, the amic acid of the polyimide or its precursor is dissolved in a solvent, and then N-bromosuccinic anhydride (NBS), 1,3-dibromo-5,5'- is added thereto.
A bromine-containing polyimide film is formed by reacting with a brominating agent such as dimethylhydantoin (DBMH) to introduce an appropriate amount of bromine into an alkyl group to form a film and, if necessary, imidization. Then, this membrane is reacted in a vapor or an aqueous solution of one or a mixture of one or more kinds of ammonia, a primary amine compound or a secondary amine compound, and a substitution for satisfying the target carbon dioxide gas permeation performance and separation performance. It can be changed to a film having an amino group side chain structure and a substituted amino group amount.

The primary amine compound or the secondary amine compound may be provided with a functional group such as a hydroxyl group or a tertiary amino group to further improve the carbon dioxide gas permeation performance. However, on the other hand, if the size of these functional groups or the hydrocarbon groups of primary amine and secondary amine becomes too large, the separation performance between carbon dioxide gas and other gases such as nitrogen gas and methane gas will decrease, Separation performance can be balanced and maintained by forming crosslinks with a polyfunctional amino compound such as alkylenediamine or dialkylenetriamine having an appropriate chain length to suppress expansion of free volume.

In the present invention, an amine compound used for reacting with a side chain bromine alkyl group having bromine introduced into an alkyl group of a polyimide skeleton to induce a polyimide having an amino residue side chain by dehydrobromination is an amino compound. It is an aliphatic primary or secondary amine compound having one or more groups. Specific examples of the aliphatic amine compound (here, a compound having an amino group bonded to an alkylene group) include methylamine, ethylamine, benzylamine, dimethylamine, ethanolamine, diethanolamine (D
Alkyl group or functional group-substituted alkylamines such as EA); alicyclic amines such as morpholine (M) and piperazine (PD); alkylenediamines such as ethylenediamine (EDA) and propylenediamine (PDA); metaxylenediamine ( MXD), para-xylene diamine (PX
D) and the like aralkylene diamines; bis (3-aminopropyl) -polyethylene oxide (BAPPEO) and other polyether diamines; diethylenetriamine (DE)
TA), triethylenetetramine (TETA), polyethyleneimine (PEI), and other polyamines. These aliphatic amine compounds may be used alone or in combination of two or more.

In the method for producing an amine-modified polyimide separation membrane of the present invention, as described above, the bromine derivative polyimide solution may be cast to form a membrane and then reacted with an amino compound. The compound may be reacted to modify the amine-derived polyimide and then cast to form a film. In the film forming method, these polyimide solutions are used as a dope solution to form a film by a dry film forming method or a wet film forming method. When a film is formed from a bromine derivative, a functionally gradient film having a distribution in the amino residue concentration in the film thickness direction can be obtained by controlling the amine modification conditions.
Further, the film can be amine-crosslinked by further treating with ammonia, diamine or the like after forming the film with the bromine left behind. As a film form capable of forming a film, it is possible to form a flat film form or a hollow fiber film form by adjusting the concentration and temperature of the dope solution to control the viscosity.

An example of a suitable method for producing the amine-modified polyimide separation membrane of the present invention will be described with respect to the case of producing a film from a brominated polyimide solution and the case of producing a film from an amine-modified polyimide solution. To indicate.

[Production Method from Brominated Polyimide Solution] Aromatic tetracarboxylic dianhydride and an equimolar amount of aromatic diamine are polymerized in an organic polar solvent such as N, N-dimethylacetamide (DMAc) at room temperature. To obtain a polyamic acid, and then an imidization reaction is performed using acetic anhydride and triethylamine to produce a polyimide. The obtained polyimide was treated with N-bromosuccinimide (NBS), 1,3 in an organic solvent, preferably an alkyl halide solvent.
-Dibromo-5,5'-dimethylhydantoin (DBM
H) and other brominating agents are reacted under visible light irradiation to produce a polyimide in which side chain alkyl groups are brominated. The bromination rate is adjusted to contain 0.1 to 3, preferably 0.5 to 2 Br atoms per polymer repeat unit. This brominated polyimide is dissolved in an organic polar solvent such as methylene chloride or N-methylpyrrolidone (NMP) to obtain a dope solution for film formation having a polymer concentration of 3 to 30% by weight. This is applied or cast on a base material at a temperature of 10 to 100 ° C., and the solvent is removed by evaporation to obtain a thin film. Then, this is immersed in a 0.1 to 10% amine aqueous solution such as diethanolamine (DEA) or an acol solution at 5 to 80 ° C for 10 seconds to 10 hours for amine modification, and then dried at 80 to 200 ° C. Thus, the intended amine-modified polyimide separation membrane is obtained.

[Production Method from Amine-Modified Polyimide Solution] The brominated polyimide produced by the above method is reacted with a secondary amine such as diethanolamine or morpholine in an organic solvent such as NMP at 5 to 80 ° C. Obtain a modified polyimide. Amine-modified polyimide is dissolved in an organic polar solvent such as methylene chloride or NMP to give a polymer concentration of 3 to 3
The dope solution for film formation is 0% by weight. 10 to 10
A thin film is obtained by coating or casting on a base material at a temperature of 0 ° C. and removing the solvent by evaporation. Next, this is dried at 80 to 200 ° C. to obtain the target amine-modified polyimide separation membrane. Also,
Amine compound having two or more amino groups such as ammonia or ethylenediamine, diethylenetetramine, etc. after forming a film by controlling the reaction between brominated polyimide and amine and leaving some of the bromine unreacted. 0.1 to 1
The membrane can be amine cross-linked by immersion in 0% aqueous solution or alcohol solution at 5-80 ° C. for 10 seconds to 10 hours. In addition, 2 or more ammonia or amino groups from the beginning
It is also possible to form a crosslinked structure in one step by using an amine compound having one or more.

[0024]

EXAMPLES Next, examples and comparative examples of the present invention will be shown to demonstrate the effects of the present invention. In each example, the gas permeation coefficient of pure gas was measured by a high vacuum time lag method using a permeation cell having an effective area of 20 cm ² . Supply gas pressure 2 atm and temperature 2 for hydrogen, oxygen, nitrogen, methane and carbon dioxide
Measured at 5 ° C or 35 ° C, transmission coefficient Barrer = 1
^{0 - 10 cm 3 (STP)} cm / (cm 2 s cmHg)
Shown in units. The separation coefficient is shown by the ratio of the permeation coefficient of each gas.

The permeability coefficient in the carbon dioxide / nitrogen system separation is as follows: a mixed gas of carbon dioxide gas 18% and nitrogen 82% is used as a supply gas,
The measurement was performed by gas chromatography using the permeation measuring device shown in FIG. The membrane is installed in a cell with an effective membrane area of 20 cm ² , a mixed gas of 1.1 to 5 atm is supplied on the upstream side of the membrane, and helium is used as a sweep gas on the downstream side of the membrane.
Flowing at atm, the permeated gas was introduced into a gas sampler of a gas chromatograph, and gas chromatograph analysis was performed. The measurement was performed at 25 ° C. or 35 ° C. in a dry state, humidifying the supply gas and the sweep gas, and coexisting with water vapor. The permeation coefficient of each gas is shown by Barrer unit, and the separation coefficient is shown by the permeation coefficient ratio. In FIG. 1, A is a supply gas, B is a flow control valve, C is a humidifier, D is a constant temperature bath, E is a sweep gas, and F is a gas.
Is a dehumidifier, G is a permeation cell, H is a pressure gauge, I is a hygrometer, J
Is a six-way cook.

(Example 1) N-bromosuccinimide (NB) was added to a 0.5 wt% polyimide solution of BPDA-TrMPD polyimide or 6FDA-TrMPD polyimide.
S) was added and the mixture was brominated by irradiation with light. The brominated polyimide was analyzed by proton NMR to obtain the bromination rate from the peak intensity of the bromomethylene group and that of the methyl group. In addition, the bromination rate here is 100% when one bromine atom is substituted per polymer repeating unit.

The obtained brominated polyimide was cast to form a film having a thickness of 20 to 40 μm. An amine-modified polyimide film was obtained by immersing this film in a 1 wt% aqueous solution of various amines for 1 to 3 hours. Brominated BPDA-
Diethanolamine (DEA) on TrMPD polyimide
Was reacted with BPDA-TrMPD (Br0.5
0 / DEA) and diethylenetriamine (DETA) were reacted and crosslinked to obtain BPDA-TrMPD (Br
0.50 / DETA), brominated 6FDA-TrMP
D polyimide was reacted with polyethyleneimine (PEI) and crosslinked to obtain 6FDA-TrMPD (Br0.2
It is displayed as 0 / PEI). Here, (Br 0.50) indicates that the bromination rate is 50%. Table 1 shows the density, pure gas permeation coefficient, and permeation coefficient ratio of the prepared polyimide film. Table 2 and FIG. 2 show the results of permeation measurement in a mixed gas of CO ₂ / N ₂ .

[0028]

[Table 1] Measurement conditions Measurement temperature: 35 ℃, Supply pressure: 2 atm * 1) 10 ^-10 cm ³ (STP) cm / (cm ² s cmHg)

From the results shown in Tables 1 and 2 and FIG.
Recognize. That is, amine modification in the measurement of dry gas
The film performed as well as the cardo type polyimide. Dry
When comparing the performance in the presence of gas and water vapor, amine modification
The permeation coefficient of the non-decorated membranes 1 and 5 is
1 decreased about 40%, and membrane 5 decreased about 50%.
Coefficient ratio) Membrane 1 increased by 30% and Membrane 5 increased by 15%. Transparency
The decrease in the number is due to the water and CO in the membrane.₂Because of the competitive adsorption of
The increase in the separation factor is due to the affinity of water sorbed on the membrane for N ₂than
CO₂Is considered to be higher. Component of polyimide
The acid anhydride is BPDA-based membrane 1 is 6FDA-based
A greater decrease in permeation and an increase in separation than membrane 5 is
The membrane 5 having a trifluoromethyl group is more hydrophobic.
Because it is big. Amine modified films 3 and 4 are in the presence of water vapor
The transmission coefficient decreased to about 50%, but the separation coefficient was 1.6.
Doubled CO₂/ N₂Including PEO that shows high performance in separation
The performance was similar to that of polyimide. Of this separation factor
The large increase is due to the coexistence of water
CO₂It is thought that this is because the carrier is transported. Well
Also, the membrane 3 treated with an amine having one amine group
However, the one that showed higher separation performance than the membrane 4 with three
Not only the amine group but also the polar group OH contributes to the separation.
You might also say that.

[0030]

[Table 2]

Reference Example 1 1.17 g of BPDA-TrMPD polyimide was dissolved in 150 g of methylene chloride, to which 1.68 g (2.2 equivalents per polymer repeating unit) of N-bromosuccinimide (NBS) was added. It was melted and reacted for 4 hours under reflux while irradiating with a 50 W tungsten lamp. Flow the reaction solution into methanol,
The polymer was precipitated. After the polymer was filtered off, it was reprecipitated and purified twice with methylene chloride-methanol. From the proton NMR analysis, the bromination rate was 60%. A 5% methylene chloride solution of this brominated polyimide was cast on a glass plate, dried at room temperature and then vacuum dried at 50 ° C. for 5 hours to obtain a brominated polyimide film having a thickness of about 30 μm. Table 3 shows the measurement results of the pure gas permeation performance of this membrane.

Example 2 The brominated polyimide film obtained in Reference Example 1 was mixed with 0.5% by weight of diethanolamine (D
EA) After being immersed in an aqueous solution for 10 hours, vacuum dried at 70 ° C. for 10 hours to obtain a DEA-modified polyimide film (BPDA-T).
rMPD (Br0.60 / DEA)) was obtained. Table 3 shows the measurement results of the pure gas permeation performance of this membrane, and Table 4 shows the measurement results of the gas separation performance of the CO ₂ / N ₂ mixed gas. Further, the results of examining the effect of coexisting steam on the CO ₂ / N ₂ separation performance of this membrane are shown in FIG.

Example 3 The brominated polyimide film obtained in Reference Example 1 was dipped in a 0.5% by weight aqueous solution of diethylenetriamine (DETA) for 10 hours and then at 70 ° C. for 1 hour.
After vacuum drying for 0 hours, DETA-modified polyimide film (BP
DA-TrMPD (Br0.60 / DETA)) was obtained. The measurement results of the pure gas permeation performance of this membrane are shown in Table 3 and C
Table 4 shows the measurement results of the gas separation performance with the O ₂ / N ₂ mixed gas.
Shown in.

Example 4 The brominated polyimide film obtained in Reference Example 1 was immersed in a 0.5 wt% morpholine (M) aqueous solution for 10 hours, and then vacuum dried at 50 ° C. for 10 hours to obtain morpholine. Modified polyimide film (BPDA-TrMP
D (Br 0.60 / M)) was obtained. CO ₂ / N of this film
Table 4 shows the measurement results of the gas separation performance with the _two mixed gases.

Reference Example 2 1.00 g of BPDA-TrMPD polyimide was dissolved in 150 g of methylene chloride, and 1.23 g (3.5 equivalents per polymer repeating unit) of 1,3-dibromo-3,5-dimethyl was dissolved in the solution. Hydantoin (DBMH) was added and dissolved, and the mixture was reacted for 7 hours under reflux while irradiating with a 50 W tungsten lamp. The reaction solution was poured into methanol to precipitate the polymer. After the polymer was filtered off, it was reprecipitated and purified twice with methylene chloride-methanol. From the proton NMR analysis, the bromination rate was 150%. A 5% methylene chloride solution of this brominated polyimide was cast on a glass plate, dried at room temperature and then vacuum dried at 70 ° C. for 10 hours to obtain a brominated polyimide film having a thickness of about 30 μm. Table 3 shows the measurement results of the pure gas permeation performance of this membrane.
Shown in.

Example 5 The brominated polyimide film obtained in Reference Example 2 was mixed with 0.5% by weight of diethanolamine (D
EA) After being immersed in an aqueous solution for 10 hours, vacuum dried at 70 ° C. for 10 hours to obtain a DEA-modified polyimide film (BPDA-T).
rMPD (Br1.50 / DEA)) was obtained. Table 3 shows the measurement results of the pure gas permeation performance of this membrane, and Table 4 shows the measurement results of the gas separation performance of the CO ₂ / N ₂ mixed gas.

Example 6 3.00 g of 6FDA-TrMPD polyimide was dissolved in 150 g of methylene chloride, to which 2.12 g (2.2 equivalents per polymer repeating unit) of N-bromosuccinimide (NBS) was added. It was melted and reacted for 5 hours under reflux while irradiating with a 50 W tungsten lamp. The reaction solution was poured into methanol to precipitate the polymer. After the polymer was collected by filtration, it was reprecipitated and purified twice with methylene chloride-methanol. Proton NMR
From the analysis, the bromination rate was 130%. A 5% methylene chloride solution of this brominated polyimide was cast on a glass plate, dried at room temperature, and then vacuum dried at 70 ° C. for 10 hours to obtain a brominated polyimide film (6FDA) having a thickness of about 30 μm.
-TrMPD (Br1.30)) was obtained.

0.5% by weight of this brominated polyimide film
Of the DEA-modified polyimide film (6FDA-TrMPD (Br1.30 / D) after being immersed in a diethanolamine (DEA) aqueous solution for 10 hours and then vacuum dried at 70 ° C. for 10 hours.
EA)) was obtained. Table 3 shows the measurement results of the pure gas permeation performance of this membrane, and Table 4 shows the measurement results of the gas separation performance of the CO ₂ / N ₂ mixed gas.

Comparative Examples 1 to 4 Base Polyimide Resin B
PDA-TrMPD and 6FDA-TrMPD,
The gas permeation performances of the polyimide (6FDA-DAF) from 6FDA and 2,7-diaminofluorene (DAF) and the polyethersulfone (PSF) membrane in pure gas and CO ₂ / N ₂ mixed gas were measured. The results are shown in Table 3 and Table 4, respectively.

[0040]

[Table 3]

[0041]

[Table 4]

From the results of Examples 2 to 7 and Comparative Examples 1 to 4, the separation membrane of the present invention is widely excellent as a gas separation membrane for hydrogen / methane, oxygen / nitrogen, carbon dioxide / nitrogen, carbon dioxide / methane and the like. As shown in FIG. 3, the separation performance of carbon dioxide gas / nitrogen mixed gas is 40 to 50% higher than that of the conventional polyimide membrane, and the separation performance is 80 to 90 under high humidity conditions. It can be seen that a high separation performance is obtained.

[0043]

The gas separation membrane of the present invention is excellent in heat resistance, chemical stability and mechanical properties, and also hydrogen / methane, oxygen /
It has high gas separation performance for nitrogen, carbon dioxide / nitrogen, carbon dioxide / methane, etc., and has suitable gas permeability and separation performance for separating acidic gases such as carbon dioxide and sulfur dioxide from combustion exhaust gas. . In addition, the combustion gas (CO ₂ , SO
₂ ) / (N ₂ , O ₂ ) separation characteristics and CO ₂ / CH
_{4 Although} it has excellent separation performance, H, which is also a polar gas,
It is expected to be suitable for the separation of ₂ S, and is expected to be applied to improve the quality of natural gas and anaerobic fermentation gas as fuel.

Considering the combustion gas of a large-scale boiler such as a thermal power plant, it is expected that water vapor having a relative humidity of 30 to 40% will coexist, but as shown in the data of Example 2 in FIG. It is considered that the performance of 50 Barrer or more and the carbon dioxide / nitrogen separation coefficient of 60 or more has practically important significance as a separation membrane for the purpose of separating and recovering carbon dioxide in exhaust gas. Further, since SO ₂ gas is a gas having a higher acidity than carbon dioxide gas, it is expected to have the same or even higher permeation performance and separation performance as carbon dioxide gas. Further, according to the method for producing a gas separation membrane of the present invention, the gas separation membrane having the above-mentioned performance can be easily produced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a gas permeation measuring device used in Examples in the presence of mixed gas and water vapor.

FIG. 2 is a comparison diagram of carbon dioxide permeation coefficient and carbon dioxide / nitrogen gas separation coefficient of the separation membrane manufactured in Example 1.

FIG. 3 is a comparison diagram of carbon dioxide permeation coefficient and carbon dioxide / nitrogen gas separation coefficient of the separation membranes of Examples 2 to 7 and Comparative Examples 1 to 4.

FIG. 4 is a diagram showing the humidity dependence of the carbon dioxide permeability coefficient and the carbon dioxide / nitrogen gas separation coefficient of the separation membrane of Example 2.

[Explanation of symbols]

A Supply gas B Flow rate control valve C
Humidifier D Constant temperature bath E Sweep gas F
Dehumidifier G Permeation cell H Pressure gauge I
Hygrometer J Rokuhoko

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Matsumoto Hikiyo 1-1-1, Niihama, Arai-cho, Takasago-shi, Hyogo Prefecture Mitsubishi Heavy Industries, Ltd. Takasago Research Laboratory (72) Inventor Shigekazu Hatano 2-chome, Niihama, Arai-cho, Takasago-shi, Hyogo No. 1 Mitsubishi Heavy Industries, Ltd. Takasago Research Laboratory (72) Inventor Yoshimasa Ando 1-1-1, Wadasaki-cho, Hyogo-ku, Kobe-shi, Hyogo Prefecture Mitsubishi Heavy Industries, Ltd. Kobe Shipyard (56) Reference Japanese Patent Laid-Open No. 3- 106426 (JP, A) JP 63-111921 (JP, A) JP 6-71148 (JP, A) JP 3-21336 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B01D 61/00-71/82 B01D 53/22

Claims (4)

(57) [Claims] 1. An aromatic polyimide having a repeating unit represented by the general formula (A) as a basic skeleton, wherein a part or all of hydrogen atoms of an alkyl group in the general formula (A) are amine compound residues. A gas separation membrane comprising a substituted amine-modified polyimide. [Chemical 1] In the formula (A), X and Y have the following meanings. X: aromatic tetracarboxylic acid compound residue Y: aromatic diamine compound residue having at least one alkyl group as a substituent 2. An aromatic polyimide having a repeating unit represented by the general formula (A) as a basic skeleton, wherein a part or all of hydrogen atoms of an alkyl group in the general formula (A) are amine compound residues. A gas separation membrane, which is substituted and is composed of an amine-modified polyimide in which some or all of the amine compound residues form a crosslinked structure with another basic skeleton. 3. A brominating agent is allowed to act on a polyamic acid, which is a precursor of an aromatic polyimide having a repeating unit represented by the general formula (A) as a basic skeleton, to introduce bromine into a part of an alkyl group. Obtained by imidizing the obtained brominated polyamic acid or by causing a brominating agent to act on an aromatic polyimide having a repeating unit represented by the general formula (A) as a basic skeleton to introduce bromine into a part of an alkyl group. The brominated polyimide obtained is reacted with an amine compound to obtain an amine-modified polyimide in which a part of hydrogen atoms of the alkyl group in the general formula (A) is substituted with an amine compound residue, and the brominated polyamic acid, before bromination A method for producing a gas separation membrane, which comprises forming the membrane at the stage of the polyimide, brominated polyimide or amine-modified polyimide. 4. The gas separation membrane according to claim 3, wherein a film is formed in the form of an amine-modified polyimide in which a part of bromine remains, and the amine compound is further reacted to crosslink. Manufacturing method.