JPH05146650A - Fluorine-containing polyimide-based asymmetric or dual membrane, and gas separating/concentrating method using the membrane - Google Patents

Abstract

PURPOSE:To provide a dual membrane or an asymmetric membrane to be used for separation and concentration of a specified component from mixed gases. CONSTITUTION:A membrane for separation and concentration of a gas is a fluorine-containing polyimide-based asymmetric membrane which is made of polyimide resin prepared from a fluorine atom-containing diamine and an acid anhydride and has an anisotropic structure or a fluorine-containing polyimide- based dual membrane consisting of an asymmetric membrane and a thin film of elastomer formed on the membrane.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluorine-containing polyimide-based gas separation membrane, and more specifically, to a composite membrane or asymmetric membrane used for separating and concentrating a specific component from an industrial mixed gas. The present invention relates to a manufacturing method and a mixed gas separation / concentration method using the same.

[0002]

2. Description of the Related Art Polyimide has a high glass transition temperature and a rigid structure, and is known as a membrane separation material having excellent heat resistance and chemical resistance. However, conventional polyimides have high selectivity as compared with other glassy polymers, but their transparency is insufficient, which is not satisfactory.

In recent years, fluorine-containing polyimides have a large volume of hexafluoroisopropyl group (-C (CF ₃ ) _2- ) group and improved solubility of gas due to fluorocarbon.
It has been found that compared to conventional polyimide, it is possible to improve high permeability while maintaining high selectivity, for example, 5,5 '
-2,2,2-Trifluoro-1- (trifluoromethyl) ethylidene-bis-1,3-isobenzofurandione (6FDA) A polyimide containing aromatic acid anhydrides and aromatic diamines or methylenedianiline Homogeneous films have been proposed (for example, JP-A-63-123420, US Pat. No. 4,705,540, JP-A-1-262925, JP-A-2-261524, etc.).

[0004]

However, these polyimide homogeneous membranes are still unsatisfactory in their permeability, selectivity and applicability to various gases, and in order to have sufficient mechanical strength, they are homogeneous. Since the membrane becomes thick and it is not possible to provide an industrially satisfactory permeation flux,
It was difficult to use in practice.

The present invention has been made to solve these problems, and provides a fluorine-containing polyimide composite membrane or an asymmetric membrane having a very high gas permeation flux while maintaining a high gas separation coefficient. The inventors of the present invention have found that they can practically and efficiently separate and concentrate various mixed gases by using these membranes, and have completed the present invention.

[0006]

That is, the present invention provides a fluorine-containing polyimide asymmetric film having an anisotropic structure composed of a polyimide resin obtained from a diamine containing a fluorine atom and an acid anhydride, or a support composed of the polyimide resin. Provided is a fluorine-containing polyimide-based composite film in which a thin film of an elastomer polymer is formed on the film.

The fluorine-containing polyimide resin used in the present invention comprises a diamine containing a fluorine atom and an acid anhydride.

The portion of the polyimide resin formed from the fluorine-containing diamine is a divalent aromatic, alicyclic or aliphatic hydrocarbon group containing a fluorine atom, or an organic bonding group in which these hydrocarbon groups are divalent. It is composed of a divalent organic group bonded by.

Preferred divalent aromatic hydrocarbon groups include, for example, phenylene groups having 6 to 12 carbon atoms, and such divalent aromatic hydrocarbon groups are bonded to form an organic group. Examples of the organic bonding group to be used include a methylene group, an isopropylidene group, an ether group, a sulfide group, a sulfone group, and a hexafluoroisopropyl group. Moreover, as a preferable divalent aliphatic hydrocarbon group, a C1-C10 linear or branched alkylene group can be mentioned, for example, it couple | bonds with this divalent aliphatic hydrocarbon group, and it is a divalent organic group. Examples of the organic bonding group forming the group include an ether group, a sulfide group, a polyoxyalkylene group and the like. More preferable divalent alicyclic hydrocarbon group has, for example, 6 carbon atoms.
To 12 cyclohexylene groups and alkyl-substituted cyclohexylene groups, and examples of the organic bonding group that forms a divalent organic group by bonding such a divalent alicyclic hydrocarbon group include a methylene group. , Isopropylidene group, ether group, sulfide group, sulfone group and the like.

Particularly in the present invention, the divalent organic group is an aromatic hydrocarbon group or two aromatic hydrocarbon groups so that the obtained film has high heat resistance and hydrocarbon resistance. Is preferably an aromatic hydrocarbon group formed by bonding with an organic bonding group such as a methylene group, an isopropylidene group, an ether group, a sulfide group, a sulfone group, and a hexafluoroisopropyl group, and a preferred specific example of such an aromatic group. As an example, the following [Chemical formula 1] can be mentioned.

[0011]

[Chemical 1]

The portion of the polyimide resin formed of an acid anhydride is not particularly limited structurally, but an acid anhydride having the structure of the following [Chemical Formula 2] is preferable.

[0013]

[Chemical 2]

The glass transition temperature of the fluorine-containing polyimide resin of the present invention comprising these fluorine-containing diamine and acid anhydride is from 200 to 40 from the viewpoint of good physical properties and gas permeation selectivity.
The temperature is preferably 0 ° C, particularly 300 to 400 ° C.

Further, its intrinsic viscosity η (η = 1 / 0.5l
n solution viscosity / solvent viscosity, measurement temperature 30 ° C., solution concentration 0.5 g polymer / 100 ml solvent, solvent N-methyl-2-pyrrolidone) is preferably 0.1 to 7, particularly preferably 0.5 to 3.
The intrinsic viscosity is closely related to the degree of polymerization or the molecular weight, and if the intrinsic viscosity is too small, the film forming performance of the polymer is poor,
On the other hand, if it is too large, it becomes difficult to dissolve in a solvent, resulting in poor workability in film formation.

The fluorine-containing polyimide resin used in the present invention can be obtained by a known polymerization method, for example, N-
An acid anhydride added to a methylpyrrolidone solvent and a fluorine-containing diamine can be synthesized at room temperature, and the obtained polyamic acid solution can be produced by thermal imidization by azeotropic distillation or chemical imidization with a dehydrating agent.

The method for producing the support membrane of the asymmetric membrane or composite membrane having an anisotropic structure in the present invention is not particularly limited, but the following method is preferable. That is, after applying a film-forming solution prepared from a fluorine-containing polyimide resin and a first organic solvent having compatibility with water on an appropriate supporting substrate, 1 second to 5 minutes, preferably
It is left as it is for 20 seconds to 3 minutes, preferably, the humidity of the atmosphere is reduced as much as possible, a part of the solvent is evaporated, and then the fluorine-containing polyimide resin is not dissolved. By immersing in a second organic solvent having compatibility with each other for a short time, and then immersing in water, an asymmetric film having an anisotropic structure is obtained, which is dried and further heat-treated to obtain a fluorine-containing polyimide. Asymmetric membranes or supporting membranes consisting of

Examples of the first organic solvent used for preparing the film forming solution include N-alkyl-2-pyrrolidone such as N-methyl-2-pyrrolidone and N-such as N-methyl-2-piperidone.
Examples thereof include dialkylacetamide such as alkyl-2-piperidone and dimethylacetamide, dialkylformamide such as dimethylformamide, and particularly N-methyl-2-pyrrolidone is preferably used.

The concentration of the polyimide resin in the film forming solution is usually 3 to 40% by weight, preferably 5 to 30% by weight.
The range is. When the above concentration is too high, the viscosity of the membrane forming solution becomes excessively high, which makes it difficult to uniformly coat it on a supporting substrate, and the gas permeation rate of the obtained membrane becomes small, resulting in a gas separation membrane. This is because it lacks in practicality. The viscosity of the film-forming solution is usually adjusted to 50 to 5000 poise, preferably 100 to 2000 poise in relation to the concentration of the polyimide resin in the film-forming solution.

In the present invention, when pursuing a gas permeation flux higher than the separation coefficient of the obtained membrane, a swelling agent may be added to the membrane-forming solution to facilitate formation of the sponge-like porous support layer. .. Such a swelling agent dissolves in both the first organic solvent and water and is added to 50 ml of a 2% by weight polyimide resin N-methyl-2-pyrrolidone solution at 25 ° C.
The solidification number defined as the minimum number of ml that should be added to cause cloudiness due to the precipitation of resin at a temperature of 50 ~
It has a boiling point of 50 to 120 at atmospheric pressure in the range of 200.
C. cyclic ether, aliphatic ketone, alicyclic ketone,
It is a liquid organic compound selected from a lower aliphatic carboxylic acid and a lower aliphatic carboxylic acid lower alkyl ester.

Specific preferred examples of the swelling agent include:
For example, tetrahydrofuran, dioxane, acetone,
Methyl ethyl ketone, diethyl ketone, cyclohexane, acetic acid, formic acid, methyl formate, ethyl formate, methyl acetate and the like are preferably used. These swelling agents are usually used in a film forming solution in an amount of 30 to 30 parts by weight per 100 parts by weight of the polyimide resin.
300 parts by weight, preferably 50 to 150 parts by weight are blended.
When the amount of the swelling agent is too large, it may impede the uniformity of the film-forming solution, and when it is too small, a film having sufficient gas permeability to some fluorine-containing polyimide resin may be obtained. You may not be able to These swelling agents are dissolved in the film-forming solution, for example, by adding a predetermined amount to a solution in which a polyimide resin is dissolved in advance, and stirring the mixture at room temperature or under heating as necessary.

The thickness of the film-forming solution applied to the supporting substrate is usually 50 to 400 μm, preferably 100 to 30 μm.
It is adjusted to be in the range of 0 μm. Examples of the supporting base material include a plate material having a smooth surface, woven cloth, and non-woven cloth. A film obtained by using a woven fabric or a non-woven fabric as a base material is reinforced by these base materials and can be preferably used in the present invention.

In this way, the film-forming solution was applied onto the supporting substrate, and then dipped in the second organic solvent for a short period of time, and then dipped in water to obtain a surface having a dense skin layer. The fluorine-containing polyimide asymmetric film according to the present invention can be obtained by drying and heat-treating the film having an isotropic structure by an appropriate means.

Here, the second organic solvent is an organic solvent which does not dissolve the polyimide resin, but is miscible with both the first organic solvent and water, and is, for example, methanol, ethanol or propanol (particularly, Lower aliphatic alcohols such as isopropanol), butanol (particularly t-butanol), alkylene glycols such as ethyl glycol and propylene glycol, etc. are used. In addition to these, acetone, glycerin, tetrahydrofuran,
Ethylene glycol monomethyl ether, monoethyl ether or the like is used.

The dipping in the second organic solvent is usually 0 to
At a temperature of 100 ° C., it is within 1 hour, preferably within 5 minutes. Immersion in water is usually 0 to 50 ° C, preferably 0 to 30
C., particularly preferably 0 to 20.degree.

Since the membrane thus obtained contains water, it is immersed in an organic solvent miscible with both water and the organic solvent, such as alcohols, and then immiscible with water. An asymmetric membrane having a sufficient gas permeation flux can be obtained by immersing in an organic solvent such as hexane and then drying at room temperature or under heating if necessary. However, the method for drying the water-containing film is not limited to the above method.

Further, in the present invention, by further heat treating the dried membrane obtained above, a fluorine-containing polyimide membrane having higher gas separation performance and stable permeation performance can be obtained. The conditions of the heat treatment are not particularly limited, but for example, the heating rate may be 10 ° C./min or less, and the maximum temperature may be around the glass transition temperature of the fluorine-containing polyimide resin, preferably at 150 to 350 ° C. for 1 to 3 hours. ..

The thus obtained fluorine-containing polyimide asymmetric membrane is also used as a support membrane for the composite membrane of the present invention. The composite membrane of the present invention can be obtained by forming a thin film of an elastomer polymer on the dense skin layer of the asymmetric membrane.

In the present invention, the elastomeric polymer means a polymer capable of forming a flexible film, and specific examples thereof include polypropylene, polyvinyl chloride,
Ethylene-propylene copolymer, ethylene-propylene-diene copolymer, polybutadiene, polyisoprene,
Chloroprene rubber, poly (4-methyl-pentene-1), butadiene-styrene copolymer, isoprene-isobutylene copolymer, or homopolymer of ethylenic monomer or conjugated diene monomer such as polyisobutylene. A copolymer or copolymer, or a copolymer containing a monomer component having a functional group such as acrylonitrile, (meth) acrylic acid ester, (meth) acrylic acid, etc. in addition to the above monomer component, or Mention may be made of copolymers having a combination of so-called soft segments and hard segments, such as polyether polyols, polyurethane polyethers, polyurethane polyesters or polyamide polyethers. Furthermore, in addition to the above, an epoxy resin cured by a linear long-chain curing agent, ethyl cellulose,
Butoxy resin and the like can also be used as the elastomer polymer in the present invention.

In the present invention, in particular, these elastomeric polymers have a separation coefficient for a specific gas of 3 or more, a permeability coefficient larger than that of the fluorine-containing polyimide resin of the support film, and a softening temperature of 50 ° C. or more, particularly 80. It is preferably at least ° C, and among the above-mentioned examples, a homopolymer or a copolymer of an ethylenic monomer or a conjugated diene monomer is preferable.

The composite membrane of the present invention is prepared by dissolving the above-mentioned elastomer polymer in an appropriate organic solvent to form a solution, which is applied onto the skin layer of the support membrane made of the above-mentioned fluorine-containing polyimide resin and cured if necessary. And can be obtained by drying.

The above elastomer polymer solution is usually 0.05
-10 wt% concentration, preferably 0.1-5 wt% concentration, 0.01-5 μm, preferably 0.05-1 μm on the support membrane
It is applied so as to form a thin film having a thickness of. The means for applying the elastomer polymer solution to the support film is not limited at all, and for example, an applicator, a micro gravure coater or the like is used. Alternatively, the support film may be dipped in the elastomer polymer solution.

In the present invention, the form of the membrane or the module is not limited at all, and a spiral type module, a hollow fiber type module or the like can be used.

In the present invention, a mixed gas containing two or more components is brought into contact with the obtained composite membrane or asymmetric membrane to selectively permeate a specific component to separate or concentrate the mixed gas. be able to. The mixed gas to which the present invention is applied is not particularly limited, but for example,
Examples thereof include a mixed gas containing carbon dioxide / methane, oxygen / nitrogen, hydrogen / carbon monoxide, or the like, or a mixed gas containing water vapor and oxygen or nitrogen or the atmosphere. In particular, the mixed gas contains carbon dioxide and methane, It is preferably used for selectively permeating carbon dioxide through a membrane and for concentrating methane or for removing atmospheric water vapor.

[0035]

EFFECTS OF THE INVENTION The fluorine-containing polyimide resin asymmetric membrane or composite membrane according to the present invention has gas permeability and gas selectivity superior to those of conventional polyimide membranes, and further has heat resistance,
Since it has good chemical resistance and mechanical strength, it is practically preferable as a gas separation membrane.

The composite membrane of the present invention has, for example, a working temperature of 25.
Carbon dioxide permeation rate 7 × 10 ^-4 cm ³ / cm ² · s · cmHg, carbon dioxide /
It has an ideal separation factor of 40 or more for methane. Further, the asymmetric membrane of the present invention has, for example, a use temperature of 25 ° C. and a pressure difference of 2 on both sides of the membrane.
Permeation rate of carbon dioxide under the condition of atm 1.0 × 10 ^-3
It has cm ³ / cm ² · s · cmHg and an ideal separation factor of carbon dioxide / methane of 40 or more.

[0037]

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

Examples 1 to 4 Repeating unit [Chemical formula 3]

[Chemical 3] Fluorine-containing aromatic polyimide resin containing a precursor polyamic acid solution (solvent N-methyl-2-pyrrolidone)
Acetic anhydride and pyridine were added to the mixture at room temperature to obtain a compound by chemical imidization.

8 parts by weight of this fluorine-containing polyimide resin was added to 92 parts by weight of N-methyl-2-pyrrolidone as the first organic solvent and dissolved while stirring for 48 hours or more to obtain a viscous polyimide solution. This polyimide solution was filtered under pressure with nitrogen gas, and defoamed under reduced pressure to obtain a uniform transparent yellow film-forming solution. This film-forming solution is 5 with an applicator.
It is cast at a surface speed of cm / sec on a polyester non-woven fabric with a thickness of 200 μm, left for 60 seconds as it is, and after evaporating a part of the solvent, it is immersed in t-butanol at 40 ° C.
It was immersed for a time to obtain a water-containing film having an anisotropic structure. These hydrous membranes were first immersed in ethanol and then in hexane for 3 hours, respectively, and then air-dried at room temperature to obtain a support membrane composed of a dense skin layer reinforced with a nonwoven fabric and a porous support layer.

On this support film, Table 1

[Table 1] A solution of the elastomer polymer shown in (3) was applied to a thickness of about 3 to 10 μm and then dried at 80 ° C. for 30 minutes to obtain a composite film.

Table 1 also shows the permeation rate of carbon dioxide and the ideal separation coefficient of carbon dioxide / methane for each of the composite membranes thus obtained.

Examples 5 to 8 Permeation of carbon dioxide and methane in a fluorine-containing polyimide resin composite membrane obtained in the same manner as in Examples 1 to 4 except that 4 parts by weight of swelling agent dioxane was added to the membrane forming solution. Table 2 shows the separation factors for.

[0043]

[Table 2]

Examples 9 to 19 The fluorine-containing polyimide polymers obtained in Example 1 were mixed with N, N'-dimethylacetamide (DMAc) or N-methyl-2 as the first organic solvent in the proportions shown in Table 3. -In addition to pyrrolidone, 48
A viscous polyimide solution was obtained by dissolving with stirring for more than one hour. This polyimide solution was filtered under pressure with nitrogen gas, and defoamed under reduced pressure to obtain a uniform transparent yellow film-forming solution. The film-forming solution was cast with an applicator at a predetermined surface speed on a polyester non-woven fabric to a predetermined thickness to partially evaporate the solvent and then immersed in a second organic solvent at a predetermined temperature.
Then, it was immersed in ice water to obtain a water-containing film having an anisotropic structure. These water-containing membranes were first immersed in ethanol and then in hexane for 3 hours, respectively, and then air-dried at room temperature.
Heat treatment was performed at 100 and 150 ° C for 1 hour each and at 200 ° C for 0.5 hour to obtain an asymmetric membrane composed of a dense skin layer reinforced with a non-woven fabric and a porous support layer.

Table 3 shows the permeation rates of carbon dioxide and methane and the ideal separation factor of carbon dioxide / methane for each asymmetric membrane thus obtained.

[Table 3]

Examples 20 to 23 Fluorine-containing polyimide asymmetric membranes obtained in the same manner as in Examples 11 to 21 except that a swelling agent was added to the membrane forming solution and a relatively rough polyester nonwoven fabric was used. Table 4 shows the permeation rates of carbon dioxide and methane and the ideal separation coefficient for methane.

[0047]

[Table 4]

Example 24 Using the fluorine-containing polyimide polymer obtained in Example 1, the asymmetric membrane obtained by the method shown in Example 18 had a water vapor transmission rate and a nitrogen transmission rate of 5.0 × 10 ⁻³ (cm ^3), respectively. (STP) cm ²・ se
c ・ cmHg), 1.4 × 10 ^-6 (cm ³ (STP) cm ²・ sec ・ cmHg),
The ideal separation factor of water vapor / nitrogen was 3600.

Claims (5)

[Claims] 1. A fluorine-containing polyimide asymmetric film having an anisotropic structure made of a polyimide resin obtained from a diamine containing a fluorine atom and an acid anhydride. 2. A fluorine-containing polyimide composite film comprising a support film made of a polyimide resin obtained from a diamine containing a fluorine atom and an acid anhydride, and a thin film of an elastomer polymer formed on the support film. 3. Separation / concentration of a mixed gas, wherein a specific gas is selectively permeated by bringing a mixed gas containing two or more components into contact with the membrane of claim 1 or 2. Method. 4. The method for separating / concentrating a mixed gas according to claim 3, wherein the mixed gas contains carbon dioxide and methane, and the carbon dioxide is selectively permeated through the membrane to concentrate the methane. 5. The mixed gas according to claim 3, wherein the mixed gas contains water vapor and another gas, and the water vapor is selectively permeated through the membrane,
A method for separating and concentrating a mixed gas, which comprises concentrating water vapor.