JP2000042342A - External pressure type composite hollow fiber membrane for gas separation and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an external pressure type composite hollow fiber membrane for gas separation combining high gas permeability and high gas separating property, moreover, heat resistance and pressure resistance and to provide its production method. SOLUTION: The external pressure type composite hollow fiber membrane for gas separation is composed of a dense layer being an outer surface and a porous layer supporting integrally the dense layer, and the membrane has a porous unsymmetrical hollow supporting membrane having a fractional molecular weight within a range of 5000-100000 and strong supporting function and a nonporous thin film consisting of 6FDA based fluorine-containing polyimide resin and having gas separating function on the dense layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite hollow fiber membrane for gas separation having high gas permeability and high gas separation, heat resistance and pressure resistance, and a method for producing the same. More specifically, the separation and recovery of hydrogen from platform off-gas, the separation and removal of carbon dioxide contained in alternative natural gas (SNG) containing methane as a main component, and the use of landfill gas (generated from waste buried underground) The present invention relates to an external-pressure-type composite hollow fiber membrane for gas separation which can be suitably used for separation and removal of carbon dioxide contained in organic gas) and a method for producing the same.

[0002]

2. Description of the Related Art In the early days of gas separation membranes, a so-called asymmetric structure membrane composed of a single material in which a dense layer on the surface is integrally supported by a porous layer continuous thereto is mainly used. As a typical example of the asymmetric structure film, a film made of a cellulose resin or a polysulfone resin has been used. However, such an initial asymmetric structure film has a drawback that film defects such as pinholes are likely to occur during the film formation,
Since a single membrane material is responsible for the gas separation function and the strength support function, there is also a problem that available polymer materials are limited. Therefore, the mainstream of research and development of gas separation membranes has since shifted to composite structure membranes, in which the gas separation function and the strength support function are shared and assigned to separate thin films, and the gas separation membrane material is accordingly The types of polymer polymers that have the potential as above have increased dramatically.

Thus, since then, many technologies have been developed for composite membranes for gas separation, but the flow of development of composite membranes for gas separation is roughly divided into two. The first is the development of a gas separation membrane material having excellent gas permeability and gas separation properties, and the second is the development of a thinning technique for increasing the gas permeation rate. As one method of this thinning technique, a method of forming a thin film having gas separation properties by a dip coating method on a dense layer of a porous asymmetric supporting film has been conventionally proposed.

In the design of a composite membrane, it is ideal to make the gas permeation resistance of the support membrane negligible as much as possible compared to that of a thin film having a separation function in order to maximize the gas permeation rate. It is a target. However, when using such a porous asymmetric support membrane, the polymer of the material for gas separation flows into the pores of the dense layer of the support membrane and membrane defects are likely to occur, and the original gas separation performance of the material In order to express, the thin film has to be thickened, and as a result,
A practical membrane permeation rate cannot be obtained. On the other hand, when a support membrane having a smaller pore diameter is used to suppress the occurrence of membrane defects, there is a trade-off that the gas permeability resistance of the support membrane increases and the gas permeability rate of the composite membrane is impaired.

[0005]

SUMMARY OF THE INVENTION The present inventors have conducted intensive studies to solve the above-mentioned problems in the conventional composite hollow fiber membrane for gas separation and the method for producing the same, and as a result, integrated the dense layer on the surface with the dense layer. A gas separation function comprising a 6FDA-based fluorine-containing polyimide resin on the dense layer of a porous asymmetric hollow support membrane having a limited molecular weight cut-off in a limited range and having a strong support function. By forming a non-porous thin film having the above, it is possible to obtain a composite hollow fiber membrane for external pressure gas separation having both high gas permeability and high separability, and further, both heat resistance and pressure resistance, In addition, the present inventors have found that such a composite hollow fiber membrane can efficiently perform separation of carbon dioxide and methane, separation and recovery of hydrogen, and the like, leading to the present invention.

[0006]

The composite medium-filament membrane for external pressure gas separation according to the present invention comprises a dense layer on the outer surface and a porous layer integrally supporting the outer layer, and has a fraction in the range of 5,000 to 100,000. A porous asymmetric hollow support membrane having a molecular weight and a strong support function, and a non-porous thin film having a gas separation function comprising a 6FDA-based fluorine-containing polyimide resin on the dense layer. It is characterized by.

[0007] The composite medium-filtration membrane for external pressure gas separation according to the present invention comprises a dense layer on the outer surface and a porous layer integrally supporting the outer layer, and has a molecular weight cut-off in the range of 5,000 to 100,000. Then, a solution obtained by dissolving a 6FDA-based fluorine-containing polyimide resin in an organic solvent is brought into contact with the dense layer of the porous asymmetric hollow support membrane having a strong support function, and then the organic solvent is removed by evaporation. Then, it can be obtained by forming a non-porous thin film made of the 6FDA-based fluorine-containing polyimide resin on the dense layer.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The primary factor governing the economics of gas separation is the required gas permeation rate. When the required gas permeation rate is low, the necessity of pressurizing the gas supplied to the membrane becomes higher, and as a result, the equipment cost and operation cost increase. The increase in the membrane area of the membrane housed in the membrane module helps to solve the above problem. It is conventionally known that the membrane area that can be accommodated per unit capacity of a membrane module is larger in a hollow fiber membrane module filled with a hollow fiber membrane than in a spiral type module wound in a flat membrane.

Further, in the hollow fiber membrane structure, it is obvious that the membrane area is larger when the thin film having the gas separation function is located on the outer surface than on the inner surface of the hollow support membrane. From such a viewpoint, the present invention also employs an external pressure type composite hollow fiber membrane structure.

In the present invention, the external pressure type composite hollow fiber membrane for gas separation refers to a thin film having a gas separation function on the outer surface of a porous asymmetric hollow support membrane having a strong support function, that is, on a dense layer. A hollow fiber membrane that is formed and can supply a gas mixture to be separated to the outside of the composite hollow fiber membrane and obtain a separated gas (mixture) inside the composite hollow fiber membrane.

Hereinafter, a composite hollow fiber membrane for external pressure gas separation according to the present invention and a method for producing the same will be described in detail.

In the present invention, the porous asymmetric hollow support membrane having a strong support function is a hollow fiber membrane having an asymmetric structure composed of a dense layer on the outer surface and a porous layer integrally supporting the dense layer. The inner and outer diameters of such a hollow support membrane are:
Although not particularly limited, the outer diameter is preferably 200 to 600 μm from the viewpoint of increasing the membrane surface area of the membrane module. Also, in consideration of the pressure resistance and the efficient discharge of the permeated gas, the inner diameter is preferably in the range of 100 to 500 μm.

According to the present invention, such a porous asymmetric support membrane has a cut-off molecular weight in the range of 5,000 to 100,000. When the molecular weight cut-off of the porous asymmetric support membrane is smaller than 5000, the gas permeation rate of the obtained composite membrane is not sufficient. On the other hand, when it is larger than 100,000, as described later, the composite membrane of the present invention has In the production, when a solution of 6FDA-based fluorine-containing polyimide resin is brought into contact with the dense layer on the outer surface of the porous asymmetric support membrane, 6FD
The solution of the A-based fluorinated polyimide resin penetrates into the inside of the support membrane, and also forms a dense layer of 6FDA-based fluorinated polyimide resin inside the support membrane, thereby reducing the gas permeation rate of the obtained composite membrane. Because you do.

Here, the molecular weight cutoff of the porous asymmetric support membrane is determined by measuring the exclusion ratio of the support membrane with respect to a solute whose molecular weight is known when the porous asymmetric support membrane is in a wet membrane state. Can be. In the present invention, an aqueous solution containing polyethylene glycol having a molecular weight distribution of monodisperse at a concentration of 5000 ppm as a solute is supplied to the membrane surface at a temperature of 25 ° C. and a pressure of 4 kg / cm ² , and the rejection is at least 90%. The molecular weight of polyethylene glycol is defined as the molecular weight cut off of the membrane.

The properties required of the material of the porous asymmetric support membrane having such a strong support function include, of course, the durability against the organic solvent and heat used in the production of the composite middle fiber membrane for gas separation according to the present invention. In order to enhance the durability in a gas separation system, the general formula (I) which is particularly excellent in heat resistance and solvent resistance

[0016]

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(Wherein, R is a divalent aromatic, alicyclic or aliphatic hydrocarbon group comprising a carbon atom and a hydrogen atom, or these hydrocarbon groups are bonded by a divalent organic bonding group. A repeating unit represented by the following formula: wherein the intrinsic viscosity [η] measured as an N-methyl-2-pyrrolidone solution at 30 ° C. is in the range of 0.5 to 2 dL / g. Resins are particularly preferably used.

Such a polyimide resin is 1,2,3,4-
Butanetetracarboxylic acid and the following general formula (II)

[0019]

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(Wherein R is a divalent aromatic, alicyclic or aliphatic hydrocarbon group comprising a carbon atom and a hydrogen atom, or these hydrocarbon groups are bonded by a divalent organic bonding group. The divalent organic group is obtained by a reaction with a diamine, and is hereinafter referred to as a BTC-based polyimide resin. When the intrinsic viscosity of the BTC-based polyimide resin is too small, the film forming property of the asymmetric film is not sufficient. On the other hand, when it is too large, it becomes difficult to dissolve in various solvents and the film forming workability becomes poor. .

In the present invention, the divalent group R in the diamine is not particularly limited, but preferred specific examples include, for example,

[0022]

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And the like.

Therefore, in the present invention, preferred specific examples of the diamine include 4,4'-diaminodiphenyl ether and 4,4'-diaminodiphenylmethane.

The composite aerial fiber membrane for external pressure type gas separation according to the present invention uses the porous asymmetric hollow fiber membrane made of the BTC-based polyimide resin as a support membrane, and has a porous membrane on the dense layer on the outer surface.
A non-porous thin film having a gas separation function and made of an FDA-based fluorine-containing polyimide resin is formed.

As is well known, a porous asymmetric hollow fiber membrane made of a BTC-based polyimide resin and having a dense layer on the outside is prepared by preparing a wet membrane by wet membrane formation, as is well known.
It may be dried.

The 6FDA fluorine-containing polyimide used in the present invention is represented by the following formula (III)

[0028]

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5,5'-2,2,2-trifluoro-1- (trifluoromethyl) ethylidene-bis-1,3
-Refers to a polyimide resin obtained by the reaction of isobenzofurandione (6FDA) with a diamine.

As described above, the diamine is not particularly limited, and various diamines can be used. 6FD
A-based fluorine-containing polyimide, due to its bulky structure,
It has a high gas permeability coefficient and is very good as a gas separation material.

In general, a polyimide resin is excellent in solvent resistance and can be dissolved only in a solvent having a strong dissolving power. Fortunately, a 6FDA-based fluorine-containing polyimide resin having a fluorine atom has a medium solubility. Dissolves in various solvents.
As such a solvent having a medium solubility, for example,
Ketone solvents and ether solvents can be mentioned. More specifically, for example, acetone, acetonylacetone, diisobutyl ketone, diethyl ketone, dipropyl ketone, methyl amyl ketone, methyl butyl ketone, methyl cyclohexanone, methyl ethyl ketone, methyl n-hexyl ketone, methyl isobutyl ketone, methyl propyl ketone , Diethylene glycol dimethyl ether, diethylene glycol diethyl ether and the like. In the present invention, among these, a medium-boiling solvent is particularly preferably used in order to prepare a solution of a 6FDA-based fluorine-containing polyimide resin.

By contacting a relatively dilute solution of the 6FDA fluorine-containing polyimide resin in such an organic solvent with the dense layer outside the porous asymmetric hollow fiber membrane made of the BTC polyimide resin, the 6FDA It is possible to form a non-porous thin film having a gas separation function and made of a fluorine-containing polyimide resin. In practice,
The above 6FDA-based fluorinated polyimide resin solution is applied to the outer surface of the porous asymmetric hollow fiber membrane made of the BTC-based polyimide resin, or the 6FDA-based fluorinated polyimide resin solution is made of a porous asymmetric hollow fiber made of the BTC-based polyimide resin. After immersing the porous asymmetric hollow fiber membrane in a 6FDA-based fluorinated polyimide resin solution so as not to enter the interior of the fiber membrane, depending on the organic solvent of the 6FDA-based fluorinated polyimide resin solution, and as necessary When the organic solvent is removed by heating to an appropriate temperature, usually about 50 to 150 ° C., and the organic solvent is removed, the above-mentioned 6FDA-based fluorine-containing polyimide resin is formed on the dense layer of the porous asymmetric hollow fiber membrane made of the BTC-based polyimide resin. A non-porous thin film having a gas separation function can be formed.

It is desirable that the non-porous thin film made of the 6FDA fluorine-containing polyimide resin is as thin as possible. That is, as described above, the gas permeation rate of the obtained composite membrane is substantially governed by the thickness of the 6FDA-based fluorine-containing polyimide resin thin film, and the gas permeation rate increases as the film thickness decreases. Therefore, the above 6FD
A type fluorine-containing polyimide resin solution usually has a resin concentration of
It is prepared so as to be 0.01 to 15% by weight, preferably 0.1 to 12% by weight. When the resin concentration is less than 0.01% by weight, defects such as pinholes tend to occur in the formed thin film, which is not preferable. On the other hand, when the resin concentration is more than 15% by weight, the thickness of the formed thin film is large. It is not preferable because the gas permeation rate of the composite membrane is too low in practical use.

As described above, the non-porous thin film having a gas separation function of the 6FDA-based fluorinated polyimide resin laminated on the dense layer of the porous asymmetric hollow fiber membrane made of the BTC-based polyimide resin is composed of 6FDA Although it depends on the concentration of the system fluorine-containing polyimide resin solution and its coating thickness, it is usually 0.01 to 5 μm, preferably 0.01 to 2 μm.
m. If the thin film is too thin, the film is likely to have defects, while if it is too thick, the gas permeation rate is too low for practical use.

[0035]

As described above, according to the present invention, a porous asymmetric hollow support membrane having a strong support function having a molecular weight cut-off in the range of 5,000 to 100,000 is supported. As a membrane, it is possible to form a non-porous thin film having a gas separation function made of an extremely thin 6FDA-based fluorine-containing polyimide resin on a dense layer on the surface thereof, thereby increasing the gas permeation rate as a composite membrane. Can be.

Further, if the outer diameter of the porous asymmetric hollow support membrane is reduced, the membrane area of the hollow fiber membrane module produced by converging the obtained composite hollow fiber membrane can be extremely large, and thus, the gas It is possible to obtain a membrane module having a high permeation rate, and by using such a membrane module, it is possible to reduce equipment costs and operation costs in gas separation.

In addition to the above, according to the present invention, since a porous asymmetric hollow support membrane made of a BTC-based polyimide resin having excellent heat resistance and organic solvent resistance is used, various kinds of organic solvent vapor mixed therein can be used. It can also be suitably used for gas separation.

[0038]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to the examples.
In the following, parts are parts by weight.

Example 1 The diamine component comprising the repeating unit (I) was 4,4 '
Dissolving 16 parts of BTC-based polyimide resin (intrinsic viscosity [η] 0.91 dL / g) which is diaminodiphenyl ether, 16 parts of diethylene glycol dimethyl ether and 27 parts of N, N-dimethylformamide in 41 parts of N-methyl-2-pyrrolidone Then, a solution was obtained. This solution is extruded from an annular nozzle into a hollow shape, and water is used as a coagulating liquid to coagulate from the inner and outer surfaces.
A 0 μm porous asymmetric hollow fiber membrane was obtained.

As a result of observing the cross section of the porous asymmetric hollow fiber membrane with a scanning electron microscope, it was found that the porous asymmetric hollow fiber membrane had a dense layer on the surface and had a porous structure that became coarser toward the inside. The molecular weight cutoff of this support membrane is 2000
0 and the pure water permeation rate was 31 L / m ² · hr · atm. The porous asymmetric hollow fiber membrane was dried at 50 ° C. to obtain a dried membrane, which was used as a porous asymmetric hollow support membrane.

On the other hand, 6FDA-BA having an average molecular weight of 60,000, which is a kind of 6FDA-based fluorine-containing polyimide resin, is used.
AF (Formula (IV)

[0042]

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And a repeating unit represented by 1) 1 part was dissolved in 99 parts of diethylene glycol dimethyl ether to prepare a resin solution having a concentration of 1.0% by weight.

The above 6FDA-BAAF solution was uniformly applied to the outer surface of the porous asymmetric hollow fiber membrane made of the BTC-based polyimide resin by a dipping method.
After heating to 0 ° C. to evaporate and remove diethylene glycol dimethyl ether from the coating, leave it at room temperature for 1 hour.
About 0.2 μm thick on the dense layer of the porous asymmetric hollow fiber membrane
A composite hollow fiber membrane for gas separation according to the present invention having a non-porous thin film of 6FDA-BAAF of m was obtained.

The gas permeation rate of this composite hollow fiber membrane was measured.
Then, at room temperature, CO_TwoPermeation speed (P (CO_Two)) is 0.
26Nm^Three/ M^Two・ Hr ・ atm, methane permeation rate (P
(CH_Four)) Is 0.0063 Nm^Three/ M^Two・ Hr ・ atm
Therefore, the separation factor (P (CO _Two) / P (CH_Four)) Is 41.3
Met.

Claims (4)

[Claims] 1. A porous asymmetric hollow support membrane comprising a dense layer on the outer surface and a porous layer integrally supporting the outer layer, having a molecular weight cutoff in the range of 5,000 to 100,000 and having a strong support function. A non-porous thin film having a gas separation function comprising a 6FDA-based fluorine-containing polyimide resin on the dense layer, and a composite hollow fiber membrane for external pressure type gas separation. 2. A porous asymmetric hollow support membrane having a strong support function is represented by the general formula (I): (Wherein, R is a divalent aromatic, alicyclic or aliphatic hydrocarbon group composed of a carbon atom and a hydrogen atom, or a divalent group formed by bonding these hydrocarbon groups with a divalent organic bonding group. The composite hollow fiber membrane for external pressure type gas separation according to claim 1, which is formed of a polyimide resin comprising a repeating unit represented by the following formula: 3. A porous asymmetric hollow support membrane comprising a dense layer on the outer surface and a porous layer integrally supporting the outer layer, having a molecular weight cut-off in the range of 5,000 to 100,000 and having a strong support function. After contacting a solution obtained by dissolving a 6FDA-based fluorinated polyimide resin in an organic solvent on the dense layer, the organic solvent is evaporated and removed, and the 6FDA-based fluorinated polyimide resin is removed on the dense layer. A method for producing a composite hollow fiber membrane for external pressure type gas separation, comprising forming a non-porous thin film comprising: 4. A porous asymmetric hollow support membrane having the general formula (I): (Wherein, R is a divalent aromatic, alicyclic or aliphatic hydrocarbon group composed of a carbon atom and a hydrogen atom, or a divalent group formed by bonding these hydrocarbon groups with a divalent organic bonding group. The method for producing a composite hollow fiber membrane for external pressure gas separation according to claim 3, comprising a polyimide resin represented by the following formula: