JPS6393326A - Preparation of gas separating membrane - Google Patents

Abstract

PURPOSE:To prepare a gas separating membrane having a homogeneous layer of aromatic polyimide with an improved gas permeability, by adhering a monomer having a vinyl radical to a gas separating membrane having a homogeneous layer of aromatic polyimide and then heat treating the same. CONSTITUTION:A gas separating membrane having a homogeneous layer of aromatic polyimide is immersed in a solution of a monomer having a vinyl radical, constituted with a mixture of, for instance, a monomer having one vinyl radical and a monomer having two vinyl radicals, with, for instance, a monomer concentration of 0.1-10wt% and a solution temperature of 10-100 deg.C, and 0.01-5% of said monomer is adherred to said separating membrane. The, said immersed polyimide separating membrane is normally heat treated in air or inactive gas for 30-200min at a temperature of 100-300 deg.C, and solvents and volatile monomers adhered to or immersed in said separating membrane are removed.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a method for manufacturing a gas separation membrane.

More specifically, the present invention provides a gas component R1 membrane having a homogeneous layer made of aromatic polyimide useful as a hydrogen component membrane, a carbon gas separation membrane, a water vapor component R1 membrane, an oxygen enrichment membrane, and the like.
The present invention relates to an improved method of manufacturing a llll film.

[Background of the Invention] Gas fraction l11 membranes are used for purposes such as separation of various gases and eLlil, and their typical configurations are as follows:
Homogeneous membranes consisting of entirely homogeneous layers, asymmetric membranes consisting of a homogeneous layer and a porous layer, and porous membranes consisting entirely of porous layers are known. Asymmetric membranes can be divided into integral membranes obtained by forming a homogeneous layer on one side of a porous membrane by coating, and composite membranes obtained by attaching a separately prepared homogeneous membrane to one side of a porous membrane. .

An example of a composite membrane is disclosed in Japanese Patent Publication No. 59-51321. Examples include gas separation membranes in which a porous membrane is coated with a polymer and utilizes the separation performance inherent to a support polymer.

An example of an integral membrane is a gas separation membrane obtained by laminating a single layer of polymer on a porous membrane, as disclosed in Japanese Patent Publication No. 4B-17589. In this separation membrane, the separation performance is dependent on the single layer of polymer formed by coating.

Among these gas separation membranes, gas fraction 11 having a homogeneous layer
1114, that is, average j! III! fJ and asymmetric membranes are being actively researched because they have high gas separation performance. Among these, those using aromatic polyimide resin as the homogeneous membrane material are attracting attention as they are said to be suitable for use under harsh conditions due to their high heat resistance and weather resistance. ing.

However, when a gas component GL membrane is actually used, gas molecules Ia
It is often observed that gas permeability decreases over time during operation. This phenomenon occurs even in gas separation membranes made of aromatic polyimide, which is a heat-resistant polymer, used as a homogeneous membrane material, so it is necessary to improve it. In other words, in order to effectively utilize the high heat resistance of gas separation membranes using aromatic polyimide, which has high heat resistance, as a homogeneous membrane material, it is necessary to minimize the decrease in gas separation distance under continuous use conditions. is necessary.

[Object of the Invention] An object of the present invention is to provide a method for manufacturing a gas separation membrane having a homogeneous layer made of aromatic polyimide with improved gas permeability.

An object of the present invention is to provide a method for producing a gaseous component aS having a homogeneous layer made of aromatic polyimide, which exhibits less deterioration in gas separation performance especially under conditions of continued use.

[Structure of the Invention] The present invention involves immersing a gas separation membrane having a homogeneous layer made of aromatic polyimide in a solution of a monomer having a vinyl group to attach a layer on the gas separation membrane, and then soaking the monomer in a solution of a monomer having a vinyl group. The present invention provides a method for producing a gas separation membrane, which comprises heat-treating the gas-separated GL membrane to which is adhered.

A typical example of a gas separation membrane to be treated in the present invention has a carbon dioxide permeability (P'C02) of 1 x l
O-' c c / c rrr' ・sec・cmHg or more, and the ratio of permeability of carbon dioxide to methane (separation degree:
Examples include those in which p'[CO2]/P' [CHal) is 15 or more.

By the present invention 'I! A The gas separation membrane to be crushed may be a homogeneous membrane or an asymmetric membrane, and the gas separation membrane of the present invention may be in any shape such as a hollow fiber shape or a sheet shape. .

The gas separation membrane of the present invention is obtained by treating a gas separation membrane having a homogeneous layer made of aromatic polyimide with the aromatic group-containing polymer specified above.

Gas separation membrane with a homogeneous layer made of aromatic polyimide (
As ``polyimide gas separation membrane'' (hereinafter also referred to as ``polyimide gas separation membrane''), those obtained from various aromatic polyimides have been known, and the polyimide gas molecule a membrane to be treated in the present invention is made of such a membrane. The gas separation membrane may be made from any aromatic polyimide.

Aromatic polyimides are generally composed of an aromatic tetracarboxylic acid skeleton and an aromatic diamine skeleton, and by selecting compounds with various chemical structures for each, aromatic polyimides with various physical and chemical properties can be created. known to be obtained.

That is, the aromatic tetracarboxylic acid skeleton of the aromatic polyimide includes 3.3', 4.4'-benzophenonetetracarboxylic acid, and 2,3.3'.

4'-benzophenonetetracarboxylic acid, pyromellitic acid, 3,3°,4.4°-biphenyltetracarboxylic acid, and 2,3,3',4'-biphenyltetracarboxylic acid, and these aromatic tetracarboxylic acids. Examples include carboxylic acid skeletons derived from acid dianhydrides, esters, salts, etc. of carboxylic acids. Of these, 3.3'
, 4°, 4″-biphenyltetracarboxylic acid dianhydride, and 2.3.3″, 4°-biphenyltetracarboxylic acid dianhydride, etc. The present invention is particularly useful when an aromatic polyimide gas component aS having an earth acid skeleton is used.

The aromatic diamine skeleton of aromatic polyimide includes para-phenylene diamine, meta-phenylene diamine, 2.4
-diaminotoluene, 4.4'-diaminodiphenyl ether, 4.4'-diaminodiphenylmethane, 0-
)-lysine, 1,4-bis(4-aminophenoxy)benzene, 2,8-dimethyl-3,7-diamitudibenzothiophene-5,5-dioxide, bis(aminophenoxy-phenyl)propane and bis( Examples include aminophenoxy-phenyl) sulfone.

Various methods for producing polyimide using the above aromatic carboxylic acid component and aromatic diamine component are also known. For example, a method of obtaining polyimide by heating the above-mentioned aromatic carboxylic acid component and aromatic diamine component dissolved in an organic polar solvent to perform polymerization and imidization in a one-step reaction.

and an aromatic carboxylic acid component and an aromatic diamine component dissolved in an organic polar solvent, a polymerization reaction is caused at a low temperature near room temperature to once form a polyamic acid, and then a polyimide homogeneous layer is obtained from this amic acid. Methods are known.

The aromatic polyimide used in the present invention may be obtained by any method.

An example of a method for manufacturing an aromatic polyimide gas separation membrane that can be treated in the present invention will be described below using a method for manufacturing a gas separation membrane in the form of a hollow fiber membrane as an example.

First, an aromatic polyimide solution is extruded from a hollow fiber spinning nozzle into the air or directly into a coagulating liquid in the form of a hollow fiber. The extruded hollow filament is preferably stretched by about -1, while being slightly stretched under tension if necessary.
Immediately coagulate in a coagulation solution at 0 to 60'C to continuously form wet hollow fibers (hollow fibers that are self-supporting after coagulating or solidifying), and thoroughly wash the wet hollow fibers. Then, an aromatic polyimide hollow fiber membrane is obtained.

To describe this in more detail, the filtered and defoamed dope liquid is supplied to the nozzle head, and the gap between the inner peripheral surface of the opening of the orifice at the bottom of the nozzle head and the outer peripheral surface of the core tube is supplied to the nozzle head. (doughnut-shaped cavity or annular cavity)
While extruding the dope liquid under appropriate back pressure from the core tube and simultaneously supplying gas (nitrogen gas, etc.) or liquid (also called core liquid) from the internal hole of the core tube, a hollow filament of the dope liquid is formed, and the hollow fibers of the dope liquid are Hollow fibers are formed by bringing the filamentous body into contact with a coagulating liquid and coagulating it.

The coagulating liquid mentioned above must be an organic polar solvent with a low viscosity (rotational viscosity) that does not substantially dissolve the aromatic polyimide mentioned above and has excellent compatibility with the phenolic compound used in the tope liquid. Needless to say, for example, a mixed solvent of water and a lower alkyl alcohol having 1 to 5 carbon atoms such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, n-pentyl alcohol, etc. A mixed solvent mainly containing a lower alcohol or water is preferable, and an aqueous solution in which the concentration of the lower alcohol is about 40 to 9% by volume, more preferably 45 to 90% by volume is most suitable.

It is preferable that the washing step is carried out in two parts, a first washing and a second washing. The first washing is preferably carried out using a lower alcohol that is the same as or similar to the above-mentioned coagulating liquid.

After the first washing, the hollow fibers wetted with the first washing liquid are mainly composed of hydrocarbon solvent (approximately 70% by volume).
(above) The lower alcohol content of the hollow fibers is reduced to 1% by weight or less, preferably 0.5% by weight or less after the second cleaning liquid comes into contact with the hollow fibers being cleaned. It is desirable to carry out a second cleaning until then.

The hydrocarbon solvent used for the second cleaning liquid has a carbon number of 5.
~20. In particular, it is 5 to 15It1 degree, and the boiling point is about 25 to 15 degrees.
Desirable are aliphatic or alicyclic hydrocarbon compounds having a temperature of about 300°C, especially about 25 to 200'C. Examples of aliphatic hydrocarbon compounds include pentane, hexane, heptane,
Examples include octane, nonane, decane, and dodecane. Examples of alicyclic hydrocarbon compounds include cyclohexane, cyclopentane, cyclooctane, cyclododecane, methylcyclohexane, and the like.

The first washing is preferably carried out at a temperature up to the boiling point of the lower alcohol, particularly at a temperature of 0°C or higher and 5°C or more lower than the boiling point of the lower alcohol; The washing is preferably carried out at a temperature in the range of about 0'C or more and lower than the boiling point of the hydrocarbon compound, and the temperature of the second washing is from 30 to 30 °C.
It is preferable to carry out the reaction at a temperature of about 100°C, particularly about 40 to 80°C.

After the washing process is completed, the hollow fibers are subjected to a dry heat treatment, or without being subjected to a dry heat treatment, the hollow fibers are left wet in the second washing solution, which is a characteristic requirement of the present invention, and the vinyl group-containing supernatant solution is applied. Perform the soaking process.

In the present invention, polyimide gas molecules! 1 membrane is first immersed in a solution of a monomer having a vinyl group,
The above monomer is attached to the polyimide gas mixture & membrane.

The above monomers include styrene monomers such as styrene, α-methylstyrene, and vinyltoluene, monomers having one vinyl group such as acrylic acid or lower alkyl esters such as methyl, ethyl, propyl, and butyl methacrylate, and divinyl monomers. Examples include monomers having two vinyl groups such as benzene. Particularly preferred is a mixture of a monomer having - vinyl groups and a monomer having two vinyl groups.

As a solvent for the monomer solution, the above monomer is dissolved,
There are no particular limitations on the substance as long as it does not inhibit the polymerization of the above monomers. Mention may be made of alicyclic hydrocarbons such as pentane, cyclohexane, methylcyclohexane, etc., and halogenated hydrocarbons such as chloroform, chlorobenzene.

In addition, if the solvent of the monomer solution mentioned above is a solvent other than a saturated hydrocarbon, such as an aromatic hydrocarbon or a halogenated hydrocarbon, the solvent of the monomer solution should be used after the above-mentioned separation membrane immersion treatment. washed with the above saturated hydrocarbon solvent,
It is desirable to replace the monomer solvent with a saturated hydrocarbon.

The above-mentioned immersion treatment includes: - the above-mentioned monomer concentration is 0.001 to 10% by weight, preferably 1 to 5% by weight, and the solution temperature is 10% by weight.
By immersing the polyimide gas separation membrane in the above-mentioned seven-mer solution at ~100°C, preferably 40-80°C, so that 0.01-5% by weight of the above monomer adheres to the polyimide gas separation membrane. It is preferable to carry out
Further, the above-mentioned immersion treatment can be carried out under normal pressure or, if necessary, under increased pressure.

Furthermore, in the monomer solution, a polymerization initiator generally used for the polymerization of vinyl group-containing polymers, such as an organic peroxide such as benzoyl peroxide, or an azo compound such as azobisisobutyronitrile, is usually used. Preferably, the amount is present.

In the present invention, the above-mentioned immersion-treated polyimide gas separation membrane is then usually heated in air or an inert gas at a temperature of 100 to 300°C, preferably 150 to 250°C.
Heat treatment for 30-200 minutes. This heat treatment is continued until the solvent and volatile monomer attached to or impregnated in the polyimide gas separation membrane are removed.

It should be noted that although the explanation has been given using a hollow fiber gas separation membrane as an example, it goes without saying that the gas separation membrane used as the base membrane may have a flat membrane or tubular type shape.

[Effects of the invention] Although the gas separation rate of the polyimide gas separation membrane treated according to the present invention may be inferior to that of the untreated membrane in terms of initial rate, the performance deterioration when used for a long period of time is greater than that of the untreated membrane. As a result, after the initial stage, the gas separation rate is significantly higher than that of untreated gas.

Although the mechanism of action that produces such excellent effects is not necessarily clear, the monomers polymerize during the immersion treatment and heat treatment to form a polymer, which forms a polyimide gas component l! It is presumed that this is because it is attached to one film or is adsorbed.

Reference examples and examples of the present invention are shown below.

[Reference Example] Preparation of aromatic polyimide solution 3.3',4.4''-biphenyltetracarboxylic dianhydride (s-BPDA) 500 mmol, 2.8-dimethyl-3,7-diamitudibenzothiophene -5.5-
450 mmol of dioxide, 50 mmol of 4,4'-diaminodiphenyl ether, and 1,470 g of parachlorophenol were placed in a separable flask equipped with a stirrer, a nitrogen gas introduction tube, and a cooling tube, and heated from room temperature to 180'C while flowing nitrogen gas. After heating and raising the temperature for about 1 hour, polymerization was carried out at 180°C for 10 hours to obtain an aromatic polyimide solution (polymerization reaction liquid).

Body) Separation of the medium yarn ゛Use the above polymerization reaction solution as it is as a dope solution, and insert it into the tube-in-orifice type hollow fiber spinning nozzle of the spinning device (the center of the opening of the orifice with an inner diameter of 1.0 mm). The outer diameter is 0.6mm and the inner diameter is 0.3m.
70°C
A dope solution heated to 100% is supplied under pressure, and while a small amount of nitrogen gas is supplied from the core tube, the dope solution is supplied from the annular space between the inner periphery of the opening of the orifice of the spinning nozzle and the outer periphery of the core tube. extrusion to form a hollow filament, followed by
The hollow fibers are sufficiently immersed in a coagulation solution (approximately O''C) consisting of an aqueous solution of approximately 70% ethanol, and the hollow fibers are coagulated (solidified) in a wet state (parachlorophenol content: :5% by weight).The hollow fibers were wound up in a skein in a wet state, and the wound body of the hollow fibers was further immersed in a flow of ethanol (first cleaning solution) at about 50°C. After the first washing, the wet thread wound body was immersed in a flow of n-hexane (second washing liquid) at 50°C to perform a second washing.Finally, the hollow fibers after the second washing were washed. was dried with hot air and heat treated at 150° C. for 1 hour to obtain a hollow fiber membrane for gas separation made of aromatic polyimide.

[Example 1] In the manufacturing process of the hollow fiber membrane for gas separation of the reference example, the hollow fibers after the second washing were treated with styrene, which has a weight ratio of styrene:divinylbenzene:benzoyl peroxide of 85:10:5. divinylbenzene and benzoyl peroxide,
It was immersed in a cyclohexane solution containing a total amount of 5 rfL and treated at 60'C for 5 hours. Next, the immersed hollow fibers were immersed in n-hexane at 50° C. to replace cyclohexane adhering to the hollow fibers with n-hexane. Hollow fibers to which 1% by weight of monomers (styrene and divinylbenzene) were attached were manufactured by the above method. Thereafter, the hollow fibers were heat-treated at 150° C. for 1 hour in a hot air dryer to produce a hollow fiber membrane for gas separation.

A gas permeation test module was created for the above hollow fibers, and the module was used to test 2.3 kg/cm"G for carbon dioxide and methane gas (carbon dioxide: 0.6 kg/
crn'G, methane: 1.7 kg/cm''G), and gas permeation rate at room temperature (initiality t@>) were measured.

Further, the gas permeation rate (performance after nitrogen flow) was measured after nitrogen was flowed into this module for 20 hours at an apparent linear velocity of 3.5 m/sec under normal pressure.

Table 1 shows the measured permeation rate of carbon dioxide and the selective permselectivity calculated based on the measured value of the permeation rate of carbon dioxide and the measured value of the permeation rate of methane gas. In addition, the display of each numerical value is as follows.

Carbon dioxide gas permeation rate (P'Co□):
α=P'CO2/P'COa The results are shown in Table 1.

Table 1 p'co2(α) p'co, (α) Example 1
24 (27) 22 (27) Reference example 2
4 (22) 16 (19) [Example 2.3] The total concentration of styrene, divinylbenzene and benzoyl peroxide was changed to 0.5% by weight, and the solvent was changed to benzene (
Hollow fiber membranes for gas separation were produced in the same manner as in Example 1, except for the immersion treatment using a solution of Example 2) or cyclohexane (Example 3). The performance test results (however, the nitrogen flow time was 70 hours) are shown in Table 2.

Table 2 P”CO2 (a) P”CO2 (a) Example 2 28 (20) 24 (21) Example 3
29 (21) 25 (22) Reference example 2
4 (22) 12 (16) ffS1 table and 2nd
As is clear from the results in the table, the untreated reference example hollow fiber membrane for gas separation shows a significant decrease in carbon dioxide gas permeation rate after long-term use.

On the other hand, the hollow fiber membrane for gas separation treated according to the present invention shows less decrease in carbon dioxide gas permeation rate after long-term use.

Claims (1)

[Claims] 1. A gas separation membrane having a homogeneous layer made of aromatic polyimide is immersed in a solution of a monomer having a vinyl group to adhere the monomer to the gas separation membrane, and then the monomer is 1. A method for producing a gas separation membrane, which comprises heat-treating the gas separation membrane to which is adhered. 2. The manufacturing method according to claim 1, characterized in that the immersion treatment is carried out so that the amount of the monomer deposited on the gas separation membrane before deposition is 0.01 to 5% by weight. 3. The manufacturing method according to claim 1, characterized in that a polymerization initiator for the monomer is present in the solution of the monomer. 4. The manufacturing method according to claim 1, wherein the immersion treatment is performed at a temperature of 10 to 100°C, and the heat treatment is performed at a temperature of 100 to 300°C.