JPH06350A - Production of separation membrane - Google Patents

Abstract

PURPOSE:To obtain a separation membrane having heat resistance which can be used in an org. solvent by treating a polymer membrane having an asymmetric structure and a dense layer prepared by using polymers having haloalkyl groups with high concn. sulfuric acid. CONSTITUTION:A membrane of assymmetric structure having haloalkyl groups is dipped in a conq. sulfuric acid of >=80% concn., more preferably >=85% concn. at room temp., or by heating or cooling, to effect the reaction. The sulfuric acid acts as Lewis acid to give catalytic effect to form bonds between haloalkyl groups or between haloalkyl groups and aromatic rings to introduce three- dimensional crosslinked structure. Thereby, the membrane becomes insoluble in the solvent which dissolves the polymer which constitutes the separation membrane, nor causes swelling. Since heat resistance of the membrane is significantly improved, the membrane can be subjected to steam sterilization.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polymer membrane having an asymmetric structure having a dense layer on at least one surface layer and having a three-dimensional cross-linking structure and having particularly heat resistance and organic solvent resistance. Manufacturing method.

[0002]

2. Description of the Related Art Separation membranes are widely used in various industrial fields today.
For example, electrodialysis using an ion-exchange membrane, diaphragm for electrolytic reaction, diffusion dialysis, production of pure water by a reverse osmosis membrane, and use of ultrafiltration membranes in various fields can be enumerated. As the applications of such separation membranes are diversified, the performance required for the membranes is also diversified.

Generally, there are various non-asymmetric polymer film materials such as ion exchange membranes, that is, non-crosslinked membranes and crosslinked membranes, but crosslinked ion exchange membranes are used.
That is, although the crosslinked membrane has some problems in terms of flexibility and the like, the solvent resistance and heat resistance of the separation membrane are remarkably improved by forming a tertiary crosslinked structure. on the other hand,
The polymer film having an asymmetric structure having a dense layer on the surface layer,
Since it is generally produced by a phase inversion method, it is difficult to form a crosslinked structure. For example, a selective permeable membrane in which a quaternary ammonium salt group is introduced simultaneously with amine crosslinking by a method of polyamine treatment of a membrane of an aromatic polyetherimide polymer having a halomethyl group after the membrane formation (JP-A-63-240
No. 901) has been proposed.

However, a good separation membrane having a crosslinked structure and a dense layer in the negative or uncharged surface layer has not been developed, and therefore, ultrafiltration, reverse osmosis or microfiltration is used as the separation membrane. However, its uses such as pervaporation are limited.

Therefore, an object of the present invention is to form a tertiary cross-linking structure in a separation membrane having an asymmetric structure and having a negative charge or non-charge surface layer portion with a dense layer, thereby providing heat resistance and organic solvent resistance. To produce separation membranes with

[0006]

In view of the above problems, the inventors of the present invention have selected a polymer separation membrane having an asymmetric structure having a dense layer on at least one surface layer portion and having a three-dimensional crosslinked structure formed therein. I studied hard.

As a result, surprisingly, by treating a polymer film having an asymmetric structure having a dense layer made of a polymer having a haloalkyl group with 80% or more, preferably 85% or more of sulfuric acid, three-dimensional The cross-linking structure of is introduced, and the cross-linking structure can be mainly introduced by selecting the sulfuric acid concentration.
Further, they have found that it is possible to introduce a sulphonic acid group at the same time as forming a crosslinked structure, and thus have provided the present invention.

In the present invention, the term "asymmetric structure polymer film top product having a dense layer" generally means that when a polymer solution is put into a poor solvent to form a film, the film surface layer becomes a dense thin film, and the inside is sponge-like. Which is a membrane obtained by a so-called phase inversion method, the dense layer may be completely non-porous, and may have pores of a degree corresponding to an ultrafiltration membrane or a microfiltration membrane. As a material used for the polymer film having an asymmetric structure having the dense layer of the present invention, a polymer used in the production of a conventionally known film having an asymmetric structure can be used without any limitation. For example, polysulfone, polyether sulfone, polyphenylene oxide, polyetherimide, polyetheretherketone, polyamideimide resin and the like are generally called engineering plastics. In addition to a single polymer,
It may be a mixture of the above polymers, or may be a polymer of the polymerization system such as polyacrylonitrile mixed with the above-mentioned engineering plastics.

Generally, a film having an asymmetric structure having a dense layer on the surface layer is obtained by uniformly dissolving one or more of the above-mentioned polymers in a polar solvent such as N-methylpyrrolidone, dimethylformamide or dimethylsulfoxide. Is cast on a flat plate or spun into a flat plate and placed in a liquid which is a poor solvent for the above-mentioned polymers such as water and alcohol, and is produced by the phase inversion method. At this time, it is also possible to mix different types of polymers such as an inorganic salt, an organic substance, and polyvinylpyrrolidone in a solution of the polymer, and elute them at the time of phase inversion to form pores in the dense layer of the surface layer portion according to the purpose. You can

As a method for introducing a haloalkyl group into a polymer film having a dense layer on the surface layer portion, a haloalkyl group is previously introduced into a polymer as a raw material by a conventionally known method, and a film is formed using this. Is desirable. For example, polysulfone is dissolved in a chlorine-based solvent, and chloromethyl methyl ether and anhydrous tin tetrachloride, titanium tetrachloride, zinc chloride,
It is introduced by the Friedel-Crafts reaction by adding a Lewis acid such as iron chloride or tin oxide. Of course, it is also possible to introduce a halomethyl group by leaving it in a mixed vapor of chloromethyl methyl ether and Lewis acid after making it into a film.
Often accompanied by deformation of the dense layer in the surface layer. Alternatively, a polymer having a haloalkyl group and a polymer not having a haloalkyl group bonded may be uniformly mixed, dissolved in a common solvent, and a film may be formed by a phase inversion method. However, a polymer introduced with a haloalkyl group generally becomes difficult to dissolve in a common solvent with a polymer not introduced with a haloalkyl group, depending on the amount of the haloalkyl group. Preferred is a film-like product having an asymmetric structure, in which a haloalkyl group is introduced into a starting polymer in advance, and then the polymer is used to form a film by a phase inversion method to have a dense layer on at least one surface layer portion. In this case, the ratio of the haloalkyl group in the polymer film is
It depends on the structure of the polymer to be used and is difficult to determine unconditionally, but 5% to 100% is introduced, preferably 10% to 70% is introduced into the unit such as a benzene ring into which a haloalkyl group can be introduced. In principle, the quantification of this haloalkyl group can be confirmed by elemental analysis.

Next, in the present invention, the above-mentioned asymmetric structure film-form material having a haloalkyl group is immersed in 85% or more concentrated sulfuric acid at room temperature, under heating, or under cooling to carry out a reaction treatment. The treatment temperature varies depending on the structure (type of polymer) of the polymer film material used in the reaction. In this case, if it is desired to mainly carry out the crosslinking reaction, it should be treated with a relatively dilute sulfuric acid, and if it is desired to carry out the sulfonation reaction simultaneously with the crosslinking reaction, it is desirable to treat it with a relatively high concentration of sulfuric acid.

By the treatment of the present invention, since sulfuric acid is a kind of Lewis acid, it is considered that it acts as a catalyst to form a bond between the haloalkyl groups and between the haloalkyl group and the aromatic ring. At this time, when the concentration of sulfuric acid is relatively high, it acts as a Lewis acid and at the same time acts as a sulfonic acid group-introducing reagent. The Lewis acid is not limited to sulfuric acid, and there are various kinds of Lewis acids, and the action of the crosslinking reaction can be similarly considered for these. However, other Lewis acids generally require a solvent of carbon disulfide or chlorine. Therefore, these solvents are at the same time Lewis solvents and
It becomes a solvent for a polymer film having an asymmetric structure in which a haloalkyl group is bonded. For example, when a film made of chloromethylated polysulfone is immersed in a solution of a catalytic amount of tin tetrachloride in carbon disulfide, the film is formed. Swells significantly with carbon disulfide and eventually loses its asymmetric structure. Further, for example, when the above film-like material is treated with a solvent such as ethylene dichloride, it will be dissolved before the crosslinking reaction. Therefore, in the present invention, it is significant to use sulfuric acid having a specified concentration when performing the crosslinking reaction. The reaction time with sulfuric acid is completely different depending on the type of polymer used as the raw material of the membrane to be treated, the reaction temperature, and the sulfuric acid concentration, but is generally appropriately selected from 30 seconds to 200 hours.

The film of the present invention, which has been appropriately treated with 80% or more sulfuric acid, is heated as it is soaked in water and the structure of the dense layer in the surface layer of the film is deformed. The treated concentrated sulfuric acid needs to be removed.
That is, a film reacted with 80% or more concentrated sulfuric acid has, for example, 80%
%, 60%, 40%, 20%, etc., and then washed with water, finally neutralized with a rare alkali, and then washed with water.

The separation membrane of the present invention is not particularly limited in shape, and examples thereof include various separation membranes such as flat membranes, tubular membranes and hollow fibers.

[0015]

Since the separation membrane of the present invention has a three-dimensional crosslinked structure, it is insoluble in the solvent in which the polymer constituting the separation membrane is dissolved and hardly swells. Therefore,
It is possible to use a separation membrane in an organic solvent. Further, since it has a three-dimensional structure, the heat resistance is remarkably improved, and steam sterilization can be performed, which contributes to remarkably expanding the field of use of the membrane. Furthermore, the problem of separation of ionic substances due to electric charges and organic contamination in the separation membrane can be solved.

[0016]

EXAMPLES The contents of the present invention will be specifically illustrated by the following examples, but the present invention is not limited to these examples.

Example 1 Polysulfone (manufactured by Amou Chemical Japan Co., weight average molecular weight 35,000)

[0018]

[Chemical 1]

Polymer 350 having the above repeating unit
0 part was uniformly dissolved in 3600 parts of ethylene dichloride, 31 parts of anhydrous zinc chloride and 500 parts of chloromethyl methyl ether were added thereto, and the mixture was stirred at 25.0 ° C. for 12 hours, and then 100 parts of pure water was added to react. Was stopped, and then the mixture was poured into a large excess of methanol to precipitate a polymer.

After drying this polymer, it was dissolved again in chloroform and then poured into a large excess of methanol to precipitate the polymer. This operation was repeated twice to purify the polymer. The polymer obtained was dried under reduced pressure, and then a part of the polymer was taken and the content of chlorine was examined by elemental analysis.
%Met. Further, the presence of a chloromethyl group was confirmed by the infrared absorption spectrum, and it was found that the chloromethyl group was contained in the polymer unit at a ratio of about one.

20 parts of this polysulfone having a chloromethyl group introduced therein was dissolved in 80 parts of N-methylpyrrolidone, filtered through a mesh filter, and the dope was extruded into water from a spinning device having a double tube nozzle to give an inner diameter of A hollow fiber having a diameter of 0.8 mm and an outer diameter of 1 mm was obtained. When the cross section of this hollow fiber was observed with a scanning electron microscope, there were dense layers on both surface layers, and the middle portion had a finger-like porous structure.

After air-drying this hollow fiber,
%, 90%, 95%, 98% concentrated sulfuric acid, 2 each
After soaking for 4 hours, 24 hours, 4 hours, 30 minutes, 80
%, 60%, 40%, and 20% sulfuric acid (equal to 70% sulfuric acid soaked membrane from 60%), washed with water, and then equilibrated in 0.1N caustic soda solution. I chose Each of the obtained films was dipped in a 2% aqueous solution of methyl orange for 4 hours, washed with water, and the degree of dyeing was examined. The films dipped in 95% and 98% sulfuric acid were markedly dyed, but 80% The membrane soaked in sulfuric acid was hardly stained.

The acid type hollow fiber membrane was washed thoroughly with water, immersed in 0.5N saline to equilibrate, and the hydrogen ions produced by ion exchange were determined by titration with 1 / 10N NaOH. It was Methyl orange was used as the indicator. 9
The membranes soaked in 8% sulfuric acid and 95% sulfuric acid had exchange capacities of 0.74 meq / g dry membrane and 0.36 meq / g dry membrane, respectively. It was 05 meq / g dry film. When the membrane was immersed in chloroform or ethylene dichloride, it swelled slightly but neither membrane dissolved.

For comparison, when a film was prepared by immersing it in 70% sulfuric acid for 24 hours, it was not dyed with methyl orange and was dissolved in either chloroform or ethylene dichloride.

Further, 5 hollow fibers (length 20 cm)
Was sealed in a glass tube with an epoxy resin, and a permeation apparatus was set with a supply port for supplying a liquid into the hollow fiber and a take-out port for collecting the permeated material outside the hollow fiber. Next, 90% hydrous isopropyl alcohol (60 ° C.) was flown inside the hollow fiber, and the pressure outside the hollow fiber was reduced to 5 torr. The vapor that has passed through the hollow fiber is dry ice-
It was collected in a trap cooled with methanol and then analyzed by gas chromatography. When the permeation amount per unit time was calculated from the permeation amount, it was 1250 g / hr ・ m
² , the concentration of isopropyl alcohol in the permeate was 1.
It was only 8%.

Example 2 10 parts of the chloromethylated polysulfone obtained in Example 1 together with 10 parts of non-chloromethylated polysulfone
-Methylpyrrolidone 80 parts dissolved uniformly. After filtering this with a mesh filter, deaeration and 0.1 mm on a polyester non-woven fabric on a roller with a diameter of 40 cm
The slit was coated from the time it was made, and it was put in water as it was, and the phase was converted to form a film. The flat membrane obtained here was once dried, then immersed in 90% concentrated sulfuric acid for 5 hours, then equilibrated in order of 80% sulfuric acid and 40% sulfuric acid, washed with water, and then 0.1 N. After equilibrating with an aqueous solution of potassium hydroxide, the solution was dried again. The surface layer having an asymmetric structure of this film was markedly stained with methyl red. In addition, the original membrane not soaked in sulfuric acid was not stained.

Further, as a result of immersing the membrane soaked in sulfuric acid and the original membrane not soaked in ethylene dichloride, the membrane soaked in sulfuric acid showed a slight swelling and no change, but the original membrane not soaked in sulfuric acid was not changed. The membrane was completely dissolved, leaving only the reinforcing non-woven fabric.

Using these two kinds of flat membranes, dehydration of 95% hydrous ethanol was carried out by the same immersion vaporization method as in Example 1. When the temperature of the membrane was reduced to 2 torr at 60 ° C and the gas permeated through the membrane was collected and analyzed, the membrane without sulfuric acid treatment had a permeate volume of 2100 g / hr · m ² and an ethanol concentration of 32% in the permeate. However, the sulfuric acid-treated membrane had an ethanol concentration of 8.9% at a permeated liquid amount of 1800 g / hr · m ² .

Example 3 Chloromethylation of polysulfone was carried out in the same manner as in Example 1 with a shorter reaction time. As a result, the Cl content in the chloromethylated polysulfone produced was 4.2%. 15 parts of this chloromethylated polysulfone and a molecular weight of 6
Ten parts of polyvinylpyrrolidone were dissolved in 80 parts of N-methylpyrrolidone. After filtering with a mesh filter, the viscous liquid was applied onto a polyester non-woven fabric in the same manner as in Example 2, and immediately passed through a water bath for coagulation. The obtained film had a dense layer in the surface layer and had a sponge inside.

When this membrane was installed in an apparatus for evaluating an ultrafiltration membrane and the water permeation rate was measured under a pressure of 3 kg / cm ² , it was 350 l / hr · m ² . The molecular weight cut-off was measured with monodisperse polyethylene glycol and was about 2
It was 10,000.

Next, this film was treated with 20% sulfuric acid, 40% sulfuric acid,
After equilibrating with 80% sulfuric acid in sequence, dipping in 90% concentrated sulfuric acid for 5 hours, and then again dipping in dilute sulfuric acid,
It was washed with water and further immersed in 0.1 N caustic soda. When the water permeability of this membrane was measured in the same manner, it was 500 l / m ² ·
and the molecular weight cut-off was about 20,000, which was unchanged.

Then, a solution prepared by dissolving polyethylene glycol in a 3: 1 mixed solvent of water and acetone was filtered in the same manner. The membrane treated with sulfuric acid had a molecular weight cut-off of 20,000.
Although the fractionation property was 0, the molecular weight of the membrane not treated with sulfuric acid was 50,000 and the elution curve was broad.

Example 4 Repeating unit represented by the following formula

[0034]

[Chemical 2]

Polyether imide having (general
15 parts of Ultem 1000, weight average molecular weight 40,000) manufactured by Electric Co., and 5 parts of chloromethylated polysulfone synthesized in Example 1 are uniformly dissolved in 80 parts of N-methylpyrrolidone, and after filtration, a double-tube nozzle. The hollow fiber is put into water by using to solidify, and has a dense layer on the inner surface.
A hollow fiber having a porous exterior was obtained. The membrane was air-dried and further dried by heating at 150 ° C. for 30 minutes, then concentrated sulfuric acid cooled to 90% and 4 ° C. was passed through the hollow fiber for 10 minutes, and then 80% and 40% sulfuric acid were sequentially hollowed. After passing through the thread, wash with water,
Finally, 0.1 N caustic soda was poured into the hollow fiber and then dried.

Ethylene dichloride was poured inside the obtained membrane, but there was no change in the hollow fiber itself. On the other hand,
When ethylene dichloride was put into the membrane not treated with sulfuric acid, the hollow fiber immediately dissolved.

Example 5 The ultrafiltration membrane produced in Example 3 was immersed in steam at 127 ° C. for 1 hour.
After standing for a time, the molecular weight cut off was measured with polyethylene glycol. As a result, the water permeability of the membrane treated with sulfuric acid was 470 l / hr · m ² , and the molecular weight cutoff was about 20,0.
However, the membrane not treated with sulfuric acid had a water permeability of 120 l / hr · m ² and a molecular weight cut-off of about 8,000.

Claims (1)

[Claims] 1. A method for producing a separation membrane, which comprises subjecting a polymer membrane having an asymmetric structure having a dense layer on at least one of surface layers bound with a haloalkyl group to a contact treatment with 80% or more concentrated sulfuric acid. .