JPH0696104B2 - Method for producing aromatic polysulfone hollow fiber membrane - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an aromatic polysulfone hollow fiber semipermeable membrane which is excellent in both water permeability and mechanical strength.

(Prior Art) Since aromatic polysulfones have excellent heat resistance and chemical resistance, various hollow fiber semipermeable membranes made of them have been conventionally proposed. However, according to the conventionally known methods, a hollow fiber membrane having high mechanical strength and excellent water permeability cannot be obtained.

For example, JP-A-49-23183 proposes a hollow-fiber-like semipermeable membrane having a dense layer on the inner surface and having a cavity with a diameter of 10 μm or more in which the polymer is missing on the outer surface. However, such a structure has particularly low mechanical strength. Therefore, in JP-A-54-145379, both the inner surface and the outer surface have dense layers, and a porous polymer layer continuous from this dense layer has a pore size continuously increasing from the membrane surface. An aromatic polysulfone hollow fiber semipermeable membrane having such a structure has been proposed. However, this membrane has a large dependence of water permeability on the film thickness, and particularly when the film thickness exceeds 200 μm, the water permeability is significantly deteriorated.

On the other hand, in JP-A-59-228017, the present inventors have already described that when an aromatic polysulfone is extruded from a double-tube type nozzle and formed into a hollow fiber membrane by a wet method, A method for producing a hollow fiber membrane is disclosed in which a coagulating liquid is brought into contact with the inner surface, and air having a predetermined humidity is brought into contact with the outer surface, and then immersed in water to remove the solvent and coagulate to produce a hollow fiber membrane. According to this method, it is possible to obtain a hollow fiber membrane in which micropores having a pore diameter smaller than that of the outer surface are formed on the inner surface while controlling the micropore diameter of the outer surface.

In order to solve the above-mentioned problems in the conventional aromatic polysulfone hollow fiber membranes, the inventors of the present invention, as described above, use aroma by a method of changing the coagulation conditions of the inner and outer surfaces during molding into the hollow fiber membranes. As a result of further diligent research on the production of a group hollow fiber membrane, an aromatic polysulfone was extruded from a double tube type nozzle, and when forming a hollow fiber membrane by a wet method, a coagulating liquid was brought into contact with the inner surface of the membrane, By contacting the outer surface with vapor of a non-solvent of aromatic polysulfone having a predetermined vapor pressure, the pore diameter of the outer surface can be controlled more easily, while the inner surface has a smaller pore diameter than that of the outer surface. With forming pores, it is possible to obtain a hollow fiber membrane in which a thick reticulated porous layer is formed between the inner and outer surfaces, and thus the hollow fiber membrane having such a structure is particularly excellent in burst strength, If the thickness is thicker, and found to have a practical use sufficiently large water permeation performance, but was Itaritsu the present invention.

(Object of the invention) Accordingly, the present invention generally aims to provide a method for producing an aromatic polysulfone hollow fiber semipermeable membrane excellent in both mechanical strength and water permeability, and in particular, Compared with the conventional manufacturing method, while controlling the micropore diameter of the outer surface more easily, the micropores having a smaller pore diameter than that of the outer surface are formed on the inner surface. It is an object of the present invention to provide a method for producing an aromatic polysulfone hollow fiber semipermeable membrane which is basically different from the conventional hollow fiber membranes, and as a result has excellent mechanical strength and water permeability.

(Structure of the Invention) A method for producing an aromatic polysulfone hollow fiber semipermeable membrane according to the present invention is a mixed solvent of a polar organic solvent capable of dissolving aromatic polysulfone and a solvent which is miscible with the solvent but does not dissolve aromatic polysulfone. Aromatic polysulfone is dissolved in to form a film-forming solution, and while the coagulating liquid is allowed to flow out from the inner tube of the double-tube type nozzle, the above-mentioned film-forming solution is extruded from the outer tube, and the outer surface is vaporized at the temperature of the film-forming solution. After contacting with a non-solvent vapor of aromatic polysulfone having a vapor pressure higher than the pressure by 15 mmHg or more, it is immersed in water and molded into a hollow fiber, and the solvent remaining in the hollow fiber is desolvated to form an inner surface. To form a dense surface having micropores substantially in the range of 10 to 100Å, and to form a dense surface having micropores substantially in the range of 0.01 to 0.5 μm on the outer surface, Any of the above pore sizes Greater than microporous having a surface, and, and having a pore pore size is in the range of substantially 0.05 to 5 [mu] m, continuous with the respective surfaces, and, 20 to a thickness of the total thickness
It is characterized by forming a reticulated porous layer occupying 50%.

In the method according to the present invention, the aromatic polysulfone is dissolved in a polar organic solvent, and a solvent that is miscible with the solvent but does not dissolve the aromatic polysulfone is used as a film-forming solution by dissolving the aromatic polysulfone into a film-forming solution. When the polysulfone is extruded from the outer tube of the tubular nozzle to solidify the solvent to form a hollow fiber membrane, the inner surface is contacted with the coagulating liquid and the outer surface is a non-solvent of aromatic polysulfone having a predetermined vapor pressure. Of steam, and then immersed in water to remove the solvent remaining in the hollow fiber. Therefore, in this method, the polysulfone extruded from the double-tube nozzle has an inner surface coagulated by displacement with a coagulating liquid and an outer surface coagulated by a non-solvent, but The surface does not have to be completely solidified, and by being subsequently immersed in water, the outer surface is also completely solidified,
The remaining solvent is removed to obtain the hollow fiber membrane according to the present invention.

According to such a method of the present invention, the inner surface of the membrane is substantially
Form a dense surface with fine pores of 10 to 100Å,
Substantially 0.01-0.5 μm, usually 0.1-0.
While forming the other dense surface having micropores having a pore diameter in the range of 3 μm, a fine pore having a pore diameter substantially in the range of 0.05 to 5 μ is formed between them while forming the other dense surface. A finger-like structure having pores and a continuous network porous layer on each of the above-mentioned surfaces, and a cavity continuous with the network porous layer located approximately in the middle of the membrane and extending substantially in the radial direction of the membrane. It is possible to obtain an aromatic polysulfone hollow fiber-shaped semipermeable membrane having a layer and excellent in mechanical strength and water permeability.

In particular, according to the method of the present invention, the total thickness of the obtained hollow fiber semipermeable membrane is usually 50 to 500 μm, of which the reticulated porous layer is usually 20 to 50% of the total thickness. , In most cases,
It accounts for 25 to 40%, and there are no cavities lacking polysulfone in this reticulated porous layer. Therefore, the hollow fiber membrane according to the present invention is particularly excellent in mechanical strength and pressure densification. The diameter of the cavity of the finger structure layer in the transverse direction is usually 10 mμ or more.

Incidentally, the reticulated porous layer is a porous layer coarser than the outer surface, the pore size of the pores of the reticulated porous layer is usually about 10 times or more than the pore size of the micropores of the outer surface. is there.

In the method of the present invention, the aromatic polysulfone typically has the following repeating units.

However, X _{1 to} X ₆ represent non-dissociative substituents exemplified by alkyl groups such as methyl group and ethyl group, halogens such as chlorine and bromine, and l, m, n, o, p and q are 0. Indicates an integer of ˜4. Generally, polysulfone in which all of l, m, n, o, p and q are 0 is easily available and is preferably used in the present invention. However, the polysulfone used in the present invention is not limited to the above.

In the method of the present invention, a film-forming solution containing aromatic polysulfone is prepared by dissolving aromatic polysulfone in a mixed solvent of a polar organic solvent capable of dissolving it and a non-solvent not capable of dissolving it. As the polar organic solvent, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide and the like are preferably used, and as the non-solvent, glycerin, ethylene glycol, aliphatic polyhydric alcohols such as propylene glycol and the like, Preferably used are polyalkylene glycols such as diethylene glycol and polyethylene glycol, lower aliphatic alcohols such as methanol, ethanol and isopropyl alcohol, cyclic ethers such as dioxane and tetrahydrofuran, lower aliphatic ketones such as acetone and methyl ethyl ketone.

In the method of the present invention, the non-solvent in the film forming solution is
It is used to enhance the water permeability of the resulting aromatic polysulfone hollow fiber membrane. The content of the non-solvent in the mixed solvent of the non-solvent and the polar organic solvent is not particularly limited as long as the obtained mixed solvent is uniform, but is usually in the range of 5 to 50% by weight. Generally, the higher the proportion of non-solvent in the mixed solvent, the higher the water permeability of the obtained hollow fiber permeable membrane. On the contrary, when a non-solvent is not used in the film-forming solution, the water permeability of the obtained film is about 1/2 to 1/10 of that of the film obtained by using the non-solvent as a component of the film-forming solution. However, in the mixed solvent, if the proportion of the non-solvent is too large, it becomes difficult to dissolve the polysulfone in the mixed solvent, and the resulting hollow fiber membrane may form film defects such as pinholes. Not preferable.

The concentration of the aromatic polysulfone in the film forming solution is usually 5 to
It is 35% by weight, preferably 10 to 30% by weight. When it exceeds 35% by weight, the water permeability of the obtained semipermeable membrane is too small for practical use, while when it is less than 5% by weight, the obtained membrane becomes inferior in mechanical strength. Is.

Next, as the coagulating liquid flowing out to the inner pipe of the double pipe type nozzle, water is generally used, but as described above, a solvent that does not dissolve the aromatic polysulfone but is miscible with the polar organic solvent. Any non-solvent mentioned above or a mixed solvent of water and water may be used. Further, even a solvent that dissolves aromatic polysulfone alone can be used as a coagulating liquid as long as it is in a range that does not dissolve polysulfone by mixing with another solvent. In this way, the time from when the film-forming solution is extruded into the non-solvent vapor from the double-tube nozzle until it is immersed in water depends on the composition of the film-forming solution and the thickness of the film-forming solution when extruded from the nozzle. Depending on the condition, it is usually 0.1 seconds or longer, preferably 0.5 to 10 seconds.

In the method of the present invention, as the non-solvent vapor when the film-forming solution is extruded into the non-solvent vapor of polysulfone, in addition to water vapor, the vapor of the non-solvent organic solvent used for the preparation of the film-forming solution is also used. . Particularly, in the present invention, the non-solvent vapor is preferably steam and vapor of a lower aliphatic alcohol such as methanol, ethanol, isopropyl alcohol.

In the method of the present invention, the vapor pressure of the non-solvent is 20 to 50 of the total thickness of the reticulated porous layer in the resulting hollow fiber membrane.
%, It is necessary to be higher than the vapor pressure at the temperature of the film-forming solution used by 15 mmHg or more, preferably 20 mmHg or more. Especially when the vapor pressure of the non-solvent is lower than 15 mmHg than the vapor pressure at the temperature of the film-forming solution to be used, the thickness of the reticulated porous layer on the outer surface is thin, and as a result, the relative finger-like structure occupies. Since the thickness is large and the dispersion density of the fine pores on the outer surface is small, such a hollow fiber membrane does not have high water permeability, and is inferior in mechanical strength and pressure-resistant densification. As described above, when the reticulated porous layer is less than 20% of the total film thickness, the film does not have practically sufficient mechanical strength and pressure densification property.

FIG. 1 shows an embodiment of an aromatic polysulfone hollow fiber semipermeable membrane according to the method of the present invention, in which the inner surface has smaller pores and the outer surface has larger pores. It is an electron micrograph (200 times) showing the cross-sectional structure of a film. FIG. 2 is an electron micrograph (5000) of the outer surface of the hollow fiber membrane having micropores having a pore size of substantially 0.01 to 0.5 μm.
Times). 3 and 4 show that when a film-forming solution is extruded from a double-tube nozzle into an aromatic polysulfone non-solvent atmosphere, it has a vapor pressure of less than 15 mmHg than the vapor pressure at the temperature of the film-forming solution. Electron micrograph (200x) of the cross section of a hollow fiber membrane as a comparative example obtained by extrusion into steam, and electron micrograph (5000x) of the outer surface
Indicates. In the hollow fiber membrane as a comparative example, it is apparent that the thickness of the net-like porous layer on the outer surface is thin, the pore diameters of the pores are not uniform, and the dispersion density of the pores on the outer surface is small.

(Effect of the invention) As described above, according to the membrane of the present invention, since the fine pore diameters on the dense inner and outer surfaces of the membrane are different, if the liquid to be treated is supplied to the inner side of the membrane having the fine pores of small pore diameter, Since the outer surface having a large number of uniformly large pores does not form a passage resistance of fluid, high water permeability can be obtained. In addition, the reticulated porous layer accounts for 20 to 50% of the total thickness, and in most cases 25
Since it occupies -40%, the hollow fiber membrane prepared by the method of the present invention is also excellent in mechanical strength and pressure densification.

Incidentally, the size of the pores and cavities of the reticulated porous layer and the finger-like structure layer is evaluated by an electron micrograph, but the micropore diameter of the dense layer is polyethylene glycol, dextran, proteins having various molecular weights. It is evaluated from the removal rate for

Generally, a hollow fiber-shaped semipermeable membrane is said to have excellent mechanical strength and pressure-resistant densification when it does not have cavities, but the hollow fiber-shaped semipermeable membrane of the present invention has a reticulated porous layer as described above. Form a thick layer that occupies 20 to 50% of the total film thickness, and in most cases 25 to 40%, while the thickness of the finger-like structure is relatively small It has excellent strength and pressure-resistant densification property, and in particular, has a feature of excellent water permeability even when the thickness is large.

(Examples) Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples. In the following, the properties of the hollow fiber membrane were determined as follows. Allow pure water to permeate the membrane at a pressure of 1 kg / cm ² and a temperature of 25 ° C, and
The measured value of the water permeation rate after 5 minutes was defined as the pure water permeation rate. The removal rate of the membrane was determined by supplying an aqueous solution of polyethylene glycol (average molecular weight 20000) at an average pressure of 1 kg / cm ² and a temperature of 25 ° C., and measuring the value after 15 minutes as the removal rate.

The burst strength was defined as the pressure at which the film was burst by applying water pressure from the inside of the film.

The present invention is described below with reference to examples, but the present invention is not limited to these examples.

Example 1 In a mixed solvent of 58 parts by weight of N-methyl-2-pyrrolidone and 25 parts by weight of diethylene glycol, Aromatic polysulfone 17 having a repeating unit represented by
A part by weight was dissolved to obtain a film forming solution.

The film-forming solution is extruded at a temperature of 25 ° C from the outer tube of the double-tube nozzle at a temperature of 25 ° C under the steam having a vapor pressure of 25 mmHg higher than the vapor pressure of the film-forming solution at a temperature of 25 ° C. Water is allowed to flow out and kept in the above atmosphere for 1 second to be solidified from both its inner and outer surfaces, then immersed in water and desolvated to obtain a hollow fiber semipermeable membrane with an inner diameter of 0.5 mm and an outer diameter of 0.9 mm. It was
The total film thickness of this film was 200 μm, and the thickness of the reticulated porous layer was about 25% of the total film thickness.

This hollow fiber membrane had a pure water permeation rate of 600 / m ² · hour · atmospheric pressure, and the removal rate for polyethylene glycol having a molecular weight of 20,000 was 88%. The burst strength was 30 kg / cm ² .

An electron micrograph (200 times) of the cross section of the hollow fiber semipermeable membrane obtained above is shown in Fig. 1, and an electron micrograph of the outer surface (500) is shown.
0 times) is shown in FIG.

Comparative Example 1 Using the same film-forming solution as used in Example 1, the film-forming solution was extruded from a double-tube nozzle in a steam atmosphere having a vapor pressure 10 mmHg higher than the vapor pressure at the temperature of the film-forming solution. A hollow fiber membrane was manufactured in the same manner. The thickness of the reticulated porous layer in this film was about 16% of the total film thickness.

This hollow fiber membrane has a pure water permeation rate of 400 / m ² · hour · atmospheric pressure,
The removal rate for polyethylene glycol having a molecular weight of 20,000 was 85%, and the burst strength was 18 kg / cm ² . Therefore,
It is clear that this membrane has a lower pure water permeation rate and a significantly lower burst strength than the hollow fiber membrane according to Example 1.

An electron micrograph (200 times) of a cross section of the hollow fiber semipermeable membrane obtained above is shown in Fig. 3, and an electron micrograph of the outer surface (500 times).
0 times) is shown in FIG.

Example 2 18 parts by weight of the same aromatic polysulfone as in Example 1 was dissolved in a mixed solvent of 63 parts by weight of N, N-dimethylformamide and 19 parts by weight of ethylene glycol to obtain a film forming solution.

The film-forming solution is extruded at a temperature of 25 ° C from the outer tube of the double-tube type nozzle under isopropyl alcohol vapor having a vapor pressure of 30 mmHg higher than the vapor pressure of the film-forming solution at a temperature of 25 ° C, and at the same time the temperature from the inner tube is increased. Water at 25 ° C is allowed to flow out and kept in the above atmosphere for 1 second to be solidified from both its inner and outer surfaces, then immersed in water and desolvated to obtain a total film thickness of 200 to 500 μm, an inner diameter of 1.0 mm and an outer diameter of 1.4. Hollow fiber semipermeable membranes with various thicknesses up to 2.0 mm were obtained.

Regarding these hollow fiber membranes, the relationship between the membrane thickness, the water permeation rate of pure water and the polyethylene glycol removal rate is shown in FIG. 5, and the relation between the thickness of the reticulated porous layer and the burst strength relative to the membrane thickness is shown in FIG. Show. According to the hollow fiber membrane according to the present invention, the burst strength is high, and even if the film thickness increases,
It is clear to maintain a high water penetration rate.

Comparative Example 2 A hollow fiber membrane was obtained in the same manner as in Example 2 except that the vapor pressure of isopropyl alcohol was increased by 11 mmHg from the vapor pressure at the temperature of the membrane forming solution. Regarding these films, the relationship between the film thickness, the pure water permeation rate and the polyethylene glycol removal rate is shown in FIG. 5, and the relationship between the thickness of the reticulated porous layer and the burst strength with respect to the film thickness is shown in FIG. .

These hollow fiber membranes have a lower pure water permeation rate than the membranes of the present invention having the same film thickness, and the reticular porous layer occupying the entire film thickness is thin, so that the burst strength is high. Obviously it is significantly smaller.

[Brief description of drawings]

FIG. 1 is a graph showing the film thickness dependence of the pure water permeation rate and the removal rate of polyethylene glycol for the hollow fiber membranes of the present invention and the hollow fiber membranes of Comparative Examples, and FIG.
3 is a graph showing the relationship between the thickness of the reticulated porous layer and the burst strength with respect to the film thickness of the hollow fiber membrane according to the present invention and the hollow fiber membrane as a comparative example.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location D01F 6/76 D 7199-3B (72) Inventor Akio Iwama 1-1-Shimohozumi, Ibaraki-shi, Osaka No. 2 within Nitto Denki Kogyo Co., Ltd. (56) Reference JP-A-60-246812 (JP, A) JP-A-61-209011 (JP, A) JP-A-58-174618 (JP, A) JP-A-59 -209615 (JP, A)

Claims (4)

[Claims] 1. A film forming solution by dissolving aromatic polysulfone in a mixed solvent of a polar organic solvent capable of dissolving aromatic polysulfone and a solvent which is miscible with the solvent but does not dissolve aromatic polysulfone, thereby forming a double tube. While letting the coagulating liquid flow out from the inner tube of the mold nozzle, the film forming solution is extruded from the outer tube, and the non-solvent of aromatic polysulfone having a vapor pressure higher than the vapor pressure at the temperature of the film forming solution by 15 mmHg or more on the outer surface. After being contacted with the steam of the above, it is immersed in water to form a hollow fiber, and the solvent remaining in the hollow fiber is desolvated, and the inner surface is dense with micropores in the range of 10 to 100Å. A fine surface is formed, and a fine surface having micropores substantially in the range of 0.01 to 0.5 μm is formed on the outer surface, while the pore diameter is larger than the micropores of any of the above surfaces, and
It has pores whose pore size is substantially in the range of 0.05 to 5 μm, is continuous with each of the above surfaces, and has a thickness of 20% of the total thickness.
A method for producing an aromatic polysulfone hollow fiber membrane, which comprises forming a reticulated porous layer occupying ˜50%. 2. The method for producing an aromatic polysulfone hollow fiber membrane according to claim 1, wherein the non-solvent vapor deposition is steam. 3. The method for producing an aromatic polysulfone hollow fiber membrane according to claim 1, wherein the non-solvent vapor is a lower aliphatic alcohol vapor. 4. The method for producing an aromatic polysulfone hollow fiber membrane according to claim 1, wherein the reticulated porous layer occupies 25 to 40% of the total thickness.