JPH0696105B2 - Method for producing aromatic polysulfone hollow fiber membrane - Google Patents

Description

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

Since aromatic polysulfone has excellent heat resistance and chemical resistance, various hollow fiber semipermeable membranes made of this material have been proposed. For example, in JP-A-49-23183, there is proposed a hollow fiber-like semipermeable membrane having a dense layer on the inner surface and having a cavity having 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, JP-A-54-145379 discloses that both the inner surface and the outer surface have dense layers, and a porous polymer layer continuous from this dense surface has a pore size continuously increasing from the membrane surface. An aromatic polysulfone hollow fiber-like semipermeable membrane having such a structure has been proposed. However, this film has a large dependence on the film thickness of the water permeability, and especially when the film thickness exceeds 200 μ,
The water permeability is extremely poor.

The present invention has been made to solve the various problems described above, and the structure thereof is basically different from the conventional hollow fiber semipermeable membrane, and as a result, the mechanical strength and water permeability of It is an object of the present invention to provide a method for producing an aromatic polysulfone hollow fiber-shaped semipermeable membrane, which is excellent in both cases.

The method for producing an aromatic polysulfone hollow fiber semipermeable membrane according to the present invention comprises a polar organic solvent capable of dissolving an aromatic polysulfone, and an aromatic polysulfone mixed with a solvent which does not dissolve the aromatic polysulfone. When the polysulfone is solidified by dissolving it into a film-forming solution and extruding it from the outer tube of the double-tube type nozzle, the relative humidity on one surface is 20
% Air or less, the other surface is contacted with a coagulating liquid, and then immersed in water to remove the solvent,
A dense surface having micropores with a pore size of 10 to 100Å is formed on the coagulation liquid side, and the pore size is larger than the above micropores on the air side, and the pore size is substantially less than 0.1 μm. A dense surface having pores is formed, and the pore diameter is larger than the micropores of any of the above surfaces, and substantially
A network porous layer having pores in the range of 0.05 to 5 μm and having a thickness of 5 to 50 μm which is continuous with each of the above-mentioned surfaces, and which is located approximately in the middle of the film and continuous with the network porous layer. And a finger-shaped structure layer having cavities extending substantially in the radial direction are formed to obtain a hollow fiber membrane having a film thickness in the range of 50 to 450 μm.

FIG. 1 is an example of an aromatic polysulfone hollow fiber semipermeable membrane according to the method of the present invention, in which the inner surface has micropores with a smaller pore size and the outer surface has micropores with a larger pore size. 3 shows an electron micrograph of a cross section of a film. More specifically, in the hollow fiber membrane shown in FIG. 1, the micropores on the outer surface are substantially less than 0.1 μm. The film thickness is usually 50 to 450 μm.

As described above, since the fine pore diameters on the dense inner and outer surfaces of the membrane are different, if the membrane to be treated is supplied to the surface side having the fine pores having a small pore diameter according to the membrane of the present invention, the fine pore having a large pore diameter can be obtained. Since the other surface having pores does not form a fluid passage resistance, the water permeability has a small dependency on the film thickness, and as will be described later in Examples, the film has a large water permeability even when the film thickness exceeds 200 μm.

In the hollow fiber membrane of the present invention, the inner and outer surfaces of the membrane have continuous pores having a pore size substantially in the range of 0.05 to 5 μm and larger than the micropore diameter of any surface. Reticulated porous layers are formed respectively, and each surface is integrally supported. The thickness of this porous layer is usually 5 to 50 µ. In the hollow fiber-like semipermeable membrane of the present invention, since the network-like porous layer continuous to the dense surface is present, the membrane is excellent in mechanical strength and pressure-resistant densification. Further, substantially independent finger-shaped cavities extending substantially in the radial direction of the film are formed in the middle of the membrane continuous to the reticulated porous layer to form a finger-shaped structure layer.

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

In 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.

According to the method of the present invention, by setting the relative humidity of the air atmosphere to 20% or less, preferably 10% or less, a dense surface having micropores having a pore size substantially in the range of 10 to 100Å on the coagulating liquid side. Is formed, the hole diameter on the air side is larger than the fine holes,
In addition, it forms a dense surface having micropores of substantially less than 0.1 μm, and is finer than the micropores of any of the above-mentioned surfaces, and has a pore diameter substantially in the range of 0.05 to 5 μm. 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-like semipermeable membrane having a layer and excellent in mechanical strength.

When the relative humidity of air is between 20% and 60%, the reason is not clear, but the physical properties of the hollow fiber membranes generally obtained, especially lack of uniformity in mechanical strength, partially inferior in strength. There are cases. Further, the water permeability and the removal rate may vary considerably. Therefore, in the present invention, the relative humidity of air is set to 20% or less as described above so that a hollow fiber membrane having stable physical properties can be obtained.

In the usual method, the membrane-forming solution is extruded into the air from the outer tube of the double-tube type nozzle, the coagulating liquid is allowed to flow out from the inner tube, and a hollow fiber membrane having a denser surface on the inner surface than the outer surface is obtained. Therefore, the case of extruding the film forming solution into the air will be described below.

According to the method of the present invention, an 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 mixed with the aromatic polysulfone to form a film-forming solution. When the polysulfone is extruded from the outer tube of the heavy-tube nozzle into the air to solidify the polysulfone, the relative humidity of the air is set to 20% or less, and then it is immersed in water to solidify the outer surface to form a hollow fiber. , The solvent remaining in the hollow fiber is removed. For this person, the humidity
Polysulfone extruded in dry air of 20% or less is solidified only on the inner surface side that comes into contact with the coagulating liquid and does not substantially solidify on the outer surface side, but the polysulfone extruded from the double-tube nozzle is the inner surface. The outer surface is completely solidified while the outer surface is completely solidified while the shape is maintained by the solidification of the side, and the solvent remaining in the hollow fiber is removed to give the hollow fiber membrane according to the present invention.

On the contrary, if the polysulfone membrane-forming solution is extruded into the coagulation liquid and the air having a predetermined humidity is discharged from the inner tube, it will be apparent that a hollow fiber membrane having a more dense surface can be obtained on the outer surface. .

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, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide and the like are preferably used as the polar organic solvent for dissolving the above-mentioned aromatic polysulfone to prepare a film-forming solution. Further, as the non-solvent, ethylene glycol, diethylene glycol, propylene glycol, polyethylene glycol, aliphatic polyhydric alcohols such as glycerin,
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, and dimethyl sulfoxide are preferably used. The content of the non-solvent in the mixed solvent is not particularly limited as long as the obtained mixed solvent is uniform, but is usually 5 to 50% by weight, preferably 20 to 45% by weight. The non-solvent in the film-forming solution contributes to the formation of the reticulated porous layer and / or cavities in the above coagulation process and is effective in increasing the water permeability of the film. The higher the ratio, the higher the water permeability of the obtained hollow fiber semipermeable membrane. On the contrary, when non-solvent is not used for the film forming solution,
The water permeability of the obtained membrane is about 1/2 to 1/10 of that of the membrane of the present invention.

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 coagulation time from when the film-forming solution is extruded into the air 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 time, it is usually 2 seconds or longer, preferably 3 to 10 seconds.

The hollow fiber semipermeable membrane thus obtained has a total film thickness of usually 50 to 450 μm, of which the reticulated porous layer is usually 5 to 50 μm, and in most cases 20 to 50 μm.
The layer was 40 μm thick and there were no voids devoid of polysulfone in this layer. This porous layer is 5 μm
When the thickness is thinner than this, the film does not have practically sufficient mechanical strength and pressure densification, which is not preferable. The diameter of the cavity of the finger-shaped structure layer in the transverse direction is usually 10 μm or more.

FIG. 1 is an example of a hollow fiber membrane obtained by the method of the present invention, which shows a membrane having micropores with a small pore size on the inner surface and micropores with a larger pore size on the outer surface. Electron micrographs of the cross section (200x), Figures 2 and 3 show the inner surface (10000x) and outer surface (5000x), respectively, as above.
2) is an electron micrograph showing the same. The outer surface of the hollow fiber membrane obtained by the method of the present invention usually has a pore size of substantially 50 to 500Å.

As described above, according to the membrane of the present invention, since the micropore diameters on the dense inner and outer surfaces of the membrane are different, if the liquid to be treated is supplied to the surface side having the micropores having the small pore diameter, the micropores having the large pore diameter are provided. Since the other surface having the above does not form a fluid passage resistance, the water permeability has a small film thickness dependency, and as will be seen in Examples described later, it has a large water permeability even in a film having a film thickness of more than 200 μm.

Generally, a hollow fiber-shaped semipermeable membrane is said to have excellent mechanical strength and pressure-resistant densification when it has no cavity, but the hollow fiber-shaped semipermeable membrane of the present invention has a cavity as described above. However, it has excellent mechanical strength and pressure resistance. This may be because the reticulated porous layer is relatively thick. At the same time, the hollow-fiber-like semipermeable membrane of the present invention has such a structure that has never existed in the prior art, and therefore has a characteristic that it is excellent in water permeability even when it is particularly thick.

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

Example 1 A mixed solvent of 58 parts by weight of N-methyl-2-pyrrolidone and 29 parts by weight of diethylene glycol was added with the formula An aromatic polysulfone having a repeating unit represented by 13
A part by weight was dissolved to obtain a film forming solution.

In an atmosphere with a relative humidity of 5% and a temperature of 24 ° C., the film-forming solution is extruded from the outer tube of the double-tube nozzle, water is allowed to flow out from the inner tube, and the inner surface is kept for 5 seconds while maintaining the atmosphere. The hollow fiber-shaped semipermeable membrane having an inner diameter of 0.5 mm and an outer diameter of 0.9 mm was obtained by solidifying and then immersing in water to solidify the outer surface and desolvation.

This semipermeable membrane had a pure water permeation rate of 18.0 m ³ / m ² · day · atmospheric pressure, and the removal rate for dextran having a molecular weight of 100,000 was 78%. In addition, room temperature water was pressed into the hollow fiber semipermeable membrane with one end sealed, and the burst strength was measured to be 18 kg / cm ²
It was.

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 inner surface (10000) is shown.
2) and an electron micrograph (5000 times) of the outer surface are shown in FIG.

Examples 2 to 4 Polysulfone was dissolved in the same mixed solvent as in Example 1 to obtain film forming solutions having different polysulfone concentrations. The hollow fiber semipermeable membranes having the same size were obtained by the same method as in Example 1. The physical properties of these films are shown in Table 1.

Example 5 63 parts by weight of dimethylformamide and ethylene glycol 20
17 parts by weight of the same polysulfone as in Example 1 was dissolved in a mixed solvent with parts by weight to obtain a film forming solution. Using this membrane-forming solution, a hollow fiber-shaped semipermeable membrane having the same size was obtained as in Example 1. This membrane has a pure water permeability of 14.5 m ³ / m ² · day · atmosphere and The removal rate for dextran with a litter size of 100,000 was 83%.

Example 6 A hollow fiber semipermeable membrane was obtained by the same method as in Example 2 except that the same membrane forming solution as in Example 2 was used and the diameter of the nozzle was changed. The relationship between the pure water permeation rate of these membranes and the membrane thickness is
Shown in the figure.

The hollow fiber-like semipermeable membrane of the present invention has a small water vapor permeability dependency on a film thickness, and a membrane having a thickness of 200 μ has a significantly large water permeability as compared with a conventional membrane.

Example 7 In Example 1, as the aromatic polysulfone, Except that one having a repeating unit represented by
A hollow fiber-like semipermeable membrane having the same size was obtained in the same manner as in Example 1. This membrane has a pure water permeation rate of 32 m ³ / m ² · day · atmosphere and a removal rate of 80% for dextran with a molecular weight of 100,000.
The burst strength was 18 kg / cm ² .

Comparative Example 1 13 parts by weight of the same polysulfone as in Example 1 was dissolved in 87 parts by weight of N-methyl-2-pyrrolidone to prepare a film forming solution.
A hollow fiber-like semipermeable membrane having the same size was obtained in the same manner as in Example 1. This membrane has a pure water permeation rate of 3.0 m ³ / m ² · day · atmospheric pressure and a removal rate of 70% for dextran with a molecular weight of 100,000.
The burst strength is 18 kg / cm ² and the water permeability is extremely poor.

Comparative Example 2 A hollow fiber semipermeable membrane was obtained in exactly the same manner as in Example 1 except that the spinning atmosphere was set to 40% relative humidity and the coagulation time in this atmosphere was set to 2 seconds. .

This membrane has a pure water permeability of 29.3 m ³ / m ² · day · atmosphere,
The removal rate for dextran having a molecular weight of 100,000 was 74%, and the performance of these membranes was the same as that of the membrane of Example 1, but
A part with a breaking strength of 10 kg / cm ² was partially observed. still,
The breakage in this film is due to partial delamination between the outer surface side net-like porous layer and the finger-like cavity structure layer, and is considered to be due to the nonuniformity of the film structure.

[Brief description of drawings]

1 to 3 are scanning electron micrographs showing the shape of the fibers of the hollow fiber-shaped semipermeable membrane obtained by the method of the present invention, and FIG. 1 shows a cross section (200 times), The illustration shows the inner surface (1
0000 times), FIG. 3 is the outer surface (5000 times), and FIG. 4 is a graph showing the relationship between the film thickness and the water permeability of the hollow fiber membrane obtained by the method of the present invention.

Continuation of front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location D01F 6/76 D 7199-3B (72) Inventor Keisuke Nakagome 1-2 Hoshitazumi Shimohozumi, Ibaraki-shi, Osaka Nitto Within Denko Co., Ltd. (56) Reference JP-A-58-174618 (JP, A) JP-A-59-209615 (JP, A)

Claims (1)

[Claims] 1. A film forming solution by dissolving an aromatic polysulfone in a mixed solvent of a polar organic solvent capable of dissolving the aromatic polysulfone and a solvent which is miscible with the solvent but does not dissolve the aromatic polysulfone, thereby forming a double tube. When extruding from the outer tube of the mold nozzle to solidify polysulfone, the relative humidity on one surface
20% or less of air is brought into contact, the other surface is brought into contact with the coagulating liquid, which is then immersed in water to remove the solvent, so that the coagulating liquid side has substantially 10 to 100Å micropores. A dense surface is formed, and a dense surface having a pore size larger than the above-mentioned micropores and having a pore size in the range of substantially less than 0.1 μm is formed on the air side. The net-like porous layer having a pore diameter larger than that of the micropores and having pores substantially in the range of 0.05 to 5 μm, and having a thickness of 5 to 50 μm continuous with each of the above surfaces, and the net-like porous layer A hollow fiber membrane having a film thickness in the range of 50 to 450 μm is formed by continuously forming a finger-shaped structure layer having a cavity extending substantially in the radial direction of the membrane while being located substantially in the middle of the membrane. For producing aromatic polysulfone hollow fiber semipermeable membrane