JPS6249911A - Production of aromatic polysulfone hollow yarn membrane - Google Patents

Abstract

PURPOSE:To easily control the diameter of the fine pore on the outer surface by introducing a coagulating liq. into the inner tube, bringing the outer surface into contact with the vapor of a nonsolvent and then immersing the hollow yarn in water when the hollow yarn is spinned from an aromatic polysulfone film forming soln. CONSTITUTION:Aromatic polysulfone is dissolved in a mixed solvent of a polar org. solvent dissolving the polysulfone and a nonsolvent not dissolving the polysulfone. The amt. of the nonsolvent is regulated to 5-50wt% and the concn. of the polymer is controlled to 5-35wt%. When a hollow yarn is spinned from the soln., a coagulating liq. such as water is passed through the inner tube of a double-tube nozzle. The membrane forming soln. is extruded from the nozzle and passed through the vapor of the nonsolvent for >=0.1sec. The pressure of the nonsolvent vapor is made higher by >=15mmHg than the vapor pressure at the temp. at which the membrane is formed. Water or alcohols are used as the nonsolvent. Consequently, the thickness of the reticular porous layer can be regulated to 20-50% of the total membrane thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing an aromatic polysulfone hollow fiber semipermeable membrane having excellent water permeability and mechanical strength.

(Prior Art) Since aromatic polysulfone has excellent heat resistance and chemical resistance, various hollow fiber semipermeable membranes made from aromatic polysulfone have been proposed. However, according to conventionally known methods, it is not possible to obtain a hollow fiber membrane with high mechanical strength and excellent water permeability.

For example, Japanese Patent Application Laid-Open No. 49-23183 discloses a film having a diameter of 10 μm with a dense layer on the inner surface and no polymer on the outer surface.
A hollow fiber-like semipermeable membrane having a cavity of m or more in size has been proposed, but such a structure has particularly low mechanical strength. For this reason, Japanese Patent Application Laid-Open No. 54-145379 discloses that a porous polymer layer has a dense layer on both the inner and outer surfaces, and a porous polymer layer that continues from this dense layer has a pore size that continuously increases from the membrane surface. An aromatic polysulfone hollow fiber semipermeable membrane with the following structure has been proposed. However, the water permeability of this membrane is highly dependent on the film thickness, and in particular, when the film thickness exceeds 200 μm, the water permeability becomes significantly poor.

On the other hand, in JP-A No. 59-228017, the present inventors have already reported that when aromatic polysulfone is extruded from a double tube wall nozzle and formed into a hollow fiber membrane by a wet method, the inner surface of the membrane is A method is disclosed in which a hollow fiber membrane is produced by contacting a coagulating liquid with a coagulating liquid, contacting the outer surface with air at a predetermined humidity, and then immersing the membrane in water to remove the solvent and coagulating it. According to this method, in particular, it is possible to obtain a hollow fiber membrane in which micropores having a smaller pore diameter than those on the outer surface are formed on the inner surface while controlling the diameter of the micropores on the outer surface.

In order to solve the problems with the conventional aromatic polysulfone hollow fiber membranes described above, the present inventors have developed an aromatic polysulfone membrane using a method of varying the coagulation conditions of the inner and outer surfaces during forming into a hollow fiber membrane, as described above. As a result of further intensive research into the production of hollow fiber membranes, we found that when aromatic polysulfone is extruded from a double tube wall nozzle and formed into a hollow fiber membrane using a wet method, a coagulating liquid is brought into contact with the inner surface of the membrane. By contacting the outer surface with vapor of a non-solvent of aromatic polysulfone at a predetermined vapor pressure, the diameter of the micropores on the outer surface can be controlled more easily, and micropores with a smaller pore diameter than those on the outer surface are formed on the inner surface. At the same time, it is possible to obtain a hollow fiber membrane in which a thick reticular porous layer is formed between the inner and outer surfaces. Therefore, a hollow fiber membrane having such a structure has particularly excellent burst strength and a small membrane thickness. The inventors have discovered that even when the material is thick, it has a water permeability that is sufficiently high for practical use, leading to the present invention.

(Object of the Invention) Therefore, the present invention generally aims to provide a method for manufacturing an aromatic polysulfone hollow fiber semipermeable membrane having excellent mechanical strength and water permeability, and in particular: Compared to conventional manufacturing methods, the diameter of the micropores on the outer surface can be controlled more easily, and micropores with smaller diameters than those on the outer surface are formed on the inner surface. An object of the present invention is to provide a method for producing an aromatic polysulfone hollow fiber semipermeable membrane that is fundamentally different from the hollow fiber membranes of the present invention and, as a result, has excellent mechanical strength and water permeability.

(Structure of the Invention) The method for producing an aromatic polysulfone hollow fiber semipermeable membrane according to the present invention uses a mixed solvent of a polar organic solvent that dissolves aromatic polysulfone and a solvent that is miscible with this solvent but does not dissolve aromatic polysulfone. Aromatic polysulfone is dissolved in the liquid to form a membrane forming solution, and while the coagulating liquid flows out from the inner tube of the double wall nozzle, the membrane forming solution is extruded from the outer tube, and the outer surface is filled with steam at the temperature of the membrane forming solution. After bringing the aromatic polysulfone into contact with non-solvent vapor having a vapor pressure 151 mHg or more higher than the pressure, it is immersed in water to be formed into a hollow fiber, and the solvent remaining in the hollow fiber is removed, and the inner surface is forming a dense surface with micropores in the range of substantially 10 to 100 μm, with substantially 0.01 to 0.5 micropores on the outer surface.
Forms a dense surface with micropores in the range of 0.05 to 5 μm, the pore size of which is larger than the pores of any of the above surfaces, and the pore size is substantially in the range of 0.05 to 5 μm. having holes and being continuous with each of the above surfaces, and
In the method according to the present invention, which is characterized in that a reticular porous layer having a thickness of 20 to 50% of the total film thickness is formed, a polar organic solvent that dissolves aromatic polysulfone and an aromatic polysulfone that is miscible with this solvent are used. Aromatic polysulfone is dissolved in a mixed solvent with a solvent that does not dissolve group polysulfone to form a membrane forming solution, and the solution is extruded from the outer tube of a double wall nozzle to remove the solvent and solidify the polysulfone to form a hollow fiber membrane. The inner surface is brought into contact with a coagulating liquid, the outer surface is brought into contact with aromatic polysulfone non-solvent vapor at a predetermined vapor pressure, and then immersed in water to remove the solvent remaining in the hollow fibers. Therefore, in this method, the polysulfone extruded from the double wall nozzle is
The inner surface is coagulated by displacement with a coagulating liquid, and the outer surface is coagulated by a non-solvent, but the outer surface does not need to be completely coagulated; by subsequent immersion in water, the outer surface is also completely coagulated. The hollow fiber membrane according to the present invention can be obtained by solidifying the membrane and removing the remaining solvent.

According to the method of the present invention, a dense surface having micropores having a diameter of substantially 10 to 100 pores is formed on the inner surface of the membrane, and a dense surface having micropores having a diameter of substantially 0.01 to 0.5 pores is formed on the outer surface of the membrane. ．． crm
, typically forming a dense surface with micropores of pore size ranging from 1 to 0.3 p m, while
A network porous layer having pores larger than the micropores of any of the above surfaces and having a pore size substantially in the range of 0.05 to 5μ, and continuous to each of the above surfaces; An aromatic polysulfone hollow fiber semipermeable membrane having excellent mechanical strength and water permeability, comprising a finger-like structure layer that is continuous with a porous layer and located approximately in the middle of the membrane, and has a cavity that extends approximately in the radial direction of the membrane. can be obtained.

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

Note that the network porous layer is a porous layer that is coarser than the outer surface, and the pore diameter of the pores in the network porous layer is usually about 10 times or more than the diameter of the micropores in the outer surface. be.

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

However, X1 to X6 represent non-dissociable substituents exemplified by alkyl groups such as methyl groups and ethyl groups, and halogens such as chlorine and bromine, and l, m, n, 0, p and q are 0 to 4. indicates an integer. Generally, 1. Polysulfone in which m, n, o, p and q are all 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 membrane forming solution containing aromatic polysulfone is prepared by dissolving aromatic polysulfone in a mixed solvent of a polar organic solvent that dissolves aromatic polysulfone and a non-solvent that does not dissolve aromatic polysulfone. As the polar organic solvent, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, etc. are preferably used, and as the non-solvent, aliphatic polyhydric alcohols such as glycerin, ethylene glycol, propylene glycol, etc. 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, and lower aliphatic ketones such as acetone and methyl ethyl ketone.

In the method of the present invention, the non-solvent in the membrane forming solution is
It is used to increase 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 mixed solvent obtained is uniform, but is usually in the range of 5 to 50% by weight. Generally, the higher the proportion of the non-solvent in the mixed solvent, the higher the water permeability of the resulting hollow fiber semipermeable membrane.

On the other hand, when a non-solvent is not used in the membrane-forming solution, the water permeability of the resulting membrane is about 1/2 to 1/10 that of a membrane obtained using a non-solvent as a component of the membrane-forming solution. However, increasing the proportion of non-solvent in the mixed solvent too much makes it difficult to dissolve polysulfone in the mixed solvent and may cause membrane defects such as pinholes to be formed in the resulting hollow fiber membrane. Undesirable.

The concentration of aromatic polysulfone in the membrane forming solution is usually 5 to 5.
35% by weight, preferably 10-30% by weight. 35
If it exceeds 5% by weight, the water permeability of the resulting semipermeable membrane will be too low for practical use, while if it is less than 5% by weight, the resulting membrane will have poor mechanical strength. be.

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

In the method of the present invention, as the non-solvent vapor when extruding the film-forming solution into the non-solvent vapor of polysulfone, in addition to water vapor, vapor of a non-solvent organic solvent used for preparing the film-forming solution is also used. .

In particular, in the present invention, such non-solvent vapors include:
Water vapor and vapors of lower aliphatic alcohols such as methanol, ethanol, and isopropyl alcohol are preferred.

In the method of the present invention, the vapor pressure of the non-solvent is such that the thickness of the reticulated porous layer in the resulting hollow fiber membrane is 20 to 20% of the total membrane thickness.
In order to make it 50%, it is necessary that the vapor pressure at the temperature of the membrane forming solution used is higher than the vapor pressure by 15 mHg or more, preferably by 23 mmHg or more.

If the vapor pressure of the non-solvent is less than 15 m[1 g] than the vapor pressure at the temperature of the membrane-forming solution used, the thickness of the reticulated porous layer on the outer surface is particularly small, resulting in a relatively finger-like structure. In addition to the large thickness occupied by the hollow fibers, the dispersion density of micropores on the outer surface is small, so such hollow fiber membranes do not have high water permeability and are inferior in mechanical strength and consolidation resistance.

As described above, when the network porous layer is less than 20% of the total film thickness, the film does not have practically sufficient mechanical strength and compaction resistance.

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 pores with a smaller pore size and the outer surface has pores with a larger pore size. Electron micrograph showing the cross-sectional structure of the membrane (200x magnification)
It is. FIG. 2 shows an electron micrograph (5000x magnification) of the outer surface of a hollow fiber membrane having micropores with a pore size of substantially 0.01 to 0.5 μm. Figures 3 and 4 show that when extruding a membrane forming solution from a double-front nozzle into an aromatic polysulfone non-solvent atmosphere, a non-solvent having a vapor pressure lower than 15 wmllg at the temperature of the membrane forming solution is used. An electron micrograph (200x) of a cross section of a hollow fiber membrane as a comparative example obtained by extrusion into solvent vapor and an electron micrograph (5000x) of the outer surface are shown. The hollow fiber membrane as a comparative example has a thin reticulated porous layer on the outer surface;
It is also clear that the pore diameter is not uniform and the distribution density of the pores on the outer surface is small.

(Effects of the Invention) 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 inside of the membrane having micropores with a small pore diameter, The outer surface, which has a large number of uniformly large pores, does not create resistance to fluid passage, so high water permeability can be achieved. In addition, since the network porous layer accounts for 20 to 50%, and in most cases 25 to 40%, of the total membrane thickness, the hollow fiber membrane produced by the method of the present invention has excellent mechanical strength and consolidation resistance. There is.

The diameters of the pores and cavities in the network porous layer and the finger-like structure layer are evaluated using electron micrographs, but the micropore diameter in the dense layer can be measured using polyethylene glycol, dextran, and proteins with various molecular weights. It is evaluated from the removal rate against etc.

It is generally said that a hollow fiber semipermeable membrane has excellent mechanical strength and consolidation resistance when it does not have a cavity, but the hollow fiber semipermeable membrane of the present invention has a network porous layer as described above. forms a thick layer that accounts for 20-50% of the total film thickness, and in most cases 25-40%, and on the other hand, because the finger-like structure is relatively thin, it has a cavity but is not mechanically It has excellent strength and compaction resistance, and is particularly characterized by excellent water permeability even when it is thick.

(Examples) The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples in any way. In the following, the characteristics of the hollow fiber membrane were determined as follows. Pure water was permeated through the membrane at a pressure of 1 kg/0.111% and a temperature of 25° C., and the measured value of the water permeation rate after 15 minutes was taken 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: 20,000) at an average pressure of 1 kg/cIi and a temperature of 25° C., and taking the value measured after 15 minutes as the removal rate.

Moreover, the bursting strength was determined by applying water pressure from inside the membrane and determining the pressure at which the membrane burst.

The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples in any way.

Example I A membrane forming solution was obtained by dissolving 17 parts by weight of an aromatic polysulfone having a repeating unit represented by the formula in a mixed solvent of 58 parts by weight of N-methyl-2-pyrrolidone and 25 parts by weight of diethylene glycol.

25n+ than the vapor pressure of the membrane forming solution at a temperature of 25°C.
While extruding the above film-forming solution from the outer tube of the double-walled nozzle under water vapor having high Hg vapor pressure at a temperature of 25°C,
Water at a temperature of 25°C is flowed out from the inner tube, kept in the above atmosphere for 1 second to solidify from both the inner and outer surfaces, and then immersed in water to remove the solvent to form a tube with an inner diameter of 0.5 mm and an outer diameter of 0.5 mm. 911
A hollow fiber semipermeable membrane was obtained.

The total thickness of this membrane was 200 μm, and the thickness of the reticulated porous layer was about 25% of the total membrane thickness.

This hollow fiber membrane has a pure water permeation rate of 6001/d・hour・atmosphere, and molecules! The removal rate for polyethylene glycol 20,000 was 88%. In addition, the bursting strength is 3
It was 0 kg/c+a.

In addition, Fig. 1 shows an electron micrograph (200x magnification) of the cross section of the hollow fiber semipermeable membrane obtained above, and an electron micrograph of the outer surface (
5000x) is shown in Figure 2.

Comparative Example 1 Using the same membrane forming solution as used in Example 1, the membrane forming solution was extruded through a double tube wall nozzle into a steam atmosphere having a vapor pressure 10 mHg higher than the vapor pressure at the temperature of the membrane forming solution. A hollow fiber membrane was produced in the same manner. The thickness of the network porous layer in this membrane is approximately 16% of the total membrane thickness.
Met.

This hollow fiber membrane has a pure water permeation rate of 4001/rd・hour・
Atmospheric pressure, molecules! The removal rate for 20,000 polyethylene glycol is 85%, and the bursting strength is 18 kg/ad.
Met. Therefore, it is clear that this membrane has a lower pure water permeation rate and a significantly lower bursting strength than the hollow fiber membrane according to Example 1.

Figure 3 shows an electron micrograph (200x magnification) of the cross section of the hollow fiber semipermeable membrane obtained above, and an electron micrograph of the outer surface (
5000 times) is shown in FIG.

Example 2 A membrane forming solution was obtained by dissolving 18 parts by weight of the same aromatic polysulfone as in Example 1 in a mixed solvent of 63 parts by weight of N,N-dimethylformamide and 19 parts by weight of ethylene glycol.

30 mm higher than the vapor pressure of the membrane forming solution at a temperature of 25°C.
The above film-forming solution was heated at 25°C from the outer tube of a double-walled nozzle under isopropyl alcohol vapor having a high Hg vapor pressure.
At the same time, water at a temperature of 25°C was extruded from the inner tube, kept in the above atmosphere for 1 second, solidified from both the inner and outer surfaces, and then immersed in water to remove the solvent to form a film with a total film thickness of 200°C.
~500μm, inner diameter 1. OIm, outer diameter 1.4-2.
Hollow fiber semipermeable membranes having various thicknesses of OIm were obtained.

Regarding these hollow fiber membranes, Figure 5 shows the relationship between membrane thickness, pure water permeation rate, and polyethylene glycol removal rate, and Figure 6 shows the relationship between the thickness of the reticulated porous layer and bursting strength with respect to membrane thickness. show.

It is clear that the hollow fiber membrane according to the present invention has high burst strength and maintains a high water permeation rate even when the membrane thickness increases.

Comparative Example 2 A hollow fiber membrane was obtained in the same manner as in Example 2, except that the isopropyl alcohol vapor pressure in Example 1 was made 11n+Hg higher than the vapor pressure at the temperature of the membrane forming solution.

For these membranes, the relationship between membrane thickness, pure water permeation rate, and polyethylene glycol removal rate is shown in Figure 5, and the relationship between the thickness of the reticulated porous layer and bursting strength with respect to membrane thickness is shown in Figure 6.
Each is shown in the figure.

These hollow fiber membranes have a lower pure water permeation rate than the membrane according to the present invention with the same membrane thickness, and because the thickness of the porous porous layer in the entire membrane thickness is small, they are prone to rupture. It is clear that the strength is significantly lower.

[Brief explanation of the drawing]

FIG. 1 is a scanning electron micrograph (200x) showing the cross-sectional structure of an aromatic polysulfone hollow fiber membrane produced by the method of the present invention, and FIG. 2 is a scanning electron micrograph (5000x) showing the outer surface structure. Figure 3 is a scanning electron micrograph (200x) showing the cross-sectional structure of an aromatic polysulfone hollow fiber membrane as a comparative example, and Figure 4 is a scanning electron micrograph (5000x) showing the structure of the outer surface. . Further, FIG. 5 is a graph showing the dependence of pure water permeation rate and polyethylene glycol removal rate on membrane thickness for the hollow fiber membrane according to the present invention and the hollow fiber membrane as a comparative example. It is a graph showing the relationship between the membrane thickness, the reticular porous layer thickness, and the bursting strength for the hollow fiber membrane according to the invention and the hollow fiber membrane as a comparative example. Patent Applicant Nitto Electric Industry Co., Ltd. Agent Patent Attorney Ittsu Makino Department Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Thickness (μmK) Figure 6 Thickness (μmK) Procedural Amendment (Formula) ) % formula % 2. Name of the invention: Method for producing aromatic polysulfone hollow fiber membrane 3. Relationship with the case of the person making the amendment Patent applicant address: 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Name: Nitto Electric Industry Co., Ltd. Co., Ltd. 4, agent address: 1-8-3-5 Shinmachi, Nishi-ku, Osaka City, date of amendment order: November 6, 1985 (shipment date: January 1, 1988)
(January 26) 6. Number of inventions increased by amendment Contents of the amendment (1) "Figure 1 is..." in lines 12-19 of page 20 of the specification
・It is. ” to be deleted. (2) On page 20, line 20 of the specification, ``Also, FIG. 5 is shown above'' is corrected to ``FIG. 1 is''. (3) ``Figure 6'' on page 21, line 3 of the specification is replaced with ``Figure 2.''
and correct it. (4) Delete drawings 1 to 6 and submit new drawings 1 and 2. Above is Figure 1 γy insult (μ峨)

Claims (4)

[Claims] (1) a polar organic solvent that dissolves aromatic polysulfone;
Aromatic polysulfone is dissolved in a mixed solvent with a solvent that is miscible with this solvent but does not dissolve aromatic polysulfone to form a film forming solution. The solution is extruded from the outer tube, and the outer surface is brought into contact with the vapor of an aromatic polysulfone non-solvent having a vapor pressure 15 mmHg or more higher than the vapor pressure at the temperature of the membrane forming solution, and then immersed in water to form a hollow fiber. At the same time, the solvent remaining in the hollow fibers is removed, forming a dense surface with micropores substantially in the range of 10 to 100 Å on the inner surface, and substantially pores in the range of 0.01 to 100 Å on the outer surface. 0.5μ
Forms a dense surface having micropores in the range of m, with a pore size larger than the micropores of any of the above surfaces, and having a pore size substantially in the range of 0.05 to 5 μm. A method for producing an aromatic polysulfone hollow fiber membrane, which comprises forming a network-like porous layer having pores, continuous on each of the surfaces, and having a thickness of 20 to 50% of the total membrane thickness. (2) The method for producing an aromatic polysulfone hollow fiber membrane according to claim 1, wherein the non-solvent vapor is water vapor. (3) The method for producing an aromatic polysulfone hollow fiber membrane according to claim 1, wherein the non-solvent vapor is lower aliphatic alcohol vapor. (4) The method for producing an aromatic polysulfone hollow fiber membrane according to claim 1, wherein the network porous layer occupies 25 to 40% of the total membrane thickness.