JP7369577B2 - Manufacturing method of polysulfone porous hollow fiber membrane - Google Patents

Description

The present invention relates to a method for producing polysulfone porous hollow fiber membranes. More specifically, the present invention relates to a method for producing a polysulfone porous hollow fiber membrane suitable for use as a water purification membrane or the like.

Filtration operations using porous membranes such as microfiltration membranes and ultrafiltration membranes have been put to practical use in many fields, such as sterilization in the pharmaceutical field, water purification field, or food industry, and ultrapure water production in the semiconductor industry. In recent years, membranes made of polysulfones have been widely used for sterilization in the water purification field.

Examples of polysulfones include polysulfone, polyethersulfone, polyphenylsulfone, and the like, and polysulfone is often used for household water purification (see Patent Document 1).

Recently, water purifiers that combine water purification membranes and activated carbon are increasingly being used to remove residual chlorine, etc. However, while these combinations increase the size, there is also a demand for smaller size from the standpoint of design. The reality is that it is increasing year by year. Therefore, there is an increasing demand for high water permeability of water purification membranes, and as a countermeasure to this, when spinning polysulfone as a membrane raw material, a water-soluble organic solvent that is soluble in polysulfone, such as N,N-dimethylformamide (DMF), is used. (Patent Document 2).

At this time, by using a water-soluble organic solvent that is soluble in polysulfone as the core liquid, the inner wall of the hollow fiber membrane becomes a loose structure, so a hollow fiber membrane with high water permeability can be obtained. When water is passed through a hollow fiber membrane formed by using the core liquid as a core liquid, foreign matter consisting of membrane constituents may be mixed into the filtrate water, especially the initial filtrate water at the beginning of the flow. As foreign matter, fine particles of polysulfone resin are observed.

The mechanism by which these foreign substances are generated is that when a membrane is formed by phase separation, it takes a certain amount of time for the inner wall to undergo solvent exchange. This is thought to be because, in the case of dimethylformamide, a portion of the dope liquid diffuses into the core liquid, and then the dope liquid that diffuses into the coagulation liquid precipitates inside the hollow fiber membrane.

Special Publication No. 3-47127 Japanese Patent Application Publication No. 2-268821 Japanese Patent Application Publication No. 5-168881

The purpose of the present invention is to prevent contamination of hollow fiber membrane components into filtrate when water is passed through a polysulfone porous hollow fiber membrane manufactured by dry-wet spinning using a non-solvent induced phase separation method. , and a two-layer structure of the hollow fiber inner membrane, for example, in a hollow fiber membrane with a membrane thickness of 50 to 70 μm, a sparse structure is formed approximately 3 to 8 μm from the inner surface of the membrane in the membrane thickness direction. It is an object of the present invention to provide a method for producing a film in which peeling does not occur between the dense structure portion and the dense structure portion formed approximately 45 to 60 μm in the film thickness direction from the outer surface of the film.

The object of the present invention is to prepare a spinning dope consisting of an N,N-dimethylformamide solution containing 12 to 25 % by weight of polysulfone, 5 to 20 % by weight of polyvinylpyrrolidone, and 1 to 5 % by weight of ethylene glycol, and add 25 to 30% by weight of isopropyl alcohol. Using a mixed solution of 75 to 70 % by weight of N,N-dimethylformamide as the core liquid, dry-wet spinning is performed using a non-solvent induced phase separation method using a double annular nozzle to produce a polysulfone porous hollow fiber membrane. This is achieved by

In hollow fiber membranes obtained by conventional manufacturing methods, it was difficult to avoid the generation of fine grains of polysulfone resin, but in hollow fiber membranes obtained by the method for manufacturing porous polysulfone hollow fiber membranes of the present invention, It has an excellent effect in that no foreign matter from the hollow fiber membrane components is found in the filtered water when water is passed through it. On the other hand, in the case of a two-layer structure formed on the inner membrane of a hollow fiber membrane, for example, a hollow fiber membrane with a membrane thickness of 50 to 70 μm, the membrane is formed approximately 3 to 8 μm in the thickness direction from the inner surface of the membrane. Peeling does not occur between the sparse structural portion and the dense structural portion formed approximately 45 to 60 μm in the film thickness direction from the outer surface of the film.

FIG. 2 is a diagram showing (a) a cross section of the polysulfone porous hollow fiber membrane obtained in Examples, (a) SEM 1000x cross section, and (b) SEM 3000x inner surface. FIG. 2 is a diagram showing (a) a cross section of the polysulfone porous hollow fiber membrane obtained in Comparative Example 1, viewed at 1000x SEM, and (b) an inner surface viewed at 3000x SEM. FIG. 4 is a diagram showing (a) a cross section of the polysulfone porous hollow fiber membrane obtained in Comparative Example 2 (SEM 1000 times), and (b) SEM 3000 times the inner surface. FIG. 3 is a diagram showing (a) a cross section of the polysulfone porous hollow fiber membrane obtained in Comparative Example 3, viewed at 1000x SEM, and (b) an inner surface viewed at 3000x SEM.

As the polysulfone, commercially available products such as Solvay Specialty Polymers products can be used as they are.

A water-soluble organic solvent containing polyvinylpyrrolidone and ethylene glycol is further blended into the spinning stock solution containing polysulfone as a film-forming component. As the water-soluble organic solvent other than ethylene glycol (hereinafter simply referred to as "water-soluble organic solvent"), N,N-dimethylformamide is used from the viewpoint of spinning stability .

The spinning stock solution used has a blending ratio of about 12 to 25% by weight of polysulfone, about 5 to 20% by weight of polyvinylpyrrolidone, and about 1 to 5% by weight of ethylene glycol, with the remainder being a water-soluble organic solvent. If the blending ratio of polysulfone is lower than this, the strength of the hollow fiber membrane will decrease during spinning, making it difficult to form a hollow fiber membrane, making spinning impossible. On the other hand, if the blending ratio of polysulfone is higher than this, spinning will not be possible. , it becomes difficult to form holes in the hollow fiber membrane, resulting in a decrease in permeation performance. In addition, if the blending ratio of polyvinylpyrrolidone or ethylene glycol is lower than this, the hydrophilicity of the membrane will decrease and the pore size of the hollow fiber membrane will decrease, resulting in a decrease in permeation performance. When the blending ratio of is high, the membrane-forming stock solution becomes unstable and becomes cloudy, making it difficult to perform spinning.

To form a polysulfone porous hollow fiber membrane using such a spinning dope, a mixture of 25 to 30% by weight of isopropyl alcohol and 75 to 70% by weight of N,N-dimethylformamide is added to the core liquid using a double ring nozzle. It is carried out by dry-wet spinning using a non-solvent induced phase separation method. If the proportion of isopropyl alcohol is lower than this, foreign matter consisting of membrane components will be mixed into the filtered water using the hollow fiber membrane produced, whereas if the proportion of isopropyl alcohol is higher than this, Separation occurs between the dense structural portion formed on the inner wall of the hollow fiber membrane and the sparse structural portion formed on the outer surface of the hollow fiber membrane, resulting in inner wall peeling.

Note that the example of Patent Document 3 discloses a porous polysulfone hollow fiber membrane manufactured using a mixed solution of 95% by weight of isopropyl alcohol and 5% by weight of N,N-dimethylformamide as the core liquid. If such a mixed liquid is used as a core liquid, peeling of the inner wall may occur, and this is clearly excluded from the embodiments of the present invention.

Next, the present invention will be explained with reference to examples.

Example A spinning stock solution consisting of 16% by weight of polysulfone (P1700, manufactured by Sovay), 11% by weight of polyvinylpyrrolidone (PVP K-30, manufactured by ISP), 2% by weight of ethylene glycol, and 71% by weight of N,N-dimethylformamide was brought to room temperature. It was prepared using

The obtained spinning stock solution was discharged from a double annular nozzle into a water coagulation bath by a wet-dry spinning method using a core liquid consisting of 25% by weight of isopropyl alcohol and 75% by weight of N,N-dimethylformamide. Thereafter, it was passed through a cleaning tank, wound up onto a bobbin, and washed in an autoclave at 121°C for 60 minutes, followed by drying at 25°C for 15 hours to obtain a polysulfone porous hollow fiber membrane.

Water was passed through the obtained porous hollow fiber membrane at a pressure of 40kPa, and the presence of foreign matter in the filtrate water collected within 5 seconds was visually confirmed. No foreign matter was found. When formazin turbidity was measured using (2100AN), filtrate water turbidity/NTU was 0.20.

Furthermore, when the presence or absence of peeling of the inner wall of the hollow fiber membrane was confirmed using a SEM image, no peeling of the inner wall was confirmed. SEM images of the cross section of the hollow fiber membrane and the inner surface of the hollow fiber membrane are shown in Figures 1(a) and 1(b).

Comparative example 1
In the example, when 100% by weight N,N-dimethylformamide was used as the core liquid, no peeling of the inner wall was observed, but the contamination of foreign matter into the filtrate water was confirmed, and the filtrate turbidity/NTU was 1.91. SEM images of the cross section of the hollow fiber membrane and the inner surface of the hollow fiber membrane are shown in FIGS. 2(a) and 2(b).

Comparative example 2
In the example, when a core liquid consisting of 5% by weight of isopropyl alcohol and 95% by weight of N,N-dimethylformamide was used, no peeling of the inner wall was observed, but contamination of foreign matter into the filtered water was confirmed. The filtered water turbidity/NTU was 3.71. SEM images of the cross section of the hollow fiber membrane and the inner surface of the hollow fiber membrane are shown in FIGS. 3(a) and 3(b).

Comparative example 3
In the example, when a core liquid consisting of 50% by weight of isopropyl alcohol and 50% by weight of N,N-dimethylformamide was used, no foreign matter was observed in the filtrated water, and the filtrated water turbidity/NTU was 0.27. However, peeling of the inner wall was confirmed. SEM images of the cross section of the hollow fiber membrane and the inner surface of the hollow fiber membrane are shown in FIGS. 4(a) and 4(b).

Claims (1)

A spinning stock solution consisting of an N,N-dimethylformamide solution containing 12-25 % by weight of polysulfone , 5-20 % by weight of polyvinylpyrrolidone and 1-5 % by weight of ethylene glycol was mixed with 25-30 % by weight of isopropyl alcohol and N,N- A method for producing a polysulfone porous hollow fiber membrane, which is characterized by performing wet-dry spinning using a non-solvent induced phase separation method using a 75 to 70 % by weight mixture of dimethylformamide as a core liquid using a double annular nozzle.