JP2528893B2 - Method for producing polysulfone hollow fiber membrane - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a polysulfone hollow fiber membrane. The polysulfone hollow fiber membrane produced by the present invention is suitable for an external pressure total filtration system, and can be effectively used for water purification, for example.

[Prior Art] In recent years, a technique using a membrane having selective permeability in a separation operation has been remarkably progressing and is being put to practical use in a considerable field. In particular, when the shape of the membrane is a hollow fiber shape, the membrane area per occupied volume is much larger than that of a flat membrane shape, which is advantageous, and is greatly researched, developed, and partially commercially available. Cellulose-based polymers have been mainly used as the membrane material, but as the conditions of use such as the temperature of the treatment liquid and PH become severe, the cellulose-based polymer deteriorates, so various synthetic polymers are also considered. ing. Among them, polysulfone-based polymers are promising as a material excellent in heat resistance, acid resistance, alkali resistance, oxidation resistance, and microbial resistance, and various studies have been conducted. For example, in Japanese Patent Laid-Open No. 54-145379, hollow fiber membranes have fine pores (substantially skin layers) of 10 to 100Å on the inner and outer surfaces, and the inside of the membrane is a slanted type structure. Polysulfone hollow fiber membranes are disclosed. In addition, JP-A-56-1
Japanese Patent No. 15602 discloses a polysulfone hollow fiber membrane having skin layers on both surfaces and having a tube bundle structure inside the membrane. Also, a polysulfone hollow fiber membrane having a skin layer on the inner surface and micropores of 1 μm or more on the outer surface is commercially available from Amicon under the name of HP series. Further, Japanese Patent Laid-Open No. 56-86941 discloses a polysulfone-based flat membrane and a hollow fiber membrane having a specific structure made of a mixed polymer of aromatic polysulfone manufactured by Union Carbide Corp. of USA and polyether sulfone manufactured by ICI of England. .

Further, in JP-A-58-91822, the inner surface is a skin layer similar to the above-mentioned prior invention, but reduces the film resistance,
Moreover, a hollow fiber membrane in which the open area ratio of the outer surface is increased in order to reduce clogging is also disclosed.

[Problems to be Solved by the Invention] However, all of the above polysulfone membranes have a structure having an inner surface and an outer surface or a skin layer on the inner surface. Therefore, the method of use is also directed from the inside to the outside of the hollow fiber membrane. The main method was an internal pressure circulation filtration system that allows liquid to pass through. Such an internal pressure circulation filtration method is not necessarily a good measure from an energy point of view, and there is a demand for a hollow fiber membrane suitable for use in an external pressure total filtration method that can be used in a simpler system.

When the above-mentioned conventionally disclosed hollow fiber membrane is used as an external pressure filtration method, a hollow fiber membrane having a skin layer on the inner surface and the outer surface has large filtration resistance, and a hollow fiber having a skin layer only on the inner surface is used. Since the outer surface of the membrane is porous, when it is used for filtering dirty water containing a lot of SS component, the SS component is clogged even inside the membrane wall, which makes cleaning difficult.

[Means for Solving Problems] The inventors of the present invention have conducted extensive studies, and a hollow fiber membrane having a structure in which the outer surface is a skin layer and the inner side is porous is suitable for use in an external pressure total filtration method. It was found that the film was a different film, and as a result of further investigation, the present invention was achieved. That is, according to the present invention, in producing a hollow fiber membrane by a dry-wet spinning method by extruding a spinning dope prepared by dissolving a polysulfone, a micropore-forming agent and a common solvent thereof through a ring nozzle, the atmosphere of [1] dry zone is It is in a state of dry air or nitrogen having a dew point of -10 ° C or lower, [2] water of 50 ° C or lower is used as an external coagulating bath, and [3] the common solvent is used as an internal coagulating liquid to be injected into the core. Is used in an aqueous solution of 50% by weight or more and 90% by weight or less, and a method for producing a polysulfone hollow fiber membrane.

The polysulfone used in the present invention is not particularly limited, and for example, those commercially available under the Udel trademark manufactured by Amoco and those sold under the VICTREX-PES trademark manufactured by ICI can be preferably used.

Examples of the micropore-forming agent include water-soluble polymers such as polyalkylene glycol represented by polyethylene glycol and polypropylene glycol, polyvinylpyrrolidone, and nonsolvents such as ethyl alcohol, propyl alcohol, ethylene glycol, and glycerin.

In addition, dimethylformamide (DMF), dimethylacetamide (D
A water-miscible polar solvent such as MA) or N-methyl-2-pyrrolidone (NMP) is preferably used. These may be used alone or in combination. These polysulfones, micropore-forming agents and spinning dope prepared by using these common solvents are subjected to dry-wet spinning while introducing an internal coagulation liquid into the core using an annular nozzle, and coagulated in an external coagulation bath, The polysulfone hollow fiber membrane of the present invention can be obtained by extracting the solvent and the micropore-forming agent. The structure of the outer surface of the hollow fiber membrane depends on the spinning method. For example, a wet spinning method can provide a hollow fiber membrane having a dense outer surface, but since it is solidified immediately after being discharged from the nozzle surface and a draft is applied during solidification, a vertical streaky structure is formed in the fiber axis direction. It tends to be formed, and a uniform skin layer cannot be obtained. On the other hand, in the dry-wet spinning carried out in the present invention, the spinning dope is discharged from the nozzle into the air and enters the coagulating bath in a state where the draft is relaxed, and therefore such a vertical streak structure is not recognized. Further, since a part of the phase change is started when passing through the dry zone, micropores are easily formed on the outer surface.

In the present invention, when the polysulfone hollow fiber membrane is produced by the dry-wet spinning method, the atmosphere of the dry zone has a dew point of -10 ° C or lower, preferably kept in a state of being replaced with dry air or nitrogen having a temperature of -30 ° C or lower. is important. If the dew point of the atmosphere in the dry zone is -10 ° C or lower, phase change due to moisture absorption from the atmosphere does not substantially occur until the stock solution discharged from the annular nozzle enters the coagulating liquid consisting of water and solidifies. Therefore, a uniform and dense structure is formed on the outer surface. Even better results are obtained if the dew point is below -30 ° C. Normally -10 ℃ to -50 ℃
Dew point dry air or nitrogen is used.

If the coagulation bath temperature exceeds 50 ° C, it will be difficult to completely remove the influence of the vapor pressure of the coagulation bath even if the atmosphere in the dry zone is adjusted to the above conditions.
It is desirable to spin at 30 ° C. Practically
It is preferably carried out at 10 ° C to 30 ° C. The length of the dry zone is usually 10 mm to 200 mm.

The internal coagulating liquid injected into the core directly affects the structure of the inner surface. In order to make the outside of the hollow fiber porous, it is better to delay coagulation, and it is desirable to use an aqueous solution of the solvent used in the stock solution. When the solvent concentration in the internal coagulation liquid is 50% by weight or less, a dense structure is formed, and when it is 90% by weight or more, coagulation becomes too slow and the shape of the hollow fiber is easily deformed. Therefore, in the present invention, 50% by weight or more, It is necessary to use an aqueous solvent solution of 90% by weight or less. The polysulfone hollow fiber membrane produced by the present invention has a skin layer on the outer surface of which substantially no pores of 100 liters or more substantially exist. If the thickness of the skin layer is too thin, the filtration performance will be lowered, and if it is too thick, the water permeability will be lowered and the filtration resistance will be high, so it is usually set in the range of 1 to 10 μm.

Further, the polysulfone hollow fiber membrane produced according to the present invention has micropores having an average pore diameter of 200Å to 3000Å at an opening ratio of 5 to 50%. The micropore size can be measured by observing with a scanning electron microscope.
The average pore size can be measured by the above-mentioned conventionally known method. The porosity is the percentage of the total surface area of the micropores formed on the inner surface with respect to the inner surface area. If the average pore size is smaller than 200Å, the filtration resistance will increase, and if it is larger than 3000Å, the filtration performance will decrease. If the porosity is less than 5%, the filtration performance will decrease,
If it is more than 50%, the mechanical strength becomes weak.

Further, the inside of the polysulfone hollow fiber membrane produced by the present invention has a fine porous structure. The fine porous structure referred to here is a sponge structure such as a mesh structure, a honeycomb structure, and a fine gap structure. In addition, although a finger-like structure or a macrovoid structure may be present on the inner and outer surfaces of the film and inside the film, it is preferable that there is substantially no giant cavity having a size of 10 μm or more. Such a uniform sponge structure without a huge cavity of 10 μ or more has excellent pressure resistance, particularly pressure densification after long-term use, and also has excellent strength.

[Examples] Hereinafter, the present invention will be specifically described with reference to Examples.
The present invention is not limited thereby.

Example 1 20 parts by weight of polysulfone Udel P1700 manufactured by Amoco, 36 parts by weight of polyethylene glycol (PEG, # 600) manufactured by Sanyo Kasei Co., Ltd. and 44 parts by weight of dimethylformamide (DMF) were heated and stirred to dissolve and then cooled to 25 ° C. to be uniform. An undiluted spinning solution was obtained. The stock solution became non-uniform due to phase separation at 36 ° C., but remained uniform at temperatures below that. After degassing at 25 ° C, using an annular nozzle with an outer orifice diameter of 1.0 mm and an inner orifice diameter of 0.5 mm, the stock solution was discharged from the outer orifice at 3 cc / min, and the DMF 80% aqueous solution was discharged from the inner orifice at 1.5 cc / min. ,
After passing the atmosphere through a dry zone 10 cm in which N ₂ with a dew point of −58 ° C. was replaced at a flow rate of 5 l / min, was introduced into water at 30 ° C. and solidified,
It was wound up at a speed of 7 m / min. At this time, the dew point of the dry zone atmosphere was kept in the range of -42 ° C to -48 ° C during the spinning.

The wound hollow fiber is immersed in water to complete the coagulation, and the temperature is 95 ° C.
Wash again with hot water to completely remove DMF and PEG
A hollow fiber membrane having a good roundness of 780μ and an inner diameter of 450μ was obtained. When the outer surface and the inner surface of the hollow fiber were examined by a scanning electron microscope (SEM), the outer surface was a homogeneous and dense skin layer, and no pores of 100 Å or more were observed. On the other hand, the inner surface is the average pore size.
It had 1000 Å holes with a porosity of 15%.

A schematic diagram showing the structure of the obtained hollow fiber membrane is shown in FIGS. 1 and 2.

Example 2 Air dehumidified to a dew point of -29 ° C in a dry zone
Spinning was carried out under the same conditions as in Example 1 except that the atmosphere was replaced by flowing 10 l / min. Dry zone atmosphere has a dew point of -18 ° C to -21
It was kept at ℃.

The same treatment as in Example 1 was performed, and the outer diameter was 790μ and the inner diameter was 450.
A hollow fiber membrane having a good roundness of μ was obtained. The outer surface of the hollow fiber membrane was a uniform and dense skin layer, and no pores of 100 Å or more were observed. In addition, the structure of the inner surface and the porosity were also determined in Example 1.
It was similar to.

Comparative Example 1 Spinning was carried out under the same conditions as in Example 1 except that 10 l / min of air having a dew point of 0 ° C. was passed through the dry zone to replace the atmosphere. The atmosphere in the dry zone had a dew point of 4 ° C to 8 ° C.

The same treatment as in Example 1 is performed, and the outer diameter is 780 μ and the inner diameter is 440.
A hollow fiber membrane having a good roundness of μ was obtained. Micropores having an average pore diameter of 1300Å were observed on the outer surface of the hollow fiber, which was clearly different from the examples. A schematic diagram showing the structure of the obtained hollow fiber membrane is shown in FIG.

Example 3 A hollow fiber membrane was obtained under the same conditions as in Example 2 except that N-methyl-2-pyrrolidone (NMP) was used as the solvent and the NMP 50% aqueous solution was used as the internal injection solution. The outer surface of the hollow fiber was a uniform and dense skin layer, and no pores of 100 Å or more were observed. A large number of pores with an average pore diameter of 400Å were found on the inner surface.
The open area ratio was 10%. The structure of the obtained hollow fiber membrane was almost the same as in Example 1.

Comparative Example 2 A hollow fiber was obtained by spinning under the same conditions as in Example 3 except that the dry zone was the same as in Comparative Example 1. A large number of pores having an average pore diameter of 600Å were opened on the outer surface of the hollow fiber, which was clearly different from the hollow fibers obtained in the examples.

Example 4 Using the hollow fibers obtained in Examples 1 to 3 and Comparative Examples 1 and 2, the results of examining the water permeation performance of pure water and the performance recovery after filtration of tap water are shown in Table 1. Clearly, the examples are superior to the comparative examples in cleaning recovery.

[Effects of the Invention] According to the present invention, a hollow fiber membrane suitable for an external pressure total filtration system can be obtained. The hollow fiber membrane is excellent in the external pressure total filtration system, and can be widely used for purification of water such as tap water, and the industrial utility of the present invention is great.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a cross section of the hollow fiber membrane obtained in Example 1, and FIG. 2 is an enlarged schematic diagram of the inner surface portion thereof. FIG. 3 is an enlarged schematic view of the outer surface portion of the hollow fiber membrane obtained in Comparative Example 1. 1 ... Hollow fiber outer surface portion, 2 ... Hollow fiber central portion 3 ... Hollow fiber inner surface portion, 4 ... Micropores

Claims (1)

(57) [Claims] 1. When a hollow fiber membrane is produced by a dry-wet spinning method by extruding a spinning dope prepared by dissolving a polysulfone, a micropore-forming agent and a common solvent thereof through an annular nozzle, [1] the atmosphere of the dry zone is It is in the state of dry air or nitrogen having a dew point of -10 ° C or lower, [2] water of 50 ° C or lower is used as an external coagulation bath, and [3] the common solvent is used as an internal coagulation liquid to be injected into the core. But
A method for producing a polysulfone hollow fiber membrane, which comprises using an aqueous solution of 50% by weight or more and 90% by weight or less.