JP2009240899A - Composite hollow fiber membrane and its method for manufacturing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite hollow fiber membrane which can be reused for a long time, by suppressing the decrease of separation function due to a membrane surface scratch during air scrubbing operation of an external pressure type hollow fiber membrane module, and also to provide its method for manufacturing. <P>SOLUTION: The composite hollow fiber membrane is formed of an outer layer of a three-dimensional network structure, a subsequent dense intermediate layer, and a support layer with a spherical structure which supports the intermediate layer. In the method for manufacturing of the composite hollow fiber membrane, the composite hollow fiber membrane is manufactured through a process where a resin solution A forming the spherical structure from an inner layer slit and a resin solution B forming the intermediate layer from an outer layer slit are concentrically extruded together with internal coagulation liquid from a central pipe by using a triple pipe spinneret nozzle and are cooled and coagulated in external coagulation liquid, a process where a solvent is discharged, a process where nonsolvent is separated by coating of a resin solution C forming the three-dimensional network structure on the obtained hollow fiber membrane material using a coating nozzle, and a process where the solvent is discharged. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a hollow fiber membrane used for solid-liquid separation. More specifically, the present invention relates to a composite hollow fiber membrane suitably used in waste water treatment, water purification treatment, industrial water production, and the like, and a method for producing the same.

In recent years, hollow fiber membrane modules for microfiltration or ultrafiltration have been applied to the water purification field such as turbidity of river water and groundwater, clarification of industrial water, and advanced treatment of wastewater. In order to sterilize the permeated water and prevent biofouling of the membrane, a hollow fiber membrane module in this field is added with a bactericidal agent such as sodium hypochlorite, or the membrane itself is acid, alkali, chlorine, surfactant. Excellent chemical resistance is required for chemical cleaning. In addition, a separation characteristic that pathogenic microorganisms and the like are not mixed in the permeated water and a physical strength that does not break the yarn are required.

  Polyvinylidene fluoride resin films have come to be used in response to such characteristic requirements. However, the polyvinylidene fluoride resin film has a drawback that the film surface is easily contaminated by hydrophobic interaction, and the stain resistance has been improved by making the polyvinylidene fluoride resin film hydrophilic or composite. For example, a composite hollow fiber membrane has been developed in which a separation functional layer having a small pore and a support layer having a relatively coarse pore are formed on the membrane surface.

  When the total amount of filtration is performed with such a composite hollow fiber membrane module, turbid components accumulate on the outer surface of the hollow fiber membrane to increase the filtration resistance, but intermittent physical scrubbing such as air scrubbing and backwash pressure Alternatively, it can be recycled by chemical cleaning as appropriate. In normal air scrubbing, air is fed into the raw water in the module container, the hollow fibers are rocked and the hollow fibers slide against each other, and the accumulated turbid components are peeled off. However, if separation of turbid components proceeds, the hollow fiber is swung while the raw water turbidity in the module container is high, and if the turbid component contains a hard component, membrane surface abrasion is likely to occur. If film damage accumulates through continuous use, it may become a film defect or damage, resulting in poor turbidity and sterilization performance, and it may be difficult to use for a long time.

A film structure in which the separation functional layer is protected against such inconvenience during scrubbing can be considered. For example, Patent Documents 1 and 2 disclose a composite hollow fiber membrane in which a separation functional layer is formed inside the hollow fiber. However, a polymer solution is coated on the inner side of the hollow fiber membrane to form a separation function, and there is a difficulty in uniformly coating the inside of the membrane wall. Patent Document 3 discloses a composite hollow fiber membrane in which a non-porous functional layer is sandwiched between support layers on both sides by melt spinning. However, such a composite hollow fiber membrane is intended for gas separation, and is difficult to apply to the water purification treatment field. On the other hand, as a method for producing a composite hollow fiber membrane made of polyvinylidene fluoride resin used in the field of water purification treatment, Patent Documents 4 and 5 disclose non-solvent phase separation by discharging two types of polyvinylidene fluoride resin solutions. A composite hollow fiber membrane manufactured using heat-induced phase separation is disclosed. Although these are excellent in chemical resistance, water permeability, mechanical properties, stain resistance, etc., the scratch resistance during air scrubbing of the outermost layer is not always sufficient.
JP-A-2-2842 JP-A-4-310222 JP-A-62-1404 International Publication No. 03/106545 Pamphlet JP 2006-239680 A

  An object of the present invention is to provide a composite hollow fiber membrane that can be regenerated and used for a long period of time, and a method for producing the same, in view of the problems during air scrubbing operation of the external pressure hollow fiber membrane module described above.

To achieve the above object, the present invention is constituted as follows.
(1) A composite hollow fiber membrane formed by an outer layer having a three-dimensional network structure, a dense intermediate layer following the outer layer, and a support layer having a spherical structure that supports the intermediate layer.
(2) Using a triple tubular spinning nozzle, concentrically extrude resin solution A that forms a spherical structure from the inner slit, resin solution B that forms an intermediate layer from the outer slit, and inner solidified liquid from the center pipe. A step of cooling and solidifying in an external coagulation liquid, a step of removing the solvent, and coating the obtained composite hollow fiber membrane material with a resin solution C that forms a three-dimensional network structure using a coating nozzle. The manufacturing method of the composite hollow fiber membrane manufactured through the process of carrying out a solvent phase separation, and the process of removing a solvent.
(3) Using a quadruple tubular spinning nozzle, a resin solution A that forms a spherical structure from an inner slit, a resin solution B that forms an intermediate layer from an intermediate slit, and a resin solution C that forms a three-dimensional network structure from an outer slit A method of manufacturing a composite hollow fiber membrane manufactured by passing through a process of extruding an inner coagulating liquid concentrically from a central pipe, cooling and solidifying in an external coagulating liquid, and a process of removing the solvent.

  In view of the problems in the conventional hollow fiber membrane module operation technology described above, the present invention has a multilayer separation function layer of the hollow fiber membrane, so that even if the outermost layer is damaged during air scrubbing, the intermediate dense layer It aims at providing the composite hollow fiber membrane which can suppress the fall of a separation function by backing up with a layer, and its manufacturing method.

  The composite hollow fiber membrane of the present invention and the production method thereof will be described below. 1 and 2 are scanning electron micrographs in place of drawings for explaining the form of the composite hollow fiber membrane of the present invention.

  FIG. 1 is a drawing-substituting photograph (1000 ×) showing a cross-sectional structure of the membrane wall constituting the hollow fiber membrane of the present invention. The structure of the hollow fiber membrane is formed by an outer layer of a three-dimensional network structure, a dense intermediate layer that follows, and a support layer of a spherical structure that supports it. Since the intermediate layer is laminated on the support layer having such a spherical structure, the layers are formed by entering each other at the interface. That is, when the average diameter of the spherical structure is increased, the gap formed by the spherical shape is widened, and the intermediate layer is thickly stacked so that the layers are deeply interleaved with each other.

  On the other hand, when the average diameter is reduced, the gap is narrowed, and the interpenetrating structure at the interface is formed shallow, so that the intermediate layer is formed thin. Here, the dense intermediate layer has an average thickness of 10 μm or less, more preferably 5 μm or less, and an average pore diameter of less than 0.1 μm, more preferably 0.05 μm or less, still more preferably 0.01 μm or less. Say something. A thickness of 0.01 μm or less is preferable because poliovirus (about 0.03 μm), which is the smallest virus, can be blocked.

  The average thickness of the support layer having a spherical structure is 60 μm to 500 μm, more preferably 120 μm to 350 μm, and the average diameter of the spherical structure is 0.1 μm to 5 μm, more preferably 0.5 μm to 3 μm. is there. When the average diameter is less than 0.1 μm, the gap formed in a spherical shape is narrowed and the mechanical strength is increased, but the water permeability may be lowered. On the other hand, when the average diameter exceeds 5 μm, the gap formed by the spherical structure becomes wide and the water permeability increases, but the mechanical strength may tend to decrease. If the thickness of the support layer is less than 60 μm, the buckling pressure due to the external pressure is reduced, and if it exceeds 500 μm, the water permeability may be lowered. Here, the spherical structure means a structure in which a large number of spherical or substantially spherical solid components are connected directly or in a streak shape through the solid components.

  The average thickness of the outer layer having a three-dimensional network structure is 5 μm to 60 μm, more preferably 5 μm to 30 μm, and the average pore diameter of the three-dimensional structure is 0.1 μm to 10 μm. Here, the three-dimensional network structure refers to a structure in which the solid content spreads in a three-dimensional network. In addition, the three-dimensional network structure has pores and voids partitioned by solid contents forming a network. The outer layer made of a three-dimensional network structure is a continuous structure, but may have a layer having a thickness of 2 μm or less that is not a three-dimensional network structure on the outermost surface side.

  FIG. 2 is a drawing substitute photograph (30000 times) showing the form of the outermost surface following the outer layer of the three-dimensional network structure of the hollow fiber of the present invention. In the composite hollow fiber membrane of the present invention, the average pore diameter on the outermost surface is 0.01 μm or more and 1 μm or less, preferably 0.01 μm or more and 0.2 μm or less, more preferably 0.01 μm or more and 0.1 μm or less. If the average pore diameter on the outermost surface exceeds 1 μm, membrane fouling tends to occur, and if it is less than 0.01 μm, the water permeability tends to decrease.

  The method for producing a composite hollow fiber membrane of the present invention is, for example, a method in which a support membrane is produced with a commonly used double tubular spinning nozzle and then a multilayer coating is applied to a separation functional layer, or a molding resin is simultaneously produced using a multilayer nozzle. It is possible to manufacture by combining these manufacturing methods. Therefore, it is not limited to the manufacturing method illustrated below.

  As a manufacturing method of the composite hollow fiber membrane of this invention, it can manufacture, for example by using together a triple tubular spinning nozzle and a coating nozzle. Here, the three-tubular spinning nozzle is a spinning nozzle made of a metal or ceramic made of a double (double layer) pipe inserted into a circular nozzle and having an outer layer slit, an inner layer slit, and a center pipe at regular intervals. Say. Moreover, the coating nozzle used by this invention means the coating nozzle comprised by the elastic body of Unexamined-Japanese-Patent No. 2004-314059, for example, or the circular nozzle comprised by a metal or ceramics.

  The composite hollow fiber membrane of the present invention uses a triple tubular spinning nozzle, and a resin solution A that forms a spherical structure from the inner slit, a resin solution B that forms an intermediate layer from the outer slit, and an internal coagulating liquid from the center pipe Both are extruded concentrically, cooled simultaneously with an external coagulation liquid, and solidified through a process of removing the solvent to obtain a composite hollow fiber membrane formed with an intermediate layer. Thereafter, the composite hollow fiber membrane can be manufactured by applying a resin solution C that forms a three-dimensional network structure using a coating nozzle and then solidifying the resin solution C.

  In the composite hollow fiber membrane of the present invention, the resin solution B forming the intermediate layer comes into contact with the external coagulation liquid and the intermediate layer (periphery) is solidified by non-solvent phase separation, and at the same time, the resin solution A is thermally induced phase separation by cooling. As a result, nuclei are generated in the resin solution A and crystal growth is performed to obtain a composite hollow fiber membrane-like product that forms a spherical structure on the support layer. Thereafter, a resin solution C that forms a three-dimensional network structure on the intermediate layer is further laminated with a coating nozzle and subjected to non-solvent phase separation, whereby the outer layer is formed into multiple layers.

  In addition to the above manufacturing method, stretching is also preferably used as an improvement in water permeation performance by expanding the voids in the membrane wall. As a stretching method, stretching is preferably performed 1.1 times to 4 times in a temperature range higher than the glass transition point of the thermoplastic resin constituting the hollow fiber membrane and lower than the melting point. As the heating medium for stretching, those having easy temperature control such as liquid and gas can be appropriately used.

  The composite hollow fiber membrane of the present invention may be manufactured using a quadruple tubular spinning nozzle. Here, the quadruple tubular spinning nozzle is a metal or ceramic made of an outer layer slit, an intermediate slit, an inner layer slit, and a center pipe having a constant interval in a configuration in which a triple (three layer) pipe is inserted into a circular nozzle. This refers to spinning nozzles. Using this quadruple tubular spinning nozzle, a resin solution A that forms a spherical structure from the inner layer slit, a resin solution B that forms an intermediate layer from the intermediate slit, and a resin solution C that forms a three-dimensional network structure from the outer layer nozzle, The composite hollow fiber membrane of the present invention is manufactured through a process of concentrically extruding together with the internal coagulating liquid from the center pipe, and simultaneously cooling and solidifying with the external coagulating liquid and a process of removing the solvent.

  In the composite hollow fiber membrane of the present invention, the external coagulation liquid penetrates into the extruded resin solution C and resin solution B, and solidification progresses from the outermost layer (periphery) by non-solvent phase separation. A film structure is formed by crystal growth progressing by induced phase separation. At this time, it is possible to manufacture by controlling each supply amount of the resin solution A, the resin solution B, and the resin solution C, and further controlling the non-solvent concentration and the cooling temperature of the external coagulation liquid. As long as it is in the resin solution B and forms the intermediate layer of the present invention, either non-solvent phase separation or thermally induced phase separation may occur predominantly to form a membrane structure.

  The resin used in the present invention refers to a thermoplastic resin composed of a chain polymer. For example, polyethylene, polypropylene, acrylic resin, polyacrylonitrile, acrylonitrile-butadiene-styrene (ABS) resin, polystyrene, acrylonitrile-styrene (AS) resin, vinyl chloride resin, polyethylene terephthalate, polyamide, polyacetal, polycarbonate, modified polyphenylene ether, polyphenylene sulfide , Polyvinylidene fluoride, polyamideimide, polyetherimide, polysulfone, polyethersulfone, and mixtures and copolymers thereof. Other resins miscible with these and polyhydric alcohols or surfactants may be contained in an amount of 50% by weight or less. Among them, a polyvinylidene fluoride resin having high chemical resistance is preferably used.

  The polyvinylidene fluoride resin means a resin containing a vinylidene fluoride homopolymer and / or a vinylidene fluoride copolymer, and may contain a plurality of types of vinylidene fluoride copolymers. The vinylidene fluoride copolymer is a polymer having a vinylidene fluoride residue structure, and is typically a copolymer of a vinylidene fluoride monomer and other fluorine-based monomers. Examples of the copolymer include a copolymer of vinylidene fluoride and at least one selected from vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, and trifluoroethylene chloride. In addition, a monomer such as ethylene other than the fluorine-based monomer may be copolymerized to such an extent that the effects of the present invention are not impaired.

  With the resin solution A forming the spherical structure of the present invention, the polyvinylidene fluoride resin is used in an amount of 20 wt% to 60 wt%. More preferably, it is 25 weight% or more and 45 weight% or less. When it is 20% by weight or more, the mechanical strength of the yarn is high, and when it is 60% by weight or less, the permeation performance is improved.

  In addition, the resin solution B forming the intermediate layer of the present invention and the resin solution C forming the outer layer of the three-dimensional network structure, when the polyvinylidene fluoride resin is used, are 5 wt% or more and 25 wt% or less, more Preferably they are 10 weight% or more and 20 weight% or less. When it is 5% by weight or more, the mechanical strength of the outer layer is improved, and when it is 25% by weight or less, the permeability is improved. The resin used for the resin solution A, the resin solution B, and the resin solution C may be the same resin or different resins. As appropriate, various properties such as the strength and elongation properties, the permeability properties, and the fraction blocking properties of the hollow fiber membrane to be produced can be adjusted in a wider range. The solvent for the resin solution B and the resin solution C is preferably a good solvent for the polyvinylidene fluoride resin. As a solvent for the resin solution A, a poor solvent for the polyvinylidene fluoride resin is preferable. Moreover, as a solvent of the resin solution B and the resin solution C, the good solvent of the good solvent containing the good solvent of the said polyvinylidene fluoride type resin and 5 weight% or less nonsolvent is preferable.

  Here, examples of the poor solvent for the polyvinylidene fluoride resin include, for example, cyclohexane, isophorone, γ-butyrolactone, methyl isoamyl ketone, dimethyl phthalate, propylene glycol methyl ether, propylene carbonate, diacetone alcohol, glycerol triacetate, etc. Examples include ketones, esters, glycol esters and organic carbonates, and mixed solvents thereof.

  Examples of the good solvent for the resin include N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, dimethylformamide, methyl ethyl ketone, acetone, terahydrofuran, tetramethylurea, trimethyl phosphate, and other lower alkyl ketones, esters, and amides. Etc. and mixed solvents thereof. Examples of the non-solvent for the resin include water, hexane, pentane, benzene, toluene, methanol, ethanol, carbon tetrachloride, o-dichlorobenzene, trichloroethylene, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, and butylene glycol. , Pentanediol, hexanediol, low molecular weight polyethylene glycol and other aliphatic hydrocarbons, aromatic hydrocarbons, aliphatic polyhydric alcohols, aromatic polyhydric alcohols, chlorinated hydrocarbons, or other chlorinated organic liquids and their Examples thereof include mixed solvents.

  Here, the poor solvent is defined as a solvent capable of dissolving 5% by weight or less of a polyvinylidene fluoride-based resin at 60 ° C. or less but not more than 5% by weight at 60 ° C. or more and below the melting point of the resin. In contrast, a solvent capable of dissolving 5% by weight or more of a polyvinylidene fluoride resin at 60 ° C. or less is a good solvent, and a solvent that does not dissolve or swell up to the melting point is a non-solvent.

  The internal coagulation liquid used in the present invention is preferably a mixed solution containing 75% to 95% by weight of the poor solvent of the resin solution A and 25% to 5% by weight of the non-solvent. When the non-solvent is 25 wt% or less and 5 wt% or more in the internal coagulating liquid, the smoothness of the inner wall forming the hollow portion is improved.

  As the external coagulation liquid used in the present invention, a non-solvent for the resin solution B and the resin solution C, a non-solvent of 70% by weight or more and a poor solvent of 30% by weight or less for the resin solution B and the resin solution C, or good It is preferable to use a mixed solvent composed of a solvent. When the ratio of the non-solvent in the external coagulation liquid is 70% by weight or more, the non-solvent diffusion between the resin solution B and the resin solution C occurs more rapidly than the heat-induced phase separation of the resin solution A, and the outer surface coagulates. Solidify in solution A with thermally induced phase separation. The temperature of the external coagulation liquid is preferably 30 ° C. or less, more preferably 20 ° C. or less, when both non-solvent phase separation and thermally induced phase separation are used immediately after ejection from the spinning nozzle. On the other hand, non-solvent phase separation can be adjusted to a temperature of 5 ° C. or higher and 80 ° C. or lower when used by being pulled out from the coating nozzle.

  Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to these examples. Here, the physical properties related to the present invention were measured by the following methods.

(1) Thickness of the outer layer When the cross section of the composite hollow fiber membrane was photographed at 1,000 times and 3,000 times using a scanning electron microscope, the thickness of the outer layer was arbitrarily selected at 10 locations. The number was measured and averaged.

(2) Thickness of the intermediate layer Using a scanning electron microscope, a cross section of the composite hollow fiber membrane was photographed at a magnification of 3,000 times, and the thickness of the intermediate layer was measured at 10 arbitrarily selected locations. Obtained on average.

(3) Support layer thickness Using a scanning electron microscope, when the cross section of the film was photographed at 100 times and 1,000 times, the thickness of the support layer was measured at 10 arbitrarily selected locations, Obtained by number average.

(4) Average pore diameter of outermost surface Using a scanning electron microscope, the surface of the composite hollow fiber membrane was photographed at 60,000 times, and the diameters of 20 arbitrarily selected pore diameters were measured, and the number average And asked.

(5) Average pore diameter of outer layer three-dimensional network structure Using a scanning electron microscope, the cross-section of the composite hollow fiber membrane was photographed at a magnification of 6,000, and an arbitrary range in which the outer layer three-dimensional network structure was observed The diameters of the 20 pore diameters selected in the above were measured and obtained by number averaging.

(6) Average pore diameter of intermediate layer Using a scanning electron microscope, a cross-section of the composite hollow fiber membrane was photographed at 60,000 times, and the diameters of 20 pore diameters arbitrarily selected in the intermediate layer were measured. The number average was obtained.

(7) Average diameter of the spherical structure of the support layer Using a scanning electron microscope, the cross-section of the composite hollow fiber membrane was photographed at a magnification of 10,000 times, and the diameters of 20 arbitrarily selected spherical structures were measured. Obtained by number average.

(8) Inner diameter / outer diameter of hollow fiber membrane Using a scanning electron microscope, the cross section of the composite hollow fiber membrane was photographed at 50 times and 100 times, the major axis and minor axis were measured, and the number average was obtained. .

(9) Air scrubbing durability evaluation A hollow fiber membrane module in which 1500 hollow fiber membranes were inserted into a module container (inner diameter 10 cm, length 100 cm) was produced. Next, the membrane module container was filled with a 5000 ppm kaolin aqueous solution, and 100 L / min of air was continuously supplied from the bottom of the container for 30 days for air scrubbing.

(10) Blocking performance The hollow fiber membrane after scrubbing durability evaluation is taken out from an arbitrarily selected location, and a small module having an effective length of 20 cm consisting of four hollow fiber membranes is produced, and the temperature is 25 ° C. and the filtration differential pressure is 16 kPa. Under conditions, raw water in which polystyrene latex particles having an average particle diameter of 0.309 μm are dispersed is subjected to external pressure total filtration for 30 minutes, and the concentration of latex particles in raw water and permeated water is measured for an ultraviolet absorption coefficient at a wavelength of 234 nm. The blocking performance was obtained from the ratio. A spectrophotometer (U-3200, manufactured by Hitachi, Ltd.) was used to measure the ultraviolet absorption coefficient at a wavelength of 234 nm.

(11) Water permeability performance A small module having an effective length of 20 cm consisting of four hollow fiber membranes was prepared, and distilled water was fed under conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and external pressure total filtration was performed for 30 minutes. The amount of permeated water (m ³ ) was determined. Next, it was calculated in terms of unit time (hr), unit membrane area (m ² ), and 50 kPa.

<Example 1>
Resin solution A was obtained by dissolving 38% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 417,000 in 62% by weight of γ-butyrolactone. In the resin solution B, an acrylonitrile homopolymer having an intrinsic viscosity of 3.1 (dl / g) was diluted with dimethyl sulfoxide to obtain a polymer concentration of 11% by weight. Resin solution C was 12% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 5% by weight of cellulose acetate (Eastman Chemical Co., CA435-75S, cellulose triacetate), N-methyl-2-pyrrolidone 83 It was obtained by dissolving% by weight.

The resin solution A was extruded from the inner layer slit of the triple tubular spinning nozzle, the resin solution B was extruded from the outer layer slit, and an 85% by weight γ-butyrolactone aqueous solution was extruded concentrically from the central pipe and solidified in an aqueous solution at a temperature of 10 ° C. Thereafter, a hollow fiber membrane was obtained through a 1.5-fold stretching step and a solvent removal step. Next, the resin solution C was uniformly coated on the hollow fiber membrane using a coating nozzle, and solidified in an aqueous solution at a temperature of 35 ° C., and a composite hollow fiber membrane was produced through a solvent removal step. The membrane wall structure of the obtained hollow fiber membrane has an average thickness of the support layer of 256 μm, an average thickness of the intermediate layer of 5.4 μm, an average thickness of the outer layer of 34 μm, and an average pore diameter of the outermost surface of 0.07 μm. The outer diameter was 1322 μm and the inner diameter was 740 μm. The average particle diameter of the spherical structure is 1.8 μm, the average pore diameter of the three-dimensional network structure is 1.6 μm, the average pore diameter of the intermediate layer is 0.04 μm, and the water permeability is 0.38 m ³ / m ² · hr. Met. Air scrubbing durability evaluation was performed with this composite hollow fiber membrane, and as a result of measuring the water permeability and blocking performance with the hollow fiber membrane after the evaluation, the water permeability was 0.28 m ³ / m ² · hr, and the blocking rate was 99%. High blocking performance. The evaluation results are summarized in Table 1.

<Example 2>
Using the same resin solution A, resin solution B, and resin solution C as in Example 1, the resin solution A from the inner layer slit of the triple tubular spinning nozzle, the resin solution C from the outer layer slit, and 85% by weight of γ-butyrolactone The aqueous solution was extruded concentrically from the center pipe and solidified in cold water having a temperature of 10 ° C., and then a composite hollow fiber membrane was produced through a 1.5-fold drawing process and a solvent removal process. Next, the resin solution B was uniformly coated on the composite hollow fiber membrane using a coating nozzle, and solidified in a 20% by weight dimethyl sulfoxide aqueous solution, and a composite hollow fiber membrane was produced through a desolvation step. The membrane wall structure of the obtained hollow fiber membrane has an average thickness of the support layer of 264 μm, an average thickness of the intermediate layer of 4.4 μm, an average thickness of the outer layer of 37 μm, and an average pore diameter of the outermost surface of 0.31 μm. The outer diameter was 1360 μm and the inner diameter was 749 μm. The average particle diameter of the spherical structure is 1.9 μm, the average pore diameter of the three-dimensional network structure is 0.3 μm, the average pore diameter of the intermediate layer is 0.09 μm, and the water permeability is 0.37 m ³ / m ² · hr. Met. Air scrubbing durability evaluation was performed with this composite hollow fiber membrane, and as a result of measuring the water permeability and blocking performance with the hollow fiber membrane after the evaluation, the water permeability was 0.27 m ³ / m ² · hr, the blocking rate was 99%, Met. The evaluation results are summarized in Table 1.

<Comparative Example 1>
Using the resin solution A and the resin solution C of Example 1, the resin solution A from the inner layer slit of the triple tubular spinning nozzle, the resin solution C from the outer layer slit, and the 85% by weight γ-butyrolactone aqueous solution together from the central pipe After extruding concentrically and solidifying in an aqueous solution having a temperature of 10 ° C., a composite hollow fiber membrane was produced through a 1.5-fold stretching step and a solvent removal step. The membrane structure of the obtained hollow fiber membrane was that the average thickness of the support layer was 260 μm, the average thickness of the outer layer was 42 μm, the average pore diameter of the outermost surface was 0.08 μm, the outer diameter was 1354 μm, and the inner diameter was 750 μm. . The average particle diameter of the spherical structure was 1.9 μm, and the average pore diameter of the three-dimensional network structure was 1.9 μm. The pure water permeation performance was 0.68 m ³ / m ² · hr. This composite hollow fiber membrane was evaluated for air scrubbing durability, and as a result of measuring the water permeability and blocking performance with the hollow fiber membrane after the evaluation, the water permeability was 0.48 m ³ / m ² · hr, and the blocking rate was 54%. there were. The evaluation results are summarized in Table 1.

<Comparative Example 2>
Using the resin solution A and the resin solution B of Example 1, the resin solution A was extruded from the outer slit of the double tubular spinning nozzle, and an 85% by weight γ-butyrolactone aqueous solution was extruded concentrically from the center pipe. After solidifying in an 85% by weight γ-butyrolactone aqueous solution at 0 ° C., a hollow fiber support membrane was produced through a solvent removal step and a 1.5-fold drawing step. Thereafter, the resin solution B was uniformly coated on the hollow fiber support membrane and coagulated in a 20% by weight dimethyl sulfoxide aqueous solution, and a composite hollow fiber membrane was produced through a solvent removal step. The hollow fiber membrane thus obtained had an average wall thickness of 264 μm, an average thickness of the outer layer of 41 μm, an outer diameter of 1370 μm, and an inner diameter of 760 μm. The average particle diameter of the spherical structure is 1.9 μm, the average pore diameter of the three-dimensional network structure is 0.3 μm, the average pore diameter of the outermost surface is 0.23 μm, and the water permeability is 0.48 m ³ / m ² · hr. Met. Air scrubbing durability was evaluated with this composite membrane, and after evaluation, the hollow fiber membrane was taken out from the container and measured for blocking performance and water permeability. As a result, the blocking rate was 78% and the water permeability 0.35 m ³ / m ^2. hr. The evaluation results are summarized in Table 1.

<Example 3>
Using the same resin solution A, resin solution B, and resin solution C as in Example 1, resin solution A from the inner layer slit of the quadruple tubular spinning nozzle, resin solution B from the intermediate slit, and resin solution C from the outer layer slit, A 85% by weight γ-butyrolactone aqueous solution is extruded concentrically from the center pipe, solidified in an aqueous solution at a temperature of 10 ° C, and then a composite hollow fiber membrane is produced through a solvent removal step and a 1.3 times stretching step. did. The membrane wall structure of the obtained hollow fiber membrane has an average thickness of 268 μm of the support layer, an average thickness of 4.4 μm of the intermediate layer, an average thickness of 40 μm of the outer layer, and an average pore diameter of the outermost surface of 0.02 μm. The outer diameter was 1379 μm and the inner diameter was 754 μm. The average particle diameter of the spherical structure is 1.8 μm, the average pore diameter of the three-dimensional network structure is 2.1 μm, the average pore diameter of the intermediate layer is 0.05 μm, and the water permeability is 0.54 m ³ / m ² · hr. Met. After evaluating the air scrubbing durability with this composite membrane and taking out the hollow fiber membrane from the container and measuring the blocking performance and water permeability, the blocking rate was 99% and the water permeability 0.41 m ³ / m ² · hr. Met. The evaluation results are summarized in Table 1.

  According to the present invention, since the separation function of the hollow fiber membrane is multi-layered, the deterioration of the separation function due to membrane rubbing in the conventional air scrubbing operation is suppressed, and the quality of the permeated water is stabilized. This makes it possible to use the membrane for a long time.

It is an electron micrograph (1000-times multiplication factor) which shows the cross section (part) of the one aspect | mode regarding the hollow fiber membrane of this invention. It is an electron micrograph (magnification 30000 times) of the outer surface of the hollow fiber membrane shown in FIG.

Claims (3)

A composite hollow fiber membrane formed by an outer layer having a three-dimensional network structure, a dense intermediate layer following the outer layer, and a support layer having a spherical structure that supports the intermediate layer. Using a triple tubular spinning nozzle, the resin solution A that forms a spherical structure from the inner layer slit, the resin solution B that forms the intermediate layer from the outer layer slit, and the inner coagulation liquid from the center pipe are extruded concentrically together to form an outer solidification. A step of cooling and solidifying in a liquid, a step of removing the solvent, and coating the obtained composite hollow fiber membrane material with a resin solution C that forms a three-dimensional network structure by using a coating nozzle, and performing non-solvent phase separation And a method for producing a composite hollow fiber membrane produced through a step of removing the solvent and a step of removing the solvent. Using a quadruple tubular spinning nozzle, center the resin solution A that forms a spherical structure from the inner slit, the resin solution B that forms the intermediate layer from the intermediate slit, and the resin solution C that forms the three-dimensional network structure from the outer slit. A method for producing a composite hollow fiber membrane produced by a process of extruding an inner coagulating liquid concentrically from a pipe, cooling it in an external coagulating liquid and coagulating it, and removing a solvent.