JP2008178868A - Fiber-reinforced type hollow fiber membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fiber-reinforced type hollow fiber membrane suppressed from the occurrence of pinholes in a semipermeable membrane layer. <P>SOLUTION: The fiber-reinforced type hollow fiber membrane on the surface of a braid and the semipermeable membrane layer is formed from a liquid film forming composition containing 15-25 mass% of a polymer component (a), 40-80 mass% of a good solvent (b), 1-40 mass% of a poor solvent (c) and 1-20 mass% of inorganic fine particles (d) selected from silica, titania and alumina. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fiber-reinforced hollow fiber membrane in which the generation of pinholes is suppressed and leakage during filtration is small.

  A hollow fiber porous membrane is generally produced by extruding a polymer solution, which is a spinning dope (liquid film-forming composition), from a double spinneret and then coagulating and drying. It is widely used in various fields such as industrial field and water treatment field.

  When the hollow fiber porous membrane is applied to the water treatment field having a relatively low turbidity, for example, a required number of hollow fiber porous membranes are accommodated in a case housing and used as a membrane module. However, when applied to the water treatment field with relatively high turbidity, it is used as a casing-free membrane module (a membrane module in which a hollow fiber membrane is exposed without using a casing).

  In the case of such a casing-free membrane module, one hollow fiber porous membrane is very thin and has a low mechanical strength. There is a problem that the processing capacity is reduced. Furthermore, since the mechanical strength is low, there is a problem that it is difficult to recover the processing capacity sufficiently because it is impossible to perform intense air bubbling cleaning or back pressure cleaning.

  Patent Document 1 discloses a separation membrane containing inorganic particles having an average particle diameter of 5 to 5000 nm and a bulk density of 0.05 to 0.5 ml / g. Application to a hollow fiber membrane which is a membrane and is more difficult to form is not disclosed.

Patent Document 2 discloses a photocatalyst of stabilized anatase-type titanium oxide particles in which the surface of fine anatase-type titanium oxide particles having a particle size of about 30 to 40 nm that promotes decomposition of organic substances by light irradiation is coated with porous calcium phosphate. A hollow fiber separation membrane holding a substance is disclosed. However, this separation membrane may lose anatase-type titanium oxide particles during use.
JP 2005-270707 A JP 2000-42382 A

  In the production of hollow fiber membranes, particularly when a thin film made of a polymer porous material is formed on a base membrane, pinholes frequently occur in the formed semipermeable membrane layer, and leakage occurs during filtration (not sufficiently filtered). The phenomenon that the liquid to be treated passes) may occur.

  An object of the present invention is to provide a fiber-reinforced hollow fiber membrane that can suppress the occurrence of pinholes in the semipermeable membrane layer and can suppress the occurrence of leakage during filtration operation.

  The invention of claim 1 has a semipermeable membrane layer on the braid outer surface, and the semipermeable membrane layer is formed from a liquid film-forming composition containing the following components (a) to (d). A fiber-reinforced hollow fiber membrane is provided.

(A) Polymer component 15-25 mass%
(B) Good solvent 40-80 mass%
(C) 1-40 mass% of poor solvents
(D) 1 to 20% by mass of inorganic fine particles selected from silica, titania and alumina
The invention according to claim 2 is the fiber-reinforced hollow fiber membrane according to claim 1, wherein the inorganic fine particles of component (d) have an average primary particle diameter of 1 to 50 nm and an apparent specific gravity of 10 to 200 g / L. provide.

  The invention of claim 3 provides the fiber-reinforced hollow fiber membrane according to claim 1 or 2, wherein the good solvent of component (b) is selected from N-methylpyrrolidone, dimethylsulfoxide, dimethylformamide, and dimethylacetamide. To do.

  The invention according to claim 4 is the fiber-reinforced hollow fiber membrane according to any one of claims 1 to 3, wherein the poor solvent of component (c) is selected from glycols, diols, glycerin and polyvinylpyrrolidone. provide.

  The invention of claim 5 is a fiber-reinforced hollow fiber according to any one of claims 1 to 4, wherein the braid has an inner diameter of 0.2 to 3.0 mm and an outer diameter of 0.5 to 5.0 mm. Providing a membrane.

  In the fiber reinforced hollow fiber membrane of the present invention, the occurrence of pinholes in the semipermeable membrane layer is suppressed, and even when the filtration operation is carried out by the filtration membrane module using the fiber reinforced hollow fiber membrane of the present invention Occurrence is suppressed.

<Fiber-reinforced hollow fiber membrane>
The fiber-reinforced hollow fiber membrane of the present invention has a semipermeable membrane layer formed of a specific liquid film-forming composition on the outer surface of a braid serving as a base material. The semipermeable membrane layer may have a structure in which a part thereof penetrates into the braid, but is not formed on the inner surface of the braid.

  The thickness of the semipermeable membrane layer is preferably 50 to 500 μm, more preferably 100 to 400 μm, and still more preferably 150 to 300 μm.

  The fiber-reinforced hollow fiber membrane of the present invention preferably has an outer diameter of 1.5 to 3.0 mm, more preferably 1.8 to 2.5 mm, and an inner diameter of preferably 0.5 to 1.5 mm. Is 0.7 to 1.3 mm.

〔braid〕
Braid is made of fluororesin, polyester, polyamide, polyurethane, acrylic resin, methacrylic resin, polyethylene, polypropylene, polystyrene, vinyl chloride, cellulose, cellulose acetate and other natural or synthetic resin fibers, stainless steel, brass, copper and other metal fibers, glass What consists of a fiber, carbon fiber, etc. can be used.

  The inner diameter and outer diameter of the braid are not particularly limited, but from the viewpoint of ease of handling and manufacturing technology, the inner diameter is preferably 0.2 to 3.0 mm, more preferably 0.5 to 2.0 mm. The outer diameter is preferably 0.5 to 5.0 mm, more preferably 1.0 to 3.0 mm.

[Liquid film-forming composition]
The polymer component of component (a) may be a hydrophobic polymer or a hydrophilic polymer. Examples of the hydrophilic polymer include cellulose materials such as cellulose acetate, cellulose propionate, cellulose butyrate, regenerated cellulose, and a mixture thereof. Moreover, polyvinyl alcohol etc. can also be used. Examples of the hydrophobic polymer include polysulfone resins, polyethersulfone resins, polyvinylidene fluoride resins, polyacrylonitrile resins, polyimide resins, polyaramid resins, polypropylene resins, and polyethylene resins.

  The content of the component (a) in the composition is preferably 15 to 25% by mass, more preferably 16 to 24% by mass, and still more preferably 17 to 23% by mass.

  Examples of the good solvent for component (b) include those selected from N-methylpyrrolidone, dimethyl sulfoxide, dimethylformamide, and dimethylacetamide.

  40-80 mass% is preferable, as for content of (b) component in a composition, 45-75 mass% is more preferable, and 50-70 mass% is still more preferable.

  The poor solvent of component (c) is selected from glycols, diols, glycerin and polyvinylpyrrolidone, and glycols such as polyethylene glycol, tetraethylene glycol, propylene glycol and ethylene glycol, pentanediol, hexanediol and heptane. Examples include diols such as diol, glycerin, polyvinylpyrrolidone, and the like. Among these, glycols are preferable, and polyethylene glycol and ethylene glycol are more preferable. Further, polyethylene glycol or a combination of ethylene glycol and polyvinyl pyrrolidone is preferable.

  The content of the component (c) in the composition is preferably 1 to 40% by mass, more preferably 2 to 35% by mass, and still more preferably 3 to 30% by mass.

  The inorganic fine particles of component (d) are selected from silica, titania and alumina.

  The average primary particle size of the inorganic fine particles of component (d) is preferably 1 to 50 nm, more preferably 5 to 40 nm, and still more preferably 10 to 30 nm. When the average primary particle size is in the above range, the dispersibility in the liquid film-forming composition is good, and precipitation and non-uniformity do not occur.

  The apparent specific gravity of the inorganic fine particles as component (d) is preferably 10 to 200 g / L, more preferably 20 to 170 g / L, still more preferably 30 to 150 g / L. When the apparent specific gravity is within the above range, the dispersibility in the liquid film-forming composition is good and does not rise during handling.

  1-20 mass% is preferable, as for content of (d) component in a composition, 1-15 mass% is more preferable, and 1-10 mass% is still more preferable.

  The liquid film-forming composition used in the present invention can contain known film-forming components other than the components (a) to (d) within the range in which the problems of the present invention can be solved.

<Method for producing fiber-reinforced hollow fiber membrane>
An embodiment of a method for producing a fiber-reinforced hollow fiber membrane of the present invention will be described. First, as a first step, a process of attaching a liquid film-forming composition to the surface of a hollow fiber braid is performed.

  As a process of the first step, using a nozzle, a method of applying a liquid film-forming composition to the outer surface of a hollow fiber-shaped braid that runs in the nozzle, a hollow fiber-shaped braid is placed in a container containing the liquid film-forming composition. In a method of immersing and allowing to stand for a required time, a method of continuously hollowing a hollow fiber-like braid in a container containing a liquid film-forming composition, For example, a method of continuously spraying, spraying, or applying the liquid film-forming composition to the braid surface in a state of being applied can be applied.

  The processing time of the first step is adjusted so that a semipermeable membrane layer having a desired thickness is formed according to the type and concentration of the liquid membrane-forming composition, the braid density, the water permeability of the hollow fiber porous membrane, and the like. To do.

  Specifically, when the same braid and the same liquid film-forming composition as those described in each example are used, the concentration of the liquid film-forming composition is based on the thickness of the semipermeable membrane layer in each example. The thickness of the semipermeable membrane layer can be increased / decreased by increasing / decreasing or increasing / decreasing the immersion time in the liquid film-forming composition.

  The second step is a step of solidifying the liquid film-forming composition attached to the braid surface. For the treatment in this step, a wet method, a dry method, or the like can be applied, but a wet method or a semi-dry wet method that can be molded instantaneously is preferable.

  When the wet method is applied, a method of drying after braiding the braid in a coagulation bath such as water can be applied. In the case of applying the dry method, depending on the concentration of the liquid film-forming composition and the type of the solvent, it can be processed in one step, or two or more steps can be performed by changing the temperature and humidity conditions. The treatment temperature and humidity are 30 to 200 ° C., preferably 60 to 150 ° C., 30 to 95% relative humidity, preferably 60 to 90%, and the treatment time is 0.5 to 60 minutes, preferably 2 to 30. For minutes.

  The fiber reinforced hollow fiber membrane of the present invention can be applied to various water treatments as an internal pressure type or external pressure type hollow fiber membrane (hollow fiber membrane module).

(1) Average primary particle diameter It measured by the dynamic light scattering method.

(2) Apparent specific gravity An inorganic fine particle was filled only in gravity into a graduated cylinder having a known volume, the mass was measured, and the mass was divided by the volume.

(3) Pure water permeation rate One end of a hollow fiber membrane having a length of 1 m is sealed, pure water is dead-end filtered by applying a pressure of P1 (= 0.1 MPa) to the inside of one end of the hollow fiber membrane, filtration time, The amount of pure water permeating and the pressure P2 at the other end were measured. The transmembrane pressure was calculated by (P1 + P2) / 2, and the amount of pure water permeating per unit pressure (= 0.1 MPa), unit time, and unit membrane area (external surface area conversion) was calculated.

(4) Air generation pressure Air was gradually applied to the inside of both ends of the hollow fiber membrane (length 1 m) immersed in water, and the pressure at which air was first generated from the outer surface of the hollow fiber membrane was measured. This pressure is generally defined as a bubble point and is used to calculate the membrane pore diameter, but is smaller than the bubble point in a membrane having a pinhole. The bubble point can be easily calculated using the membrane pore diameter, the contact angle between the membrane and water, and the surface tension of water.

Example 1
Polyethersulfone (manufactured by Sumitomo Chemical) 18% by mass, 53% by mass of dimethylacetamide, 21% by mass of polyethylene glycol (# 200), silica-1 (Nippon Aerosil 90G; average primary particle size 20 nm, apparent specific gravity 50 g / L) 8 A film-forming solution (liquid film-forming composition) consisting of mass% was used. This film-forming solution is heated to 80 ° C. and pumped to the coating container with a gear pump. At the center of the coating container, a Tetron sleeve (braid, fiber density with an inner diameter of 1.0 mm, an outer diameter of 1.9 mm, and a thickness of 0.45 mm). The film forming solution was applied from the outer surface side of the Tetron sleeve.

  The applied tetron sleeve passes through the slit during running, and after removing excess coating solution / roundness and adjusting the knitting thickness, it is solidified / washed in water at 30 ° C. to form a fiber-reinforced hollow fiber membrane. Obtained.

Comparative Example 1
A film-forming solution (liquid film-forming composition) comprising 18% by mass of polyethersulfone (manufactured by Sumitomo Chemical), 37% by mass of dimethyl sulfoxide, and 45% by mass of polyethylene glycol (# 200) was used. Using this membrane-forming solution, a hollow fiber membrane was obtained in the same manner as in Example 1.

Example 2
Cellulose acetate propionate (manufactured by Eastman Chemical) 20% by mass, 71% by mass of dimethyl sulfoxide, 5% by mass of polyethylene glycol (# 6000), 2% by mass of calcium chloride, silica-2 (R972 manufactured by Nippon Aerosil); average primary particle size 16 nm A film-forming solution (liquid film-forming composition) composed of 2% by mass with an apparent specific gravity of 50 g / L was used. Using this membrane-forming solution, a fiber-reinforced hollow fiber membrane was obtained in the same manner as in Example 1.

Comparative Example 2
A film-forming solution (liquid film-forming composition) comprising 21% by mass of cellulose acetate propionate (manufactured by Eastman Chemical), 72% by mass of dimethyl sulfoxide, 5% by mass of polyethylene glycol (# 6000), and 2% by mass of calcium chloride was used. . Using this membrane-forming solution, a hollow fiber membrane was obtained in the same manner as in Example 2.

Example 3
A film-forming solution consisting of 22% by mass of polyethersulfone (manufactured by Sumitomo Chemical), 51% by mass of N-methylpyrrolidone, 10% by mass of ethylene glycol, 15% by mass of polyvinylpyrrolidone, and 2% by mass of silica-1 (Nippon Aerosil 90G) ( Liquid film-forming composition) was used. This film-forming solution is heated to 60 ° C. and pumped to the coating container with a gear pump. At the center of the coating container, a Tetron sleeve (braid, fiber density with an inner diameter of 1.0 mm, an outer diameter of 1.9 mm, and a thickness of 0.45 mm). No. 38 / inch) was run at a speed of 9 m / min, and the film forming solution was applied from the outer surface side of the Tetron sleeve.

  The applied Tetron sleeve passes through the slit during running, and after removing excess coating solution / roundness and adjusting the knitting thickness, it is solidified / washed in water at 60 ° C. to form a fiber-reinforced hollow fiber membrane. Obtained.

Example 4
Polyethersulfone (manufactured by Sumitomo Chemical) 22% by mass, N-methylpyrrolidone 51% by mass, ethylene glycol 10% by mass, polyvinylpyrrolidone 15% by mass, titania (Nippon Aerosil P-25; average primary particle size 21 nm, apparent specific gravity 130 g) / L) A film-forming solution (liquid film-forming composition) composed of 2% by mass was used. Using this membrane-forming solution, a fiber-reinforced hollow fiber membrane was obtained in the same manner as in Example 3.

  For the hollow fiber membranes obtained in Examples 1 to 4 and Comparative Examples 1 and 2, the pure water permeation rate (value under 0.1 MPa) and the air generation pressure were measured. The results are shown in Table 1.

Claims (5)

A fiber-reinforced hollow fiber membrane having a semipermeable membrane layer on the braid outer surface, wherein the semipermeable membrane layer is formed from a liquid membrane-forming composition containing the following components (a) to (d).
(A) Polymer component 15-25 mass%
(B) Good solvent 40-80 mass%
(C) 1-40 mass% of poor solvents
(D) 1 to 20% by mass of inorganic fine particles selected from silica, titania and alumina   The fiber-reinforced hollow fiber membrane according to claim 1, wherein the inorganic fine particles of component (d) have an average primary particle diameter of 1 to 50 nm and an apparent specific gravity of 10 to 200 g / L.   The fiber-reinforced hollow fiber membrane according to claim 1 or 2, wherein the good solvent of component (b) is selected from N-methylpyrrolidone, dimethyl sulfoxide, dimethylformamide, and dimethylacetamide.   The fiber-reinforced hollow fiber membrane according to any one of claims 1 to 3, wherein the poor solvent of component (c) is selected from glycols, diols, glycerin and polyvinylpyrrolidone.   The fiber reinforced hollow fiber membrane according to any one of claims 1 to 4, wherein the braid has an inner diameter of 0.2 to 3.0 mm and an outer diameter of 0.5 to 5.0 mm.