JP2008168224A - Hollow fiber porous membrane and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hollow fiber porous membrane small in contraction percentage of an inner diameter before and after making a membrane. <P>SOLUTION: In the hollow fiber porous membrane having a semipermeable membrane layer formed from a solution for making the membrane on the interlace outside surface, the contraction percentage of the inner diameter before and after making the membrane represented by the following equation: contraction percentage (%)=(d<SB>1</SB>-d<SB>2</SB>)/d<SB>1</SB>×100 [wherein d<SB>1</SB>is an inner diameter before making the membrane (before making the semipermeable membrane layer) and d<SB>2</SB>is an inner diameter after making the membrane (after making the semipermeable membrane layer)] is 25% or smaller. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a hollow fiber porous membrane that can be used for water treatment in various fields and a method for producing the same.

  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.

As a means for increasing the mechanical strength of the hollow fiber membrane, a method of forming a semipermeable membrane layer made of a membrane-forming solution on the surface of a braid serving as a substrate is known.
JP 2003-31133 A JP 2003-225542 A JP 53-104578 A

  In the case of a production method in which a semipermeable membrane layer is formed on the braid surface using a membrane forming solution, it is difficult to control the thickness of the semipermeable membrane layer, and in particular, the membrane forming solution penetrates into the braid and As a result, the water permeability of the resulting hollow fiber membrane is lowered.

  An object of the present invention is to provide a hollow fiber porous membrane capable of exhibiting high water permeability by suppressing the reduction of the inner diameter due to shrinkage before and after membrane formation, and a method for producing the same.

  The invention of claim 1 is a hollow fiber porous membrane having a semipermeable membrane layer formed from a membrane-forming solution on the braid outer surface as a means for solving the problem, and has an inner diameter before and after membrane formation represented by the following formula A hollow fiber porous membrane having a reduction ratio of 25% or less is provided.

Shrinkage rate (%) = (d ₁ −d ₂ ) / d ₁ × 100
d ₁ : Inner diameter before film formation (before forming the semipermeable membrane layer) d ₂ : Inner diameter after film formation (after forming the semipermeable membrane layer) The invention of claim 2 is another means for solving the problems. The hollow fiber porous membrane according to claim 1, wherein the shrinkage rate is 25% or less.

Invention of Claim 3 is a manufacturing method of the hollow fiber porous membrane of Claim 1 or 2 as a solution of other problems,
(I) Fiber density of braid 35-50 stitches / inch (II) Viscosity of film forming solution 10,000-100,000 mPas
(III) Provided is a method for producing a hollow fiber porous membrane, in which a braid is run in a membrane-forming solution, and the membrane is produced by adjusting any one or more conditions at a running speed of 1 to 20 m / min.

  The hollow fiber porous membrane of the present invention can exhibit high water permeability because the shrinkage of the membrane inner diameter before and after membrane formation is suppressed.

<Hollow fiber porous membrane>
In the hollow fiber porous membrane of the present invention, the reduction ratio of the inner diameter before and after film formation represented by the following formula is 25% or less, preferably 22% or less, more preferably 20% or less.

Shrinkage rate (%) = (d ₁ −d ₂ ) / d ₁ × 100
d ₁ : Inner diameter before film formation (before forming the semipermeable membrane layer) d ₂ : Inner diameter after film formation (after forming the semipermeable membrane layer) d ₁ is equal to the inner diameter of the braid.

  In the hollow fiber porous membrane of the present invention, the semipermeable membrane layer has a structure in which a part thereof penetrates into the braid, and may also be formed on the inner surface of the braid.

  The thickness of the semipermeable membrane layer (thickness based on the outer surface of the braid) is preferably 100 to 1000 μm, more preferably 200 to 800 μm, and still more preferably 300 to 600 μm.

  The hollow fiber porous 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, more preferably 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.

[Film forming solution]
As the film forming solution used in the present invention, known solutions can be used, but those containing (a) a polymer component, (b) a good solvent, (c) a poor solvent, and (d) other components are preferable.

  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.

  15-25 mass% is preferable, as for content of (a) component in a film forming solution, 16-24 mass% is more preferable, and 17-23 mass% is still more preferable.

  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 film forming solution, 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.

  1-40 mass% is preferable, as for content of (c) component in a film forming solution, 2-35 mass% is more preferable, and 3-30 mass% is still more preferable.

  Examples of the other component (d) include inorganic particles such as silica, titania, alumina, calcium chloride and the like.

  The average primary particle size (measurement method: dynamic light scattering method) of the inorganic fine particles of component (d) is preferably 1 to 50 nm, more preferably 5 to 40 nm, and even more preferably 10 to 30 nm.

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

  The film-forming solution 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 hollow fiber porous membrane>
Next, an embodiment of the production method of the present invention will be described. The production method of the present invention is produced by adjusting so as to satisfy one or more of the requirements (I) to (IV).

  First, as a first step, a process of attaching a film forming solution 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 film forming solution to the outer surface of a hollow fiber braid running inside the nozzle, a hollow fiber braid is immersed in a container containing the film forming solution. , A method of standing for a required time, a method of continuously burying a hollow fiber braid in a container containing a film-forming solution, and a braid in a state of being knitted in a braiding process of a hollow fiber braid (step of knitting a braid) A method of continuously spraying, spraying or applying the film forming solution on the surface can be applied.

  In the first step, adjustment is performed so as to satisfy one or more of requirements (I) to (III), but it is preferable to satisfy all of requirements (I) to (III).

(I) Fiber density of braid 35-50 stitches / inch (II) Viscosity of film forming solution 10,000-100,000 mPas
(III) Traveling speed when braid travels in film forming solution As per requirement (I), braid uses a fiber density of 35-50 stitches / inch, preferably 36- The one having 45 eyes / inch, more preferably 38 to 43 eyes / inch is used.

  As the requirement (II), the film forming solution has a viscosity adjusted to 10,000 to 100,000 mPas, preferably adjusted to 40,000 to 90,000 mPas, and more preferably adjusted to 50,000 to 80,000 mPas. In order to bring the viscosity of the film forming solution into the above range, the temperature is preferably adjusted to 100 ° C. or lower, more preferably 90 ° C. or lower, and further preferably 60 to 90 ° C.

  As the requirement (III), the traveling speed when the braid travels in the film forming solution is adjusted to 1 to 20 m / min, preferably 3 to 15 m / min, more preferably 6 to 12 m / min.

  The second step is a step of solidifying the film forming solution attached to the surface of the braid. 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. When the dry method is applied, one-stage treatment can be performed according to the concentration of the film forming solution and the type of solvent, or two or more stages 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) 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.

(2) 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
A film-forming solution comprising 22% by mass of cellulose acetate propionate (manufactured by Eastman Chemical), 71% by mass of dimethyl sulfoxide, 5% by mass of polyethylene glycol (# 6000), and 2% by mass of calcium chloride was used.

  The film-forming solution is heated to 80 ° C. and pumped to the coating container with a gear pump. 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 obtain a hollow fiber porous membrane. It was.

The obtained hollow fiber porous membrane has an inner diameter of 0.80 mm, an outer diameter of 2.0 mm, a pure water permeation rate under 0.1 MPa, 984 L / m ² / hr, and an air generation pressure of 0.3 MPa. Met.

Example 2
The same film-forming solution as in Example 1 was heated to 80 ° C. and pumped to the coating container with a gear pump. At the center of the coating container, a Tetron sleeve (inner diameter 1.0 mm, outer diameter 1.9 mm, thickness 0.45 mm) The braid, fiber density 43 mesh / 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. Thereafter, a hollow fiber porous membrane was obtained in the same manner as in Example 1.

The obtained hollow fiber porous membrane has an inner diameter of 0.82 mm and an outer diameter of 2.0 mm. The pure water permeation rate under 0.1 MPa is 800 L / m ² / hr, and the air generation pressure is 0.3 MPa. Met.

Comparative Example 1
A hollow fiber porous membrane was obtained in the same manner as in Example 1 except that the same membrane-forming solution as in Example 1 was heated to 90 ° C. The obtained hollow fiber porous membrane has an inner diameter of 0.69 mm, an outer diameter of 2.0 mm, a pure water permeation rate under 0.1 MPa of 36 L / m ² / hr, and an air generation pressure of 0.1 MPa. Met.

Example 3
A film forming solution consisting of 22% by mass of polyethersulfone (manufactured by Sumitomo Chemical), 51% by mass of N-methylpyrrolidone, 9% by mass of ethylene glycol, 15% by mass of polyvinylpyrrolidone, and 2% by mass of silica (90G manufactured by Nippon Aerosil) was used. .

  This film-forming solution is heated to 60 ° C. and is pumped to the coating container with a gear pump. No. 43 / 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. Thereafter, a hollow fiber porous membrane was obtained in the same manner as in Example 1.

The obtained hollow fiber porous membrane has an inner diameter of 0.85 mm, an outer diameter of 1.9 mm, a pure water permeation rate under 0.1 MPa of 1250 L / m ² / hr, and an air generation pressure of 0.3 MPa. Met.

Comparative Example 2
A hollow fiber porous membrane was obtained in the same manner as in Example 3, except that the same membrane-forming solution as in Example 3 was heated to 90 ° C., and the fiber density of the braid was 38 mesh / inch. The hollow fiber porous membrane thus obtained has an inner diameter of 0.70 mm and an outer diameter of 2.0 mm. The pure water permeation rate under 0.1 MPa is 553 L / m ² / hr, and the air generation pressure is 0.1 MPa. Met.

Sectional drawing of the hollow fiber porous membrane obtained in Example 2. FIG.

Claims (3)

A hollow fiber porous membrane having a semipermeable membrane layer formed from a membrane-forming solution on the braid outer surface, wherein the inner diameter reduction rate before and after membrane formation represented by the following formula is within 25% film.
Shrinkage rate (%) = (d ₁ −d ₂ ) / d ₁ × 100
d ₁ : Inner diameter before film formation (before forming the semipermeable membrane layer) d ₂ : Inner diameter after film formation (after forming the semipermeable membrane layer)   The hollow fiber porous membrane according to claim 1, wherein the shrinkage rate is 25% or less. A method for producing a hollow fiber porous membrane according to claim 1 or 2,
(I) Fiber density of braid 35-50 stitches / inch (II) Viscosity of film forming solution 10,000-100,000 mPas
(III) A method for producing a hollow fiber porous membrane, in which a braid is run in a membrane-forming solution, and the membrane is produced by adjusting any one or two conditions of a running speed of 1 to 20 m / min.