JP2000218141A - Hollow fiber membrane and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a hollow fiber membrane excellent in permeability, pressure resistance, and strength and high in reliability concerning turbidity removal and bacteria removing performance by specifying the bubbling point, thickness, inside diameter, pressure resistance, and permeation coefficient of the hollow fiber membrane. SOLUTION: In a hollow fiber membrane, a bubbling point BP is made at least 250 kPa. The bubbling point means a pressure when gas is introduced from one end of the membrane with the other end closed, and the bubbles of the gas begins to appear and is an index indicating the presence/absence of minute defects. The thickness of the membrane is made 40-120 μm, the inside diameter is made 250-420 μm, the pressure resistance is made at least 400 kPa, and the permeation coefficient is made at least 4.2 m3/(m2.h.MPa). The tensile strength and the elongation are preferably at least 6 MN/m2 and at least 50% respectively. An acrylonitrile copolymer which contains 95 mole % of acrylonitrile and has limiting viscosity number of at least 0.25 m3/kg (2.5 dl/g) is preferably incorporated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hollow fiber membrane which can be suitably used for turbidity of river water and groundwater and clarification of industrial water.

[0002]

2. Description of the Related Art A membrane separation method using a reverse osmosis membrane, an ultrafiltration membrane, a microfiltration membrane, or the like is a technique used in various fields because it has features such as energy saving and space saving. For example, the ultrafiltration method is used for the purpose of producing ultrapure water and clarifying fruit juice, and a separation membrane in the form of a flat membrane or a hollow fiber membrane is used.

[0003] In recent years, hollow fiber membranes can be used for microfiltration or ultrafiltration because they can increase the membrane area per unit volume and can easily seal the processing solution and the stock solution. There is an active movement to apply the separation membrane to fields such as clarification of river water and groundwater, clarification of industrial water, and advanced treatment of wastewater. For example, a system that performs total filtration using an external pressure type module that supplies an undiluted solution from the outside of the hollow fiber membrane requires less energy for operation, and suppresses contamination of raw water treated water when the hollow fiber membrane breaks. Furthermore, since the suspended matter deposited on the surface of the hollow fiber membrane can be easily removed by physical swinging (for example, air scrubbing) of the hollow fiber membrane, the hollow fiber membrane is adopted in the above field.

[0004] However, the hollow fiber membrane is not initially supposed to be applied to the above-mentioned water purification treatment field on the assumption of long-term operation. There is room for significant improvement in properties such as easy-to-clean, durability, chemical resistance, and reliability against turbidity and sterilization performance. So, for example, about improvement of water permeability,
A hollow fiber membrane having a porous layer in which the average pore diameter is inclined in the radial direction and a reticulated porous layer including cavities (Japanese Patent Publication No.
No. 2-15072) has been proposed and has a certain effect, but the strength and elongation are not disclosed, and the durability against physical cleaning such as air scrubbing is insufficient. there were. In general, it is known that, in order to increase water permeability in the case of having a uniform membrane structure, it is preferable to reduce the film thickness (for example, Japanese Patent Publication No. 6-53976). In the above, there is a problem that the membrane is deformed or crushed by the filtration pressure difference between the raw water side and the treated water side, so that the flow resistance is increased and the quality of the treated water is rapidly lowered.
Furthermore, such transformations are often irreversible,
Regeneration of the film has been difficult.

[0005]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a hollow fiber membrane which is excellent in water permeability, pressure resistance and strength, and has high turbidity and sterilization performance, and its production. It is to provide a method.

[0006]

The present invention for achieving the above-mentioned invention is characterized by a hollow fiber membrane satisfying the following conditions (A) to (E). (A) The bubble point is at least 250 kPa (B) The film thickness is in the range of 40 to 120 μm (C) The inner diameter is in the range of 250 to 420 μm (D) The withstand pressure is at least 400 kPa (E) The transmission coefficient of pure water is at least 4.2 m ³ / (M ²
H · MPa) Here, when the tensile strength of the hollow fiber membrane is 6 MN / m ² or more,
It is also preferable that the elongation is 50% or more.

[0007] At least 95% of acrylonitrile
mol%, and the intrinsic viscosity is 0.25m ³ / kg
A hollow fiber membrane containing the acrylonitrile-based polymer described above is also preferable.

Furthermore, the present invention provides a composite spinneret comprising a sheath comprising a solution containing at least 95 mol% of acrylonitrile and an acrylonitrile polymer having an intrinsic viscosity of 0.25 m ³ / kg or more and water. The method is characterized by a method for producing a hollow fiber membrane in which a component and a core component are dry-wet spun and then stretched at a magnification of 1.1 to 3 times.

Here, water is used as the sheath component in an amount of 0.5 to 0.5.
It is also preferable to use a solution containing dimethylsulfoxide containing 6% by weight as a solvent.

It is also preferable to use dimethyl sulfoxide containing water in the range of 5 to 25% by weight as the core component.

Furthermore, a hollow fiber membrane element for water purification using the hollow fiber membrane of the present invention is also preferable.

Further, a water purifier using the above-mentioned hollow fiber membrane element for water purification is also preferable.

[0013]

1 to 3 are scanning micrographs of a hollow fiber membrane obtained according to the present invention. FIG. 1 is a photograph (1,000-fold magnification) showing a cross section of the hollow fiber membrane of the present invention, and it can be seen that macrovoids (giant vacancies) having a pore diameter of 10 μm or more are not substantially contained. FIG. 2 is a photograph (magnification: 10,000 times) showing the outer surface. It can be seen that the outer surface of the hollow fiber membrane of the present invention has a dense structure. FIG. 3 is a photograph (magnification: 10,000) of the inner surface of the hollow fiber membrane of the present invention. The inner surface has a net-like structure as shown in the photograph, with a diameter of 0.1.
Voids are formed so that solids of about 5.0 μm can pass through.

The hollow fiber membrane according to the present invention has a bubble point (BP) of at least 250 kPa. Here, the bubble point refers to the pressure at which gas is introduced from the other end into the hollow fiber membrane whose one end is sealed and bubbles of the gas start appearing from the surface of the hollow fiber membrane. It is an index that indicates the presence or absence of That is, if there is a defect such as a void penetrating the film, gas tends to leak from that portion, and the bubble point value decreases.

[0015] In the present invention, the length 5 with one end sealed.
A hollow fiber membrane of 00 mm is immersed in water at a temperature of 25 ° C.
a / sec, and the applied pressure (kPa) at which separation of air bubbles from the outer surface of the hollow fiber membrane began to be observed was changed to 10
Times, and the lowest pressure value (kPa) is defined as a bubble point.

Normally, when a technique for generating voids in a film and improving water permeability is used, the above bubble point value is reduced due to the presence of voids penetrating the film. In the present invention, since the film has substantially no voids (macrovoids) having a pore diameter of 10 μm or more and has a dense structure near the outer surface, a high bubble point value is achieved. When macrovoids are present, the eccentricity of the hollow fiber membrane increases, and the performance is likely to decrease due to the decrease in pressure resistance and strength.
Here, the macro void refers to a space in which microspheres having a diameter of 10 μm can enter.

The hollow fiber membrane of the present invention has a thickness in the range of 40 to 120 μm, more preferably 50 to 110 μm.
μm, the inner diameter is in the range of 250 to 420 μm, the withstand voltage is 400 kPa or more, and the transmission coefficient is at least 4.2 m ³ / (m ² · h · MPa).

With respect to the above pressure resistance, a metal tube miniature module having an inner diameter of 10 mm made of a single hollow fiber membrane having a length of 200 mm is prepared, and after performing external pressure total filtration of raw water at a predetermined filtration pressure difference for 5 minutes. With respect to the hollow fiber membrane, the minor axis (a ₀ ) and major axis (b ₀ ) of the outer diameter are measured at intervals of 20 mm, and the roundness is calculated by the following formula (A) for each, and the average is roundedness ₁ It means the highest filtration differential pressure that can maintain an average of roundness ₁ of 60% when this is repeated 20 times.

Roundness (%) = {small diameter of outer diameter (a ₀ ) / long diameter of outer diameter (b ₀ )} × 100 (A) The transmission coefficient is 20 hollow fiber membranes having a length of 200 mm. A miniature module of a glass tube made of is made and subjected to an external pressure total filtration of pure water substantially free of solids such as fine particles at a temperature of 25 ° C. and a filtration pressure difference of 0.05 MPa, and the amount of permeated water ( m ³ ) in terms of a value per unit time (h) and effective membrane surface area (m ² ). The unit is m ³ / (m ² · h · MPa).

The hollow fiber membrane of the present invention has a tensile strength of 6 MN.
/ M ² or more and the elongation are preferably 50% or more. When the tensile strength and the elongation are in this range, the handling property when handling the hollow fiber membrane is good, and the membrane is less likely to be broken or crushed during filtration.

Here, the tensile strength and elongation are 5
A 0 mm sample was pulled at a tensile speed of 5 using a tensile tester.
The measurement is performed 30 times while changing the sample at 0 mm / min, and the average is taken as the measured value.

Further, the hollow fiber membrane of the present invention preferably contains at least 95 mol% of acrylonitrile and has an intrinsic viscosity of 0.25 m ³ / kg (2.5 dl / g) or more. Here, the acrylonitrile polymer is preferably a homopolymer of acrylonitrile, but 5 mol% or less, preferably 3 mol%.
In the following, a copolymer component may be contained. The copolymer component is preferably a vinyl compound, and examples thereof include acrylic acid, methyl acrylate, methyl methacrylate, vinyl acetate, sodium acrylate, and sodium p-styrenesulfonate as copolymer monomers.

The intrinsic viscosity of the acrylonitrile polymer is
It is preferably at least 0.25 m ³ / kg (2.5 dl / g), more preferably 0.27 to 0.36 m ³ / kg
(2.7 to 3.6 dl / g), more preferably 0.28 to 0.34 m ³ / kg (2.8 to 3.4 dl / g).
g). Intrinsic viscosity 0.25m ³ / kg
If it is less than (2.5 dl / g), macrovoids having a pore diameter of 10 μm or more are likely to be generated in the process of forming the hollow fiber membrane, resulting in a coarse structure, which tends to reduce bubble points, strength and elongation. In addition, the intrinsic viscosity is 0.34 m ³ / kg (3.
If it exceeds 4 dl / g), the formation of the hollow fiber membrane itself tends to be difficult.

The above intrinsic viscosity is a value measured by a dilution method using a Ubbelohde viscometer at a measurement temperature of 35 ° C. (dimethylformamide (DMF) is used as a solvent).

Next, a method for producing a hollow fiber membrane according to the present invention will be described.

The hollow fiber membrane is dried and wet-spun by, for example, simultaneously discharging a sheath component comprising a solution containing a substance constituting the membrane and a core component by using a composite spinneret having a double tube structure, and spinning. Obtained by stretching.

First, the acrylonitrile polymer described above is preferably added to the solution as the sheath component, preferably in an amount of 10 to 15% by weight.
, More preferably in the range of 11 to 14% by weight, even more preferably in the range of 12 to 14% by weight. If the polymer concentration is less than 10% by weight, macrovoids are likely to be generated in the film structure, and the strength and elongation tend to decrease. On the other hand, when the content exceeds 15% by weight, the membrane structure becomes dense and water permeability tends to decrease.

As the solvent used for the above solution, for example, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMA
C), ethylene carbonate and γ-butyl lactone. These solvents contain water in order to promptly perform coagulation and precipitation during spinning. In addition, it is preferable to include an alcohol in addition to water since spinnability is improved. Water and alcohols may contain inorganic salts. In addition, in the case of the combination with the above-mentioned solvent, the use of dimethyl sulfoxide and water is preferable because the coagulation and precipitation during spinning is performed more quickly. In this case, the content of water is preferably in the range of 0.5 to 6% by weight, and more preferably in the range of 1 to 5% by weight.

When spinning, the temperature of the sheath component is 45.
The range is preferably from 95 to 95 ° C, more preferably from 50 to 9 ° C.
It is in the range of 0 ° C. If the temperature is lower than 45 ° C., gelation of the polymer occurs, and the polymer tends to be unsuitable for spinning, and thixotropy remarkably appears, and the thickness unevenness tends to increase in the axial direction of the hollow fiber membrane. On the other hand, when the temperature exceeds 95 ° C., poor spinnability such as thread breakage tends to occur.

As the core component, a mixture of the solvent used for the solution of the sheath component and water, alcohols, aliphatic ketones, glycerin, polyethylene glycol, or the like is preferably used. Among them, it is preferable to use water which has a relatively large coagulation force and is easy to handle. The solvent concentration is preferably in the range of 70 to 95% by weight, more preferably in the range of 75 to 90% by weight, and still more preferably 78 to 95% by weight.
It is in the range of 86% by weight. When the concentration is lower than 70% by weight or higher than 95% by weight, the injection liquid drips from the mouthpiece, the thread breaks, or the like, and the spinnability tends to be greatly affected.

For the discharge, the solution as the above-mentioned sheath component is discharged at a discharge temperature of preferably 45 to 95 ° C., more preferably 50 to 95 ° C.
It is performed so as to be in a range of up to 90 ° C. Then the dry length is 2
It is passed through a gaseous phase of 、 20 cm, preferably 3-15 cm, leading to a coagulation bath. The gas phase has an ambient temperature of 20 to 5
When the temperature is in the range of 5 ° C. and the absolute humidity is in the range of 2 to 120 kPa, the vicinity of the outer surface of the film has a uniform dense structure, which is preferable.

The temperature of the coagulation bath is preferably in the range of 60 to 85 ° C., more preferably in the range of 65 to 80 ° C., in order to control the diffusion rate of the sheath component. When the coagulation bath temperature is lower than 60 ° C., macrovoids tend to be generated and the hollow fiber tends to be eccentric.
If the temperature exceeds 5 ° C., the take-up roll may be loosened and the running property of the hollow fiber may be reduced. For the coagulation bath, for example, a mixed solution similar to the above-mentioned core component can be used, and a hollow fiber membrane that does not form macrovoids can be obtained by appropriately adjusting the mixing ratio thereof. it can.

Next, the hollow fiber membrane is pulled out of the coagulation bath and stretched at a stretching ratio of 1.1 to 3 times. The stretching temperature at this time is preferably in the range of 60 to 95 ° C. For the stretching method, various methods can be adopted, for example, a method of performing wet heat stretching by using a stretching bath in the above temperature range and changing the rotation ratio between rollers provided before and after the stretching bath. it can. In particular, the stretching bath is 70 ~
When the stretching temperature is in the range of 95 ° C. and the stretching ratio is in the range of 1.1 to 2 times, a high-quality hollow fiber membrane with less crushing, eccentricity and unevenness in the axial direction can be obtained, which is preferable.

The hollow fiber membrane of the present invention is usually used as an element with a housing disposed around it. Particularly, an external pressure type in which raw water is introduced from the outer surface side of the membrane and treated water is obtained from the inner surface side. Can be suitably used as a hollow fiber membrane element for water purification.

The above-described hollow fiber membrane element for water purification can be suitably used as a water purifier in combination with a raw water supply device such as a flow path switching device or a pump.

[0036]

EXAMPLES (Example 1) The limiting viscosity number is 0.31 m ³ / k
g (3.1 dl / g) of an acrylonitrile homopolymer was prepared in a dimethyl sulfoxide solvent containing 2.6% by weight of water at a dissolution temperature of 80 ° C., and the polymer concentration was 13.0% by weight. I got The solution is discharged at a temperature of 85 ° C. and a discharge amount of 7.3 g from a composite spinneret (circular orifice outer diameter 1.2 mm, slit interval 0.3 mm, center pipe inner diameter 0.35 mm) provided at a position where the dry length is 5 cm. /
And discharge dimethyl sulfoxide from the center pipe in 8 minutes.
After discharging an aqueous solution containing 2% by weight as a core component at a discharge rate of 2.1 g / min and spinning into a coagulation bath, the hollow fibers drawn from the coagulation bath are washed with a first washing bath, a stretching roll bath, and a second washing bath. The treatment was performed in the order of the tank and the third washing tank, and the wound fiber was wound on a winder to obtain a hollow fiber membrane. The coagulation bath used was an 18% by weight aqueous solution of dimethyl sulfoxide at a temperature of 70 ° C. The stretching bath was at a bath temperature of 75 ° C and the stretching ratio was 1.3 times.
0 ° C.

The obtained hollow fiber membrane has the structure shown in FIGS. 1 to 3 and has a dense structure near the outer surface. The average outer diameter is 498 μm, the average thickness is 82 μm, and the inner surface is The gap in the vicinity was 1.0 to 3.5 μm. Table 1 shows the measurement results. (Example 2) The limiting viscosity number was 0.31 m ^{3 /} kg (3.1
dl / g) of an acrylonitrile homopolymer in a dimethyl sulfoxide solvent containing 3.8% by weight of water at a melting temperature of 80%.
C. to give a spinning solution having a polymer concentration of 12.0% by weight. This solution was discharged at a discharge temperature of 75 ° C. and a discharge rate of 7.2 g / min from an annular die (same die as in Example 1) provided at a position where the dry length was 10 cm, and the same as in Example 1 from the central pipe. After the coagulating solution was discharged to spin out the coagulating bath, a hollow fiber membrane was obtained through the same spinning process as in Example 1.
The coagulation bath was dimethyl sulfoxide 1 at a temperature of 70 ° C.
An 8.5 wt% aqueous solution was used, the stretching bath was at a bath temperature of 75 ° C., the stretching ratio was 1.4 times, and the temperature of each washing bath was 60 ° C.

The obtained hollow fiber membrane has a dense structure near the outer surface, the average outer diameter is 482 μm, the average thickness is 77 μm, and the void near the inner surface is the same as in Example 1. It was 1.0 to 4.0 μm. Table 1 shows the measurement results.
Shown in (Example 3) A hollow fiber membrane was obtained by spinning in the same manner as in Example 1 except that the discharge temperature of the sheath component solution was 40 ° C. Table 1 shows the measurement results. (Example 4) A hollow fiber membrane was obtained by spinning in the same manner as in Example 1 except that the temperature of the coagulation bath was set to 40 ° C. Table 1 shows the measurement results. (Example 5) A hollow fiber membrane was obtained by spinning in the same manner as in Example 1 except that the polymer concentration of the sheath component solution was 9.0% by weight. Table 1 shows the measurement results.

[0039]

Comparative Example (Comparative Example 1) A hollow fiber membrane was obtained by spinning in the same manner as in Example 1 except that no stretching roll bath was used and stretching was not performed. Table 1 shows the measurement results. (Comparative Example 2) A hollow fiber membrane was obtained by spinning in the same manner as in Example 2 except that the solvent of the sheath component solution was dimethyl sulfoxide alone. Table 1 shows the measurement results. (Comparative Example 3) 93.9 mol% of acrylonitrile, 5.8 mol% of methyl acrylate, and 0.3 mol% of sodium methallylsulfonate were polymerized in DMSO to have an intrinsic viscosity of 0.12 m ³ / kg ( 1.2 dl / g), and a hollow fiber membrane was obtained in the same manner as in Example 2 except that a solution containing 16.5% by weight of the copolymer was used as a sheath component solution. Table 1 shows the measurement results. (Comparative Example 4) Example 2 was repeated except that the stretching ratio was 4.5 times.
Spinning was performed in the same manner as described above to obtain a hollow fiber membrane. Table 1 shows the measurement results.
Shown in

[0040]

[Table 1]

[0041]

According to the present invention, the bubble point, the film thickness, the inner diameter, the pressure resistance, and the permeability of pure water of the hollow fiber membrane are set to specific ranges. Thus, it is possible to provide a hollow fiber membrane that can be suitably used for clarification of industrial water, advanced treatment of wastewater, and the like.

Further, the tensile strength of the hollow fiber membrane is 6 MN / m
^When the elongation is ² or more and the elongation is 50% or more, a highly reliable hollow fiber membrane having stable turbidity and sterilization performance over a long period of time can be provided.

Further, the hollow fiber membrane contains at least 95 mol% of acrylonitrile and has an intrinsic viscosity of 0.2
When an acrylonitrile-based polymer containing 5 m ³ / kg or more is contained, it is excellent in hydrophilicity and chemical resistance, so that it is possible to obtain a hollow fiber membrane that can be particularly suitably used for removing suspended substances in water. it can.

When dry-wet spinning is performed using the acrylonitrile-based polymer at a draw ratio of 1.1 to 3 times, hollow fibers having a well-balanced water permeability, pressure resistance and strength are achieved. A thread membrane can be obtained.

Further, when dimethyl sulfoxide containing water in a specific range is used as a solvent for the sheath component and the core component used in performing the dry-wet spinning, a hollow material having more excellent water permeability, pressure resistance and strength can be obtained. A thread membrane can be obtained.

[Brief description of the drawings]

FIG. 1 is a photograph (1,000 times) of a cross section of a hollow fiber membrane according to an embodiment of the present invention.

FIG. 2 is a photograph (10, 10) of the outer surface of the hollow fiber membrane in FIG.
000 times).

FIG. 3 is a photograph (10, 10) of the inner surface of the hollow fiber membrane in FIG.
000 times).

[Explanation of symbols]

 1: outer surface 2: inner surface

Continued on the front page F term (reference) 4D006 GA06 GA07 HA19 MA01 MA21 MA22 MA31 MA33 MB02 MB09 MB11 MB16 MB20 MC32 MC36 MC37 MC39X MC89 NA04 NA10 NA17 NA18 NA36 NA68 PA01 PB04 PB05 PB08 PC51

Claims (8)

[Claims] 1. A hollow fiber membrane which satisfies the following conditions (A) to (E). (A) The bubble point is at least 250 kPa (B) The film thickness is in the range of 40 to 120 μm (C) The inner diameter is in the range of 250 to 420 μm (D) The withstand pressure is at least 400 kPa (E) The transmission coefficient of pure water is at least 4.2 m ³ / (M ²
・ H ・ MPa) 2. Tensile strength is 6 MN / m ² or more, and
The hollow fiber membrane according to claim 1, wherein the elongation is 50% or more. (3) at least 95 mol of acrylonitrile
%, And an acrylonitrile-based polymer having an intrinsic viscosity of 0.25 m ³ / kg or more.
Or the hollow fiber membrane according to 2. 4. A sheath component comprising a solution containing at least 95 mol% of acrylonitrile and having an intrinsic viscosity of 0.25 m ³ / kg or more and a acrylonitrile-based polymer and water, using a composite spinneret. A method for producing a hollow fiber membrane, comprising spin-dry spinning the components and stretching the resultant at a magnification of 1.1 to 3 times. 5. A water content of 0.5 to 6% by weight as the sheath component.
The method for producing a hollow fiber membrane according to claim 4, wherein a solution containing dimethyl sulfoxide contained in the range described above as a solvent is used. 6. The method for producing a hollow fiber membrane according to claim 4, wherein dimethyl sulfoxide containing water in a range of 5 to 25% by weight is used as said core component. 7. A hollow fiber membrane element for water purification, comprising the hollow fiber membrane according to claim 1. 8. A water purifier comprising the hollow fiber membrane element for water purification according to claim 7.