JP2948856B2 - Porous hollow fiber membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention has a porous hollow fiber membrane, particularly a dense surface layer provided with intermittent protrusions on the inner surface, and the inside and the outer surface of the membrane are fine. The present invention relates to a porous hollow fiber membrane having a porous structure.

(Prior Art) In recent years, techniques using a membrane having selective permeability in a separation operation have been put to practical use in various fields. In particular, when the shape of the membrane is a hollow fiber, the membrane area per occupied volume can be overwhelmingly larger than that of a flat membrane, so that a hollow fiber membrane is mainly used. Further, as the material, conventionally, a cellulose-based resin has been used, but as the use conditions such as the temperature of the liquid to be treated and the pH become severe, various synthetic resins other than the cellulose-based resin, for example, polyimide, polyacrylonitrile, and the like. Resins, such as resins based on polyvinyl alcohol, polyvinyl alcohol, and polysulfone, have come to be used.

Above all, polysulfone resins are excellent in heat resistance, acid resistance, alkali resistance, oxidation resistance, and microbial resistance. Therefore, recently, hollow fiber membranes using polysulfone resins have been studied. In the present invention, a hollow fiber membrane using a polysulfone-based resin will be described below, but it goes without saying that the present invention can be applied to a hollow fiber membrane made of a resin other than the polysulfone-based resin. As a hollow fiber membrane made of a polysulfone resin, for example, Japanese Patent Application Laid-Open No. 54-145379 discloses a hollow fiber membrane having 10-100 mm fine holes (substantially dense layer) on the inner surface and outer surface thereof. Discloses a polysulfone hollow fiber membrane having an inclined structure, and JP-A-56-115602 discloses a polysulfone hollow fiber membrane having a dense layer on both surfaces of the membrane and having a tube bundle structure inside the membrane. ing.

(Problems to be Solved by the Invention) However, since all of these hollow fiber membranes have a dense layer on the inner surface and / or outer surface of the membrane, the molecular weight cut off is 500,000 or less and the water permeability is 1,000 / m ^2.・ Hr ・ Kg / cm ²
The following are low. As means for restoring membrane performance when clogging occurs due to excessive clogging, only conventional permeated liquid backwashing and chemical liquid washing can be applied to conventional hollow fiber membranes, and other means cannot be applied. In order to remove various insoluble suspended substances and microorganisms, a permeable membrane that allows most of the dissolved polymer to pass through and blocks suspended substances and microorganisms is required. Application to such uses was not possible.

Accordingly, an object of the present invention is to provide a porous hollow fiber membrane having excellent fractionation properties, high water permeability, and easy regeneration of the hollow fiber membrane.

(Means for Solving the Problems) The present inventors have conducted intensive studies to achieve the above object, and as a result, when spinning into a hollow fiber, the viscosity as a coagulating solution was reduced.
By using a coagulation solution of 20 centipoise or more, a porous hollow fiber that has a unique surface structure that does not belong to any of the above structures, has excellent fractionation properties, high water permeability, and is easy to regenerate the membrane Invented the film. That is, the present invention is a porous hollow fiber membrane having a dense layer on the inner surface, the outer surface and the inside of the membrane having a microporous structure, and having a height along the length direction on the inner surface of the hollow fiber membrane. 0.01-0.3μ
Intermittent ridge-shaped protrusions are provided, and water permeability is 10
It is a porous hollow fiber membrane having a rejection of 80% or more of dextran having a molecular weight of 2,000,000 or more, which is not less than 00 / m ² · hr · Kg / cm ² .

The porous hollow fiber membrane of the present invention extrudes a solution containing a film-forming resin from an annular nozzle, and a non-solvent of the film-forming resin or a mixed solution of the non-solvent and water on a core portion of the annular nozzle, It is obtained by introducing a coagulating solution having a viscosity of 20 centipoise or more. The thread extruded from the annular nozzle forms an extremely thin dense layer on the inner surface by the coagulation action of the coagulation solution, followed by micro phase separation along with desolvation, and the coagulation of the resin occurs, which reduces resistance to water permeability. A microporous structure is formed so as not to have.

As the spinning solution, for example, a solution in which a resin such as polysulfone, polyethersulfone, polyimide, or polyvinylidene fluoride which can be produced by a wet or dry method and an additive for forming pores are dissolved in a solvent is used. As additives, for example, ethylene glycol, propylene glycol,
Glycols such as polyethylene glycol, alcohols such as methanol, ethanol, propanol, glycerin, water, LiCl, and inorganic salts such as ZnCl ₂ and the like. As the solvent, for example, N, N-dimethylformamide, dimethylacetamide, N-methylpyrrolidone,
Examples thereof include a single liquid such as dimethyl sulfoxide or a mixture of two or more of the above. The combination of the resin for forming the stock solution, the additive, and the solvent is arbitrary. The spinning solution is extruded together with the internal coagulation liquid from a double annular nozzle, and immersed in the coagulation liquid to produce a hollow fiber membrane.

In the present invention, a non-solvent of the film-forming resin or a mixed solution of the non-solvent and water and having a viscosity of 20 centipoise or more is used as the internal coagulation liquid. As the non-solvent for the film-forming resin, for example, a single or mixed solution of ethylene glycol, propylene glycol, polyethylene glycol, glycerin and the like is used.

In the present invention, the use of the internal coagulating liquid having a viscosity of 20 centipoise or more results in unexpected formation of intermittent projections on the inner surface of the hollow fiber membrane. Need to be slow. Therefore, the concentration of the non-solvent in the internal coagulation liquid is usually 40 to 100% by weight,
It is preferable to adjust the amount to 0 to 90% by weight. The composition of the internal coagulation liquid can be selected in consideration of viscosity and coagulation. In addition, when the ratio of the nozzle draft at the time of spinning is increased, the length of the concave portion and the projecting body formed between the projecting bodies can be increased, and the width between the adjacent projecting bodies can be reduced. Poor stability. Therefore, it is preferable that the nozzle draft ratio be kept within the range of 10 to 300%.

Here, the intermittent projecting body refers to a structure in which irregularities are present on the inner surface of the membrane, and the recesses and projections extend intermittently along the length direction of the hollow fiber. The shape of the protrusion is usually three times or more the width of the protrusion, and the distance between adjacent protrusions in the longitudinal direction of the hollow fiber is 0.2 μm or less. The height of the protrusion is usually 0.01 to 0.3 μm.

The porous hollow fiber membrane of the present invention is extremely thin (3 μm or less, usually 0.1 μm) provided with intermittent projections in the length direction on the inner surface.
A microporous structure having a dense layer, in which fine pores having a thickness of about 1 to 500μ, preferably about 5 to 100μ and an average pore diameter of 0.025 to 3μ are uniformly present in contact with the dense layer. The outer surface has pores having a maximum pore diameter of 0.5 to 5 µ formed by partially opening the microporous structure.

The hollow fiber membrane of the present invention, the inner surface of a smooth hollow fiber membrane Yotsute the presence of projecting member intermittently in comparison with, in particular internal pressure effective membrane area in the transmission in an over for increases 1000 / m ² · hr
・ High water permeability of Kg / cm ² or more can be obtained. Furthermore,
Since a non-solvent of the film-forming resin or a mixed solution of the non-solvent and water is used as the internal coagulating liquid, excellent fractionation properties can also be provided. This is because when the above internal coagulation liquid is used, a dense layer is formed on the inner surface in the same manner as in the case of water, but due to the high viscosity, the replacement speed of the solvent is slow, microphase separation is promoted, and the dense layer is near the surface. Since only the inside becomes porous, a hollow fiber membrane having high water permeability as well as excellent fractionability can be obtained. The hollow fiber membrane of the present invention has a high water permeability of 1.5 to 2 times or more in spite of the same level of fractionation properties as the conventional hollow fiber membrane due to the improvement in the effective membrane area and the reduction in the thickness of the dense layer. Have. For this reason, the hollow fiber membrane is particularly excellent as a hollow fiber membrane for internal pressure passage, and since it has intermittent projections on the inner surface, the permeability is not easily reduced, and the hollow fiber membrane can be easily regenerated by backwashing or the like. For this reason, it can be applied to fields where the service life is longer than conventional hollow fiber membranes and economical, and where the separation operation with conventional hollow fiber membranes is difficult.

(Examples) Hereinafter, the present invention will be described more specifically with reference to examples.
In addition, the measurement of water permeability and fractionation was performed by the following methods.

(I) Permeability A 25 mm hollow fiber open-ended LapoModule with an effective length of 15 cm is manufactured, and pure water at 25 ° C is allowed to permeate from the inside of the membrane at an overpressure of 1 kg / cm ² , and is allowed to reach the outside during a certain time. The amount of permeated pure water was measured.

(Ii) Fractionability 1% of dextran (molecular weight = 2,000,000) as a measurement solution
An aqueous solution was prepared, and the internal pressure was increased at an overpressure of 1 kg / cm ² and a circulating linear velocity of 0.3 m / sec. The total organic carbon in the collected permeate and the measurement solution was measured, and the removal rate was calculated.

Example 1 20% by weight of polysulfone resin (Udel P-1700 manufactured by Amoco), polyethylene glycol (PEG # 600 manufactured by Sanyo Chemical)
36% by weight and 44% by weight of dimethylformamide were dissolved to prepare a spinning stock solution. A viscosity consisting of 75% by weight of glycerin and 25% by weight of water maintained at the same temperature as the spinning dope kept at 28 ° C.
0cp internal coagulation liquid is simultaneously discharged from the double annular nozzle,
After passing 10 cm through humidified air at 50 ° C. and 85% at a draft rate of 80%, it was coagulated in water at 50 ° C. Next, after performing a hot water treatment at 90 ° C. and glycerin impregnation, the resultant was dried at 40 ° C. for 10 hours to obtain a hollow fiber membrane having an outer diameter of 1300 μm and an inner diameter of 800 μm. The hollow fiber membrane had a water permeability of 2200 / m ² hr · Kg / cm ² and a dextran rejection of 90%. The average width of the intermittent protrusion on the inner surface measured from the SEM photograph is 0.1 μm and the average length is 1.5 μm
m, the average height of the protrusions was 0.2 μm, the interval between the protrusions in the length direction was 0.1 μm, and the thickness of the dense layer was about 0.2 μm. FIGS. 1 to 5 show photographs of the hollow fiber membrane taken by a scanning electron microscope. 1 shows the outer surface of the hollow fiber membrane, FIG. 2 shows the inner surface, FIG. 3 shows the cross section on the outer surface side, FIG. ing.

Example 2 85% by weight of ethylene glycol and 25% of water in the internal coagulating liquid
A hollow fiber membrane having an outer diameter of 1300 μm and an inner diameter of 800 μm was prepared in the same manner as in Example 1 except that a solution having a viscosity of 200 cp was used. Permeability of the hollow fiber membrane is ^{2300 / m 2 · hr · Kg} / c
m ² , dextran rejection was 91%. The average width of the protrusions on the inner surface measured from the SEM photograph was 0.1 μm, the average length was 1.0 μm, and the average height was 0.1 μm. The average interval between the protrusions in the length direction was 0.15 μm.

Comparative Example 1 A hollow fiber membrane having an outer diameter of 1300 µm and an inner diameter of 800 µm was produced in the same manner as in Example 1 except that water was used as the internal coagulating liquid. Permeability of the hollow fiber membrane is ^{1100 / m 2 · hr · Kg} / cm 2,
Dextran inhibition was 90%. The inner surface was smooth from the SEM photograph.

Comparative Example 2 A hollow fiber membrane having an outer diameter of 1300 μm and an inner diameter of 800 μm was produced in the same manner as in Example 1 except that a solution composed of 80% by weight of dimethylformamide and 20% by weight of water was used as an internal coagulating liquid. Permeability of the hollow fiber membrane is ^{3000 / m 2 · hr · Kg} / cm 2,
Dextran inhibition was less than 10%. The inner surface was smooth from the SEM photograph.

Example 3 18 parts by weight of a polyimide (2080D, manufactured by APPJION CORPORATION), 18 parts by weight of ethylene glycol, and 64 parts by weight of dimethylformamide were dissolved to prepare a stock solution for spinning.
A hollow fiber membrane having an inner diameter of 1300 μm and an inner diameter of 800 μm was produced. The hollow fiber membrane had a water permeability of 1300 / m ² · hr · Kg / cm ² and a dextran rejection of 96%. The average width of the protrusions on the inner surface measured from the SEM photograph is 0.1 μm, the average length is 1.2 μm, the average height is 0.2 μm, and the average interval in the length direction of the protrusions is 0.15 μm
m.

Example 4 Using the hollow fiber membranes of Example 1, Example 2 and Comparative Example 1, internal pressure type modules each having an effective membrane area of 1 m ² and an effective length of 0.9 m were produced. Using these three types of modules, tap water was subjected to an internal pressure overpressure of 1 kg / cm ² and the excess amount when the permeation rate was reduced by half was measured. The module containing the hollow fiber membrane of Comparative Example 1 was 20 m ^In contrast to ³ , the module containing the hollow fiber membrane of Example 1 was 55 m ³ ,
The module containing the hollow fiber membrane of Example 2 was 45 m ³ . Next, these modules were backwashed with a permeate 5 times at a water pressure of 1 kg / cm ² for 30 seconds, and the water permeability was measured. The module containing the hollow fiber membrane of Comparative Example 1 recovered only 50% of the water permeability. In contrast, the module containing the hollow fiber membrane of Example 1 recovered the water permeability by 80%, and the module containing the hollow fiber membrane of Example 2 recovered the water permeability by 85%.

Example 5 Effective membrane area using the hollow fiber membranes of Example 2 and Comparative example 1
1 m ² , 0.9 m effective length module for internal pressure
Using these two modules, processing solution side inlet pressure 2.5K
FIG. 6 shows the results obtained when the electrodeposition paint was drained by g / cm ^{2 at} a circulating linear velocity of 2 m / sec by cross-flow system internal pressure. Sixth
As shown in the figure, the module containing the hollow fiber membrane of Comparative Example 1 showed a decrease in overspeed with time, whereas the module containing the hollow fiber membrane of Example 2 showed a decrease in overspeed. Without constant overspeed.

(Effects of the Invention) The hollow fiber membrane of the present invention has high permeation performance and excellent fractionation performance especially for use in internal pressure, and has a small decrease in permeation performance. Therefore, the service life is longer than that of the conventional film, and it is economical. The unique membrane structure enables application not only in fields where membrane separation operations are currently applied, but also in fields where membrane separation operations are difficult.

[Brief description of the drawings]

FIG. 1 shows the structure of the outer surface of the polysulfone hollow fiber membrane obtained in Example 1, FIG. 2 shows the structure of the inner surface, FIG. 3 shows the cross-sectional structure on the outer surface side, and FIG. Structure and Fifth
The figure is a scanning electron micrograph (× 5,000) showing the cross-sectional structure on the inner surface side, and FIG. 6 is a graph showing the change of the overspeed with time in the treatment of the effluent from the electrodeposition coating.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-200806 (JP, A) JP-A-61-200805 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B01D 69/08 B01D 71/68 D01D 5/24 D01F 6/00

Claims (1)

(57) [Claims] 1. A porous hollow fiber membrane having a dense layer on the inner surface and a fine porous structure on the outer surface and the inside of the membrane, wherein the inner surface of the hollow fiber membrane has a high height along the length direction. 0.01 ~ 0.3μ
Intermittent protrusions are provided, and the water permeability is 1000 / m ²
-A porous hollow fiber membrane that has a rejection of 80% or more for dextran having a molecular weight of 2,000,000 and an hr.kg/cm ² or more.