JPH0768142A - Composite holoow fiber membrane - Google Patents

Abstract

PURPOSE:To obtain excellent durability of a membrane and high separation performance of a hollow fiber membrane in which microvoides do not penetrate through the membrane but are opened only in one side of the membrane, by coating the inner surface of microvoides with a polymer material. CONSTITUTION:This hollow fiber membrane has microvoides which do not penetrate through the membrane but are opened only in one surface. At least the inner surfaces of the microvoides are coated with a polymer material. The aperture of a microvoid is a circle having 1-100mu diameter or an oval having 10-1000mum major axis and 1-50mu minor axis. The total area of aperture of microvoids is >30 % of the whole surface area of the membrane. It is preferable that the hollow fiber membrane consists of a polyacrylonitrille copolymer and the polymer material is polyvinylalcohol. Thereby, damages in the membrane due to peeling of a coating film from the supporting body membrane are hardly caused so that excellent durability of the membrane and high separation performance can be maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite hollow fiber membrane having a novel structure with excellent mechanical strength. More specifically, a hollow fiber membrane for the purpose of separating and concentrating liquid polymer substances, colloids, ions, fine particles, etc., gas separation or pervaporation separation of organic mixed liquid or organic mixed vapor,
The present invention relates to a composite hollow fiber membrane having a structure in which a membrane surface having open macrovoids is coated with a polymer substance.

[0002]

2. Description of the Related Art Generally, a membrane separation method is simpler in operation and more energy-saving than separation methods such as a drying method, a vapor method, an adsorption method, etc., so that the chemical industry, the food industry, the pharmaceutical industry,
It is used in a wide range of fields such as the electronics industry. Conventionally, most of separation membranes used in such fields have a skin layer having a separation activity on the surface of the separation membrane and a machine of the skin layer for the purpose of increasing the permeation rate of the substance to be separated and enhancing the separation performance. An asymmetric membrane structure having a sponge layer that maintains the desired strength and a composite membrane structure in which a polymer coating is applied on a porous support membrane to form a thin layer are used.
The asymmetric membrane formed by the phase conversion method of the membrane forming solution can obtain a thin separation active layer, but on the other hand, the separation active layer on the surface of this membrane often has relatively large pores which cause a defect in the membrane, and thus the separation target layer is separated. Since the substance passes through the defective holes as it is, high resolution may not be obtained.

On the other hand, the composite membrane prepared by the polymer coating method has a uniform polymer coating layer on the surface of the membrane, and thus has no defect holes on the surface of the membrane and can provide high resolution. However, in general, the polymer material coated on the membrane surface is different from the membrane material of the support membrane, and since the coated polymer material does not firmly adhere to the support membrane, this composite membrane can be used for a long time. When used, the coated polymeric substance may peel off due to the difference in thermal linear expansion coefficient between the polymeric substance and the support film.
In the conventional composite membrane, since the membrane surface of this support membrane is a skin layer having relatively fine pores and the membrane surface is smooth,
There is a problem that the physical adhesion to the coated polymer substance, that is, the anchoring action does not work effectively, and peeling of the both easily occurs. When this peeling occurs, a crack is generated in the coating layer of the polymer substance that is the separation active layer, and the separation performance of the composite membrane is significantly reduced. Such peeling phenomenon often occurs especially in a hollow fiber membrane in which it is difficult to form a uniform coating layer of a polymer substance.

On the other hand, there is an attempt to improve the water permeability of the membrane by forming large circular holes of several μm or more on the surface of the hollow fiber membrane. For example, in Japanese Examined Patent Publication No. 60-29282, a liquid dispersant having a low solubility in a dope solvent is uniformly dispersed in the film-forming dope of the hollow fiber membrane, and the dispersant is retained.
A hollow fiber membrane having a large pore size is disclosed, which comprises forming a hollow fiber membrane and then extracting and removing the dispersant to form a large number of recesses on the surface of the membrane. Further, in Japanese Patent Application Laid-Open No. 5-76736, in the production of a polysulfone-based hollow fiber membrane, the liquid injected into the hollow fiber induces phase separation in the membrane dope and has no coagulation ability. By this, a circular hole of 10 μm or more is formed on the inner surface of the hollow fiber membrane. Furthermore,
Japanese Unexamined Patent Publication (Kokai) No. 49-90684 discloses a method for producing a hollow fiber membrane having pores with a diameter of 10 μm or more on the inner surface of a polyacrylonitrile type hollow fiber membrane.

However, the film surface as described above has several μs.
The hollow fiber membrane having a large circular pore of m or more has a three-dimensional mesh structure on the inner wall of the circular pore and the membrane surface portion other than the circular pore. When used as an ultrafiltration membrane or a pervaporation membrane, its separation performance is extremely poor. Further, such a hollow fiber membrane generally has low mechanical strength against pressure from the inner surface or outer surface of the membrane, resulting in poor durability of the membrane.

[0006]

DISCLOSURE OF THE INVENTION The present invention has the drawback that in a conventional composite hollow fiber membrane in which a polymer material is coated on a hollow fiber support membrane, the coating layer is easily peeled off from the support membrane to cause membrane damage. It is an object of the present invention to overcome the above problems and provide a composite membrane having a novel structure having excellent membrane durability and excellent separation performance for low molecular weight substances.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have invented a composite hollow fiber membrane having a novel structure.

That is, according to the present invention, in a hollow fiber membrane in which at least one of the inner and outer surfaces of the macrovoid is open without penetrating the inner and outer surfaces, at least the inner surface portion of the macrovoid is coated with a polymer substance. And a composite hollow fiber membrane.

In the present invention, a hollow fiber membrane having macrovoids formed on at least one of the inner and outer surfaces of the hollow fiber membrane is used, and the macrovoids are provided on the surface side of the hollow fiber membrane having the macrovoids. By coating the inner surface of the polymer material with the polymer material, the area of the coating portion can be increased and the adhesion between the coating layer and the support membrane can be increased, as compared with the surface of a normal hollow cylindrical fiber.

The present invention will be described in detail below. The macrovoids referred to in the present invention mean giant pores having a pore diameter of 1 to 200 μm existing in the membrane thickness of the hollow fiber membrane, and a mesh-like porous material having a pore diameter of 0.05 to 1 μm continuously formed from the membrane surface layer. Distinguished from layers. The hollow fiber support membrane used in the present invention is characterized in that the macrovoids are open on at least one of the inner and outer surfaces of the membrane. The shape of the opening is not particularly limited, but a circular or elliptical shape can be used. For circular holes, the hole diameter is 1 to
In the case of an elliptical hole, the major axis is preferably 10 to 1000 µm and the minor axis is 1 to 50 µm. The area of one open hole is larger than the area of one open hole of the three-dimensional mesh-like porous layer, the former is preferably 5 times or more the latter, and the area occupied by all open holes is the open area. Having a total membrane surface area of 30
% Or more, and preferably 60% or more, the effect of the present invention can be more enhanced. The size of the macrovoids in the film thickness direction is not particularly limited as long as it does not penetrate from the film surface on the opening side to the other film surface, but is 80% or less of the total film thickness. It is preferable.

Furthermore, the composite hollow fiber membrane of the present invention is characterized in that at least the inner surface portion of the above macrovoid is coated with a thin layer of a polymer substance having a thickness of 0.1 μm or more, (1 ) When the polymer substance covers the entire surface of the hollow fiber membrane having macrovoids, (2) when the portion other than the inner surface of the macrovoids on the surface of the hollow fiber membrane is not substantially covered, and (3) the macro There are modes such as the case where the entire void interior is filled with a polymer substance.

In the present invention, the polymer substance used for coating the above macrovoids is not particularly limited, and examples thereof include polyvinyl alcohol, cellulose acetate,
Examples thereof include polyacrylamide, polyvinylpyrrolidone, chitosan, polyacrylic acid, polysulfone, polymethylmethacrylate, polyvinylidene fluoride and carboxymethylcellulose.

The polymer used in the hollow fiber support membrane of the present invention is not particularly limited, and examples thereof include polyacrylonitrile-based polymers, polysulfone-based polymers, cellulose-based polymers, polyamide-based polymers, polymethylmethacrylate-based polymers, and polyfluorinated polymers. There are various types such as vinylidene-based polymers, polyolefin-based polymers, polystyrene-based polymers and the like. The polymer used for the support film and the polymer used for the coating may be made of different materials.

There are various methods for forming the support membrane in the form of hollow fibers, but in general, they are classified into a wet spinning method, a dry-wet spinning method and a melt spinning method. In order to open macrovoids on the membrane surface by using wet and dry wet spinning methods, the type and composition of the polymer and its solvent and additives are appropriately combined, and the polymer dope is solidified into hollow fibers. It is necessary to adjust the coagulation force of the coagulation liquid inside and outside the hollow fiber. For example, in order to form macrovoids on the inner surface of the hollow fiber membrane, a nonsolvent or the like is added to the polymer dope to reduce the solubility, while the coagulating liquid on the inner surface side of the hollow fiber has a small coagulating force of the polymer dope. Just choose one. In the melt spinning method, macrovoids can be formed on the surface of the membrane by stretching the hollow fiber during or after spinning the hollow fiber membrane. Macrovoids can also be obtained on the membrane surface by forming a hollow fiber membrane using a polymer dope to which a dispersant is added and then extracting this dispersant with an appropriate solution.

In order to coat the polymer material on the hollow fiber support membrane formed as described above, the support membrane is immersed in a solution containing the polymer material and then adhered to the surface of the support membrane. Insolubilize the polymer substance to form a stable coating layer,
A method is known in which a polymer solution is pressed into a support membrane to form a polymer substance layer on the membrane surface. In these cases, it is also a preferred embodiment in the present invention to use a crosslinking agent or perform thermal crosslinking. The thickness of the coating layer can be adjusted by changing the concentration of the polymer solution and the press-fitting pressure. That is, when the polymer substance is pressed into the support membrane at a higher concentration and a higher pressure, the thickness of the coating layer can be increased.

In the composite hollow fiber membrane of the present invention, a coating layer of a macromolecular substance is formed relatively thin on the surface of the hollow fiber support membrane having macrovoids, and the macrovoids are not filled with the macromolecular substance. When the surface is coated, the surface area of this composite hollow fiber membrane is the conventional hollow fiber membrane in which macrovoids are not opened on the surface or the conventional type composite hollow fiber membrane in which this type of hollow fiber membrane is coated with a polymer substance. It can be expected that the coating layer is significantly larger than the surface area of the thread membrane, that is, a remarkably high permeation rate is obtained, and at the same time, the coating layer is unlikely to peel off due to the increase in the coating area. Further, even when the coating layer is relatively thick, the macromolecular substance fills the inside of the macrovoid, and the inner surface of the hollow fiber support membrane is also coated, this coating layer forms a support membrane surface with the anchoring effect. Since they are firmly bonded, the problem that the coating layer peels off from the support film during use of the film is solved, and it is expected to obtain a film having excellent durability.

[0017]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1 Diacyl sulfoxide (hereinafter abbreviated as DMSO) was used as a solvent for a polyacrylonitrile-based copolymer (acrylonitrile content: 85 mol%, hereinafter abbreviated as PAN), and water was used as an additive. PAN / DMSO / water = 16/74
The mixture was mixed at 80 ° C. for about 20 hours so as to be / 10 to prepare a film forming dope. DMSO / water = 50/50 in the inner coagulation liquid of the hollow fiber membrane
This film-forming dope was heated at a temperature of 5
It was spun into a hollow fiber membrane spinning nozzle at 0 ° C by press fitting. The film-forming dope discharged from this spinning nozzle port was passed through a water vapor phase part adjusted to a temperature of 20 ° C. for 20 cm and then coagulated while passing through a water bath at a temperature of 50 ° C. to give a hollow fiber membrane. The inner and outer diameters of the obtained hollow fiber membrane were 0.8 and 1.3 mm, respectively.As a result of observing the inner surface of the hollow fiber membrane with an electron microscope (500 times), the circular pores with an average pore diameter of 15 μm showed about 40%. It was open with a porosity (Fig. 1). A polyvinyl alcohol aqueous solution (5 wt%) having a degree of polymerization of 2000 was pressed into the hollow fiber membrane having macrovoids formed on the inner surface of the membrane at a pressure of 100 kPa for about 30 minutes to form a polyvinyl alcohol gel layer on the inner surface of the membrane. Was formed. This membrane was washed with a small amount of pure water and then dried in a dryer at 70 ° C. for about 20 hours to obtain a composite hollow fiber membrane of the present invention. Macrovoids having pores were observed on the inner surface of the hollow fiber membrane as in FIG.

A mini-module (membrane area 0.1 m ² ) was prepared using the hollow fiber membrane obtained above, and a mixture of isopropyl alcohol (hereinafter abbreviated as IPA) / water at a temperature of 75 ° C. was prepared.
(Mixed weight ratio: IPA / water = 95/5) was circulated to the inner surface side of the hollow fiber membrane, and the pressure on the permeation side of the membrane was about 5 Torr to about 5
Time pervaporation experiments were performed. The same experiment was repeated several times while repeating the procedure of once setting the pressure on the permeation side to 1 atm and, after about 20 hours, again setting to 10 Torr. The permeated vapor of the membrane is condensed as a permeate by condensing in a cold trap using liquid nitrogen as a refrigerant, the permeation rate is calculated from the weight of the permeate, and the composition of the permeate is analyzed by gas chromatography. The separation factor was calculated by the formula.

[0020]

[Equation 1]

Table 1 shows the results of the permeation rate and the separation coefficient obtained by the above repeated experiments.

Comparative Example 1 A membrane-forming dope having the same composition and composition ratio as in Example 1 was spun under the same spinning conditions by using water as the internal coagulating liquid of the hollow fiber membrane. In an electron microscope observation with a magnification of 10,000 times,
No openings could be confirmed on the inner surface of this hollow fiber membrane (Fig. 2). Using this hollow fiber membrane, the same operation as in Example 1 was performed to form a polyvinyl alcohol coating layer on the inner surface of the membrane to obtain a composite hollow fiber membrane. The results of the pervaporation experiment conducted in the same manner as in Example 1 using this membrane are shown in Table 1.
Compared to. In the third experiment, the separation coefficient obtained from this membrane was remarkably reduced, and the feed liquid leaked to the permeate side. After the experiment, when the inner surface of this film was observed with an electron microscope, cracks having a width of about 2 μm were found.

Comparative Example 2 When the same pervaporation experiment as in Example 1 was carried out using the hollow fiber support membrane not coated with polyvinyl alcohol in Example 1, the feed liquid was not separated as in the case of the leak and the membrane was left as it was. It has passed.

[0024]

[Table 1]

[0025]

INDUSTRIAL APPLICABILITY The composite hollow fiber membrane of the present invention uses a hollow fiber membrane having macrovoids open on at least one of the inner and outer surfaces as a support membrane, and the membrane surface including the inner surface of this macrovoid. It is a hollow fiber membrane in which the polymer is coated with a polymer substance, and membrane damage due to peeling of the coating layer from the support membrane is unlikely to occur, so that excellent membrane durability and high separation performance can be maintained. Further, according to the present invention, the inner surface of the macrovoid can also be used as a membrane surface that contributes to permeation, so that a high permeation rate can be obtained by increasing the surface area.

[Brief description of drawings]

1 is an electron micrograph showing the shape of fibers on the inner surface of a support membrane used in a composite hollow fiber membrane of Example 1. FIG.

FIG. 2 is an electron micrograph showing the shape of fibers on the inner surface of the support membrane used in the composite hollow fiber membrane of Comparative Example 1.

Claims (7)

[Claims] 1. A hollow fiber membrane in which macrovoids are opened in at least one of the inner and outer surfaces without penetrating the inner and outer surfaces, and at least the inner surface portion of the macrovoids is coated with a polymer substance. A composite hollow fiber membrane characterized by the following. 2. The macro void opening has a hole diameter of 1 to 100 μm.
m circular hole, major axis 10-1000 μm, minor axis 1-50 μm
The composite hollow fiber membrane according to claim 1, which is an elliptical hole. 3. The composite hollow fiber membrane according to claim 2, wherein the area occupied by all the open pores of the macrovoid is 30% or more of the total membrane surface area. 4. The composite hollow fiber membrane according to claim 3, wherein the entire surface of the hollow fiber membrane having macrovoids is coated with a polymer substance. 5. The composite hollow fiber membrane according to claim 3, wherein only the inner surface of the macrovoid is coated with a polymer substance. 6. The composite hollow fiber membrane according to claim 3, wherein the entire interior of the macrovoid is covered with a polymer substance. 7. The composite hollow fiber membrane according to claim 4, wherein the hollow fiber membrane is a polyacrylonitrile copolymer and the polymer substance is polyvinyl alcohol.