JPH10263373A - Polyacrylonitrile based membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a polyacrylonitrile based membrane excellent in balance between a high filter performance and a fraction performance. SOLUTION: In the membrane having a dense layer at one surface of the membrane, plural voids having 50-500 μm length and 30-150 μm width are present in a cross section in the membrane thickness direction of a layer having a reticular structure succeeding to the dense layer and the length of the largest void among them is more than 1/2 of the membrane thickness. The membrane has the excellent performance capable of being used widely in the general industry since the membrane is excellent in balance between the high filter performance and the fraction performance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyacrylonitrile-based membrane having an excellent balance between water permeability and fractionation performance.

[0002]

2. Description of the Related Art In recent years, the technology of using a membrane having a selective filtration property in a separation operation has been remarkably advanced, and is currently used in fields such as food industry, pharmaceutical industry, electronics industry, medical treatment, drinking water, and nuclear power condensate treatment. Has been put to practical use. As the material of the membrane, cellulose-based, polyamide-based, polyacrylonitrile-based, polycarbonate-based, and polysulfone-based resins are used. It has the advantages of excellent heat resistance and water permeability and good mechanical properties. Polyacrylonitrile-based membranes have been developed with emphasis on separation performance, water permeation performance, or mechanical strength, and various membrane structures and chemical compositions have been proposed according to the purpose.

[0003] For example, Japanese Patent Publication No. 60-39404 discloses a film structure comprising a dense layer, a porous layer, and huge pores. The membrane of this structure has excellent fractionation performance but low water permeability, so in applications where large quantities of water, such as waterworks, are purified, a large number of membrane modules must be used. And the processing cost increases.

On the other hand, Japanese Patent Application Laid-Open No. 63-190012 discloses a structure using an acrylonitrile polymer having a very high degree of polymerization, having a dense layer only on the outer surface of the film, and containing no macropores. ing. This membrane is excellent in mechanical strength, but has insufficient water permeability. Japanese Patent Application Laid-Open No. 6-65809 also describes a membrane structure composed of a dense layer and huge pores using an acrylonitrile polymer having a very high degree of polymerization, but the pore diameter of the dense layer is large. Poor balance between water permeability and fractionation performance.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a membrane having high water permeability despite having a dense layer capable of blocking a substance having a small molecular weight, that is, a membrane having high water permeability and fractionation performance. An object of the present invention is to provide a polyacrylonitrile-based film having an excellent balance.

[0006]

The present invention has solved the above-mentioned problems. That is, the present invention provides (1) a film having a dense layer on one surface of a film, wherein a cross-section in the thickness direction of a layer having a network structure following the dense layer has a length of 50 μm to 500 μm.
m, a polyacrylonitrile-based film having a plurality of voids each having a width of 30 μm to 150 μm, wherein the maximum void length is at least half the thickness of the film, (2) (1) the polyacrylonitrile-based membrane of (1) above, wherein the membrane is a hollow fiber membrane; (3) the polyacrylonitrile-based membrane of (2) above, which has a dense layer as the outermost layer of the membrane; (1) to above
(3) A polyacrylonitrile-based film.

Hereinafter, the structure of the film of the present invention will be described. The film of the present invention has a structure integrally and continuously from one surface to the other surface of the film. The film has a dense layer on one surface, and has a continuous network structure from the dense layer to the other surface. The cross section of the network structure layer in the film thickness direction has a length of 50 μm to 500 μm and a width of 30 μm to 1 μm.
It has a structure in which a plurality of voids each having a thickness of 50 μm are provided, and the length of the void having the largest area is half or more of the film thickness. By providing the huge voids in the layer of the network structure, the water permeability of the membrane can be improved without lowering the separation performance of the membrane. The shape of the membrane is not limited, but is preferably a hollow fiber shape. Hollow fiber membranes can increase the effective membrane area per unit volume compared to planar membranes,
There is an advantage that the size of the membrane filtration device can be reduced.

Further, in the case of a hollow fiber membrane, it is preferable that the outermost layer of the membrane has a dense layer. For example, when filtering a large volume of water, if a method of filtering water from the outer surface to the inner surface (called “external pressure filtration”) is used, the filtration membrane area in the module becomes the outer surface, The effective membrane area can be further increased as compared with internal pressure filtration. In the case of external pressure filtration, in order to reduce fouling of the membrane, it is preferable that the dense layer of the membrane is located at or near the outermost layer of the membrane.

Further, in order to improve the water permeability of the membrane,
It is preferable that the length of the void is 100 μm to 500 μm. Representative examples of the film of the present invention will be described in more detail with reference to the drawings. 1 is an electron micrograph showing a cross section perpendicular to the length direction of the hollow fiber membrane, that is, a part of a cross section in the film thickness direction, and FIG. 2 is an electron micrograph showing a state of the outer surface of the membrane. It is. As shown in FIG. 1, this film has a dense outer surface, and has a plurality of voids in a cross section in the thickness direction of a layer having a network structure following the dense layer. Has a structure that is at least half the thickness of the film.

The dense layer referred to in the present invention refers to a layer which has small pores, ie, small pores, of the polymer constituting the film in a cross section in the film thickness direction when viewed microscopically, and contributes to the fractionation performance of the film. In FIG. 1, this corresponds to an outer surface whose pore size is much smaller than that of an adjacent layer. The pore size of the dense layer is
Although not observed with an electron microscope, the extremely small one that can block 100% of insulin with a molecular weight of 5700,
It can be adjusted over a wide range up to a pore size of 0.1 μm observed with an electron microscope. Further, the thickness of the dense layer is optional, but if it is too thick, the water permeability decreases. Therefore, it is usually 30 μm or less, preferably 10 μm or less.

The membrane of the present invention has an excellent effect of exhibiting a larger water permeability than conventionally expected from the value of the average pore diameter of the dense layer. Generally, in order to increase the water permeability of the membrane, it is necessary to increase the average pore diameter of the dense layer. Therefore, it has been difficult to obtain a membrane that satisfies the performance of a small molecular weight cut-off and a high water permeability. In contrast, the membrane of the present invention has a pore diameter of the dense layer,
Although the range is from a very small value that can inhibit 100% of the insulin having a molecular weight of 5700 to a small value of 0.1 μm, as the average pore size increases, 3
00 to 30,000 liters / hr · m ² · atm (2
(Measured at 5 ° C.), indicating a good balance between fractionation performance and water permeability.

The length of the void is 50 μm to 500 μm,
Preferably, it is necessary to be 100 μm to 500 μm. If the length is less than 50 μm, it is difficult to improve the water permeability of the membrane. If the length is longer than 500 μm, the strength of the membrane tends to decrease, which is not preferable. The width of the void is required to be 30 μm to 150 μm, and if the width is 30 μm or less, the water permeability of the membrane is unpreferably reduced. On the other hand, the width is 150 μm.
When it is larger than the above, it is not preferable because the film tends to be clogged.

In the present invention, "length" indicates the maximum length in the film thickness direction, and "width" indicates the maximum width perpendicular to the length.
For example, in the cross section in the film thickness direction, when the void located between the film surfaces is a void having a shape as shown in FIG. 3, the length is a and the width is b. Similarly, a void having a shape as shown in FIG. 4 has a length c and a width d. In the void having the shape shown in FIG. 5, the length is e and the width is f. In a void having a shape as shown in FIG. 6, the length is g and the width is h.

Further, in order to further improve the water permeability of the membrane, voids may be opened on the surface having no dense layer. In such a case, for example, in a void having a shape as shown in FIG. 7, the length is i and the width is j. As described above, the voids of the film of the present invention are large, and the length of the void having the largest area when observed in a cross section in the film thickness direction is one half or more of the film thickness.

Hereinafter, an example of the method for producing a film of the present invention will be described. The hollow fiber membrane is manufactured by simultaneously discharging a film-forming stock solution obtained by dissolving a polyacrylonitrile-based polymer in an organic solvent from a double annular nozzle into a coagulation bath together with an internal solution, and coagulating the same. In the case of a flat film, the film-forming stock solution is placed on a flat plate with a smooth surface, or on an endless belt,
Alternatively, it is produced by uniformly casting a thin film on a rotating drum using a knife edge or the like and coagulating it in a coagulation bath.

As the polyacrylonitrile polymer used in the present invention, at least 70% by weight, preferably 85% to 100% by weight of acrylonitrile and one or two kinds of vinyl compounds copolymerizable with acrylonitrile. These are 30% by weight or less, preferably 0% to 15% by weight or less of acrylonitrile homopolymer or acrylonitrile copolymer. The intrinsic viscosity of the acrylonitrile polymer is preferably 0.4 or more and less than 2.0. If the intrinsic viscosity is less than 0.4, the strength of the film tends to be low, and if it is 2.0 or more, the solubility tends to be poor.

The vinyl compound is not particularly limited, as long as it is a known compound having copolymerizability with acrylonitrile. Preferred copolymerization components include acrylic acid, methyl acrylate, ethyl acrylate and itacone. Acid, vinyl acetate, sodium acrylsulfonate, sodium methallylsulfonate, sodium p (para) -styrenesulfonate, hydroxyethyl methacrylate,
Examples thereof include ethyl triethyl ammonium methacrylate, ethyl trimethyl ammonium methacrylate, and vinylpyrrolidone.

As the organic solvent for dissolving the acrylonitrile polymer, N, N-dimethylformamide, N, N
-Dimethylacetamide, dimethylsulfoxide, γ-butyrolactone, ethylene carbonate, N-methyl-2-pyrrolidone, 2-pyrrolidone, hexamethylenephosphamide and the like. Further, a mixed solvent of the above two or more types may be used.

The concentration of the acrylonitrile polymer in the stock solution is not particularly limited as long as it can be formed into a film and the obtained film has the performance as a film.
It is 5% by weight, preferably 10 to 30% by weight. In order to achieve high water permeation performance or a high molecular weight cut-off, the lower the acrylonitrile-based polymer concentration, the better.
% By weight is preferred. It is also possible to add a plurality of non-solvents such as water, salts and glycols for the purpose of controlling the viscosity of the stock solution and the state of dissolution, and the type and the amount of addition may be determined as needed depending on the combination.

The internal liquid used in the production of the hollow fiber membrane is used for forming the hollow part of the hollow fiber membrane. When a dense layer is formed on the outer surface, an acrylonitrile-based polymer such as N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, γ-butyrolactone, ethylene carbonate, N-methyl-2-pyrrolidone is used as the internal liquid. An aqueous solution of a good solvent that dissolves is used. When a dense layer is formed on the inner surface, those described in a coagulation bath described later are employed as the internal liquid.

The aqueous solution of a good solvent is preferably an aqueous solution containing 30% by weight or more of a good solvent, preferably 50% by weight or more of a good solvent. In order to open the voids on the inner surface to make the membrane more water-permeable, the content is more preferably 75% by weight or more. Also, for the purpose of controlling the viscosity of the internal liquid, tetraethylene glycol,
It is also possible to add glycols such as polyethylene glycol and non-solvents such as glycerin.

The hollow fiber membrane can be formed using a known tube-in-orifice type double annular nozzle. More specifically, the hollow fiber membrane of the present invention can be obtained by simultaneously discharging the above-mentioned stock solution and the internal solution into the coagulation bath from the double annular nozzle and coagulating the same. It is also possible to manufacture by providing a gap (air gap) between the nozzle and the coagulation bath.

As the coagulation bath, for example, a liquid that does not dissolve the polymer such as water; alcohols such as methanol and ethanol; ethers; aliphatic hydrocarbons such as n-hexane and n-heptane is used. Preferably, it is used. The solidification rate can also be controlled by adding the good solvent to the coagulation bath. In the case of a planar film, a dense layer is formed on the surface of the film on the side contacting the coagulation bath.

The temperature of the coagulation bath is from -30 ° C to 90 ° C, preferably from 0 ° C to 90 ° C, more preferably from 0 ° C to 80 ° C. The temperature of the coagulation bath exceeds 90 ° C or -30
If the temperature is lower than ℃, the state of the surface of the film in the coagulation bath is difficult to be stabilized.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. Each measuring method is as follows. In addition, the hollow fiber membrane and the planar membrane used as the measurement samples were all completely impregnated with water.

The amount of water permeation of the hollow fiber membrane is determined by permeating ultrafiltration water at 25 ° C. from the inner surface to the outer surface of the hollow fiber membrane sample having a length of 50 mm, and the amount is liter / hr · m ² · a.
tm. However, the effective film area was converted to the inner surface.
The water permeability of the flat membrane is 25 m in ultrafiltration water with a diameter of 25 m.
The sample was permeated through a sample of a flat membrane punched out to a diameter of m, and the amount was expressed in liter / hr · m ² · atm.

The film strength was measured using an Autograph AGS-5D manufactured by Shimadzu Corporation at a sample length of 50 mm and a pulling speed of 10 mm / min. The breaking strength is
The load at break per hollow fiber membrane is expressed as the calculation per kg of the cross-sectional area of the membrane before pulling (kgf / cm ² ), and the elongation (elongation) is the length of the original length up to the break. (%).

The fractionation performance was 0.02 for the hollow fiber membrane.
Phosphate buffer 5 wt% of bovine serum albumin (molecular weight 67,000) (phosphate buffer concentration = 6 × 10 ^-3
mol / liter) aqueous solution, with respect to a 70 mm hollow fiber membrane, the average pressure of the input pressure and the output pressure is 0.5 kgf / c
The rejection after 40 minutes when filtering from the outer surface to the inner surface under the condition of cross flow of m ² and fluid linear velocity = 1 m / sec is shown. The fluid linear velocity was calculated using the area (see FIG. 8) obtained by subtracting the cross-sectional area calculated from the outer diameter of the hollow fiber membrane from the cross-sectional area of the cylindrical container.

In the case of a flat membrane, the flat membrane punched out to a diameter of 25 mm was incorporated into a filter holder, and the rejection after 2 minutes when the above bovine serum albumin aqueous solution was supplied at a membrane differential pressure of 0.5 kgf / cm ^2. Is shown. The intrinsic viscosity of the acrylonitrile-based polymer is determined by Journal of pol
ymer Science (A-1) Vol. 6, 147-
157 (1968),
The measurement was performed at 30 ° C. using N, N-dimethylformamide as a solvent.

The size of the void was measured by an electron micrograph.

[0031]

EXAMPLE 1 A copolymer having 91.5% by weight of acrylonitrile, 8.0% by weight of methyl acrylate, 0.5% by weight of sodium methallylsulfonate and an intrinsic viscosity [η] = 1.2 was prepared as N, N- It was dissolved in dimethylformamide to prepare a 20% by weight stock solution. The solution is kept at 40 ° C.
-Discharged from a spinneret (double annular nozzle 0.5 mm-0.7 mm-1.3 mm) together with an internal solution consisting of a mixed solution of 85% by weight of dimethylformamide and 15% by weight of water and made of water at 80 ° C. The mixture was discharged into a coagulation bath to complete coagulation. The spinning speed was fixed at 10 m / min. The obtained hollow fiber membrane has a dense layer on the outer surface, a large number of voids in the cross section in the thickness direction of the layer of the network structure, and the size of each void has a major axis of 50 μm or more and a minor axis of It had a size of 30 μm or more. Table 1 shows the structure and performance of this film.

[0032]

Example 2 16% by weight of the copolymer used in Example 1
1.5 weight% of polyethylene glycol having a weight average molecular weight of 8,000 (PEG6000 manufactured by Kanto Chemical Co.)
It was dissolved in 82.5% by weight of N-methyl-2-pyrrolidone to obtain a uniform solution. This was kept at 60 ° C. and spun (with a double annular nozzle 0.5 m
m-0.7 mm-1.3 mm)
And discharged into a coagulation bath consisting of water at 80 ° C. to complete the coagulation. The spinning speed was fixed at 10 m / min. Table 1 shows the structure and performance of this film.

[0033]

Example 3 The stock solution used in Example 1 was cast on a glass plate to a thickness of 400 μm, and was made of a mixed solution of 85% by weight of N, N-dimethylformamide and 15% by weight of water.
The casting surface was immersed in a solution at 0 ° C. and solidified to obtain a planar film. The water permeability of the obtained membrane is 2100 liter / hr ·
m ² · atm (measured at 25 ° C.) and a fractionation performance of 10
It was 0%. The maximum void size in the film thickness direction was 260 μm in length and 60 μm in width.

[0034]

Comparative Example 1 A hollow fiber membrane was obtained in the same manner as in Example 1, except that water was used as the internal liquid. Table 1 shows the membrane structure and performance of the obtained hollow fiber membrane.

[0035]

[Table 1]

[0036]

According to the present invention, it is possible to obtain a polyacrylonitrile-based membrane having a very good balance between water permeability and fractionation performance.

[Brief description of the drawings]

FIG. 1 is an electron micrograph (× 200) showing a cross section (part) of one embodiment of the hollow fiber filtration membrane of the present invention.

FIG. 2 is an electron micrograph (magnification: 50,000 times) of the outer surface of the hollow fiber filtration membrane shown in FIG.

FIG. 3 is an example of a void shape in a cross section in a film thickness direction.

FIG. 4 is an example of a void shape in a cross section in a film thickness direction.

FIG. 5 is an example of a void shape in a cross section in a film thickness direction.

FIG. 6 is an example of a void shape in a cross section in a film thickness direction.

FIG. 7 is an example of a void shape in a cross section in a film thickness direction.

FIG. 8 is a cross-sectional view showing the positioning of the hollow fiber membrane and the container when measuring the fluid linear velocity.

[Procedure amendment]

[Submission date] April 8, 1997

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

FIG.

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Figure 2

[Correction method] Change

[Correction contents]

FIG. 2

Claims (1)

[Claims] 1. A film having a dense layer on one surface of a film, wherein a cross section in a thickness direction of a layer having a network structure following the dense layer has a length of 50 μm to 500 μm and a width of 30 μm to 150 μm.
A polyacrylonitrile-based film having a plurality of voids, wherein the length of the largest void among the voids is at least half the thickness of the film.