JPS6253414A - Production of aromatic polysulfone hollow fiber membrane - Google Patents

Abstract

PURPOSE:To obtain the titled fiber membrane having excellent water- permeability and mechanical strength, by forming a hollow fiber membrane from a film-forming solution containing an aromatic polysulfone, applying a polyhydric alcohol to the membrane and heat-treating the alcohol-containing membrane. CONSTITUTION:An aromatic polysulfone is dissolved in a mixture or a polar organic solvent of the polysulfone and a non-solvent of the polysulfone (the ratio of the non-solvent is 5-50wt%), and the obtained film-forming solution is formed to obtain a hollow fiber membrane. The solvent is removed from the inner and outer surfaces of the membrane. A polyhydric alcohol is impregnat ed in the obtained membrane to obtain a membrane containing >=10wt% polyhydric alcohol based on the aromatic polysulfone, and the membrane is heat-treated at >=100 deg.C and <=Tg-10 deg.C (Tg is glass transition temperature of the aromatic polysulfone).

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing an aromatic polysulfone hollow fiber semipermeable membrane having excellent water permeability and mechanical strength.

(Prior Art) Since aromatic polysulfone has excellent heat resistance and chemical resistance, various hollow fiber semipermeable membranes made from aromatic polysulfone have been proposed. However, according to conventionally known methods, mechanical strength is particularly high at high temperatures, and
A hollow fiber membrane with excellent water permeability cannot be obtained.

For example, Japanese Patent Application Laid-Open No. 49-23183 discloses a film with a diameter of 108 mm with a dense layer on the inner surface and no polymer on the outer surface.
A hollow fiber-like semipermeable membrane having a cavity of m or more in size has been proposed, but such a structure has particularly low mechanical strength. For this reason, JP-A-54-145379 discloses that a porous polymer layer having a dense layer on both the inner and outer surfaces, and a porous polymer layer continuous from this dense layer, has a continuous pore size from the membrane surface.
An aromatic polysulfone hollow fiber semipermeable membrane with a structure that increases in size has been proposed. However, the water permeability of this membrane is highly dependent on the film thickness, and in particular, when the film thickness exceeds 200 μm, the water permeability becomes significantly poor.

In addition, JP-A-56-86941 discloses that by using a membrane-forming solution prepared by dissolving two types of aromatic polysulfones having different chemical structures in an organic solvent, a hollow film with excellent mechanical strength and water permeability is formed. Methods have been proposed for producing filamentous membranes. However, since the membrane material of this hollow fiber membrane is made of polysulfone having a different chemical structure, its mechanical strength at high temperatures is significantly inferior. Furthermore, JP-A-56-3435
Publication No. 2 discloses that aromatic polysulfone is dissolved in a single polar organic solvent such as N-methylpyrrolidone to form a membrane forming solution, which is formed into a hollow fiber membrane by a wet membrane forming method, and then
A method has been proposed for producing hollow fiber membranes with improved strength and water permeability by heating in glycerin. However, when using this method, the mechanical properties at high temperatures of the hollow fiber membrane obtained, especially the bursting strength, are poor.

(Object of the Invention) The present invention was made to solve the above-mentioned problems in conventional hollow fiber membranes made of aromatic polysulfone, and has excellent mechanical strength, especially bursting strength, at high temperatures. The object of the present invention is to provide a method for manufacturing an aromatic polysulfone hollow fiber semipermeable membrane having high water permeability.

(Structure of the Invention) The method for producing an aromatic polysulfone hollow fiber semipermeable membrane according to the present invention comprises: a polar organic solvent that dissolves aromatic polysulfone; Aromatic polysulfone is dissolved in a mixed solvent with 100% carbon dioxide to form a membrane forming solution, and while the coagulating liquid is flowing out from the inner tube of the double tube type nozzle, the above membrane forming solution is applied to the outside from the outer tube of the double tube type nozzle. It is extruded into a coagulating liquid, the inner and outer surfaces are brought into contact with the coagulating liquid to remove the solvent, and then impregnated with a polyhydric alcohol to maintain the polyhydric alcohol in an amount of 10% by weight or more based on the weight of the aromatic polysulfone. After that, 1
It is characterized by heat treatment at a temperature of 00°C or higher.

In the present invention, the aromatic polysulfone typically has the following repeats.

However, X1 to X6 represent non-dissociable substituents such as alkyl groups such as methyl group and ethyl group, and halogens such as chlorine and bromine, and m, n, o, p and q represent O to 4. Indicates an integer. Generally, m, n, o, p and q are all 0
Polysulfone is easily available and is preferably used in the present invention. However, the polysulfone used in the present invention is not limited to the above.

In the method of the present invention, the membrane forming solution 1 containing aromatic polysulfone is prepared by dissolving the aromatic polysulfone in a mixed solvent of a polar organic solvent that dissolves the aromatic polysulfone and a non-solvent that does not dissolve the aromatic polysulfone. As the polar organic solvent, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, etc. are preferably used, and as the non-solvent, aliphatic polyhydric alcohols such as glycerin, ethylene glycol, propylene glycol, etc. Preferably used are polyalkylene glycono C such as diethylene glycol and polyethylene glycol, lower aliphatic alcohols such as methanol, ethanol, and isopropyl alcohol, cyclic ethers such as dioxane and tetrahydrofuran, and lower aliphatic ketones such as acetone and methyl ethyl ketone.

In the method of the present invention, the non-solvent in the membrane forming solution is
It is used to increase the water permeability of the resulting aromatic polysulfone hollow fiber membrane. The content of the non-solvent in the mixed solvent of the non-solvent and the polar organic solvent is not particularly limited as long as the mixed solvent obtained is uniform, but is usually in the range of 5 to 50% by weight. Generally, the higher the proportion of the non-solvent in the mixed solvent, the higher the water permeability of the resulting hollow fiber semipermeable membrane.

On the other hand, when a non-solvent is not used in the membrane-forming solution, the water permeability of the resulting membrane is about 1/2 to 1/10 that of a membrane obtained using a non-solvent as a component of the membrane-forming solution. However, increasing the proportion of non-solvent in the mixed solvent too much makes it difficult to dissolve polysulfone in the mixed solvent and may cause membrane defects such as pinholes to be formed in the resulting hollow fiber membrane. Undesirable.

The concentration of aromatic polysulfone in the membrane forming solution is usually 5 to 5.
35% by weight, preferably 10-30% by weight. 35
If it exceeds 5% by weight, the water permeability of the resulting semipermeable membrane will be too low for practical use, while if it is less than 5% by weight, the resulting membrane will have poor mechanical strength. be.

In the method of the present invention, the aromatic polysulfone is removed by extruding the above membrane forming solution into the coagulating liquid from the outer tube of the double tube nozzle while the coagulating liquid flows out from the inner tube of the double tube nozzle. The solvent is removed, solidified, and wet-formed into a hollow fiber membrane. Here, water is generally used as the coagulating liquid, but as described above, any solvent can be used as long as it does not dissolve the aromatic polysulfone but is miscible with the polar organic solvent. For example, , the above-mentioned non-solvent or a mixed solvent of this and water may be used. Further, even a solvent that dissolves aromatic polysulfone alone can be used as a coagulating liquid by mixing it with another solvent, as long as it does not dissolve polysulfone. Thereafter, the hollow fiber membrane thus obtained is further washed with water, if necessary, to completely remove the solvent.

Next, according to the method of the present invention, the hollow fiber membrane thus obtained is immersed in polyhydric alcohol to impregnate the membrane with polyhydric alcohol, and then pre-dried or not pre-dried. After holding a predetermined amount of polyhydric alcohol, heat treatment is performed at a predetermined temperature.

When the hollow fiber membrane is immersed in the polyhydric alcohol, the polyhydric alcohol is used as it is or as an aqueous solution. In the latter case, the concentration is preferably between 2 and 50
% by weight, preferably from 5 to 40% by weight. Such a polyhydric alcohol must not dissolve or swell the aromatic polysulfone used and must not easily volatilize during the heat treatment described below. Therefore, in the method of the present invention, for example, glycerin, ethylene glycol, propylene, etc. Glycol, aliphatic lower polyhydric alcohol such as butanediol, polyalkylene glycol such as diethylene glycol, triethylene glycol, dipropylene glycol, etc. are used, and glycerin and diethylene glycol are particularly preferably used.

In the method of the present invention, it is necessary that the hollow fiber membrane retains 10% by weight or more of the polyhydric alcohol based on the weight of the aromatic polysulfone during the heat treatment. This is because when the amount of polyhydric alcohol held in the hollow fiber membrane is less than 10% by weight based on the aromatic polysulfone, the water permeability of the hollow fiber membrane obtained by the subsequent heat treatment is extremely low. In order to make the hollow fiber membrane hold a predetermined amount of polyhydric alcohol in this way, after the hollow fiber membrane is impregnated with the polyhydric alcohol, the hollow fiber membrane is pre-dried if necessary. The temperature for this preliminary drying is about 5 to 50°C, but usually room temperature is sufficient.

The temperature of the heat treatment of the hollow fiber membrane retaining the polyhydric alcohol is 100° C. or higher, and a temperature that is 10° C. lower than the glass transition temperature of the aromatic polysulfone used. When the heat treatment temperature is lower than 100°C, a hollow fiber membrane with excellent mechanical strength cannot be obtained. On the other hand, when the heat treatment is performed at an excessively high temperature, the polyvalent Since alcohol evaporates more than necessary, a hollow fiber membrane with excellent water permeability cannot be obtained. The heating time is not particularly limited, but is usually about 1 minute to 10 hours, preferably 2 hours.
It takes about an hour.

In this way, the aromatic polysulfone hollow fiber membranes according to the invention are obtained as dry membranes and can be stored, transported or assembled into modules as such dry membranes. but,
When using it, it is desirable to immerse the hollow fiber membrane in an organic solvent with low surface tension that is compatible with water, such as lower alcohols such as methanol, ethanol, and propyl alcohol, or aqueous solutions thereof. The polyhydric alcohol in the film diffuses into the lower alcohol or its aqueous solution and is removed from the solvent, and these lower alcohols or its aqueous solution are included in the film.
This is because they are easily replaced by water during membrane treatment of aqueous liquids. Note that the evaluation of membrane properties described below was performed on the hollow fiber membrane treated with lower alcohol in this manner.

(Effects of the Invention) According to the method of the present invention, as described above, after a hollow fiber membrane is wet-formed with a membrane-forming solution containing aromatic polysulfone, the membrane is immersed in polyhydric alcohol, and a predetermined amount of polysulfone is By retaining the alcohol and heat-treating it at a predetermined temperature, it is possible to obtain a hollow fiber membrane that has excellent mechanical strength, particularly burst strength, at high temperatures without impairing water permeability.

(Examples) The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples in any way. In the following, the characteristics of the hollow fiber membrane were determined as follows. Pure water was permeated through the membrane at a pressure of 1 kg/cd and a temperature of 25° C., and the measured value of the water permeation rate after 15 minutes was defined as the pure water permeation rate. In addition, the removal rate of the membrane is as follows: when an aqueous solution of polyethylene glycol (average molecular weight 20,000) is applied at an average pressure of 1 kg/cJ
, at a temperature of 25° C., and the measured value after 15 minutes was taken as the removal rate.

Further, the porosity of the membrane was calculated from the cross-sectional area of the membrane and the weight per unit length using the following formula.

(1-(membrane weight/aromatic polysulfone density/membrane cross-sectional area)
)X100(%) Moreover, the burst strength was defined as the pressure at which water pressure was applied from the inside of the membrane and the membrane burst.

Example I Aromatic polysulfone having a repeating unit represented by the following formula (m) was added to a mixed solvent of 63 parts by weight of N-methyl-2-pyrrolidone and 19 parts by weight of diethylene glycol.
P-1700 (manufactured by Union Carbide) 18 parts by weight was dissolved to obtain a membrane forming solution.

This film-forming solution is extruded from the outer tube of the double-walled nozzle into water at a temperature of 25°C, and the inner tube of the double-walled nozzle is also extruded at a temperature of 25°C.
Water at 5°C is poured out, the polysulfone is removed from the solvent, and solidified.
A hollow fiber semipermeable membrane was obtained.

Next, this wet film was immersed for 2 hours in a glycerin aqueous solution with a concentration of 20% by weight at a temperature of 20°C, and then pre-dried at 20°C to retain 45% by weight of glycerin based on the weight of the polysulfone. Thereafter, this membrane was heated at a predetermined temperature for 1 hour to obtain a hollow fiber membrane according to the present invention. Its characteristics are shown in Table 1. It is clear that the burst strength of the hollow fiber membrane according to the present invention is significantly improved by heat treatment.

Furthermore, the temperature dependence of bursting strength was measured for membrane B, and the results are shown in FIG. The hollow fiber membrane obtained by the present invention has high burst strength even at high temperatures.

Comparative Example 1 In Example 1, except that the heating temperature was 180°C,
Polysulfone hollow fiber membrane E was obtained in the same manner as in Example 1. The properties of this membrane are shown in Table 1 together with the properties of the hollow fiber membrane F itself after wet membrane formation. When the heat treatment temperature is too high, the resulting membrane has high burst strength but extremely low water permeability. On the other hand, membranes without polyhydric alcohol treatment and heat treatment have significantly lower burst strength.

Example 2 Aromatic polysulfone (containing a repeating unit represented by the following formula (IV)) was added to a mixed solvent consisting of 65 parts by weight of dimethylacetamide and 16 parts by weight of polyethylene glycol (molecular weight 400).
200P (manufactured by IC1) was dissolved to prepare a membrane forming solution, and coagulated in the same manner as in Example 1 to obtain a hollow fiber semipermeable membrane.

This wet film was immersed in a diethylene glycol aqueous solution of a predetermined concentration at a temperature of 20° C. for 1 hour to retain 15 to 98% by weight of diethylene glycol based on the weight of the polysulfone. Thereafter, this membrane was heated at a temperature of 110° C. for 2 hours to obtain a hollow fiber membrane according to the present invention. The properties are shown in Table 2. The hollow fiber membrane according to the present invention has high burst strength.

Comparative Example 2 In Example 2, the characteristics of the film itself after wet film formation were
As shown in the table, when polyhydric alcohol treatment and heat treatment are not performed, the bursting strength of the resulting membrane is low.

Example 3 In a mixed solvent of 70 parts by weight of N,N-dimethylformamide and 13 parts by weight of 2-propylene glycol,
Aromatic polysulfone having a repeating unit represented by t/) (P-3500 manufactured by Union Carbide) 17
A film-forming solution was obtained by dissolving parts by weight.

30% by weight of N,N-dimethylformamide as coagulation liquid
Polysulfone was coagulated by removing the solvent in the same manner as in Example 1, except that an aqueous solution containing .

Next, this wet membrane was immersed in an aqueous glycerin solution having a concentration of 30% by weight at 20°C for 3 hours, and then pre-dried at 20°C for 2 days to retain 100% by weight of glycerin based on the weight of the polysulfone.

A bundle of 1,000 hollow fiber membranes was placed in a polysulfone case, and both ends were cast with epoxy resin to produce a hollow fiber membrane module.

The module was heated at a temperature of 140° C. for 1 hour, after which ethanol was circulated through the hollow fiber membrane and then water was circulated to replace the solvent in the membrane with water.

The characteristics of the hollow fiber membrane module manufactured in this way are as follows: pure water permeation rate: 42012/rd・hour・kg/cI
+! , 0.5% by weight polyethylene glycol (molecular weight 2
0000), the removal rate was 90%. In addition, when pressure was applied to this module from the inside of the hollow fiber membrane, 25
kg/cm! The membrane was destroyed by the pressure.

Comparative Example 3 In Example 3, the hollow fiber membrane obtained by wet membrane formation was assembled into a polysulfone case as it was to produce a module. This module has a pure water permeability rate of 440J! /m・hour・kg/-10.5% by weight The removal rate of polyethylene glycol was 89%, but when pressure was applied to this module from the inside of the hollow fiber membrane, the membrane was removed at a pressure of 18 kg/cd. Destroyed.

[Brief explanation of drawings]

The drawing is a graph showing the temperature dependence of the burst strength of a hollow fiber membrane according to the method of the present invention and a hollow fiber membrane as a comparative example.

Claims (3)

[Claims] (1) a polar organic solvent that dissolves aromatic polysulfone;
Aromatic polysulfone is dissolved in a mixed solvent with 5 to 50% by weight of a solvent that is miscible with this solvent but does not dissolve aromatic polysulfone to form a film forming solution, and the coagulated liquid is flowed out from the inner pipe of a double pipe nozzle. At the same time, the above membrane forming solution is extruded from the outer tube of the double tube type nozzle into the outer coagulating liquid, the inner and outer surfaces are brought into contact with the coagulating liquid to remove the solvent, and then impregnated with polyhydric alcohol, After retaining the polyhydric alcohol at 10% by weight or more based on the weight of the aromatic polysulfone, 10
A method for producing an aromatic polysulfone hollow fiber membrane, the method comprising heating to a temperature of 0° C. or higher. (2) The method for producing an aromatic polysulfone hollow fiber membrane according to claim 1, wherein the polyhydric alcohol is a dihydric alcohol having 4 or less carbon atoms. (3) The method for producing an aromatic polysulfone hollow fiber membrane according to claim 2, wherein the dihydric alcohol is glycerin.