JPH0621373B2 - Porous hollow fiber membrane and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Object of the Invention) The present invention relates to a porous hollow fiber membrane and a method for producing the same. In recent years, needs for functional membrane materials used in the industrial and medical fields have been increasing, and research and development have been actively conducted. For example, in the industrial field, UF and RO for desalination of seawater, production of pure water, uranium enrichment, food refining / concentration, oil / water separation, helium enrichment recovery, oxygen enrichment, methane / carbon dioxide separation, etc. Membranes and gas separation membranes have been developed, and in the medical field, artificial kidneys, artificial lungs, blood / plasma separation membranes, capsule membranes for local drug administration, artificial blood vessels, antithrombotic catheters, etc. have been developed. Although some of these have been put to practical use, satisfactory characteristics have not necessarily been obtained.

The ones that have been used for membrane separation until now are typically cellulose-based porous membranes such as cellulose acetate and ethyl cellulose, porous membranes of engineering plastics such as polysulfone, amide-based and imide-based porous membranes, and polypropylene. A porous film, a fluorine-based porous film such as tetrafluoroethylene, or the like can be used.

Of these, ethyl cellulose is used as an oxygen-enriched membrane material because it has a higher oxygen permeability than other material groups and has a relatively high oxygen / nitrogen selective permeability. On the other hand, polysulfone and polyimide are used as a membrane material for hydrogen separation and helium concentration / recovery because they have a relatively low gas permeability but have a high selective permeability for hydrogen and carbon monoxide. In addition, regenerated cellulose and polypropylene porous membranes are used for artificial kidneys, and tetrafluoroethylene resin porous membranes are preferably used for applications requiring solvent resistance such as excess of organic solvent.

As described above, various applications have been made depending on the characteristics such as gas permeation characteristics, solvent resistance, mechanical characteristics and workability of the material. Under such a circumstance, poly (2,6 dimethylphenylene oxide) (hereinafter referred to as PPO) is one of the materials attracting attention as a gas separation membrane material. PPO is a material that has excellent gas permeability, high mechanical strength, high heat resistance, and high solvent resistance, and exhibits properties equal to or higher than those of engineering plastics such as polysulfone.

However, the excellent solvent resistance is rather a problem in processing. That is, it was difficult to arbitrarily process the solution. USP 3,709,774
And Ger.off.2153,646, a porous film was obtained by a mixed solvent system in which a poor solvent as a swelling agent was added to a chlorine-based solvent which is a good solvent but difficult to obtain a porous film by itself. There is. However, with these systems, it is difficult to obtain a porous film having excellent strength, and since the coagulant system is limited to methanol and the like, it is difficult to control the structure precisely and widely.

On the other hand, in recent years, attempts have been made to modify PPO to improve solubility to improve workability and gas permeation characteristics.

For example, JP-A-57-117321 is halogenated or amination of PPO at the benzyl position, JP-A-58-5008 is a prenylation at the benzyl position, JP-A-58-216703 is a chlorosulfonated aryl arylated, JP-A-58-58703. -39
304 is a brominated ring or benzyl position, JP-A-59-22
2203 is amino-siliconized, but none of them satisfy both the selective permeability and the permeation rate. On the other hand, as a method for increasing the permeation rate while maintaining the selective permeation, an attempt to obtain an asymmetric pore size membrane mixed with silicone oil has been made in JP-A-58-95538, but sufficient selective permeation is obtained. I have not caught up with. JP-A-60-41524, 60-51524,60
In the case of -51525, PPO is brominated to improve the solubility, and then an asymmetric pore size membrane is formed, followed by amine cross-linking to insolubilize the PPO to obtain satisfactory properties in both permeability and selectivity.

Further, it is preferable in terms of good solvent resistance. However, many steps such as solubilization-film formation-insolubilization are required, and active points are likely to remain in the solubilization and insolubilization steps, which may cause deterioration with time.

(Structure of the Invention) As a result of intensive investigations on such problems of the prior art, the present inventors forcedly dissolved unmodified PPO using a nitrogen-containing cyclic compound as a solvent while heating it at a high temperature, and at that temperature. By extruding into a hollow fiber shape in a coagulation bath while maintaining the above, coagulation and solvent extraction, a porous hollow fiber membrane with excellent permeability, selectivity, solvent resistance, and mechanical strength is obtained. They have found that they can be obtained by a simple process, and have reached the present invention.

When using the porous hollow fiber membrane of the present invention for gas separation applications,
Although sufficient selectivity and permeability can be obtained as they are, it is also possible to form a composite membrane by taking advantage of good solvent resistance in order to obtain higher selectivity. In addition, by controlling the pore size by changing the spinning conditions, it can be applied to a reverse osmosis membrane or an ultrapermeability membrane, or can be used as a support for a liquid membrane by utilizing solvent resistance. .

PPO used in the present invention is obtained by polymerizing 2,6-dimethylphenol by an oxidative coupling reaction using a cuprous chloride-pyridine complex as a catalyst, and has a structural formula; Is a poly (2,6-dimethylphenylene oxide) having a repeating unit represented by:

Solvents for PPO include N.I. Formyl piperidine N.I. Nitrogen-containing cyclic compounds such as formylmorpholine and N-methyl-2-pyrrolidone, amide solvents such as dimethylformamide and dimethylacetamide, and chlorine-based hydrocarbons such as tetrachloroethane chloroform, chlorobenzene, and O-dichlorobenzene can be used alone or The mixture can be used, but a nitrogen-containing cyclic compound is preferably selected. Particularly preferably, N-methyl-2-pyrrolidone is selected.

The feature of the present invention resides in that PPO is formed into a porous hollow fiber membrane, and further, either or both of the outer surface and the inner surface of the hollow fiber is a dense surface, and each of the thick portions has a dense surface. It has continuous sponge-like holes and finger-like or void-like holes oriented substantially in the radial direction of the hollow fiber on the surface. In order to arbitrarily form such a structure, it is preferable to use a nitrogen-containing cyclic compound as a solvent.

The solution concentration is preferably 10 to 50%, particularly 20 to 40%.
When a solution is obtained, it is necessary to dissolve it while heating it at room temperature or higher. At this time, care must be taken so that the decomposition and reaction of PPO and the solvent do not occur. Generally, about 100 ° C. is suitable, but it is not particularly limited.

The solution thus obtained is extruded from the outer tube of the double-tube nozzle into the coagulation bath, at which time the temperature of the solution must be maintained above the gelling temperature of the solution and below the boiling point of the solvent. I have to. Below the gelling temperature, it is difficult to obtain a hollow fiber membrane having practical strength, and above the boiling point, bumping of the solvent occurs, making it difficult to control the membrane structure. However, by controlling the solution temperature within the temperature range from the gelation temperature of the solution to the boiling point of the solvent, it is possible to control the dense surface thickness, porosity, pore shape, hollow fiber membrane strength, etc. It is possible.

From the inner tube of the double tube nozzle, the core liquid is allowed to flow out in order to form the hollow of the porous hollow fiber or to control the state of the inner surface. The double-tube nozzle may be immersed in the coagulation bath, or may be above the liquid surface of the coagulation bath, but when it is located above the liquid surface, a chimney or the like may be used to suppress the evaporation amount of the solvent. The state of the outer surface of the hollow fiber can be controlled by, for example, inhaling the chimney to promote evaporation.

A non-solvent miscible with the solvent is used as the coagulant. When the nitrogen-containing cyclic compound is used as a solvent, water, alcohols and mixtures thereof are used. By changing the type and temperature composition of the coagulant, the thickness of the dense surface of the porous hollow fiber membrane, the porosity, the shape of the pores, the strength of the hollow fiber membrane, etc. can be controlled. In addition, the structure and physical properties of the film can be controlled by adding a solvent or an inorganic salt to the coagulant. The core liquid is also selected from the same viewpoint as the coagulation bath.

The solidified hollow fiber is further washed with water to extract the solvent and fix the membrane structure. At this time, the hot water treatment can accelerate the extraction of the solvent and stabilize the film structure and characteristics.

The hollow fiber that has been subjected to solvent extraction is further dried and heat-treated using hot air, a metal roll, or the like as a heat medium. The drying temperature is preferably not higher than the boiling point of the non-solvent contained in the hollow fiber after solvent extraction. The heat treatment is performed below the heat distortion temperature of PPO.

By replacing the non-solvent contained in the hollow fiber with another non-solvent before performing the drying / heat treatment, the shrinkage rate of the hollow fiber during the drying / heat treatment is changed, and as a result, the membrane characteristics are improved. It is possible to control.

Hereinafter, the present invention will be further described with reference to examples.

Example 1 35 parts by weight of PPO and 65% by weight of N-methyl-2-pyrrolidone
Then, the mixture was stirred and dissolved while heating to about 120 ° C. to obtain a uniform solution. While extruding into the water of 31 ° C from the outer pipe (outer diameter 2 mm, inner diameter 1 mm) of the double pipe nozzle heated to 120 ° C while maintaining the temperature of this solution, at the same time, the inner pipe (diameter 0.5 mm)
A mixture of N-methyl-2-pyrrolidone / water (9: 1) was discharged as a core liquid to solidify while forming a hollow. The distance between the nozzle and the water surface was kept at 4 cm, and the evaporation of the solvent was controlled using a chimney.

Continue to introduce into water at 41.5 ° C for solvent extraction,
Further, it was wound on a bobbin in water.

Then immerse the bobbin in isopropyl alcohol for about 4
Extraction and solvent replacement were performed for 8 hours. The obtained porous hollow fiber was dried in the order of 60 ° C. and 70 ° C. for 150 seconds each, and then heat-treated at 100 ° C. for 150 seconds.

Table 1 shows the measurement results of the basic substances. Scanning electron micrographs of the cross sections of the obtained porous hollow fibers are shown in FIGS. 1, 2 and 3.

(Effect of the invention) According to the present invention, gas and liquid permeability and selectivity are excellent,
A porous hollow fiber membrane having excellent solvent resistance and good mechanical strength can be obtained by a simple process.

Its application range is diverse, including gas separation membranes, reverse osmosis membranes,
Typical examples are ultrapermeabilization membranes and liquid membrane supports. Further, since it has excellent solvent resistance, radiation resistance, and plasma resistance, it can be used as a support for a composite membrane using various methods, and can be applied to a wide range of products.

[Brief description of drawings]

1, 2 and 3 are scanning electron micrographs replacing the drawings showing the shape of the fiber. FIG. 1 is a scanning electron micrograph of a cross section of a PPO porous hollow fiber membrane, with a magnification of 100 times. FIG. 2 is an enlarged view near the inner surface of the hollow fiber membrane shown in FIG.
It is 000 times. FIG. 3 is an enlarged view of the vicinity of the outer surface of the hollow fiber membrane shown in FIG. 1, and the magnification is 5,000 times.

Claims (4)

[Claims] 1. A structural formula; One or both of the outer surface and the inner surface of the porous hollow fiber membrane made of poly (2,6-dimethylphenylene oxide) having a repeating unit represented by The porous hollow fiber membrane, wherein the thick portion is porous in which the pore diameter is continuously changed on each surface. 2. A structural formula; A poly (2,6-dimethylphenylene oxide) having a repeating unit represented by is dissolved in a nitrogen-containing cyclic compound, and the solution is heated while being extruded from an outer tube of a double tube nozzle into a coagulation bath, Outflow the core fluid from the inner tube,
Claim 1 characterized in that coagulation and desolvation are performed.
Item 8. A method for producing a porous hollow fiber membrane according to item. 3. The porous hollow membrane according to claim 2, wherein the solution is extruded while maintaining the temperature above the gelling temperature of the solution and below the boiling point of the nitrogen-containing cyclic compound. Production method. 4. The method for producing a porous hollow fiber membrane according to claim 2, wherein the nitrogen-containing cyclic compound is N-methyl-2-pyrrolidone.