METHOD FOR PRODUCING POLYPHENYLSULFONE HOLLOW FIBER MEMBRANE FOR HUMIDIFYING MEMBRANES

Abstract

The obtained hollow fiber membrane has high water permeability, and has, when used as a humidifying membrane, a linear relationship between supply humidity and humidification amount. Therefore, the hollow fiber membrane is effectively used, for example, as a humidifying membrane for fuel cells. The method for producing a polyphenylsulfone hollow fiber membrane according to present invention can provide a humidifying membrane that suppresses segregation and crosslinking of hydrophilic polymers associated with the operation of the humidifying membrane, and that prevents the deterioration of humidification performance due to the operation. In addition, the producing method of the present invention can produce a polyphenylsulfone hollow fiber membrane for humidifying membranes, wherein the hollow fiber membrane has high water permeability, and has, when used as a crosslinked humidifying membrane, a linear relationship between water vapor supply humidity and humidification amount.

Claims

1-5. (canceled)

6. A method for producing a polyphenylsulfone hollow fiber membrane for humidifying membranes, the method comprising subjecting a hollow fiber membrane to washing in pressurized water at 121 C. for 0.5 hours or more, following a crosslinking treatment by heating at 160 to 180 C. for 5 to 12 hours, wherein the hollow fiber membrane is obtained by a wet spinning method or a dry-wet spinning method using a spinning dope comprising polyphenylsulfone, hydrophilic polyvinylpyrrolidone, and a water-soluble organic solvent solution.

7. The method for producing a polyphenylsulfone hollow fiber membrane for humidifying membranes according to claim 6, wherein the membrane is used as a humidifying membrane for fuel cells.

8. A polyphenylsulfone hollow fiber membrane for humidifying membranes produced by the method according to claim 6, which has, when used as a crosslinked humidifying membrane, a linear relationship between water vapor supply humidity and humidification amount.

9. The polyphenylsulfone hollow fiber membrane for humidifying membranes according to claim 8, which is used for a fuel cell.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0017] FIG. 1: A graph showing the relationship between Wet-In relative humidity and initial water vapor permeability coefficient for the polyphenylsulfone hollow fiber membranes obtained in the Example (.circle-solid.) and Comparative Example 1 (.square-solid.).

[0018] FIG. 2: A graph showing the relationship between Wet-In relative humidity and initial humidification performance ratio for the polyphenylsulfone hollow fiber membranes obtained in the Example (.circle-solid.) and Comparative Example 1 (.square-solid.).

EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0019] Polyphenylsulfone resin refers to one having a repeating unit represented by the following formula:

##STR00001##

that is, one having biphenylene group and no isopropylidene group. In practice, commercial products, such as produced by Solvay Specialty Polymers, can be used as they are.

[0020] The spinning dope comprising polyphenylsulfone as a film-forming component is prepared by compounding polyphenylsulfone with a water-soluble organic solvent of hydrophilic polyvinylpyrrolidone. Examples of the water-soluble organic solvent include aprotic polar solvents, such as dimethylacetamide [DMAc], dimethylformamide [DMF], N-methyl-2-pyrrolidone [NMP], and dimethylsulfoxide [DMSO].

[0021] The spinning dope used is one having a compounding ratio in which polyphenylsulfone accounts for about 17 to 23 wt. %, preferably about 19 to 22 wt. %, and hydrophilic polyvinylpyrrolidone having various molecular weights accounts for about 8 to 20 wt. %, preferably about 11 to 18 wt. %. If hydrophilic polyvinylpyrrolidone is used at a ratio less than this range, water vapor permeability decreases. In contrast, if hydrophilic polyvinylpyrrolidone is used at a ratio higher than this range, the film-forming solution becomes unstable, so that spinning cannot be performed.

[0022] The formation of a polyphenylsulfone hollow fiber membrane using such a spinning dope is performed by a wet spinning method or a dry-wet spinning method, preferably a dry-wet spinning method. In this case, water, a mixed solvent of water and a water-soluble organic solvent, specifically an aprotic polar solvent mentioned above, or the like is used as the core liquid. The spun hollow fiber product is coagulated in an aqueous coagulation bath (gelation bath), typified by water, and then washed in pressurized water at 121 C. for about 0.5 hours or more, preferably about 1 to 5 hours. Subsequently, a heat treatment is performed in a constant temperature bath at about 160 to 180 C., preferably 165 to 175 C., for about 5 to 12 hours, preferably 6 to 10 hours. When the heating temperature is lower than the above range, or when the heating time is shorter than the above range, the desired humidification performance cannot be obtained.

EXAMPLES

[0023] The following describes the present invention with reference to Examples.

Example

[0024] (1) An uniform spinning dope at room temperature comprising 20 parts by weight of polyphenylsulfone (RADEL R-5000, produced by Solvay Specialty Polymers), 15 parts by weight of hydrophilic polyvinylpyrrolidone (K-30G, produced by ISP), and 65 parts by weight of dimethylacetamide was discharged from a double annular nozzle into a water coagulation bath by a dry-wet spinning method, while using water as the core liquid. Then, washing was performed in pressurized water at 121 C. for 1 hour, followed by heating in a constant temperature bath at 170 C. for 8 hours to perform a crosslinking treatment, thereby obtaining a porous polyphenylsulfone hollow fiber membrane having an outer diameter of 1.0 mm, an inner diameter of 0.7 mm, and a pore diameter of 2.2 nm. Here, the pore diameter indicates the Knudsen diffusion average diameter based on the number standard of pores measured using a nano-perm porometer (produced by Seika Digital Image).

[0025] The obtained hollow fiber membrane was inserted into a SUS tube mini-module having an inner diameter of 4 mm, both ends of the mini-module were sealed with epoxy resin, and a hollow fiber membrane module for measurement was produced so that the effective length of the hollow fiber membrane was 170 mm. While supplying dry air at a temperature of 80 C. and a relative humidity of 2% from one end of the hollow fiber membrane module to the hollow part of the hollow fiber membrane at a linear velocity of 13 m/s, water vapor at a temperature of 80 C. was supplied to the outer surface of the hollow fiber membrane at a linear velocity of 3 msec. Here, the relative humidity of the supplied water vapor was 20%, 40%, 60%, 80% or 90%, and the amount of water permeating from the outside to the inside of the hollow fiber was determined. The determined amount of permeating water was divided by the hollow fiber inner surface area and the water vapor partial pressure difference (pressure difference between the inner and outer sides of the hollow fiber) to determine the water vapor permeability coefficient (velocity).

Comparative Example 1

[0026] In the Example, the dry-wet spun membrane was washed in pressurized water at 121 C. for 1 hour, and then heated in a constant temperature bath at 40 C. for 8 hours, thereby obtaining a porous polyphenylsulfone hollow fiber membrane having an outer diameter of 1.0 mm, an inner diameter of 0.7 mm, and a pore diameter of 2.4 nm. The porous polyphenylsulfone hollow fiber membrane was used to produce a mini-module in the same manner as described above.

Comparative Example 2

[0027] In the Example, the dry-wet spun membrane was crosslinked in a 0.1% ammonium persulfate aqueous solution at 121 C. for 1 hour, and then heated in a constant temperature bath at 40 C. for 8 hours, thereby obtaining a porous polyphenylsulfone hollow fiber membrane having an outer diameter of 1.0 mm, an inner diameter of 0.7 mm, and a pore diameter of 2.4 nm. The porous polyphenylsulfone hollow fiber membrane was used to produce a mini-module in the same manner as described above.

[0028] The membranes obtained in the Example and Comparative Example 1 were each left alone in a constant temperature bath heated to 130 C. for 120 hours, and used to produce a mini-module in the same manner as described above. While supplying dry air at a temperature of 80 C. and a relative humidity of 2% from one end of the hollow fiber membrane module to the hollow part of the hollow fiber membrane at a linear velocity of 13 m/s, water vapor at a temperature of 80 C. and a relative humidity of 90 to 20% was supplied to the outer surface of the hollow fiber membrane at a linear velocity of 3 m/s, and the water vapor permeability coefficient was measured.

[0029] The obtained relationship between Wet-In relative humidity and water vapor permeability coefficient is shown in the following table and FIG. 1, which illustrates the table, and the relationship between Wet-In relative humidity and humidification performance ratio (ratio when the water vapor permeability coefficient at a relative humidity of 90% is 100%) is shown in the following table and FIG. 2, which illustrates the table.

TABLE-US-00001 TABLE Example Comparative Example 1 Water vapor Humidifi- Water vapor Humidifi- Wet-In permeability cation permeability cation relative coefficient performance coefficient performance humidity (g/min/cm.sup.2@ ratio (g/min/cm.sup.2@ ratio (% RH) MPa) (%) MPa) (%) 90 0.0969 100.0 0.0570 100.0 80 0.0816 84.2 0.0450 79.0 60 0.0542 55.9 0.0279 48.9 40 0.0352 36.3 0.0185 32.4 20 0.0173 17.9 0.0099 17.4

[0030] Further, when the water vapor permeability coefficient at a relative humidity of 90% of a mini-module using a porous polyphenylsulfone hollow fiber membrane before heat treatment was 100%, the humidification performance at 130 C. after 120 hours was 100% in the Example, and 85% relatively in Comparative Examples 1 and 2.