Liquid purification or separation – Filter – Material
Patent
1983-04-20
1989-04-18
Spear, Frank
Liquid purification or separation
Filter
Material
21050041, 264 459, B01D 1300
Patent
active
048224898
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to an aromatic polysulfone type resin hollow fiber membrane with a novel structure, which is useful as an ultrafiltration membrane and is excellent in water permeability, mechanical strength and burst strength, and also relates to a process for producing the same. More particularly, the present invention is concerned with an aromatic polysulfone type resin hollow fiber membrane with a five-layer structure of an outer surface layer, an outer void layer, an intermediate layer, an inner void layer and an inner surface layer, which is excellent in heat resistance, acid resistance, alkali resistance, chemicals resistance and has an improved mechanical strength as well as a high water permeability, and also is concerned with a process for producing the same.
DESCRIPTION OF THE PRIOR ART
There have hitherto been published many papers concerning aromatic polysulfone membranes and aromatic polyether sulfone membranes, but a limited number of them disclose the structure of such membranes. A membrane comprising a surface layer and a void layer as the support layer is disclosed in the specification of U.S. Pat. No. 3,691,068 assigned to Amicon Corporation as well as in Journal of Applied Polymer Science, 20, 2377-2394 (1976), and ibid 21, 165-180 and 1883-1900 (1977) in which the reporter is Gulf South Research Institute. A hollow fiber membrane disclosed in the U.S. Pat. No. 3,691,068 specification has a dense surface layer on the inner surface thereof but has no such a layer on the outer surface thereof. The hollow fiber membrane of this prior art has a plurality of voids which opens at the outer surface of the memrane, said voids are being defined by portions where the polymer is deficient, and each having a size as large as 10 .mu.m or more. The hollow fiber membrane with such a structure has such drawbacks that:
1 they are poor in mechanical strength;
2 they are impossible to back-wash; and
3 they are liable to be plugged or fouled. reverse osmosis membrane, and each of the membranes has, in both surface portions thereof, a number of pores of 250 .ANG. to 0.44 .mu.m in average diameter. The water permeability of such membranes is at most 1.3 m.sup.3 /m.sup.2.day.atm and, hence, of little practical use in ultrafiltration.
Each of the aromatic polysulfone hollow fiber membrane and the aromatic polyether sulfone hollow fiber membrane disclosed in the specification of U.S. Pat. No. 4,286,015 has such a structure that the membrane comprises inner and outer surface layers, inner and outer void layers and an intermediate layer. However, such membranes are mechanically weak, and in addition, each has a poor water permeability because the intermediate layer of the membrane has a structure insufficient in communication. Further, in these hollow fiber membranes, the thickness ratio of the inner void layer to the outer void layer is larger than 1.5, that is, the inner void layer has a thickness larger than that of the outer void layer. This means that the amount of the polymer is relatively large in the outer portion of the membrane and relatively small in the inner portion of the membrane. Therefore, such a hollow fiber membrane has a high permeation resistance in the proximity of the outer surface thereof, and further, is poor in mechanical strength against the pressure from the inside of the membrane.
As described hereinbefore, each of the conventional aromatic polysulfone membrane and the aromatic polyether sulfone membrane is of little practical use because of its poor mechanical strength and low water permeability and, hence, there has been a strong demand for development of a hollow fiber membrane having an improved mechanical strength as well as a high water permeability.
DISCLOSURE OF THE PRESENT INVENTION
A hollow fiber membrane according to the present invention has a structure which is basically similar to that of a hollow fiber membrane disclosed in the specification of U.S. Pat. No. 4,286,015. However, the difference of the hollow fiber membrane of the presen
REFERENCES:
patent: 4286015 (1981-08-01), Yoshida et al.
patent: 4385094 (1983-05-01), Tanaka et al.
Hashino Yasuo
Nohmi Takashi
Asahi Kasei Kogyo Kabushiki Kaisha
Spear Frank
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