Process for preparing modified porous membrane

Details Process for preparing modified porous membrane Process for preparing modified porous membrane

1990-12-11

1993-12-28

Spear, Frank

Liquid purification or separation

Processes

Liquid/liquid solvent or colloidal extraction or diffusing...

210651, 210654, 21050041, 264 41, B01D 7168

Patent

active

052736571

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a process for preparing a membrane comprised of an aromatic sulfone resin which has excellent heat and solvent resistance and is used for a selective permeability. The membrane of the present invention can be used for the separation of substances, for example, as a separating membrane and as a diaphragm for batteries.
2. Description of the Prior Art
The method of separating a substance through the use of a porous membrane having a selective permeability is generally called "membrane separation" and is widely utilized in various fields including desalination of sea water, production of pure water used in the electronics industry, processes for the food industry and treatment of industrial waste water. With diversification of the use of these membranes, a permselective membrane usable at a higher temperature in a wider pH range and capable of withstanding various kinds of chemical substances has become desired in the art. A porous membrane utilizing an aromatic polysulfone polymer as the membrane material and having excellent chemical resistance has been proposed in Japanese Patent Laid-Open No. 16381/1979. This porous membrane has been used as a permselective membrane or as a base membrane of a composite membrane. The above-described aromatic polysulfone polymer is characterized as being soluble in an aprotic polar organic solvent, etc. Thus a porous membrane could easily be prepared by dissolving said polymer in an organic solvent and forming a film from the resultant solution. Porous membranes may be made by a process called "phase conversion." Phrase conversion comprises processing a polymer solution by casting or the like and immersing the processed solution in a nonsolvent of said polymer, which is compatible with the solvent of said polymer solution, and allowing said solution to gel. By such a process it is possible to prepare a porous membrane having both a pore diameter suitable for the separation of the desired substance as well as asymmetric (anisotropic) membrane structure wherein the dense portion of the membrane surface (called an active layer where the separation is conducted) is supported by a structure called a porous layer comprising a network structure containing macrovoids, or the like which occupies a major portion of the membrane structure. The phrase conversion process is thus a very desirable process and has been used extensively for preparing membranes.
The aforedescribed asymmetric membrane structure has very excellent features. In particular, the dense layer, which is provided with minute pores having a separatory function, is very thin and has a very high permeability to a liquid to be separated. The membrane also has a very high mechanical strength since the thin dense layer is supported by the thicker porous layer. This porous layer generally has no separatory function. These features ensure easy handling of the membrane in practical use.
Further, the phase conversion method is used to form a porous membrane partly because the structure and pore diameter of the porous membrane can be adjusted according to the substance to be separated and the separation system by varying several parameters, such as the composition of the polymer solution, the composition of the immersion bath and the solvent to be evaporated [see "Maku ni yoru Bunriho (Method of Separation by Means of Membrane) edited by Bunji Hagiwara and Koichi Hashimoto, pp. 25-41, Kodansha Scientific (1974)].
For the production of porous membranes having enhanced characteristics, proposals have been made to use a membrane material comprising a polymer which barely dissolves or swells in an organic solvent; for example, engineering plastics having excellent heat and solvent resistances, such as a fluoropolymer described in Japanese Patent Publication No. 25332/1983, and a polyphenylene sulfide described in Japanese Patent Laid-Open Nos. 202659/1985 and 213813/1987. Since there is no solvent capable of completely dissolving these polymers,

REFERENCES:
patent: 4110265 (1978-08-01), Hodgdon
patent: 4711907 (1987-12-01), Sterzel et al.
patent: 4942091 (1990-07-01), Umezawa et al.

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