polymeric membranes for reverse osmosis high flow of water and high salt rejection and method of preparing such membranes

摘要

1391559 Reverse osmosis membranes MONTECATINI EDISON SpA 1 Jan 1973 [30 Dec 1971] 59662/72 Heading B5B An isotropic reverse osmosis membrane of a polypiperazinamide having recurring units of the general formula is disclosed, where R is an organic substituent of the piperazine ring, x is from 1 to 8 and Y is an oxygen or sulphur atom. Preferably R is C 1 to C 4 alkyl, especially methyl or ethyl and x = 1 or 2. Specified polypiperazinamides include poly (2-methyl piperazin-thiofurazanamide), poly (2 - methylpiperazin - furazanamide), poly (trans - 2,5 - dimethylpiperazin - thio furazanamide), and poly (trans - 2,5 - dimethyl piperazin-furazanamide). A solution of the polypiperazinamide in an organic water soluble aprotic polar solvent is spread preferably at room temperature, on a smooth surface to form a film suitably of 0À002 to 0À2 cm. thickness, a membrane made therefrom by surface evaporation of the solvent, e.g. at 70‹ to 200‹ C., especially 80‹ to 180‹ C., for from 1 min. to 3 hours, especially 3 to 30 mins. and the membrane congulated by immersion in a coagulating bath, suitably water or an aqueous saline solution, e.g. of sodium or calcium chloride or magnesium sulphate, or alternatively mixtures of water with methanol, ethanol or isopropyl alcohol. The congulating liquid temperature is suitably 0‹ to 30‹ C. especially 0‹ to 5‹C. Specified solvents include dimethylformamide, dimethyl-acetamide, dimethyl sulphoxide, N- methylpyrrolidone and tetramethyl sulphone, which may also contain dissolved therein, water, and a salt soluble in water and in the organic solvent, e.g. lithium chloride, bromide and nitrate, calcium, zinc and magnesium chlorides and magnesium chlorate. The membrane may be subjected to a heat treatment before use by immersion in water at 60-100‹ C. for from 1 min. to 5 hours.