Patent ID: 8051991

Claim:
A process for manufacturing an asymmetric hollow fiber membrane, comprising the steps of extruding a polymer solution through an outer ring slit of a hollow fiber spinning nozzle and simultaneously extruding a center fluid through an inner bore of the hollow fiber spinning nozzle into a precipitation bath, whereby the polymer solution contains 10 to 26 wt-% of polysulfone, polyethersulfone, or polyarylethersulfone, 8 to 15 wt-% polyvinylpyrrolidone, 55 to 75 wt-% N-alkyl-2-pyrrolidone and 3 to 9 wt-% water; the center fluid contains 70 to 90 wt-% N-alkyl-2-pyrrolidone and 10 to 30 wt-% water; and the precipitation bath contains 0 to 20 wt-% N-alkyl-2-pyrrolidone and 80 to 100 wt-% water.