PREPARATION AND CHARACTERIZATION OF POLYETHERIMIDE ASYMMETRIC HOLLOW-FIBER MEMBRANES FOR GAS SEPARATION

Integral asymmetric polyetherimide (PEI) hollow fiber membranes were p repared using N-methyl-2-pyrrolidone (NMP) as a solvent and ethanol as a nonsolvent-additive (NSA). Two polymer dopes with polymer concentra tions 30 and 25 wt% and the coagulation value 1.0 g were formulated. T he mass ratio of ethanol NMP in these polymer dopes was 0.2. Water was used as both an internal and external coagulant. Hollow fibers with a n outer diameter of about 600 mu m and an inner diameter of about 300 mu m were prepared at different air-gaps. The membrane structure and g as separation properties were examined. The results reveal that the le ngth of air-gap plays an important role in the spinning process and gr eatly affects the membrane separation performance. Non-coated asymmetr ic membranes with He/N-2 selectivity as high as about 90 were obtained within an optimum range of air-gap lengths. After silicone-coating, t he membranes prepared exhibit outstanding selectivity and moderate per meation flux. Gas permselection properties for N-2, CH4, Ar, CO2, O-2, H-2, and He through the PEI membranes were investigated in some detai l as a function of pressure and temperature. (C) 1998 Elsevier Science B.V.