Preparation and characterization of polyetherimide asymmetric hollow fiber membranes for gas separation

Integral asymmetric polyetherimide (PEI) hollow fiber membranes were prepared using N-methyl-2-pyrrolidone (NMP) as a solvent and ethanol as a nonsolvent-additive (NSA). Two polymer dopes with polymer concentrations 30 and 25 wt% and the coagulation value of 1.0 g were formulated. The mass ratio of ethanol to NMP in these polymer dopes was 0.2. Water was used as both an internal and external coagulant. Hollow fibers with an outer diameter of about 600 μm and an inner diameter of about 300 μm were prepared at different air-gaps. The membrane structure and gas separation properties were examined. The results reveal that the length of air-gap plays an important role in the spinning process and greatly affects the membrane separation performance. Non-coated asymmetric membranes with HeN2 selectivity as high as about 90 were obtained within an optimum range of air-gap lengths. After silicone-coating, the membranes prepared exhibit outstanding selectivity and moderate permeation flux. Gas permselection properties for N2, CH4, Ar, CO2, O2, H2, and He through the PEI membranes were investigated in some detail as a function of pressure and temperature.