Permeation of H2, N2, CH4, C2H6, and C3H8 through asymmetric polyetherimide hollow-fiber membranes

Permeation properties of pure H-2, N-2, CH4, C2H6, and C3H8 through asymmetric polyetherimide (PEI) hollow-fiber membranes were studied as a function of pressure and temperature. The PEI asymmetric hollow-fiber membrane was spun from a N-methyl-2-pyrrolidone/ethanol solvent system via a dry-wet phase-inversion method, with water as the external coagulant and 50 wt % ethanol in water as the internal coagulant. The prepared asymmetric membrane exhibited sufficiently high selectivity (H-2/N-2 selectivity >50 at 25degreesC). H-2 permeation through the PEI hollow fiber was dominated by the solution-diffusion mechanism in the nonporous part. For CH4 and N-2, the transport mechanism for gas permeation was a combination of Knudsen flow and viscous flow in the porous part and solution diffusion in the nonporous part. In our analysis, operating pressure had little effect on the permeation of H-2, CH4, and N-2. For C2H2 and C2H2 however, capillary condensation may have occurred at higher pressures, resulting in an increase in gas permeability. As far as the effect of operating temperature was concerned, H-2 permeability increased greatly with increasing temperature. Meanwhile, a slight permeability increment with increasing temperature was noted for N-2 and CH4, whereas the permeability of C2H2 and C2H2 decreased with increasing temperature. (C) 2002 Wiley Periodicals, Inc.