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

Abstract

Permeation properties of pure H2, N2, 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 (H2/N2 selectivity >50 at 25°C). H2 permeation through the PEI hollow fiber was dominated by the solution-diffusion mechanism in the nonporous part. For CH4 and N2, 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 H2, CH4, and N2. For C2H6 and C3H8, 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, H2 permeability increased greatly with increasing temperature. Meanwhile, a slight permeability increment with increasing temperature was noted for N2 and CH4, whereas the permeability of C2H6 and C3H8 decreased with increasing temperature.