Gas permselection properties in silicone-coated asymmetric polyethersulfone membranes

Abstract

The gas permeation properties of H2, He, CO2, O2, and N2 through silicone-coated polyethersulfone (PESf) asymmetric hollow-fiber membranes with different structures were investigated as a function of pressure and temperature and compared with those of PESf dense membrane and silicone rubber (PDMS) membrane. The PESf asymmetric hollow-fiber membranes were prepared from spinning solutions containing N-methyl-2-pyrrolidone as a solvent, with ethanol, 1-propanol, or water as a nonsolvent-additive. Water was also used as both an internal and an external coagulant. A thin silicone rubber film was coated on the external surface of dried PESf hollow-fiber membranes. The apparent structure characteristics of the separation layer (thickness, porosity, and mean pore size) of the asymmetric membranes were determined by gas permeation method and their cross-section morphologies were examined with a scanning electron microscope. The results reveal that the gas pressure normalized fluxes of the five gases in the three silicone-coated PESf asymmetric membranes are nearly independent of pressure and did not exhibit the dual-mode behavior. The activation energies of permeation in the silicone-coated asymmetric membranes may be larger or smaller than those of PESf dense membrane, which is controlled by the membrane physical structure (skin layer and sublayer structure). Permselectivities for the gas pairs H2/N2, He/N2, CO2/N2, and O2/N2 are also presented and their temperature dependency addressed. © 1997 John Wiley & Sons, Inc.