GAS PERMSELECTION PROPERTIES IN SILICONE-COATED ASYMMETRIC POLYETHERSULFONE MEMBRANES

The gas permeation properties of H-2, He, CO2, O-2, and N-2 through si licon-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 si licone rubber (PDMS) membrane. The PESf asymmetric hollow-fiber membra nes were prepared from spinning solutions containing N-methyl-2-pyrrol idone as a solvent, with ethanol, 1-propanol, or water as a nonsolvent -additive. Water was also used as both an internal and an external coa gulant. A thin silicone rubber film was coated on the external surface of dried PESf hollow-fiber membranes. The apparent structure characte ristics of the separation layer (thickness, porosity, and mean pore si ze) of the asymmetric membranes were determined by gas permeation meth od and their cross-section morphologies were examined with a scanning electron microscope. The results reveal that the gas pressure normaliz ed fluxes of the five gases in the three silicone-coated PESf asymmetr ic membranes are nearly independent of pressure and did not exhibit th e dual-mode behavior. The activation energies of permeation in the sil icone-coated asymmetric membranes may be larger or smaller than those of PESf dense membrane, which is controlled by the membrane physical s tructure (skin layer and sublayer structure). Permselectivities for th e gas pairs H-2/N-2, He/N-2, CO2/N-2, and O-2/N-2 are also presented a nd their temperature dependency addressed. (C) 1997 John Wiley & Sons, Inc.