Abstract
AbstractIn this study, we focused on effect of the molecular weight of polyimide on the gas selectivity of the asymmetric membrane with an oriented surface skin layer prepared at different shear stresses. Asymmetric polyimide membranes, which have a defect‐free surface skin layer supported by a porous substructure, were prepared by a dry/wet phase inversion process. The structures of the asymmetric polyimides consisted of a thin skin layer and a porous substructure characterized by the presence of finger‐voids. The gas selectivities of the asymmetric polyimide membranes increased with an increase in the shear rate or a decrease in the molecular weight, indicating that the oriented polyimide structure in the surface skin layer provided a high size and shape discrimination between the gas molecules. The selectivity values of (O2/N2) and (CO2/CH4) in the asymmetric polyimide membrane prepared from the 7.2 × 104 molecular weight material at 1000 sec−1 shear rate were 12 and 143, respectively. Copyright © 2003 John Wiley & Sons, Ltd.
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