Effect of solvent evaporation conditions on gas separation performance forasymmetric polysulfone membranes

Asymmetric polysulfone membranes were prepared by the phase inversion techn ique under different solvent evaporation conditions prior to the gelation s tep. The membranes were cast from the two component system of polymer and N ,N-dimethylacetamide in which the polymer concentration was changed from 25 .0 to 30.0%. The solvent evaporation temperature was changed from 70 to 120 degrees C, and the evaporation time was 0-15 min. Ethanol, water, or 2-pro panol was used as the gelation media. The membranes were characterized by t he measurement of oxygen/nitrogen permeation with the lamination technique and by observation with scanning electron microscopy. With an increase in t he solvent evaporation time, the oxygen permeance decreased and its selecti vity over nitrogen increased; although the permeance was in the range of 1- 2 GPU, the oxygen selectivity over nitrogen exceeded 8. A correlation betwe en the permeation performance and the operational parameters involved in th e solvent evaporation process was obtained. (C) 1999 John Wiley & Sons, Inc .