Effect of evaporation time on the pervaporation characteristics through homogeneous aromatic polyamide membranes .2. Pervaporation performances for ethanol/water mixture

Pervaporation of ethanol/water mixtures through symmetric dense aromatic polyamide membranes was investigated. The membrane structure was controlled by varying the solvent evaporation time before gelation. The membranes were water-selective and the selectivity increased with an increase in the solvent evaporation time. On the other hand, the water flux as well as the ethanol flux decreased with an increase in the evaporation time. These results were consistent with the morphology change of the membrane which takes place with solvent evaporation: the decrease in the channel size. The effects of the downstream pressure on the pervaporation performances were also studied for membranes with different solvent evaporation times. The ethanol concentration in the permeate side increased with an increase in the downstream pressure to certain point, showed a maximum there, then decreased thereafter. The water flux decreased with an increase in the downstream pressure for all membranes studied; the dependence was expressed by a parabolic curve in the lower pressure range. The ethanol flux also decreased with an increase in the downstream pressure for the membrane with shorter evaporation time, while this flux was slightly affected by the downstream pressure for the membrane with longer evaporation time. (C) 1996 John Wiley & Sons, Inc.