Effect of evaporation time on the pervaporation characteristics through homogeneous aromatic polyamide membranes. I. Pure water permeation and membrane characterization by sorption measurements

Abstract

The pervaporation of pure water through homogeneous aromatic polyamide membranes was investigated. The structure of the prepared membranes was controlled by varying the solvent evaporation times before the gelation step from 5 min to 240 min. The permeation flux of pure water decreased rapidly when the solvent evaporation time increased from 5 min to 30 min, and the decrease was rather moderate at higher evaporation times. Vapor and liquid sorption measurements were used to characterize the membranes. The amount of vapor sorption at a given relative pressure increased with an increase in the solvent evaporation time. The specific surface area of the membranes, calculated from the vapor sorption isotherm, increased with evaporation time up to 30 min, and remained constant thereafter. Liquid sorption volume, on the other hand, decreased monotonically with an increase in evaporation time. The formation of channels in the membrane is used to explain the morphology change during the solvent evaporation. The increase in the solvent evaporation time gradually increases the number of the channels in the membrane and decreases their average size. Good correlation was observed between the average size of the channels (represented by the ratio of specific volume to the specific surface area) and the parameters associated with pervaporation transport. © 1995 John Wiley & Sons, Inc.

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“…The opposite occurred for CF-NA-A membrane resulting in a finger-like structure formation. The effect of solvent evaporation on membrane structure was investigated by Yamasaki et al who claimed that more solvent evaporation time resulted in a thicker skin layer and more uniform structure [32]. Moreover, Friedrich et al [33] investigated the effect of different solvents viscosity on the membrane structure and reported that the lower the solution viscosity resulted in a higher occurrence of cavities through the membrane.…”