Application of the pervaporation process to separate azeotropic mixtures

Pervaporation through poly(tetrafluoroethylene) films grafted with N-vinylpyrrolidone has been successfully used to fractionate positive azeotropic liquid systems. Selectivities higher than 10 have often been attained and daily productions above 100 kg per square meter of membrane can be easily obtained. This procedure can be used for separating water—aprotic solvent, water—alcohol and alcohol—alkane constant boiling mixtures. It is shown that a temperature gradient can also be used as the driving force for the transport. By this “thermopervaporation” technique, the condensation of the pervaporate occurs at ambient temperature and an increase of the feed temperature leads to an increase of both selectivity and flux.

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