INTEGRAL ASYMMETRIC POLY(VINYLIDENE FLUORIDE) (PVDF) PERVAPORATION MEMBRANES

A new asymmetric pervaporation membrane, composed of the fluoropolymer poly (vinylidene fluoride) (PVDF), has been fabricated and preliminar y tests have been carried out to assess membrane performance for the r emoval of non-polar organics from water. Formation of an asymmetric mi crostructure proceeds via an unusual phase inversion process where a d ense polymer layer forms at the membrane/casting surface interface. As ymmetric membranes are made by either a dry cast method involving comp lete air-drying of a PVDF film or a wet cast method of partial air-dry ing followed by film immersion in a series of aqueous precipitation ba ths. For aromatic/water and chloroform/water separations, the PVDF fil ms performed remarkably well. For example, a benzene separation factor of 1,530 and a benzene flux of 105 g/m2-hr has been obtained for an 8 90 ppm benzene in water feed solution at 25-degrees-C and 0.05 atm dow nstream pressure. When the feed solution contained 625 ppm chloroform in water, the performance of asymmetric PVDF films at 25-degrees-C is characterized by a high organic flux (25.3-58.7 g/m2-hr) and a high se paration factor (302-823).