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 preliminary tests have been carried out to assess membrane performance for the removal of non-polar organics from water. Formation of an asymmetric microstructure proceeds via an unusual phase inversion process where a dense polymer layer forms at the membrane/casting surface interface. Asymmetric membranes are made by either a dry cast method involving complete air-drying of a PVDF film or a wet cast method of partial air-drying followed by film immersion in a series of aqueous precipitation baths. For aromatic/water and chloroform/water separations, the PVDF films 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 890 ppm benzene in water feed solution at 25-degrees-C and 0.05 atm downstream 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 separation factor (302-823).