Silane-modified PVC pervaporation membranes for bromoform/water separation

The transport properties of a unique family of silane-modified poly(vinyl c hloride) (PVC) pervaporation membranes for the separation of halogenated hy drocarbons from water were investigated. The PVC was modified by using a vi nyl silane to improve its resistance to attack by halogenated hydrocarbons and to increase the flux. Two preparation routes were used: Route i include d an initiator to promote the vinyl reaction before the hydrolysis and cond ensation of the methoxy silane group, whereas Route ni did not. The structu res of the membranes were characterized and related to the transport proper ties, as derived from batch pervaporation experiments. The permeability of unmodified PVC membranes increases with exposure to haloorganics at low con centrations. Initially, the modified membranes exhibited a higher permeabil ity than PVC and a lower selectivity. At long pervaporation times, the sila ne-modified membranes exhibited a higher selectivity than PVC. The differen t preparation routes led to different morphologies, which affected the perf ormance of the membranes; Route ni membranes exhibited higher permeabilitie s and selectivity than Route i membranes. Rubbery polydimethylsiloxane memb ranes were resistant to haloorganics but their high water permeability and low selectivity make them unsuitable for this pervaporative separation. (C) 2001 John Wiley & Sons, Inc.