soft segments for selectivity could overcome this limitation. Recently, a new pervaporation technology based on a polyimide/polyester copolymer membrane system was developed for the separation of heavy catalytically cracked naphtha into an aromatics-rich permeate for gasoline blending and an aromatics-lean retentate for distillate (jet and diesel fuel) blending (Ho et al., 1996). Current pervaporation membrane systems will probably be most effective in hybrid pervaporation/distillation processes where pervaporation performs a first, crude, low-energy, low-cost separation, leaving the polishing operation for distillation. Higher selectivity/flux membranes and modules that can withstand aggressive organic mixtures at relatively high temperature pervaporation conditions (about 120°C to 250°C) would be more cost-effective and have more applications. Controlling membrane swelling is critical to improving selectivity. If high selectivity could be achieved with pervaporation, it could replace distillation in many separation processes.


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