Olefin/paraffin gas separations with 6FDA-based polyimide membranes

Pure gas permeation and sorption experiments were carried out for the gases ethylene, ethane, propylene and propane using polyimides based on 4,4'-(he xafluoroisopropylidene) diphthalic anhydride (6FDA), Composite membranes an d free films were used. Experiments were performed at 308 K and feed pressu res up to 17 atm for ethylene and ethane and 9 atm for propylene and propan e, Mixed gas permeation experiments were carried out with 50 : 50 olefin/pa raffin feed mixtures, For all investigated polyimides, the ideal ethylene/e thane separation factor ranged between 3.3 and 4.4 and the ideal propylene/ propane separation factor ranged between 10 and 16 at a feed pressure of 3. 8 atm and 308 K, In mixed gas permeation experiments, up to 20% lower selec tivity was found for the ethylene/ethane separation and up to 50% reduced s electivity for the propylene/propane separation compared to the ideal selec tivity, The influence of feed temperature on separation and permeation prop erties will be discussed based on pure gas permeability data at 298 and 308 K. (C) 2000 Elsevier Science B.V. All rights reserved.