Transport properties of PA12-PTMO/AgBF4 solid polymer electrolyte membranes for olefin/paraffin separation

A rubbery nylon-12/tetramethylene oxide block copolymer (PA12-PTMO) was used as a polymeric matrix material for silver tetrafluoroborate (AgBF4) based solid polymer electrolyte membranes. Ethane sorption uptake of PA12-PTMO/AgBF4 increased linearly with increasing feed pressure. Moreover, the ethane sorption capacity decreased by increasing the AgBF4 concentration in the polymer electrolyte. Ethylene sorption of pure PA12PTMO also followed Henry’s law. On the other hand, the ethylene sorption isotherms of PA12-PTMO/AgBF4 showed a completely different behavior. As the silver concentration increased in the polymer electrolyte membranes, the sorption isotherms showed a dual-mode sorption behavior. The initial sorption enhancement provides clear evidence of complex formation between ethylene and silver ions. Mixed-gas permeation studies performed with dry ethylene/ethane mixture demonstrated that PA12-PTMO/AgBF4 composite membranes exhibited good stability. In a 14-day test period, the ethylene/ethane selectivity of this membrane decreased from 25–20. This performance is far better than that of any polymeric membrane for ethylene/ethane separation. The decline in membrane performance occurred only during the first 3 days of operation; thereafter, the membrane showed excellent long-term stability.

PA12-PTMO/AgBF4 solid polymer electrolyte composite membranes exhibit both high ethylene/ethane mixed-gas selectivity of up to 30 and high ethylene flux of 20×10–6 cm3(STP)/ cm2·s·cmHg. This performance is far better than any polymeric membrane for ethylene/ethane separation. Ethylene/ethane selectivity increased significantly with AgBF4 concentration in the membranes. PA12-PTMO/AgBF4 solid polymer electrolyte composite membranes showed good mechanical stability. Previous studies with facilitated transport membranes indicate that immobilized liquid membranes and solventswollen ion-exchange membranes were mechanically unstable, prohibiting their use in industrial operation. Furthermore, these membranes require the addition of water vapor to the feed gas to achieve facilitated olefin transport. The solid polymer electrolyte membrane reported here can be operated with a dry olefin/saturated-