(121e) 6FDA-6FpDA Membranes for Propane/Propylene Separations

Propylene is among the most important chemical feedstocks of the petrochemical industry. Propylene/propane separation via cryogenic distillation is a highly energy intensive, large scale separation. Membrane separation is an attractive alternative for this separation. A significant amount of work has been done with pure polymer membranes; however, these materials have not provided a satisfactory permeability and selectivity of propylene/propane tradeoff for commercial viability.

In this research we have successfully synthesized characterized 6FDA-6FpDA polyimide for propylene/propane separations. Propylene and propane have shown a trend of plasticization with operating pressures higher than 2 atm. We have successfully suppressed this plasticization behavior by annealing the film and performing high temperature experiments. High molecular weight appears to reduce segmental free volume and mobility in the polymer. Our mixed gas results also did not show any trend of plasticization. We have not observed any plasticization behavior until 4.5 atm. This material, therefore, provides a platform for advanced ?mixed matrix? materials that can boost selectivities into a highly attractive range for commercial viability.

We have been able to explain our experimental results with dual mode model diffusion-sorption model with bulk flow effect, which will be discussed.