Temperature effects on gas permselection properties in hexafluoro aromatic polyimides

Abstract

Temperature dependencies of gas permeabilities, solubilities, diffusivities, and selectivities for various gas pairs (He/CH 4, CO 2/CH 4, O 2/N 2, and N 2/CH 4) are reported for two hexafluoro-substituted aromatic polyimides prepared in our laboratory. The activation energies for gas permeation and diffusion, and the heats of sorption are also reported. These polyimides have exceptionally high permeabilities and permselectivities as compared to typical glassy polymers used in gas separation membrane applications. The temperature dependency of the permeabilities of all penetrants in these polyimides also is smaller than in other standard glassy polymers having more flexible backbones. The differences in activation energies between larger and smaller penetrants in these packing-disrupted rigid matrices, however, are more extreme than in standard glassy polymers, thereby causing a stronger temperature dependency of the permselectivity than for more flexible backbone glassy polymers.