Abstract
This paper reports the transport and sorption properties of poly(fluoroalkoxyphosphazene) (PFAP) membranes for carbon dioxide and nitrogen in both pure and mixed gas experiments. The CO 2 permeability decreased from 336 to 142 Barrers with an increase in the CO 2/N 2 ideal separation factor from 12 to 21 as the membrane temperature was decreased from 303 K to 258 K at feed pressure of 2.9 bars. At lower feed pressure (1.5 bars) the CO 2 permeability decreased from 327 to 140 Barrers, while the CO 2/N 2 ideal separation factor increased from 13 to 22 over the same temperature range. CO 2 sorption isotherms were measured using the pressure decay equilibrium method. Solubility of CO 2 was determined using the sorption isotherms and the diffusion coefficients were calculated from CO 2 permeabilities and solubilities. Sorption isotherms were linear at each temperature for the pressure range studied and the enthalpy of sorption was −5.8 kcal/mol. The solubility coefficient values for CO 2 increased from 0.95 to 5.43 cm 3 CO 2(STP)/cm 3 polymer atm whereas the diffusion coefficient decreased from 2.71 × 10 −6 to 0.19 × 10 −6 cm 2/s as the temperature decreased from 303 K to 258 K.
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