Characterization of Substituted Polyphosphazene Membranes - Pure and Mixed Gas Results

Here, we report the transport properties of substituted polyphosphazenes membranes for separation and purification of CO2 for in-situ resource utilization (ISRU) processes. This paper includes pure and mixed gas permeation data of gases for the methoxy ethoxy ethanol (MEE)-substituted polyphosphazenes. Significant differences in transport properties of gases have been observed for the cross-linked and un-cross-linked polymer membranes. The CO2/N2 ideal separation factors for the un-cross-linked and cross-linked membrane for 74% MEE polyphosphazene were 16 and 43 at 22 °C, respectively. An effort has been made to relate these differences to polymer structure through apparent energy of activation calculations and observed glass transition temperatures. The CO2 permeability for the cross-linked 74% MEE polyphosphazene membrane decreased from 71 to 20 barrrers with an increase in the CO2/N2 ideal separation factor from 43 to 110 as the membrane temperature is reduced from 22 to -20 °C. Also, experiments were performed under simulated Martian atmospheric conditions for the 48% MEE polyphosphazene at 80 and 800 mbar feed pressure. The permeability of all gases is independent of the feed pressure in the range 1500-3000 mbar for the 74% MEE polyphosphazene and at low pressures (80-800 mbar) for 48% MEE polyphosphazene. The variations in permeability of gases with temperature for both the 74% and the 48% MEE polyphosphazenes are also reported in this article.