Membranes on Mars for In-Situ Resource Utilization Processes 2004-01-2316
The goal of this project is the development and characterization of synthetic membranes for the separation and purification of CO2 from the Martian atmosphere for in-situ resource utilization (ISRU) applications such as in-situ propellant production. Candidate materials should have high selectivity for carbon dioxide over nitrogen and argon, and a glass transition temperature of -40 °C or less to remain in rubbery state at low temperature for high permeance (flux/driving force). Membrane materials we identified include the rubbery polymers poly(dimethyl siloxane) (PDMS) and the copolymer poly(dimethyl, methylphenyl siloxane) (PMPS). Pure and mixed gas permeation experiments with CO2, N2 and Ar were performed with these membrane materials in the temperature range -25 to 21 °C. In experiments with the commercially available PDMS membranes, the pure gas CO2 permeability increases from 1932 Barrers to 2755 Barrers as the temperature decreases from 22 to -30 °C. The ideal CO2/N2 separation factor (ratio of pure gas permeabilities/permeances) increases from 7.5 to 17.5 over the same temperature range. However, in mixed gas experiments, the CO2/N2 separation factor for PDMS was much lower, increasing from 4.5 to 6 as the temperature decreased from 22 to -30 °C. Pure gas permeation results with PMPS membranes also show an increase in CO2 permeability from 1450 Barrers to 1650 Barrers as the temperature decreases from 21 °C to -10 °C for differential feed pressure of 20 psi. The CO2/N2 ideal separation factor increased from 12 to 27 over the same range of temperature. Unlike PDMS, the mixed gas CO2/N2 selectivities are nearly the same as the pure gas values. We will also present reasons for these differences and discuss the design of membrane modules.