Supported Ionic Liquid Membrane for Selective CO2 Capture

In situ utilization of carbon dioxide (CO2) from the Mars atmosphere provides a critical element for on-surface crop production. The atmosphere management system for the MarsOasis� growth chamber provides CO2, recovers water and oxygen, and removes ethylene to maintain a hospitable atmosphere for the crops. A supported ionic liquid membrane (SILM) can selectively provide CO2 while rejecting carbon monoxide (CO) back to the Mars atmosphere. The SILM comprises an ionic liquid infiltrated into the pores of a thin physical membrane support such as polyethersulfone or nylon. Ionic liquids are most promising for their negligible vapor pressure, low melting points (many remain liquid below 0�C), thermal stability up to 100�C or greater, and solubilities (especially for water and/or acid gases) that depend upon the cation and anion that comprise the IL. The negligible vapor pressure means that fluid will not be lost from the membrane, a common problem with other liquid sorbents. The physical processes of sorption and solution-diffusion through the membrane are enhanced; in part, because the supported liquid membrane can be made much thinner than a purely physical membrane without blowing liquid out of the support or losing it to vaporization. Then, amine-, fluorine-, or nitrile-functionalized groups in the IL can further facilitate the highly selective transport since these compounds chemically interact with CO2 to increase its uptake and rate of diffusion. In this paper we report experiments to characterize a SILM for selective CO2 capture from surrogate atmospheres.