Low-Pressure CO2 Capture Using Ionic Liquids to Enable Mars Propellant Production

Room-temperature ionic liquids offer a potential technological approach for propellant production on Mars using in situ resources. These unique salts can be employed to preferentially capture carbon dioxide (CO2) from the atmosphere of the planet for subsequent processing. To explore this application, CO2 and argon solubility experiments were performed with 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM][Tfo]) and 1-butyl-3-methylimidazolium acetate ([BMIM][Ac]) over partial pressures of 0–84 kPa. The benchtop data are then extrapolated to anticipated specifications required for a flight-scale capture system on Mars. An artificial increase in CO2 partial pressure from local atmospheric conditions (0.8 kPa) to 84 kPa will significantly reduce the required mass of ionic liquid due to enhanced uptake. Meanwhile, the mass and volume specifications of [BMIM][Ac] are more competitive than [BMIM][Tfo]. The time interval for CO2 capture with [BMIM][Ac] is also shown to be a driving factor in required mass because 81% of the maximum uptake capacity is absorbed in approximately a third of the time needed to fully load the ionic liquid with CO2.