(324d) Ionic Liquids Functionalized, Polymerized, and Encapsulated for CO2 Capture from Cabin Air and the Atmopshere

Sorbents to capture CO2 need to be highly selective, benign, regenerable with minimal energy input, and stable upon absorption-desorption cycling. In particular, the removal of CO2 from cabin air and the atmosphere require that the sorbent has chemical functionality to bind with CO2 such as amines, N-heterocycles, carbenes, alkoxides, ...etc. Absorption by chemical complexation are exothermic reactions and require heat to regenerate the sorbent. Ionic liquids (ILs) are known to be tunable, nonvolatile, and thermally stable solvents that have been shown to high CO2 solubilities. The main challenge is the high viscosity and consequently the mass transport limit in ILs. Our work focusing on addressing this specific challenge of ILs is three-fold: (1) forming eutectics through mixtures with hydrogen bond donors such as ethylene glycol; (2) (2) encapsulating ILs as liquid droplets in polymeric architectures with large surface area ; and (3) polymerizing ILs as fixed CO2-carriers in membranes. These approaches work in different technology platforms including absorption and adsorption processes that are based on cyclic operation driven by temperature-swing and membrane separations that is a continuous process driven by transmembrane pressure.

Superior binding capacity and CO2 selectivity in the first two approaches by a reactive IL with multiple functional moieties demonstrate the suitability of these sorbents for direct air capture (DAC). However, that the eutectics are often not as thermally stable as ILs and present low vapor pressures; both issues can be addressed by non-thermal regeneration approaches that we are currently working on. Similarly, the capsules fabricated to date are tens of microns in size and present non-ideal breakthrough curves as a result of pressure drop in the absorber column. Further studies optimizing the capsule dimensions are needed. Finally, the membranes that we fabricated from graphene oxide nano framework that is impregnated with functional poly(IL)-IL gel demonstrate CO2 permeance that crosses over the Robeson upper bound demonstrating facilitated transport of CO2. The CO2/N2 and CO2/air separation ratios are measured as 1200 and 300, respectively, at 22 °C and 40% relative humidity. These results represent one of the very few studies in facilitated transport membranes for DAC.