(659a) Amine Functionalized Supported Ionic Liquid Membranes (SILMs) for Direct Air Capture

Supported ionic liquid membranes (SILMs), containing phosphonium ionic liquids with aprotic N-heterocyclic anions (AHA ILs) in an inorganic inert support were tested under both dry and humidified (40 % RH) mixed-gas conditions down to 420 ppm CO₂ balanced with N₂ at 35 C. In the dry case, the best performing IL, triethyl(octyl)phosphonium 4-bromopyrazolide ([P₂₂₂₈][4BrPyra]) exhibited high CO₂ permeabilities and CO₂/N₂ permselectivities, reaching as high as 29,000 barrer and 7,200, respectively. Under the presence of humidity, the CO₂ permeability and CO₂/N₂ selectivities increased to 54,000 barrer and 13,500, respectively. Humidity amplifies CO₂ permeabilities and CO₂/N₂ permselectivities by orders of magnitude from the substantial increase in CO₂ capacity in the AHA ILs at these dilute conditions and from the faster mobility of the mobile carrier. N₂ permeability stayed roughly the same in the presence of humidity where we suspect there are competing effects of viscosity reduction and higher N₂ rejection.