Facilitated Transport Membrane with Ionic Liquid and Poly(ionic liquid) Carriers for CO2 Separation from Air

CO₂ separation technologies are crucial for the global aim of carbon neutral and even carbon negative. Conventional CO₂ capture by liquid or solid sorbents are energy intensive. On the other hand, membrane separation is of great research interest due to its modularity and high energy efficiency. However, little attention has been given to CO₂ separation from air (direct air capture (DAC)) or cabin air where the CO₂ concentration, temperature, and humidity level are low. This work focuses on a functionalized ionic liquid (IL) and poly(ionic liquid) (PIL) based facilitated transport membrane (FTM) tailored for such need. The active layer composed of a highly plasticized PIL-IL gel that is nanoconfined within the deposited graphene oxide nanosheet framework (GONF). The resulting PIL-IL/GO FTM exhibited high performance of CO₂ carrier-facilitated transport at conditions relevant to DAC (3090 GPU and CO₂/N₂ selectivity of 1180) and cabin air by virtue of the high CO₂ reactivity of carrier as well as high mobility of the CO₂-complex within the FTM. The transport of CO₂-complex was revealed to be the bottleneck of the overall process, as confirmed by studying the CO₂ absorption and viscosity change of IL upon various feed composition. To the best of our knowledge, this result represents one of the few FTMs for DAC with permeation properties crossing over the Robeson upper bound, indicating the potential for practical CO₂ separation from air or cabin air.