Physically Gelled Ionic Liquids: Solid Membrane Materials with Liquidlike Gas Transport Properties, Innovative Membranes for Post-Combustion CO2 Capture

Recently, membrane processes have shown great potential for post-combustion CO₂ capture compared to chemical absorption processes. Supported ionic liquid membranes (SILMs) exhibit higher permeability and selectivity than traditional polymer membranes but lack mechanical stability. In our work, imidazolium room-temperature ionic liquids (RTILs) are solidified with an aspartame-based low molecular-weight gelator (LMOG) and loaded in a microporous support to afford supported gelled ionic liquid membranes (SGILMs).  These completely infused SGILMs have demonstrated high pressure resistance, negligible vapor pressure, and thermal stability along with good CO₂/N₂ separation properties since the gels are composed of >90 wt % ionic liquid. However, SGILM performances are limited by the thickness of the support (~100 µm) since it defines the thickness of the membrane active material. For this reason, a method has been developed to coat thin top layers (<10 µm) of physically gelled RTIL on microporous support to afford thin-film composite membranes with higher CO₂ permeances. Moreover, several additives such as free amines or functional inorganic fillers have been mixed with the gelled RTILs in order to improve intrinsic gas separation properties. Given these initial promising results, these new composite membranes can be considered as good contenders for membrane-based CO₂/light gas separation processes.