Physically Gelled Room-Temperature Ionic Liquid-Based Composite Membranes for CO₂/N₂ Separation: Effect of Composition and Thickness on Membrane Properties and Performance

An aspartame-based, low molecular-weight organic gelator (LMOG) was used to form melt-infused and composite membranes with two different imidazolium-based room-temperature ionic liquids (RTILs) for CO 2 separation from N 2 . Previous work demonstrated that LMOGs can gel RTILs at low loading levels, and this aspartame-based LMOG was selected because it has been reported to gel a large number of RTILs. The imidazolium-based RTILs were used because of their inherent good properties for CO 2 /light gas separations. Analysis of the resulting bulk RTIL/LMOG physical gels showed that these materials have high sol–gel transition temperatures (ca. 135 °C) suitable for flue gas applications. Gas permeabilities and burst pressure measurements of thick, melt-infused membranes revealed a trade-off between high CO 2 permeabilities and good mechanical stability as a function of the LMOG loading. Defect-free, composite membranes of the gelled RTILs were successfully fabricated by choosing an appropriate porous membrane support (hydrophobic PTFE) using a suitable coating technique (roller coating). The thicknesses of the applied composite gel layers ranged from 10.3 to 20.7 μm, which represents an order of magnitude decrease in active layer thickness, compared to the original melt-infused gel RTIL membranes.