CO2 separation membranes using ion gels by self-assembly of a triblock copolymer in ionic liquids

CO2 separation ion gel membranes with compatible permselectivity for supported ionic liquid membranes (SILMs) and good mechanical stability were developed using a triblock copolymer that self-assembles in CO2-selective ionic liquids (ILs). Three ion gels with 1-n-hexyl-3-methylimidazolium ([hmim]) cation base, each containing different anions ([Tf2N−], [BF4−], and [PF6−]) and a small amount of poly(styrene-block-ethylene oxide-block-styrene) (SEOS) triblock copolymer were prepared and characterized using differential scanning calorimetry and wide-angle X-ray diffraction analysis. Mechanically stable composite membranes made with three different ion gels were prepared by the self-assembly of IL/SEOS on the surface of the nylon support membrane and characterized by the measurement of their CO2 separation performance. The ideal CO2/CH4 separation factors were 9.0, 9.5 and 9.9 for the ion gel membranes containing [hmim][Tf2N], [hmim][BF4] and [hmim][PF6], respectively. These values are consistent with or higher than those of SILMs due to the microstructure formation inside the ion gels.

► Long-term mechanical stable ion gel membranes for CO2 separation were prepared.
► Much less triblock copolymer was needed to form the ion gel.
► Ion gel membrane retains favorable diffusion of a liquid state of ion liquids.
► High selectivity was obtained due to CO2 solubility and selective diffusivity inside ion gels.