(137e) Ionic Liquid Membranes Using Isoporous Polymeric Supports

Chemical separations are responsible for approximately half of all industrial energy use and 10-15% of the total U.S. energy consumption. This is primarily because distillation accounts for roughly 80% of all industrial separations. Alternative technologies, that do not rely on phase change, offer the potential to dramatically decrease the energy needed to perform a wide variety of chemical separations. One of these technologies involves the use of membranes, which can be effective for separation of both gas and liquid mixtures. Many polymeric membranes rely on size-sieving for selectivity. However, incorporation of liquids, with significant solubility selectivity for target species, into membranes can greatly expand potential applications. Supported liquid membranes are particularly well suited for gas separations. Ionic liquids (ILs) have the added advantage over organic liquids or aqueous solutions in the pores of a porous support because they are nonvolatile and will not evaporate into the gas streams. A disadvantage is that supported ionic liquid membranes (SILMs) are subject to blowout if the transmembrane pressure exceeds the capillary forces holding the IL in the pores. As a result, most studies evaluating SILMs for gas separations limit the transmembrane pressure to no more than 1-2 bar. Even if the nominal pore diameter is relatively small (e.g., 30 nm), there is always a pore size distribution and the blowout pressure will be determined by the largest pores. In this work, we use isoporous polymeric membranes, that have a much narrower pore size distribution than conventional porous polymer membranes, as supports for a variety of SILMs. As a result, the SILMs can operate at transmembrane pressures up to approximately 12 bar, depending on the particular IL. We will show results for polystyrene-b-poly(4-vinylpyridine) isoporous SILMs designed for propane/ethane and propane/methane separation, as well as CO₂/methane and CO₂/N₂ separations.