Facilitated olefin transport through room temperature ionic liquids for separation of olefin/paraffin mixtures

The ideal separation factor for propylene over propane approached 3.2 through the use of room temperature ionic liquids (ILs) such as 1-methyl-3-octyl imidazolium nitrate (MOIM+NO3−, 98%) and 1-butyl-3-methyl imidazolium tetrafluoroborate (BMIM+BF4−, 98%), which may be attributable to facilitated olefin transport via specific and reversible interactions between ILs and propylene, but not propane. Specific and reversible interactions were verified experimentally from transient sorption/desorption data and FT-IR spectroscopy and theoretically by quantum mechanical calculations. The mixed gas selectivity for propylene/propane mixtures (50/50 vol%) was 2.8 through ILs whereas with PEG 400 (Mw=400), which has nearly the same viscosity, the selectivity was only 1.2. This study demonstrated for the first time facilitated olefin transport through ILs.