(196b) Measuring Henry’s Law Constants and Infinite Dilution Activity Coefficients of Gases and Liquids in Ionic Liquids Using Gas Chromatography for Olefin/Paraffin Separations

Ionic liquids (ILs) are widely studied for gas separations because of their low vapor pressures and high gas solubilities. Volumetric and gravimetric apparatuses are used to accurately determine solubilities of gases in ILs; however, they can be incredibly time consuming. A faster method that can be used to screen ionic liquid for specific separation applications is gas chromatography (GC). It yields Henry’s Law Constants (ℋ, for gases) and infinite dilution activity coefficients (γ^∞, for liquids), which are good measures of the IL-solute interactions. As a result, the GC method can be used to quickly and easily screen numerous ILs for the strength of their interactions with multiple gases and liquids. We present ℋ and γ^∞ values of various solutes, including ethane, ethylene, propane, propylene, a family of C₅-C₈ linear alkanes and alkenes, and aromatics in imidazolium ionic liquids, including 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf₂N]), and 1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([allylmim][Tf₂N]). Finally, we show the dramatic changes in ℋ and γ^∞ values one can achieve for olefins when mixing these ionic liquids with silver salts (Ag bis(trifluoromethylsulfonyl)imide) at concentrations up to 2 M, in order to improve the selectivity when using ILs for of olefin/paraffin separations.