(489g) Ammonia Absorption in Ionic Liquids

The history of ionic liquids (ILs) effectively started in 1914, when the physical properties of ethylammonium nitrate ([CH₃CH₂NH₃⁺][NO₃^-], m.p. 13-14 °C) were first reported. ILs are generally defined as salts composed of discrete cations and anions with melting points below 100 °C, and many are liquid at ambient temperature. IL research has grown rapidly over the past decade due to the realization that these materials have many unique properties such as negligible vapor pressure and outstanding solvation potential. Ionic liquids have been further emphasized by the fact that their physical and chemical properties can be finely tuned by varying both the cation and anion. Our research has focused on accurately measuring vapor-liquid equilibria (VLE) and vapor-liquid-liquid equilibria (VLLE) and using thermodynamic models to understand the phase behavior of binary and ternary gas mixtures in ILs. We published for the first time in 2006-2007 the first ammonia (NH₃) gas solubilities in 8 room temperature ionic liquids (RTILs): 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]), 1-hexyl-3-methylimidazolium chloride ([hmim][Cl]), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf₂N]), 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]), 1-ethyl-3-methylimidazolium acetate ([emim][Ac]), 1-ethyl-3-methylimidazolium thiocyanate ([emim][SCN]), 1-ethyl-3-methylimidazolium ethylsulfate ([emim][EtOSO₃]), and N,N-dimethylethanolammonium acetate ([DMEA][Ac]). The VLE experiments were performed using static equilibrium cells over a temperature range from 283 to 373 K. Now, for the first time a gravimetric microbalance (XEMIS) is available from Hiden Isochema (United Kingdom) which is capable of measuring VLE using corrosive gases such as NH₃ over broad temperature (77 to 773 K) and pressure (0 to 170 bar) ranges. This presentation will focus on our new VLE measurements with NH₃ in RTILs using the highly accurate XEMIS gravimetric microbalance. Pressure-temperature-composition (PTx) data for NH₃ in RTILs at isothermal temperatures will be reported and correlated using the Peng-Robinson equation of state. Knowledge of NH₃ and RTIL phase behavior has led to several practical applications which will be highlighted.