Ionic liquids (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.  Interest in commercial use of ILs in the chemical industry is expanding rapidly, but commercialization is hampered by a lack of physical property data, particularly for mixtures of ILs with ordinary gases and liquids.  Our research has focused on accurately measuring vapor-liquid equilibria (VLE) and liquid-liquid equilibria (LLE) and using thermodynamic models to understand the phase behavior of binary gas mixtures in ILs.This presentation will focus on the importance of characterizing the global phase behavior of gases in ionic liquids and how this can provide insight into new gas separation applications.  Solubility measurements of several gases in ILs will be discussed and important experimental details regarding VLE measurements using a gravimetric microbalance and VLLE measurements using a mass-volume technique will be highlighted.  VLE data have been successfully correlated with a modified Redlich-Kwong equation of state (EOS), and in certain cases (e.g. hydrofluorocarbons) the EOS predicts partial immiscibilities (LLE) with lower critical solution temperatures (LCSTs) in the fluorocarbon-rich side solutions.  We have also found that gases such as CO2 can exhibit different solubility behaviors in ILs (i.e. physical and chemical absorption) and that these behaviors can be analyzed with the EOS using a simple association model and excess thermodynamic functions. Knowledge of gas and IL phase behavior has led to several practical applications including separation of azeotropic gas mixtures and removal of CO2 from flue gas.  These along with a few additional examples will be discussed.

Phase behavior to separation of gases using ionic liquids

248th National Meeting (2014)

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