(262ba) Consideration of Ionic Liquid Dissociation in Thermodynamic Modeling of Ionic Liquids and Mixtures

Ionic liquids (ILs) are considered as â??green solventâ? for their negligible vapor pressure, and are potential candidates of replacing conventional volatile solvents which are not environment friendly. Some of the applications are CO₂ capturing, separation solvents, refrigerants, novel electrolytes in batteries and photovoltaic cells, etc. Like all electrolytes, properly accounting for the dissociation chemistry of ionic liquids whether in pure or in solvents is essential in developing accurate thermodynamic models to account for the liquid phase non-ideality as function of compositions and temperature. Experimental data show that ionic liquids are partially dissociated [refs]. However, in literature, Ionic liquids are often approximated as all molecular form, completely dissociated, or constant dissociation in solutions for the thermodynamic modeling. Ionic liquids are sometimes treated with different extents of dissociation in the two liquid phases [1]. In this work, we investigate three common ILs, i.e., [emim][EtSO₄], [emim][TFO], and [emim][TFA] in water, ethanol, and methanol. Partial dissociation of ionic liquids is explicitly considered together with Symmetric electrolyte Non-Random Two Liquid (eNRTL)[2]. The binary interaction parameters are correlated with experimental data on vapor pressure [1,3-5], infinite dilution activity coefficient [6], excess enthalpy [6], and dissociation extent [1]. Our new approach accurately correlates all available data and the model predicts the ionic liquid dissociation phenomena over the entire concentration and temperature ranges. In next steps, molecular dynamic simulation and experimental measurements are to be conducted to elucidate the nature of the complex formation resulting from the ionic liquids dissociation chemistry.

[1] Simoni LD.â??Predictive Modeling of Fluid Phase Equilibria for Systems containing Ionic Liquids.â?University of Notre Dame.2009.(Doctoral dissertation)

[2] Song Y,Chen C-C.â??Symmetric Electrolyte Nonrandom Two-Liquid Activity Coefficient Model.â? Industrial Engineering Chemistry Research.2009;48:7788-7799.

[3] Orchillés, AV,Miguel PJ,Vercher E,Martínez-Andreu A.â??Isobaric Vapor-Liquid Equilibria for 1-Propanol+Water+1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate at 100 kPa.â?Journal of Chemical & Engineering Data.2008;53:2426-2431.

[4] Wang JF,Li CX,Wang ZH.â??Measurement and Prediction of Vapor Pressure of Binary and Ternary Systems Containing 1-Ethyl-3-methylimidazolium Ethyl Sulfate.Journal of Chemical & Engineering Data.2007;52:1307-1312.

[5] Calvar N,González B, Gómez E, Domínguez Á.â??Vaporâ??Liquid Equilibria for the Ternary System Ethanol + Water + 1-Ethyl-3-methylimidazolium Ethylsulfate and the Corresponding Binary Systems Containing the Ionic Liquid at 101.3 kPa.â?Journal of Chemical & Engineering Data.2008;53:820-825.

[6] Kato R,Gamehling J.â??Systems with ionic liquids: Measurement of VLE and γ^â?? data and prediction of their thermodynamic behavior using original UNIFAC, mod. UNIFAC(Do) and COSMO-RS(Ol).â?Journal of Chemical Thermodynamics.2005;37:603-619.