Study On The Selectivity Of Imidazolium Ionic Liquids In Extractive Separaction

Ionic liquids (ILs), serving as "green solvents" , are more and more used in extractive separation processes. The selectivity of ILs, which can be described by the ratio of the infinite dilution activity coefficients of different solutes in ILs, are of great significance for selecting appropriate ILs in azeotropic rectify, extractive rectify and other separation processes. In this work, the activity coefficients at infinite dilution and the selecticity of ILs have been studied as follows:1. Activity coefficients at infinite dilution were measured for 27 solutes in six ILs at 323.15～353.15 K by inverse gas chromatography (IGC). The infinite dilution selectivities of these ILs in separation of organic, aquiferous azeotropic and binary systems with similar property were determined. The results show that [EMIM][N(CN)₂], [RMIM][OAc] are good extractants or entainers for binary aqueous azeotropes and the systems with large asymmetric polarity except isomers.2. The theromadynamic properties at infinite dilution were derived. The partial excess molar enthalpies at infinite dilution of solutes in the ILs were derived from the temperature dependence of the values of infinite dilution activity coefficient; the infinite dilution enthalpies of solutes in the ILs were regressed from the temperature dependence of the values of probe specific retention volume. Additional partial mole free energy of mixing and partial mole entropy of mixing of solutes in the ionic liquid were calculated.3. UNIFAC group contribution method has been used to calculate the infinite dilution activity coefficients of solutes in ILs. The interaction parameters of the fragements were regressed by using the experimental data obtained in this work. The total relative average deviation is 9.31% . The selectivities of binary systems including azeotropes, isomers were predicted and satisfactory results were derived.