| Extractive distillation, a special distillation technology, is widely used in petrochemical engineering. Where an extractive agent is used for its special affinity to some components of the mixture to be separated, and hence the relative volatility of the component can be improved, and even azeotropic point can be removed, which greatly facilitate the separation efficiency. As is well known that the key factor for extractive distillation is whether a suitable and efficient extractive solvent is available. In recent years, a new class of compounds, known as "ionic liquids" (ILs) has emerged, which may give rise to some breakthrough in the separation technology of chemical engineering, as some attributes of ionic liquids are quite unique compared to traditional molecular solvents, for example, it is nonvolatile and is a molten salt, hence its salt effect on fluid phase equilibrium can be expected.In this study, salt effect of ionic liquid on vapor-liquid equilibrium is investigated experimentally, which is helpful in exploiting the possibility of using ionic liquid as a green extractive solvent in the extractive distillation. As a prototype of azeotropic mixture, water-ethanol system was studied experimentally. A systematic measurement was conducted on the vapor pressure of pure water and ethanol, the vapor pressure of binary systems: water-ethanol, water-1-propyl-3-methylimidazolium bromide [PMIM][Br] and ethanol-PMIM][Br], and the corresponding ternary system water-ethanol-[PMIM][Br] at different temperatures by using a modified boiling point method in various concentrations of ionic liquid. The experimental results were well correlated with an Antoine-type equation. The experimental results indicate that thevapor pressure of the solvents decrease noticeably while to a different extent due to the affinity difference between ionic liquid and solvent, which is similar to the salt effect of common inorganic salts.Vapor pressure was also measured for pure benzene and binary systems of water or ethanol with one of the three ionic liquids l-butyl-3-methylimidazolium bromide [BMIM][Br], l-butyl-3-methylimidazolium bibutylphosphate [BMIM][P(O)(OBu)2O] and [BMIM][C1]. For benzene-ionic liquid systems, the experiment vapor pressure was measured only for benzene-[BMIM][P(0)(0Bu)20] system, and not for the others due to the very low mutual solubility between benzene and [BMIM][Br] or [BMIM]C1]. As all three ionic liquids mentioned above is soluble to water and ethanol, hence vapor pressures for binary mixtures of water-IL and ethanol-IL were measured by using ebulliometric method in various concentrations of ionic liquids at different temperature ranges, and the vapor pressures were well correlated with the NRTL-equation and Antoine-equation. In addition, activity coefficients of solvents in the ILs containing binary mixtures have been calculated by using the experimental equilibrium temperatures and pressures and were correlated with NRTI^equation. The results indicate that the vapor pressure of ethanol, water and benzene can be decreased noticeably by ionic liquid while to different degree, which changes the relative volatility of a solvent mixture to be separated by adding ionic liquids wherein.In addition to the vapor pressure measurement, isobaric vapor-liquid equilibrium data at 101.3 kPa were also measured for the binary system benzene(l)-ethanol(2) and ternary systems benzene(l)-ethanol(2)-[BMIM][P(OXOBu)2O](3) and benzene(l)-ethanol(2)-[BMIM][Cl](3). The isobaric VLE data for ionic liquid-free binary system were compared with that predicted by using NRTL model, and good agreement between the experimental and predicted results was obtained. The experimental results showed that ionic liquids [BMIM][C1] and [BMIM][P(OXOBu)2O] were effective solvents for separating benzene and ethanol via extractive distillation. Further, the azeotropic point was eliminated therefore by adding ionic liquids. In conclusion, ionic liquid may find industrial applications in the extractive distillations...
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