Study On Thermodynamitic Properties And Application Of Systems Containing Alkyl Imidazolium Ionic Liquids

Ionic liquids（ILs）have the advantages of low vapor pressure,high thermal stability,stable chemical properties and non-flammability.They are expected to replace traditional solvents.In order to apply ILs as extractants in the field of chemical separation,it is necessary to study the thermodynamic properties of the mixture systems containing ILs.The infinite dilution activity coefficient（γi∞）is one of the most important thermodynamic parameters in chemical engineering.It can reflect the interaction mechanism between ILs and different solute molecules,and indicate the thermodynamic distribution behavior of solutes in ILs.Other thermodynamic parameters of the system containing ILs are calculated byγi∞,including gas-liquid partition coefficient（KL）and infinite dilution selectivity(S_ij^∞),etc.Therefore,the seperation ability of ILs can be evaluated and preliminary screened out ILs suitable for difficult separation systems.In addition,the vapor-liquid equilibrium data of the ternary system containing ILs can provide theoretical basis for calculation design,simulation and optimization of chemical process.This thesis focuses on the thermodynamic properties of tri-substituted alkyl imidazole ionic liquid systems and their applications.Three gas chromatography packed columns were prepared with the ILs 1-hexyl-2,3-dimethylimidazolium tetrafluoroborate（[HMMIM][BF₄]）,1-octyl-2,3-dimethylimidazolium tetrafluoroborate（[OMMIM][BF₄]）and 1-propyl-2,3-dimethylimidazolium bis（trifluoromethylsulfonyl）imide（[PMMIM][NTf2]）as a stationary phase.The infinite dilution activity coefficients and gas-liquid partition coefficients of organic solutes（alkanes,alkenes,alkylbenzenes,alcohols,etc.）in the three ILs have been measured using the gas chromatographic method（GC）at T=（303.15-353.15）K.The values of γi∞ were fitted with the temperature.According to Gibbs-Helmholtz equation,at T=298.15 K,the other infinite dilution thermodynamic parameters including partial molar excess enthalpy（HiE,∞）and the entropies（TrefSiE,∞）and Gibbs free energies（GiE,∞）were obtained from the fitting equation.According to the Hildebrand-Scatchard theory（RST）combined with Flory "combinatorial"equation,the solubility parameters of ILs were estimated by γi∞.The experimental value of KL was multivariately regressed by linear free energy model（LFER）to establish the KL prediction model.According to selectivity formula,at T=323.15 K,the selectivity S_ij^∞of three ILs for common difficult separation systems and capacity factor（kj∞）were calculated.The results show that the anion of ILs is the same and the cation of ILs has an effect on S_ij^∞ by compared with S_ij^∞ of ILs containing[BF₄]-or[NTf2]-in the literature.For the same type of cations,the shorter the substituent chain length,the better the S_ij^∞ of ILs.Vapor-liquid equilibrium data was determined at P=101.3 kPa including binary system cyclohexane+benzene and ternary system cyclohexane+benzene+[HMMIM][BF₄],cyclohexane+benzene+[OMMI M][BF₄]by vapor-liquid equilibrium analyzer.The effects of the ILs on the equilibrium of cyclohexane+benzene system were analyzed from several aspects,including system equilibrium temperature,activity coefficient of cyclohexane and relative volatility of cyclohexane to benzene.The results show that[HMMIM][BF₄]has a greater influence on the vapor-liquid equilibrium of the cyclohexane+benzene system compared with[OMMIM][BF₄]at the same dosage.Therefore,the separation performance of[HMMIM][BF₄]for cyclohexane+benzene system is better than[OMMIM][BF₄].