Determination And Application Of Activity Coefficients At Infinite Dilution Of Organic Compounds In Imidazolium Ionic Liquids

As an effective separation method,liquid-liquid extraction process is widely applied.Ionic liquids?ILs?,compared with conventional organic solvents,are almost non-volatile and exhibit good solubility for many inorganic and organic compounds.The application of ILs in the extraction separation process is developing vigorously,especially for some difficult separation systems in chemical production.The selectivity of solvents on solutes is an important parameter to evaluate the extraction performance of solvents.Activity coefficients at infinite dilution??_i^??)is one of important thermodynamic parameters for the chemical engineering.It reflects the solubility and selectivity of solvent on solute.By measuring the ?_i^? of organic compounds in ILs and studying the thermodynamic distribution of organics in ILs,it is possible to evaluate the separation selectivity of ILs and screen out extractants that are suitable for the difficult separation systems.In this paper,two ILs 1-butyl-3-methylimidazolium perchlorate?[BMIM][Cl O₄]?and1-octyl-2,3-dimethylimidazolium bis?trifluoromethylsulfonyl?imide?[OMMIM][NTf₂]?were synthesized.?_i^?)and gas-liquid partition coefficients?K_L?for 35 organic compounds such as alkanes,aromatic hydrocarbons,alcohols,and chloromethanes in two ILs have been measured by the gas chromatographic method in the temperature range of?303.15 to 353.15?K.The measured ?_i^? was fitted to the temperature and the corresponding fitting parameters were obtained.The ?_i^?,entropies(T_ref???_i^E,?) and Gibbs energies????_i?^E,?)of organic compounds at a reference temperature T_ref=298.15 K were also determined from the fitting parameters values.The solubility parameters of two ILs were calculated based on the measured?_i^?).The selectivity(S_ij^?)))of the two ILs were determined for several difficult separation systems at 323.15 K.In addition,for the two typical difficult separation systems,hexane/benzene and cyclohexane/benzene systems,S_ij^?))and benzene capacity ?k_j^??of the same type of ILs and other organic solvents were compared with the measured values.The results indicate that the[BMIM][ClO₄]had the largest S_ij^? value for the alkane/aromatic and alkane/alcohol systems,and had a S_ij^? value of 17.87 for the cyclohexane/benzene system.The selectivity was better than that of other ILs and organic solvents.It is a good extraction solvent for the separation of cyclohexane/benzene.For the cyclohexane/benzene system,the S_ij^? value is 17.87,that selectivity was better than other ILs and organic solvents.It is a good solvent for cyclohexane/benzene separation.Thecorrespondingliquid-liquidequilibriawere experimentally determined for the mixtures of{cyclohexane+benzene+[BMIM][ClO₄]}at 298.15 K and 313.15 K.The effect of the[BMIM][ClO₄]for cyclohexane/benzene separation was studied.The linear free energy relationship?LFER?salvation model was applied to correlate the K_L values and theoretical linear solvation energy?TLSER?model was applied to correlate the ?_i^?)values.A theoretical prediction model describing the?_i^?)andK_L of organic compounds in two ILs was established.