Thermodynamic Properties And Application Of Organic Solute/Alkyl Imidazole Chloride Ionic Liquid Solutions

Compared with traditional organic solvents,ionic liquids（ILs）have been increasingly used in extraction and separation processes because of their unique properties such as low melting point,good thermal stability,non-volatility,strong solvency,and wide range of liquid temperature.The important parameter for evaluating the performance of solvent extraction is the separation selectivity of solvents,which can be obtained by calculating the infinite dilution activity coefficient(₄^∞))of solutes in ILs.Meanwhile,₄^∞)is an important thermodynamic reference data for selecting solvents in the process of chemical separation,which reflects the solvent selectivity and solubility as well as the strength of the intermolecular interactions between solute and solvent,and therefore it becomes the key basis for engineering design.Therefore,the study of thermodynamic properties of ILs-containing systems is crucial to provide a theoretical basis for the selection of suitable extractants in extractive distillation and extractive separation.Among them,alkyl imidazolium chloride ionic liquids have the advantages of easy synthesis,low price and cost,and the related research data are less,so it is of great significance to carry out the research on the thermodynamic properties of the ionic liquid system containing such ionic liquids and its application in the extraction and separation process,especially for some difficult separation systems in chemical production.In this work,two ionic liquids,1-pentyl-3-methylimidazole chloride（[C₅MIm]Cl）and 1-heptyl-3-methylimidazole chloride（[C₇MIm]Cl）,were synthesized.The infinite dilution activity coefficients(₄^∞))of 31organic solutes including alkanes,aromatic hydrocarbons,alcohols and some polar solutes in[C₅MIm]Cl and[C₇MIm]Cl were determined at atmospheric pressure in the temperature range of 313.15K to 363.15K.The relationship between₄^∞)and 1/T was fitted using the Gibbs Helmholtz equation,and thermodynamic parameters such as infinite dilution partial molar excess enthalpy(?₄)^E,∞),partial molar excess Gibbs free energy(?₄)^E,∞)and entropy(_ref^E?₄),^∞)at_ref=298.15K were calculated.The solubility parameters（₃）of two ionic liquids were estimated using the regular solution theory combined with the Flory equation,and compared with the solubility parameters(₄))of solutes.The gas-liquid distribution coefficient（_L）of solute in ionic liquid was calculated in the temperature range of 313.15K to 363.15K.The linear regression was performed for the experimental value of_L and a prediction model for_L was established,based on the linear free energy relationship model（LFER）.The infinite dilution selectivity(₄^∞5)))of[C₅MIm]Cl and[C₇MIm]Cl for various difficult to separate systems was calculated at 333.15K.The results showed that the two ionic liquids as extractants have good separation performance for most difficult to separate systems,with the best separation performance for fatty hydrocarbon/alcohol systems.The₄^∞5))and capacity coefficient（6）₅^∞))of of benzene for n-hexane/benzene and cyclohexane/benzene systems with two ionic liquids at 323.15K were compared with other ionic liquids containing Cl^-anions,and it was found that[C₅MIm]Cl is an excellent extractant for the separation of n-hexane/benzene and cyclohexane/benzene,two typical difficult separation systems The₄^∞5))values are 76.93 and 27.55,respectively,which are much higher than other similar ionic liquids,indicating that[C₅MIm]Cl is an excellent extractant for separating n-hexane/benzene and cyclohexane/benzene systems.The liquid-liquid equilibrium data of{cyclohexane+benzene+[C₅MIm]Cl}terpolymer system at 298.15K and323.15K were determined,and the separation effect of[C₅MIm]Cl on cyclohexane/benzene system was investigated.In addition,[C₅MIm]Cl was used as stationary phase to prepare a capillary column.The conditions of pretreatment,staining and aging of the column were optimized,and the separation efficiency of benzene series and alcohols mixed samples on the[C₅MIm]Cl capillary column was determined by the number of theoretical plates.