The Methodological Research Of Inverse Gas Chromatography For Determining The Physical-chemical Properties Of Midazolium-based Ionic Liquid

The ionic liquid （IL） is a liquid having a wide liquid range at or near roomtemperature which entirely composed of an anion and cation. The physical-chemicalproperties of ILs such as surface properties, solubility parameter, interactionparameter and activity coefficients make a great contribution to reveal and in-depthunderstand of the inherent nature of the interaction between ILs and other materials indifferent areas. Due to these special characteristics and performances, in recent years,the study of ILs is concerned about the growing number of scholars’ concerns andattentions. In this work, a series of ILs were studied by using inverse gaschromatography （IGC）, the work done by the following aspects:（1） The non-polar solvents were used as the probes in the temperature rangebetween343.15K and373.15K to determine the surface dispersion energy of1-ethyl-3-methylimidazolium hexafluorophosphate （[EMIM]PF₆）,1-butyl-3-methylimidazolium hexafluorophosphate （[BMIM]PF₆）,1-hexyl-3-methyli midazoliumhexafluorophosphate （[HMIM]PF₆）,1-hexyl-3-methylimidazolium tetrafluoroborate（[HMIM]BF₄）,1-hexyl-3-methylimidazolium chloride （[HMIM]Cl） and1-hexyl-3-methylimidazolium trifluoromethansulfonate （[HMIM]TFO） by using theretention time. The results showed that in the investigated temperature range, thedispersive surface energy decreased almost linearly as the temperatures increase. Andthe surface free energy values were [EMIM]PF₆>[BMIM]PF₆>[HMIM]Cl>[HMIM]PF₆>[HMIM]TFO>[HMIM]BF₄>[OMIM]PF₆.The IGC characterization encompassed the adsorption thermodynamicparameters, including the standard enthalpy and the free energy change of adsorption.The results showed that all the studied ILs were amphoteric material withpredominant basic character, as confirmed by the values of Kb/Karatio. As the fourILs with the same anion, the basic ability decreased with the imidazole ring side chaincarbon number increasing; and the same cationic ILs,[HMIM]Cl had the highest basic ability.（2） The molar enthalpy of sorption, partial enthalpy heat of mixing, enthalpyvaporization, weight fraction activity coefficient, Flory-Huggins interaction parameterof alkanes, halogenated hydrocarbons, benzene, alcohols, ketones, esters, ethers,tetrahydrofuran and cyclohexane in [HMIM]Cl,[EMIM]PF₆,[BMIM]PF₆,[HMIM]TFO,[HMIM]PF₆,[OMIM]PF₆,[HMIM]BF₄, as well as the solubilityparameters of the ILs were investigated by using IGC in the temperature range of343.15-373.15K. The Flory-Huggins interaction parameter values reflected that n-C6,n-C7, n-C8, n-C9, diethyl ether, tetrahydrofuran, benzene and cyclohexane were poorsolvents for studied ILs. In addition, it can be noticed that the strongest interactionswere found for ethanol, methanol, dichloromethane, tetrachloromethane, chloroformand acetone. All the results were consistently with the weight fraction activitycoefficient values. The solubility parameters of various ILs were reduced with theincreasing temperature within the studied temperature range; and the solubilityparameter of same anion ILs decreased with the imidazole ring side chain carbonnumber increasing; while the ILs with same cationic, the solubility parameters were[HMIM]Cl>[HMIM]PF₆>[HMIM]TFO>[HMIM]BF₄.（3） Within the temperature range of343.15to373.15K, the IGC method wasused to determine the activity coefficients at infinite dilutionγ∞12of18organicsolvents in [HMIM]Cl,[EMIM]PF₆,[BMIM]PF₆,[HMIM]TFO,[HMIM]PF₆,[OMIM]PF₆and [HMIM]BF₄, which further validation of the dissolution of ILs in theselected solvent. The results showed that n-C₆, n-C₇, n-C₈, n-C₉, diethyl ether,tetrahydrofuran, benzene and cyclohexane had higherγ∞12values, while ethanol,methanol, toluene, m-xylene, dichloromethane, tetrachloromethane, chloroform andacetone had lowerγ∞12values.