Measurement And Study On The Liquid-liquid Equilibrium Of Ionic Liquids With Organic Solvent

Room-temperature ionic liquids, which are liquids at ambient temperatures, are normally composed of relatively large organic cations and inorganic or organic anions. Ionic liquids (ILs) have been suggested as a kind of potential"green"solvents to replace volatile organic compounds in electrochemistry, organic synthesis and separation processes due to their superb physicochemical properties, such as wide liquid range, strong solubility, negligible vapor pressure, etc.In order to develop ILs for these applications, it is important to understand the factors that control their phase behavior with other liquids. In this work, liquid-liquid equilibrium (LLE) in binary mixtures of alcohol (1-butanol, isobutanol, 1-pentanol, 1-hexanol, 1-octanol), aromatic compounds (benzene, toluene, ethylbenzene, o-xylene, m-xylene, p-xylene), cycloalkane(cyclohexane, methylcyclohexane), esters(butyl acetate, isobutyl acetate), thiophene, with ionic liquids 1-hexyl-3-methylimidazolium tetrafluoroborate ([hmim][BF4]) and 1-octyl-3-methylimidazolium tetrafluoroborate ([omim][BF4]), have been measured by the cloud point method from 280K to the boiling point of the solvents. Some rules for the solubility of ILs with the organic solvents can be concluded by analyzing the experimental data. And these rules can give some instructions to the extraction and separation process. Liquid-liquid equilibrium in binary systems of alcohol with ILs exhibit upper critical solution temperature (UCST), with low solubility of the ILs in the alcohol and high solubility of the alcohol in the ILs. Increasing the alkyl chain length on the alcohol causes an increase in the UCST of the system. By contrast, increasing the alkyl chain length on the imidazolium cation results in a decrease in the UCST of the system. Temperature has little impact on the solubilities of aromatic compounds and thiophene in the ILs, since the solubilities change little when increasing temperature. In general, as the solute molecular size increased (benzene < toluene < ethylbenzene) and the polarity decreased (o-xylene < m-xylene < p-xylene), the immiscibility gap also increased. While the solubilities of cyclohexane and methylcyclohexane in the ILs have something to do with temperature, because the solubilities increase when temperature increases.The phase behavior of ILs and organic solvents can provide some possible ways to separate some azeotropic or close-boiling mixtures.The solubilities of m-xylene and p-xylene in ILs are very similar, so it is impossible to separate these close-boiling mixtures by using these two kinds of ILs. However, the solubilities of the close-boiling mixtures including benzene/cyclohexane, and benzene/thiophene, are different in the ILs, so they can be separated by multi-stage extraction. Both of the solubilities of the azeotropic mixtures 1-butanol/butyl acetate and isobutanol/isobutyl acetate in [hmim][BF4] are close, so this kind of ILs can't be used to separate these mixtures. But 1-butanol and butyl acetate have different solubilities in [omim][BF4], so [omim][BF4] can be used to separate these mixtures by multi-stage extraction.The liquidus curves were correlated by means of the non-random two liquid (NRTL) solution model, the interaction parameters of the systems were obtained. The minimum and maximum of the overall-average deviation were 1.9% and 11.5%.