Abstract
In recent years, many papers describing ionic liquids (IL) as promising solvents in separation techniques have been published. The conscious choice of appropriate ionic liquid as absorption media in effective extraction of selected types of analytes requires deeper understanding of the analyte−IL interactions. Therefore, intensive research is conducted to determine the values of activity coefficient at infinite dilution, which allows us to characterize the nature of these interactions. Based on the inverse gas chromatography retention data, activity coefficients at infinite dilution of 48 different organic compounds in the ionic liquids N-ethyl-N-methylmorpholinium bis(trifluoromethanesulfonyl)imide [C2C1Mor][TFSI] and N-octyl-N-methylmorpholinium bis(trifluoromethanesulfonyl)imide [C8C1Mor][TFSI] were determined. The measurements covered a broad range of volatile organic compounds, including n-alkanes, n-alkenes, n-alkynes, alcohols, aldehydes, ketones, aromatic compounds and common polar solvents, representing different types of interactions. Activity coefficients at infinite dilution were measured in the temperature range from 313.15 to 363.15 K. The excess partial molar enthalpies and entropies at infinite dilution were determined. Selectivity at infinite dilution was also calculated for exemplary separation processes in the hexane/benzene system. The obtained results were analyzed and compared with literature data for ionic liquids containing the same anion [TFSI]¯ and different cations. The study results indicate that some potential applications of the investigated ionic liquids in separation problems exist.
Highlights
The fifth principle of Green Chemistry introduces a requirement for searching new substances that will become alternatives for toxic organic solvents, contributing in this way to the reduction of the unfavorable environmental impact of chemical processes [1]
We investigated the interactions between the different types of organic compound groups and two new ionic liquids based on morpholinium cation [Cn Cm Mor]+ and bis(trifluoromethanesulfonyl)imide anion [TFSI] ̄
Where indices 1, 2 and 3 denote a solute, carrier gas and ionic liquid, respectively; T is the column temperature (K), R is the gas constant (8.31446 J·K−1 ·mol−1 ), P1 is the saturated vapor pressure of solute at temperature T, P0 is the outlet pressure, n3 is the number of moles of ionic liquid at stationary phase, VN is net retention volume of the solute, B11 is the second virial coefficient of pure solute, B12 is the cross second virial coefficient, V1 is the molar volume of pure solute, V1∞ is the partial molar volume of solute at infinite dilution in the solvent and J23 is the pressure correction term
Summary
The fifth principle of Green Chemistry introduces a requirement for searching new substances that will become alternatives for toxic organic solvents, contributing in this way to the reduction of the unfavorable environmental impact of chemical processes [1]. Due to the huge number of possible combinations of different cations and anions (1018 ), it is possible to model its properties, such as density, viscosity, refractive index and sound velocity, in dependence on the requirements of a given solution [3] Their popularity in potential usage is a result of a unique set of properties, i.e., negligible vapor pressure and relatively high thermal stability. Temperature, the values of partial molar excess enthalpy at infinite dilution were estimated Research conducted on both ionic liquids allowed us to analyze the effect of the chain length of alkyl substituent on the solute-solvent interactions and to determine its influence on the separation processes in aliphatic/aromatic hydrocarbon mixtures
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