Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

Separation of aliphatic and aromatic compounds was studied using the high molecular weight trihexyl-tetradecyl-phosphonium cation (thtd-Ph) based ionic liquids (ILs) with the anions chloride [Cl], tetrafluoroborate [BF4], and bis(trifluoromethane sulfonylimide)[(Tf)2N]. Infinite dilution activity coefficients () for these novel solvents have been measured at T = (308.15, 318.15, and 328.15) K, using gas-liquid chromatography. The aliphatic solutes studied were normal alkanes (pentane, hexane, heptane, octane), alkenes (hexene, heptene, octene), alkynes (hexyne, heptyne, octyne), cycloalkanes (cyclopentane, cylcohexane, cycloheptane), and alcohols (methanol, ethanol). The aromatic solute studied was benzene. The molar excess enthalpy at infinite dilution (HE,) was calculated using the temperature dependency of data. The selectivity values for the phosphonium-based ILs indicate a poorer separation capability than imidazolium- or pyridinium-based ILs. The values of have been found to be in the following order: alkanes greater than alkenes greater than alkynes greater than aromatics. Selectivity values indicate the IL [thtd-Ph][BF4] as an effective solvent for the separation of benzene + alcohol systems. The measurements on the phosphonium ILs were further validated using the a priori COSMO-RS method. The COSMO-RS prediction was first benchmarked on the values obtained with [thtd-Ph] tris(pentafluoroethyl) trifluorophosphate, which gave the average absolute deviation (AAD) to be 15 %. Using COSMO-RS, values were obtained for the three phosphonium ILs, and the corresponding AADs were 9 %, 8 %, and 16 %.