Interactions of Volatile Organic Compounds with the Ionic Liquid 1-Butyl-1-methylpyrrolidinium Dicyanamide
journal contributionposted on 08.12.2011, 00:00 by Aleš Blahut, Vladimír Dohnal
Interactions of volatile organic compounds with the ionic liquid (IL) 1-butyl-1-methylpyrrolidinium dicyanamide [BMPYR][DCA] were explored through systematic gas–liquid chromatography retention measurements. Infinite dilution activity coefficients γ1∞ and gas–liquid partition coefficients KL of 30 selected hydrocarbons, alcohols, ketones, ethers, esters, haloalkanes, and nitrogen- or sulfur-containing compounds in [BMPYR][DCA] were determined at five temperatures in the range from (318.15 to 353.15) K. Partial molar excess enthalpies and entropies at infinite dilution were derived from the temperature dependence of the γ1∞ values. The linear free energy relationship (LFER) solvation model was used to correlate successfully the KL values. The LFER correlation parameters and excess thermodynamic functions were analyzed to disclose molecular interactions operating between the IL and the individual solutes. Among other ILs, [BMPYR][DCA] was identified to be a fairly cohesive solvent medium, which is capable of interacting specifically through all modes (lone electron pairs, dipolarity/polarizibility, and hydrogen bonding) with solutes of complementary capabilities. The hydrogen-bond basicity of [BMPYR][DCA] is somewhat lower than that of [EMIM][NO3] and [EMIM][MeSO3], but in contrast to these latter ILs studied by us previously [BMPYR][DCA] appears to possess also some proton-donating capability. The selectivities of [BMPYR][DCA] for the separation of aromatic hydrocarbons and thiophene from saturated hydrocarbons were found to be only (30 to 70) % of those exhibited by the most selective ILs, as [EMIM][SCN], [EMIM][MeSO3], or [EMIM][NO3]. On the other hand, the use of [BMPYR][DCA] as an entrainer in extractive distillations of some other mixtures which are difficult to separate (e.g., acetone + methanol) appears to be very promising.