Vapor-Liquid Equilibria of Imidazolium Ionic Liquids with Cyano Containing Anions with Water and Ethanol

Abstract

Isobaric vapor-liquid equilibria of 1-butyl-3-methylimidazolium thiocyanate ([C(4)C(1)im][SCN]), 1-butyl-3-methylimidazolium dicyanamide ([C(4)C(1)im][N(CN)(2)]), 1-butyl-3-methylimidazolium tricyanomethanide ([C(4)C(1)im] [C-(CN)(3)]), and 1-ethyl-3-methylimidazolium tetracyanoborate ([C(2)C(1)im][B(CN)(4)]), with water and ethanol were measured over the whole concentration range at 0.1, 0.07, and 0.05 MPa. Activity coefficients were estimated from the boiling temperatures of the binary systems, and the data were used to evaluate the ability of COSMO-RS for describing these molecular systems. Aiming at further understanding the molecular interactions on these systems, molecular dynamics (MD) simulations were performed. On the basis of the interpretation of the radial and spatial distribution functions along with coordination numbers obtained through MD simulations, the effect of the increase of CN-groups in the IL anion in its capability to establish hydrogen bonds with water and ethanol was evaluated. The results obtained suggest that, for both water and ethanol systems, the anion [N(CN)(2)](-) presents the higher ability to establish favorable interactions due to its charge, and that the ability of the anions to interact with the solvent, decreases with further increasing of the number of cyano groups in the anion. The ordering of the partial charges in the nitrogen atoms from the CN-groups in the anions agrees with the ordering obtained for VLE and activity coefficient data.