Thermophysical properties of alkyl-imidazolium based ionic liquids through the heterosegmented SAFT-BACK equation of state

Abstract

Heterosegmented molecular model combined with SAFT-BACK EOS was developed to predict the pVT and second derivative properties including speed-of-sound, isothermal compressibility and isobaric thermal expansivity of some alkyl-imidazolium ionic liquids (ILs) with [PF6]−, [BF4]− and [NTf2] anions. In this work, an IL was considered as two components, a cation and an anion. The cation of IL is treated as chain-like entity and was divided into several kinds of segments including cation head (imidazolium ring) and several segments of CH2 (including CH3) in the alkyl tails of the IL molecule, while the anion is not divided into segments and treated as a whole. The segment shape is described by a non-spherical parameter with using a hard convex body term as the reference. To account for the association scheme, the cation head and the anion of ILs each was considered one association site, which can only cross-associate. Moreover, we have considered a dipolar interaction between anion and cation head where the effective dipole moment is approximated as a linear function of density. The heterosegmented SAFT-BACK model was found to be able to correctly describe the second-order thermodynamic derivative properties as well as pVT properties of ILs studied in this work.