Thermodynamic evaluation of imidazolium based ionic liquids with thiocyanate anion as effective solvent to thiophene extraction

Abstract

In order to have deep insight on the molecular interactions between thiophene (TS) and ionic liquids, the density, speed of sound and refractive index of binary liquid mixture of TS with 1-hexyl-3-methylimidazolium thiocyanate [HMIM][SCN], and 1-octyl-3-methylimidazolium thiocyanate [OMIM][SCN] at T=(288.15 to 303.15)K and at atmospheric pressure have been measured in dilute region of TS. Various thermophysical parameters including partial molar volumes, v̅m,i, apparent molar volumes, Vᵩ, standard partial molar volumes Vϕ0, partial molar isentropic compressibility, κϕ0, excess molar volumes, VE, excess partial molar volumes, v̅m,iE, and molar refractions, RD, have been calculated using these data. The densitometric and refractometric non-intrinsic contributions to the partial molar volume, θd and θr have been obtained using the measured experimental data. Also, interaction volume, Vint, and cavity volume, Vcav, have been calculated from scaled particle theory (SPT). The results demonstrate that the ionic liquids with shorter alkyl chain length interact effectively with thiophene as according to the calculated interaction volumes and excess partial molar volumes. One would expect that the extraction efficiency of [HMIM][SCN] is slightly better than the other ionic liquid. The calculated quantities such as v̅m,iE and Vint can be used to predict extraction capability of these ionic liquids to thiophene extraction from fuel.