Dicyanamide-based ionic liquids in the liquid-liquid extraction of aromatics from alkanes: Experimental evaluation and computational predictions

In this work, we have studied the potential use of the 1-allyl-3-methylimidazolium dicyanamide ([amim][DCA]) and the 1-benzyl-3-methylimidazolium dicyanamide ([bzmim][DCA]) ionic liquids (ILs) in the liquid-liquid extraction of aromatic hydrocarbons. To design an industrial process of extraction of aromatic hydrocarbons from alkanes, it is essential to measure the liquid-liquid and vapor-liquid equilibria between solutes and solvent, and to perform also a thermophysical characterization of the solvent. Because of this, we have studied the liquid-liquid extraction of toluene from n-heptane at 313.2 K and the vapor-liquid separation of n-heptane from toluene in the presence of [amim][DCA] and [bzmim][DCA] at 323.2 K, 343.2 K, and 363.2 K. Densities and viscosities as a function of temperature and the thermal stability of both ILs were also determined. The [amim][DCA] showed suitable extractive and physical properties to replace sulfolane and an adequate maximum operation temperature (MOT) to be employed at industrial scale. The ([bzmim][DCA]) showed good extractive properties but high viscosities. To complete the study, the Conductor-like Screening Model for Real Solvents (COSMO-RS) methodology was employed to predict the liquid-liquid and vapor-liquid equilibria between the hydrocarbons and ILs and the physical properties of ILs. A comparative evaluation between experimental results and COSMO-RS calculated values was performed.