Phase equilibria of toluene/heptane with tetrabutylphosphonium bromide based deep eutectic solvents for the potential use in the separation of aromatics from naphtha

Abstract

In this work, new solvents are introduced to conduct the task of removing aromatic hydrocarbons from the feed stream to ethylene cracker. Liquid–liquid equilibrium (LLE) data for ternary systems of toluene and heptane with two newly introduced deep eutectic solvents (DESs) were estimated experimentally at 40, 50 and 60°C and atmospheric pressure. The DESs are made from tetrabutylphosphonium bromide as salt and either ethylene glycol or sulfolane as hydrogen bond donor (HBD). The reliability of the LLE data were ascertained by applying the Othmer–Tobias and Hand correlations. The non-random two liquid (NRTL) model was used to correlate the experimental tie-lines and to calculate the phase compositions of the ternary systems. The results showed a very good agreement between calculated and experimental compositions. Further LLE data are presented to estimate the improvement of the separation by changing the salt:HBD molar ratio used to synthesize the DES at 30, 40, 50 and 60°C. This work illustrates the possibility of applying these two DESs as solvents for this extraction task.