Deep Eutectic Solvents for the Separation of Toluene/1-Hexene via Liquid–Liquid Extraction

The separation of aromatic/olefin mixtures is a difficult task in the petrochemical industry, since the boiling points of these hydrocarbons are very similar. This work aims to use deep eutectic solvents (DESs) for the extraction of toluene from 1-hexene by liquid–liquid extraction. A total of 53 DESs were studied qualitatively and quantitatively using the COSMO-RS approach to separate the binary mixture of toluene and 1-hexene. The selectivity, capacity, and performance index of all DESs were evaluated by calculating the activity coefficient at infinite dilution. The σ-profile and σ-potential of each component were interpreted to evaluate the interactions between the different species. We then selected three DESs for experimental validation, namely benzyltriphenylphosphonium chloride:triethylene glycol BzTPPCl:TEG (1:8), tetrabutylammonium bromide:triethylene glycol TBABr:TEG (1:3), and tetrabutylammonium bromide:ethylene glycol TBABr: EG (1:4). Experimental liquid–liquid equilibrium data were obtained for the ternary mixtures {1-hexene (1) + toluene (2) + DES (3)} at T = 298.15 K and atmospheric pressure. Based on the selectivity data and the solute distribution ratio, the feasibility of different DESs as extractive solvents was tested. Finally, 1H NMR was performed to elucidate the extraction mechanism. No DES was found in the raffinate phase, indicating minimal cross-contamination.