Roles of a hydrogen bond donor and a hydrogen bond acceptor in the extraction of toluene from n-heptane using deep eutectic solvents

As analogues of ionic liquids, deep eutectic solvents (DESs) have attracted considerable attention in the field of separating aromatics from aromatics/aliphatics mixtures. In this work, the performance of a series of DESs was evaluated for their selective extraction of toluene from toluene/n-heptane mixtures. The results showed that the extraction ability for toluene using DESs was greatly influenced by hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs) which formed the DESs. The selectivity of toluene was distinctly enhanced by short side chains, a small central atom of the cation and a large anion of the HBA, together with a suitable position for an alkyl chain and appropriate functional group of the HBD. It was also found that an increase of extraction temperature at the studied range could enhance the selectivity for toluene. This work makes the roles of HBAs and HBDs clear in the extraction of aromatics, providing information for designing more effective DESs for aromatics extraction.