Formation and Extractive Desulfurization Mechanisms of Aromatic Acid Based Deep Eutectic Solvents: An Experimental and Theoretical Study.

The formation and extractive desulfurization (EDS) mechanisms of aromatic acid based deep eutectic solvents (DESs) were studied experimentally and through quantum chemistry calculations. Hydrogen bonding and van der Waals forces were investigated as the driving forces for the formation of aromatic acid based DESs by means of 1 H NMR and FTIR spectroscopy, and DFT calculations. The driving forces of EDS were also studied. The results showed that van der Waals forces and other weak interactions were the main diving forces for EDS, and the structures of the aromatic acid based DESs did not change after EDS. The interaction energy between the aromatic acid based DESs and thiophene (TH), benzothiophene (BT), and dibenzothiophene (DBT) were calculated by DFT to understand the EDS order: TH<BT<DBT. Moreover, the optimal EDS conditions were studied. The amount of BT (500 ppm) was reduced to below 10 ppm under the optimal conditions of using triethylamine/o-hydroxybenzoic acid ([TEA]/[OHBA]). The desulfurization efficiency of [TEA]/[OHBA] was stable after ten cycles, and the mechanical loss of [TEA]/[OHBA] could be ignored.