Highly efficient separation of anthracene and carbazole in crude anthracene by composite extractants with low viscosity

Efficient separation of anthracene (AN) and carbazole (CAR) from crude anthracene presents a significant challenge. In this study, composite extractants were synthesized using quaternary ammonium-based deep eutectic solvents (DESs) combined with N, N-dimethylformamide (DMF) to address this issue. The incorporation of DMF into DESs notably enhances the solvent–solute mixing contact efficiency and reduces the viscosity of the composite extractant, thereby accelerating mass transfer kinetics. Remarkably, within just 30 min, the purity of anthracene (P_AN) achieved was as high as 95.39%, and the distribution coefficient of carbazole reached 0.74. The underlying mechanism of the separation process was elucidated through molecular dynamics simulations, Fourier-Transform Infrared Spectroscopy, and Nuclear Magnetic Resonance spectroscopy. Adding DMF disrupts the complex hydrogen-bonding network in the original DESs system, allowing N-H… Cl hydrogen bonds to form quickly. These bonds are essential for the extraction process. Furthermore, DMF reduces interactions among DES components, leading to high mass transfer efficiency and a shortened separation time for AN and CAR. The composite extractant developed in this study demonstrates outstanding efficacy in the separation of AN and CAR, providing a promising prospect for the separation of other high-value products in the coal tar.