Screening deep eutectic solvents as green solvents for efficient extraction of carbazole from model crude anthracene oil

Carbazole is a high value-added component of crude anthracene. Highly efficient and sustainable extraction solvents are extremely significant for carbazole separation. Deep eutectic solvents (DESs), as a new class of green solvents, have gained extensive attention from researchers in the field of separation. However, a large number of DESs are generated due to the enormous combinations of hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs), which makes it challenging to identify the most suitable DES for specific separation process. Therefore, a reliable and effective method for DESs screening was highly desirable. In this work, a DESs screening method was proposed for the separation of carbazole. Initially, the COSMO-RS model was employed to calculate thermodynamic properties at infinite dilution. Subsequently, the liquid–liquid phase equilibrium behavior of prescreened DESs was further predicted by COSMO-RS to eliminate those that were miscible with toluene. Finally, the practical extraction performance of the top DES candidates was evaluated through experimental investigation. The results well validated the reliability of the screening method, identifying tetraethylammonium chloride/propionic acid (1:2) as the most promising DES for carbazole separation. Furthermore, the extraction mechanism was explored using FT-IR analysis and quantum chemical calculations.