An Effective Approach for Separating Carbazole and Its Derivates from Coal-Tar-Derived Anthracene Oil Using Ionic Liquids

Carbazole and its derivates are important value-added chemicals (VACs) in anthracene oil (AO), which is one of the coal tar fractions. In this work, imidazolium-based ionic liquids (ILs) were used as novel extractants to extract carbazole from AO and the effects of anionic substituents and cationic structures on carbazole extraction were investigated. The results show that the recovery and purity of carbazole reached up to 96.2 and 98.0%, respectively, by extracting AO-related model oil with the ILs. The hydrogen-bond force existing between 1-butyl-3-methylimidazolium dicyanamide (IL_a) and carbazole was revealed by Fourier transform infrared spectroscopy and two-dimensional nuclear magnetic resonance and further confirmed by density functional theory simulation. π–π interactions and hydrogen bonds formed between ILs and carbazole play crucial roles in effectively separating carbazole from AO. Simultaneously, the stability test shows that IL_a is easily recyclable and highly stable for carbazole separation. Moreover, the recovery and purity of carbazole extracted from AO are 66.6 and 90.2%, respectively, with IL_a as the extractant by flash chromatography. This study provides a green and effective approach for separating VACs from coal tar and its derived fractions.