Extraction and interaction insights for enhanced separation of phenolic compounds from model coal tar using a hydroxyl-functionalized ionic liquid

Abstract

Phenols are valuable chemicals and widely applied in chemical industry, which have a high content in coal cracking oils. The separation of phenols from coal tar oils is of significance. Usually, the caustic washing technology is adopted in industry, which is environmental unfriendly due to the discharge of a large amount of waste water. This work aims to effectively recover the high-added value phenolic compounds from coal tar oil using m-cresol as a typical phenolic compound by means of a hydroxyl supported ionic liquid N-hydroxyethyl-4-picoline nitrate ([C2OH-4-pic][NO3]). The ionic liquid (IL) ([C2OH-4-pic][NO3]) was synthesized and characterized by 1H NMR. The factors of separation temperature, mass ratio of IL to coal tar model oil, extraction time and coexistent aromatic content in coal tar model oil were investigated. Also, the extraction performance of the prepared IL for the different phenolic components were explored. The separation efficiency (E) of [C2OH-4-pic][NO3] were 98.99% for m-cresol, 98.39% for o-cresol, 98.65% for p-cresol and 99.99% for phenol at 298.15 K with the mass ratio of 1:5 and the extraction time of 30 min. Afterwards, the intermolecular interactions between the IL and m-cresol were investigated by calculating the spatial and radial distribution function, averaged noncovalent interaction and self-diffusivity using molecular dynamics (MD) simulations and the formation of hydrogen bond was validated by FT-IR. The regeneration of [C2OH-4-pic][NO3] was performed and was characterized by 1H NMR. Finally, the separation process was designed based on the above exploration.