High-Performance Separation of Phenolic Compounds from Coal-Based Liquid Oil by Deep Eutectic Solvents

The separation of phenolic compounds from coal-based liquid oil is of economic value and practical significance. Conventional separation techniques for phenolic compounds always produce a large amount of wastewater. Herein, deep eutectic solvents (DESs) are considered as effective alternatives to traditional solvents. To complete the separation of phenolic compounds from coal-based liquid oil, DESs should have stronger interactions with phenols than the oil and form new DES-phenol aggregates, breaking the original molecular aggregates in the oil. Initially, density fuunctional theorycalculations were used to explore and prove the feasibility of phenolic compound separation by a choline chloride (ChCl)-glycerol DES from the perspective of interaction type and intensity, and the calculation results were verified by spectral experiments. Then, based on the phenol removal efficiency and neutral oil entrainment, the influences of the mole ratio of glycerol to ChCl, separation temperature, and DES dose were investigated and followed by discussions on the reuse of DES and a comparison of its separation capacity with that of a reported separation agent. Finally, this DES was applied to separate phenolic compounds from real coal-based liquid oil. The results show that H-bonds between the DES and phenolic compounds are the main driving force of this separation process. Under optimal conditions, the ChCl-glycerol (1:1) DES can extract 98.3% of the phenolic compounds with only 4.2% entrained neutral oil, and the selectivity is better than that of ChCl alone. Additionally, satisfactory results were obtained in the separation of phenolic compounds from real coal liquefaction oil and real coal tar, providing a universal method for the separation of phenolic compounds from coal-based liquid oil.