a certain amount of model oil was placed in a conical flask, and then the extraction agent with a certain mole ratio to the phenols was added into the model oil. The flask was placed in an incubator shaker with a temperature controller within ±0.1 K of an appropriate temperature and 400 rpm for a known time. After the reaction, DES was formed, and two layers appeared in the model oil. The system was allowed to stand for more than 30 min. Finally, the upper and lower layers were carefully separated by using a funnel.