The experiments were performed as follows (Fig. 1): 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.