Efficient separation of phenols from phenols-containing oil mixtures via forming hydrogen bonds

Phenols, which mainly come from coal direct liquefaction oil and coal tar of medium and low temperature pyrolysis, are important chemical raw materials. At present, the main method to separate phenols from oil in industry is alkali washing method, which needs to consume a lot of inorganic acid and alkali solutions and corrodes equipments. Meanwhile, this method produce a lot of wastewater containing phenols, which is difficult to treat and costs much. Therefore, it is necessary to develop new separation methods. In this work, the separation of phenol from oil mixtures was proposed by using mildronate (THP), Girard's Reagent T, and Girard's Reagent P. The results showed that the mentioned separation agents could form deep eutectic solvent (DES) with phenol and then separate phenol. The highest separation efficiency of phenol was 96.5% by THP, and the residual phenol content in oil was as low as 1.3 g/L; it was enough to finish separation in 10 min; the initial phenol content had no effect on the minimum residual phenol content (about 8.8 g/L) in oil after separation. An n-hexane washing method was used to remove the neutral oil entrained in DES. The results showed that the neutral oil to phenol mass ratio in DES was reduced to 0.04, which indicated that the purity of phenol product was greatly improved. THP was renewable and reused for 5 times, and its properties remained unchanged. Finally, FT-IR spectra showed that there was hydrogen bonds formed between THP and phenol.