(84d) Efficient Separation of Phenols From Oils Via Forming Eutectic Solvent

Phenolic compounds, which are basic materials of the organic chemical industry, are mainly products derived from direct coal liquefaction or coal tar. The present method to separate phenol compounds from oil mixtures is to chemically extract phenols using aqueous alkaline solutions (such as aqueous NaOH) and then to acidify the extract by mineral acids (such as aqueous H₂SO₄) to recover the phenols. However there are disadvantages: the use of large amounts of both strong alkalis and acids and the production of excessive amounts of waste water containing phenols.

In this work, ammonium salts was found to be successful as eutectic media for separating phenols from direct coal liquefaction oil and coal tar. First, ammonium salts have been used to separate phenols from modeling oils (hexane, toluene and p-xylene as model oil) via forming eutectic solvents. Ammonium salts, especially choline chloride (ChCl), were found to be successful as eutectic media for separating phenols (phenol and cresols) from oils (hexane, toluene and p-xylene). ChCl shows a short eutectic equilibrium time less than 3 min and an in-sensitivity to eutectic temperature. Significantly, no ChCl was found in the upper oil phase at equilibrium with the eutectic solvent. ChCl in the eutectic solvent can be recovered by diethyl ether and reused without mass loss and reduction in separation efficiency.

Then, ChCl were used to separate phenolic compounds in coal tar and coal liquefaction oil via forming eutectic solvents. ChCl also shows a short eutectic equilibrium time for coal tar and coal liquefaction oil. The extraction efficiencies of phenols from coal tar (distillate at 130-260 ^oC) with a total phenol content of 24.1% and direct coal liquefaction oil (distillate at 20-220 ^oC) with a total phenol content of 34.7 % are 76% and 86%, respectively, with only ChCl to phenol mass ratio of 1:1. Significantly, no ChCl was also found in the upper oil phase. ChCl in the eutectic solvents can also be recovered by diethyl ether and reused without mass loss and reduction in separation efficiency.

Compared with the traditional methods, this proposed method involving the formation of eutectic solvent with ChCl avoids the use of alkali and acid and the production of phenol containing waste water and shows a promising foreground in coal chemical engineering technology.

We thank Prof. Chengyue Li, Prof. Zhenyu Liu, and Dr. Qingya Liu for their help. This work is financially supported by the National Basic Research Program of China (2011CB201300) and by Shanxi Scholarship Council of China (2011-086).