Separation of phenol and pyridine from coal tar via liquid–liquid extraction using deep eutectic solvents

Abstract Phenolic compounds are important industrial substances that derived from coal tar, and traditional acid–base method not only causes serious environmental problem, but remain a certain amount of pyridine in the dephenolized oil due to the complexation of phenol and pyridine. In this research, deep-eutectic solvents (DES) were developed as efficient extraction agent to separate both phenol and pyridine from coal tar with extraction efficiencies more than 90%. The extraction efficiency and distribution coefficient were selected as the evaluation indexes of extraction ability. The influences of the DES structure and composition were explored. The experiment factors, such as volume ratio of oil to DES, extraction temperature, extraction time were investigated, and the optimum parameters were obtained. Hydrogen bond was confirmed to be the extraction mechanism by spectrographic analysis. DES was recycled by back-extraction with excellent recycling properties and high extraction efficiencies. Finally, a specific extraction process was proposed and the preliminary simulation was carried out by Aspen Plus.