Ternary phase diagram of phenanthrene and carbazole in different solvents and its application in the separation of them

Highlights: • Only PHE-rich solid solution can be formed in PHE-CAR-solvent ternary phase diagram. • Pure CAR can be separated from PHE-CAR mixture through solvent crystallization. • The difference coefficient of solubility (Ds) was put forward to assist screening solvents for separating PHE-CAR mixture. • Among DMF, acetone, MeCN and toluene, toluene is the most suitable solvent for separating PHE-CAR mixture. -- Abstract: The separation of phenanthrene (PHE) and carbazole (CAR) has been a tough job since the formation of solid solutions. Development of new separation strategy for PHE-CAR mixture highly depends on their phase equilibrium behaviour. In this work, ternary phase diagrams of phenanthrene (PHE) and carbazole (CAR) in dimethylformamide (DMF), acetone, acetonitrile (MeCN) and toluene at T = 308.15 K under normal atmosphere were determined through wet residue method. It was found that PHE-rich solid solution α was formed in the particular composition range of PHE-end. On the contrary, no CAR-rich solid solution was formed in CAR-end. These results were further verified through powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC). Based on the ternary phase diagrams, a difference coefficient of solubility (Ds) was put forward to assist screening and evaluation of solvents for solution crystallization. Among the four tested solvents, toluene is the most suitable one for separating PHE-CAR mixture.