High-Purity Purification of Indole Contained in Coal Tar Fraction－ Separation of Close Boiling Mixtures of Indole by Solute Crystallization －

The purification of indole from 54.3wt% indole fraction (temperature range of distillate: 250-255 ) recovered by extraction-distillation combination of coal tar fraction (temperature range of distillate: 240-265 ) was examined by solute crystallization. The feed consists of eight components such as quinoline, iso-quinoline, indole, quinaldine, 1-methylnaphthalene, 2-methylnaphthalene, biphenyl and phenyl ether. Hexane and an aqueous solution of methanol (50 : 50 vol%) were used as the crystallization solvent and the coolant, respectively. A batch stirred tank of glass material was used as a crystallization apparatus. By increasing the operation temperature and the volume ratio of solvent to feed at initial, the purity of indole increas ed, but yields of indole showed a decreasing tendency. Solute crystallization method using hexane as a solvent was excellent because the purity of 99.3 wt% indole was recovered at the yield of 50% without washing operation.