(2c) Separation of p-Cresol from the Cresol Isomers by Stripping Crystallization

Stripping crystallization (SC) is a new separation technique which combines distillation and crystallization. Basically, SC is operated at a triple-point condition, in which the liquid is simultaneously vaporized and crystallized due to the three-phase equilibrium. In essence, the process is continued until the liquid phase is completely eliminated and only the pure solid crystals remain in the feed. Thus, crystal washing is not required since only pure solid crystals remain in the feed and no impurities are adhered on the crystal surfaces at the end of SC. In the previous research, SC has been successfully applied to separate p-xylene from the mixed xylenes by Shiau et al. [1-3].

SC is applied in this study to separate the p-cresol/m-cresol mixture. Due to the close boiling points, it is very difficult to separate them by conventional distillation. The SC experiments show that p-cresol can be purified from 90% to 96%+ ,from 95% to 98%+ , from 97% to 98%+ , or from 98% to 99%+ in the p-cresol-enriched mixture. The experimental results are consistent with the simulation results. The recovery rate of p-cresol in the experiments can be greatly improved by adjusting the operating temperature and pressure during the SC process.

[1] Shiau, L. D.; Wen, C. C.; Lin, B. S., 2005, ?Separation and purification of p-xylene from the mixture of m-xylene and p-xylene by distillative freezing?, Ind. Eng. Chem. Res. , 44(7), p.2258-2265

[2] Shiau, L. D.; Wen, C. C.; Lin, B. S., 2006, ?Application of distillative freezing in the separation of o-xylene and p-xylene?, A.I.Ch.E. Journal, 52(5), p.1962-1967.

[3] Shiau, L. D.; Wen, C. C.; Lin, B. S., 2008, ?Separation of p-xylene from the multicomponent xylene system by stripping crystallization?, A.I.Ch.E. Journal, 54(1), p.337-342.