(185e) Separation of the Xylene 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 m-xylene from the mixed xylenes, including m-xylene, p-xylene, o-xylene and ethylbenzene. Due to the close boiling points, it is very difficult to separate them by conventional distillation. The SC experiments show that m-xylene can be purified from 90% to 99% in the mixed xylenes. The experimental results are consistent with the simulation results. The recovery rate of m-xylene in the experiments can be 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.