(55c) A New Separation Method - Distillative Freezing | AIChE

(55c) A New Separation Method - Distillative Freezing

Authors 

Shiau, L. - Presenter, Chang Gung University
Wen, C. - Presenter, Chang Gung University


The distillative freezing (DF) operation is applied to separate the mixture of the volatile compounds. In principle, the DF process is operated at triple point condition, in which the liquid mixture is simultaneously vaporized and solidified due to the three-phase equilibrium. By lowering temperature and reducing pressure during the operation, the DF process results in the formation of pure solid, and liquid phase and vapor phase of mixtures. The process is continued until the liquid phase is completely eliminated and only the pure solid crystals remain in the feed. Due to the very close boiling points of p-xylene (PX, bp=138.37°C), m-xylene (MX, bp=139.12°C), ethylbenzene (EB, bp=136.19°C), it is very difficult to separate them by conventional distillation. The DF process has been successfully applied to separate PX from a liquid mixture of 10% MX and 90% PX (Shiau et al., 2005). DF is applied in this work to separate and produce the solid PX crystals from the multi-component xylene mixture containing PX, MX, EB and OX. The experimental results indicate that solid PX crystals can be produced and the purity of PX crystals can reach 99.5%~99.9 for the xylene mixture of MX, PX EB and OX with PX ranging from 87 to 90%.

Shiau, L. D.; Wen, C. C.; Lin. B. S., Separation and purification of p-xylene from the mixture of m-xylene and p-xylene by distillative freezing. Ind. Eng. Chem. Res. 2005, 44, P2258-2265.