Separation of the Cresol Isomers by a New Technique Combining Distillation and Crystallization

A new separation technology, called stripping crystallization (SC) or distillative freezing (DF), has been recently developed in our laboratory to separate the mixtures with close boiling temperatures, including the mixed xylenes [1-3] and the benzene/cyclohexane mixture [4]. In principle, SC is operated at a triple-point condition, in which the liquid mixture is simultaneously vaporized and crystallized due to the three-phase equilibrium. Thus, SC combines distillation and crystallization to produce pure crystals. Due to the close boiling points of p-cresol (201.98°C) and m-cresol (202.27°C), it is very difficult to separate them by conventional distillation. The experiments show that the SC operation can be applied to purify p-cresol from the cresol isomer while it is rather difficult to purify m-cresol. In the purification of p-cresol by SC, the recovery rate increases with increasing operating pressure while the final purity of the product decreases with increasing operating pressure.

References:

[1] L.D. Shiau, C.C. Wen, B.S. Lin, Ind. Eng. Chem. Res., 2005; 44, 2258-2265.

[2] L.D. Shiau, C.C. Wen, B.S. Lin, AIChE J., 2006; 52, 1962-1967.

[3] L.D. Shiau, C.C. Wen, B.S. Lin, AIChE J., 2008; 54, 337-342.

[4] L.D. Shiau, C.C. Yu, Sep. Purif. Technol., 2009; 66, 422-426.