Product Yield and Purity in Stripping Crystallization of L-Menthol from the Enantiomer Mixture

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. (2008, 2013, 2018).

Stripping crystallization (SC) is introduced in this work for chiral purification of L-menthol from the enantiomer mixture. As SC is operated in a series of the three-phase transformation conditions, SC combines melt crystallization and vaporization to produce the L-menthol crystalline product and mixture vapor from the mixture melt. The operating pressure for the three-phase transformation during the SC cooling process is determined based on the thermodynamic calculations. Sweating is applied at the end of SC to expel the mixture melt remained with the final L-menthol product. A model based on the mass and energy balances is proposed to determine the product yield and enantiomeric purity of L-menthol for SC.

References:

1. 1. Shiau, L. D. “Purification of styrene from a styrene/ethylbenzene mixture by stripping crystallization”, Eng. Chem. Res, 2018, 57, p6759-6765.

2. Shiau, L. D.; Liu, K. F. ”Investigations into the effects of the cooling rate on stripping crystallization”, Ind. Eng. Chem. Res, 2013, 52, p1716-1722.

3. Shiau, L. D., Wen, C. C. and Lin, B. S. “Separation of p-xylene from the multicomponent xylene system by stripping crystallization”, AIChE Journal, 2008, 54(1), p337-342, 2008.

Keywords: crystallization; distillation; purification