(376bn) Purification of L-Menthol Enantiomers from the Racemic Mixture By Stripping Crystallization
Menthol is widely used in perfumery, cigarette, cough drops, and nasal inhalers for its cooling effect and refreshing flavor. Only L-menthol has been reported to have analgesic effect whereas D-menthol is lack of analgesic and flavor properties. Although natural L-menthol is obtained by distillation from the leaves of various subspecies of mint, menthol can also be synthesized via a number of routes, by which a racemic mixture is obtained. Thus, separation and purification of L-menthol from the racemic mixture has been an important research issue. A thermodynamic model is developed in this work to simulate the three-phase equilibrium during the SC operation and to direct the batch SC experiments. The experiments show that no crystallization occurs during SC without stirring due to subcooling of the liquid enantiomers. Stirring can eliminate subcooling during SC, leading to the L-menthol crystals gradually formed. The experimental results, including the final enantiomeric purity and recovery ratio of L-menthol, are consistent with the simulation results predicted by the model.
Keywords: crystallization; vaporization; purification; menthol; thermodynamics process
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