The invention provides a preparation method of a variety specifications of dementholized peppermint oil and
menthol by combined
azeotropic distillation and
vacuum distillation technology. The method comprises the following steps that (1),
azeotropic distillation to remove front distillate: peppermint trichomes oil is taken, after azeotropic agent water is added,
azeotropic distillation is carriedout, front distillate is separated and detected, when olefin content in the front distillate is less than 1%, the azeotropic
distillation is stopped; oil and water separation is carried out, oil phasewaits for treatment; (2),
vacuum distillation to obtain post distillate: the above front distillate removed
oil phase is subjected to
vacuum distillation to obtain post distillate, the post distillate is detected, when the content of L-
menthol is more than 50% in the distillate, the vacuum
distillation is stopped; (3), atmospheric vapor
distillation. The method reduces the loss of the front distillate, at the same time, the
aroma of the front distillate can withstand 150 DEG C without being damaged by high temperature, the quality of dementholized peppermint oil is well guaranteed. And a variety specifications of dementholized peppermint
oil can be prepared by the method, at the same time, the high content of
menthol in the redundant post distillate can also be applied to the physical
crystallization process to produce high purity natural
menthol crystals.