Direct Steam Distillation Direct Steam Distillation 

In case of direct steam distillation, the freshly cut drug is introduced into the distillation flask. The generated steam is made to pass through the drug material as shown in Fig. 5.1, and the volatile oil content along with the steam on being passed through the water condenser is collected in Florentine Flasks of the type FLW or FHW depending on whether the resulting oil is lighter than water or heavier than water.

Assembly for Preparation of Volatile Oils by Steam Distillation
Fig. 5.1 Assembly for Preparation of Volatile Oils by Steam Distillation
The various parts of the assembly for the preparation of volatile oils by steam distillation are as follows:
A = Steam generator (Copper),
B = Distillation Flask,
C = Sand bath,
D = Water condenser,
E1 = Florentine Flask for oils lighter than water (OLW),
E2 = Florentine Flask for oils heavier than water (OHW), and
F = Beaker.
Caution The distillation flask is heated initially to start the process of steam distillation. Once the distillation commences the heat of the steam entering the flask not only maintains the high-temperature required but also in removing the volatile components to the water condenser for ultimate collection in the respective Florentine Flask.
In actual practice, however, there are three different modes of distillation depending exclusively on the condition of the plant substance, namely:
(a) Water Distillation: It is mostly applicable to such plant material which is dried initially in air and the constituents are not degraded by boiling upto 1000C.
Example: Turpentine Oil—In this instance, the crude turpentine oleoresin is added directly into the distillation flsk and subsequently subjected to distillation.
(b) Water and Steam Distillation: It is often suitable for such plant material, whether fresh or dried, the constituents of which undergo degradation by direct boiling.
Example: Clove Oil, Cinnamon Oil—In this case, the crude drug is first macerated with water for several hours, prior to steam distillation.
(c) Direct Steam Distillation: It is invariably applicable to fresh drugs that is loaded with sufficient natural moisture and hence no maceration is required.
Example: Pippermint Oil, Spearmint Oil—In this instance the freshly cut drug is added directly into the distillation flask prior to steam distillation.

Source:Pharmacognosy And Pharmacobiotechnology By Ashutosh Kar

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