Vacuum distillation
The essential oil is obtained from plant materials under a vacuum
varying in intensity depending on the material [37, 38]. The
evaporation temperature of the material is lower under vacuum. As a
result, materials can be separated by consuming less energy. Vacuum
distillation is a suitable method for separating components which have a
high boiling point and prevents the destruction of volatiles materials
[17]. This method is rarely used to distill oil directly from plant
materials.
The table 2 shows a general comparison between conventional distillation
methods (hydro-distillation, water-steam distillation steam
distillation). In this table, the construction, available temperature,
available pressure, plant material suitability, use of Hydro-diffusion,
hydrolysis condition and rate of distillation and yield are compared
[17, 23].
Table 2-Comparison of Conventional distillation methods