Principles of Distillation
Thermodynamics play an important role in the distillation
of essential oils. In order to vaporize any liquid,
energy in the form of heat must be applied. This energy
is termed latent heat. When a vapor is converted back
to liquid, what is actually happening is a reduction
and release of that latent heat.
In order for a liquid to be vaporized, latent heat
must be applied to this liquid until its temperature
attains the point where its vapor pressure becomes
equal to the surrounding atmospheric pressure. When
it reaches this point the temperature will rise no
further. However, if heat continues to be applied,
the liquid will take up this latent heat and then
vaporize at the appropriate rate. At this point the
liquid has said to have reached its “boiling
point” under the prevailing pressure.
When mutually insoluble compounds such as water and
essential oil are present, the total pressure exerted
by the mixed vapor then becomes the sum of the partial
pressures exerted by each constituent present. This
liquid mixture will boil when its temperature is raised
to the point where the combined vapor pressure of
its components becomes equal to the surrounding pressure.
Essential
Oil Production
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This being said, it follows that the basic principle
of distillation consists of bringing two mutually
insoluble liquids (essential oil and water) into contact
at a temperature very close to the boiling point of
the more volatile of the two, the water. With the
addition of a small amount of vapor pressure from
the essential oil the combined pressure is equal to
the surrounding pressure. At this point the mixture
will boil and the oil will vaporize into the passing
steam as fast as its requirement of latent heat can
be applied from a external source.
When this vapor mixture enters the condenser, it is
exposed to a cool surface which again results in a
transfer of latent heat, this time causing a reduction
in latent heat of the vapor mixture. The result of
this reduction is the conversion of the vapor back
to a liquid state.
We now have a liquid that is a mixture of the insoluble
components found in the still, namely water and essential
oil. These liquid components have different densities
which allow there separation as a natural state of
separation generally occurs. In most instances the
essential oil will float to the top, however this
is not always the case. Some oils such as Vetiver
are more dense than water and thus will settle at
the bottom while other oils such as Cinnamon leaf
have differing densities, with part of the oil sinking
and another floating to the top of the water.
Heat from the Distillation process can at times change
the natural compositions found within the botanic
and may even manufacture new components of immeasurable
benefit. A classic example of this is with Chamomile,
which in distillation manufactures ‘chamazulene’,
the profound anti-inflammatory component.
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