A. DISTILLATION OF ESSENTIAL OILS
Introduction. The majority of essential oils have
always been obtained by steam distillation or, in the more general sense, by hydrodistillation.1
The practical problems connected with distillation of aromatic plants are, therefore,
of utmost importance to the actual producer of essential oils. Yet our present-day
technical literature, especially English literature, is surprisingly meager in regard
to data and information which might serve as a really practical and reliable guide.
This shortcoming has been felt severely, especially during the years of World War
II, when prospective producers in North, Central and South America sought advice
concerning the distillation of oils which, due to war conditions, could no longer
be imported from Europe and Asia. Encouraged by countless inquiries from almost
every part of the Western Hemisphere, the author finally decided to compile a
comprehensive paper on this topic which would incorporate not only his own experience
of many years in the field, but also the most important phases gathered from the
literature published so far. There exist on this subject two really outstanding
books, viz., the classical work of Dr. von Rechenberg, who spent a lifetime in the
actual distillation of essential oils and on systematic research pertaining to
the physical phenomena and laws underlying distillation. These works have never
been translated from their German text, are now out of print and, due to the ravages
of World War II, not readily available. This author would consider it an irreplaceable
loss to our industries if the most important parts of these books, at least those
dealing with the practical aspects of essential oil distillation, were not preserved
for posterity. Unfortunately, the lucid writings of Professor von Rechenberg
have not attained sufficient attention outside of Germany. In more than one way
they are so fundamental and exact that they require no modification. This
author has, therefore, translated parts of von Rechenberg's treatises, with a
view to incorporating some of the most essential features into his own text. These
books are recommended: C. von Rechenberg, "Theorie der Gewinnung und
Trennung der atherischen Ole," Schimmei & Co., Miltitz bei Leipzig,
1910.
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This
chapter by Ernest Guenther.
1 The term "hydrodistillation"
is used
by von Rechenberg
as referring to distillation
with water vapors (steam).
C. von Rechenberg, "Einfache und Fraktionierte
Destination in Theorie und Praxis,” Schimmel & Co., Miltitz bei Leipzig,
1923.
A much smaller book, "Die Fabrikation und
Verarbeitung von atherischen Olen," by Max Folsch, Hartleben's Verlag, Wien
und Leipzig, 1930, leans on von Rechenberg's text but adds much practical
advice.
Those interested particularly in the distillation
of colonial oils and in field distillation requiring simple apparatus are referred
to Gattefosse's "Distillation des Plantes Aromatiques," Librarie
Centrale des Sciences, Paris, 1926.
"Aspects of the Theory of Distillation as
Applied to Essential Oils," have been described by Leslie Bloomfield in a series
of comprehensive papers which appeared in the Perfumery and Essential Oil Record,
Vol. 27 (1936), 131, 177, 294, 334, 368, 404, 443, 483; Vol. 28 (1937), 24, 59.
"A Treatise on Distillation," by Thos.
H. Durrans, was published also in the Perfumery and Essential Oil Record, June,
1920, 154 to 198.
The mathematical and physical principles connected
writh steam distillation in general are discussed in "Wasserdampf-destillation,"
by N. Schoorl, which appeared in Rec. Trav. Chim. 62 (1943), 341-379.
This chapter will be divided into two parts, the
first dealing with the fundamental or theoretical principles underlying all distillation
processes, and the second treating more specifically the practical aspects of distillation
as applied directly in the essential oil industry.
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