Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

8 MICRODISTILLATION,THERMOMICRODISTILLATION AND MOLECULAR DISTILLATION TECHNIQUES
in signifi cant proportions. These investigations show that more than 95% of
the oil in the condensate can be recovered. The polymeric adsorbents used
are hard cross-linked macroreticular beads which can be used in adsorptionregeneration
cycles practically indefi nitely. The technique is simple to use
and does not require sophisticated instrumentation as the breakthrough
can be judged from the smell of the water coming out of the adsorbent bed.
The regeneration of the spent bed can be done using low-boiling alcohols
or ketones, and the eluate can be distilled in a relatively short distillation
column to obtain a relatively high boiling oil fraction.
8.6.2 Pervaporation Process
Membrane separation processes have been receiving increasing
attention particularly for situations involving recovery from relatively dilute
(~1000 ppm) aqueous solutions. Pervaporation is one such process which
yields very high (~1000 ppm or more) selectivity in the very dilute solution
range. Essential oil components which have high affi nity for organophilic
polymers can be recovered at very high selectivities. One study showed that
silicone rubber membranes yielded bold menthol crystals when the Mentha
condensate water was studied under the pervaporation mode. Similar results
were also obtained for basil water. Subsequent studies showed that
the high selectivity of properly selected membranes results in a permeate
concentration far exceeding the solubility limit of the organics, resulting in
phase separation.
Figure 3: Recovery of dissolved organics using pervaporation
The separate oil layer can be directly recovered to blend with
the main oil fraction to obtain premium grade oil. Figure 3 shows a schematic
of pervaporation-based recovery of dissolved essential oils in the condensate.
It is evident that this technique consists of a closed-loop operation
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