Extraction Technologies For Medicinal And Aromatic Plants - Unido
Extraction Technologies For Medicinal And Aromatic Plants - Unido
Extraction Technologies For Medicinal And Aromatic Plants - Unido
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10 SUPERCRITICAL FLUID EXTRACTION OF MEDICINAL AND AROMATIC PLANTS: FUNDAMENTALS AND APPLICATIONS<br />
To measure extraction profi les, a small pilot-scale apparatus can<br />
be used. Extractor and separator volumes do not need to exceed 1 liter each.<br />
The analytical system must be suitable to measure the concentration and purity<br />
of the products of interest. Basic requirements in terms of equipment are:<br />
1. A liquid CO2<br />
storage tank<br />
2. A pump for liquid CO2<br />
3. A cooler to prevent CO2<br />
from evaporating in the pump<br />
4. A heat exchanger to control the temperature of CO2<br />
entering<br />
the extractor<br />
5. An extraction vessel<br />
6. A heat exchanger to control the CO2<br />
plus solute mixture entering<br />
the separator<br />
7. A separation vessel<br />
Note that condensing and recycling of CO2 after separation is<br />
not needed at the laboratory-scale developmental level, whereas these are<br />
essential requirements at the industrial production level.<br />
All parts of the SFE laboratory-scale plant must be designed<br />
in order to resist the maximum operating pressure. If this does not exceed<br />
300-350 bar, the entire equipment (e.g. vessels, valves, fi ttings) is pretty<br />
much of standard type and relatively inexpensive. If, as usual, stainless<br />
steel is used, the thickness of any part of the plant can be easily calculated<br />
by applying the Von-Mises equation:<br />
with:<br />
Pi k2<br />
k2 √⎯3 < σam<br />
(5)<br />
– 1<br />
σam = σs<br />
Sf<br />
where Pi is the internal pressure, k is the external to internal diameter ratio,<br />
σs is the yield stress, and Sf is a suitable safety factor (usually Sf=1.5).<br />
From Eq. 5, it can be seen that the thickness of a cylindrical<br />
vessel depends on its diameter. Examples are given in Table 1 for a vessel<br />
of 0.2 m internal diameter, with both stainless steel and carbon steel construction<br />
materials.<br />
Table 1: Thickness (s) of a thick-wall cylindrical vessel of 200 mm internal diameter<br />
as a function of pressure (SS=stainless steel, CS=carbon steel)<br />
P [atm] 50 100 150 200 250 300<br />
s [mm]<br />
SS 3.8 8.1 12.9 18.5 25.0 32.7<br />
CS 2.2 4.6 7.2 10.0 13.0 16.2<br />
176<br />
(6)
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