Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

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