Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

8 MICRODISTILLATION,THERMOMICRODISTILLATION AND MOLECULAR DISTILLATION TECHNIQUES
Table 1: Relative effi ciencies of common heating devices
Appliance
Temperature,
°C
Rating, W
Time
Energy used,
kWh
Energy cost,
US$
Electric oven 177 2000 1 h 2 0.17
Convection
oven
163 1853 45 min 1.39 0.12
Gas oven 177 36 1 h 3.57 0.07
Microwave
oven
High 1440 15 min 0.36 0.03
A
B
Figure 1: Mint gland: (A) before and (B) after microwave irradiation
(Microphotographs courtesy of Radient Technologies Inc.)
It is evident then that the main resistance to solid-liquid mass
transfer, the transport of the solute through cell membrane, is eliminated
because of the rupture of the cells. Besides cell breakage, the other advantages
of microwave heating are:
1. Improved “existing” products
2. Increased marker recovery
3. Increased purity of the extract
4. Reduced heat degradation
5. Reduced processing costs
6. Signifi cantly faster extraction
7. Much lower energy usage
8. Much lower (order of magnitude) solvent usage
9. Potential for “new” products
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