Natural flavourings from green chemistry for foods and beverages - Natural Food Additives, Ingredients and Flavourings - page 262

Fig. 12.2 Typical components of supercritical CO 2 extraction equipment.

refrigerated at 1.7-2.4 MPa and then further cooled before entering the primary
pump. The compressed CO 2 is then heated to the desired extraction temperature
and then passed through the extractors, which may be arranged either in parallel
or in series. The extract is recovered in a series of separators that have sequentially
lower pressures, resulting in precipitation of the increasingly insoluble extracted
components, and the CO 2 is fi nally condensed and returned to the storage tank.
However, CO 2 will be lost in this closed circuit when the extractors are emptied
after decompression, although this CO 2 can be re-compressed and returned to the
storage tank. In cases when liquid CO 2 is used as the extraction, solvent separators
are replaced with evaporators.
Solubility in supercritical CO 2 is essentially proportional to density (Chrastil
1982; Hartono et al. 2001) and this in turn is proportional to pressure and inversely
proportional to temperature. Figure 12.3 shows the relationship between density
and pressure at selected temperatures and it can be seen that the density rises
rapidly once past the critical point. In addition to the temperature and pressure of
supercritical CO 2 , extraction effi ciency is directly infl uenced by other process
parameters:

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