Food Biochemistry and Food Processing (2 edition)

BLBS102-c40 BLBS102-Simpson March 21, 2012 14:23 Trim: 276mm X 219mm Printer Name: Yet to Come

40 Separation Technology in Food Processing 771

CO 2 pump

Heatexchanger

CO 2 source

Cooling

bath

Heat exchanger

Extractor column

Separator

Back pressure valve

Pressure valve Extracts outlet

CO 2 outlet

Figure 40.2.Schematic diagram of a typical single-stage supercritical fluid extraction system with CO 2.

circulates the supercritical medium throughout the system.

Figure 40.2 shows an example of a typical single-stage su-

percritical CO 2 fluid extraction system. Once the supercritical

CO 2 and the feed reach equilibrium in the extraction vessel,

through the manipulation of pressure and temperature to achieve

the ideal operating conditions, the extraction process proceeds.

The mobile phase consisting of the supercritical CO 2 fluid

and the solubilized components is transferred to the separator

where the solvating power of the fluid is reduced by raising the

temperature and/or decreasing the pressure of the system. The

extract precipitates in the separator while the supercritical CO 2

fluid is either released to the atmosphere or recycled back to the

extractor. In the case where highly volatile components are being

extracted, a multistage configuration may have to be employed

as shown in Figure 40.3 (Shi et al. 2007a, 2007b, Kasamma et al.

2008).

The processes described above are semi-batch continuous

processes where the supercritical CO 2 flows in a continuous

mode while the extractable solid feed is charged into the extrac-

tion vessel in batches. In commercial-scale processing plants,

multiple extraction vessels are sequentially used to enhance

process performance and output. Although the system is in-

terrupted at the end of the extraction period, when the process is

switched to another vessel prepared for extraction, the unload-

ing and/or loading of the spent vessels can be carried out while

extraction is in progress, reducing the downtime and improving

the production efficiency.

A semi-continuous approach on a commercial scale uses a

multiple stage extraction processes that involve running the sys-

tem concurrently by harnessing a series of extraction vessels

in tandem, as shown in Figure 40.4. In this system, the pro-

cess is not interrupted at the end of extraction period for each

Dry test

meter

Extracts

Co-solvent inlet

Extractor column

CO 2 pump

3-stage separator columns

Pressure

regulator

Mixer

CO-solvent pump

Ice water trap

CO

(^2) inlet
Figure 40.3.Schematic diagram of supercritical fluid extraction system used to fractionate bioactive components from plant matrix using
supercritical carbon dioxide.