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Handbook of Solvents - George Wypych - ChemTech - Ventech!

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21.1 Supercritical solvents 1441<br />

21.1.3.1 Leaching - generic application<br />

Leaching is usually incorrectly referred to as extraction <strong>of</strong> a solid substrate, and is commercially<br />

the most significant application <strong>of</strong> supercritical fluids. A generic flowsheet, shown in<br />

Figure 21.1.13, illustrates the basic processing concepts. A heat labile natural substrate is<br />

usually contacted with a flowing supercritical fluid in a semi-continuous mode. The supercritical<br />

fluid may optionally be doped with an entrainer. Due to the stationary (batch) nature<br />

<strong>of</strong> the leaching stage, two or more parallel vessels loaded with the substrate may be utilized.<br />

The material leached is recovered and fractionated through pressure reduction, temperature<br />

perturbation, adsorption, membranes or through absorption. During the initial stages <strong>of</strong><br />

leaching, the solute loading is high and may approach the equilibrium solubility limit, while<br />

at the latter stages kinetic and mass transfer limitations are responsible from relatively lower<br />

the concentration <strong>of</strong> the solute. Both c<strong>of</strong>fee decaffeination 59 and hops extraction 60 are popular<br />

commercial successes <strong>of</strong> this application. Further, typical applications are given in Table<br />

21.1.5.<br />

Table 21.1.6. Leaching applications <strong>of</strong> supercritical fluids<br />

Purpose Supercritical medium<br />

Food processing<br />

Substrate<br />

61<br />

Food purification<br />

Leaching <strong>of</strong> natural products<br />

CO 2<br />

CO 2<br />

Essential oils 62<br />

Leaching <strong>of</strong> natural products CO 2,N 2O, CHF 3,SF 6 Fungal oil<br />

C<strong>of</strong>fee decaffeination<br />

Cholesterol removal from egg yolk<br />

Oil from soybean, sunflower,<br />

spearmint, Camomile, thyme,<br />

rosemary sage, chervil<br />

Leaching <strong>of</strong> natural products Methanol, ethanol, acetone Liquid from hazelnut seed coat<br />

Obtaining liquids from solid fuels 63<br />

Cleaning and upgrading solid fuels 64<br />

Cleaning <strong>of</strong> parts<br />

Petrochemical<br />

Toluene, water, acetone, meth-<br />

Liquid from coal, lignite<br />

anol, THF, tetralin, ethanol<br />

Toluene, methanol, ethanol,<br />

water, acetone, tetralin, CO 2<br />

CO 2<br />

Chemical 65<br />

Sulfur, nitrogen, oxygen removal<br />

Oil from contaminated glass grinds,<br />

organic additives from extrusion-molded<br />

ceramic parts<br />

Cleaning <strong>of</strong> parts CO 2, fluorocarbon solvents Particles from precision devices<br />

Biochemical 66<br />

Vitamin, pharmaceutical compounds CO 2 Natural plants<br />

Extraction <strong>of</strong> soils<br />

Environmental 67<br />

CO 2 + modifier<br />

Polycyclic-aromatic hydrocarbons,<br />

pesticides

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