Handbook of Solvents - George Wypych - ChemTech - Ventech!

21.1 Supercritical solvents 1443
Table 21.1.8. Fractionation applications of supercritical fluids
Purpose Supercritical medium Substrate
Fractionation 74
CO 2
Essential oils
Glycerol, fatty acids, glycerides
Chemical
Fractionation CO 2 Xylenes, glycerides, alkanes, aromatics
Fractionation CO 2 + entrainer Methyl esters, fullerenes
Petrochemical
Fractionation Toluene, pentane, propane, Petroleum pitch, asphalt
CO 2
Polymer processing
Figure 21.1.14. The pressure reduction path for nucleation of particles
from supercritical fluids.
Polydimethylsiloxane, fluoropolymers, polypropylene
The methods useful in design
of extraction systems are the same
as those traditional methods applicable
to liquid and gaseous systems
and include Kremser, McCabe
Thiele, Panchon Savarit (including
Janecke), and more rigorous
rate-based as well as equilibrium
based methods. Due to the highly
non-linear nature of the physical-chemical
properties in the critical
region, great care has to be
taken in representing both the properties
and the solution algorithms.
21.1.3.3 Crystallization -
generic applications
Particles nucleated from supercritical
fluids have unique particle size,
shape, and particle size distributions.
75 The means of achieving nu-
cleation and growth are many, and include pressure reduction, temperature perturbation,
and addition of anti-solvents. Time profiling and staging have profound effect on the particle
characteristics. The effect of pressure reduction on the resulting nucleated material for
different solute concentrations 16 is illustrated in Figure 21.1.14.
21.1.3.4 Sorption - generic applications
The sorption applications 21 include regeneration of porous beds, 76 preparative scale supercritical
chromatography, 21 simulated moving beds, 21 thermal swing schemes, 77 and adsorption/desorptions
cycles. Although initial applications of supercritical fluids in this domain
were on regeneration of porous beds, more recent emphasis on fractionation best reflects