Handbook of Solvents - George Wypych - ChemTech - Ventech!

1420 Aydin K. Sunol and Sermin G. Sunol
ated products. Furthermore, a new wave of second-generation supercritical technologies
started to emerge, bringing forth new roles for dense gases. The motivation of this chapter is
to assess the current status of the technology in an effort to extricate the challenges both in
the current practice of processing with supercritical fluids and potential areas into which we
have as yet to venture. The foundations including transport phenomena, reactions and thermodynamics
as well as generic processing principles will be highlighted.
“Supercritical” refer to the state of the matter where the temperature and pressure of a
single component fluid is above the critical point at which the phase boundaries diminish. A
portfolio of chemical and physical operations carried out in the vicinity of this region defines
Supercritical Fluid Technology (SFT). The pressure-temperature-volume (PVT) behavior
of a substance can be best depicted by pressure-temperature and pressure-density
(volume) projections, as shown in Figure 21.1.1. Pressure-temperature diagram identifies
the supercritical fluid region, alternative separation techniques that involve phase transition
including the associated phase boundaries, and the fact that an isotherm below critical (AB)
involves phase transition while one above (A’B’) does not. Pressure density projections illustrate
tunability of the solvent density at supercritical conditions (A’B’) and again the
continuity of the isotherm that does not encounter any phase transition. The aforementioned
behavior is for a pure component, solvent. The critical properties of various organic and inorganic
substances are shown in Table 21.1.1.
Table 21.1.1. The critical properties of solvents
Solvents Critical temperature, °C Critical pressure, atm
Critical conditions for various inorganic supercritical solvents
Ammonia 132.5 112.5
Carbon dioxide 31.0 72.9
Carbonyl sulfide 104.8 65.0
Nitric oxide -93.0 64.0
Nitrous oxide 36.5 71.7
Chlorotrifluoro silane 34.5 34.2
Silane -3.46 47.8
Xenon 16.6 58.0
Water 374.1 218.3
Acetone
Critical conditions for various organic supercritical solvents
235.5 47.0
Ethane 32.3 48.2
Ethanol 243.0 63.0
Ethylene 9.3 49.7
Propane 96.7 41.9
Propylene 91.9 45.6