Handbook of Solvents - George Wypych - ChemTech - Ventech!

21.1 Supercritical solvents 1423
Figure 21.1.5 Classification of vapor-liquid phase behavior of binary systems.
21.1.2 FUNDAMENTALS
21.1.2.1 Phase behavior with supercritical solvents
The first recorded observation of supercritical fluid’s ability to dissolve solids with low volatility
goes back to 1879. 1 Since then, better understanding of high-pressure phase equilibrium
emerged partially as a result of experiments of the last century, especially those of
Timmermans, 2 Schneider, 3,4 Franck 5 on aqueous systems, McHugh 6 on polymeric systems
and more recently the Delft group in Holland. 7,8 In classification of phase diagrams, one of
the most important analytic contributions is due to Scott and Van Konynenberg. 9 They demonstrated
that most of the experimental observations could be described qualitatively by the
van der Waals equation of state. Their analysis of critical and three phase boundaries in temperature-pressure
projection of the phase behavior led to their categorization of possible
fluid phase equilibrium into five classes. Rowlinson and Swinton 10 later added a sixth class
that occurs in some aqueous systems but is not predicted by the van der Waals equation of
state. The classes described by Scott illustrate only a few of the known types of phase equilibrium
and are shown in Figure 21.1.5. This classification scheme illustrates the principal
lines (degrees of freedom = 1) and end points (degrees of freedom=0) that form the boundaries
of pressure-temperature space of the surfaces that describe the equilibrium between
two components. The types of boundaries are:
1. Solid lines (_______) are pure component vapor pressure curves.
2. The dashed lined (_ ____)areforthree phase lines.
3. The dotted lines (.........) are for critical lines.
The types of points are: