Supercritical fluid region

Eig. 1. Schematic pressure—temperature diagram for a pure material showing the supercritical fluid region, where is the pure component critical point... 

We will begin our discussion by describing (vapor + liquid) equilibrium, which we will extend into the supercritical fluid region as (fluid + fluid) equilibrium. (Liquid + liquid) equilibrium will then be described and combined with (vapor + liquid) equilibrium in the (fluid + fluid) equilibrium region. Finally, we will describe some examples of (solid + liquid) equilibrium. 

Figure 5.1 Phase diagram showing supercritical fluid region...

The supercritical fluid region, which encompasses all conditions of supercritical temperatures and pressures. 

We now extend the discussion of excess properties to examples that help us to better understand the nature of interactions in a variety of nonelectrolyte mixtures. We will give examples showing temperature and pressure effects, including an example of solutions near the critical locus of the mixture and into the supercritical fluid region. 

Recently, the first observation of reverse micelles in supercritical fluid (dense gas) solvents has been reported (2) for the surfactant sodium bis(2-ethyhexyl) sulfosuccinate (AOT) in fluids such as ethane and propane. The properties of these systems have several attributes which are relevant to secondary oil recovery. In the supercritical fluid region, where the fluid temperature and pressure are above those of the critical point, the properties of the fluid are uniquely different from either the gas... 

Fig. 4 Three reaction zones generated by acoustic cavitation. Zone 1 is the vapor phase. Zone 2 consists of the supercritical fluid region, and Zone 3 represents the bulk liquid. (View this art in color at www.dekker.com.)...

Let us now focus upon the critical temperature and consider a few of the definitions that can describe this invariant point. It is important to note that the critical point is defined by the temperature only the value of the critical pressure appears to have a lesser or secondary significance. The critical (or supercritical) fluid region exists at all pressures at or above the critical temperature for a pure substance. Above this critical temperature, there exists only one phase, completely independent of the pressure. That is, no matter how high (or how low) you cause the pressure to be, the one phase wiU not condense to a hquid. 

Figure 2 A schematic of a phase diagram for water showing solid, liquid and gas phases relative to the supercritical fluid region.

The Practical Ramifications of Operating in the Supercritical Fluid Region... 

FIGURE 24.1 Definition of the supercritical fluid region in the phase diagram of a pure substance. 

Saeki, S. (1997) Calculation of the phase diagram of polymer solution over supercritical fluid region based on the Patterson-Delmas theory of corresponding state. Fluid Phase Equilib. 136,87-92. 

There are several experimental examples of phase behavior of type Id (see above). The system UO2F2 - H2O [Marshall et al, 1954a] with some reservations can be related to type Id", since the experimental studies are limited by temperature of the critical point (L = G-Sb) and it is not clear whether or not there is the supercritical fluid region at higher temperatures as in the case of type 2d" or this region is absent as in type Id". 

Figure 14.13 The pressure temperature phase diagram of a pure substance, emphasizing the supercritical fluid region. The critical point is the highest pressure and temperature at which a pure substance can exist in a vapor iquid equilibrium.

Figure 11.2 Cartxin dioxide pressure-temperature phase diagram. In the supercritical fluid region, the COj becomes denser than gas and can approach the density of the liquid CO. At the higher densities, the solubility of the CO increases significantly as well.

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