Supercritical regions phase diagrams

Phase Behavior. One of the pioneering works detailing the phase behavior of ternary systems of carbon dioxide was presented ia the early 1950s (12) and consists of a compendium of the solubiHties of over 260 compounds ia Hquid (21—26°C) carbon dioxide. This work contains 268 phase diagrams for ternary systems. Although the data reported are for Hquid CO2 at its vapor pressure, they yield a first approximation to solubiHties that may be encountered ia the supercritical region. Various additional sources of data are also available (1,4,7,13). 

Figure 5.1 Phase diagram showing supercritical fluid region...

Figure 1.4 Phase diagram of water around the supercritical region.

The phase diagram features four phase regions, three phase boundaries, and two points of particular interest the triple point (TP) and the supercritical point (CP). Values for TP and CP from The International Association for the Properties of Water and Steam6 (IAPWS) are 273.16 K and 611.657 Pa (IAPWS, 2002) and 647.096 K and 22.064 MPa (IAPWS, 2002), respectively. Three of the phases (solid, liquid, and gas) are bounded by equilibrium... 

Figure 6.1 A typical phase diagram showing the supercritical region...

Chapter 14 describes the phase behavior of binary mixtures. It begins with a discussion of (vapor -l- liquid) phase equilibria, followed by a description of (liquid + liquid) phase equilibria. (Fluid + fluid) phase equilibria extends this description into the supercritical region, where the five fundamental types of (fluid + fluid) phase diagrams are described. Examples of (solid + liquid) phase diagrams are presented that demonstrate the wide variety of systems that are observed. Of interest is the combination of (liquid + liquid) and (solid 4- liquid) equilibria into a single phase diagram, where a quadruple point is described. 

There is a region in a gas-liquid phase diagram where a substance can exist with properties characteristic of both the gas and liquid states. This state is referred to as fluid, or more precisely, a supercritical fluid, since it exists in the region beyond the critical points for the substance. Visualize a transparent container half filled with liquid and sealed. As its temperature is increased its pressure will increase until the critical point... 

Fig. 11. A typical pressure-temperature phase diagram for a single-component system, e.g., xenon, showing the supercritical region, which can he accessed from either the liquid or gas phase without crossing a phase boundary.

Figure 4.1 Single-component phase diagram highlighting the supercritical fluid (SCF) region and the critical point.

Figure 2. A phase diagram showing the different phases and supercritical region. The critical point, critical pressure, and critical temperature are indicated.

Figure 2. Phase diagram of an. 4077water/supercritical propane system in the oil-rich comer of the temaiy phase diagram. The regions to the right of the solid lines are the one-phase, clear microemulsions. The various IV value lines ([H2O]/ [AOT]) are also indicated. The temperature of the system is 103°C. (Compositions are given in weight percent.)...

Fig. 1 Pressure-temperature phase diagram of a pure component indicating the supercritical region. (From...

Fig. 1 Idealized phase diagram depicting the supercritical region. and are the critical temperature and pressure, respectively. View this art in color at www.dekker.com.)...

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

The propane system shown in Fig. 11.3 is clearly subcritical as the critical temperature of propane is about 96°C. An increase of the C02 fraction ((3) in the mixture of C02 and propane shifts the one-phase region (1), i.e. the bicontinuous microemulsion, to lower temperatures. For pure C02 the bicontinuous microemulsion (1) exists around 35°C, which is higher than the Tc = 31°C of C02. In other words, the C02 solubilised in the microemulsion is supercritical Knowing how to tune the phase behaviour of these systems, one can easily shift phase diagrams on the temperature scale by simply choosing an appropriate surfactant. Other tuning parameters are the oil-to-water fraction and the temperature which maybe adjusted such that, e.g. a C02-in-water droplet microemulsion forms. 

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