Phase diagrams supercritical fluids

Figure 1. Solid-liquid-gas-supercritical fluid phase diagram. TP = triple point, CP - critical point, Pc = critical pressure, Tc = critical temperature.

Fig. 1. Supercritical fluid phase diagram. To convert kPa to bar, divide by 100.

Figure 8.16 (Fluid -+- fluid) phase diagram for a near-ideal system. Reproduced with permission from W. B. Streett, Chapter 1 in Chemical Engineering ai Supercritical Fluid Conditions, M. E. Paulaitis, J. M. L. Penninger. R. D. Gray Jr., and P. Davidson, editors, Ann Arbor Science Press. Michigan, 1983.

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. 

The presence of a solid phase adds considerable complexity to the fluid phase diagram [14, 16]. We discuss here only two cases, one for Type-I fluid phase behavior including a solid phase well below the critical line, and one in which the solid phase reaches into the supercritical regime. F or a full discussion of the latter case, see Peters [16]. 

In Class B1 systems branch II of the critical locus spans the entire temperature range from the critical temperature of the heavy component (if this is accessible without decomposition) down to and below the critical temperature of the solvent, as in curves (a) and (b) in Figure 1.9. On raising the pressure at a constant temperature which is above the solvent critical temperature, complete miscibility between the liquid and supercritical fluid phases occurs at the pressure (the critical pressure) corresponding to this temperature on the locus curve. The dew- and bubble-point curves then merge giving a closed loop pressure/composition diagram. 

The pressure-temperature phase (PT) diagram of CO2 is shown in Figure 2.1. The critical point (CP) occurs at a temperature of 31.1 °C. At this temperature the boiling line terminates and the gas and liquid phases merge into a single supercritical fluid phase. 

Figure 5.1 Phase diagram showing supercritical fluid region...

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