Retrograde condensation: defined

We will first consider phase diagrams. Then we will define the critical point for a two-component mixture. This will be the correct definition for multicomponent mixtures. Also, we will look at an important concept called retrograde condensation. Then the pressure-volume diagram will be discussed, and differences between pure substances and two-component mixtures in the two-phase region will be illustrated. Finally, the effects of temperature and pressure on the compositions of the coexisting liquid and gas will be illustrated. 

In other words, retrograde condensation is defined as the formation of liquid by an isothermal decrease in pressure or an isobaric increase... 

J, another dew point at the same temperature. Condensation that takes place with temperature rise or with pressure drop is known as retrograde condensation, and the temperature and pressure conditions under which this occurs define the retrograde region. In such systems, vapor and liquid can coexist at temperatures and pressures above the critical point. The highest temperature and the highest pressure where two-phases can coexist are called, respectively, the cricondentherm and cricondenbar, also shown in Figure 2.1. 

The dependence of the liquid volume and of the mixed volume on the pressure, which is shown in Fig. 13, makes it possible to define precisely the dew-point pressure at which the retrograde condensation is changed to the normal one, P = 68 bar (the point A in the phase diagram). This value is hard to define directly from the phase diagram, because the corresponding branch of the dew-point pressure curve in Fig. 7 is sharply inclined to the axis. 

---