Yx diagram

Figure 12.7 yx diagram for the ethane/heptane system. (Reproduced by permission from F, H. Ban-David, AIChE J., 2 426, 1956.)... 

A PT diagram for the ethane/heptane system is shown in Fig. 12.6, and a yx diagram for several pressures for the same system appears in Fig. 12.7. According to convention, one plots as y and x the mole fractions of the more volatile species in the mixture. The maximum and minimum concentrations of the more volatile species obtainable by distillation at a given pressure are indicated by the points of intersection of the appropriate yx curve with the diagonal, for at these points the vapor and liquid have the same composition. They are in fact mixture critical points, unless y = x = 0 or y = x = 1. Point A in Fig. 12.7... 

Figure 12.11 Equilibrium yx diagrams at a constant pressure of l(atm). (a) Tetrahydrofuran( 1)/carbon tetrachIoride(2) (b) chloroform( 1 )/tetrahydrofuran(2) (c) fuian(l)/carbon tetrachloride<2) ...

Figure 10.6 yx diagram forethaneln-heptane. (Reproduced by permission from. . H. Barr-David, AlChEJ., vol. 2, p. 426—427, 1956.)... 

The phase equilibrium data, or Equation 5.12, are first plotted on a YX diagram... 

When cmiditions required for die two simide cases just described are not met, the opoating curves may be located on the XA-yx diagram by appropriate use of the triangular diagram, as described below. 

In Fig. 12.9-la a typical equilibrium diagram is shown where solute A is infinitely soluble in solvent C, which would occur in the system of soybean oil (/l)-soybean inert solid meal (B)-hexane solvent (C). The upper curve of N versus for the slurry underflow represents the separated solid under experimental conditions similar to the actual stage process.The bottom line of N versusx, where N = Oon the axis, represents the overflow liquid composition where all the solid has been removed. In some cases small amounts of solid may remain in the overflow. The tie lines are vertical, and on a yx diagram, the equilibrium line is y = on the 45° line. In Fig. 12.9-lb the tie lines are not vertical, which can result from insufficient contact time, so that all the solute is not dissolved adsorption of solute A on the solid or the solute being soluble in the solid B. 

Schematic representation of an enthalpy-composition (Hxy) diagram and yx projection for vaporization.

Figure 10 shows the relationship between yx and xx for different values of an calculated from Eq. (8). When two components have close boiling points, by implication they have similar vapor pressures, so that an is close to unity. Separation of mixtures by distillation becomes more difficult as an approaches unity. Figure 11 indicates some of the x, y diagrams that can be obtained for distillation systems. Also shown are corresponding temperature-composition diagrams. The saturated vapor or dewpoint curve is determined by finding the temperature at which liquid starts to condense from a vapor mixture. Similarly, the saturated liquid or bubble-point curve corresponds to the temperature at which a liquid mixture starts to boil. For ideal mixtures, the dewpoint and bubble-point curves can be calculated as follows. From Eq. (3), at the dew point, since... 

Next, we specify the x, between 0 and 1, and estimate the total pressure P and yx from Eq. (1.193) to prepare the total pressure and equilibrium compositions shown in Table 1.10. In Figure 1.9, we can compare both the Tyx and Pyx diagrams obtained from Raoult s law and the NRTL model using the Aspen Plus simulator. As we see, ideal behavior does not represent the actual behavior of the acetone-water mixture, and hence we should take into account the nonideal behavior of the liquid phase by using an activity coefficient model. 

Figure 34.3 Pressure-composition diagram for Binary Ideal Liquid Mixture. Dependence of P on mole fraction (yx, Xb) of vapour...

It should be clear that expression for higher-order diagrams analogous to Fig. 3.4A but with one or more additional interaction lines connecting a and P would involve higher powers of (e, + e, — e, - Therefore, the series represented by the sum of Fig. 3.4A-C is an easily summed geometric series of the form y + yx + yx 4- yx -. The result of summing... 

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