Miscible liquids, ternary diagrams

A simple example of a real ternary diagram is shown in Fig. 2.26, where the isothermal section, determined at 200°C, of the Al-Bi-Sb system is shown together with the relevant binary diagrams Al-Bi showing a miscibility gap in the liquid state and complete insolubility in the solid state, Bi-Sb with complete mutual... 

In figure 3.29c the pressure has now been increased to a value greater than the critical pressure for the SCF-B mixture. The SCF is now miscible in all proportions with B, and the binodal curve no longer intersects the SCF-B binary axis of the ternary diagram. Even at this elevated pressure, the SCF still remains virtually insoluble in A, as would be the case if the supercritical fluid were a low molecular weight hydrocarbon and component A were water (Culberson and McKetta, 1951). As shown in figure 3.29c, the binodal curve intersects the SCF-A binary axis in two locations. The tie lines for the ternary system now indicate that a liquid phase, mostly a mixture of A and B, is in equilibrium with a fluid phase, mainly the SCF with component B. 

When a soluble third component is added to two partially miscible liquids, we obtain a ternary system in which the third component (solute) is partitioned between the two liquid phases (solvents). The phase behavior of such systems is important in liquid-liquid extraction, a process that takes advantage of the differences in solubility to transfer a solute from one solvent into another. Since two mole fractions are required to represent composition in ternary systems, it is not possible to present temperature-composition or pressure-composition graphs in a two-dimensional plot. Instead, we map out the composition of the phases at constant pressure and temperature. This is done in triangular diagrams such... 

Mixtures of three miscible liquids can be represented by a ternary diagram such as the one shown below for water-methanol-ethanol mixtures. Any coordinate on this ternary diagram corresponds to a single liquid phase. 

The two preceding exercises use ternary diagrams plotted on equilateral triangles to analyze three-component mixtures that are completely miscible (Exercise 4.37) and three-component mixtures that separate into two liquid phases (Exercise 4.38)... 

W/O gel emulsions separate into two isotropic liquid phases at equilibrium one phase is a submicellar surfactant solution in water and the other phase is a swollen reverse micellar solution (or W/O microemulsion). This phase equilibrium is represented in Figure 11.11 by the ternary diagrams at and T . Similarly, O/W gel emulsions separate into two isotropic liquid phases at equilibrium an oil phase and an aqueous micellar solution or O/W microemulsion. The phase equilibrium is represented by the ternary diagrams at Ti and T2 of Figure 11.11. Gel emulsions exist only in limited regions of the miscibility gap (the two-phase region). The boundaries of the gel emulsion regions depend on the system and also on the method of preparation. 

Ternary-phase equilibrium data can be tabulated as in Table 15-1 and then worked into an electronic spreadsheet as in Table 15-2 to be presented as a right-triangular diagram as shown in Fig. 15-7. The weight-fraction solute is on the horizontal axis and the weight-fraciion extraciion-solvent is on the veriical axis. The tie-lines connect the points that are in equilibrium. For low-solute concentrations the horizontal scale can be expanded. The water-acetic acid-methylisobutylketone ternary is a Type I system where only one of the binary pairs, water-MIBK, is immiscible. In a Type II system two of the binary pairs are immiscible, i.e. the solute is not totally miscible in one of the liquids. 

Liquid-Fluid Equilibria Nearly all binary liquid-fluid phase diagrams can be conveniently placed in one of six classes (Prausnitz, Licntenthaler, and de Azevedo, Molecular Thermodynamics of Fluid Phase Blquilibria, 3d ed., Prentice-Hall, Upper Saddle River, N.J., 1998). Two-phase regions are represented by an area and three-phase regions by a line. In class I, the two components are completely miscible, and a single critical mixture curve connects their criticsu points. Other classes may include intersections between three phase lines and critical curves. For a ternary wstem, the slopes of the tie lines (distribution coefficients) and the size of the two-phase region can vary significantly with pressure as well as temperature due to the compressibility of the solvent. 

On a ternary equilibrium diagram like that of Figure 14.1, the limits of mutual solubilities are marked by the binodal curve and the compositions of phases in equilibrium by tielines. The region within the dome is two-phase and that outside is one-phase. The most common systems are those with one pair (Type I, Fig. 14.1) and two pairs (Type II. Fig. 14.4) of partially miscible substances. For instance, of the approximately 1000 sets of data collected and analyzed by Sorensen and Arlt (1979), 75% are Type I and 20% are Type II. The remaining small percentage of systems exhibit a considerable variety of behaviors, a few of which appear in Figure 14.4. As some of these examples show, the effect of temperature on phase behavior of liquids often is very pronounced. 

Some typical phase behavior that can be exhibited by ternary mixtures is shown in Fig. 3.11. Let us consider a situation where binary mixtures of component 1 and component 2 are only partially miscible, where two coexisting liquid phases may be formed one rich in 1 and the other rich in 2. This is represented by the base of the ternary phase diagram shown in Fig. 3.11a. In addition, let us assume that components 1 and 3 are completely miscible and components 2 and 3 are also completely miscible. For this case, one might expect that if enough of component 3 is added to the system, then components 1 and 2 can be made to mix with each other, due to their mutual solubility with component 3. This is type I phase behavior. 

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