Ternary systems with three liquid phases

Example 1. Ternary system with three liquid phases. 

The LLE in the similar ternary systems [QQlm][PFJ -I- water + ethanol was measured in three temperatures (290.15,29 15, and 313.25 K) [66]. From these results it can be concluded that with decreasing temperature three liquid phases can be expected. 

This curve will, of course, lie in the plane formed by one face of the prism. In a similar manner we obtain the freezing-point curves Ak C and B gC. These curves give the composition of the binary liquid phases in equilibrium with one of the pure components, or, at the eutectic points, with a mixture of two solid components. If to the system represented say by the point ki, a small quantity of the third component, C, is added, the temperature at which the two solid phases A and B can exist in equilibrium with the liquid phase is lowered and this depression of the eutectic point is all the greater the larger the addition of C. In this way we obtain the curve which slopes inwards and downwards, and indicates the varying composition of the ternary liquid phase with which a mixture of solid A and B are in equilibrium. Similarly, the curves fegK and k K are the corresponding eutectic curves for A and C, and B and C in equilibrkim with ternary solutions. At the point K, the three solid components... 

In the absence of special symmetry, the phase mle requires a minimum of three components for a tricritical point to occur. Symmetrical tricritical points do have such s mimetry, but it is easiest to illustrate such phenomena with a true ternary system with the necessary symmetry. A ternary system comprised of a pair of enantiomers (optically active d- and /-isomers) together with a third optically inert substance could satisfy this condition. While liquid-liquid phase separation between enantiomers has not yet been found, ternary phase diagrams like those shown in figure A2.5.30 can be imagined in these diagrams there is a necessary symmetry around a horizontal axis that represents equal amounts of the two enantiomers. 

According to Gibbs phase mle, a ternary solution may separate into three liquid phases in equilibrium under certain conditions of T and . As early as 1949 Tompa [1] investigated this phenomenon theoretically with g assumed to depend on T only. In 1967, Koningsveld and Staverman [39] verified Tompa s prediction with the system in which two polyethylene samples with M = 540 x 10 and 12 x 10 or 25 x 10 were dissolved in diphenyl ether. Since these samples were considerably polydisperse, the solutions were not thermodynamically well-defined three-component systems. Later, Koningsveld et al. [12] made a similar study with a mixture of narrow-distribution polystyrenes with Mw = 51 x 10 and 1500 x 10 and observed three-phase separation to occur in the temperature range predicted by Tompa s theory. 

The importance of solubility rests in large part on the fact that within true solutions, composition is a degree of freedom, and thermodynamic parameters vary smoothly with composition [16]. It is impossible to vary temperature and pressure without changing the state of a mixture, but many real situations exist in which thermodynamic states are invariant with respect to composition. Examples include b hasic mixtures in all binary systems at constant temperature and pressure, such as a salt-water mixture containing the saturated salt solution plus salt crystals (see below). Another would be any mixture in a ternary surfactant—oil—water system containing three coexisting phases (e.g., a microemulsion liquid phase, an oil-rich liquid phase, and a water-rich liquid phase). 

An example for a partially known ternary phase diagram is the sodium octane 1 -sulfonate/ 1-decanol/water system [61]. Figure 34 shows the isotropic areas L, and L2 for the water-rich surfactant phase with solubilized alcohol and for the solvent-rich surfactant phase with solubilized water, respectively. Furthermore, the lamellar neat phase D and the anisotropic hexagonal middle phase E are indicated (for systematics, cf. Ref. 62). For the quaternary sodium octane 1-sulfonate (A)/l-butanol (B)/n-tetradecane (0)/water (W) system, the tricritical point which characterizes the transition of three coexisting phases into one liquid phase is at 40.1°C A, 0.042 (mass parts) B, 0.958 (A + B = 56 wt %) O, 0.54 W, 0.46 [63]. For both the binary phase equilibrium dodecane... 

The study of distribution coefficients—the distribution of a solute between two liquid phases—is closely related to the complete study of liquid-liquid equilibria in ternary systems. We limit the discussion to conditions of constant temperature and constant pressure. In the most general case the system is composed of two liquid phases, with all three components existing in each phase. The conditions of equilibria are... 

If the liquid mixture is extremely non-ideal, liquid phase splitting will occur. Here, we first consider the hypothetical ternary system. The physical properties are adopted from Ung and Doherty [17] and Qi et al. [10]. The catalyst is assumed to have equal activity in the two liquid phases. The corresponding PSPS is depicted in Fig. 4.5, together with the liquid-liquid envelope and the chemical equilibrium surface. The PSPS passes through the vertices of pure A, B, C, and the stoichiometric pole Jt. The shape of the PSPS is affected significantly by the liquid phase non-idealities. As a result, there are three binary nonreactive azeotropes located on... 

The proposed method allows us to obtain a good agreement with experiment for three binary systems but also to predict the two-phase equilibria of the ternary system. However it seems that the equations of state used for methanol and water are not enough accurate and that the knowlegde of vapor-liquid equilibria of binaries including carbon dioxide should be improved. 

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