Phase Diagrams of Three-Component Mixtures

However, later in this book, we wiU see that if = 1, it is impossible to get component 1 with a high degree of purity, and if = 0, it is impossible to get component 2 with a high degree of purity. 

Three-component mixtures represent the simplest type of multicomponent mixtures. The majority of multicomponent mixture peculiarities become apparent in three-component mixtures. This is why the three-component mixtures are best studied. Liquid-vapor equilibrium in the concentration triangle C3 is represented by a vector connecting a point of hquid composition with a point of equilibrium vapor composition x y. This vector is called a liquid-vapor tie-line. The opposite vector y X (vapor-liquid) is called a vapor-liquid tie-line. The tie-hnes field in the concentration triangle characterizes phase equihbrium in each of its points. 

However, tie-lines can cross each other. That is why, for phase equilibrium characteristics in the concentration space, it is convenient to use another kind of line, the so-called residue curves. Let s consider a process of open evaporation simple distillation) illustrated in Fig. 1.3. 

Let s assume that the initial amount of liquid in a fiask makes L moles and the liquid has a composition x, (i = 1,2. n). After the evaporation of a small amount of liquid AL, vapor with a composition y,- (/ = 1,2. n), will be formed which represents an equihbrium of the remaining hquid, the amount of which is equal to L - AL moles and the composition is x, -I- Ax,. 

The residue curve represents the change in a mixture composition during the open evaporation process. Each point of this line corresponds to a certain moment of time and to a portion of evaporated liquid. 

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