Azeotrope minimum boiling-point type

Figure 9.16 Different types of liquid-vapor phase diagrams for a binary liquid mixture of component A and B as functions of the mole fraction of the component with the higher boiling temperature, (a) The phase diagram for a system with a low-boiling azeotrope (minimum boiling point) and (b) the phase diagram for a system with a high-boiling azeotrope (maximum boiling point). The arrows show how the paths for various distillation processes depend upon the position of the initial composition relative to the azeotrope.

Two types of azeotrope, maximum boiling point (Figure 3.9(a)) and minimum boiling point (Figure 3.9(b)), can be represented on this type of diagram. 

As a rule the compound to be added is so chosen that it forms an azeotrope of minimum boiling point with one of the components. But it is also possible to select an entrainer forming a binary or ternary minimum azeotrope with both of the components to be separated in the latter case it is necessary for the proportion of the components in the new azeotropes to be different from their initial proportions. Discus.sing extensive investigations of various types of phase diagrams and of the elaboration of column schemes Sharov and Serafiniov [35a] have treated the problems specific to the countercurrent distillation of azeotropic multicomponent mixtures. 

Figure 8.8d shows that this system has a minimum boiling point, and two regions with different behaviors on either side of the composition at which that minimum occurs. For liquid solutions to the left of the azeotrope in Figure 8.8d (Xa < 0.685) the figure is of the same general type as Figure 8.7d. If we attempted to separate a liquid in this composition range by simple distillation we would produce practically pure water and the azeotrope. If we started with a...

In the systems that we have examined so far, the bubble point and the dew point of the mixture vary monotonically with the composition. This is the case for ideal systems. However, for very non-ideal systems, there may be a maximum or a minimum in the bubble and dew point curves. This is the case for azeotropic systems. An example of a system that exhibits a low-boiling azeotrope is a mixture of 77-heptane and ethanol, which is shown in Figure 3.5. For this type of system, both the bubble and dew point temperature curves have a local minimum at the same composition. At this composition, these two curves meet. This point is known as the azeotrope. At the azeotrope, the composition of the coexisting liquid and vapor phases are identical. In this case at the azeotrope, the boiling temperature... 

The results of the studies on separating minimum and maximum boiling azeotropes with light, intermediate, or heavy entrainers are compared according to their operation steps and feasibility domains. The decisive property for designing an effective BED process, separating azeotropes, is the relative position of the entrainer to the azeotrope in the bubble point series. But the type of the azeotrope (minimum or maximum) can modify the existence of some limiting parameters (FA a , N,., >.,). 

The boiling point temperature rankings in Table 7.4 reveal that BuAc differs from IPAc in that the acetate is the highest boiler. This implies that we can remove the acetate from the column base. Moreover, the minimum boiling azeotrope between BuOH and H2O is also a heterogeneous one (Fig. 7.1ternary composition space. Figure l.ld also reveals that the two-liquid zone in the ternary system constitutes more than 50% of the composition space. However, the BuAc and IPAc systems also share a common characteristic a minimum boiling ternary azeotrope exists in the acetate/alcohol/water ternary system, and it is located inside the... 

Binary homogeneous (single-phase) liquid mixtures having an extremum (maximum or minimum) vapor pressure P at constant temperature T, as a function of composition, are called azeotropic mixtures, or simply azeotropes. The composition is usually expressed as mole fractions, where for component 1 in the liquid phase and i for component 1 in the vapor phase are identical. Mixtures that do not show a maximum or minimum are called zeotropic. A maximum (minimum) of the P xi) or P(yi) curves corresponds to a minimum (maximum) of the boiling temperature T at constant P, plotted as a function of. Vj or yi [see T xj) and T(yi) curves. Types 1 and 111, in Fig.l]. Azeotropes in which the pressure is a maximum (temperature is a minimum) are often called positive azeotropes, while pressure-minimum (temperature-maximum) azeotropes are called negative azeotropes. The coordinates of an azeotropic point are the azeotropic temperature Taz> pressure arid the vapor-phase composition, which is the same as the liquid-phase composition... 

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