Azeotropes minimum boiling point

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.

Examples of azeotropic mixtures of minimum boiling point are collected in Table I, 4, A. 

Examples of azeotropic mixtures of maximum boiling point are tabulated below these are not as numerous as those of minimum boiling point. 

An important system in distillation is an azeotropic mixture. An azeotrope is a liquid mixture which when vaporized, produces the same composition as the liquid. The VLE plots illustrated in Figure 11 show two different azeotropic systems one with a minimum boiling point and one with a maximum boiling point. In both plots, the equilibrium curves cross the diagonal lines. 

The ethanol-water azeotrope (95%ethanol-5%water) is an example of a minimum boiling azeotrope. Its boiling point is lower than that of the components (Fig. 143). If you ve ever fermented anything and distilled the results in the hopes of obtaining 200 proof (100%) white lightning, you d have to content yourself with getting the azeotropic 190 proof mixture, instead. Fermentation usually stops when the yeast die in their own 15% ethanol solution. At room temperature, this is point A on our phase diagram. When you heat the... 

Minimum boiling point azeotrope with no data given Vapor-liquid equilibrium data are given in the original reference Azeotropic concentration is given in volume per cent. Unless so indicated, all concentrations are weight per cent Pressure in mm. of mercury absolute Approximate Greater than Less than... 

We now consider systems which include a vapour phase together with liquid mixtures with partial miscibility. The first example is a system which shows partial miscibility and a minimum boiling point azeotrope. 

Minimum boiling point azeotrope (positive azeotrope)... 

Figure 3.9 (a) Maximum boiling-point azeotrope (b) minimum boiling-point 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. 

If a mixture of ethanol and water is distilled, eventually it will form a solution that is 95 % ethanol regardless of the starting composition. Hydrochloric acid and water will form a 20.22 % HCl solution, and chloroform and acetone will form a 65.5 % CHCI, solution. These solutions are called azeotropes (Gr a + zeo to boil, trope more at). Webster s dictionary defines an azeotrope as a liquid mixture that is characterized by a constant maximum or minimum boiling point which is lower or higher than that of any of the components and that distills without change in composition. An azeotropic distillation involves the formation of an azeotrope with at least one of the components of a liquid mixture, which then can be separated more readily because of the resulting increase in the difference between the volatilities of the components of the mixture. Figure 4-1, p. 44, shows the water-ethanol system (A) and the HCl-water system (B). 

Water-dioxane solutions form a minimum-boiling-point azeotrope at atmospheric pressure and cannot be separated by ordinary distillation methods. Benzene forms no azeotrope with dioxane and can be used as an extraction solvent. At 298 K the equilibrium distribution of dioxane between water and benzene is as follows (Treybal, 1980) ... 

Figure 3.5. Minimum-boiling-point azeotrope, isopropyl ether-isopropyl alcohol system, (a) Partial and total pressures at 70°C. (i>) Vapor-liquid equilibria at 101 kPa. (c) Phase diagram at 101 kPa. [Adapted from O. A. Hougen, K. M. Watson, and R. A. Ragatz, Chemical Process Principles, Part II, 2nd ed John Wiley and Sons, N. Y. (1959).)...

Mixtures forming an azeotrope with minimum boiling point distillate azeotropic mixture of the two components bottom product the component in excess, x ure. 

Azeotropes with a minimum boiling point (for examples, see Fig. 43, column 3/III) are far more numerous than those with a maximum boiling point (Fig. 43, column o/III). According to the tables of Lecat [20], who li.sts 6287 azeotro]ies and 700 > iion-azeotropes, the ratio is about 9 to I. 

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