Azeotropes maximum boiling point

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. 

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

This example clearly shows good distribution because of a negative deviation from Raonlt s lawin the extract layer. The activity coefficient of acetone is less than 1.0 in the chloroform layer. However, there is another problem because acetone and chloroform reach a maximum-boiling-point azeotrope composition and cannot be separated completely by distillation at atmospheric pressure. 

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. 

Maximum boiling point azeotrope occurs for 68.8 wt% HNO, at a boiling point of 122°C. ... 

In systems with negative deviation from ideal behavior, maximum-boiling-point azeotropes can occur. This is illustrated in Fig. 8 for the chloroform-acetone system, treated in Example 1. This system shows negative deviation from ideal behavior due to the possibility of hydrogen bonds between chloroform and acetone, which cannot occur with the pure components. 

For both minimum- and maximum-boiling-point azeotropes, fractional distillation can only separate a solution into a pure component and the azeotrope, not into the two pure components. It is not possible to distill past an azeotropic concentration. Absolute alcohol cannot be prepared by simply distilling aqueous solutions obtained by fermenting grains. 

The mixture with the maximum boiling point is called maximum bailing azeotrope and behaves as if it is a pure chemical compound of two components, because it boils at a constant temperature and the composition of the liquid and vapour is the same. But the azeotrope is not a chemical compound, because its composition is not constant under conditions and rarely corresponds to stoichiometric proportions. 

Maximum boiling point azeotrope (negative azeotrope)... 

The chloroform-acetone azeotrope (52% chloroform-48% acetone) is an example of the much rarer maximum-boiling azeotrope. Its boiling point is higher than that of the components (Fig. 179). At compositions off the... 

Figure 3.6. Maximum-boiling-point azeotrope, acetone-chloroform system, (a) Partial and total pressures at 60°C. (i>) Vapor-liquid equilibria at 101 kPa. (c) Phase diagram at 101 kPa pressure. [Adapted from O. A. Hougen, K. M. Watson, and R. A. Ragatz, Chemical Process Principles, Part //, 2nd ed., John Wiley and Sons, N. Y. ...

Consider the system shown in Fig. 14.9, which exhibits a maximum boiling point. If a mixture described by point a, having the azeotropic composition, is heated, the vapor will first form at temperature t that vapor has the same composition as the liquid ... 

Mixtures forming an azeotrope with maximum, boiling point distillate the comj)o-nent in excess, pure bottom product azeotropic mixture of the two components. 

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. 

Fig. 231 shows the equilibrium curves of the azeotropic nii.xture acetone-chloroform to which have been added various amounts of the extracting agent, ineth>l-isobntylketone. (The quantities are mole fractions.) The binary S3 stem gives an azeotrope with maximum boiling point at 34.5 mol%. This disappears when 30 mol , of the additive is present further additions cau.se a still larger increase in the relative volatility [50]. 

Mixtures that display a maximum in the boiling point-composition curve can lead to initial separation of pure A on fractionation but as the composition of the liquid moves towards B and reaches the maximum, a constant boiling mixture L3 is reached that will distill over unchanged. An example of an azeotropic mixture of maximum boiling point is water (b.p. 100°C) and hydrogen chloride (b.p. -80°C), the azeotrope being 80% water and boiling at 108.6°C. 

A liquid mixture of two or more substances that boils at a constant minimum or maximum boiling point lower or higher than that of its constituents is called azeotropic. The liquid and the vapour produced on boiling have the same composition and, in this, the mixture acts like a single substance. Chlorotrifluoromethane and trifluoromethane forms such a mixture. 

See dicyclohexyl-, di(2-ethylbutyl)-, di(2-ethylhexyl)-, di(2-ethylhexyl)-4-thio-, di-n-hexyl-y diisobutyl-, and diisooctyl azelates. Azeotrope a-ze-o- trop [a- + zeo- (ff. Gk zein to boil) -h -trope] (1938) n, A liquid mixture that is characterized by a constant minimum or maximum boiling point which is lower or higher than any of the components, and that distills without change in composition. Goldberg DE (2003)... 

A maximum-boiling-point azeotrope results from a slight attraction between the component molecules. This attraction leads to lower combined vapor pressure than... 

Some maximum-boiling-point azeotropes are listed in Table 15.3. They are not nearly as common as minimum-boiling-point azeotropes. 

One can t independently specify the characteristic of minimum (or maximum) boiling point and the two solvent components of the azeotrope. That would be like choosing a spouse and wanting to change their height, date of birth, fingerprints, or previous life experiences. 

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