Azeotropes acetone/chloroform/benzene mixture

Fig. 25, Residue curve diagram for acetone/chloroform/benzene mixture. A residue curve boundary passes from the maximum-boiling azeotrope between acetone and chloroform to pure benzene.

Figure 3.10 shows typical RCM for nonideal mixtures involving azeotropes. For the mixture ace tone/heptane /benzene (plot a) there is only one distillation field. The problem seems similar to a zeotropic system, except for the fact that the minimum boiler is a binary azeotrope and not a pure component. With the mixture acetone/chloroform/toluene (plot b) there is one distillation boundary linking the high-boiler with the low-boiler azeotrope. Consequently, there are two distillation regions. Similar behavior shows the plot c, with two azeotropes. The mixture acetone/chloroform/methanol (plotd) has four azeotropes (3 binaries and 1 ternary) displaying a behavior with four distillation regions. 

Example. Table I (each row conies from one of the above flash computations) lists infinite-dilution T-values that were computed for a mixture of acetone, chloroform, and benzene. The infinite-dilution T-value for acetone in chloroform is 0.6 and for chloroform in acetone is 0.4. Both are less than 1 a maximumboiling azeotrope must exist. For chloroform and benzene, the values are 1.5 and 0.4. These values do not suggest the existence of an azeotrope. We assume normal behavior. A similar conclusion is obtained for acetone and benzene where the T-values are 3.0 and 0.7, respectively. 

In Fig. 2.4b, another example of the trajectory bundles is shown (let s call the picture of trajectory bundles a distillation diagram), but already for a three-component azeotropic mixture acetone(l)-benzene(2)-chloroform(3). 

Therefore, the mixture acetone(l)-benzene(2)-chloroform(3)-toluene (4) of the composition (0.25 0.30 0.20 0.25) can be separated into three columns without recycles into acetone, benzene, toluene, and the azeotrope of acetone and chloroform. 

Let s illustrate the location of trajectory bundles of reversible distillation by the example of three-component acetone(l)-benzene(2)-chloroform(3) mixture with one binary saddle azeotrope with a maximum boiling temperature (Fig. 4.7)... 

The diagrams of reversible distillation were constructed for some types of three-component azeotropic mixtures. It is interesting that some types of mixtures with one binary azeotrope and with two distillation regions [types 3 and 5 according to classification (Gurikov, 1958)] permit sharp separation into component and binary zeotropic mixture at some feed compositions. The mixture acetone(l)-benzene(2)-chloroform(3) is an example of such mixture. 

Figure 4.16. Bundles of sharp reversible stripping trajectories in region reversible distillation Regjigy j for the acetone(l)-benzene(2)-chloroform(3)-tolnene(4) mixture (a) node is component 1, (b) node is azeotrope 13, and (c) nodes are component 1 and azeotrope 13.

It is expedient to discuss the influence of these pecuharities on the evolution of distillation trajectories at the concrete example of azeotropic mixture, such as acetone(l)-benzene(2)-chloroform(3). At side 2-3, there is reversible distillation trajectory tear-off segment of the bottom section from vertex 2 to 0 13-point... 

The structure of trajectory bundle also has interesting peculiarities at the best nonsharp separation. In this case, trajectory bundle also has saddle-node and node points (Shafir et al., 1984). Figure 5.21a shows for the azeotropic mixture acetone(l)-benzene(2)-chloroform(3) the line of best bottom product (Poelhnann Blass, 1994), connecting the end of possible segment Reg at side 2-3 at sharp... 

The example of tangential pinch for four-component mixture is quasisharp separation of azeotropic mixture acetone (l)-benzene (2)-chloroform (3)-toluol (4) of composition Xf (0,350 0,250 0,150 0,250) at intermediate split 1,3(2) 2,4(3) (admixture components heavy and light key are in brackets correspondingly) at the following composition the products xd (0,699 0,001 0,300,0) and xb (0 0,500 10 0,500). The same top product composition, as in the previous example (Fig. 5.18b) of separation of three-component mixture in the top section, is accepted for convenience of analysis. In this case, the boundary elements of top section trajectory bundle, located in face 1-2-3, completely coincides with top section trajectory bundle at separation of previously mentioned three-component mixture. 

Unlike ideally behaved systems, the acetone/benzene/chloroform system exhibits an azeotrope. An azeotrope is a point in the compositional space where a liquid mixture has a constant boiling point because the vapor has the same composition as the liquid. Azeotropes can occur between two or more species, and the boiling temperature determines the nature of the azeotrope. In this case (refer to Figure 2.5b), the azeotrope is a high (or maximum) boiling binary azeotrope between acetone and chloroform. 

The best solvents for hexaorganodisiloxanes are benzene, diethyl ether and chloroform. Their solubility in petroleum ether, acetone and alcohols is only moderate, so that these solvents can be used for recrystallization. The hexaorganodisiloxanes have a remarkable tendency to form binary and tertiary azeotropic mixtures with organosilanols and solvents, and these are difficult to separate by distillation. 

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