Binary x-y Diagrams

Vapor-Liquid Equilibria 371 Relative Volatility 374 Binary x-y Diagrams 375... 

Solution To determine the location of the azeotrope for a specified pressure, the liquid composition has to be varied and a bubble-point calculation performed at each liquid composition until a composition is identified, whereby X = y,-. Alternatively, the vapor composition could be varied and a dew-point calculation performed at each vapor composition. Either way, this requires iteration. Figure 4.5 shows the x—y diagram for the 2-propanol-water system. This was obtained by carrying out a bubble-point calculation at different values of the liquid composition. The point where the x—y plot crosses the diagonal line gives the azeotropic composition. A more direct search for the azeotropic composition can be carried out for such a binary system in a spreadsheet by varying T and x simultaneously and by solving the objective function (see Section 3.9) ... 

For the unary diagram, we only had one component, so that composition was fixed. For the binary diagram, we have three intensive variables (temperature, pressure, and composition), so to make an x-y diagram, we must fix one of the variables. Pressure is normally selected as the fixed variable. Moreover, pressure is typically fixed at 1 atm. This allows us to plot the most commonly manipulated variables in a binary component system temperature and composition. 

Hengstebeck a (15) procedure extends the x-y diagram to multicomponent distillation, A multicomponent separation is treated as a binary separation between the keys, Flows and compositions are based on the two keys alone, that is,... 

Identifying mislocated feed points The feed point should be where the g-line intersects the equilibrium curve. This rule works well for binary distillation (Sec, 2,2,5), but not so well for multicomponent distillation (Sec, 2.3.7). In Fig, 2,22 it works well the x-y diagram... 

Figure 15.6. Binary liquid adsorption equilibria on X-Y diagrams (1) toluene + iso-octane on silica gel (Eagle and Scott, 1950) (2) toluene+ iso-octane on charcoal (Eagle and Scott, 1950) (3) ethylene dichloride -I- benzene on boehmite (Kipling) (4) ethylene dichloride + benzene on charcoal (Kipling). (Kipling in Proceedings of the Second International Congress of Surface Activity. (1957), Vol. Ill, p. 462.)...

Figure 2. T-x-y diagram for the binary systems of hexane-benzene (left) and ethyl acetate-benzene (right) at a pressure of 101.33 kPa.

F re 7.19 Phase diagrams for the isopropyl ether-isopropyl alcohol binary computed using ASPEN PLUS (a) P-x-y diagram at 70°C (b) x-y diagram at 101 kPa (c) T-x-y diagram at 101 kPa. 

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