Mo! fraction of1 water •085
¿-Wafer Moi fraction of water *0,S5
Fig. 10-10. Extractive distillation system for isopropanol-ethanol.
3. The number of theoretical plates required for O/D equal to 1.5 minimum O/D.
The equilibrium data (Refs. 5, 6) for this system are given in Figs. 10-8 and 10-9. A schematic diagram is shown in Fig. 10-10.
Let I » isopropyl alcohol E = ethyl alcohol H — water Basis: 100 mols of undiluted feed.
Since, in the presence of water, isopopanol is more volatile than ethanoi, the latter will be largely in the bottoms. By an ethanoi balance
For design conditions,
-—^L— - 0.002; Wxi = 0.149 Wxi + Wxe and, by difference,
The water in the distillate cannot be determined until the composition of the top plate is known, and this calculation is complicated by the fact that the water concentration on the top plate is not known. The water content of the reflux to the tower is 0.85, but there will be some change of this on the top plate; however, as a first approximation, a mol fraction of water equal to 0.85 will be assumed for this plate. Then using the relative volatilities from Figs. 10-8 and 10-9 a balance is applied to the top plate.
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