Unformatted text preview: hase
o
pt., C
WB
69.4 Heterogeneous 29.8% W
0.26% W
99.98% W
70.2% B
99.74% B
0.02% B
WP
80.4
Homogeneous 31.7% W
68.3% P
BP
71.5
Homogeneous
60.6% B
39.4% P
Also, the following heterogeneous ternary azeotrope is formed:
Ternary Normal
Type
Mol%
Mol% Mol% lower
System
boiling
Azeotrope
overall
upper liquid phase
o
pt., C
liquid phase
WBP
65.7 Heterogeneous 26.7% W
8.8% W
95.1% W
54.0% B
68.5% B
0.1% B
19.3% P
22.7% P
4.8% P
The column calculations were made with the ChemCad program. Important decisions were the
choice of activity coefficient method for the liquid and the binary interaction parameters for the
selected method, because these decisions can have a significant influence on the results of the
calculations. The UNIQUAC method was selected, with builtin values of the binary interaction
parameters for pairs with isopropanol; but for the benzenewater pair, values were taken from the
Appendix of the article by Bekiaris, Meski, and Morari, IEC Res., 35, 207227 (1996). They
give the parameters as values of (uij  ujj)/R in K. For the ChemCad program, the parameters Exercise 11.20 (continued)
Analysis: (continued)
must be given as (uij  ujj) in cal/mol. Therefore, the Bekiaris, Meski, and Morari values were
multiplied by 1.987 cal/molK. In summary, the following values of (uij  ujj) were used for the
ChemCad runs:
i
j
Water
Benzene
Isopropanol
Water
719.890
109.550
Benzene
1795.85
319.618
Isopropanol
300.190
54.883
With these values, the computed azeotropes at 1 atm, which deviate somewhat from the above
experimental values, were as follows, where the homogeneous azeotropes were determined with
the TPYX plot feature of ChemCad and the heterogeneous azeotropes were determined by
running threephase flash calculations with the LLVF model of ChemCad until the assumed feed
composition gave vapor and overall liquid compositions that were equal. The most serious
deviations are for the ternary heterogeneous azeotrope. From the builtin vapor pressure
correlations in ChemCad, the normal boiling points of water and benzene are the same as the
above literature values, but the isopropanol value is 82.5oC.
Binary pair Type
Azeotrope Mol%
overall WB Normal
boiling
pt., oC
69.2 Heterogeneous WP 80.2 Homogeneous BP 71.6 Homogeneous 29.8% W
70.2% B
32.6% W
67.4% P
58.5% B
41.5% P Ternary
System
WBP Normal
boiling
pt., oC
60.6 Mol%
upper
liquid phase
0.47% W
99.53% B Mol% lower
liquid phase
99.94% W
0.06% B Type
Azeotrope Mol%
overall Mol% upper
liquid phase Mol% lower
liquid phase Heterogeneous 23.8% W
52.3% B
23.9% P 4.6% W
67.6% B
27.8% P 89.3% W
0.3% B
10.4% P A binodal plot for the liquidliquid equilibrium of the ternary system, as computed with
ChemCad at a temperature of 66oC, is given on the next page. Many liquidliquid phase
equilibrium tie lines are shown. Added to the diagram are the above computed temperatures and
compositions for the azeotropes, and estimates of the distillation boundary lines, which divide
the composition plot into three distillation regions. Analysis: (continued) Exercise 11.20 (continued) As disc...
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 Spring '11
 Levicky
 The Land

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