Separation Process Principles- 2n - Seader & Henley - Solutions Manual

The azeotropic column column 2 in fig 1131a was then

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Unformatted text preview: hase o pt., C W-B 69.4 Heterogeneous 29.8% W 0.26% W 99.98% W 70.2% B 99.74% B 0.02% B W-P 80.4 Homogeneous 31.7% W 68.3% P B-P 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 W-B-P 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 built-in values of the binary interaction parameters for pairs with isopropanol; but for the benzene-water pair, values were taken from the Appendix of the article by Bekiaris, Meski, and Morari, IEC Res., 35, 207-227 (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/mol-K. 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 three-phase 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 built-in 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 W-B Normal boiling pt., oC 69.2 Heterogeneous W-P 80.2 Homogeneous B-P 71.6 Homogeneous 29.8% W 70.2% B 32.6% W 67.4% P 58.5% B 41.5% P Ternary System W-B-P 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 liquid-liquid equilibrium of the ternary system, as computed with ChemCad at a temperature of 66oC, is given on the next page. Many liquid-liquid 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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