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

The best ethanol purity achieved was 95 mol for that

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Unformatted text preview: gn. However, because the feed is at near-azeotropic composition, the first (Preconcentrator) column is not needed. Analysis: The molecular weights and normal boiling points of the three components of interest are: Component Molecular Normal boiling Weight Point, oC Water, W 18.02 100.0 Benzene, B 78.11 80.1 Ethyl alcohol, E 46.07 78.5 From the Handbook of Chemistry and Physics, the binary azeotropes are: Binary pair Normal Type Mol% Mol% Mol% lower boiling Azeotrope overall upper liquid phase pt., oC liquid phase W-B 69.4 Heterogeneous 29.8% W 0.26% W 99.98% W 70.2% B 99.74% B 0.02% B W-E 78.2 Homogeneous 10.5% W 89.5% E B-E 67.8 Homogeneous 55.2% B 44.8% E 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-E 64.6 Heterogeneous 23.3% W 5.0% W 66.7% W 53.9% B 76.0% B 1.7% B 22.8% E 19.0% E 31.6% E 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 values of the binary interaction parameters 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 must be given as (uij - ujj) in cal/mol. Therefore, the Bekiaris, Meski, Exercise 11.19 (continued) Analysis: (continued) and Morari values were multiplied by 1.987 cal/mol-K, giving the following values of (uij - ujj) for input to ChemCad: i j Water Benzene Ethanol Water ---719.890 405.036 Benzene 1795.85 ---764.780 Ethanol -65.995 -85.507 ---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 and the heterogeneous azeotropes were determined by running three-phase flash calculations with the LLVF model until the vapor and overall liquid compositions were equal. The most serious deviation is the lower liquid phase composition of the ternary 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 ethanol value is 78.3oC. Binary pair Type Azeotrope Mol% overall W-B Normal boiling pt., oC 69.2 Heterogeneous W-E 78.2 Homogeneous B-E 67.8 Homogeneous 29.8% W 70.2% B 9.7% W 90.3% E 55.0% B 45.0% E Ternary System W-B-E Normal boiling pt., oC 63.8 Type Azeotrope Mol% overall Heterogeneous 19.7% W 53.1% B 27.2% E Mol% upper liquid phase 0.47% W 99.53% B Mol% upper liquid phase 2.4% W 81.7% B 15.9% E Mol% lower liquid phase 99.94% W 0.06% B Mol% lower liquid phase 47.7% W 7.0% B 45.3% E The above values also differ so...
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