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

To begin a bubble point is run with chemcad on the

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Unformatted text preview: tion curve starting from a bubble-point liquid of 20 mol% n-Hexane (1), 60 mol% methanol (2), and 20 mol% methyl acetate (3), at 1 atm, using a simulation program. Analysis: The distillation curve is computed stagewise using the FLASH model in Chemcad, in the same manner as in Example 11.2, except that here the calculation is made in both directions. To begin, a bubble point is run with Chemcad on the above initial liquid composition, xi(1), at 1 atm. The computed vapor composition, yi(1), is set equal to xi(2), according to Eq. (11-14) so that the compositions of passing vapor and liquid streams are made equal, and the bubble-point calculation is repeated. In this manner, we step in the first direction. The sequence is repeated, starting again from xi(1), but this time running a sequence of dew points to step in the opposite direction. The results are as follows, with a plot on the following page. x (1) 0.3753 0.3783 0.3822 0.3873 0.3939 0.2000 0.0272 0.0022 0.0002 0.0000 0.0000 0.0000 x (2) 0.3594 0.3635 0.3689 0.3757 0.3840 0.6000 0.8662 0.9586 0.9869 0.9958 0.9987 0.9996 x (3) 0.2653 0.2582 0.2489 0.2370 0.2221 0.2000 0.1066 0.0392 0.0129 0.0042 0.0013 0.0004 y (1) 0.3731 0.3753 0.3783 0.3822 0.3873 0.3939 0.2000 0.0272 0.0022 0.0002 0.0000 0.0000 y (2) 0.3562 0.3594 0.3635 0.3689 0.3757 0.3840 0.6000 0.8662 0.9586 0.9869 0.9958 0.9987 y (3) 0.2707 0.2653 0.2582 0.2489 0.2370 0.2221 0.2000 0.1066 0.0392 0.0129 0.0042 0.0013 T, o C 47.84 47.84 47.85 47.86 47.89 47.99 55.01 61.89 63.74 64.25 64.41 64.46 In the plot on the next page, the distillation curve is seen to take a sharp turn at a n-hexane mole fraction of approximately 0.40. This may be due to the drastic changes that occur to the K-values along the distillation curve for this very non-ideal system. Starting from almost pure methyl alcohol and moving along the distillation curve to right, the K-values change as follows: Analysis: (continued) Exercise 11.3 (continued) Component nC 6 MeOH MeAc K-values: 14.29 1.00 3.16 12.20 0.90 2.73 7.37 0.69 1.88 1.97 0.64 1.11 0.98 0.98 1.07 0.99 0.99 1.01 Note how the final K- values are tending toward the azeotropic condition. This may explain the sharp turn of the distillation curve on the plot below. Exercise 11.4 Subject: Azeotropes and approximate residue curve map for the system n-hexane - methanol methyl acetate at 1 atm Given:. Ternary system acetone - benzene - n-heptane at 1 atm. Find: All binary and ternary azeotropes from suitable references. Approximate distillation curve map showing distillation boundaries. Type of node for each azeotrope and pure component. Analysis: The following azeotrope data were obtained from the "Handbook of Chemistry and Physics". At 1 atm, the molecular weights and boiling points of the three components are: Component Molecular weight Normal b. pt., oC n-Heptane 100.2 98.4 Benzene 78.11 80.1 Acetone 58.08 56.5 Binary azeotropes (all minimum boiling): Mixture, A/B Boiling pt., oC n-Heptane/Benzene 80.1...
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