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

Operation of both columns must be outside the two

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Unformatted text preview: eboiler) Combined feed stage = 16 from the condenser Reflux ratio =3 Bottoms flow rate = 50 mol/s (from above material balance) Estimated (actual) distillate rate = 192 mol/s Estimated (actual) reflux rate = 576 mol/s Estimated temperatures: Stage 1, 60oC Stage 31, 60oC Stage 2, 60oC Stage 30, 60oC This column was difficult to converge, but with the above specifications, plus a 0.50 damping factor, converge was achieved in 25 iterations. The calculated material balance was as follows: mol/s: Component Feed Entrainer Distillate Bottoms T 50 0 0.3 49.7 H 50 0 49.8 0.2 M 0 192 191.9 0.1 Total: 100 192 242.0 50.0 The liquid phase composition profile is on the following page. The condenser and reboiler duties are 12.37 x 104 MJ/h and 12.50 MJ/h respectively. The column profiles are given on a following page. The azeotropic distillation column was sized with Chemcad for sieve trays, with: 24-inch tray spacing 12% downcomer area 10% hole area 1/4-inch holes 80% of flooding The resulting column inside diameter was determined to be 16 feet For a final design, the computations should be repeated taking into account tray pressure drop and tray efficiency. Exercise 11.17 (continued) Analysis: (continued) A feasible separation sequence would include the azeotropic distillation column, considered above, to separate the feed into 99.5 mol% toluene and a near azeotropic mixture of methanol and 2,5 dimethylhexane. The M-H azeotrope would be separated by liquid-liquid extraction with water to give nearly pur H and a methanol-water mixture. The latter would be separated by ordinary distillation to recover the methanol for recycle to the azeotropic tower, and water for recycle to the extraction section. Exercise 11.17 (continued) Analysis: (continued) Exercise 11.18 Subject: Feasibility of the separation of a mixture of methyl acetate (A) and methanol (M) by a sequence that includes homogeneous azeotropic distillation using as the entrainer either n-hexane (H), cyclohexane (C), or toluene (T). Given: Feed rate of 16,500 kg/h of 55 wt% A and 45 wt% M. Desired products are 99.5 wt% A and 99 wt% M. H, C, and T as potential entrainers. Find: Feasibility of a separation sequence that includes homogeneous azeotropic distillation with one the three potential entrainers. If not feasible, find an alternative feasible process. Analysis: The molecular weights and normal boiling points of the five components of interest are: Component Molecular Normal boiling point, o Weight C Methyl acetate, A 74.08 57.1 Methanol, M 32.04 64.7 n-Hexane, H 86.17 69.0 Cyclohexane, C 84.16 80.7 Toluene, T 92.13 110.8 Convert the feed specification from a weight to a mole basis. Component Feed, kg/h Feed, kmol/h Feed, mol% Methyl acetate, A 9,075 122.5 34.58 Methanol, M 7,425 231.7 65.42 Total: 16,500 354.2 100.00 From the Handbook of Chemistry and Physics, the homogeneous binary azeotropes are: Binary pair Normal boiling pt., Mol% o C A-M 54.0 65.3, 34.7 A-H 51.8 64.2, 35.8 A-C 55.5 80.1, 19.9 M-T 63.7 88.3, 11.7 Also, heterogeneous binary azeotropes are formed by the pairs M-H and M-C. No azeotrope is formed with the pair A-T. The f...
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