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

Exercise 1117 continued analysis continued a feasible

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Unformatted text preview: was only 79.2 mol% B. Several of the parameters, including total stages, methanol entry stage, feed entry stage, reflux ratio, methanol flow rate, reflux ratio, and bottoms flow rate. The best result was obtained with the following specifications: Number of equilibrium stages = 100 + total condenser = 101 Methanol flow rate = 115 kmol/h sent to stage 56 from the top, counting the total condenser. Feed sent to stage 71 from the top, counting the total condenser. Reflux ratio = 10 Bottoms flow rate = 24.0 kmol/h Products were as follows, with 99.58 mol% benzene bottoms, but only a 95.6% recovery of benzene: Component Feed Entrainer Distillate Bottoms B 25 0 1.1 23.9 C 75 0 75.0 0.0 M 0 115 114.9 0.1 Total: 100 115 191.0 24.0 Analysis: (continued) Exercise 11.16 (continued) Exercise 11.17 Subject: Separation of toluene (T) from 2,5-dimethylhexane (H) by a sequence that includes homogeneous azeotropic distillation with methanol (M) as the entrainer. Given: Feed of 100 mol/s of 50 mol% T and 50 mol% H. Reference to an article by Benedict and Rubin. Find: A separation sequence that includes homogeneous azeotropic distillation with M as the entrainer. A feasible design for the azeotropic distillation column. Analysis: The normal boiling points of the three components are: Component Normal b. pt., oC T H 110.64 109.15 M 64.48 From use of the UNIFAC equation for activity coefficients with the Chemcad program, the following predicted minimum boiling binary azeotropes are found for a pressure of 1 atm. Binary mixture: T H T M UNIFAC, prediction T, oC Mol% 106.9 47.5 52.5 63.8 11.2 88.8 H 60.3 20.7 M 79.3 No ternary azeotrope is known. A residue curve map, produced by the Aspen Plus program with the UNIFAC equation, for the T-H-M system at 1 atm is shown on the next page, where the three binary azeotropes are marked with dots. There are two distillation boundaries, one from the T-M azeotrope to the H-M azeotrope with little curvature, and one from the T-H azeotrope to the H-M azeotrope, with much curvature. These two boundaries divide the diagram into three distillation regions. Also included on the diagram are two straight lines, one from the T-M feed of 50 mol% H to pure M. The composition of the combined feed and entrainer must lie somewhere on this line. If we take advantage of the high degree of curvature of the second distillation boundary, we can assume that ideally the bottoms product can be pure toluene, with a distillate of the H-M azeotrope. Another straight line connects these two product points. The intersection of the two lines is the mixing Exercise 11.17 (continued) Analysis: (continued) Exercise 11.17 (continued) Analysis: (continued) point. By the inverse lever-arm rule or by material balance, the following preliminary, ideal material balance is obtained: mol/s: Component Feed Entrainer Distillate Bottoms T 50 0 0 50 H 50 0 50 0 M 0 192 192 0 Total: 100 192 242 50 An initial run is made with the Chemcad SCDS model using the following specifications: Combined feed and entrainer at 1 atm and the bubble point. Column ∆P = 0 Top pressure = 1 atm Condenser ∆P = 0 No. of stages = 31 (includes total condenser and partial r...
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