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

5 feet the condenser duty was computed to be 853

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Unformatted text preview: relative volatility of n-heptane with respect to toluene is about 1.7. At low concentrations of n-heptane and 50 mol% phenol in the liquid, the relative volatility of nheptane with respect to toluene is even higher at about 2.8. Thus, phenol makes the separation of n-heptane and toluene quite favorable. Extractive Distillation Column: The following Chemcad results, using the Tower (inside-out) model, give a reasonable n-heptane distillate product. Convergence was achieved in 15 iterations. Other combinations of stages, reflux, and solvent and feed stage locations could also give satisfactory results. Number of stages = 21 (includes total condenser and partial reboiler) Solvent enters stage 6 from the top Feed enters stage 13 from the top Reflux ratio = 5 Bottoms flow rate = 1400 lbmol/h (based on toluene + phenol) Initial guesses: Distillate rate = 200 lbmol/h Reflux rate = 1000 lbmol/h o o Temperatures: Stage 1, 200 F Stage 21, 300 F Stage 2, 220oF Convergence was achieved in 34 iterations with the following material balance: Solvent Feed Distillate Bottoms Temperature, oF 220 200 229.2 323.4 Flow rates, lbmol/h: n-Heptane 0 200 198.2 1.8 Toluene 0 200 1.2 198.8 Phenol 1200 0 0.6 1199.4 Exercise 11.12 (continued) Analysis: Extractive Distillation Column (continued) The liquid phase composition profile is shown below. The condenser and reboiler duties are 15.99 million Btu/h and 24.30 milllion Btu/h, respectively. The extractive 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 8 feet For a final design, the computations should be repeated taking into account tray pressure drop and tray efficiency. Exercise 11.12 (continued) Analysis: (continued) Ordinary Distillation Column to separate toluene from phenol: A starting point for this separation is obtained by using the ShortCut Column (FUG) model of Chemcad with an operating reflux ratio of 1.3 times the minimum ratio, with an operating pressure of 20 psia. The feed is assumed to be at the bubble point. To achieve reasonable product purities, the following material balance is assumed: Component n-Heptane Toluene Phenol Total: lbmol/h: Feed Distillate 1.8 1.8 198.8 196.8 1199.4 1.2 1400.0 199.8 Bottoms 0.00 2.0 1198.2 1200.2 The specifications for the ShortCut Column model are 196.8/198.8 = 0.99 for the recovery of toluene to the distillate, and 1.2/1199.4 = 0.001 for the recovery to the distillate of phenol. The results are: Minimum number of equilibrium stages = 7.7 Minimum reflux ratio = 1.50 Reflux ratio = 1.3(1.50) = 1.95 Number of equilibrium stages = 15.5 Feed stage location (Kirkbride equation) = 11.4 from the top The Tower model of the Chemcad program is then used to make a rigorous calculation based on the following input data, using the FUG results: Pressure constant at 20 psia. Number of stages = 16 (includes the total condenser and...
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This document was uploaded on 02/24/2014 for the course CBE 2124 at NYU Poly.

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