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

This reduced the phenol rate in the distillate from

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Unformatted text preview: with a composition of 59.70 mol% N2, 1.47 mol% A, and 38.83 mol% O2, entering tray 12 from the top. Column operates at 131.7 kPa, with a vapor distillate flow rate = 2487 lbmol/h. Assumptions: Ideal solutions and ideal gas law. Raoult's law K-values. Find: Effect of % flooding on the Murphree vapor tray efficiency for oxygen and the separation. Analysis: The rate-based calculations were made with the Chemsep program using the reboiled absorber/stripper option, no condenser, a partial reboiler, and 49 stages (48 trays + reboiler). To simulate the split reboiler, a vapor sidestream was withdrawn from stage 49. Antoine vapor pressure and default properties were used. A total material balance around the column gives: F1 + F2 = D + BV + BL with BV = BL . Thus, the bottoms flow rate, BL , was specified as: (1349 + 1832 - 2487)/2 = 347 lbmol/h. The vapor sidestream flow rate from stage 49, BV , was also specified as 347 lbmol/h. The Chan-Fair method was used to estimate mass-transfer coefficients and interfacial area. Mixed flow was specified for vapor and liquid phases. Defaults were used for solving the problem. The feed to tray 1 was computed to be 69 mol% vaporized, while the feed to tray 12 was all liquid. Convergence of the calculations was achieved without difficulty, with the following results: % Flood 25 50 75 85 95 Mole fraction of O2 in the vapor distillate 0.0317 0.0314 0.0313 0.0313 0.0314 Mole fraction of N2 in the liquid bottoms 0.0063 0.0059 0.0060 0.0064 0.0072 Median Murphree efficiency for O2, % 50 54 53 48 40 Exercise 12.15 (continued) The peak efficiency was achieved in the neighborhood of 50% flooding, but the separation was little affected over the range of 25 to 85% of flooding. The complete material balance for 85% of flooding was as follows: Component Nitrogen Argon Oxygen Total: Feed to tray 1 1320 5 24 1349 Feed to tray 12 1094 27 711 1832 Vapor Distillate 2398.83 10.36 77.81 2487.00 Vapor bottoms 12.95 12.69 321.36 347.00 Liquid bottoms 2.22 8.95 335.83 347.00 Exercise 12.16 Subject: Separation of methanol (M), n-hexane (HX) , and n-heptane (HP), from toluene (T) by extractive distillation with phenol (P), using a rate-based method. Given: Bubble-point feed of 50 kmol/h of M, 20 kmol/h of HX, 180 kmol/h of HP, and 150 kmol/h of T at 1.4 atm. Entrainer of 10 kmol/h of T and 800 kmol/h of P, at 1.4 atm and same temperature as the feed. Sieve-tray column with 30 trays, a total condenser, and partial reboiler. Thus, 32 stages are needed. Entrainer to tray 5 from top {Stage 6) and feed to tray 15 from top (Stage 16). Condenser outlet pressure = 1.1 atm. Condenser inlet pressure = 1.2 atm. Bottom tray pressure = 1.4 atm. Reflux ratio = 5 and bottoms rate = 960 kmol/h. Use UNIFAC method with Antoine equation for liquid phase and SRK EOS for the vapor phase. Vapor and liquid on each tray are well mixed. Use Chan-Fair for mass-transfer coefficients and interfacial area. Operation at about 75% of flooding. Find: The separation and average Murphree vapor tray efficiencies. Any improvement in the separation by moving the entrainer and feed tr...
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