Exam 1 Fall 2017.pdf - 1[15 pt Use the x‐y and T‐x‐y...

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Unformatted text preview: 1) [15 pt] Use the x‐y and T‐x‐y diagrams below for isopropanol/water mixtures at a pressure of 101.3 kPa to answer the following based on a feed of 130 kmol/h of a mixture of 20% isopropanol and 80% water. You can draw on the charts to indicate your procedure, or describe it. (a) If the mixture is flashed so that the vapor contains 30 mol% isopropanol, what temperature is required and what flowrate of vapor is generated? [6 pt] (b) If the feed (containing 20% isopropanol) is flashed so that 80% of the product is liquid, what would be the mole fraction of isopropanol in the vapor and liquid produced? [6 pt] (c) If any number of flash units were used in any configuration, what is the highest mole fraction of isopropanol that could be generated in any vapor product at this pressure? [6 pt] 2) [25 pt] A feed is available at 30 °C as a mixture of 50 mol% n‐pentane (C5) and 50 mol% n‐hexane (C6) with F=100 kmol/h. The mixture is ideal, so the K values can be found using Raoult’s law with the Antoine equation for vapor pressure. (a) If this mixture is fed to a flash drum with Tdrum = 53 °C and Pdrum = 760 mm Hg, determine the vapor flowrate exiting the drum. Note: This is not a trial and error calculation. [20 pt] At this temperature, PvapC5 = 1349 mm Hg and PvapC6 = 451 mm Hg. (b) Show that the bubble point of the feed mixture is 47.68 °C. [5 pt] At this temperature, PvapC5 = 1147 mm Hg and PvapC6 = 373 mm Hg 3) [30 pt] At 101.3 kPa, vapor‐liquid equilibrium data of ethanol‐water mixtures are reproduced below. A continuous fermentation process generates a mixture of 5 mol% ethanol (95% water) after filtering. It is to be distilled in a column with a partial reboiler and a total condenser at 101.3 kPa. (a) If the distillate is to contain 80% ethanol, and the bottoms product 2% ethanol, the feed is a subcooled liquid which condenses 1 mole of vapor for every 3 moles of feed, and the reflux ratio is R=2, determine the number of trays needed for this distillation, and the optimal feed location. [15 pt] (b) If the feed flowrate is 150 kmol/h, calculate the distillate and bottoms flowrates for the conditions described in part (a), and the recovery of ethanol in the distillate. [10 pt] (c) If the distillation column is built with the number of trays from (a), and the bottoms composition is kept constant, what would be the maximum composition of distillate available from this column (at infinite reflux ratio)? [5 pt] 4) [20 pt] The McCabe‐Thiele diagram below was developed for a binary mixture that is to produce 100 kmol/h of distillate. The column produces three streams: a distillate, sidestream, and bottoms. Based on this diagram: a) What are the composition (zF) and quality (q) of the feed? [4 pt] b) Which trays above the reboiler are the feed stage, and the one from which is the sidestream withdrawn? [4 pt] c) If the reflux ratio is 3.5, determine the sidestream flowrate based on the slope of the operating line below the sidestream. [10 pt] d) A dashed line indicates the middle operating line with the minimum value of L’/V’. What can this be used to calculate? [2 pt] a. The minimum sidestream flowrate c. The minimum reflux ratio b. The maximum sidestream flowrate d. The minimum number of stages Op. line with minimum L’/V’ 5) [10 pt] In a column with a total condenser and partial rebioler, a feed of 50% benzene and 50% toluene is distilled to create a distillate containing 99 mol% benzene. The reflux ratio is 3. At some point above the feed, the vapor leaving a tray contains 60% benzene. What is the composition of the vapor entering that tray? Use B/T = 2.5. ...
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  • Spring '08
  • GULLA
  • 2%, 2 Pt, Antoine, 30 °C, Tdrum, 53 °C

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