Approximate Methods for Multicomponent, Multistage Separations

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Approximate Methods for Multicomponent,
Multistage Separations
Chapter9
Exercises
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Exercise9.1

• A mixture of propionic and n-butyric acids, which
  can be assumed to form ideal solutions, is to be
  separated by distillation into a distillate
  containing 95 mol propionic acid and a bottoms
  product containing 98 mol n-butyric acid.
  Determine the type of condenser to be used and
  estimate the distillation column operating
  pressure

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Exercise9.2

• For 15 minimum equilibrium stages at 250 psia,
  calculate and plot the percent recovery of C3 in
  the distillate as a function of distillate flow
  rate for the distillation of 1,000 lbmol/h of a
  feed containing 3 C2, 20 C3, 37 nC4, 35 Cs,
  and 5 nC6 by moles. Obtain K-values from
  Figures2. 8 and 2.9.

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Exercise9.3

• Calculate and plot the minimum external reflux
  ratio and the minimum number of equilibrium
  stages against percent product purity for the
  separation by distillation of an equimolar
  bubble-point liquid feed of isobutane/n-butane at
  100 psia. The distillate is to have the same iC4
  purity as the bottoms is to have nC4 purity.
  Consider percent purities from 90 to 99.99.
  Discuss the significance of the results.

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Exercise9.4

• Use the Fenske-Underwood-Gilliland shortcut
  method to determine the reflux ratio required to
  conduct the distillation operation indicated in
  Figure 9.25 if N/Nmin 2.0, the average relative
  volatility 1.11, and the feed is at the
  bubble-point temperature at column feed-stage
  pressure. Assume that external reflux equals
  internal reflux at the upper pinch zone. Assume a
  total condenser and a partial reboiler.

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Exercise9.5

• The hydrocarbon feed to a distillation column is
  a bubble-point liquid at 300 psia with the mole
  fraction composition, C2 0.08, C, 0.15, nC4
  0.20, nCs 0.27, nC6 0.20, and nC7 0.10.
• (a) For a sharp separation between nC4 and nC5 ,
  determine the column pressure and type of
  condenser if condenser outlet temperature is
  120F.
• (b) At total reflux, determine the separation for
  eight theoretical stages overall, specifying
  0.01 mole fraction nC4 in the bottoms product.
• (c) Determine the minimum reflux ratio for the
  separation in part (b).
• (d) Determine the number of theoretical stages at
  L/D 1.5 times minimum using the Gilliland
  correlation. .

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Exercise9.6

• One hundred kilogram-moles per hour of a three
  component bubble-point mixture to be separated by
  distillation has the following composition
• Component Mole Fraction Relative k
• A 0.4 5
• B 0.2 3
• C 0.4 1
• (a) For a distillate rate of 60 kmol/h, five
  theoretical stage, and total reflux, calculate
  the distillate and bottomsi- tions by the Fenske
  equation.
• (b) Using the separation in part (a) for
  components B and C, determine the minimum reflux
  and minimum boilup ratio by the Underwood
  equation.
• (c) For an operating reflux ratio of 1.2 times
  the minimum, determine the number of theoretical
  stages and the feed-stage location.

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Exercise9.7

• One thousand kilogram-moles per hour of rich gas
  at 70F with 25, 15 C2, 25, 20 C4, and 15
  nC5 by moles is to be absorbed by 500 kmol/h of
  nC10 at 90F in an absorber operating at 4 atm.
  Calculate by the Kremser group method the percent
  absorption of each component for (a) Four
  theoretical stages, (b) Ten theoretical stages,
  and (c) Thirty theoretical stages. Use Figures
  2.8 and 2.9 for lvalues.