Single Equilibrium Stages and Flash Calculations

1
Single Equilibrium Stages and Flash Calculations
Chapter5
Exercises
2
Exercise5.1

• An aqueous acetic acid solution containing 6.0
  moles of acid per liter is to be extracted in the
  laboratory with chloroform at 25C to recover the
  acid (B) from chloroform-insoluble impurities
  present in the water. The water (A) and
  chloroform (C) are essentially immiscible. If 10
  liters of solution are to be extracted at 25CC,
  calculate the percent extraction of acid obtained
  with 10 liters of chloroform under the following
  conditions
• (a) Using the entire quantity of solvent in a
  single batch extraction
• (b) Using three batch extractions with one-third
  of the total solvent used in each batch
• (c) Using three batch extractions with 5 liters
  of solvent in the first, 3 liters in the second,
  and 2 liters in the third batch Assume that the
  volumetric amounts of the feed and solvent
• do not change during extraction. Also, assume the
  distribution coefficient for the acid, K"n
  (ck)c/(cb)a - 2.8, where (cb)c concentration of
  acid in chloroform and (cH)A concentration of
  acid in water, both in moles per liter.

3
Exercise5.2

• A 20 wt'7r solution of uranyl nitrate (UN) in
  water is to be treated with tributyl phosphate
  (TBP) to remove 90 of the uranyl nitrate. All
  operations are to be batchwise equilibrium
  contacts. Assuming that water and TBP are
  mutually insoluble, how much TBP is required for
  100 g of solution if at equilibrium (g UN/g TBP)
  5.5(g UN/g H2O) and
• (a) All the TBP is used at once in one stage?
• (b) Half is used in each of two consecutive
  stages?
• (c) Two countercurrent stages are used?
• (d) An infinite number of crosscurrent stages is
  used?
• (e) An infinite number of countercurrent stages
  is used?

4
Exercise5.3

• A stripper operating at 50 psia with three
  equilibrium stages is used to strip 1,000 kmol/h
  of liquid at 300F having the following molar
  composition 0.03 C,, 0.22 C2, 1.82 G,, 4.47
  C4, 8.59 C5, 84.87 nC,0. The stripping agent
  is 1,000 kmol/h of superheated steam at 300F and
  50 psia. Use the Kremser equation to estimate the
  compositions and flow rates of the stripped
  liquid and exiting rich gas.
• Assume a /C-value for CK) of 0.20 and assume that
  no steam is absorbed. However, calculate the
  dew-point temper-
• ature of the exiting rich gas at 50 psia. If that
  temperature is above 300F, what would you
  suggest be done?

5
Exercise5.4

• Verity the values given in Table 5.1 for AV,
  A7/., and V/, tor a partial reboiler and a
  total condenser.

6
Exercise5.5

• A mixture of maleic anhydride and benzoic acid
  contaming 10 molf/r acid is a product of the
  manufacture of phthalic anhydride. The mixture is
  to be distilled continuously in a column with a
  total condenser and a partial reboiler at a
  pressure of 13.2 kPa (100 torr) with a reflux
  ratio of 1.2 times the minimum value to give a
  product of 99.5 mol maleic anhydride and a
  bottoms of 0.5 mol anhydride. Is this problem
  completely specified

7
Exercise5.6

• Verify A//gt for the following unit operations in
  Table 12 (ft), (t), and (). How would WD change
  if two feeds were used instead of one?

8
Exercise5.7

• The following are not listed as design variables
  for the i distillation unit operations in Table
  5.2 jfa) Condenser heat duty jfb) Stage
  temperature ifc) Intermediate-stage vapor rate
  Id) Reboiler heat load Under what conditions
  might these become design variables?If so, which
  variables listed in Table 5.2 would you eliminate?