Transcript 幻灯片 1

Chapter5
Single Equilibrium
Stages and Flash
Calculations
Exercises
Exercise5.1
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An aqueous acetic acid solution containing 6.0 moles of acid per liter is to be
extracted in the laboratory with chloroform at 25°C 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.
Exercise5.2
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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?
Exercise5.3
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A stripper operating at 50 psia with three equilibrium stages is
used to strip 1,000 kmol/h of liquid at 300°F 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 300°F 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 temperature of the exiting rich gas at 50 psia. If that temperature is
above 300°F, what would you suggest be done?
Exercise5.4
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Verity the values given in Table 5.1 for AV,
A7/.;, and ;V/, tor a partial reboiler and a total
condenser.
Exercise5.5
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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
Exercise5.6
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Verify A//> for the following unit operations in
Table 12: (ft), (t), and (#). How would WD
change if two feeds were used instead of one?
Exercise5.7
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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?