CHE425: Problem set #3
1) 1A mixture of 100 mol containing 60 mol % n-pentane and 40 mol % n-heptane is
vaporized at 101.32 kpa abs until 40 mol of vapor and 60 mol of liquid in equilibrium with
each other are produced. This occurs in a single-stage system and the vapor and liquid are
kept in contact with each other until the vaporization is complete. Calculate the composition
of the vapor and liquid. The equilibrium data are follows, where x and y are mole fraction of
n-pentane.
x
0
0.059
0.145
0.254
0.398
0.594
0.876 1.000
y
0
0.271
0.521
0.701
0.836
0.925
0.984 1.000
The intersection of the operating line and the equilibrium curve gives
x = 0.43, y = 0.855
1
Geankoplis, C.J., Transport Processes and Separation Process Principles, 4th edition, Prentice Hall, 2003, p.
705
2) We have 0.01 moles (N1) of drug dissolved in 100 moles of water (N3). We then add to
this phase 50 moles (N2) of octanol. The octanol-water partition coefficient for the drug is 89.
xiI
= 89
xiII
For this system, octanol (phase I) and water (phase II) are immiscible. Estimate the mole
fractions of the drug in the two phases once equilibrium has been attained and the %
extraction of the drug from the aqueous phase.23
Ans ------------------------------------------------------------------------------------------
Ki =
x1,II = 2.197810-6
x1,I = 1.956010-4
x1,I N 2
1.956 104  50
% extraction =
100 =
100 = 97.8%
0.01
N1
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3. Benzylpenicillin is an older antibiotic effective against pneumococcal and meningoccal
infections, anthrax, and Lyme disease. As part of a purification process, 100 mg of
benzylpenicilin is mixed with 25 ml of n-octanol and 25 mL of water. After equilibrium is
established, there is a water-rich phase that contains essentially no n-octanol and an octanolrich phase that contains 74 mol % n-octanol and 26 mol % water. Determine the
concentrations of benzylpenicillin in each of these phases24
Data: The molecular weight of benzylpenicillin is 334.5, that of n-octanol is 130.23, the
liquid density of n-octanol is 0.826 g/cm3, and
KOW,B =
CBO
mg B/(ml n-octanol)
=
= 65.5
W
CB
mg B/(ml water)
Ans ------------------------------------------------------------------------------------------
CBW = 0. 057904 mg/mL
C BO = 3.7927 mg/mL
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23
24
Fournier, R. L., “Basic Transport Phenomena in Biomedical Engineering”, Taylor & Francis, 2007, p. 71
Sandler, S. I., “Chemical, Biochemical, and Engineering Thermodyanmics”, Wiley, 2006, p. 643
4. A drug is in an aqueous (phase II) stream flowing at 100 moles/min at a drug mole fraction
of 0.01. The aqueous stream is then contacted with an extractor with a pure solvent (phase I)
flowing at 120 moles/min. The distribution coefficient for this particular drug is given by
xiI
=6
xiII
Determine the equilibrium mole fraction of the drug in the streams exiting the extractor and
the % extraction of the drug from the aqueous stream25.
Ki =
Ans -----------------------------------------------------------------------------------------xII,out = 12.19510-4, xI,out = 7.317110-3
% extraction = 87.8 %
5. 1A mixture contains 100 kg of water and 100 kg of ethylaniline (mol wt = 121.1), which is
immiscible with water. A very slight amount of nonvolatile impurity is dissolved in the
organic. To purify the ethylaniline, it is steam-distilled by bubbling saturated steam into the
mixture at a total pressure of 101.32 kPa. Determine the boiling point of the mixture and the
composition of the vapor. The vapor pressure of each of the pure compound is as follows:
Temperature(oC)
80.6
96.0
99.15
113.2
PA(water, kPa)
48.5
87.7
98.3
163.3
PB(ethylaniline, kPa)
1.33
2.67
3.04
5.33
Ans -----------------------------------------------------------------------------------------At the boiling point of the mixture P = PA + PB
P = 101.34 kPa at 99.15oC
yB = PB/P = 3.04/101.34 = 0.030
6.
Vapor-liquid equilibrium for the system A-B at a constant temperature of 80oC shows that
component B obeys Henry’s law in the range 0 < xB  0.020. The partial pressure of B in this
range (in mmHg) is given by
PB = 500xB
The vapor pressure at 80oC are PAsat = 1000 mmHg and PBsat = 250 mmHg. For xB = 0.01
calculate the equilibrium pressure and vapor composition.
25
Fournier, R. L., “Basic Transport Phenomena in Biomedical Engineering”, Taylor & Francis, 2007, p. 72
Ans
P = 995 mmHg
YB = 5.025×10-3
7.
Run program VLE. You need to copy the folder CHE425 into the H: drive or your flash
drive. Open the folder CHE425 and double click on DOSBox.exe. When the prompt “C:\>”
appears, type VLE and press “ENTER” to run the program. Copy and report the performance
number from the program. Type “e” or “exit” and press “ENTER” to exit the DOSBox
program.
8.
Run program BASIS. You need to copy the folder CHE425 into the H: drive or your flash
drive. Open the folder CHE425 and double click on DOSBox.exe. When the prompt “C:\>”
appears, type BASIS and press “ENTER” to run the program. Copy and report the
performance number from the program. Type “e” or “exit” and press “ENTER” to exit the
DOSBox program.