ChE 344
Chemical Reaction Engineering
Winter 1999
Exam I
Part 1 (80%)
Closed Book, Notes, Disk, and Web
Name_______________________________
Honor Code________________________________________________________________
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1) ____/10 pts
2) ____/30 pts
3) ____/20 pts
4) ____/10 pts
5) ____/10 pts
Total ____/80 pts
(10 pts) 1) The trimerization
3A(g) → A3 (g,l)
is carried out isothermally and without pressure drop in a PFR at 298 K and 2
atm. As the concentration of A3 increases down the reactor and A3 begins to
condense. The vapor pressure of A 3 at 298 K is 0.5 atm. If an equal molar mixture
of A and inert, I, is fed to the reactor at what conversion of A will A3 begin to
condense?
W’99Exam I, Part 1
(30 pts) 2) In order to study the photochemical decay of aqueous bromine in bright sunlight,
a small quantity of liquid bromine was dissolved in water contained in a glass
battery jar and placed in direct sunlight. The following data were obtained:
Time (min) 10 20 30 40 50 60
ppm Br 2.45 1.74 1.23 0.88 0.62 0.44
a) Determine whether the reaction rate is zero-, first-, or second-order in
bromine, and calculate the reaction rate constant in units of your choice.
b) Assuming identical exposure conditions, calculate the required hourly rate of
injection of bromine (in pounds) into a sunlit body of water 25,000 gal in
volume in order to maintain a sterilizing level of bromine of 1.0 ppm.
(Note: ppm parts of bromine per million parts brominated water by weight. In
dilute aqueous solutions, 1 ppm=1 milligram per liter, molecular weight of
Br = 80 Daltons.)
1 gal
→ 3.785 liters
1 lb
→ 454 gms
W’99Exam I, Part 1
(20pts) 3) The irreversible elementary gas phase reaction
2A → B + C
is currently carried out in a packed bed reactor containing 100 kg of catalyst. The
entering pressure is 20 atm and the exit pressure is 4 atm. Currently 50%
conversion is achieved. It is proposed to add a CSTR with 200 Kg of catalyst
downstream of the PBR. There is no pressure drop in the CSTR. The flow rate
and temperature remain unchanged.
a) What would be the overall conversion in such an arrangement?
b) Is there a better way to carry out the reaction, and if so what is it?
Current
P0 = 20 P=4
100 KG
X = 0.5
Proposed
P0 = 20 P=4
100 KG
200 KG
X = 0.5 X=?
W’99Exam I, Part 1
(10 pts) 4) The following reactions were found to occur while trying to make a desired
product B
(1) A
→ B −rA1 = k1A C2A
A → X −rA2 = k 2A C A
A + X → Y −rA3 = k 3A C ACX
Species X and Y are both foul pollutants
a) What is the instantaneous selectivity of B with respect to the foul pollutants X
and Y?
b) How would you carry out this reaction to maximize the formation of B?
Additional Information
k1A = .5 e–10,000/T min–1, T in degrees Kelvin
k2A = 50 e–20,000/T min–1, T in degrees Kelvin
k3A = 100 e–5,000/T min–1, T in degrees Kelvin
W’99Exam I, Part 1
(10 pts) 5) The catalytic reaction
A → B
to be carried out in a flow reaction system has the following rate law,
kCA
−rA =
(1+ K A CA )
2
where k = 1 min–1
KA = 1 dm3 /mol
The entering concentration of A is 2 mol/dm3 . What type of reactor or
combination of reactors would have the smallest volume to
a) achieve 50% conversion?
b) achieve 80% conversion?
W’99Exam I, Part 1
