Name______________________
Student # ____________________
University of Toronto
Faculty of Applied Science and Engineering
Final Examination, April 15, 2014
CHE333S1 - Chemical Reaction Engineering
Examiner: B.A. Saville
Closed Book Examination-1
The Course Textbook or Official Course Notes Package may be used
Calculators without a Graphical Interface may be used
Both sides of the page may be used
Question: Marks Possible Marks Earned
1
30
2
20
3
20
4
35
5
45
Total
150
Page 1 of 13
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Student # ____________________
1. Two 5000L CSTRs are available to process an exothermic liquid phase reaction A  2B. The
reactor operates isothermally at 350K due to careful process control. Given the following:
(-rA) = kAcA2; kA=8.2x104 e(-6,400/T) L mol-1 min-1
qo =75 L/min
cAo = 2.5 mol/L
MW(A) = 88 g/mol
-1 -1
cP = 4.0 J g K
MW(B) = 44 g/mol
To = 35oC
 = 0.95 kg/L
(-HRA) = -40 kJ per mol of A
a. What is the maximum possible conversion of A using these vessels, under isothermal
conditions?
b. Assuming fA is less than 0.80, would these reactors require a heat transfer system in order to
achieve the specified operating temperature? If so, does heat need to be removed or added to
the system? Explain and justify your answer.
c. What is the annual production rate of B (in tonnes), if fA = 0.80, the facility normally operates
24 hours per day, but is shut down for maintenance for 15 days per year?
d. Would using a 10,000L batch reactor, also operating isothermally at 350K, likely produce a
lower or higher conversion compared to your answer in (a), if the reaction time and residence
time were equivalent, and the BR down time is 25% of the reaction time? Explain and justify
your answer
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Page 3 of 13
Name______________________
Student # ____________________
2. You have been put in charge of a reactor/process design that aims to produce a partial oxidation
product, B, from an initial reactant “A”. B can undergo further oxidation to compound “C”. Both
reactions are first order. EA/R for the reaction A  B is -5,500 J/mol, and for the reaction
B  C, -7,500 J/mol.
You have the flexibility to choose the type of reactor(s), residence/reaction time, inlet reactant
concentrations, operating temperature(s) and other design features, including separation equipment,
heat exchangers, mixers, and stream splitters.
a. What type of reactor(s) and operating conditions would you select in order to maximize the
yield of B? EXPLAIN AND JUSTIFY YOUR ANSWER
b. What type of reactor(s) (and other equipment, if necessary) would you choose in order to
optimize based upon selectivity and feedstock utilization (i.e., fA), if the reactor operates
isothermally? The rate constant for the first reaction, k1, = 0.35 min-1, and k2 = 0.040 min-1.
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Page 5 of 13
Name______________________
Student # ____________________
3. A reactor must be designed for a first order gas phase reaction A  B + C . The feed contains
equimolar amounts of A and an inert, at a total molar flow rate of 100 mol/min, and a volumetric
feed rate of 650 L/min.
The target fractional conversion is 0.80, and kA = 0.47 min-1.
a) What residence time is required for a PFR in order to achieve the target conversion?
b) Using the residence time calculated in (a), what is the conversion obtained from the segregated flow
model? Either a calculation or discussion with justification is acceptable.
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Page 7 of 13
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Student # ____________________
4. The kinetics for a catalytic first order gas phase reaction A  products were studied. Pure reactant A
was fed through the catalyst bed at 150kPa and 400oC, and the observed reaction rate was measured
for several sizes of the spherical catalyst, ranging from 0.25 to 10 mm in diameter. The following
data were obtained:
dp, mm
0.25 0.50 1.0 5.0 10.0
(-rA)obs, mol L-1 h-1 175 180 155 59 30
1. Determine the effectiveness factor and shape-independent Thiele modulus (’) for the 1 mm
and 5 mm particles
2. Determine the effective diffusivity (De), the intrinsic reaction rate constant (kA) and intrinsic
reaction rate for this process
3. Predict the observed reaction rate for a bed of 25 mm (dp) catalyst particles (justify your
answer).
4. Predict the impact on the Thiele modulus and the effectiveness factor if the process was
instead conducted at 500oC (explain and justify your answer).
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Student # ____________________
Page 9 of 13
Name______________________
Student # ____________________
5. A three stage fixed bed catalytic reactor is to be designed to convert SO2 (A) into SO3. The
equilibrium curve is presented on the next page. Within each stage, the operation is adiabatic and
isobaric, and between stages, the temperature is adjusted by 100K using heat exchangers. The outlet
temperature from each stage is at least 15K less than the corresponding equilibrium temperature.
The feed contains 10 mol% SO2 (A), 12 mol% O2, 77.9% N2, and the balance is SO3.The inlet
temperature to the system is 677oC. The catalyst sinters at 800oC. Assume that the
pseudohomogeneous one-dimensional plug flow model is valid.
a. Determine the temperature and fractional conversion at the outlet of each stage, and
b. Assuming the outlet conversion from stage 1 is 0.30, estimate the catalyst mass required
in this stage. Use a step size of 0.10 for fA.
c. Considering your answer in part (b), how much catalyst would be required if the Thiele
modulus (’) was 0.10? Explain/justify your answer
FAo = 10000 mol/min; m = 3215 kg/min; cP = 0.94 J g-1 K-1; Po = 100 kPa; HRA = -95 kJ/mol;
B = 500 kg/m3
Kp = 8.0 x 10-5e12,100/T MPa-1/2 with T in Kelvins
kSO2 = 1.84 x 1011 e-26000/T mol SO2 (g cat)-1 min-1 MPa-1 with T in Kelvins
 r 
SO2
 p SO2
 k SO2 
 p SO
3





1
2
2

 p SO3  
 
 pO  
 2  p SO2 K p  


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Equilibrium conversion vs temperature relation: SO2 oxidation
1
0.9
0.8
fractional conversion
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
700
750
800
850
900
950
Temperature, K
Page 11 of 13
1000
1050
1100
1150
1200
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Student # ____________________
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Student # ____________________
Page 13 of 13