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Queen’s University
Faculty of Applied Science
Department Of Chemical Engineering
CHEE 323 – Industrial Catalysis
Final Examination
April 17, 2001
Instructor: Dr. J.S. Parent
Please write your student ID number on all examination booklets. This examination consists of
four (4) questions adding to a total of 100 marks. Attempt all questions within the three (3) hour
exam period. Remember to clearly state any assumptions made in your calculations.
The course notes and textbook are permitted. Worked out problems (tutorials, problem sets,
personal notes) of any kind are NOT allowed.
Please note:
If the instructor is unavailable in the examination room and if doubt exists as to
the interpretation of any question, the candidate is urged to submit with the
answer paper a clear statement of any assumptions made.
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Question #1 (35 marks)
Relative reaction rates (vi) for interconversion of hexanes at 25C in HF with 10% BF3 are
provided below:
a) Propose a complete and plausible mechanism for reaction 4 leading to the production of 2,2dimethylbutane from 2,3-dimethylbutane.
b) Using free energy diagrams to illustrate your reasoning, account for the high rate of reaction
1 (v1 = 12) relative to reaction 4 (v4=8.6).
c) The isomerization activity of acidic zeolites such as HZSM-5 is poisoned by compounds
such as quinoline (shown below). Propose a mechanism by which the active site(s) is
poisoned.
N
Question #2 (20 marks)
Plotted below are the activities of three enzymes as a function of aqueous solution pH.
a. Discuss briefly the factors that determine enzyme sensitivity to pH and how this sensitivity
can lead to a pH optimum.
b. Provide reasons that may account for the observed differences in optimum pH for pepsin,
saccharase and trypsin.
c. Are enzyme-catalyzed hydrolysis processes classified as general acid catalyzed reactions or
specific acid catalyzed reactions? Explain.
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Question #3 (30 marks)
Ethylene is polymerized by Cp2ZrMe2 /B(C6F5)3 in toluene at room temperature. In the
mechanism shown below, the alkyl ligand (R) of complexes 2 and 3 increases in molecular
weight through reactions r2 and r3 until the polymerization cycle is terminated by reaction r4.
You may assume that the reactivity of complex 2 and complex 3 is independent of the size of R.
R'
Cp
Zr
Cp
Me
Me
B(C6F5)3
r1
1
Cp
Cp
+
Zr
Cp
R
r4
Zr+
Cp
H
4
2
ethylene
r3
r.d.s.
r2
Cp
Zr+
R
Cp =
Cp
3
a) Determine the oxidation state, effective atomic number and coordination number of
complex 1.
b) Name reaction r3 and reaction r4.
c) The molecular weight of polymer produced by this system is dictated by the rate of chain
growth (r3) to the rate of chain termination (r4). The ratio of these reaction rates (r3 / r4)
represents the number of ethylene incorporations over the lifetime of a growing alkyl ligand,
R. Express this ratio (r3 / r4) in terms of measurable process variables, assuming that r3 is the
rate-determining step of the catalytic cycle and that all reactions follow elementary kinetics.
d) Although this system can copolymerize ethylene and propylene, attempts to use this catalyst
to copolymerize ethylene and acrylonitrile (CH2=CH-CN) have been unsuccessful. Propose
a mechanism by which acrylonitrile affects the activity of this system.
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Question #4 (15 marks)
Polyethylene (2) can be functionalized through a chain-process involving free radical
intermediates. The process uses an alkyl peroxide (ROOR, 1) to initiate the rapid addition of
maleic anhydride (3) to the polymer, followed by a slow abstraction process to yield the desired
product (4). An undesired side-reaction involving the combination of macroradicals 6 and 7
creates a crosslinked material (5).
ROOR
peroxide 1
kd
very
slow
RO
RO
crosslinked
polyethylene 5
O
polyethylene 2
O
ki
O
ROH
fast
kt
slow
O
O
O
kg 3
fast
6
kabs
O
7
O
O
slow
O
maleated
polyethylene 4
polyethylene 2
O
O
a. Using the steady-state hypothesis where appropriate, derive an expression representing the
rate of production of crosslinked polyethylene (5) as a function of measurable process
variables.
b. Develop a rate expression for the production of maleated polyethylene (4) in terms of
measurable process variables using the steady-state hypothesis where applicable.