Interdisciplinary Laboratory Learning for Chemical Engineering
Students in Organic Chemistry: Synthesis, Design and Separation
Matt Armstrong, Richard Comitz, Joseph C. Sloop, Andrew Biaglow, Russell
LaChance
This paper was completed and submitted in partial fu lfillment of the Master Teacher Program, a 2-year
faculty professional development program conducted by th e Center for Teaching Excellence, United States
Military Academy, West Point, NY, 2007.
Abstract
The well-studied Friedel-Krafts alkylation of p-xylene with n-bromopropane has been used
successfully in a multidisciplinary project for chemical engineering students in introductory organic
chemistry. The product mixture, prepared in the laboratory by students in the second semester of
introductory organic chemistry, is partially purified through simple distillation. Isolation of the individual
isomers poses a separation problem that is addressed in a chemical separations course project. Students
conduct computer modeling of the reaction with ChemCad and Mathematica, analyze chemical separation
processes and design a reactor system to best effect isolation of the individual isomeric products. A
parallel goal of the interdisciplinary learning approach was to demonstrate to the cadets that all of their
courses are meant to compliment each other, their learning and experiences, and get away from the cadets
habit of compartmentalizing their courses.
Introduction
Laboratory experiments conducted during the second semester of organic chemistry generally
illustrate practical application of topics covered in lecture. A convenient reaction which demonstrates the
utility of electrophilic aromatic substitution and carbocation rearrangement in the Friedel-Krafts alkylation
of p-xylene with 1-bromopropane yielding approximately a 2:1 ratio of n-propyl-p-xylene to isopropyl-pxylene. See Figure 1.
Br
+
AlCl3
b.p (oC)
138
2
204
:
1
196
Figure 1. Friedel-Krafts alkylation of p-xylene.
Even with activated arene systems like p-xylene, carbocation rearrangement leads to a substantial
proportion of the isopropyl p-xylene. Given that the boiling point difference between the isomeric pxylenes is only 8oC, typical microscale distillation techniques and equipment are not adequate to
fractionally separate the isomers. So, although the reaction is satisfactory from a synthetic standpoint, the
inability to isolate isomerically pure products leaves students with a problem.
For chemical engineering students, it seems a natural progression to explore solutions to this
problem in the context of a chemical separations issue and reactor design. Since these students often take
organic chemistry and chemical separations together, an interdisciplinary project such as this provides a
practical application to bridge the theory developed in their chemical separations course with an
experimental challenge.
In the Chemical Reaction Engineering class, the students were given a design project with the
following specifications: 1. υ0 is 52 L/min; 2. 50:50 ratio of n-propyl-p-xylene to isopropyl-p-xylene at
the outlet; and 3. Tmin is 15°C and Tmax is 70°C. In order to give the students the most realistic data to
model their reactors using ChemCad, it was necessary to conduct some preliminary experiments to gather
data that the students could use to calculate frequency factor k0 and activation energy, Ea of each parallel
reaction. Three independent experiments were run at different temperatures to collect the data required for
the concentration vs. time plot. These plots were then used to find reaction rate constants, k, for each
temperature for each parallel reaction. The kinetic data was collected following the same procedures the
students used in the organic chemistry laboratory earlier in the semester at these temperatures: 22.5°C,
38°C and 60°C. At two minute intervals, a microliter sample was extracted from the reaction vessel and
quenched in water. After a simple work up with an organic agent the samples were examined in the Gas
Chromatograph/MS to determine the concentrations of reactants and products in each sample.
Using the equations developed in the course textbook, Chemical Reaction Engineering, by Octave
Levenspiel, for second order reactions with two reactants a plot was made of ln(CB/CA) vs. time. From this
plot an overall reaction rate constant for the forward reaction was calculated.
 C 
ln B  = ( C B0 − C A0 )kt
 MC A 
M=
C B0
C A0
Second Order Check (Levenspiel pg 43)
-0.3
0
5
10
15
20
-0.35
ln (Cb/Ca)
-0.4
y = -0.0136x - 0.3203
R2 = 0.9896
-0.45
-0.5
-0.55
-0.6
Tim e (m in)
The concentration vs. time data was plotted, then a line fit to the data. The slope of this line was
used to calculate the ktot. To find the individual reaction rate constants of the individual parallel reactions
we used the relationship:
C R − C R0 k1
=
CS − CS 0
k2
This equation with the total k gives two equations and two unknowns which were entered into
Mathematica as follows:
eq1=k1+k2.06477;
eq2=(k1/k2).833;
Solve[{eq1,eq2},{k1,k2}]
When all of the reaction rate constants were calculated it was then possible to solve for individual
frequency factor, k0, activation energy Ea, again with a graphical use of the Arrhenius relationship:
k = k0 exp( − Ea / RT )
By plotting ln k vs. 1/T it was possible to calculate both k0 and Ea.
y = -6192.1x + 14.934
R2 = 0.9479
0
0.0029
-1
0.003
Calculation of Ea1
0.0031
0.0032
0.0033
0.0034
0.0035
ln k1
-2
-3
-4
-5
-6
-7
1/T
With all of the necessary data it is now possible to utilize ChemCad to search the most
economically feasible reactor design. A cursory analysis of the data yielded an appropriate plot of 1/-rA vs.
XA. Analysis of the plot makes it clear that the best reactor design should be a plug flow setup. Again
using Mathematica the mean residence time and volume for the initial guess can be estimated. The only
questions left to resolve are reactor volume, heat duty, and isothermal versus adiabatic operation. Perhaps
parallel versus series reactor setup designs should be explored. All of this and more is possible in
ChemCad.
(1/-ra vs. Xa)
30
25
1/-ra
20
15
10
5
0
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
1
Xa
When the reactor design was complete the outlet streams can also be manipulated in ChemCad for
optimum separations. ChemCad has distillation column, and separators, to help develop both an
economically feasible and realizable separation strategy. The Cadets had to separate the Aluminum
Chloride catalyst and recycle this, as well as any other unused product. They did this by quenching with
water. The Cadets also utilized the liquid/liquid/vapor separator which allowed separation of the organic
layer from the water Aluminum Chloride layer. Any products in the gas phase were flashed off
The students were also able to apply their military decision making skills. This was done by
careful analysis of the problem statement to determine specified and implied tasks, course of action
development, and backwards planning.
Results and Discussion
To analyze the results the students were given a quiz consisting of representative questions from
the organic chemistry, chemical reaction engineering and separations disciplines. The same quiz was then
re-administered at the end of the project cycle to see if there was improvement, and retention of knowledge.
In addition to this the students were asked to answer a series of questions regarding their individual
experiences with the capstone project. These questions were answered on a scale of 1 to 5. Where 1
represented the most positive feedback and 5 was the least positive. These questions are listed below
accompanied by the average response. Finally, a comparison will be made of term end examination results
from AY06-02 to AY07-2 in the chemical reaction engineering course, to see if this project impacted
performance at all.
Master Teacher Data:
Pre-test:
Organic Chem
Chem. Reaction
Eng.
Separations
Question #
1
2
3
4
5
6
7
1
2
3
4
5
6
7
8
9
10
11
AVE. # correct
Correct
5
3
2
0
0
8
8
Total Score (#
correct):
3.00
4.00
2.00
0.00
4.00
4.00
6.00
2.00
2.00
2.00
3.00
2.91
Post-test:
Incorrect
6
8
9
11
11
3
3
Question #
1
2
3
4
5
6
7
1
2
3
4
5
6
7
8
9
10
11
AVE. #
correct
Correct
7
9
Incorrect
4
2
8
7
2
10
10
Total Score (#
correct):
6.00
6.00
6.00
2.00
1.00
7.00
5.00
7.00
6.00
4.00
7.00
5.18
3
4
9
1
1
Survey Results on scale of 1 to 5:
Very much 1
much
2
3
4
5
Not so
Question:
1. Was this capstone project useful in terms of helping the learning process?
1
IIIIII
6
2
IIII
4
3
0
4
I
1
5
AVE:
1.636364
0
2. Was this capstone project helpful to wrap up the course material at the end of the semester?
1
IIII
4
2
IIIIII
6
3
I
1
4
5
0
0
AVE:
1.727273
3. Did this capstone project aid your learning in organic chemistry and separations?
1
II
2
2
IIIIII
6
3
I
1
4
II
2
5
AVE:
2.272727
AVE:
2.090909
0
4. Would you recommend this project format next year?
1
IIIII
5
2
II
2
3
III
3
4
0
5
I
1
5. Did you like the capstone project?
1
II
2
2
IIII
4
3
III
3
4
I
1
5
I
1
AVE:
2.545455
AVE:
2.090909
6. Do you think the capstone experience helped your TEE preparation?
1
III
3
2
IIIII
5
3
II
2
4
I
1
5
0
To summarize the results it is clear that the Capstone experience had a positive outcome in terms
of mastery of the material. The cadet’s responses to the questions were also quite positive. The TEE
results will be incorporated when as soon as possible.
Some End Results: