ChE 404
Chemical Reaction Engineering
2nd Semester Final Examination 1428/1429 H (2007/2008 G)
Instructions: Answer All Questions
Question
Marks
1
2.a
2.b
2.c
2.d
3.a
3.b
4.a
4.b
5
6
7
Total
5
15
5
5
5
20
10
10
5
5
10
5
100
Time
Allowed
(minutes)
10
35
15
30
5
15
15
10
15
10
15
5
180
1
Question 1
The gas phase reaction
2𝐴 + 𝐵 → 2𝐶
is carried out isothermally and isobarically. The reaction is first order in
B and first order in A. The feed is equal molar in A and B and the
entering concentration of A is 0.5 mol/dm3. The specific reaction rate is
k = 4.0 dm3/mol•s. Write the rate of reaction, –rA, solely as a function
of conversion, evaluating all parameters.
2
Question 2
The following reversible, elementary, liquid phase reaction occurs in a
PFR:
𝐴⇔𝐵
The entering flow rate is 10 dm3/s with an entering concentration of
2 M of A and the feed temperature is 310 K.
a) Complete the following table
T
310
330
350
370
390
410
KC
K
Xmb
Xeb
-rA
1/-rA
b) What are the adiabatic equilibrium conversion and temperature?
c) What is the reactor volume necessary to achieve 90% of the adiabatic
equilibrium conversion in one PFR operated adiabatically?
d) Now consider a series of reactors with interstage cooling so that the
temperature is cooled to 300 K in each interstage cooler. How many
reactors are necessary to achieve 95% conversion assuming 99.9% of
the equilibrium conversion is achieved in each reactor?
Additional information:
CpA = CpB = 50 cal/mol/K
3
H°rxn = -10,000 cal/mol A
k and KC are given in Figure 1 and Figure 2, consequently.
Figure 1: k vs. T curve.
4
Figure 2: KC vs. T curve.
5
Question 3
The gas phase irreversible reaction
A+BC
is elementary. The entering flow rate of A is 10 mol/min and is equal
molar in A and B. The entering concentration of A is 0.4 mol/dm3.
a) What is the CSTR reactor volume necessary to achieve 90%
conversion?
b) What PFR volume is necessary to achieve 90% conversion?
Additional Information:
k = 2 dm3/mol•min
T0 = 500 K
6
Question 4
The irreversible zero order gas phase dimerization
2A  A2
is carried out in a packed bed reactor with 5 kg of catalyst. The entering
pressure is 10 atm and the exit pressure is 1 atm. Pure A enters at a
flow rate of 10 mol/min. The reaction is zero order in A.
a) What is the exit conversion?
b) What is the pressure drop parameter ?
Additional Information
k = 1.5 mol/kg•min
T0 = 500 K
𝑑𝑦
𝑑𝑊
=−
∝
2𝑦
(1 + 𝜀𝑋)
𝑇
𝑇0
7
Question 5
The gas phase reaction
2A  B
 C
is carried out in a PFR. The feed is equal molar in A and B and the
entering temperature is 500K and the entering pressure is 16.4 atm. If
the exit conversion is X, then the exit concentration of B (in mol/dm3) is
a)
C B  0.4 1  X 1  .5X
b)
C B  0.41  X1 1.5X
c)
C B  0.4
d)
C B  0.4 1  0.5X 1  X
e) None of the above
f) Cannot be calculated without knowing the exit conversion.
8
Question 6
The following elementary liquid phase reactions are to be carried out
A  B
 R
R  B
 S
Species R is the desired product. Which of the following schemes in
Figure 3 should be used?
B
A
(b)
(a)
A
(c)
B
t=0
(e)
(d)
A
B
A
(f)
B
A
(g)
(i)
Figure 3: Reactors schemes.
9
Question 7
There are two reactors of equal volume, one a CSTR and one a PFR
available for your use. The following second order irreversible reaction
𝐴→𝐵
Is to be carried out isothermally. Determine, if possible, which of the
following schemes of equally sized reactors (V1=V2) would give the
i.
ii.
Lowest conversion?
Highest conversion?
A
B
C
10