To produce more moles of product per
time in a flow reactor system, what can
we do?
a) Use less catalyst
b) Make the reactor bigger
c) Make the flow rate through the reactor
smaller
When designing a PBR, why would we ever
want to use a bunch of skinny tubes instead
of one large-diameter tube?
a) Easier catalyst replacement
b) Better heat transfer
c) Lower gas compression costs
For the reaction below, which is the
limiting reactant?
A + 2 B + 3 C → products
FA0 = 2 mol/sec, FB0 = FC0 = 3 mol/sec
a) A
b) B
c) C
To increase the concentration of
product formed in a PFR, what
should we do?
a) Decrease the reactor diameter
b) Decrease the reactor length
c) Decrease the feed flow rate
An decrease in which of the following
variables will increase the
concentration of product formed?
a)
b)
c)
d)
e)
Volumetric flow rate
Initial oxygen concentration
Initial butadiene concentration
Rate constant k’
Catalyst mass
What is the volume of a CSTR needed to achieve 60%
conversion for the liquid-phase reaction A→B+C if the
inlet volumetric flow rate of liquid is 100 L/min, and the
inlet concentration is 3 mol/L. The reaction rate -rA
has been measured to be 2 mol/L-min at CA = 3 mol/L
and 1 mol/L-min at CA = 1.2 mol/L.
a)
b)
c)
d)
30 L
60 L
90 L
180 L
1
Which reactor type will require the lowest
volume to achieve a conversion of 40%?
In the previous CSTR sizing example, what
happens to the conversion if you double the
volume?
a)
b)
c)
d)
It doubles
It goes up by less than a factor of 2
It goes up by more than a factor of 2
It goes down
1/-rA
(a) CSTR
(b) PFR
(c) Need more
data
0
What batch time is required to achieve 80%
conversion for the following kinetics, if the beginning
concentration of the limiting reactant A is 10 mol/L?
(a) 2.9 min
(b) 5.6 min
(c) 29 min
(d) 56 min
(e) Can’t tell. Data
only work for flow
reactors.
The figure below describes the kinetics with 3 different
reactors in series indicated. By swapping the order of
the reactors, it may be possible to increase the
conversion. What would you do?
a)
b)
c)
d)
Swap 1
and 2
Swap 1
and 3
Swap 2
and 3
Leave
them the
way they
are
0.4
X
Assuming that the reaction rate decreases continually as
conversion increases, what will be the effect on a
process of taking two equal-size CSTRs in series and
placing them in parallel? (In a parallel set-up, the feed is
divided in half and each stream is routed through one
CSTR; the product streams are then combined.)
a)
b)
c)
d)
Conversion will go down
Conversion will go up
Conversion will remain the same
Conversion will change to become more
“PFR-like”
Which of the following reactions does
not follow an elementary rate law?
a) CH3Cl + Br- → CH3Br + ClPd
b) 2,5-DHF →
2,3-DHF
c) C4H6 + ½ O2 Ag
→ C4H6O
-rA = k CCH3ClCBr-rA = k C2,5-DHF
-rA = k CO2
2
Under what condition will the rate appear to
be 1st-order in EO and zero-order in water?
Given the following liquid-phase reaction and feed
conditions, what is the correct expression for CD as a
function of X?
A + 3B
FA0 = FD0 = 1 mol/min
a) When there is a large excess of water
b) When there is a large excess of EO
c) When the feed rates of EO and water
are equal
FA0 = FB0
(a)
FT
X
= 1−
FT 0
3
(b)
FT
2X
= 1−
FT 0
3
(c)
FT
2X
= 1+
FT 0
3
(d)
FT
3X
= 1−
FT 0
2
2A+3B →C+2D
2C + D
FB0 = 2 mol/min
(a)
C D = C B 0 (1 − X )
(b)
C D = C B 0 (1 + X )
(c)
C D = C B 0 (1 − X / 3)
(d)
(e)
For the gas-phase reaction
below, what is the relation
between the total and initial
number of moles? Assume
that X is based on the limiting
reactant
↔
FC0 = 0
⎛1 X ⎞
CD = CB 0 ⎜ + ⎟
⎝2 3 ⎠
⎛1 X ⎞
CD = CB 0 ⎜ − ⎟
⎝3 2 ⎠
For the gas-phase reaction
below, what is the relation
concentration of A exiting the
reactor? Assume that X is
based on the limiting reactant
FA0 = FB0
(a)
2A+3B →C+2D
(b)
(c)
X
3
2X
1−
3
2X
1−
3
C A = CB 0
X
1−
3
2 − 3X
C A = CB 0
X
1−
3
C A = CB 0
1−
Solve this first.
An encyclopedia that consists of 5 volumes is resting
on a library bookshelf. In an individual volume, each
cover is 0.25” thick and the pages are cumulatively 2”
thick. What is the linear distance between the first
page of the encyclopedia and the last?
a)
b)
c)
d)
e)
8”
10”
12”
12.5”
13”
The irreversible liquid-phase reaction
A+2B→2C+D
occurs in a batch reactor. When the initial
concentration of B is twice that of A, the
conversion of A after 60 minutes of batch time
is measured to be 60%. If the initial
concentration of B is increased so that it is three
times that of A (leaving all other independent
variables constant), what batch time (in
minutes) will be required to achieve 60%
conversion of A?
3
What is the material balance
(appetizer) for this problem?
V
X
(a)
=
FA0 − rA
dX
(b)
FA0
= −rA
dV
dX
(c) C
= − rA
A0
dt
What are the appropriate expressions for CA
and CB as a function of conversion of A in
this problem (first part)?
(a)
C A = C A0 (1 − X ), C B = C A0 (1 − X )
(b)
C A = C A0 (1 − X ), C B = 2C A0 (1 − X )
(c)
C A = C A0 (1 − X ), C B = C A0 (2 − X )
What is the rate expression for this
problem?
(a)
− rA = kC AC B
(b)
− rA = kC AC B
(c)
− rA = kC A C B
2
2
What material balance expression do you
obtain when you combine the first three
steps?
0.6
dX
t= ∫
(a)
(1 − X )
0
0.6
(b)
dX
∫ (1 − X )
2kC A0t =
2
0
0.6
dX
∫ (1 − X )
kC A0 t =
2
(c)
2
0
What is the concentration of B as a function
of conversion of A for part (ii) of the
problem?
(a)
C B = 2C A0 (1 − X )
(b)
C B = C B 0 (1 − X )
(c)
C B = 2C A0 ( 3 − X )
2
What material balance expression do you
obtain when you combine the first three
steps?
0.6
(a)
2kC A0t =
dX
∫ (1 − X )
2
0
0.6
(b)
2kC A0t =
dX
∫ (3 / 2 − X )
2
0
0.6
(c)
2kC A0t =
dX
∫ (1 − X )(3 / 2 − X )
0
4
When is the equation listed below valid?
τk
X=
1 + τk
a)
b)
c)
d)
If Km<<CA, how would you express Da?
For any reaction in any kind of reactor
For any liquid-phase reaction in any kind of reactor
For any liquid-phase reaction in a CSTR
For a first-order, irreversible reaction of a liquid in a
CSTR
How will the magnitude of the effect of replacing a
single CSTR with two CSTRs change as the
reaction order increases?
Da =
vmax
V
v0
(b)
Da =
vmax
V
K m v0
(c)
Da =
vmax C A0
V
v0
(d)
Da =
vmax
V
v0C A0
For the isothermal, elementary gas-phase reaction
2A --> B, how does the PFR volume required for a
given conversion change with increasing mole
fraction of A if the inlet concentration of A and total
volumetric flow rate remain constant?
a) Increase
b) Decrease
c) Remain the same regardless of order
Fogler Problem 4-13(a): Compound A undergoes a
reversible reaction, A ↔ B, over a supported metal
catalyst. The equilibrium constant for the reaction is
5.8, and the reaction is elementary. In a PBR, a
feed of pure A undergoes a net conversion to B of
55%. If a second, identical flow reactor at the same
temperature is placed downstream from the first,
what overall conversion of A would you expect?
(a)
a) V increases
b) V decreases
c) No change in V
Which of the following expressions results from
the first two steps of Fogler’s methodology?
(a)
(b)
(c)
dX
= k ' CA
dW
⎛
dX
C ⎞
= k ' ⎜⎜ C A − B ⎟⎟
FA0
dW
KC ⎠
⎝
dX
FA0
= k (C A + KC CB )
dV
FA0
5
Which result is obtained after the “combine” step?
(a)
(b)
(c)
⎛
dX
k' ⎡
1 ⎞⎤
⎟⎟⎥
= ⎢1 − X ⎜⎜1 +
dW v0 ⎣
⎝ KC ⎠⎦
⎡
⎛
dX
1 ⎞⎤
⎟⎟⎥
= k ' v0 ⎢1 − X ⎜⎜1 −
dW
⎝ KC ⎠⎦
⎣
dX k ' C A0
(1 − X )
FA0
=
dV
KC
FA0
To increase the conversion from a membrane
reactor for ethane dehydrogenation, what can be
done?
a) Increase the thickness of the membrane
b) Increase the temperature
c) Decrease the flow rate of the permeateside stream
d) Increase the diameter of the reactor
(keeping total volume constant)
How many moles of hydrogen are consumed during the
reaction when a final conversion of 80% is achieved?
The initial number of moles of polyunsaturated fatty
acids in the reactor is 400 moles.
a)
b)
c)
d)
500
400
320
200
Which of the following steps will decrease the P
drop in a PBR for the gas phase reaction
A → 2 B?
a)
b)
c)
d)
Increase flow rate
Decrease reactor diameter
Increase particle size
Decrease entering mole fraction of A (at
constant total flow).
e) Both (c) and (d)
Which of the following is an advantage for
membrane reactors?
a) Low capital cost
b) Low complexity compared to other
reactors
c) Reduced reactor volume
What will be the trend in the flow rate of
hydrogen into the reactor versus time?
A
FH2
B
C
D
t
6
The reaction A(l) + B(l) ↔ C(g) + D(l) is being conducted
in a batch process. Because C is produced as a gas, it
tends to accumulate in the headspace of the reactor.
Which of the following strategies would be useful for
increasing the conversion?
a) Increase agitation to mix the vapor and liquid
streams better
b) Attach a pipe to the top of the reactor and allow
vapor streams to exit the reactor through it
c) Make the reactor smaller to minimize the head
space available for vapor to accumulate
Differential reactor data are shown below for a reaction of
the type 2A + 2B → 3C + D. What are the reaction orders
in each reactant?
PA
PB
mmoles C in outlet sample
200
200
0.0125
400
200
0.0252
800
200
0.0497
400
400
0.1010
400
800
1st
From the following plot, what is the
reaction order with respect to A?
ln (-dCA/dt)
a)
b)
c)
d)
e)
y=1.01 x + 0.78
0
0.5
0.78
1
2
ln (CA)
Differential reactor data are shown below for three different
catalysts. Which catalyst has the highest activation
energy?
mmoles in outlet stream
Inlet PA
T(K)
Cat. A
Cat. B
Cat. C
Cat. D
200
400
0.015
2.1
2.8
0.010
200
420
0.167
9.5
9.1
0.024
200
440
1.454
36.7
27
0.055
0.3950
a)
b)
c)
d)
1st
a)
order in A,
order in B
b) 2nd order in A, 2nd order in B
c) 2nd order in A, 4th order in B.
d) 1st order in A, 2nd order in B.
In the batch phase reaction, A + B → C, the
concentration of C is measured after 1 minute of
reaction time for several sets of initial conditions.
What are the approx. reaction orders of A and B?
CA0
1
1
2
2
4
CB0
1
2
1
2
2
CC
0.00051
0.00049
0.00201
0.00203
0.00798
a)
b)
c)
d)
e)
0 and 0
0 and 1
1 and 0
2 and 0
2 and 1
Catalyst A.
Catalyst B.
Catalyst C.
Catalyst D.
Consider the reaction network below: if the overall
selectivity of W to P is 4.0, what is the overall yield
of P?
A
a)
b)
c)
d)
W
P
0.20
0.75
0.80
4.0
7
If the following reactions are elementary as
written, which reactor configuration would
you use to improve selectivity?
A+2B
D
2A+B
U
The endothermic reaction A + B → C + D is
conducted adiabatically. Initially, the feed is
stoichiometric. In a process change, the
concentration of B in the feed is doubled, but the
conversion of A is not changed. How will the outlet
temperature change from the stoichiometric case?
a) T will go up
b) T will go down
c) T will not change
A+2B→C+D
B
-15
50
C
-10
50
D
-20
50
D
2
U
(a) -5 kJ/mol
(b) 0 kJ/mol
(c) 5 kJ/mol
(d) 10 kJ/mol
Note that A → D is a slightly
endothermic, reversible process.
Reaction order α = 1 for rxn 1, α = 2 for rxn 2
EA1 = 20 kcal/mol, EA2 = 16 kcal/mol
a)
b)
c)
d)
Feed pure A at high temperature; keep space time long.
Feed diluted A at high temperature; keep space time short.
Feed pure A at low temperature; keep space time short.
Feed diluted A at low temperature; keep space time long.
The reaction A → D is conducted adiabatically.
The heat capacities of A and D are approximately
equal at 20 cal/mol-K. When a conversion of 50%
is achieved in a PFR, the outlet temperature is 50
K higher than the inlet. What is the heat of
reaction?
a)
b)
c)
d)
What is the enthalpy change of reaction for
the following system at 500 K?
A
1
A
a) Feed A to a PFR, inject side streams of low B
concentration
b) Load A into a semibatch reactor, add B as a
side-stream
c) Feed B through a series of CSTRs, add a
little A to each one
Cp
∆Hf
(kJ/mol) (J/mol-K)
-5
50
Which of the reactor conditions would you choose
to optimize selectivity to D in a PBR for the
following reaction network?
0.5 kcal/mol
-0.5 kcal/mol
2 kcal/mol
-2 kcal/mol
How will the slope of the X vs. T plot for an
adiabatic CSTR change if the flow rate of water
is increased above the stoichiometric level?
a) Slope will increase
b) Slope will decrease
c) Slope will remain the same
Data collected at 298 K.
8
What would we do to make the CSTR operate
isothermally?
a) Isothermal operation is not possible
b) Use a heat exchanger with a coolant flow
c) Use a lower conversion
What heat exchange area is
needed for isothermal operation?
∆HRx = -4 kcal/mol
U = 5 kcal/hr-m2-K
T – Ta = 100 K
100 moles/hr B formed
a)
b)
c)
d)
Which of the following will increase the needed
heat exchange area to maintain isothermal
operation in a CSTR?
a) An increase in feed temperature.
b) A decrease in the overall heat transfer coefficient.
c) A decrease in the molar flow rate of inert relative
to A (leaving the production rate of B constant).
d) All of the above.
The temperature curve for the adiabatic reaction is shown
in black. What will the curve the reaction with a constant
cooling water temperature (high coolant flow) look like?
A→B
a
0.8 m2
1.0 m2
4.0 m2
Impossible to compute from given info.
b
T
c
d
W
If we increase the feed temperature, which of the following
is a possible temperature profile?
a
b
T
c
Which of the following will make the
temperature easier to control?
a) Allow coolant temperature to increase
down the length of the reactor.
b) Make the feed stoichiometric.
c) Increase the reaction temperature so that
the initial rate is very high.
d) None of the above.
W
9
Which of the following approaches
will increase equilibrium
conversion?
a) Decrease the feed temperature
b) Increase the mole fraction of inert
c) Increase the stoichiometric ratio of steam
to CO
d) All of the above
Suppose that the reaction can still continue to
occur in the heat exchanger (but that the outlet T
from the exchanger is to remain the same). Which
of the following is true?
a) The equilibrium conversion after the 2nd
reactor will increase
b) The equilibrium conversion after the 2nd
reactor will decrease
c) Impossible to predict the direction of the
effect
What would be a good idea?
a) Open a valve that allows inert of the
same inlet temperature to flow into the
reactor
b) If you have a way of cooling the reactor,
turn on the coolant
c) Close the valves into/out of the reactor
d) (a) and (b)
e) All of the above
For an endothermic reaction, which of the following
approaches will experience the most severe
equilibrium limitations?
a) Adiabatic
b) Isothermal
c) Use of a heat exchanger so that Tout>T0.
You are in charge of managing a CSTR for a 1storder, adiabatic and exothermic reaction. Because
of a process upset, the inlet temperature is nearing
that where one would expect thermal runaway. An
operator suggests using valves on the inlet and
outlet to cut the flow rate through the reactor. Is
that a good idea?
a) Yes
b) No
c) Maybe
What is the form of the energy balance when the
combustion of ethylene oxide is included?
(a)
(b)
(c)
Ua
(T − Ta ) − (r1∆H Rx1 − r2 ∆H Rx 2 − r3∆H Rx 3 )
dT
ρ
=
dW
∑ C piθi
Ua
(T − Ta ) − (r1∆H Rx1 − r2 ∆H Rx 2 − 2r3∆H Rx 3 )
dT
ρ
=
dW
∑ C piθi
Equation doesn’t change, because reaction is a series reaction.
10
Consider the following system of reactions in a
CSTR. How much heat must be removed to
maintain isothermal operation?
A+2B→ C+D
B+C → E
CA0 = 1 mol/L
CB0 = 3 mol/L
a)
b)
c)
d)
e)
∆HRx = 20 kcal/mol B
∆HRx = 10 kcal/mol B
For the following reaction, batch experiments are
conducted to evaluate the reaction kinetics. The
slope of a ln (rB) versus ln (CB) plot is measured to
be 1.02 and the intercept is 0.42 when A is in great
excess. What is the overall reaction order?
rD = 1 mol/sec
rE = 0.5 mol/sec
A + 2B → products
10 kcal/sec
15 kcal/sec
20 kcal/sec
25 kcal/sec
None of the above
a)
b)
c)
d)
If the following reactions are elementary, which
would be an appropriate scheme for increasing
SDU?
In a particular differential reactor experiment for
A→B , the entering volumetric flow rate is cut in
half, leaving all intrinsic variables constant. How
would you expect the measured outlet flow rate of
B to change under conditions of differential
conversion?
A+B↔D
2A + B → U
a) Flow rate of product will go up
b) Flow rate of product will go down
c) No change
For the following system of reactions, what
is the mole balance on D for a PFR?
A + B → 2C + D
C+B→D+E
2D + A → F
(a)
(b)
(c)
rC1 = k1CA2CB
r E = k 2C C
rF = k3CACD
dFD
2
= k1C A CB + k2CC − k3C ACD
dV
dFD
2
= −k1C A CB − k2CC + 2k3C ACD
dV
dFD k1 2
= C A CB + k2CC − 2k3C ACD
dV
2
0.42
1.02
1.44
Can’t tell on the basis of this experiment
a) Semibatch reactor in which B is slowly
added to a vat of A
b) Semibatch reactor in which D is
continuously removed
c) Series of CSTRs with a 2:1 feed of A:B
For the following plot, which shows energy balance
lines for a series of reactors with intermediate heat
exchange, at what point is the reaction rate
highest?
A
X
equil.
line
B
C
D
E
T
11
The following shape is observed for an
Arrhenius plot in an enzymatic reaction at
[S]>>KM. What is likely happening?
Which of the following is true about the energy
balance for an isothermal reaction in a CSTR at
fixed conversion?
ln (rate)
1/T
a) The amount of inert has a strong effect
on the heat exchange requirements
b) Changes in the feed ratio have no effect
c) The term Ua is set to zero
How will the Lineweaver-Burk plot
change as [I] is increased for
competitive inhibition?
a) Slope and intercept will go up
b) Slope and intercept will go down
c) Slope will go up, intercept will stay the
same
d) Intercept will go down, slope will stay
same
For what space time will wash-out be achieved
for an inlet substrate concentration of 5.0 g/L,
KS = 10.0 g/L, µmax = 1.0 hr-1?
a)
b)
c)
d)
0.33 hr
1.0 hr
3.0 hr
10 hr
a) As T is increased, transition state becomes lower
in energy than reactants
b) As T is increased, enzyme begins to unfold and
lose activity
c) As T is increased, all enzyme becomes bound to
substrate, “choking off” reaction
In a particular fermentation reaction, the YC/S =
0.2. If the inlet concentration of substrate is 4.0
g/L and the substrate conversion is 75%, what
concentration of cells has been produced?
a)
b)
c)
d)
0.08 g/L
0.20 g/L
0.60 g/L
0.80 g/L
The following data were measured in a differential
reactor for the CO oxidation reaction. Which
model is consistent with the data?
PO2
1.5
6.0
6.0
PCO
0.5
0.5
2.0
a)
b)
c)
d)
rate
10.1
20.0
68.4
Reaction-limited
O2 adsorption-limited
Neither
Both
12
For butadiene (B) oxidation to epoxybutene (E),
the following differential kinetic data are obtained.
Which of the following statements is true?
PB
0.5
0.5
2.0
2.0
a)
b)
c)
d)
PO2
1.5
6.0
1.5
1.5
PE
0.1
0.1
0.1
0.5
A particular catalyst is used in a reactor where
the rate determining step is surface reaction.
That same catalyst is loaded into a different
reactor operating at the same temperature, but
where external mass transfer is slow and limits
the reaction. Does the rate go up or down?
rate
1.0
3.9
1.1
0.4
a) Up
b) Down
c) Stays the same
The product binds strongly to the catalyst surface
Surface reaction of B and O2 is likely the rate
determining step
The surface coverage of O is high
None of the above
It is known that a catalyst particle with a diameter of
0.05 cm exhibits no internal MT limitations. When the
catalyst size is increased to 1.0 cm, the rate of
reaction goes down by a factor of 4; when it’s
increased again, the rate is a factor of 10 lower than
for the 0.05 cm particles. What is the particle size in
the final measurement?
a)
b)
c)
d)
2.0 cm
2.5 cm
7.5 cm
50 cm
A step tracer experiment is conducted, and the
tracer concentration is reported as a function of
time below. Where is the value of E highest?
C
B
C
A
time
The black curve shows E(t) for a CSTR with
perfect mixing. Which curve corresponds to a
CSTR with a significant dead volume?
The black curve shows F(t) for a tubular reactor with
perfect plug flow. Which curve corresponds to a
tubular reactor in which the fluid velocity at the
centerline is higher than that near the wall ?
B
D
A (no change)
E(t)
F(t)
C
C
B
A (no change)
time
time
13