Lecture 25
Chemical Reaction Engineering (CRE) is the
field that studies the rates and mechanisms of
chemical reactions and the design of the reactors in
which they take place.
Web Lecture 25
Class Lecture 21– 4/2/2013
CSI
• Ammonium Nitrate Explosion
• Monsanto Explosion
• T2 Laboratories Explosion
2
Case 1 – Ammonium Nitrate Explosion
Massive blast at Terra plant kills four.
3
Example 1: Safety in Chemical Reactors
H 2 O

Gas
N
O
 2
T0  200 F
m A0  310 lb h
17 % H 2 O
P
200°F
Liquid

83 % NH 4 NO 3
510°F

Ta

4

X
NH 4 NO 3
M  500 lb
NH 4 NO 3  N 2O  2H 2O


Ta 0
Example 1: Safety in Chemical Reactors
Only liquid A in the vat as the product gases N2O
and H2O escape immediately after being formed.
dT
dt

Qg  Qr
N A C PA
Q g  ( r AV )(  H Rx )
Q r  F A 0 C PA (T  T 0 )   B ( H B  H B 0 )   UA (T  T a )
5
Unsteady State Energy Balance
Q
dT

Q

g 

       r       
  H Rx  r A V   FA 0   i C Pi T  T 0    UA T  T a 

 N i C Pi
dt
Adiabatic

Q r  FA 0 C P
A
T  660    W 1134
 CP
W
T  960 
FA 0  0
dT
dt

  H Rx rA V 
 N iC P
T
i
If the flow rate is shut off, the temperature
6 will rise (possibly to point of explosion!)
t (min)

Case 2 – Monsanto Chemical Company
 Keeping MBAs away from Chemical Reactors
 The process worked for 19 years before “they”
showed up!
 Why did they come?
 What did they want?
7
Nitroanline Synthesis Reaction
NO2
NO2
Cl
NH2
+
ONCB
Chloride
8
+
2NH3
Ammonia
+
Nitroanaline
NH4Cl
+ Ammonium
Nitroanline Synthesis Reaction
NH3 in H2O
ONCB
Autoclave
175 oC
~550 psi
O-Nitroaniline
Product Stream
NH3
Separation
Filter
Press
To Crystallizing Tanks
9
“fast” Orange
Nitroanline Synthesis Reactor
Old
10
3 kmol ONCB
43 kmol Ammonia
100 kmol Water
V = 3.25 m3
Same Nitroanline Synthesis Reaction
NO2
NO2
Cl
NH2
+
ONCB
Chloride
+
2NH3
Ammonia
+
Nitroanaline +
NH4Cl
Ammonium
Batch Reactor, 24 hour reaction time
Management said: TRIPLE PRODUCTION
11
MBA-Style:
Nitroanline Synthesis Reactor
New
12
9 kmol ONCB
33 kmol Ammonia
100 kmol Water
V = 5 m3
Batch Reactor Energy Balance
Qg
dT

dt
NC
P
( r A V )(  H rx ) 
UA ( T  T 0 )
N A 0 C pA  N B 0 C pB  N W C pW
 N A 0 C pA  N B 0 C pB  N W C pW
dT
dt
13
Qr

Qg  Qr
NC p
Batch Reactor Energy Balance
dT

Qg  Qr
dt
NC
p
The rate of “heat removed” is


  UA

Q r  m c C Pc  T a 1  T 1  exp 
 m C


 c Pc
  
 

  
Equation
(12 - 13) p547
 c , the maximum rate of heat removal is
For high coolant flow rates, m
Q r  UA T  Ta 
The rate of “heat generated” is Q g  ( r A V )  H Rx    r A V    H Rx

14
 rA  k 1 C A C B
Q g  k 1 C A C B    H Rx


Batch Reactor Energy Balance
Recall
dT
dT

Qr  Qg
NC P
S
For isothermal operation at Qr = Qg, T = 448 K
Q g  k  448 K C A 0 1  X  B  X    H Rx
2

15

Qr  Qg
 cC P
m
c


  UA

 T a 1  T 1  exp 



 m c C Pc
  
    0 . 0001167

  
Vary
m c to keep “heat removed” equal to “heat generation”
C 2A 0 1  X 
Isothermal Operation for 45 minutes
At the time the heat exchanger
fails
X  0.033, T  448 K
Q g  r AV  H Rx  3850 kcal / min
The maximum
rate of removal
at T  448 K is
Q r  UA T  T a   35 . 85 ( 448  298 )  5378 kcal / min
Qr  Qg
Everything is OK
Adiabatic Operation for 10 minutes
t  45 min
X  0 . 033
t  55 min
X  0 . 0424
T  448 K
T  468 K
Q g  6591 kcal / min
Q r  6093 kcal / min
Qg  Qr
dT
dt

Qg  Qr
NC
p
 0 . 2  C / min
Temperature-Time trajectory
dT

Temperature oC
dt
 0 . 2  C / min
N Cp
400
Qr = 0
200
175
18
Qq  Qr
9:55
t=0
Cooling Restored
Isothermal
Operation
fuse
10:40 10:50
midnight 12:18
Disk Rupture
The pressure relief disk should have ruptured when the temperature
reached 265°C (ca. 700 psi) but it did not.
If the disk had ruptured, the maximum mass flow rate out of the
reactor would have been 830 kg/min (2-in orifice to 1 atm).
 vap  H vap  UA T  T a
Qr  m
Q r  449 , 000
Q g  27 , 460
kcal
min
kcal
min
Q r  Q g
No explosion

All the following three things must have
occurred for the explosion to happen
1. Tripled Production
2. Heat Exchange Failure
3.Relief Valve Failure
20
Case 3 – Manufacture of Fuel Additive
methylcyclopentadiene manganese tricarbonyl (MCMT)
21
Production of methylcyclopentadienyl manganese tricarbonyl (MCMT).
Step 1a. Reaction between methylcyclopentadiene (MCP) and sodium in a
solvent of diethylene glycol dimethyl ether (diglyme, C6H14O3) to
produce sodium methylcyclopentadiene and hydrogen gas:
Step 1b. At the end of Step 1a, MnCl2 is added to the reactor. It reacts with
sodium methylcyclopentadiene to produce manganese
dimethylcyclopentadiene and sodium chloride:
Step 1c. At the end of Step 1b, CO is added. The reaction between
manganese dimethylcyclopentadiene and carbon monoxide produces the
final product, methylcyclopentadienyl manganese tricarbonyl (MCMT), a fuel
additive.
22
Only consider Step 1
Desired Reaction
Undesired Reaction of Dygline
Simplified Model
Let A = methycylcopentadiene, B = sodium, S = Solvent (diglyme), and D = H2.
These reactions are:
(1) A + B  C + 1/2 D (gas)
r1A  r1B  k 1A C A C B
(2) S  3 D (gas) + miscellaneous liquid and solid products r2 S  k 2s C S
 H Rx1A   45 , 400 J mol
23
 H Rx2S   3.2  10
5
J mol

Case 3 – Manufacture of Fuel Additive
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Case 3 – Manufacture of Fuel Additive
25
Case 3 – Manufacture of Fuel Additive
(2) Rates
Laws:
Net Rates:
26
(3) Stoichiometry – Liquid Phase
Case 3 – Manufacture of Fuel Additive
(4) Energy Balance:
7
 1.26  10 J K

 H Rx1A   45 , 400 J mol
 H Rx2S   3.2  10
27

5
J mol
28
End of Web Lecture 25
Class Lecture 2
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