Reaction-Engineering

1. 1. Mole Balances
2. Conversion and Reactor Sizing
3. Rate Laws and Stoichiometry
4. Collection and Analysis of Rate Data
1
Chemical Process Engineering
Book:
H. SCOTT FOGLER, Elements of Chemical
Reaction Engineering Fifth Edition, 2011

2. 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.
Lecture 1
2
Chapter 1

3. Lecture 1
3
 Introduction
 Definitions
 General Mole Balance Equation
 Batch (BR)
 Continuously Stirred Tank Reactor (CSTR)
 Plug Flow Reactor (PFR)
 Packed Bed Reactor (PBR)

4. Chemical Reaction
Engineering
4
 Chemical reaction engineering is at the heart of
virtually every chemical process. It separates the
chemical engineer from other engineers.
Industries that Draw Heavily on Chemical
Reaction Engineering (CRE) are:
CPI (Chemical Process Industries)
Examples like Dow, DuPont, Amoco, Chevron
Chapter 1

5. 5
Chapter 1

6. Chemical Plant for Ethylene Glycol (Ch. 5)
Smog (Ch. 1)
Plant Safety
(Ch. 11,12,13)
Lubricant Design
(Ch. 9)
Cobra Bites
(Ch. 8 DVD-ROM)
Oil Recovery
(Ch. 7)
Wetlands (Ch. 7 DVD-ROM)
Hippo Digestion (Ch. 2)
6
Chapter 1

7. http://www.umich.edu/~elements/6e/
Materials on the Web
7

8. Let’s Begin CRE
8
 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.
Chapter 1

9. Chemical Identity
9
 A chemical species is said to have reacted when
it has lost its chemical identity.
 The identity of a chemical species is determined
by the kind, number, and configuration of that
species’ atoms.
Chapter 1

10. Chemical Identity
10
 A chemical species is said to have reacted when
it has lost its chemical identity.
 There are three ways for a species to loose its
identity:
1. Decomposition CH3CH3  H2 + H2C=CH2
2. Combination N2 + O2  2 NO
3. Isomerization C2H5CH=CH2  CH2=C(CH3)2
Chapter 1

11. Reaction Rate
11
 The reaction rate is the rate at which a species
looses its chemical identity per unit volume.
 The rate of a reaction (mol/dm3/s) can be
expressed as either:
 The rate of Disappearance of reactant: -rA
or as
 The rate of Formation (Generation) of product: rP
Chapter 1

12. Reaction Rate
12
Consider the isomerization
A  B
rA = the rate of formation of species A per unit
volume
-rA = the rate of a disappearance of species A
per unit volume
rB = the rate of formation of species B per unit
volume

13. Reaction Rate
13
EXAMPLE: AB
If Species B is being formed at a rate of
0.2 moles per decimeter cubed per second, i.e.,
rB = 0.2 mole/dm3/s
Then A is disappearing at the same rate:
-rA= 0.2 mole/dm3/s
The rate of formation (generation of A) is:
rA= -0.2 mole/dm3/s
Chapter 1

14. Reaction Rate
14
 For a catalytic reaction we refer to –rA’ , which is the
rate of disappearance of species A on a per mass of
catalyst basis. (mol/gcat/s)
NOTE: dCA/dt is not the rate of reaction
Chapter 1

15. Reaction Rate
15
Consider species j:
1. rj is the rate of formation of species j per unit volume
[e.g. mol/dm3s]
2. rj is a function of concentration, temperature,
pressure, and the type of catalyst (if any)
3. rj is independent of the type of reaction system
(batch, plug flow, etc.)
4. rj is an algebraic equation, not a differential equation
(e.g. -rA = kCA or -rA = kCA
2
)
Chapter 1

16. General Mole Balances
16
Building Block 1:
Fj0 Fj
Gj
System
Volume, V









































































time
mole
time
mole
time
mole
time
mole
dt
dN
G
F
F
j
Species
of
on
Accumulati
Rate
Molar
j
Species
of
Generation
Rate
Molar
out
j
Species
of
Rate
Flow
Molar
in
j
Species
of
Rate
Flow
Molar
j
j
j
j0
Chapter 1

17. General Mole Balances
17
Building Block 1:
If spatially uniform:

Gj  rjV
If NOT spatially uniform:
2
V

2
j
r
1
1
1 V
r
G j
j 

2
2
2 V
r
G j
j 

1
V


rj1
Chapter 1

18. General Mole Balances
18
Building Block 1:




n
i
i
ji
j V
r
G
1
Gj 
lim V 0 n
rjiVi
i1
n
  rjdV

Take limit
Chapter 1

19. General Mole Balances
19
Building Block 1:
General Mole Balance on System Volume V
In  Out  Generation  Accumulation
FA0  FA  rA
 dV 
dNA
dt
FA0 FA
GA
System
Volume, V
Chapter 1

20. Batch Reactor - Mole Balances
20
20
0
0
0




 
A
A
A
A
A
A
F
F
dt
dN
dV
r
F
F
dNA
dt
 rAV
Batch
V
r
dV
r A
A 

Well-Mixed
Chapter 1

21. Batch Reactor - Mole Balances

dt 
dNA
rAV
Integrating
Time necessary to reduce the number of moles of A from NA0 to NA.
when
 

A
A
N
N A
A
V
r
dN
t
0
21
A
A
A
A
N
N
t
t
N
N
t



 0 0
Chapter 1

22. Batch Reactor - Mole Balances
 

A
A
N
N A
A
V
r
dN
t
0
NA
t
22
Chapter 1

23. CSTR - Mole Balances

FA 0  FA  rA
 dV 
dNA
dt
dNA
dt
 0
Steady State
CSTR
23
Chapter 1

24. CSTR - Mole Balances

FA0  FA  rAV  0

V 
FA 0  FA
rA
V
r
dV
r A
A 

Well Mixed
CSTR volume necessary to reduce the molar flow
rate from FA0 to FA.
24
Chapter 1

25. 25
CSTR – Example Problem
0
0
0
0
3
0 min
dm
10
A
A
A
C
F
C




A
A
A
A
C
F
C
C







0
3
0
1
.
0
min
dm
10
  0
FA  0CA
Liquid phase

V ?
Given the following information, Find V

26. 26
CSTR – Example Problem
(1) Mole Balance:
 
A
A
A
A
A
A
A
A
A
r
C
C
r
C
C
r
F
F
V








 0
0
0
0
0
0 


A
A kC
r 

(2) Rate Law:
(3) Stoichiometry:
0


A
A
A
F
F
C 


27. 27
CSTR – Example Problem
(4) Combine:

V 
0 CA0 CA
 
kCA
(5) Evaluate:
 
  
 
  
3
0
1
0
0
3
0
1
.
0
23
.
0
1
.
0
1
10
1
.
0
min
23
.
0
1
.
0
min
10
1
.
0
dm
C
C
C
dm
V
C
C
A
A
A
A
A






3
391
3
.
2
900
dm
V 


28. Plug Flow Reactor - Mole
Balances
28
Chapter 1

29. Plug Flow Reactor - Mole
Balances
29

V

V V
V 


FA

FA
0
0






























V
r
F
F
V
in
Generation
V
V
at
Out
V
at
In
A
V
V
A
V
A
Chapter 1

30. Plug Flow Reactor - Mole
Balances
30
A
V
A
V
V
A
V
r
V
F
F






 0
lim
Rearrange and take limit as ΔV0

dFA
dV
 rA
This is the volume necessary to reduce the entering molar
flow rate (mol/s) from FA0 to the exit molar flow rate of FA.
Chapter 1

31. Plug Flow Reactor - Mole
Balances
31
0
0 

  dV
r
F
F A
A
A
0

dt
dNA
Steady State
dt
dN
dV
r
F
F A
A
A
A0 

 
PFR
Chapter 1

32. Plug Flow Reactor - Mole
Balances
32

dFA
dV
 rA
A
A
r
dV
dF



0
Differientiate with respect to V


A
A
F
F A
A
r
dF
V
0
The integral form is:
This is the volume necessary to reduce the
entering molar flow rate (mol/s) from FA0 to the
exit molar flow rate of FA.
Alternative Derivation Chapter 1

33. Packed Bed Reactor - Mole
Balances
33
   
dt
dN
W
r
W
W
F
W
F A
A
A
A 






A
W
A
W
W
A
W
r
W
F
F







 0
lim
0

dt
dNA
Steady State
PBR
W

W W
W 


FA

FA
Chapter 1

34. Packed Bed Reactor - Mole
Balances
34

dFA
dW
 
rA
Rearrange:
PBR catalyst weight necessary to reduce the
entering molar flow rate FA0 to molar flow rate FA.
 

A
A
F
F A
A
r
dF
W
0
The integral form to find the catalyst weight is:
Chapter 1

35. Reactor Differential Algebraic Integral
The GMBE applied to the four major reactor types
(and the general reaction AB)

V 
FA 0  FA
rA
CSTR
V
r
dt
dN
A
A

0


A
A
N
N A
A
V
r
dN
t
Batch
NA
t

dFA
dV
 rA 

A
A
F
F A
A
dr
dF
V
0
PFR
FA
V
dFA
dW
 
rA  

A
A
F
F A
A
r
dF
W
0
PBR
FA
W
35
Reactor Mole Balances
Summary
Chapter 1

36. End of Lecture 1
36

37. Supplemental Slides
Additional Applications of CRE
37

38. 38
Supplemental Slides
Additional Applications of CRE

39. 39
Supplemental Slides
Additional Applications of CRE
Hippo Digestion (Ch. 2)

40. 40
Supplemental Slides
Additional Applications of CRE

41. 41
Supplemental Slides
Additional Applications of CRE