Lecture 1
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.
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Lecture 1 – Thursday 1/6/2011
 Introduction
 Definitions
 General Mole Balance Equation




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Batch (BR)
Continuously Stirred Tank Reactor (CSTR)
Plug Flow Reactor (PFR)
Packed Bed Reactor (PBR)
Chemical Reaction Engineering
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
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Smog (Ch. 1)
Wetlands (Ch. 7 DVD-ROM)
Hippo Digestion (Ch. 2)
Oil Recovery
(Ch. 7)
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Chemical Plant for Ethylene Glycol (Ch. 5)
Lubricant Design
(Ch. 9)
Cobra Bites
(Ch. 8 DVD-ROM)
Plant Safety
(Ch. 11,12,13)
Materials on the Web and CD-ROM
http://www.umich.edu/~essen/
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Let’s Begin CRE
 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.
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 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.
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 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
2. Combination
3. Isomerization
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CH3CH3  H2 + H2C=CH2
N2 + O2  2 NO
C2H5CH=CH2  CH2=C(CH3)2
 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
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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
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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
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 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
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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 = kCA2)
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Building Block 1:
System
Volume, V
Fj0
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Gj
Fj
 Molar Flow  Molar Flow   Molar Rate   Molar Rate 
 Rate of
   Rate of
  Generation    Accum ulation

 
 
 

 Species j in   Species j out of Species j  of Species j 
dN j
Fj 0

Fj

Gj

dt
 m ole
 m ole
 m ole
 m ole











tim
e
tim
e
tim
e
tim
e








Building Block 1:
If spatially uniform:
G j  r jV
If NOT spatially uniform:

V1
rj1
G j1  rj1V1
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

V2
rj 2
G j 2  rj 2 V2
Building Block 1:
n
G j   rji Vi
i 1
Take limit
n
Gj  
rjiVi
i1 lim V  0 n  
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
 r dV
j
Building Block 1:
System
Volume, V
FA0
GA
FA
General Mole Balance on System VolumeV
 Out  Generation  Accumulation
dN A
FA 0  FA
  rA dV

dt
In
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Batch
FA 0  FA 

dN A
rA dV 
dt
FA 0  FA  0
Well-Mixed

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r
A
dV  rAV
dNA
 rAV
dt
dN A
dt 
rAV
Integrating
when
t  0 N A  N A0
t  t NA  NA

t
NA

N A0
dN A
 rAV
Time necessary to reduce the number of moles of A from NA0 to NA.
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t
NA

N A0
NA
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t
dN A
 rAV
CSTR
dNA
FA 0  FA   rA dV 
dt
Steady State

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dNA
0
dt
Well Mixed
 r dV  r V
A
A
FA 0  FA  rAV  0

FA 0  FA
V 
rA
CSTR volume necessary to reduce the molar flow rate from
FA0 to FA.
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
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V
FA
FA


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V
V  V
 In  Out
 Generation

0
at V   



 at V  V  in V

FA V  FA V  V  rA V
0
Rearrange and take limit as ΔV0
lim
V  0

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FA V V  FA V
V
 rA
dFA
 rA
dV
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 –
PFR
dN A
FA0  FA   rA dV 
dt
Steady State
dN A
0
dt
FA0  FA   rA dV  0
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Alternative Derivation –
Differientiate with respect to V
dFA
0
 rA
dV

The integral form is:
dFA
 rA
dV
V 
FA

FA 0
dFA
rA

This is the volume necessary to reduce the entering molar flow
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rate (mol/s) from FA0 to the exit molar flow rate of FA.
W
PBR
FA
FA
W  W
W


dN A
FA W   FA W  W   rA W 
dt
dN A
Steady State
0
dt
lim
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W 0
FA W  W  FA W
W
 rA
Rearrange:
dFA
 rA
dW
The integral form to find the catalyst weight is:

W
FA

FA 0
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dFA
rA
PBR catalyst weight necessary to reduce the entering molar
flow rate FA0 to molar flow rate FA.
Reactor
Batch
Differential
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Integral
t
dN A
 rAV
dt
NA

N A0
dN A
rAV
NA
t
FA 0  FA
V 
rA
CSTR
PFR
Algebraic
dFA
 
rA
dV
V
FA

FA 0
FA
dFA
drA
V
Reactors with Heat Effects
 EXAMPLE: Production of Propylene Glycol in an
Adiabatic CSTR
 Propylene glycol is produced by the hydrolysis of propylene
oxide:
H 2 SO4
CH2  CH  CH3  H2O 
CH2  CH  CH3
O
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OH
OH
v0
Propylene Glycol
What are the exit conversion X and exit temperature T?
Solution
Let the reaction be represented by
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A+BC
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Evaluate energy balance terms
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Analysis
We have applied our CRE algorithm to calculate the
Conversion (X=0.84) and Temperature (T=614 °R) in a 300
gallon CSTR operated adiabatically.
T=535 °R
A+BC
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X=0.84
T=614 °R
KEEPING UP
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Separations
Filtration
Distillation
These topics do not build upon one another.
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Adsorption
Reaction Engineering
Mole Balance
Rate Laws
These topics build upon one another.
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Stoichiometry
Heat Effects
Isothermal Design
Stoichiometry
Rate Laws
Mole Balance
CRE Algorithm
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Mole Balance
Rate Laws
Be careful not to cut corners on any of the
CRE building blocks while learning this material!
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Heat Effects
Isothermal Design
Stoichiometry
Rate Laws
Mole Balance
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Otherwise, your Algorithm becomes unstable.
End of Lecture 1
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Smog (Ch. 1)
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Hippo Digestion (Ch. 2)
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Chemical Plant for Ethylene Glycol (Ch. 5)
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Wetlands (Ch. 7 DVD-ROM)
58
Oil Recovery (Ch. 7)
Cobra Bites
(Ch. 8 DVD-ROM)
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Lubricant Design (Ch. 9)
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Plant Safety
(Ch. 11,12,13)
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