This document contains slides from a lecture on chemical reaction engineering (CRE). It introduces CRE as the synthesis of thermodynamics, kinetics, fluid mechanics, heat and mass transfer, and economics to design and understand chemical reactors. It discusses how to design reactors by considering the reaction stoichiometry, kinetics, type of reactor, and size of reactor. Basic concepts covered include the different types of reactors (CSTR, batch, PFR) and using material balances to model reactors.

1. L1-1
Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
CHBE 424:
Chemical Reaction Engineering
Introduction & Lecture 1

2. L1-2
Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
Understanding how chemical reactors work lies at the heart of
almost every chemical processing operation.
Design of the reactor is no routine matter, and many
alternatives can be proposed for a process. Reactor design
uses information, knowledge and experience from a variety of
areas - thermodynamics, chemical kinetics, fluid mechanics,
heat and mass transfer, and economics.
CRE is the synthesis of all these factors with the aim of
properly designing and understanding the chemical reactor.
What is Chemical Reaction Engineering
(CRE) ?
Chemical
process
Raw
material
Separation
Process
Products
By-products
Separation
Process

3. L1-3
Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
How do we design a chemical reactor?
Type & size
Maximize the space-time yield of the desired product
(productivity lb/hr/ft3)
Stoichiometry
Kinetics
Basic molar balances
Fluid dynamics
Reactor volume
Use a lab-scale reactor to determine the kinetics!

4. L1-4
Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
Reactor Design
Reaction
Stoichiometry
Kinetics: elementary vs non-elementary
Single vs multiple reactions
Reactor
Isothermal vs non-isothermal
Ideal vs nonideal
Steady-state vs nonsteady-state

5. L1-5
Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
What type of reactor(s) to use?
in
out
Continuously Stirred
Tank Reactor (CSTR)
Well-mixed batch reactor
Plug flow reactor (PFR)

6. L1-6
Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
What size reactor(s) to use?
Answers to this questions are based on the desired
conversion, selectivity and kinetics
Reactor type
&
size
Conversion
&
selectivity
Kinetics
Material &
energy
balances

7. L1-7
Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
Chemical Reaction
• A detectable number of molecules have lost their identity
and assumed a new form by a change in the kind or number
of atoms in the compound and/or by a change in the atoms’
configuration
• Decomposition
• Combination
• Isomerization
• Rate of reaction
– How fast a number of moles of one chemical species are
being consumed to form another chemical species

8. L1-8
Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
Rate Law for rj
• rA: the rate of formation of species A per unit volume [e.g., mol/m3•s]
• -rA: the rate of a consumption of species A per unit volume
rj depends on concentration and temperature:
A B products
  C
kC
r B
A
A

1st order in A, 1st order in B, 2nd order overall
kC
r n
A
A
 nth order in A
A
2
A
1
A
C
k
1
C
k
r


 Michaelis-Menton: common in enzymatic reactions
a
E
RT
A A
A
-r A e C Arrhenius dependence on temperature
A: pre-exponential factor E : activation energy
R : ideal gas constant T:temperature

 
 
 


9. L1-9
Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
Basic Molar Balance (BMB)
 
mol
dt
d
s
mol
s
mol
s
mol
dt
dN
G
F
F
j
j
j
0
j





















Rate of
flow of j
into
system
-
Rate of
flow of j
out of
system
+
Rate of
generation of j
by chemical
rxn
-
Rate of
decomposition
of j
= Rate of
accumulation
combine Nj: moles j in
system at time t
System volume
Fj0 Fj
Gj
in - out + generation = accumulation

10. L1-10
Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
Basic Molar Balance (BMB)
 
mol
dt
d
s
mol
s
mol
s
mol
dt
dN
G
F
F
j
j
j
0
j





















Rate of
flow of j
into
system
-
Rate of
flow of j
out of
system
+
Rate of
generation of j
by chemical
rxn
-
Rate of
decomposition
of j
= Rate of
accumulation
If the system is uniform throughout its entire volume, then:
V
r
G j
j 
Moles j
generated
per unit time
(mol/s)
=
Moles
generated per
unit time and
volume
(mol/s•m3)
Volume
(m3)

11. L1-11
Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
Non-Uniform Generation
DV
If rj varies with position (because
the temperature or concentration
varies) then rj1 at location 1 is
surrounded by a small subvolume
DV within which the rate is uniform
Rate is rj1
within this
volume
DV
Rate is rj2
within this
volume

j
G lim
m→∞
DV→0
 

D

m
1
i
V
j
j dV
r
V
r
1
1
1 y
x
z
 
  

1
0
1
0
1
0
j
j dz
dy
dx
z
,
y
,
x
r
G
then
Plug in rj and integrate over x, y, and z
system

12. L1-12
Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
Basic Molar Balance Equations
j
j0 j j
dN
F F G
dt
  
j
j0 j j
dN
F F r V uniform rate n V
dt
i
  
V j
j0 j j
dN
F F r dV nonuniform rate in V
dt
  

In Out
- +Generation = Accumulation
Next time: Apply BME to ideal batch, CSTR, & PFR reactors
System volume
Fj0 Fj
Gj

13. L1-13
Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
Review of Frequently Encountered
Math Concepts

14. L1-14
Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
   

y
ln x yln x     
 
  
 
x
ln x ln y ln
y
     
a
ln bt 1 ln x ln y
b

  
 
 
a b
ln bt 1
x
ln
y

 

 
 
 
 
 
a b x
ln bt 1 ln
y
e e
 
 
 


 
  a b x
bt 1
y

     a b
y bt 1 x

  
 
ln a
e a

     
ln x ln y ln xy
 
Solve for X:
Basic Math Review

 n
n
1
x
x 
p
q p
q
x x
     
a
ln bt 1 ln x n y
b
l


 
Example: Problems that Contain Natural Logs

15. L1-15
Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
b b
n
n
a a
1
dx x dx
x


     
b
n 1
a
x n 1
 
 
  
 
 
For n≠1:
n 1 n 1
b a
n 1 n 1
   
 
   


 
5 t
2
1 0
dx c
dt
d
x
 
    
 
 
 

5
t
0
1
1 c
t
x d
 
     
 
   
 

1 1 c
t 0
5 1 d

   
c
0.2 1 t
d
  
c
0.8 t
d
  
d
0.8 t
c

 n
n
1
x
x
 
 

  
b b
a
n
a
1
dx ln x
x
For n=1:

p
q p
q
x x
   
 
ln b ln a
b
ln
a
 
  
 
Review of Basic Integration
Solve
for t:

16. L1-16
Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
       
d
0
d d
d
1 1
t 0
1 1
k ln ln ln c l
k k
k k
n c
 
      
 
 
 
 
 

 
d
k
c
1 k t
dc
dt
 
  
 

 
d
k
dt
1 k t
dc
c
  
 

0
t c
0 c
d
1 dc
k dt
1 c
t
k
Do NOT move t or c outside of the integral
  
 

0
t
d
c
0 c
1 dc
k dt
c
1 t
k
From
Appendix A:
 
x
x
0 0
dx 1
ln 1 x
1 x

 
 
 

 
 
x
x
0 0
dx 1
ln 1
x
1
x

 
 
 

 
    c
c0
0
d
d
t
k
k
1
k ln 1 t ln c
 
    
   
 
0
     
d 0
d
k
ln k t 1 ln c ln c
k

     
d
d 0
k c
ln k t 1 ln
k c
 

    
 
 
c
k
ln
ln k t 1
d c
k 0
d
e e
 
 
 

  
 
 
 
   
 
 
k
ln k t 1
d
kd
0
c
e
c
 


 
 
 
 
k
ln k t 1
d
kd
0
c e c
 


 
 
 
Solve for c:
ε is a
constant