This document provides an overview of reaction engineering and key concepts in chapter 1 such as mole balances. It introduces chemical species and reactions, and defines the rate of reaction. The general mole balance equation is presented for batch, continuous stirred tank (CSTR), plug flow, and packed bed reactors. Industrial examples of packed bed and fluidized bed reactors are also briefly described.

1. ERT 316: REACTION ENGINEERING
CHAPTER 1
MOLE BALANCES
Lecturer: Miss Anis Atikah Ahmad
Email: anisatikah@unimap.edu.my
Tel: +604-976 3245
1

2. OUTLINE
 Introduction
 Chemical Species
 Chemical Reaction
 Rate of Reaction
 General Mole Balance Equation
 Batch Reactor
 Continuous-Flow Reactors
 Industrial Reactors
2

3. INTRODUCTION
 Application of Chemical Reaction Engineering
3
Waste treatment
Microelectronics
Nanoparticles
Manufacturing of
chemical &
pharmaceuticals
Living system

4. 1. CHEMICAL SPECIES
What are chemical species?
 Any chemical component or element with a given
identity.
 Identity of a chemical species is determined by the
kind, number, and configuration of that species’
atoms.
 Kind of species- methane, butene, butane
 Number of atoms- eg: CH4: 1 C, 4 H
 Configuration of atoms- arrangement of the
atoms
4

5. Can they be considered as different
SPECIES?
Kind: Same (Butene)
Number of atoms: Same (C4H8)
Configuration: Different arrangement
ANSWER: Yes. We consider them as two different species
because they have different configurations. 5

6. 2. CHEMICAL REACTION
 Chemical reaction is any reaction when one or
more species lost their identity and produce a
new form by a change in the kind or number of
atoms in the compound, and/or by a change in
structure or configuration of these atoms.
HOW????
6

7. 2. CHEMICAL REACTION
 Species may lose its chemical identity by:
1) Decomposition (by breaking down the
molecule into smaller molecule)
Eg: C ⇌ A + B
2) Combination (reverse of decomposition)
3) Isomerization ( neither add other molecule nor
breaks into smaller molecule)
7

8. It tells how fast a
number of moles of one
chemical species to
form another
chemical species.
3. RATE OF REACTION, A
r

,the rate of reaction: is the number of moles of A
reacting (disappearing) per unit time per unit volume (
).
, is the rate of formation (generation) of species A.
, is a heterogeneous reaction rate: the no of moles of A
reacting per unit time per unit mass of catalyst (
catalyst)
A
r

s
dm
mol 
3
/
A
r
A
r
g
s
mol 
/
8

9. 4. THE GENERAL MOLE BALANCE EQUATION
 A mole balance of species j at any instant time:
Rate of flow
of j into the
system
(moles/time)
Rate of flow
of j out of
the system
(moles/time)
Rate of generation
of j by chemical
reaction within the
system
(moles/time)
Rate of
accumulation
of j within the
system
(moles/time)
In - Out + Generation = Accumulation
dt
dNj
Fj0 - Fj + =
dt
dNj

V
jdV
r
0
Fj0 - Fj + Gj =
9

10. 4. THE GENERAL MOLE BALANCE EQUATION
Gj
Fj0 Fj
General mole balance:
Fj0 - Fj + Gj = dNj/dt
In - Out + Generation = Accumulation
Consider a system volume :
System volume
10

11. THE GENERAL MOLE BALANCE EQUATION
Condition 1:
 If all the the system variables (eg: T, C) are
spatially uniform throughout a system volume:
Gj = rj.V
volume
volume
time
moles
time
moles



11

12. Condition 2:
 If the rate of formation, rj of a species j for the
reaction varies with position in the system volume:
 The rate of generation ∆Gj1:
∆Gj1=rj1∆V1
THE GENERAL MOLE BALANCE EQUATION
Fj0 Fj
rj1
rj2
∆V1
∆V2
12

13.  The total rate of generation within the system
volume is the sum of all rates of generation in each
of the subvolumes.
 Taking the limit M∞, and ∆V0 and integrating,
4. THE GENERAL MOLE BALANCE EQUATION








M
i
i
ji
M
i
ji
j V
r
G
G
1
1


V
jdV
r
G
0
13

14. TYPE OF REACTORS
REACTORS
Batch
Continuous
Flow
in
out

15. 5. BATCH REACTORS
 The reactants are first placed inside the
reactor and then allowed to react over time.
 Closed system: no material enters or leaves
the reactor during the time the reaction takes
place.
 Operate under unsteady state condition.
 Advantage: high conversion
15
the conditions inside
the reactor (eg:
concentration,
temperature) changes
over time

16. 5. BATCH REACTORS: DERIVATION
 Batch reactor has neither inflow nor outflow of
reactants or products while the reaction is carried
out:
FA0 = FA = 0
 General Mole Balance on System Volume V
FA0 - FA + =
dt
dNA

V
AdV
r
0


V
A
A
dV
r
dt
dN
0 16

17.  Assumption: Well mixed so that no variation in the
rate of reaction throughout the reactor volume:
 Rearranging;
 Integrating with limit at t=0, NA=NA0
& at t=t1, NA=NA1,
5. BATCH REACTORS: DERIVATION
17
V
r
dt
dN
A
A

V
r
dN
dt
A
A


 


0
1
1
0
1
A
A
A
A
N
N A
A
N
N A
A
V
r
dN
V
r
dN
t

18. 6. CONTINUOUS-FLOW REACTORS: STEADY STATE
1. Continuous-Stirred Tank Reactor
(Backmix/ vat)
 open system: material is free to enter
or exit the reactor
 reactants are fed continuously into the
reactor.
 products are removed continuously.
 operate under steady state condition
 perfectly mixed: have identical
properties (T, C) everywhere within the vessel.
 used for liquid phase reaction 18

19. 6.1 CONTINUOUS-STIRRED TANK REACTOR
DERIVATION
 General Mole Balance:
 Assumption:
1.steady state:
2. well mixed:
 Mole balance: FA - FA + = 0
19
FA0 - FA + =
dt
dNA

V
AdV
r
0
0

dt
dNA
V
r
dV
r A
V
A 

0
V
rA
A
A
A
A
A
A
r
F
F
r
F
F
V




 0
0
design equation
for CSTR

20. 6. CONTINUOUS-FLOW REACTORS: STEADY STATE
2. Plug Flow/Tubular Reactor
 Consist of cylindrical hollow pipe.
 Reactants are continuously
consumed as they flow down the
length of the reactor.
 Operate under steady state cond.
 No radial variation in velocity, conc,
temp, reaction rate.
 Usually used for gas phase reaction
20

21. 6.2 PLUG FLOW REACTOR
DERIVATION
 General Mole Balance:
 Assumption:
1.steady state:
 Differentiate with respect to V:
21
FA0 - FA + =
dt
dNA

V
AdV
r
0
0

dt
dNA
,
0 A
A
r
dV
dF



FA0 - FA + = 0

V
AdV
r
0
A
A
r
dV
dF


22. 6.2 PLUG FLOW REACTOR
DERIVATION
 Rearranging and integrating between
V = 0, FA = FA0
V = V1, FA = FA1
22
A
A
r
dV
dF

A
A
r
dF
dV  
 
1
0
1
0
A
A
F
F A
A
V
r
dF
V

 


0
1
1
0
1
A
A
A
A
F
F A
A
F
F A
A
r
dF
r
dF
V

23. 6. CONTINUOUS-FLOW REACTORS: STEADY STATE
3. Packed-Bed Reactor
(fixed bed reactor)
 Often used for catalytic process
 Heterogeneous reaction system
(fluid-solid)
 Reaction takes place on the surface
of the catalyst.
 No radial variation in velocity,
conc, temp, reaction rate
23

24. 6.3 PACKED BED REACTOR
24
DERIVATION
 General Mole Balance:
 Assumption:
1.steady state:
 Differentiate with respect to W:
FA0 - FA + =
dt
dNA
 dW
rA
'
0

dt
dNA
FA0 - FA + = 0
 dW
rA
'
'
A
A
r
dW
dF

the reaction rate is based
on mass of solid catalyst,
W, rather than reactor
volume

25. 6.2 PACKED BED REACTOR
DERIVATION
 Rearranging and integrating between
W = 0, FA = FA0
W = W1, FA = FA1
25
'
A
A
r
dF
dW  
 
1
0
1
'
0
A
A
F
F A
A
V
r
dF
W





0
1
1
0
'
'
1
A
A
A
A
F
F A
A
F
F A
A
r
dF
r
dF
W
'
A
A
r
dW
dF


26. SUMMARY OF REACTOR MOLE BALANCE
Reactor Differential Form
Algebraic
Form
Integral Form Comment
Batch
No spatial
variations,
unsteady
state
CSTR - -
No spatial
variations,
steady state
PFR Steady state
PBR Steady state
26
V
r
dt
dN
A
A

A
A
A
r
F
F
V


 0
 

0
1
1
A
A
F
F A
A
r
dF
V
A
A
r
dV
dF

'
A
A
r
dW
dF
 


0
1
'
1
A
A
F
F A
A
r
dF
W
 

0
1
1
A
A
N
N A
A
V
r
dN
t

27. INDUSTRIAL REACTORS
27
Packed-Bed Reactor at Sasol Limited
Chemical

28. INDUSTRIAL REACTORS
28
Fixed-Bed Reactor at British Petroleum (BP): using a
colbalt-molybednum catalyst to convert SO2 to H2S

29. INDUSTRIAL REACTORS
29
Fluidized Catalytic Cracker at British Petroleum (BP): using
H2SO4 as a catalyst to bond butanes and iso-butanes to make
high octane gas