1. Mustafa Nasser, PhD, MSc, BSc Chemical Engineering
CHE402: Kinetics and Reactor Design CHAPTER ONE Mole Balances in Reacting Systems & Reactor Design Equations
Mustafa Nasser, PhD, MSc, BSc
Chemical Engineering
Dr Mustafa Nasser 2012

2. Objectives Describe photos of real reactors.
Define the rate of chemical reaction.
Apply a general mole balance to
a batch reactor,
a continuous stirred tank reactor (CSTR),
a plug flow reactor (PFR), and
a packed bed reactor (PBR).
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3. Industrial Reactors
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4. Industrial Reactors
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5. Industrial Reactors
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6. Spherical Reactors
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7. Industrial Reactors
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8. Industrial Reactors
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9. Industrial Reactors
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10. Industrial Reactors
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11. Packed Bed Reactor
Packed Bed Reactor in use for a Fisher-Tropsch synthesis reaction at Sasol Limited Chemical.
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12. Straight Through Transport Reactor
Straight Through Transport Reactor (STTR) in use for a Fisher-Tropsch synthesis reaction at Sasol Limited Chemical.
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13. Laboratory CSTR/Batch Reactor
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14. Laboratory CSTR
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15. RC1e Reaction Calorimeter
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16. Chemical Identity
A chemical species has 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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17. Loss of Chemical Identity
Decomposition; AB  A + B
Combination; A + B  AB
Isomerization; A  B
single displacement (substitution); A + BC  AC + B
double displacement (metathesis); AB + CD  AD + CB
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18. Reaction Rate
The reaction rate is the rate at which a species looses its chemical identity per unit volume.
The rate of a reaction can be expressed as the rate of disappearance of a reactant or as the rate of appearance of a product.
Reaction rates are associated with reaction stoichiometry, which describe molar relationships
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19. Reaction Rate Consider species A:
rA = rate of formation of A per unit vol
-rA = rate of a disappearance of A per unit vol
For a catalytic reaction, -rA' is the rate of disappearance of species A on a per mass of catalyst basis.
NOTE: dCA/dt is not the rate of reaction
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20. Reaction Rate Consider in general terms, species j… The rate, rj is
the rate of formation of species j per unit volume
a function of concentration, temperature, pressure, and the type of catalyst (if any)
independent of the type of reaction system (batch, plug flow, etc.)
an algebraic equation, not a differential equation
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21. Reaction Rate rA = the rate of formation of species A per unit volume
Consider species A: 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
EXAMPLE: A  B
If B is being formed at 0.2 moles per decimeter cubed per second, ie,
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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22. Which reaction type characterizes the combusion of ethane
Which reaction type characterizes the combusion of ethane? 2 C2H6 + 7 O2  4 CO2 + 6 H2O
combination
isomerization
decomposition
single displacement
double displacement E
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23. Which statement is always false?D
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24. General Mole Balance EquationGj
Fjo Fj
where N is the moles of j
in the system at time t.
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25. General Mole Balance EquationGj
Fjo Fj
if all variables are spatially uniform
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26. General Mole Balance Equation
If rj varies with position in the system,
rj,1
V1
rj,2
V2
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27. General Mole Balance EquationGj
Fjo Fj
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28. Reaction Rate and Rate Law
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29. Reaction Rate and Rate Law
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30. GMBE Applied to Batch Reactors
For a batch reactor (no flows):
GMBE reduces to:
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31. GMBE Applied to Batch Reactors
Assuming perfect mixing:
Batch Reactor
Design Equation
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32. GMBE Applied to Batch Reactors
For the simple reaction A  products:
In a constant volume reactor,
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33. GMBE Applied to Batch Reactors
For the simple reaction A  products:
In a constant pressure reactor,
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34. Batch Reactors
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35. Which is NOT a characteristic of an ideal batch reactor ?
Absence of concentration gradients (i.e., perfect mixing)
Steady state operation
No material crosses system boundary (i.e., no flows)
Derivative with respect to time B
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36. GMBE Applied to Flow Reactors
Continuous Stirred-Tank Reactor (CSTR):
reactants
steady
state
perfect
mixing
volumetric
flow rate
products
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37. GMBE Applied to Flow Reactors
Continuous Stirred-Tank Reactor (CSTR):
reactants
steady
state
perfect
mixing
CSTR
Design Equation
products
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38. Which is NOT a characteristic of an ideal CSTR?
Absence of concentration gradients (i.e., perfect mixing)
Steady state operation
Material crosses system boundary (i.e., flows in and out)
Derivative with respect to time D
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39. GMBE Applied to Flow Reactors
Tubular (Plug Flow) Reactor (PFR): y
y+y y
reactants
products V
Fj(y)
Fj(y+y)
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40. GMBE Applied to Flow Reactors
Tubular (Plug Flow) Reactor (PFR):
steady
state
spatially
uniform V V
Fj(y)
Fj(y+y)
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41. GMBE Applied to Flow Reactors
Tubular (Plug Flow) Reactor (PFR):
steady
state
spatially
uniform V
uniform
cross-section
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42. GMBE Applied to Flow Reactors
Tubular (Plug Flow) Reactor (PFR):
PFR
Design Equation
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43. Which IS a characteristic of an ideal Plug Flow Reactor?
Absence of concentration gradients (i.e., perfect mixing)
Steady state operation
Material crosses system boundary (i.e., flows in and out)
Derivative with respect to time C
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44. GMBE Applied to Packed Bed Reactors
PBR used for fluid/solid catalytic reaction: W
W+W W
FAo FA W
FA(W)
FA(W+W)
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45. GMBE Applied to Packed Bed Reactors
PBR used for fluid/solid catalytic reaction:
dimensions of
generation term W
FA(W)
FA(W+W)
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46. GMBE Applied to Packed Bed Reactors
PBR used for fluid/solid catalytic reaction:
PBR
Design Equation
When pressure drop and catalyst decay can
be neglected, integral form can be used:
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47. Which IS a characteristic of an ideal Packed Bed Reactor?
Absence of concentration gradients (i.e., perfect mixing)
Steady state operation
No material crosses system boundary (i.e., no flows)
Derivative with respect to position D
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48. Design Equation Summary
Batch
CSTR
PFR
PBR
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49. Example 2: Batch Reactor Times
A  B
Calculate the time to reduce the number of moles by a factor of 10 (NA = NA0/10 ) in a batch reactor for the above reaction with
-rA = kCA,  when k = min-1
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50. Solution Mole balance: In - Out + Generation = Accumulation
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51. Dr Mustafa Nasser 2012

52. Example 3
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53. Solution
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54. Some General Quiz
1. In the formula for CSTR, if the rate of reaction is not constant and is dependent on the concentration, should we take to mean? the integral mean?

55. Some General Quiz
Because the reactor is well-mixed, the concentrations, temperature, and rate of reaction are the same throughout the reactor volume, including the point at which it exits the reactor. Consequently, the concentrations, temperature, and rate of reaction in the reactor are all evaluated at the exit conditions of the CSTR.

56. P1-8
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57. P1-8 Solution (a) Batch Reactor
- Closed system, No Input or output streams.
- Well mixed and no spatial variation in system properties.
- Constant Volume or constant Pressure.
(b) CSTR
- Steady state
- No spatial variation in concentration, temperature, or reaction rate through the vessel.
(c,d) PFR and PBR
Steady State
No Radial variation in properties of the system
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58. P1-8 Solution (e) State the meaning of
- rA is the number of Moles of A reacting (disappearing) per unit of time per unit of volume.
- rA’ is the number of Moles of A reacting (disappearing) per unit of time per unit of mass of catalyst (or Surface Area).
rA’ is the number of Moles of A generated per unit of time per unit of mass of catalyst (or Surface Area).
In General: Rate of reaction is an intensive property that is, it is a function of concentration, temp, pressure and the type of catalyst if any. And is defined at any point (location) within the system. It is independent of the amount of reactants.
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59. P1-13A(Fogler) Complete the table: Type of reactor characteristics
phases
present uses
advantages
disadvantages
Batch
CSTR
PFR
PBR
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60. P1-13A(Fogler)
Batch Reactor
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61. P1-13A(Fogler)
CSTR
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62. P1-13A(Fogler)
PFR
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63. P1-13A(Fogler)
PBR
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65. P15a (CSTR)

66. P15a (PFR)

67. P1-15b (CSTR)

68. P1-15b (PFR)
P1-15c (Take home)

69. Try now:
(c)
(a)
(b)
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70. Dr Mustafa Nasser 2012