1. ERT 316: REACTION ENGINEERING CHAPTER 1 MOLE BALANCES
Lecturer: Miss Anis Atikah Ahmad
Tel:

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

3. Manufacturing of chemical & pharmaceuticals
Introduction
Application of Chemical Reaction Engineering
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

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.

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????

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)

8. It tells how fast a number of moles of one chemical species to form another chemical species.
3. Rate of Reaction,
,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)

9. 4. The General Mole Balance Equation
A mole balance of species j at any instant time:
Rate of generation of j by chemical reaction within the system (moles/time)
Rate of accumulation of j within the system (moles/time)
Rate of flow of j into the system (moles/time)
Rate of flow of j out of the system (moles/time)
In Out Generation = Accumulation
Fj Fj Gj =
Fj Fj =

10. 4. The General Mole Balance Equation
Consider a system volume :
System volume
Fj0 Gj Fj
General mole balance:
Fj Fj Gj = dNj/dt
In Out Generation = Accumulation

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

12. The General Mole Balance Equation
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
∆V1
rj1
rj2
∆V2
Fj0 Fj

13. 4. The General Mole Balance Equation
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,

14. TYPE OF REACTORS
Batch in
out
REACTORS
Continuous
Flow

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
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
FA FA =

17. 5. Batch Reactors: Derivation
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,

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

19. 6.1 Continuous-Stirred Tank Reactor
DERIVATION
General Mole Balance:
Assumption:
1.steady state:
2. well mixed:
Mole balance: FA - FA = 0
FA FA =
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

21. 6.2 Plug Flow Reactor DERIVATION General Mole Balance: Assumption:
1.steady state:
Differentiate with respect to V:
FA FA =
FA0 - FA = 0

22. 6.2 Plug Flow Reactor DERIVATION
Rearranging and integrating between    V = 0, FA = FA0    V = V1, FA = FA1

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

24. 6.3 Packed Bed Reactor DERIVATION General Mole Balance: Assumption:
1.steady state:
Differentiate with respect to W:
the reaction rate is based on mass of solid catalyst, W, rather than reactor volume
FA FA =
FA0 - FA = 0

25. 6.2 Packed Bed Reactor DERIVATION
Rearranging and integrating between    W = 0, FA = FA0    W = W1, FA = FA1

26. Summary of Reactor Mole Balance
Differential Form
Algebraic Form
Integral Form
 Comment
Batch
No spatial variations, unsteady state
CSTR -   -
No spatial variations, steady state
PFR
Steady state
PBR

27. Packed-Bed Reactor at Sasol Limited Chemical
Industrial Reactors
Packed-Bed Reactor at Sasol Limited Chemical

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

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