1. ERT 208/4 REACTION ENGINEERING: Bioreaction in Bioreactors
By; Mrs Hafiza Binti Shukor
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)
By; Mrs Hafiza Binti Shukor

2. Students should be able to;
APPLY pseudo-steady-state hypothesis (PSSH) in
gas-phase reactions and in order to DEVELOP
rate laws.
DESCRIBE reaction mechanism, chain reaction &
reaction pathways utilizing biomolecular reaction
(yeast fermentation)
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

3. Common form of the RATE LAW
homogeneous reaction,
If n=1 (interger), reaction was 1 order
If n=not interger number?
Eg,
The rate law for the decomposition of acetaldehyde
Reaction involving active intermediate
Reaction Order
cannot de defined
(polynomial fuction)
NON ELEMTARY REACTION
Reaction Order are described only for limiting values of reactant and/or product conc.
No direct correspondence between reaction order & stoichiometry
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)
By; Mrs Hafiza Binti Shukor

4. Fundamentals of Nonelementary Reaction
For Gas-Phase Decomposition of azomethane, AZO
EXPERIMENTAL OBSERVATIONS SHOWS ;
1st order at;
high conc
pressure >1atm
2nd order at;
Low conc
Pressure < 50mmHg
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)
By; Mrs Hafiza Binti Shukor

5. results from collision or interaction between molecules’
Fundamentals of Nonelementary Reaction…cont…
Active Intermediates
change in reaction order can be explained by the theory
developed by Lindemann
‘ an active molecule,
results from collision or interaction between molecules’
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)
By; Mrs Hafiza Binti Shukor

6. Fundamentals of Nonelementary Reaction…cont…
Lindemann Theory
the decomposition of intermediate does not occur instantaneously after internal activation of the molecule …rather, there is a time lag although infinitesimally small during which the species remains activated.
Other types of active intermediates that can be formed are;
Free radicals > unpaired electrons like H)
Ionic internidiates (eg. Carbonium ion)
Enzymes substrate complexes
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

7. Fundamentals of Nonelementary Reaction…cont…
where.,
2 reaction path that active intermediate may follow;
Activated molecule become deactivated through collision with another molecule
where.,
Activated molecule decomposes spontaneously to form ethane & nitrogen
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)
By; Mrs Hafiza Binti Shukor

8. Fundamentals of Nonelementary Reaction…cont…
The overall reaction is NON ELEMENTARY consist of sequence of ELEMENTARY reactions 1.
2 AZO molecules collide & the kinetic energy of one AZO molecule is transferred to internal rotational & vibrational energies of the other AZO molecule & it becomes activated & highly reactive. 2.
Activated AZO* is deactivated through collision with another AZO 3.
Activated AZO* is widely vibrating, spontaneously decomposes into ethane & nitrogen
Nitrogen & Ethane only form from 3rd equation. The net rate of formation of nitrogen is;
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)
By; Mrs Hafiza Binti Shukor

9. Fundamentals of Nonelementary Reaction…cont…
Rate of formation of active intermediate = sum of the rates of formation of all reaction
Where,
The concentration of the active intermediate, AZO* is very difficult to measure because it is highly reactive and very short lived about 10-9 s
To express CAZO* in term of MEASURABLE CONC, we have to use STEADY STATE HYPOTHESIS (PSSH)
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)
By; Mrs Hafiza Binti Shukor

10. Pseudo-Steady-State Hypothesis (PSSH)..
Its not possible to eliminate the concentration of active
intermediate
Active intermediate molecule has a very short lifetime
because of its high reactivity (large specific reaction rates).
Have to consider it present at very low concentrations
Pseudo-Steady-State approximation
The rate of formation = is assumed to be equal to its rate of disappearance.
As a results, the net rate of formation of the active intermediate r* is ZERO
Rate of formation of product, nitrogen;
Rate of formation of AZO*;
Using PSSH;
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

11. Pseudo-Steady-State Hypothesis (PSSH)cont..
At low conc azomethane;
2nd order
At high conc azomethane;
The final
form of rate law
1st order
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)
By; Mrs Hafiza Binti Shukor

12. Pseudo-Steady-State Hypothesis (PSSH)cont..
Rules of Thumb For Development of Mechanism
1. Species having the conc(s) appearing in the denominator of the rate law probably collide with the active intermediate.
2. If a constant in the denominator, one of the reaction steps is probably the spontaneous decomposition of the active intermediate.
3. Species having the conc(s) appearing in the numerator of the rate law probably produce the active intermediate in one of the reaction step
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

13. Pseudo-Steady-State Hypothesis (PSSH)cont..
Exercise 1;
Mechanism For Azomethane????
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

14. Pseudo-Steady-State Hypothesis (PSSH)cont..
Ans;
Mechanism For Azomethane
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

15. Pseudo-Steady-State Hypothesis (PSSH)cont..
Exercise 2;
By assuming the main product for the reaction below is ethane, write down the final form equation for rate of formation for ethane.
Ans;
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

16. Pseudo-Steady-State Hypothesis (PSSH)cont..
CHAIN REACTIONS
Initiation……….
Formation of an active intermediate
Propagation / Chain Transfer……….
Interaction of an active intermediate with the reactant/product to produce another active intermediate
Termination……….
Deactivation of the active intermediate
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

17. EXAMPLE 1; PSSH Applied to Thermal Cracking
of Ethane (Gas-Phase Reaction)
The thermal decomposition of ethane to ethylene, methane, butane and hydrogen is believed to proceed in the following sequence;
Initiation;
Propagation ;
Termination ;
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

18. EXAMPLE 1; PSSH Applied to Thermal Cracking of Ethane ….cont
a)Use PSSH to derive a rate law for the RATE OF FORMATION OF ETHYLENE & RATE OF DISAPPEARANCE OF ETHANE….
Solutions……
Rate of formation of ethylene (Reaction 3) is,
Active intermediates :
The net of reactions are:
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

19. EXAMPLE 1; PSSH Applied to Thermal Cracking of Ethane ….cont
From reaction stoichiometry, we have;
Then,
Finally got
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

20. EXAMPLE 1; PSSH Applied to Thermal Cracking of Ethane ….cont
From substituting the concentrations into the elementary equation gives;
Where,
Solving for the conc of the free radical ,
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

21. EXAMPLE 1; PSSH Applied to Thermal Cracking of Ethane ….cont
Adding this 2 equations…..
get…
Substituting for conc in the rate laws…..
where…
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

22. EXAMPLE 1; PSSH Applied to Thermal Cracking of Ethane ….cont
PSSH solution…..
from
Solving for gives us,
where…
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

23. EXAMPLE 1; PSSH Applied to Thermal Cracking of Ethane ….cont
Substituting for in equation
yields the rate of formation of ethylene;
where…
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

24. EXAMPLE 1; PSSH Applied to Thermal Cracking of Ethane ….cont
Next, we write the net rate of formation in
In terms of concentration,
where…
Using eq to substitute for gives the
conc of the hydrogen radical
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

25. EXAMPLE 1; PSSH Applied to Thermal Cracking of Ethane ….cont
from
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

26. EXAMPLE 1; PSSH Applied to Thermal Cracking of Ethane ….cont
Rate of disappearance of ethane is
Where,
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

27. EXAMPLE 1; PSSH Applied to Thermal Cracking of Ethane ….cont
Substituting for the concentration of free radicals, the rate law of disappearance of ethane is….
Where,
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

28. Conclusions Reaction that not follow elementary rate law (NON
ELEMENTARY involve a number of reaction steps, each
of which is ELEMENTARY
After finding net rates of reaction for each species, we use
PSSH to derive a rate law of the reaction.
PSSH not only can be used in gas-phase reaction, but also
can be used in biological reactions (enzymatic reactions).
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)
By; Mrs Hafiza Binti Shukor

29. BIOLOGICAL REACTIONS BIOREACTORS Lab Scale Bioreactor
Industrial Scale Bioreactor
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)
By; Mrs Hafiza Binti Shukor

30. Fermentation Process
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

31. Major Functions of a Bioreactor
1) Provide operation free from contamination;
2) Maintain a specific temperature;
3) Provide adequate mixing and aeration;
4) Control the pH of the culture;
5) Allow monitoring and/or control of dissolved oxygen;
6) Allow feeding of nutrient solutions and reagents;
7) Provide access points for inoculation and sampling;
8) Minimize liquid loss from the vessel;
9) Facilitate the growth of a wide range of organisms.
Ref;(Allman A.R., 1999: Fermentation Microbiology and Biotechnology)
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

32. Biotechnological Processes Of Growing Microorganisms In A Bioreactor
Batch culture: microorganisms are inoculated into a fixed volume of medium and as growth takes place nutrients are consumed and products of growth (biomass, metabolites) accumulate.
2) Semi-continuous: fed batch-gradual addition of concentrated nutrients so that the culture volume and product amount are increased (e.g. industrial production of baker’s yeast);
Perfusion-addition of medium to the culture and withdrawal of an equal volume of used cell-free medium (e.g. animal cell cultivations).
3) Continuous: fresh medium is added to the bioreactor at the exponential phase of growth with a corresponding withdrawal of medium and cells. Cells will grow at a constant rate under a constant condition.
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

33. Biotechnological processes of growing microorganisms in a bioreactor
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

34. Batch Culture VS Continuous Culture
Continuous systems: limited to single cell protein, ethanol productions, and some forms of waste-water treatment processes.
Batch cultivation: the dominant form of industrial usage due to its many advantages.
Ref;(Smith J.E, 1998: Biotechnology)
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

35. Advantages of Batch Culture VS Continuous Culture
Products may be required only in a small quantities at any given time.
Market needs may be intermittent.
Shelf-life of certain products is short.
High product concentration is required in broth for optimizing downstream processes.
Some metabolic products are produced only during the stationary phase of the growth cycle.
Instability of some production strains require their regular renewal.
Compared to continuous processes, the technical requirements for batch culture is much easier.
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

36. Fermentation Technology
What is it important to know the kinetics of the reaction in the fermenter?
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

37. Typical pattern of growth cycle during batch fermentation
Cell Growth
Typical pattern of growth cycle during batch fermentation
Lag phase
Acceleration phase
Exponential (logarithmic) phase
Deceleration phase
Stationary phase
Accelerated death phase
Exponential death phase
Survival phase
From: EL-Mansi and Bryce (1999)
Fermentation Microbiology
and Biotechnology.
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

38. Exponential Growth Phase
Cell Growth...cont...
Lag Phase
Exponential Growth Phase
Stationary Phase
Death Phase
Little increase in cell conc.
Cell adjusting their new environment, synthesizing enzymes & ready to reproducing
Cell are dividing at max rate
Cell able to use the nutrients most efficiently
Cell reach a minimum biological space (lack of nutrients limits cell growth)
Net growth = 0
Fermentation product produce.
Decrease in live cell conc occur.
Results of toxic by-product
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

39. Rate Laws Cells + Substrate More Cells + Product
Rate law for the cell growth rate of new cells,
Cells + Substrate More Cells Product
The most commonly used expression is the Monod equation for exponential growth;
Where,
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

40. Rate Laws...cont... Specific cell growth rate can be expressed as,
Where,
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

41. Rate Laws...cont... Combine , and Will get,
Monod equation for bacterial cell growth rate
Parameter value for the E.coli growth on glucose.
Ks is small for a numb of different bacteria in which case the rate law reduce to,
Plz refer ERT 104 Bioprocess Eng Principle
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)

42. Thank You
ERT 208/4 REACTION ENGINEERING
SEM 2 (2009/2010)