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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. Students should be able to;. APPLY pseudo-steady-state hypothesis (PSSH) in

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ERT 208/4 REACTION ENGINEERING: Bioreaction in Bioreactors

By; Mrs Hafiza Binti Shukor

ERT 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

By; Mrs Hafiza Binti Shukor

slide2

Students should be able to;

  • APPLYpseudo-steady-state hypothesis (PSSH) in
  • gas-phase reactions and in order to DEVELOP
  • rate laws.
  • DESCRIBEreaction mechanism, chain reaction &
  • reaction pathways utilizing biomolecular reaction
  • (yeast fermentation)

ERT 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide3

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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

By; Mrs Hafiza Binti Shukor

slide4

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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

By; Mrs Hafiza Binti Shukor

slide5

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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

By; Mrs Hafiza Binti Shukor

slide6

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 (one @ > unpaired electrons like H)
  • Ionic internidiates (eg. Carbonium ion)
  • Enzymes substrate complexes

ERT 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide7

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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

By; Mrs Hafiza Binti Shukor

slide8

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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

By; Mrs Hafiza Binti Shukor

slide9

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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

By; Mrs Hafiza Binti Shukor

slide10

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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide11

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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

By; Mrs Hafiza Binti Shukor

slide12

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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide13

Pseudo-Steady-State Hypothesis (PSSH)cont..

Exercise 1;

Mechanism For Azomethane????

ERT 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide14

Pseudo-Steady-State Hypothesis (PSSH)cont..

Ans;

Mechanism For Azomethane

ERT 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide15

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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide16

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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide17

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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide18

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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide19

EXAMPLE 1; PSSH Applied to Thermal Cracking

of Ethane ….cont

From reaction stoichiometry, we have;

Then,

Finally got

ERT 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide20

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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide21

EXAMPLE 1; PSSH Applied to Thermal Cracking

of Ethane ….cont

Adding this 2 equations…..

get…

Substituting for conc in the rate laws…..

where…

ERT 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide22

EXAMPLE 1; PSSH Applied to Thermal Cracking

of Ethane ….cont

PSSH solution…..

from

Solving for gives us,

where…

ERT 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide23

EXAMPLE 1; PSSH Applied to Thermal Cracking

of Ethane ….cont

Substituting for in equation

yields the rate of formation of ethylene;

where…

ERT 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide24

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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide25

EXAMPLE 1; PSSH Applied to Thermal Cracking

of Ethane ….cont

from

ERT 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide26

EXAMPLE 1; PSSH Applied to Thermal Cracking

of Ethane ….cont

Rate of disappearance of ethane is

Where,

ERT 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide27

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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide28

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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

By; Mrs Hafiza Binti Shukor

slide29

BIOLOGICAL REACTIONS

  • BIOREACTORS

Lab Scale Bioreactor

Industrial Scale Bioreactor

ERT 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

By; Mrs Hafiza Binti Shukor

fermentation process
Fermentation Process

ERT 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide31

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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

biotechnological processes of growing microorganisms in a bioreactor
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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide33

Biotechnological processes of growing microorganisms in a bioreactor

ERT 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

batch culture vs continuous culture
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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

advantages of batch culture vs continuous culture
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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

fermentation technology
Fermentation Technology
  • What is it important to know the kinetics of the reaction in the fermenter?

ERT 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide38

Cell Growth...cont...

ERT 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

rate laws
Rate Laws

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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

rate laws cont
Rate Laws...cont...

Specific cell growth rate can be expressed as,

Where,

ERT 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

rate laws cont1
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 208/4REACTION ENGINEERING

SEM 2 (2009/2010)

slide42

Thank You

ERT 208/4REACTION ENGINEERING

SEM 2 (2009/2010)