ert 208/4 reaction engineering: bioreaction in bioreactors by; mrs haf iza bint i shu kor ert 208/4...

ERT 208/4 REACTION ENGINEERING: Bioreaction in Bioreactors

By; Mrs Hafiza Binti Shukor

ERT 208/4 REACTION ENGINEERINGSEM 2 (2009/2010)


Students should be able Students should be able to; 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)


Common form of the RATE LAW

n

AA kCr

If n=not interger number? Eg,The rate law for the decomposition of acetaldehyde

2

3

33 CHOCHCHOCH kCr

•homogeneous reaction,

•Reaction involving active intermediate

If n=1 (interger), reaction was 1 order

HIIH 222 232

2231

H

HI

HI Ckk

CCkkr

Reaction Order cannot de defined(polynomial fuction)

NON ELEMTARY REACTION

No direct correspondence between reaction order & stoichiometry

Reaction Order are described only for limiting values of reactant and/or product conc.

COCHCHOCH 43


Fundamentals of Nonelementary Reaction•For Gas-Phase Decomposition of azomethane, AZO

AZON Cr 2

EXPERIMENTAL OBSERVATIONS SHOWS ;

1st order at;•high conc•pressure >1atm

262223 NHCNCH

AZON Cr 2

2

2nd order at;•Low conc•Pressure < 50mmHg


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’

*]@[223 ANCH


Fundamentals of Nonelementary Reaction…cont…

*2232231

223223 NCHNCHNCHNCH k

•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;a)Free radicals (one @ > unpaired electrons like H)b)Ionic internidiates (eg. Carbonium ion)c)Enzymes substrate complexes

MAMA k *1



*2232231


2 reaction path that active intermediate may follow;

AZOAZO Ckr 2

1* 223 NCHAZO where.,

2232232

223223 * NCHNCHNCHNCH k

2623

223 * NHCNCH k

*2* AZOAZOAZO CCkr

*3* AZOAZO Ckr

Activated molecule become deactivated through collision with another molecule

where.,

Activated molecule decomposes spontaneously to form ethane & nitrogen


Fundamentals of Nonelementary Reaction…cont… The overall reaction is NON

ELEMENTARY consist of sequence of ELEMENTARY reactions

262223 NHCNCH

*2232231


2232232

223223 * NCHNCHNCHNCH k

2623

223 * NHCNCH k

Nitrogen & Ethane only form from 3rd equation. The net rate of formation of nitrogen is;

*32 AZON Ckr

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.

1.

2.

3.

Activated AZO* is deactivated through collision with another AZO

Activated AZO* is widely vibrating, spontaneously decomposes into ethane & nitrogen



3*2*1** AZOAZOAZOAZO rrrr

AZOAZO Ckr 2

11*

*22* AZOAZOAZO CCkr

*33* AZOAZO Ckr

Where,

Rate of formation of active intermediate = sum of the rates of formation of all reaction

*3*2

2

1* AZOAZOAZOAZOAZO CkCCkCkr

To express CAZO* in term of MEASURABLE CONC, we have to use STEADY STATE HYPOTHESIS (PSSH)

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


Pseudo-Steady-State Hypothesis (PSSH)..

0*r

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

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

Pseudo-Steady-State approximation

*32 AZON Ckr

*3*2

2


Rate of formation of product, nitrogen;

Rate of formation of AZO*;

Using PSSH; 0* AZOr

0*3*2

2



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

The final form of rate law

AZO

AZO

AZO

AZOAZOAZO

AZOAZOAZOAZO

AZOAZOAZOAZOAZO

Ckk

CkC

kCkCCk

CkCCkCk

CkCCkCkr

23

2

1*

32*

2

1

*3*2

2

1

*3*2

2

1*

0)(

0

0

AZO

AZO

N

AZON

Ckk

Ckkr

Ckr

23

2

31

2

*32

At low conc azomethane;

At high conc azomethane;

32 kCk AZO

32 kCk AZO

AZON Ckr 2

12

AZOAZON kCCk

kkr

2

31

2

1st order

2nd order



productscollisionAA __*

Rules of Thumb For Development of Mechanism1. 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

productsiondecompositA __*

productsotherAtreac __*tan




Exercise 1;Mechanism For Azomethane????






Mechanism For Azomethane



AZOAZOAZOAZO *

262* NHCAZO

AZOAZOAZOAZO *

Ans;


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. 262223 NHCNCH

AZO

AZO

HC

AZOHC

Ckk

Ckkr

Ckr

23

2

31

62

*362

Ans;



CHAIN REACTIONS

Initiation……….

Propagation / Chain Transfer……….

Termination……….

Formation of an active intermediate

Interaction of an active intermediate with the reactant/product to produce another active intermediateDeactivation of the active intermediate


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 ;

362_1

62 2CHHC HCk

5242

623 HCCHHCCH k

HHCHC k42

352

2524

62 HHCHCH k

1045

522 HCHC k

62_11

6262_162_1

_ HC

HCHC

kkLets

HCkr

623262_2 HCCHkr HC

52342_3 HCkr HC

62462_4 HCHkr HC

52_55

2

5252_552_5

_ HC

HCHC

kkLet

HCkr


EXAMPLE 1; PSSH Applied to Thermal Cracking of Ethane ….conta)Use PSSH to derive a rate law for the RATE OF FORMATION OF ETHYLENE & RATE OF DISAPPEARANCE OF ETHANE….

HHCHC k42

352 52342_3 HCkr HC

Solutions……

Rate of formation of ethylene (Reaction 3) is,

Active intermediates :

52HC

3CH

H

The net of reactions are:

0:5255245235225252 HCHCHCHCHC rrrrrHC

02:622621323133 HCHCCHCHCH rrrrrCH

0:62442343 HCHCHHH rrrrrH


EXAMPLE 1; PSSH Applied to Thermal Cracking of Ethane ….cont

From reaction stoichiometry, we have;

Then,


622522 HCHC rr 423523 HCHC rr

624524 HCHC rr





Finally got



From substituting the concentrations into the elementary equation gives;

Where,


Solving for the conc of the free radical ,

02622621

HCHC rr

02 6232621 HCCHkHCk 6262_162_1 HCkr HCHC

623262_2 HCCHkr HC 3CH

2

13

2

k

kCH



Adding this 2 equations…..



get… 0

525622 HCHC rr

Substituting for conc in the rate laws…..

623262_2 HCCHkr HC

25252_552_5 HCkr HCHC

02

5256232 HCkHCCHk where…



PSSH solution…..

from

2/1

623

5

252

HCCHk

kHC

52HC

02

5256232 HCkHCCHk

where…

Solving for gives us,

2/1

62

52

2152

2

HCkk

kkHC

2

13

2

k

kCH

2/1

62

5

152

2

HCk

kHC



52HC

where…

Substituting for in equation

yields the rate of formation of ethylene;

2/1

62

2/1

5

1352342

2HC

k

kkHCkr HC

52342_3 HCkr HC

2/1

62

5

152

2

HCk

kHC



H

where…

Next, we write the net rate of formation in In terms of concentration,



0624423 HCHC rr 52342_3 HCkr HC

62462_4 HCHkr HC 0624523 HCHkHCk

Using eq to substitute for gives the

conc of the hydrogen radical

2/1

62

5

152

2

HCk

kHC 52HC

02

624

2/1

62

5

13

HCHkHCk

kk


EXAMPLE 1; PSSH Applied to Thermal Cracking of Ethane ….contfrom

02

624

2/1

62

5

13

HCHkHCk

kk

02

624

2/1

62

5

31

HCHkHCk

kk

2/1

62

2/1

5

1

4

3 2

HC

k

k

k

kH



Rate of disappearance of ethane is

6262_162_1 HCkr HCHC

623262_2 HCCHkr HC

62462_4 HCHkr HC

62462326262_162HCHkHCCHkHCkr HCHC

Where,



Substituting for the concentration of free radicals, the rate law of disappearance of ethane is….

2/1

62

2/1

5

13621162

22 HC

k

kkHCkkr HC

2/1

62

2/1

5

1

4

3 2

HC

k

k

k

kH

2

13

2

k

kCH

62

2/1

62

2/1

5

1

4

3462

2

126262_162

22HCHC

k

k

k

kkHC

k

kkHCkr HCHC

62462326262_162HCHkHCCHkHCkr HCHC

Where,


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).


BIOLOGICAL REACTIONS

•BIOREACTORS

Lab Scale Bioreactor

Industrial Scale Bioreactor

http://en.wikipedia.org/wiki/File:Bioreaktor_quer2.jpg


Fermentation Process


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)


Biotechnological Processes Of Growing Microorganisms In A

Bioreactor1)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.


Biotechnological processes of growing microorganisms in a bioreactor


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)


Advantages of Batch Culture VS Continuous Culture

1) Products may be required only in a small quantities at any given time.

2) Market needs may be intermittent.3) Shelf-life of certain products is short.4) High product concentration is required in broth for

optimizing downstream processes.5) Some metabolic products are produced only during the

stationary phase of the growth cycle.6) Instability of some production strains require their

regular renewal.7) Compared to continuous processes, the technical

requirements for batch culture is much easier.


Fermentation Technology

• What is it important to know the kinetics of the reaction in the fermenter?


Typical pattern of growth cycle during batch fermentation

I. Lag phaseII. Acceleration phaseIII. Exponential (logarithmic)

phase IV. Deceleration phaseV. Stationary phaseVI. Accelerated death phaseVII. Exponential death phaseVIII. Survival phase

From: EL-Mansi and Bryce (1999)Fermentation Microbiology and Biotechnology.

Cell Growth


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 1@> nutrients limits cell growth)•Net growth = 0•Fermentation product produce.

•Decrease in live cell conc occur.•Results of toxic by-product


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;

cg Cr )./(__ 3 sdmgrategrowthcellrg

)(__ 1 srategrowthspecific

)/(_ 3dmgionconcentratcellCc

Where,


Rate Laws...cont...

Specific cell growth rate can be expressed as,

1

max ,

s

CK

C

ss

s

)(___max__ 1

max

sratereactiongrowthspecifica

)/(tan__ 3dmgtconsmonodtheK s

)/()( 3dmgionconcentratnutrientsubstrateCs

Where,


Rate Laws...cont...

Combine ,

1

max ,

s

CK

C

ss

s

Will get,

cg Cr and

ss

csg CK

CCr

max 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,

1

max 3.1 h35 /102.2 dmmolXK s

cg Cr maxPlz refer ERT 104 Bioprocess Eng Principle


Thank You

ert 208/4 reaction engineering: bioreaction in bioreactors by; mrs haf iza bint i shu kor ert 208/4...

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