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Credit to Ms Nor Faeqah IdrusReference: Fogler and Levenspiel

TOPIC 9

Solid Catalyzed Reactions

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Solid Catalyzed Reaction

Reaction rates are usually expressed in terms ofmass of catalyst loading.

The design equations can be derived in a mannersimilar to those for homogeneous reactors - by using

mass (w) instead of volume (V).

Examples of solid catalyzed reactions:

Steam Methane Reforming (SMR) for HYDROGEN production Conversion of NOx and CO in automobile catalytic converter

Styrene production

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in mol/timemass of catalyst)( 'Ar

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Reactors for Heterogeneous

Reactions Packed bed reactor

Fluidized bed (FCC)

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Packed Bed Reactor

Similar to PFR, but reactor is packed with catalyst Heterogeneous reactionredefine rate of reaction

as Number of moles reacting per unit time per unit

mass of catalyst.

Mole Balance: [flow in] - [flow out] + [generation] = [accumulation]

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j

jW F

F r

dFWdW

j

j'

0 0

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Applications of PBR When is it used?

Heterogeneous reactions

E.g.catalytic converter

Advantages

Easy to maintain (no moving parts) High conversion per mass of catalyst

Disadvantages

Difficult to control temperature

Can get channeling of packed bed Catalyst is difficult to replace

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Stirred Batch Reactor

Catalyst dispersed as slurry There is good contact between the catalysts

and reactants.

However, if the catalyst decays, the activity and

selectivity will vary during the course of datacollection.

Since the system is well mixed, its isothermalityis good.

Sampling can be problematic, because thecatalyst may go along with the sample.

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Differential Reactor

It is a tube containing a small amount of catalyst

arranged in the form of a thin wafer or disk. Conversion in the reactor is extremely small and

hence, it is called a differential reactor.

The concentration in the reactor is assumed to be

uniform in the catalyst bed. Heat release per unit volume is low, and hence the

reactor behaves isothermally.

Channeling must be avoided

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FA0 FAe

Catalyst Bed

Inert Filling

Catalyst weight =W

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Differential Reactor

Mole Balance

For constant volumetric flow rates

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0)(0 WrFF AAeA

W

FFr AeAA

0)(

W

CvCvr AeAoA

0)(

W

F

W

XFr

pAA

0)(

W

Cv

W

CCvr

poAeAoA

][)( 0

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References Fogler, H.S. (2006). Elements of Chemical Reaction

Engineering, 4thEdition, New Jersey: Prentice Hall.

Levenspiel, O. (1999). Chemical Reaction

Engineering, 3rdEdition, New York: John Wiley.

Schmidt, L.D. (2005). The Engineering of ChemicalReactions, 2ndedition, New York: Oxford University

Press.

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BACK UP

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12

General Mole Balance for Packed Bed

Reactors

Input - Output + Gen =

Accumulation

w w+w

0)( '

wrFFAwwAwA

)( 'AwwAwA r

w

FF

)( 'AAO r

dw

dXF

wAF wwAF

Mass of catalyst = w

XX

X A

A

r

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0

'0

)(

)( 'AA rdw

dF