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L12 CRE II Heterogeneous

Catalysis

Prof. K.K.Pant

Department of Chemical EngineeringIIT Delhi.

kkpant@chemical.iitd.ac.in

mailto:kkpant@chemical.iitd.ac.inmailto:kkpant@chemical.iitd.ac.in

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Exercise: Al2O3n-pentane i-Pentane

Suggested Mechanism:

N + N

N+ I+ II +

Rate laws for each of the steps:

NAVNA kpkAdsorptionofrateNet

vISvNS kkreactionSurfaceofrateNet

VIDID pkkDesorptionofrateNet

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Case-1

Case-2

NSANA

eq

INSAD

NpKKpK

K

ppKKk

r

1

)(

2)/1(

)(

DINA

eq

INAS

NKppK

K

ppKk

r

D

I

DS

I

eq

INA

N

K

p

KK

p

K

ppk

r

1

)(

NApkr 0

20

)1( NA

NAS

pK

pKkr

Case-3 NSANA

NSAD

pKKpK

pKKkr

10

n-pentane (N) i-Pentane (I)

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EXERCISE

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How to verify whether the rate law confirmsto experimental data or not ??

D

BCA

eq

BPCAS

C

K

ppK

KpppKk

r

1

)(

AS

D

BCA

C

eq

BPC

Kk

KppK

r

Kppp

1

BC

C

eq

BPC

cpbpar

Kppp

Use regression

How to decide whether the fit is reasonable??

If the fit is reasonable, evaluate theconstants

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Design of Fixed Bed Reactor:

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Design Equation (Reading Assignment Ch.10 (10.4 -10.6 ) Fogler IV

General Mass Balance Equation:

Rate of input = rate of output + accumulation+ rate of disappearance

FA= FA+ dFA+ 0 + (-rA) dW

- dFA= (-rA) dW

FA0 dxA= (-rA) dW

dW

AA rdWdF /

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Ax

AAA rdxFW0

0 //

General design equation for a FBR:

dt

dN

WWeightunittimeunit

ddisappeareAofMolesr AA

1

))((

Definition of rate of reaction:

When the rate is expressed in terms of catalyst weight,mass transfer effects between the catalyst and the bulkfluid & also within the catalyst are ignored. Such masstransfer aspects could be important in some cases.

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Fixed Bed Reactor Integral form

Ax

AAA rdxFW0

0 //

1 /-rA

xA

W / FA0

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Fixed Bed Reactor differential form

AA rdWdF /

FA

W

-rA xA

W/FA0

-rA

AAA rdWdxF /

0

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How to find the rate data ??

How can we calculate the weight of

the catalyst needed for obtaining thegiven conversion ??

D

BAA

eq

BCAAS

A

K

ppK

K

pppKk

r

1

)(

Ax

AAA rdxFW0

0 //

Express the partial pressures in terms of xA

AA

A

A

A

x

x

p

p

1

1

0 AA

AR

A

R

x

xarM

p

p

1

)/(

0

)( AA xfr Use numerical / graphical integration

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Finding a Mechanism consistent with the experimental data

Deducing Rate law from experimental data (Example 10.2 , 10.3:

Example : Hydrodemethylation of Toluene

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Use of Multiple regression technique (Rate or CONVERSION Data from

Differential reactor identical to CSTR)

Y = a0+ a1X1J+ a2X2J

A0

, a1

are the parameters of the model.

Use regression methods / Polymath, MATLAB,etc.

k, KB, KT are the parameters of the equation

Evaluation of Rate law Parameters