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8/13/2019 CRE II L 12
1/13
L12 CRE II Heterogeneous
Catalysis
Prof. K.K.Pant
Department of Chemical EngineeringIIT Delhi.
mailto:[email protected]:[email protected]8/13/2019 CRE II L 12
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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