catalysis and catalysts - catalyst performance testing 1 stages in catalyst development preparation...
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Catalysis and Catalysts - Catalyst Performance Testing 1
Stages in Catalyst developmentStages in Catalyst development
Preparation
Screening
Reactionnetwork
Kinetics
Life tests
Scale-up
Increasing: time money reality
Optim
ization
Optim
ization
Trends: Parallel activitiesSubcontracting
Catalysis and Catalysts - Catalyst Performance Testing 2
Transport Phenomena inPacked-bed Reactor
Transport Phenomena inPacked-bed Reactor
PLUG FLOW MIXINGDISPERSION
DIFFUSIONREACTIONTRANSPORT PHENOMENA
Catalysis and Catalysts - Catalyst Performance Testing 3
Catalytic Reaction EngineeringCatalytic Reaction Engineering
Kinetics
Mechanism Stability
ReactorEngineering
Catalyst
TransportPhenomena
CATALYSISENGINEERING
Catalysis and Catalysts - Catalyst Performance Testing 4
Classification of Laboratory Reactors:Mode of Operation
Classification of Laboratory Reactors:Mode of Operation
LABORATORY CATALYTIC REACTORS
Steady state Transient
Batch Semi-batch DiscontinuousContinuous flow
Plug flow
Integral Differential
Mixed flow
Single pass Recycle Fluidization
External Internal
Step Pulse
Packed bed
Riser reactor Thermobalance
TAPMultitrack
Berty reactor Fluid bed
Slurry
Catalysis and Catalysts - Catalyst Performance Testing 5
Classification of Laboratory Reactors:Contacting Mode
Classification of Laboratory Reactors:Contacting Mode
1 2 3 4
5 6 7 8
PFR CSTR FBR Slurry/FBR with recycle
Riser Riser FBR Slurry/FBR fluid recycle contn. cat feed fluid + cat. rec.
Catalysis and Catalysts - Catalyst Performance Testing 6
Pep versus Rep Pep versus Rep
ax
pp
ax
b
D
udPe
D
uLPe
Catalysis and Catalysts - Catalyst Performance Testing 7
Maximum allowable particle diameter versus (1 - x)n = 1, single phase, Pep = 0.5
Maximum allowable particle diameter versus (1 - x)n = 1, single phase, Pep = 0.5
0.01
0.1
1
10
0.01 0.1 1
(1 - x)
dp
(m
m)
Lb = 100 mm
Lb = 10 mm
Lb = 1 mm
dt = 1 mm
dt = 50 mm
dt = 5 mm
xPe
n
d
L
pp
b
1
1ln
8 10p
t
d
d
1 - x
dp (
mm
)
dt = 50 mm
dt = 5 mm
dt = 1 mm
Catalysis and Catalysts - Catalyst Performance Testing 8
Catalyst sizeCatalyst size
Practical catalyst:
often: dp = 1 - 3 mm
large reactor needed
Option: dilution with inerts
Catalysis and Catalysts - Catalyst Performance Testing 9
Determined by friction and gravity– particle diameter– viscosity
– linear velocity (from LHSV and Lb)
Example– LHSV = 2 m3 / (m3h)
Catalyst wetting in trickle-flow reactorsCatalyst wetting in trickle-flow reactors
62
105
gd
uW
p
lltr
Catalysis and Catalysts - Catalyst Performance Testing 10
Catalyst wetting in trickle-flow reactors, ExampleCatalyst wetting in trickle-flow reactors, Example
LHSV = 2 m3/m3h
l = 10-6 m2/s
dp = 1 mm
66
6
105101010
10
lltr
uuW
ul = LHSV.Lb = 2 Lb m/h
Lb > 90 mm
Catalysis and Catalysts - Catalyst Performance Testing 11
Maximum allowable particle diameter versus kinematic viscosity for complete wetting in trickle-flow reactors
Maximum allowable particle diameter versus kinematic viscosity for complete wetting in trickle-flow reactors
LHSV = 2 m3 / (m3h)
62
105
gd
uW
p
lltr
0.1
1
10
1.00E-07 1.00E-06 1.00E-05
l (m2/s)
dp (m
m) L b = 1000 mm
L b = 100 mm
L b = 10 mm
b
l
b
l
reactor
lv
L
u
AL
Au
VLHSV
,
Catalysis and Catalysts - Catalyst Performance Testing 12
Dilution with InertsDilution with Inerts
Hydrodynamics governed by small inert particles
Kinetic performance governed by catalyst extrudates
Catalysis and Catalysts - Catalyst Performance Testing 13
Maximum allowable particle diameter as a function of the catalyst fraction in a diluted bed
Maximum allowable particle diameter as a function of the catalyst fraction in a diluted bed
0.01
0.1
1
10
0.1 1fraction catalyst (1-b)
dp (m
m)
xn
Lb = 1 mm
xn
Lb = 10 mm
xn
Lb = 100 mm
05.0221 0
L
dxnb
L
dxn
b
b
x
xx p
b
p
bedundiluted
bedundilutedbeddiluted
Catalysis and Catalysts - Catalyst Performance Testing 14
Effect of Catalyst/Diluent Distribution in Decomposition of N2O
Effect of Catalyst/Diluent Distribution in Decomposition of N2O
0.0
0.2
0.4
0.6
0.8
1.0
600 650 700 750 800 850 900
T (K)
X(N
2O)
Catalysis and Catalysts - Catalyst Performance Testing 15
Laboratory ReactorsLaboratory Reactors– deactivation noted directly– small amounts of catalyst needed– simple– yields conversion data, not rates
– larger amounts of catalyst and flows needed– deactivation not determined directly– direct rate data from conversions
– non-ideal behaviour– continuous handling of solids possible
– limited to weight changes– careful date interpretation needed– often mass-transfer limitations
– catalyst deactivation hard to detect– yields conversion and selectivity data quickly over large range
PFR:
CSTR:
FBR:
TGA:
Batch:
Catalysis and Catalysts - Catalyst Performance Testing 16
Mass and heat transport phenomena– Extraparticle transport
– Intraparticle transport
Catalyst effectiveness Generalizations
– Catalyst shape, kinetics, volume change
Observable quantities– Criteria - transport disguises - experimental
Mass and heat transport effectscatalyst particles
Mass and heat transport effectscatalyst particles
Catalysis and Catalysts - Catalyst Performance Testing 17
T
c
Exothermic
T
c
Endothermic
Gas film
Bulk gas
Ts Tb
c sc b
T
c
Exothermic
Liquid filmGas film
Bulk liquid
Bulk gas(bubble)
Catalysis and Catalysts - Catalyst Performance Testing 18
Gradients at Particle ScaleGas/solid Reactor
Gradients at Particle ScaleGas/solid Reactor
T
c
Exothermic
T
c
Endothermic
Gas film
Bulk gas
Ts Tb
CsCb
Catalysis and Catalysts - Catalyst Performance Testing 19
T
c
Exothermic
Liquid filmGas film
Bulk liquid
Bulk gas(bubble)
Gradients at Particle ScaleGas/liquid/solid Slurry Reactor
Gradients at Particle ScaleGas/liquid/solid Slurry Reactor
Catalysis and Catalysts - Catalyst Performance Testing 20
Isothermal - External Mass TransportIsothermal - External Mass Transport
vpsbfp rVcckA
reactionmass transfer
cs
cbfilm layer
No transport limitations if:
cs cb
When?How to determine cs?When?How to determine cs?
sbfsvobsv cckacrr ')(,
Catalysis and Catalysts - Catalyst Performance Testing 21
Isothermal - External Mass TransportIsothermal - External Mass Transport
ef b s p
v b b p
k c c A
r c T V
observed raterate at bulk fluid conditions ( , )
b
sb
bf
sbf
bf
obsv
c
cc
cka
ccka
cka
rCa
)(
'
)('
',
Catalyst effectiveness:
Observable quantity:
0.001 0.01 0.1 10.01
0.1
1
10
n =
-1
0.5
1
2
Ca
e 05.011 n
e Ca
nCa
05.0
rV = kVCn
Catalysis and Catalysts - Catalyst Performance Testing 22
Nonisothermal - External TransportNonisothermal - External Transport
bb
bfre
eb
s
T
T
hT
ckH
CaT
T
max)()(
1
cc
Cas
b
1
Mass: sbobsvr
sbfobsv
TTharH
cckar
')(
'
,
,
Heat:
T and c coupled via
max. T-rise over film
Catalyst effectiveness?
T and c coupled via
max. T-rise over film
Catalyst effectiveness?
Catalysis and Catalysts - Catalyst Performance Testing 23
Nonisothermal - External TransportNonisothermal - External Transport
05.011exp)(
)(
)(
)(
)(
)(
),(
),(
s
b
b
a
bv
sv
b
s
bv
sv
bbv
ssve T
T
RT
E
Tk
Tk
cf
cf
Tk
Tk
Tcr
Tcr
05.0'
)( ,
bf
obsv
b
bfr
b
aeb cak
r
Th
ckH
TR
ECa
Series expansion:
General kinetics: Ca small
Catalysis and Catalysts - Catalyst Performance Testing 24
Isothermal - Internal Mass TransportIsothermal - Internal Mass Transport
SlabMass balance, steady state diffusion & reaction
02
2
ckdx
cdD veff
x L c c
xdcdx
s
0 0
1st order irreversible:
c cx L
scosh( / )
cosh( )
Boundary conditions:
Lk
Dv
eff
xx+dx
0L
x*
1.0 0.8 0.6 0.4 0.2 0.00.0
0.2
0.4
0.6
0.8
1.0
c*
0.1
1.0
2.0
10.0
LV
A ap
p
1
'
Catalysis and Catalysts - Catalyst Performance Testing 25
Catalyst EffectivenessCatalyst Effectiveness
0 1
1
i
i
i tanh
Slab:
Limits:
1st order
0.1 1 10
0.1
1
Catalysis and Catalysts - Catalyst Performance Testing 26
Kinetics unknown effectiveness cannot be calculated
Wheeler-Weisz: 21,
22
rate' diffusion'
rate observed n
seff
obsvi cD
rL
15.02
12,2
n
cD
Lr
beff
obsvi 15.0
2
12,2
n
cD
Lr
beff
obsvi
(nth order)
Weisz-Prater Criterion:
Diffusion Control?Diffusion Control?
i 2
i
3rd order
2nd order
1st order
0th order
Catalysis and Catalysts - Catalyst Performance Testing 27
Exothermal Endothermal
c
TTs
cs
Ts
cs
c
T
seffp
seffri T
cDH
,
)(
Typical values:0-0.3 (exothermal)
similar profilesc and T
determined by Prater number
Nonisothermal - Internal TransportNonisothermal - Internal Transport
Catalysis and Catalysts - Catalyst Performance Testing 28
SlabHeat and mass balance, steady state
)(2
2
,
2
2
rveffp
veff
Hrdx
Td
rdx
cdD
x L c c T T
xdc
dx
dT
dx
s s
0 0
Boundary conditions:
xx+dx
0L
2
2,
2
2
)( dx
Td
Hdx
cdD
r
effpeff
cc
DHTT s
effp
effrs
,
)(
seffp
seffri
s
i
T
cDH
T
T
,
max, )(
Prater numbertemperature and concentrationprofile similar (scaling)temperature and concentrationprofile similar (scaling)
Effective conductivity0.1-0.5 J/m.K.s
Nonisothermal - Internal TransportNonisothermal - Internal Transport
Catalysis and Catalysts - Catalyst Performance Testing 29
Nonisothermal - Internal TransportNonisothermal - Internal Transport
05.011exp)(
)(
)(
)(
)(
)(
),(
),(
T
T
RT
E
Tk
Tk
cf
cf
Tk
Tk
Tcr
Tcr s
s
a
sv
v
ssv
v
ssv
vi
0.1 1 100.1
1
10
-0.2
0.2
0.4
0.6i
i
Internal effectiveness factor:
s= 10i varied
Criterion:
1.02
2,
,
iis
seff
obsv
seffp
seffr
s
a
cD
Lr
T
cDH
TR
E
Catalysis and Catalysts - Catalyst Performance Testing 30
Criterion bed T-gradientCriterion bed T-gradient
Analogous to particle T-gradient:
05.01
8
1)(
,,
2,
t
p
whweffb
trobsV
w
a
r
r
BiT
rHr
RT
E
effb
pwwh
dhBi
,,
Compare with:
05.0
2
12,
,
seff
obsv
seffp
seffr
s
a
cD
Lr
T
cDH
TR
E
05.02
2
iis
)1()1(,, brr bobsvobsV
Catalysis and Catalysts - Catalyst Performance Testing 31
Criterion: = 1 ± 0.05Criterion: = 1 ± 0.05
External transfer:External transfer:
Internal transfer:Internal transfer:
nCa
i
05.0
15.02
15.02
12,2
n
cD
Lr
beff
obsvi
Cas
Bim
bf
obsv
cka
rCa
',
Also:Also:
while Bim>~10s=1,2,3 (geometry)
while Bim>~10s=1,2,3 (geometry)
Weisz-Prater more severe than Carberry criterionWeisz-Prater more severe than Carberry criterion
eff
pfm D
dkBi
Mass Transport Limitations?Mass Transport Limitations?
Internal / External
Catalysis and Catalysts - Catalyst Performance Testing 32
Criterion: = 1 0.05Criterion: = 1 0.05
External transfer:External transfer: 05.0 Caeb
Internal transfer:Internal transfer: 1.02 iis
Series expansion of expression around 1 for slab, first order irreversible reaction results in:Series expansion of expression around 1 for slab, first order irreversible reaction results in:
1
1
1exp1
CaCa
eb
ne
strongest influencestrongest influence
External gradient criterion more severe than internal gradient criterionExternal gradient criterion more severe than internal gradient criterion
Heat Transport Limitations?Heat Transport Limitations?
Internal / External
Catalysis and Catalysts - Catalyst Performance Testing 33
Heat Transport Limitations?Heat Transport Limitations?
Largest T-gradient ?
Internal:
External: sb
rfbs cc
h
HkTT
ccHD
TT seffp
reffs
,
)(
For x=0 c=0 largest T-gradient
Ca
Ca
Bi
Bi
T
T
h
m
i
e
1
Bi
Bim
h
e
i
10-104 gas-solid10-4-0.1 liquid-solid
external gradient negligible
Industrial: internal gradient largest
Laboratory: external gradient largest
Internal / External
Catalysis and Catalysts - Catalyst Performance Testing 34
Heat Transport Limitations?Heat Transport Limitations?
External / Bed
18
)1(8
)1()(2
,
,
2
,
2,
b
effb
effp
p
t
eb
weffb
btrobsvw
s
r
r
Ca
T
rHr
Comparison of external and bed gradient
(neglecting wall contribution and bed dilution):
> 100 > 1 ~ 1
Bed gradient criterion more severe than external gradient criterionBed gradient criterion more severe than external gradient criterion
Catalysis and Catalysts - Catalyst Performance Testing 35
3. External mass transfer:3. External mass transfer:
2. Internal mass transfer:2. Internal mass transfer:
bm
m
bfobsv cL
u
Lckar
1,
1'
s
an
sn
seffvchemv
obsv RT
Ec
LcDk
L
rr
2exp
11 2
11,
,
depends on: 1/L, (n+1)/2 reaction order, Eaapp= ½Ea
truedepends on: 1/L, (n+1)/2 reaction order, Eaapp= ½Ea
true
depends on: L, flow rate, 1st reaction order, Eaapp= 0depends on: L, flow rate, 1st reaction order, Eaapp= 0
How to check whether limitations are present?How to check whether limitations are present?
Observed reaction rate:Observed reaction rate: ),(),( ,,, bbchemviebbchemvobsv TcrTcrr
Summary Dependence rv,obsSummary Dependence rv,obs
1. Kinetics:1. Kinetics:nbvbbchemvobsv ckTcrr ),(,,
does not depend on L, n reaction order, Eaapp= Ea
truedoes not depend on L, n reaction order, Eaapp= Ea
true
Catalysis and Catalysts - Catalyst Performance Testing 36
Observed Temperature BehaviourObserved Temperature Behaviour
Catalysed steam gasification of carbon (coke) on Ni catalyst
C + H2O CO + H2
Ni
• p(H2O)=26 kPa• thermobalance• coked catalyst: Ni/Al2O3
0.9 1.0 1.1 1.2 1.3 1.4
1000/T
0.01
0.1
1
5
r(ob
s)
061
164
10.75
0.6
Ea(kJ/mol)
order n
Catalysis and Catalysts - Catalyst Performance Testing 37
Apparent Rate BehaviourApparent Rate Behaviour
Controlling process Apparentorder
Apparentactivation energy
DependenceL
Dependence u
Kinetics n Ea(true) - -
Internal diffusion21n ½ Ea(true) 1/L -
External mass transfer 1 0 Lm-2 * um *
Catalysis and Catalysts - Catalyst Performance Testing 38
1. Particle size variation1. Particle size variation
2. Flow rate variation at constant space time!2. Flow rate variation at constant space time!
particle size
ob
serv
ed
ra
te egg-shell catalysts?egg-shell catalysts?
Diagnostic Tests - Mass-Transport LimitationsDiagnostic Tests - Mass-Transport Limitations
xA,3
W
3
xA,2
W
2
xA,1
W
10
1,AF 0
2,AF 0
3,AF
x
0
1,AF 0
2,AF 0
3,AF
Catalysis and Catalysts - Catalyst Performance Testing 39
What’s observed? intraparticle limitationWhat’s observed? intraparticle limitation
1,
1 nseffv
chemobsv cDk
L
rr
particle size dependent
reaction order (n+1)/2
activation energy: Ea(true)/2
1.90 1.95 2.00 2.05 2.100.001
0.01
0.1
dp/mm
0.38
1.42.4
1000/T
kv
wide pore silicaeffect dp
Limiting case: ‘Falsified kinetics’
Catalysis and Catalysts - Catalyst Performance Testing 40
Proper Catalyst TestingProper Catalyst Testing
Adhere to criteria– Ideal reactor behaviour: PFR or CSTR– Isothermal bed– Absence of limitations: observables, diagnostic tests
Compare catalysts at low conversion;
For high conversions use feed/product mixtures Compare selectivities at same conversion level
Catalysis and Catalysts - Catalyst Performance Testing 41
Consecutive irreversible first order reaction A R S
Consecutive irreversible first order reaction A R S
0
0.2
0.4
0.6
0.8
1
0 20 40 60 80 100
Con
cent
ratio
n
0/ iFW
CA CS
CRSame CR
Catalysis and Catalysts - Catalyst Performance Testing 42
More Efficient Catalyst TestingMore Efficient Catalyst Testing
MFC
MFC
MFC
MFC
MFC
MFC
MFC
MFC
MFC
SV
BPC
P
VENT
ANALYSIS
FEED
• PC-controlled microreactor set-up
• Parallel reactors in one oven: Sixflow reactor set-up
• Experimental design