catalysis and catalysts - catalyst performance testing 1 stages in catalyst development preparation...

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


Transport Phenomena inPacked-bed Reactor

Transport Phenomena inPacked-bed Reactor

PLUG FLOW MIXINGDISPERSION

DIFFUSIONREACTIONTRANSPORT PHENOMENA


Catalytic Reaction EngineeringCatalytic Reaction Engineering

Kinetics

Mechanism Stability

ReactorEngineering

Catalyst

TransportPhenomena

CATALYSISENGINEERING


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


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.


Pep versus Rep Pep versus Rep

ax

pp

ax

b

D

udPe

D

uLPe


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


Catalyst sizeCatalyst size

Practical catalyst:

often: dp = 1 - 3 mm

large reactor needed

Option: dilution with inerts


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


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


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

,


Dilution with InertsDilution with Inerts

Hydrodynamics governed by small inert particles

Kinetic performance governed by catalyst extrudates


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


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)


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:


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


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)


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


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


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 ')(,


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


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?


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


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

'


Catalyst EffectivenessCatalyst Effectiveness

0 1

1

i

i

i tanh

Slab:

Limits:

1st order

0.1 1 10

0.1

1


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


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


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




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


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


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


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



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



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


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


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


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 *


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


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’


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


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


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

catalysis and catalysts - catalyst performance testing 1 stages in catalyst development preparation...

Documents

h catalyst

catalyst extrudates

catalyst fraction

p slide

small amounts of catalyst

larger amounts of catalyst

h slide

inerts slide