monolith multiphase 2012

7/21/2019 Monolith Multiphase 2012

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Monolith reactors - 1

Monoliths as G-L-S reactors

Book:“Structured Catalysts and Reactors” (2nd edition) - 2006 A. Cybulski and J.A. Moulijn, Taylor and Francis – Boca Raton

Multiphase Reactors 6PE20




History

Mono = one, single Lithos = stone

Concise Oxford (1995)

Webster (1991)

IntroductionMultiphase Reactors 6PE20




History

• Automotive Catalytic Converters

• Monolith Key Features: – no attrition

– high surface area – low pressure drop – rapid light-off

pellet filled catalytic converter

monolith catalytic converter





History

Matsumoto et al., 1993US 5266543

Air Purification





Structured ReactorsDriving forces

• Pressure drop

• Mass transfer

• Counter Current operation• Surface area

• Catalyst Efficiency

• Fluid distribution• Catalyst Separation





Ceramics: Cordierite, alumina, titania, silicaMetal

Sulzer

Packing Foams

Structured Packings-Appearance

Monoliths



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200 cpsi 400 cpsi 600 cpsi

1.80/0.27 mm1934 m2/m3 = 0.74

1.27/0.16 mm2678 m2/m3 = 0.75

1.04/0.11 mm3348 m2/m3 = 0.79

Monoliths - Cell density

1 cm




Sphere

Monolith

0.1 1 10 10010

100

1000

10000

100000

d

a

(mm)

(m2/m3)

75.0;4

V

c

V M d

a

6.0;6

S

S

S S d

a

1 S V

void solid

a

d

Specific Surface Area




0 2 4 6 8 10 300

1000

10000

10-5

10-4

10-3 Cylinder

Quadrulobe

Monolith

Sphere

Acat /V bed (m2/m3)

D (mm)

Diffusion length

D (m)

D(m2 /s) 10 mm 1 mm 0.1 mm 0.01 mm 0.001 mm

unconfined gas 10-50.5 s 50 ms 0.5 ms 0.005 ms 50 ns

unconfined liquid 10-950 ks 500 s 5 s 50 ms 0.5 ms

liquid in catalyst pore 10-10500 ks 5 ks 50 s 0.5 s 5 ms

liquid in zeolite pore 10-115 Ms 50 ks 500 s 5 s 50 ms

diffusion length

Estimated diffusion time

D

l D D

2

2

Geometric surface area and diffusion lengthfor catalytic reactors

No longer a fixed ratio

between catalyst particle

size and diffusion length!!




0 2 4 6 8 10 300

1000

10000

10-5

10-4

10-3 Cylinder

Quadrulobe

Monolith

Sphere

Acat /V bed (m2/m3)

D (mm)

Diffusion length

D (m)

Geometric surface area and diffusion lengthfor catalytic reactors

Conventional (non-structured) packings:

The price you payfor shorter diffusiondistances is thepressure drop (=energy costs)!




Structure in catalyst application

m dm cm mm mm nm Å

1 10-1 10-2 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10

Dimensions in catalytic reactor

Regular arrangement

decoupling

optimal reactor performance

‘monoliths’

zeolite pores

monolith channels

washcoat thickness

macropores

mesopores

zeolite crystals

metal crystallites




Monolithic Reactors

Advantages• No filtering of catalyst necessary• No attrition of catalyst• Low pressure drop

• High geometric surface area• Efficient mass-transfer• In the case of internal diffusion limitations:

more efficient use of catalyst dueto thin catalytic layer

DisadvantageLittle practical experience in multi-phase applications




Flow regimes in Monoliths

• Co current

• Counter current

u s,L

u s,G

gasliquid




Film flow • counter- and co-current

operation• high gas throughputs• low pressure drop

• high catalyst load• high S/V ratio• short diffusion length

Monolith

Reactor

Hydrodynamic regimes in monoliths

Taylor flow• co-current

• low pressure drop• high surface area• high mass transfer• plug flow behaviour• egg-shell catalyst




Gas

L i q u i d

L i q u i d

Film flow • counter- and co-current

operation• high gas throughputs• low pressure drop

• high catalyst load• high S/V ratio• short diffusion length

Monolith

Reactor

Hydrodynamic regimes in monoliths

Taylor flow• co-current

• low pressure drop• high surface area• high mass transfer• plug flow behaviour• egg-shell catalyst




monolith wall

Gas-liquid-solid system - monolith

porous support

active

component

zeolite

g a s e s

l i q ui d s




washcoating polymer coating

Catalyst preparation

AluminaSilica

Carbon

Cordierite




Co-Current Applications

(Taylor Flow)




S r

Mass Transfer in Taylor Flow

• Four mass-transfer steps

G/LG/SL/S

liquid circulation

thin liquid film

Internal mass transfer

thin walls

Assume liquid in slugs = ideally mixed


M T f i T l Fl



Mass Transfer in Taylor FlowGas-Solid

G/Sd

‘Direct’ fast supply of gas to catalyst

Film thickness d L slug Lbubble

uTP =u L,s+uG,s



Mass Transfer in Taylor FlowGas-Liquid

slug bubbleUC L L L

Saturation of liquid slugs with gas

OFA

LU U

s g s L

b

,,

(OFA=open frontal area)

For gas absorption mass transfer via film is also important!

G/L




Mass Transfer in Taylor FlowLiquid-Solid

Transfer from liquid slugs to solid

D

d k Sh

Mass transfer of both liquid reactant (product) AND dissolved gas

L/S





Mass Transfer in Taylor FlowInternal Mass Transfer

S r

Internal mass transfer

eff D

k

L

• Approximate using Thiele modulus (calculate efficiency) – recommended• Or calculate concentration profile in wall





S r

Mass Transfer in Taylor Flow

G/L G/SL/S

• Simplify by assuming ideal plug flow behavior (nomixing between slugs)

• Assume equal distribution over channels• Complexing factor:

• Change in bubble volume by pressuredifferences or consumption of gas

More details:Kreutzer et al. Chem.Eng.Sci. 56 (2001) 6015-6023

Chem.Eng.Sci. 60 (2005) 5895-5916





Pressure drop

(single phase water flow)

(m/s)

(Pa/m)

• Monolith

• Sphere – packed bed

Laminar Channel Flow

Ergun Equation

(mm)

Re

16;

4

2

1 2

f d

V f L

p

2

2

3

2

2 )1(75.1)1(150V

V

S V

V

S d V

d V

L p

m





Unstable !

0

L

p

0

L

p

L= 0.9 0.8 0.7 0.6 0.5

0.4

0.3

0.2

0.1

U Gs / m s-1

U Ls / m s-1

0 1

0

1

0

0

Flow map for Taylor flow

High gas and

liquid

velocitiesrequired for

stable

operation !!!

Check you are in a

stable operating regime

when designing a

monolithic reactor!!





Gas-liquid distribution

Foam layer cruc ial

no gas supply

maldistributiongas bubbles

proper distributionclear liquid

exit

inlet


M T f li it d ti




Mass Transfer limited reaction:

a-Methylstyrene hydrogenation

• Efficient catalyst use

• Excellent mass transfer

Monolith (Taylor flow)

Trickle bed

400 600200

0

1

2

3

4

5

6

7

R

e a c t i o n r a t e ( m o l / s / X )

m 3 reactor m 2

ext. cat.

*1000

g catalyst

*100

g Ni

Monolith (only liquid)

400

CH2

CH3

+ H2

CH3

CH3

CH2

CH3

+ H2

CH3

CH3

CH2

CH3

+ H2

CH3

CH3





Selectivity Improvement

Benzaldehyde hydrogenation

Ni/g-Al2O3 410 K15 bar

• Batch – slurry , monoliths or extrudates

– slurry < 50 µm, monolith 4 cm Ø, extrudates 1.7x 5mm

• Pilot – monoliths 1 cm Ø - variation cell density

– trickle bed 4.7 cm Ø, extrudates 1.7x 5 mm

OH

+ H2

OHH2

H2+

CH3OH

+ H2

OHH2

H2+

CH3





Batch reactor - monolith

0

5

10

15

20

25

30

35

0 100 200 300 400

Time (min)

C o n c e n t r a t i o n ( a . u . )

benzaldehyde

benzylalcohol

toluene

Little mass transfereffect: high

selectivity possible





0

40

80

120

160

0 1 2 3 4

Time (h)

C o n c e n t r a

t i o n ( m o l / m 3 ) benzaldehyde

benzylalcohol

toluene

Pilot reactor - trickle bed

•Internal mass transfer•Stagnant zones•Non-ideal plug flow





pu re feed

600

Monolith

Trickle bed

400

Slurry

Batch CSTR Pilot Industrial

dilu ted feed

Benzaldehyde hydrogenation -selectivities

rates up to 2.5 mol / mR 3 s

at 50% conversion

99.5 99.5

90

94

73

96 94

S e l e c t i v i t y

70

80

90

100 97.5





Taylor-flow - Summary

• Only co-current

• Very high mass transfer rates

• Stable operation only at high superficialvelocities

• Gas-liquid ratio between 1:3 and 3:1

Most suited for fast reactions





Counter-Current Applications

(Film Flow)





gas liquid

Flooding !cocurrentcountercurrent

Co-current, counter-current?????

Countercurrent:• Equilibrium reaction with gas phase reactant / product• Inhibition by gas phase product


Counter-current gas/liquid flow; how to avoid




GasLiquidCatalyst

reactants products

liquid exit phenomena

Wavy Annular

Film Flow

gas liquid

Counter-current gas/liquid flow; how to avoidflooding???





a=50o a=70o a=70o

a=70o 0.0 1.0 2.0 3.0

0.00

0.01

0.02

0.03

0.04

entrance

flooding

exit

flooding

Typical

region TBR

annular

slug

flow

Finned Unfinned

uGs (m/s)

u L s

( m / s )

Flooding - influence outlet geometry

Liquid superficial velocities are low!


Monolith




0.00 0.50 1.00 1.50 2.000.00

0.02

0.03

0.05

0.06

0.08

u s ,L

u s ,G

0.00 0.50 1.00 1.50 2.000.00

0.02

0.03

0.05

0.06

0.08

u s ,L

u s ,G

0.00 0.50 1.00 1.50 2.000.00

0.02

0.03

0.05

0.06

0.08

u s ,L

u s ,G

special IFM

▲ special square 70o tapered Sulzer Mellapak

MonolithComparison

Flooding

, air/decane, 25 cpsi IFM,▲ air/water, 50 cpsi square

Data from Lebens (1999) and Heibel (1999)

250 Y

125 Y

170 Y

Sulzer Mellapak





F z F z F

F g L p

y u

x u

2

,2

2

,2

Momentum balance for:

• developed laminar flow in both phases• Newtonian rheology• no slip at all interfaces (G-L, L-S, G-S)• “corner -flow” due to surface tension forces

High liquidvelocity

A x i a l v e l o c i t y [ m / s ]

0.60

0.45

0.30

0.15

0.00

Low liquidvelocity

Hydrodynamics - velocity profiles

Significant velocity profile !Multiphase Reactors 6PE20




Liquid

2.0

1.0

0.0 V e l o c i t y [ m / s ]

Gas

Hydrodynamic model

uLS = 2.9 cm/sLiq. = 12 %

Pwet = 75%

uLS = 0.57 cm/s

Liq. = 5.5%

Pwet = 50%

A

x i a l v e l o c i t y

[ m / s ]

0.60

0.45

0.30

0.15

0.00

Significant RTD for gas and liquid!!


Residence time distribution




t (s)

0 10 20

Et(1/s)

0.0

0.1

0.2

0.3

0.4

0.0 1.0 2.0 3.0

E

0.0

0.5

1.0

1.5

2.0

Residence time distribution

W AVE/

M ALDISTRIBUTION L AMINAR

FILM SUBSTRATE

wateruLs = 0.020 m/su

Ls = 0.025 m/s

uLs = 0.030 m/s

• Laminar flow leads to strong tailing of the RTD• Short residence time, due to wave formation & maldistribution• Lower RTD expected for organic liquids at industrial conditions





0.00 0.05 0.10

Sh

0

5

10

15

Average G/L mass transfer results

k GLa derived from experiments

a derived from hydrodynamicmodel

Sh determined from k GL andmaximum film thickness (dFm)

Sh

Sh k d

D

zD

d u

L Fm

L

L

Fm Lm

104 0 35 0 63

2

. .

;

.

uGs=0.24 - 0.47 m/s

uGs=0.71 - 0.95 m/s

model





0

50

100

150

200

250

300

350

400

450

0 2 4 6 8

Length (m)

C o n c e n t r a t i o n ( m o l / m 3 )

Ester

Water

Countercurrent

Cocurrent

No Stripping

(calculated)

Effect of stripping in IFM reactor

O H O H

O

O

O

+

+ H2O





Reactive stripping - Modeling Modeling of reactive stripping in monolithic configuration using FallingLaminar Film Flow Model (Lebens et al , 1999) and obtained kinetic data:

Reactor Length 8 mBEA loading 10 wt%Gas (sup. vel.) 5 cm/sLiq (sup. vel.) 1 cm/s

Results:Conversion (%) Selectivity (%)

Counter-current 98.7 95.2

Co-current 94.8 94.7

No stripping 82.1 94.6





Film Flow - Summary

• Laminar flow• Mass transfer relatively slow (diffusion)

• Residence time distribution

• Low liquid superficial velocities• Flooding risk at exit

• Counter Current operation !!!





Film-Flow monoliths - References• Gas and liquid distribution in the monolith film flow reactor

A. K. Heibel, F. J. Vergeldt, H. van As, F. Kapteijn, J.A. Moulijn and T. Boger AIChE Journal, Volume 49, (2003), Pages 3007-301

• Flooding performance of square channel monolith structures A. K. Heibel, F. Kapteijn and J. A. Moulijn - Ind.Eng.Chem.Res. 2002, 41, 6759-6771

• Influence of channel geometry on hydrodynamics and mass transfer in the monolith filmflow reactor

A. K. Heibel, J. J. Heiszwolf, F. Kapteijn and J. A. Moulijn

Catalysis Today, Volume 69, Issues 1-4, 15 September 2001, Pages 153-163 • Gas –liquid mass transfer in an internally finned monolith operated countercurrently in thefilm flow regime P. J. M. Lebens, J. J. Heiszwolf, F. Kapteijn, S. T. Sie and J. A. MoulijnChemical Engineering Science, Volume 54, Issue 21, November 1999, Pages 5119-5125

• Hydrodynamics and mass transfer issues in a countercurrent gas-liquid internally finnedmonolith reactor

P. J. M. Lebens, M. M. Stork, F. Kapteijn, S. T. Sie and J. A. MoulijnChemical Engineering Science, Volume 54, Issues 13-14, July 1999, Pages 2381-2389

• Potentials of internally finned monoliths as a packing for multifunctional reactors P. J. M. Lebens, F. Kapteijn, S. T. Sie and J. A. MoulijnChemical Engineering Science, Volume 54, Issue 10, May 1999, Pages 1359-1365


Novel Monolithic reactor designs

http://www.dct.tudelft.nl/race/research/publications/abstracts2003/200322.html



























• External recycle - liquid

• Internal recycle - gas

Exothermal systems

High rates - Low conversions

Liquid Gas


Co-current Monolithic reactor






vertical mode:

Staging possible

Cross-, co- and countercurrent

Liquid phase reactions

horizontal mode:


Monolithic Stirrer reactor





H2O2 decompositionin a rotating monolith reactor





Novel Monolithicreactor designs

Cross-Flow

module




Monoliths - Summary

Small Channel

• Co-Current

• Plug flow (Taylor flow)

• High velocities• High mass transfer

rates

• Low catalyst amount• Low P

• Fast reactions

Large Channels

• Counter-currentpossible

• Film flow• Low velocities

• Higher amount of

catalyst• Low P

• Slow(er) reactions

monolith multiphase 2012

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