PERFORMANCE STUDIES OF TRICKLE BED REACTORSPERFORMANCE STUDIES OF TRICKLE BED REACTORS

Mohan R. KhadilkarMohan R. Khadilkar

Thesis Advisors: M. P. Dudukovic and M. H. Al-DahhanThesis Advisors: M. P. Dudukovic and M. H. Al-Dahhan

Chemical Reaction Engineering LaboratoryChemical Reaction Engineering Laboratory

Department of Chemical EngineeringDepartment of Chemical Engineering

Washington UniversityWashington University

St. Louis, MissouriSt. Louis, Missouri

CREL

Trickle Bed ReactorsTrickle Bed Reactors

CATALYST

BED

GAS LIQUID

GAS

LIQUID Re (Liquid)

Re(G

as)

10

100

1000

10000

1 10 100 1000

TRICKLE PULSE

DISP .

BUBBLE

WAVYSPRAY

............. ......... ... .. ... ... ...

Liquid Film or Rivulet

Liquid Filled pores

Dry Pellet

Capillary Condensation

Catalyst Wetting Conditions in Trickle Bed Reactor

Flow Map (Fukushima et al., 1977)

Operating Pressures up to 20 MPaOperating Flow Ranges:High Liquid Mass Velocity (Fully Wetted Catalyst) (Suitable for Liquid Limited Reactions)Low Liquid Mass Velocity (Partially Wetted Catalyst) (Suitable for Gas Limited Reactions)

Cocurrent Downflow of Gas and Liquid on a Fixed Catalyst Bed

Limiting Reactant criterion:

Gas limited reaction if

Liquid limited reaction if

1*

AeA

BieB

CD

CD

D C

D CeB Bi

eA A* 1

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FLOW REGIMES AND CATALYST WETTING EFFECTSFLOW REGIMES AND CATALYST WETTING EFFECTS

DOWNFLOW (TRICKLE BED REACTOR) DOWNFLOW (TRICKLE BED REACTOR) UPFLOW (PACKED BUBBLE COLUMN) UPFLOW (PACKED BUBBLE COLUMN)

100

1000

10000

10 100 1000

Re (Liquid)

BUBBLE (I)

PULSE

BUBBLE (II)

CHURN

PSEUDOSPRAY

PSEUDOPULSE

10

100

1000

10000

1 10 100 1000

Re (Liquid)

TRICKLE PULSE

DISP .BUBBLE

WAVYSPRAY

PARTIAL WETTING COMPLETE WETTING

CATALYSTLIQUIDGAS

(Trickle Flow Regime) (Bubble Flow Regime)

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MotivationMotivation

A clear understanding of the differences between the two modes of operation is needed, particularly for high pressure operation. Are upflow reactors indicative of trickle bed performance under different reaction conditions?

To understand the effects of bed dilution with fines on reactor performance

To develop guidelines regarding the preferred mode of operation for scale-up/scale-down of reactors for gas or liquid reactant limited reactions

Objectives Objectives

Experimentally investigate the performance of DOWNFLOW Experimentally investigate the performance of DOWNFLOW (Trickle Bed) and UPFLOW (Packed Bubble Column) reactors (Trickle Bed) and UPFLOW (Packed Bubble Column) reactors for a test HYDROGENATION reaction for a test HYDROGENATION reaction

Study the effects of PRESSURE, FEED CONCENTRATION and Study the effects of PRESSURE, FEED CONCENTRATION and GAS VELOCITY on the performance of both modes of operationGAS VELOCITY on the performance of both modes of operation

Study the effect of FINES on the performance of the two modes Study the effect of FINES on the performance of the two modes at different feed concentrations and pressuresat different feed concentrations and pressures

Compare MODEL PREDICTIONS with experimental data at Compare MODEL PREDICTIONS with experimental data at different pressuresdifferent pressures

Reaction SchemeReaction Scheme::C CH

CH

2

3

HC CH

CH

3

3

H+2

Pd/Alumina

Limiting Reactant criterion:

B (l) + A(g) P(l)

D C

D CeB Bi

eA A*

1

D C

D CeB Bi

eA A*

1Liquid limited reaction if

Gas limited reaction if

Catalyst : 2.5 % Pd on Alumina (cylindrical 0.13 cm dia.)Fines : Silicon carbide 0.02 cm

Range of Experimentation :

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• Superficial Liquid Velocity (Mass Velocity) : 0.09 - 0.5 cm/s (0.63-3.85 kg/m2s)• Superficial Gas Velocity (Mass Velocity) : 3.8 -14.4 cm/s (3.3x10-3-12.8x10-3 kg/m2s)

• Feed Concentration : 3.1 - 7.8 % (230-600 mol/m3)• Operating Pressure : 30 - 200 psig (3-15 atm)• Feed Temperature : 24 oC

Alpha-methylstyrene cumene

Experimental SetupExperimental Setup

High PressureGas Supply

Feed Tank

Damper

LT

DPT

TT

TT

LT

TT

PT

PT

LT

LTLC

Waste Tank

GasChromatograph

Reactor

Vent

High PressureGas Supply

Solvent

Rotameter

High PressureDiaphragm Pump

Gas-LiquidSeparator

Computer

Demister

PC

PC

PC PC

PC

PC

PC

Distributor

CoolingJacket

Rotameter

Vent

Saturators

Timer

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Downflow and Upflow Experimental Results at Low Pressure Downflow and Upflow Experimental Results at Low Pressure (Gas limited Reaction) without Fines(Gas limited Reaction) without Fines

DOWNFLOW OUTPERFORMS UPFLOW DUE TO PARTIAL EXTERNAL WETTING LEADING TO IMPROVED GAS REACTANT ACCESS TO PARTICLES

0

0.2

0.4

0.6

0.8

1

0 100 200 300 400Space time , s

Con

vers

ion(

X)

UPFLOW

DOWNFLOW

CBi=7.8%v/v, P=30psig

Gas Limited

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Downflow and Upflow Experimental Results at High Pressure Downflow and Upflow Experimental Results at High Pressure (Liquid limited Reaction) without Fines(Liquid limited Reaction) without Fines

UPFLOW OUTPERFORMS DOWNFLOW DUE TO MORE COMPLETE EXTERNAL WETTING LEADING TO

BETTER TRANSPORT OF LIQUID REACTANT TO THE CATALYST

00.10.20.30.40.50.60.70.80.9

1

0 50 100 150 200Space time, s

Con

vers

ion(

X)

DOWNFLOW

UPFLOW

CBi=3.1(v/v)%,P=200psig

Liquid Limited

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ABOUT EQUAL PERFORMANCE DUE TO COMPLETE WETTING

00.10.20.30.40.50.60.70.80.9

1

0 50 100 150 200Space time,s

Con

vers

ion(

X)

DOWNFLOW

UPFLOW

CBi=6.7 %(v/v), P=30 psig

Downflow and Upflow Experimental Results at Low Pressure Downflow and Upflow Experimental Results at Low Pressure (Gas limited Reaction) with Fines(Gas limited Reaction) with Fines

Fines Packing Procedure: Vol. of Fines ~Void volume (Al-Dahhan et al. 1995)

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SAME PERFORMANCE DUE TO COMPLETE WETTING

00.10.20.30.40.50.60.70.80.9

1

0 50 100 150 200

Space time,s

Con

vers

ion(

X)

DOWNFLOW

UPFLOW

CBi=3.18%(v/v), P=200 psig.

Downflow and Upflow Experimental Results at High Pressure Downflow and Upflow Experimental Results at High Pressure (Liquid limited Reaction) with Fines(Liquid limited Reaction) with Fines

Fines Packing Procedure: Vol. of Fines ~Void volume (Al-Dahhan et al. 1995)

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Effect of Pressure on Downflow PerformanceEffect of Pressure on Downflow Performance

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50 100 150 200 250

Space time,s

Con

vers

ion(

X)

p=100psig

p=200 psig

p=30psig

Ug=3.8cm/s, CBi=4.8%v/v

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Effect of Pressure (as transition to liquid limitation occurs) on Effect of Pressure (as transition to liquid limitation occurs) on Upflow Reactor Performance.Upflow Reactor Performance.

0

0.2

0.4

0.6

0.8

1

0 50 100 150 200Space time,s

Con

vers

ion(

X)

p=30psig

p=100psig

p=200psig

CBi=3.1%,Ug=3.8 cm/s

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Slurry KineticsSlurry Kinetics

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 100 200 300Time(min)

Co

nve

rsio

n(X

)

#1p=30psig,CBi=3.9%

#2p=100psig,CBi=3.99%

#3p=200psig,CBi=4%

#4p=300psig,CBi=3.45%

LHHW FORM

rk C C

KC KCvs amsh

ams cume

2

1 21( )

Pressure (psig) kvs

(m3iq./m3cat./s)

*(mol/m3 liq)r-1

K1 K2

30 0.0814 0 0 0100 1.14 4.41 11.48 1200 0.022 0.0273 0.021 2

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El- Hisnawi (1982) modelEl- Hisnawi (1982) model

•Reactor scale plug flow equations Liquid phase gas reactant concentration

•Constant effectiveness factor Modified by external contacting efficiency

•Allowance for rate enhancement on externally dry catalyst Direct access of gas on inactively wetted pellets.

REACTOR SCALEL G

L G

........................

........................

........................

........................

..................

......

........................

................... .............................

Liquid

Film

Dry

Direct Access

to Dry AreasAccess of Gas

via Liquidof gas

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Beaudry (1987) modelBeaudry (1987) modelDRY HALF-WET FULLY WET

Catalyst Pellet

Flowing Liquid

• Pellet scale reaction diffusion equations

For fully wetted and partially wetted slabs

• Effectiveness factor weighted based on contacting efficiency

• Overall effectiveness factor changes along the bed length

Evaluation of overall effectiveness with change in concentration and contacting

Overall Effectiveness factor at any location

o ce od ce ce odw ce ow ( ) ( )1 2 12 2

CBCA

0 2V/S

01x

0 1y

CB

CA

CREL

10,0''

;10,0')1(' 2

2

222

2

2

yCdy

CdxC

dx

CdAA

AAA

A

Upflow and Downflow Performance at Low PressureUpflow and Downflow Performance at Low Pressure (Gas Limited Condition) (Gas Limited Condition)

Experimental Data and Model PredictionsExperimental Data and Model Predictions

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 100 200 300 400

Space time(s)

Con

vers

ion(

X)

down,El-Hisnawi

upflow,El-Hisnawi

downflow,Beaudry

upflow,Beaudryi

downflow,exp

upflow,exp

Ug=4.4cm/s,Co=7.6%(v/v),p=30psig

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Upflow and Downflow Performance at High Pressure Upflow and Downflow Performance at High Pressure (Liquid Limited Conditions): (Liquid Limited Conditions):

Experimental Data and Model PredictionsExperimental Data and Model Predictions

00.1

0.20.3

0.40.5

0.60.7

0.80.9

1

0 50 100 150 200 250

space time(s)

Con

vers

ion(

X)

down,El-Hisnawi

up, El-Hisnawi

down, Beaudry

up, Beaudry

downflow,exp

upflow,exp

Ug=3.8cm/s,Co=3.1%(v/v),p=200psig

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SummarySummary DOWNFLOW PERFORMS BETTER AT LOW PRESSURE.

(Hydrogenation of alpha-methylstyrene is a gas limited reaction.

Partial wetting is helpful in this situation.)

UPFLOW PERFORMS BETTER AT HIGH PRESSURE.

(Hydrogenation of alpha-methylstyrene becomes a liquid limited reaction. Complete wetting is beneficial to this situation.)

THE PREFERRED MODE FOR SCALE-UP (UPFLOW OR DOWNFLOW) DEPENDS ON THE TYPE OF REACTION SYSTEM AS WELL AS ON THE RANGE OF OPERATING CONDITIONS THAT AFFECT CATALYST WETTING.

FINES NEUTRALIZE PERFORMANCE DIFFERENCES DUE TO MODE OF OPERATION AND REACTION SYSTEM TYPE , DECOUPLE HYDRODYNAMICS AND KINETICS, AND HENCE ARE TO BE PREFERRED AS SCALE-UP TOOLS.

THE TESTED MODELS PREDICT PERFORMANCE WELL

(although improvements in mass transfer correlations are necessary)

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Unsteady State Operation in Trickle Bed ReactorsUnsteady State Operation in Trickle Bed Reactors

“Modulation of input variables or parameters to create unsteady “Modulation of input variables or parameters to create unsteady state conditions to achieve performance better than that attainable state conditions to achieve performance better than that attainable with steady state operation”with steady state operation”

MotivationMotivation

Performance enhancement in existing reactorsPerformance enhancement in existing reactors Design and operation of new reactorsDesign and operation of new reactors Lack of systematic experimental or rigorous modeling studies in Lack of systematic experimental or rigorous modeling studies in

lab reactors necessary for industrial applicationlab reactors necessary for industrial application

Two ScenariosTwo Scenarios– Gas Limited ReactionsGas Limited Reactions– Liquid Limited ReactionsLiquid Limited Reactions

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ObjectivesObjectives

To experimentally investigate trickle bed performance under unsteady state operation (flow modulation) for gas and liquid limited conditions for a test hydrogenation system

To develop model equations for unsteady state phenomena occurring in trickle-bed reactors

To simulate unsteady state transport processes in trickle-bed reactors including bulk and interphase momentum, mass, and energy transport for the test reaction system

CREL

Strategies for Unsteady State OperationStrategies for Unsteady State Operation

Flow Modulation Flow Modulation (Gupta, 1985; Haure, 1990; Lee and Silveston, 1995)(Gupta, 1985; Haure, 1990; Lee and Silveston, 1995)

– Liquid or Gas Flow– Isothermal/Non-Isothermal– Adiabatic

Composition Modulation Composition Modulation (Lange, 1993)(Lange, 1993)

– Pure or Diluted Liquid/Gas– Isothermal/Non-Isothermal – Adiabatic

Activity Modulation Activity Modulation (Chanchlani, 1994; Haure, 1994)(Chanchlani, 1994; Haure, 1994)

– Enhance activity due to pulsed component– Removal of product from catalyst site– Catalyst regeneration due to pulse

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Gas Limited ReactionsGas Limited Reactions

Partial Wetting of Catalyst Pellets -DesirablePartial Wetting of Catalyst Pellets -Desirable– Internal wetting of catalystInternal wetting of catalyst– Externally dry pellets for direct access of gasExternally dry pellets for direct access of gas– Replenishment of reactant and periodic product removalReplenishment of reactant and periodic product removal

– Catalyst reactivationCatalyst reactivation

Liquid Limited ReactionsLiquid Limited Reactions

Partial Wetting of Catalyst Pellets-UndesirablePartial Wetting of Catalyst Pellets-Undesirable– Achievement of complete catalyst wettingAchievement of complete catalyst wetting– Controlled temperature rise and hotspot removalControlled temperature rise and hotspot removal

Possible Advantages of Unsteady State OperationPossible Advantages of Unsteady State Operation

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Test Reaction and Operating ConditionsTest Reaction and Operating Conditions

C CH

CH

2

3

HC CH

CH

3

3

H+2

Pd/Alumina

Operating ConditionsOperating Conditions

• Superficial Liquid Mass Velocity : 0.1-3.0 kg/m2s• Superficial Gas Mass Velocity : 3.3x10-3-15x10-3 kg/m2

• Feed Concentration : 2 .7 - 20 % (200-1500 mol/m3)• Cycle time (Total Period) : 40-900 s• Cycle split (ON Flow Fraction) : 0.1-0.6• Max. Allowed temperature rise : 25 oC• Operating Pressure : 30 -200 psig (3-15 atm)• Feed Temperature : 20-35 oC

Alpha-methylstyrene hydrogenation to isopropyl benzene (cumene)

CREL

Experimental ResultsExperimental Results

Liquid Limited Conditions ( = 2)High Pressure,

Low Liquid Feed Concentration

Gas Limited Conditions ( = 20)Low Pressure,

High Liquid Feed Concentration

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 200 400 600 800

Space time (s)

Con

vers

ion(

X)

Steady State

Unsteady State (Cycle = 60s, S=0.5)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 100 200 300 400 500Space time (s)

Con

vers

ion

(X)

Unsteady State (Cycle=60s, S=0.5)

Steady State

D C

D CeB Bi

eA A*

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Effect of Cycle Split on Performance EnhancementEffect of Cycle Split on Performance Enhancement

Gas Limited Conditions ( = 20)Operating Conditions : Pressure=30 psig

Liquid Reactant Feed Concentration= 1484 mol/m3

Cycle Split (St)= Liquid ON Period/Total Cycle Period(T)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 0.2 0.4 0.6 0.8 1Cycle Split (ON time/Total Cycle Time)

Con

vers

ion

(X)

SteadyState

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Phenomena occurring under unsteady state operation Phenomena occurring under unsteady state operation with flow modulation in a trickle-bed reactorwith flow modulation in a trickle-bed reactor

time,t

Catalyst (Internally and Externally wetted)

Liquid Full (Holdup=Bed voidage)

Catalyst (Internally wet, externally partially wet)

Liquid films (Holdup = dynamic +static)

Gas accesing liquid and dry catalyst

Catalyst (Internally wet, externally dry)

Liquid films (Holdup = only static)

Gas Accesing dry catalyst

LIQUID PULSE ON

LIQUID PULSE TRANSITON ZONE

LIQUID PULSE OFF

Temperature, Low (=Feed Temperature)

Temperature, Rise (>Feed Temperature)

Temperature, High (>Feed Temperature)

(a)

(b)

(c)

(Only Scenario II)

(Only Scenario II)

GOALGOAL: : To Predict Velocity, Holdup, Concentration and Temperature ProfilesTo Predict Velocity, Holdup, Concentration and Temperature Profiles

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The Model StructureThe Model Structure

z=L

z=0GAS LIQUID

SOLID

C1G

C2G

.

.CnG

C1L

C2L

.

.CnL

NiGS

NiGS

NiLS

NiLS

NiGL

EGS

EGS

ELS

ELS

EGL

EGL

NiGL

t

Cz

u C N a N aG iG IG G iG iGL

GL iGS

GS( )

t

Cz

u C N a N aL iL IL L iL iGL

GL iLS

LS( )

Bulk Phase EquationsBulk Phase Equations

SpeciesSpecies

EnergyEnergy

c B CPB e

CP LSLS

GSGS

E

tk

T

zE a E a

( )( )

11

2

2

( ) ( )L L L L IL L L GLGL

LSSL

E

t

u H

zE a E a

( ) ( )G G G G IG G G GLGL

GSGS

E

t

u H

zE a E a

CREL

Advantages of Maxwell-Stefan Multicomponent Advantages of Maxwell-Stefan Multicomponent Transport Equations over Conventional ModelsTransport Equations over Conventional Models

Multicomponent effects are considered for individual component transport [k]’s are matrices

Bulk transport across the interface is considered

Nt coupled to energy balance (non zero) Transport coefficients are corrected for high fluxes

[k] corrected to [ko] = [k][[exp([])-[I]]-1

Concentration effects and individual pair binary mass transfer coefficients considered

Thermodynamic non-idealities are considered by activity correction of transport coefficients

Holdups and velocities are affected by interphase mass transport and

corrected while solving continuity and momentum equations

D Dij ij

[ ]ln

ij ij ii

j

xx

Flow Model EquationsFlow Model Equations

uiL,uiG

L,G,P

Staggered 1-D Grid

ZN

u

z

u

zt

zc

p

zG L

L iL G iG( )( ) ( ) ( )* *1 1

MomentumMomentum

ContinuityContinuity

PressurePressure

L

LL

IL L

iGL

GL i iLS

LS it

u

zN a M N a M

G G G IG G

iGL

GL i iGS

GS it

u

zN a M N a M

L L

ILL L IL

ILL L L

LD Liq IG IL IL i

GLGL i i

LSLS i

u

tu

u

zg

P

zF K u u u N a M N a M , ( ) ( )

G G

IGG G IG

IGG G G

GD Gas IL IG IG i

GLGL i i

GSGS i

u

tu

u

zg

P

zF K u u u N a M N a M , ( ) ( )

CREL

Stefan-Maxwell Flux Equations for Interphase Stefan-Maxwell Flux Equations for Interphase Mass and Energy TransportMass and Energy Transport

N J x J xq

iL

iL

i k kL

k

n

ix

1

1

Gas-Liquid FluxesGas-Liquid Fluxes

Liquid-Solid and Gas-Solid FluxesLiquid-Solid and Gas-Solid Fluxes

N J y J yq

iV

iV

i k kV

k

n

iy

1

1

E h T T N H TLL I L i

LiL

Li

n

. ( ) ( )

1

E h T T N H TVV G I i

ViV

Gi

n

. ( ) ( )

1

E h T T N H TLSLS L ILS i

LSiL

Li

n

. ( ) ( )

1 N c k xLSt LS LS [ ][ ].

N c k xGSt GS GS [ ][ ]. E h T T N H TGS

GS G IGS iGS

iG

Gi

n

. ( ) ( )

1

Bootstrap Condition for Multicomponent TransportBootstrap Condition for Multicomponent Transport• Interphase Energy Flux for the Gas-Liquid Transport and Bulk to Catalyst Interphase Energy Flux for the Gas-Liquid Transport and Bulk to Catalyst Interface TransportInterface Transport

• Net Zero Volumetric Flux for Liquid-Solid and Gas-Liquid Interface for Net Zero Volumetric Flux for Liquid-Solid and Gas-Liquid Interface for Intracatalyst FluxIntracatalyst Flux

[ ], i k G ik i ky , ik k nc y ( )/

, y i i

i

y:i i i

VG i

LLy H T H T ( (@ ) (@ ))

[ ], ikCP ik ci kx:k

k

k

nc

ncmx

MM( )/

and

mx cii

ii

xM

CREL

Catalyst Level EquationsCatalyst Level Equations

Approach I: Rigorous Single Pellet Solution of Intrapellet Profiles along with Liquid-Solid and Gas-Solid Equations

Approach II: Apparent Rate Multipellet Model Solution of Liquid-Solid and Gas-Solid Equations

G CiCP L

xc

CiCP L G CiCP L G CiCPL

cx x

dtB

x x x

xcRtCP

i ncnt

i ncnt

j

j ncnt

j ncnt

j ncnt

jncnt, ,

,

, , ,{[ ][ ] [ ]}

( )

( )

1

11

11 1

11

2 11

20

cx x

dtN a N a RtCP

int

int

iLS

jLS

j a biGS

jGS

j a bAppnt

1

1 1 1 11

1 0, ,

G

Type I: Both Sides Externally Wetted

Type II: Half Wetted Type III: Both Sides Externally Dry

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Holdup and Liquid Velocity ProfilesHoldup and Liquid Velocity Profiles

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

0 10 20 30 40time (s)

Liq

uid

Hol

dup

...

z=0.0

z=0.25

z=0.45

z=0.65

z=0.85

z=1.0

0

0.01

0.02

0.03

0.04

0.05

0.06

0 10 20 30 40

time (s)

Liq

uid

Vel

ocity

(m/s

) …..

z=0.0

z=0.25

z=0.45

z=0.65

z=0.85

z=1.0

Operating Conditions: Liquid ON time= 15 s, OFF time=65 s Liquid ON Mass Velocity : 1.4 kg/m2s Liquid OFF Mass Velocity: 0.067 kg/m2s Gas Mass Velocity : 0.0192 kg/m2s

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Pseudo-Transient Simulation ResultsPseudo-Transient Simulation Results Alpha-methylstyrene Concentration ProfilesAlpha-methylstyrene Concentration Profiles

0

50

100

150

200

250

0 0.2 0.4 0.6 0.8 1Axial Position (m)

-MS

con

cent

ratio

n (m

ol. m

-3)

0.75

1.644

2.844

6.324

10.644

16.164

29.814

40.314

46.674

0

50

100

150

200

250

0 5 10 15time, (s)

-MS

conc

entra

tion,

(mol

. m

-3 )

..

z=0

z=0.1

z=0.2

z=0.3

z=0.4

z=0.5

z=0.6

z=0.7

z=0.8

z=0.9

z=1.0

Alpha-methylstyrene Concentration buildup in the reactor to steady state or during ON cycle of flow modulationFeed Concentration : 200 mol/m3

Pressure : 1 atm. Reaction Conditions : Gas Limited ( = 10)

(Intrinsic Rate Zero order w.r.t. Alpha-MS)

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time,s

Pseudo-Transient Cumene and Hydrogen Pseudo-Transient Cumene and Hydrogen Concentration ProfilesConcentration Profiles

0

5

10

15

20

25

0 0.2 0.4 0.6 0.8 1

Axial Position (m)

Cum

ene

conc

entra

tion

(mol

.m -3

)

0.75

1.644

4.044

8.124

14.004

21.084

29.814

34.254

44.034

0

2

4

6

8

10

12

14

16

0 5 10 15 20

time (s)

Liq

. Pha

se H

ydro

gen

Con

c (m

ol.m

-3

)

z=0

z=0.1

z=0.2

z=0.3

z=0.4

z=0.5

z=0.6

z=0.7

z=0.8

z=1

CREL

Profiles show build up of Cumene and Hydrogen profiles to steady state or during ON part of the pulse

Alpha-methylstyrene and Cumene Concentration Alpha-methylstyrene and Cumene Concentration Profiles During Flow ModulationProfiles During Flow Modulation

Supply and Consumption of AMS and Corresponding Rise in Cumene Concentration

Operating Conditions: Cycle period=40 sec, Split=0.5 (Liquid ON=20 s) Liquid ON Mass Velocity : 1.01 kg/m2s Liquid OFF Mass Velocity: 0.05 kg/m2s Gas Mass Velocity : 0.0172 kg/m2s

0.341

10.479

20.644

29.291

39.455

0.1

0.2

0.3

0.4

0.5

0

10

20

30

40

50

Cum

ene

Con

c., m

ol/m

3

time, s Axial Location, m

0.1

0.3

0.5

0.7

0.9

0.2275.353

10.15615.852

20.43325.313

29.83134.725

37.225

0

40

80

120

160

200

Alp

ha-M

S co

nc.,

mol

/m3

time, s

Axial Location, m

CREL

Catalyst Level Hydrogen and Alpha-methylstyrene Catalyst Level Hydrogen and Alpha-methylstyrene Concentration Profiles During Flow ModulationConcentration Profiles During Flow Modulation

0.03

5

5.07

81

10.3

263

15.1

737

21.0

159

24.9

087

30.1

751

35.0

302

39.7

204

0.10.2

0.30.4

0.50.6

0.70.8

0.91

0

20

40

60

80

100

120

140

160

Alp

ha-M

S co

ncen

trat

ion,

m

ol/m

3

time,s

Axial Location, m

0.1

0.3 0.

5 0.7 0.

9

0.035

5.0781

15.1737

20.0057

25.459730.1751

35.0302

02468

1012

14

Hyd

roge

n C

once

ntra

tion

, m

ol/m

3

time,s

Axial Position, m

Concentration of Hydrogen during Liquid ON (1:20s, Wetted Catalyst ) and Liquid OFF(20:40 s,

Dry catalyst) for negligible reaction test case

Concentration of Alpha-MS in previously dry pellets during Liquid ON

(1:20s, Wetted Catalyst ) and Liquid OFF(20:40 s, Dry catalyst)

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ConclusionsConclusions

• Performance enhancement under unsteady state operation is demonstrated to be significantly dependent on reaction and operating conditions

• Rigorous modeling of mass and energy transport by Maxwell-Stefan equations and solution of momentum equations needed to simulate unsteady state flow, transport and reaction occurring in a trickle bed reactor has been accomplished. This algorithm can be used as a generalized simulator for any multicomponent, multi-reaction system and converted to a multidimensional code for large scale industrial reactors.

• Pseudo-transient and transient operation is simulated for the case of liquid flow modulation to demonstrate performance enhancement under unsteady state conditions. Product formation rate is enhanced due to increased supply of liquid reactant to dry pellets (during ON cycle) and gaseous reactant to previously wetted pellets (during OFF cycle). Exothermic enhancement and higher hydrogen solubility can also be taken advantage of in the OFF cycle due to systematic quenching during the ON cycle.

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