Gas-Liquid Reaction - Lecture 1

University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering

Gas - LiquidReaction Engineering

David W. Agar

Short Course

16th-25th June 2003

Chemical Engineering Department

IISc Bangalore

University of Dortmund



1997- Chair for Reaction Engineering,TCB Dortmund, D

1956 Danbury, England, GB

Curriculum Vitae

1980 Postdoctoral work Pasadena, CA, USA

1977-1980 PhD Chemical Engineering Houston, TX, USA

1981-1986 Central Research, BASF AG Ludwigshafen, D

1987-1990 Caprolactam plant, BASF AG Ludwigshafen

1990-1993 Coordinator for Isocyanate LudwigshafenResearch, BASF AG

1993-1995 Coordinator for Reaction LudwigshafenEngineering Research, BASF AG

1995-1996 Technical Support, Amine sales, Calgary, CDNBASF AG

1977 BSc Biochemical Engineering Swansea, Wales, GB

Ludwigshafen



Course content:A survey of the most important gas-liquid reactions and the reactors

employed together with appropriate modelling & design fundamentals,

with special emphasis being placed on acid gas removal from syngas

& natural gas.

Recommended Reading:1. ‚Gas-Liquid Reactions‘ P.V. Danckwerts, McGraw-Hill, 1970

2. ‚Gas treating with chemical solvents‘ G. Astarita, D.W. Savage & A. Bisio, Wiley, 1982

3. ‚Gas Purification‘ A.L. Kohl & R.B. Nielsen, Gulf Publishing Co., 1997



25.06.03 Design problem

Course schedule:

16.06.03 Introduction to gas-liquid reactor

17.06.03 Chemistry of gas-liquid reactions

18.06.03 Reaction & diffusion

19.06.03 Reaction, diffusion & convection

20.06.03 Modelling of gas-liquid reactors

23.06.03 Determination of parameters

24.06.03 Exercises



Solid

Gas

(2nd Liquid)

Liquid

Catalyst

Heterogeneous reaction systems


University of DortmundModelling analogies

• Non-catalytic gas-solid reactions- instantaneous reaction ⇔ shrinking core model- bulk phase reaction ⇔ homogenous conversion model

• Differences- heat effects slight- minimal changes in physical properties- fluid dynamics instead of porous solid structures- importance of phase equilibria- high separation factors

• Heterogeneously catalysed reactions- Ha ⇔ φ- E ⇔ h

• Reactor engineering- surface renewal ⇔ residence time distribution- M or Ha ⇔ Da



Gas Liquid

Two film model

Boundary layers

Pha

sein

terfa

ce

Bulkphase

Bulkphase

A

CA0

pA0 CA*

pA*

• mass transferlocalised insurface films

• CA* & pA* at equilibrium

• continuity ofinterfacialflux

• no reaction ⇒const. slope

δLδG



Gas LiquidSurface film

Pha

sein

terfa

ce

A

CA0

pA0

CA*

pA*

• very slow reaction

CB0

A(g) + B(aq) → C(aq)δL



Gas Liquid

A

CA0

pA0

CA*

pA*

• moderate reaction

CB0

A(g) + B(aq) → C(aq)δL



Gas Liquid

A

CA0=0

pA0

CA*

pA*

• fast reaction

CB0

A(g) + B(aq) → C(aq)

δL



Gas Liquid

ApA0

CA*

pA*

• very fast reaction

CB0


Rea

ctio

nfr

ont

δL

δR



Gas Liquid

ApA0

CA*

pA*

• instantaneousreaction

CB0


Reaction front =Phase interface

δL

δG


University of DortmundCO2(g) + 2 RNH2(aq) →

RNHCOO-(aq) + RNH3+(aq)

δL

CA [kmol/m³]1x10-5

0.6x10-5

0.2x10-5

CB [kmol/m³]

2

1

0.8x10-3

0.4x10-3

P[bar]

δG

δL

CA [kmol/m³]0.03

0.02

0.01

CB [kmol/m³]P[bar]

δG

2

1

0.5

0.3

0.1

δL

CA [kmol/m³]0.5x10-3

0.3x10-3

0.1x10-3

CB [kmol/m³]

2

1

P[bar]

δG

0.05

0.03

0.01

MonoethanolamineMEA: R=HOCH2CH2-



Relative conversion as a function ofvolumetric utilisation factor & Hatta-number

reactive volume fraction

BC

Xrel

ATPC JR

BC: bubble column

AT: aerated tank

PC: packed column

JR: jet reactor

Ha =Reaction in film

Penetration thru‘ film



Heat transport

Gas-Liquid reactors:problems & solutions

Phase interface

Homogenisation

Proprietary agitators

Extruder

Evaporative coolingFalling film reactor

Bubble column Spray tower Packed column



Interfacial area

Heat exchangeHomogenisation

• two-phase pipe flow• venturi scrubber• spray tower• segmented reactor with gas injection• stirred tank with gas injection• packed column• tray column• loop reactor• bubble column• ….

⇒ scale-up⇒ bubble & solid⇒ distribution⇒ shearing⇒ stirrer power⇒ stirrer type

• evaporative cooling• falling film reactor• internal / externalheat exchangers

• ….

• three-phasefluidised beds

• fixed bed reactors- trickle- flooded

• slurry reactors- bubble column- stirred tank

• extruder reactor• jet mixer• loop reactor• …

Critical design features of gas-liquid-reactors


University of DortmundMixing of gas-liquid-reactors

Viscosity [Pas]<0.5 0.5-5 5-50

tang

entia

l -ra

dial

flow

axia

l flo

w

Types of agitator:

a) disc turbine

b) radial impellor

c) cross blade

d) gate paddle

e) flat blade paddle

f) anchor

g) axial impellor

h) propellor

i) MIG (Ekato)

j) spiral


University of DortmundCharacteristic mixing times

Re =

j n.t m

ρ.N.Di2

µ

e,es

f i

is

habs

b

e esis

i

bsa

c,cs=1.8e

d,ds=1.25e

tm<< τ

Types of agitator:a) disc turbine d) gate paddle g) axial impeller j) spiralb) radial impeller e) flat blade paddle h) propellerc) cross blade f) anchor i) MIG (Ekato) .s) baffled

tank



Re

Ne

=P/

ρN3 D

i5

Mixing power requirements

Pg Qg N2Di4

P N.VL gWiVB2/3

-0.20 -0´25

= 0.1 ( ) ( )

Wi

N

us, Qg

Di

VB

(µ/ρ)³P/ρVR

0.25

δ = ( )

j

f c,cs,d,ds,e,es

i(s)b(s)

ashs es

asdscs

c,de hs

isbs

if,j

b

PgVR

0.4

kLa = 0.0026 us0.5( )Mass

transfercoefficient

δ << √(DAtm)

KolmogorovEddy size


University of DortmundHeat exchange in gas-liquid-reactors

a) Cooling/heatingjacket

b) Internalheatexchanger

c) Externalheatexchanger

d) Evaporativecooling

• facile maintenance• low external hold-up• flexible design

• intensive cooling• uniform T-profile• large reactors


University of DortmundHeat exchange ingas-liquid-reactors

e) Falling film reactor


University of DortmundHeat exchange vs. homogenisation

Heat removal (Qa) &

power dissipation (P)

of an anchor agitator

as a function of rota-

tional speed (n)


University of DortmundCreating interfacial area in gas-liquid-reactors

Gas-liquidcontactors

G = gas flow

L = liquid flow

Driving forces:

• pressure drop

• gravity

• mechanicalenergy


University of DortmundTaxonomy of bubble columns

a) Single stagebubble column

b) Multistagebubble column(sieve plate cascade)

c) Airlift reactors

upflow downflow jet-stream






University of DortmundTaxonomy of three phase reactors

a) Three phasefixed-bed reactor

b) Trickle bed reactor(or flooded operation)

c) Slurry reactors

bubblecolumn

stirredtank

fluidisedbed





• Catalyst in wire gauze envelopes avoids flooding• Catalyst in wire gauze envelopes avoids floodingReactive DistillationReaction requires:

• high liquid hold-up• bubbly flow / froth regime• low gas velocities• small catalyst particles• high catalyst loading

Reactive DistillationReaction requires:

• high liquid hold-up• bubbly flow / froth regime• low gas velocities• small catalyst particles• high catalyst loading

Distillation requires:• high interfacial areas• spray regime• open x-section for two phase flow

Compromise:• separate side-reactors• packing = 20-25% vol. of column



Waste air purification: solvent recycling using absorption

pure gas

raw gas

pure gas

Absorbentmake-up

raw gas with

solventvapours

Strippingcolumn

Absorber

recoveredsolvent

rich absorbentabsorbent liquid distributor

packing



Techniques for solvent regeneration

a) Flashing b) Inert stripping gas c) thermal stripping







Course schedule:

16.06.03 Introduction to gas-liquid reactors

17.06.03 Chemistry of gas-liquid reactions

18.06.03 Reaction & diffusion

19.06.03 Reaction, diffusion & convection

20.06.03 Modelling of gas-liquid reactors

23.06.03 Determination of parameters

24.06.03 Exercises

25.06.03 Design problem

Documents

Gas-Liquid Reaction - Lecture 1