Heterogeneous Reaction Engineering:
Theory and Case Studies
Module 4
Analysis of Local Transport Effects in
Gas-Liquid-Solid Systems
P.A. Ramachandran
rama@wustl.edu
1
Outline
•
•
•
•
Transport Effects
Diagnostic plots for slurry systems
Partial wetting and implications
Slurries containing fine particles
2
Heterogeneous Liquid-Phase Reaction Phenomena
ci
catalyst
Ni
Ni
ci
T
Liquid
film
Vapor
film
Bulk liquid
Bulk vapor
E
E
Liquid
film
T
Challenges: 1. Identifying reaction(s) and their location(s)
2. Accounting for internal and external catalyst
wetting / holdup phenomena
3
Mass Transfer Resistances in
Gas-Liquid-Solid Systems
4
Local Rate of Reaction for GasLiquid-Solid Catalyzed Systems
A (g) +
b B (l)
P (l)
Gas-Liquid Mass Transfer:
RA = kLaB (A* - AL )
Liquid-Solid Mass Transfer for A:
RA = ksap (AL - As )
Liquid-Solid Mass Transfer for B:
RB = ksap (BL - Bs )
Intra particle Diffusion with Reaction:
RA = wc(As, Bs)kmnAsmBsn
5
Intraparticle Diffusion Limitations
• Solution of the reaction-diffusion equations in the catalyst
particle for some simple reactions results in effectiveness factorThiele modulus relationship similar to that represented by the
enhancement factor-Hatta number relationship for gas-liquid
reactions

tanh 

k1
L
De
Other details: Froment & Bischoff (1979)
6
Observed Rate - 1st Order Reaction
in a Gas-Liquid-Solid System
• For linear kinetics and the slow reaction regime, an overall resistance can
be defined that includes the gas-liquid and liquid-solid mass transfer
and reaction terms, including intraparticle diffusion limitations
1
1 
* 1
RA  A 



 kL aB kS aPw C wk1 
-1
A*
1
 rb  rcr
RA
w
rb ( s ) 
1
k LaB
rcr ( gcat  s / m 3 ) 
1
1

k s a p  c k1
7
Diagnostic Plots: First Order Case
A*/RA
A*/RA
1/w
1/w
Gas-Liquid Mass Transfer Controls
the Process
Negligible Gas-Liquid Resistance
A*/RA
Slope = rcr
Intercept = rb
1/w
Intermediate Case
8
Diagnostic Plots (contd)
A*/RA
A*/RA
Increasing resistance
to gas absorption
Decreasing Particle Size
1/w
1/w
m>1
A*/RA
m=1
m<1
m=0
1/w
Schematic Plots for other Higher Orders
9
Commonly-Used Kinetic Models
for Gas-Liquid-Solid Systems
A (g) +
b B (liq)
Mechanism
P (liq)
Rate Form
1. Single site adsorption of dissolved gas
k11 A
B
1 K A A
2. Dissociative adsorption of dissolved gas
k11 A
B
1 K A A
3. Adsorption of both A & B on single sites
k11 AB
1 K A A  K B B
4. General single site adsorption for N species
k11 AB
N
1  Ki Ci
i 1
10
Overall Effectiveness Factor
for a (m,n) order Reaction
RA
0 
m n
wk (A*) BL
= f(A , o)
where:
(1)
1
 1
1 
A*



k
a
k
a
 L
s p 
A 
wk(A*)m BLn
R (m  1)Sp k(A*)
o 
3 
2De

(2)
m 1
n
L
1
2
B 


(3)
11
Overall Effectiveness Factor
for a Single-Site L-H Rate Form
k11 AB
Example: Glucose Hydrogenation  A 
1  KA A
Ramachandran & Chaudhari, 1983
12
Analysis of External Mass Transport
Resistance
• Overall mass transfer of H2 (gas) to catalyst
surface is :
Rgas = MA(A*-As), A* - gas concentration in the liquid phase (using
Henry’s Constant)
MA  (
1
1 1

)
K LaB ks a p
• Gas consumption by all reactions:
RH 
2
No . of rxn

j 1
H2 , j
rj
• Considering As = 0 , we have
M A A* 
No . of rxn
 r
j 1
H2 , j
j
If LHS > > RHS, then no mass transfer resistance !
13
Analysis of Internal Resistance (within the
Catalyst Pellet)
• Weisz-Prater criterion
is used
r L n1
We    
D C 2
2
2
obs
i
eff
b
n = reaction order, taken as unity
robs = net rate of consumption of limiting
Reactant (initial rate)
Cb = concentration of limiting reactant in liquid
Deff = effective diffusivity = DABp/τ
p= particle porosity ~ 0.5
τ = totuosity = 2
DAB = binary diffusivity (Wilke Chang correlation
L = (characteristic length) Vp/Sp
Internal Resistance is considered negligible if
We0.5 < 0.2
14
Parameter Estimation Method
•
•
•
•
Step-by-step approach
Start with a temperature data set
Identify the reactions
Identify the reaction form (reaction rate):
rj 
1  K C
1
Where,
n
w cat k j C gas
Cj
 K 2C 2  K 3C 3  K 4C 4  K 5C 5 
2
gas
k j (or K j )  Aoj e

E
j
RT
Aoj and Ej are estimated !
15
Kinetic Parameter Estimation (contd.)
• Non-linear Optimization Problem
N
obj  min(C
i 1
 C i , aut oc l av
)2 , t ,runs
e
i ,pr edi c t ed
s ubj:
Aut oc lav eModel / Slurryreac t or
• Identify and select the for the objective function
• Identify the species adsorbed, if any (C1 to C5 here, as an
example)
• Develop parameter estimation program and the autoclave
model / Slurry reactor model
• Autoclave model predicts the species concentration at every
instant (for the operating conditions) – set of differential
equations can be solved by VODE routine from NETLIB
libraries
• Levenberg-Marquardt algorithm for parameter estimation –
UNLSF routine from IMSL libraries
16
Trickle-Bed Reactors
17
Fixed-Bed Multiphase Reactors
(a) Trickle - Bed
Cocurrent
downflow
(b) Trickle - Bed
Countercurrent
flow
(c) Packed - Bubble Flow
Cocurrent
upflow
Semi-Batch or Continuous Operation; Inert or Catalytic Solid Packing
18
Trickle-Bed Reactors
- Pros and Cons Pros
•
Plug-flow
•
Low liquid holdup
less
homogeneous reactions
•
•
•
high conversion
Cons
•
Intraparticle diffusion resistance
•
Incomplete contacting/wetting
•
High pressure drop
•
Temperature control problems
hot spots
•
Scale-up and design is complex
•
Attrition and crush resistant
catalyst is required
High specific reaction rate
Temperature control possible by
liquid vaporization
High pressure operation possible
•
Minimal catalyst handling issues
•
Process flexibility, reasonable
throughput limitations
•
Dirty process streams cannot be
used
plugged or fouled bed
•
Lower capital & operating costs
•
Catalyst loading is complicated
19
Fundamental Phenomena
in Trickle Bed Reactors
Macroscale
•
Axial & radial RTD’s
•
Flow regime
•
Pressure drop
•
Liquid holdup
•
Liquid flashing
•
Interphase transport
•
Liquid distribution
•
Heat transfer
•
Energy dissipation
Microscale
•
LocaL texture of liquid flow (films,
rivulets, stagnant pockets)
•
Local irrigation and wetting
•
Liquid holdup in pores
•
Local transport between gas and
flowing and stagnant liquid, and
solid
•
Local transport between flowing
liquid, stagnant liquid, and solid
•
Local transport between gas and
vapor-filled pores
20
Classification of TBR Processes
Based on Volatility
1. Nonvolatile liquid reactant
• Rate limiting reactant
- Liquid
- Gas
- Both
Reaction occurs only on wetted catalyst
2. Volatile liquid reactant
• Rate limiting reactant
- Liquid
- Gas
- Both
Reaction occurs both on wet and dry catalyst
21
Key TBR Design Parameters
•
Flow regime
•
Pressure drop
•
Liquid holdup
•
Liquid - solid contacting
•
Interphase transport coefficients
•
Intraparticle diffusion
•
Extent of liquid volatilization
•
Reaction kinetics
•
Thermo - physical constants
22
Flow Regime Structures
for Gas-Liquid Flow in Fixed-Beds
Trickle-Flow
Pulse-Flow
Spray-Flow
Bubble-Flow
Mewes, Loser, and Millies (1999)
23
Three Key Factors
Affecting Flow Regimes
1. Throughput of gas and liquid
L - liquid mass velocity
G - gas mass velocity
L / G - ratio of mass velocities
2. Physical properties of the gas and liquid
- viscosity
- surface tension
- density
3. Foaming or non-foaming characteristics of
the liquid
24
Factors Affecting Choice of L / G
• Stoichiometry of the reaction
• Pressure drop limitations
• Establishment of desired flow regime
• Foaming characteristics of liquid
• Heat removal requirement
• Maximum allowed Tad
25
Flow Regime Map for
Gas-Liquid Flow in Fixed-Beds
Gianetto, Baldi, Specchia and Sicardi, AIChEJ (1978)
26
Effect of Bed Prewetting
and Hysteresis Effects
250
non-prewetted bed
prewetted bed
Intensity of image
200
CCD Video Imagesof
Liquid Flow in 2-D Beds
Axial position: 6 cm down from top
dp = 0.3 cm
150
100
50
0
0
3
6
9 12 15 18 21 24
X (dp)
L = 3.52 Kg/m2.s
channel flow
film flow
28
Models for Trickling to Pulsing Flow
Regime Transition
• Macroscopic model - balance of inertial and capillary
forces
– Grosser, Carbonell & Sundaresan, AIChE J (1988)
– Attou & Ferschneider, CES (1999)
• Microscopic model - pore blockage by balance of
inertial and capillary forces
– Ka Ng, AIChE Jnl (1986)
• Microscopic model - wave formation on surface of
liquid film
– Holub, Dudukovic & Ramachandran, AIChE J (1993)
29
Estimation of Pressure Drop for Two-phase
Flow in Packed-Beds
Various empirical correlations based on:
• Lockhart -Martinelli parameter
• Two - phase friction factor
• Energy dissipation parameter
• Relative permeability parameter
• Other dimensionless parameters
30
Key Pressure Drop
Equation Parameters
• Single - phase pressure drop
 =
P
L
150 (1 - B ) 2 u 
=
B 3
d pe 3
1.75 (1 - B ) u 2 
+
B 3 d pe
• Lockhart -Martinelli parameter
1/2


L
 = 
  G 
• Two - phase friction factor
1
f GL =
LG d PE uG 2 G
2
Validity:
• Low and high Interaction regimes
• Non-foaming and foaming systems
31
Pressure Drop - Summary
• Correlations based on single-phase gas and liquid P
(Ergun equation)
– Lockhart-Martinelli (1949), Larkins et al. (1961), Specchia
& Baldi (1974) - separate for low and high interaction, Kan
& Greenfield (1978) - hysteresis effect on P
• Flow models
– Relative permeability model: Saez & Carbonell, AIChE
J (1985); Levec, Saez & Carbonell, AIChE J (1985); Saez,
Levec & Carbonell, AIChE J (1985)
– Slit model: Holub, Dudukovic & Ramachandran, CES
(1992); AIChE J (1993); Al-Dahhan, Khadilkar, Wu, &
Dudukovic IEC Res. (1998); Iliuta & Larachi, CES (1999)
– Fluid- fluid interface model: Attou, Boyer & Ferschneider,
CES (1999), Attou & Ferschneider, CES (1999)
32
Liquid Holdup - Key Definitions
• Liquid holdup (HL , L ) is the fraction of reactor volume
that is occupied by liquid (m3 liquid / m3 reactor).
L = VL / VR
• Liquid saturation (L , L ) is the fraction of external
bed voidage (B ) occupied by liquid (m3 liquid / m3 voids).
L = L / B
• Fractional pore fill-up (Fi) is the fraction of catalyst pore
volume occupied by liquid (m3 liquid / m3 pore volume).
33
Key Liquid Holdup Relationships
Total Bed Voidage
t
= External Voidage + Internal Voidage
=
B
+
Total Liquid Holdup = External Holdup
L
=
LE
p ( 1 - B )
+ Internal Holdup
+
L
Internal Holdup for Liquid-Filled Catalyst Pores (Fi = 1)
LI
F i p ( 1 - B )
=
External Liquid Holdup = Dynamic Holdup + Static Holdup
LE
=
LD
+
LS
34
Typical External Holdup Values
External Liquid Holdup = Dynamic Holdup + Static Holdup
LE
LD
=
+
LS
0.1 < LE < 0.25 ( or higher at high L / G )
LS
=
NEo =
1
20 + 0. 9 NEo
L g dp 2 B2
L (1 - B )

Gravity force
Surface tension force
= Eotvos Number
35
Liquid Holdup - Summary
Contributions to the overall liquid holdup
• Internal liquid holdup (inside particle) ~ equal to particle porosity
• External liquid holdup
– dynamic (flowing liquid) - depends on flow regime and is determined
by viscous, gravity and inertial forces
– static - volume fraction of liquid retained when a pre-wetted bed is
drained, from balance of gravity and surface tension forces
HL= HLD + HLSe+ HLi = HLD + HLSe+ ip(1- B)
HL, HLD & HLe correlations for low & high interaction regime
• Separate correlations for low and high interaction regimes
• Empirical: Larachi et al. (1991), Lara-Marquez et al. (1992)
• Phenomenological: Holub et al. (1992, 1993);
Al-Dahhan & Dudukovic (1994)
36
Pressure Drop and
Liquid Holdup Correlations
MARE (%)*
L
P / L
Iliuta & Larachi (1999)
18
27
Ellman et al. (1988, 1990)
23
54
Saez et al. (1985)
22
41
Al-Dahhan & Dudukovic (‘95, ‘96) 17
32
Larachi et al. (1991)
73
22
*Mean Absolute Relative Error
Carbonell, O&G Sci & Tech, vol 55 (4) (2000)
37
Key Transport Resistances
• Gaseous reactant resistances
1 - Gas-to-liquid resistance
2 - Liquid-to-solid resistance
3 - Intraparticle diffusion and kinetic resistances
• Liquid reactant resistances
1 - Liquid-to-solid resistance
2 - Intraparticle diffusion and kinetic resistances
• Heat transfer resistances
1 - Bulk gas-to-particle
2 - Bulk liquid-to-particle
3 - Intraparticle
38
Transport Parameter Correlations
kLaB - Gas to liquid ( liquid - side )
volumetric mass transfer coefficient
kSL - Liquid to actively wetted solid mass transfer
coefficient
kSg - Gas to dry solid mass transfer coefficient
h
- Overall heat transfer coefficient
e
- Effective conductivity of particles
39
Interphase Mass Transfer Correlations Summary
Liquid side of gas-to-liquid mass transfer
• Separate correlations for low and high interaction regimes
• Wild et al. (1992); Larachi (1991); Cassanello et al. (1996)
Gas side of gas-to-liquid mass transfer
• For most situations negligible resistance
• Gotto et al. (1977); Fukushima & Kusaka (1978)
Liquid-to-solid mass transfer
• Some have separate correlations for low and high interaction
regimes
• Goto & Smith (1975), Satterfield et al. (1978), Specchia et al.
(1978)
40
Liquid - Solid Contacting in TBR’s
• Incomplete liquid - solid contacting can occur due to:
1. Reactor- scale (gross liquid maldistribution)
2. Particle - scale (local catalyst incomplete wetting)
• Internal particle incomplete contacting is unlikely in the
absence of highly exothermic reactions
• External particle incomplete contacting is likely in the
trickle - flow regime when Lm < 5 kg / m2 - s
41
External Contacting Efficiency
Low Gas-Liquid Interaction Regime
CE = 1.617 ReL0.146 GaL 0.9711


or
 L < 5 kg / m2  s


0.224
CE = 1.021 D

CE = 1.0
L
> 5 kg / m2  s
where: D = Dynamic liquid saturation
D = LD / B
42
Liquid-Solid Contacting - Summary
Combining flow pattern deviations from ideal liquid
plug flow, and incomplete catalyst wetting:
• Liquid not in plug flow and there is no radial mixing, but all
catalyst is wetted
• Liquid not in plug flow and extensive radial mixing, and all
catalyst is wetted
• Partial external wetting of catalyst
• Partial internal wetting of catalyst
Correlations for liquid-solid contacting:
• Ruecker & Agkerman (1987), Ring & Missen (1991), Al-Dahhan
& Dudukovic (1995)
43
Intraparticle Diffusion Resistance
Conventional Thiele-modulus/effectiveness factor
approach needs to be modified to account for
partial external and intraparticle wetting:
• Mills & Dudukovic (1980) solved the diffusion-reaction equations
for partial external wetting for slab, cylinder and sphere-shaped
particles
• The numerical solution can be approximated by weighted
average of effectiveness factor of totally wetted and totally dry
particles, the weighting factor being the contacting efficiency
TB = CE W + (1- CE) NW
• Internal wetting effects have been largely ignored
44
Catalyst Effectiveness Factor
for a Differential TBR
• Assume:
(1) Gas-limiting or volatile liquid-limiting reactant
(2) First-order reaction
(3) Incomplete external wetting, complete internal wetting
• Approximate solution only possible for large modulus p
45
Overall Effectiveness Factor for a
Trickle-Bed Reactor (limiting reactant in
Gas phase), O
o =
CE
P
BiW
2
+
P
tanh P
te rm due to inter nal pore diffus ion

 + exte rnal m ass tr ans fer 
CE x
through the active ly w e tte d surface
+




of the catalyst pe lle t
+
(1 - CE )
P 2
P
+
BiD
tanh P
te rm due to inter nal pore diffus ion 
 + exte rnal m ass tr ansfe r

(1-  ) x
through the inactively w e tte d surf ace

CE




of the catalys t pe llet
Increasing ηCE decreases conversion !
LHSV based scale-up alone is not suitable !
CE = external liquid-solid contacting efficiency
CE < 1 for cocurrent downflow; CE = 1 for upflow
46
Overall Effectiveness Factor for a
Trickle-Bed Reactor, (limiting reactant
in liquid phase) O
o =
 CE
P
P
+
BiW
tanh (  P /  CE )
2
1
  p k1 

 P  Ls 
 De 
H k L
Bi w  A gs s
De
Bi D 
k gls Ls
Bi w 
k s Ls
De
1
1/2
Increasing ηCE increases conversion !
LHSV based scale-up is suitable !
De
47
Trickle-Bed Reactor
Catalyst Effectiveness Factors
Overall effectiveness factor, O
• Both external and internal transport resistances
are included
VP
 r V dV
O =
0
VP r Vs



observed average rate in the pellet
= 
rate obtained if all the pellet exists

at the bulk conditions adjacent to the pellet
 but outside the boundary layer around it







48
Comparison of Effectiveness Factors Calculated
From Previous approximate Solution and Actual Numerical
Simulation
49
Rigorous Multicomponent Diffusion Modeling
- Gas Liquid Interphase Function Vector  N1GL  ctl  {[  L ][k Lo ][]}1, j ( x Ij  x Lj )  x1 (q) /  x 


j
o
I
L
 N GL  c

2
tl  {[  L ][k L ][ ]}2 , j ( x j  x j )  x2 ( q ) /  x


j


.


.


.


 N GL  c
o
I
L
{[  L ][k L ][]}nc 1, j ( x j  x j )  xnc 1 (q) /  x 
 nc 1 tl 
j


GL
o
V
I
N

c
1
tg  {[  G ][k G ]}1, j ( y j  y j )  y1 ( q ) /  y


j


GL
o
V
I
 N 2  ctg  {[  G ][kG ]}2, j ( y j  y j )  y2 (q ) /  y

j




.
FGL ( z , t )  

.


.


o
V
I
 N GL  c
{[  G ][kG ]}nc 1, j ( y j  y j )  ync 1 (q ) /  y 
 nc 1 tg 

j


I
I
y1  K1 x1


I
y2I  K 2 x21




.


yncI  K nc xncI


I
I
I
I


x1  x2  x3  ...xnc  1


y1I  y2I  y3I  ...yncI  1


n


GL
G
L
qG  qL   N i ( H i  H i )


i 1

 3nc 1
Khadilkar et al., 1998
50
CREL
General Geometry
• Discuss MFS use here
• See muthana. Eusebio paper
51
Level III TBR Model
-Catalyst Scale EquationsExternally Half Wetted,
Partially Liquid Filled Pellet
Liquid Filled Zone
 
d
N iLC   i Ri ,liq
dx
NiLC 
 
CiLC C nc 1
d C
NtL  {[ BL ]1[]
CiL }i , j
C
CtL
dx
j 1
d  N iLC H iLC
d2
keL 2 TLC 
0
dx
dx
| Wet Zone
| Dry Zone |
 
Lc
 
Gas Filled Zone
 
d
C
N iG
  i Ri , gas
dx
C
NiG

keG
 
C
nc
CiG
d C
C
N

{[ BG ]1
CiG }i , j

tG
C
CtG
dx
j 1
d 2 C d  NiG H iG
TG 
0
dx2
dx
 
C
Khadilkar et al., 1998
C
Intra-catalyst G-L Interface
Continuity of temperature,
mass and energy fluxes,
and equilibrium relations
for all species
Liquid imbibition velocity
v=NCtL/CCtL=(RP2/8 L)(P(x=Lc)-P(x=)+2cos/RP)
52
CREL
Methods of Determining Contacting
Efficiency
• Tracer Method
• Chemical Reaction Method
53
Prediction of TBR Multiplicity Effects
• Hysteresis Effects Predicted
1.2
• Two Distinct Rate Branches Predicted
(as Observed by Hanika, 1975)
1
Conversion
0.8
• Branch Continuation, Ignition and
Extinction Points
0.6
Wet Branch(Exp t)
0.4
• Wet Branch Conversion (~30 %)
Dry Branch (Exp t)
Wet Branch (L-II)
Dry Branch (L-II)
0.2
• Dry Branch Conversion (> 95 %)
Wet Branch, (L-III)
Dry Branch (L-III)
0
0
5
10
Hydrogen Feed Ratio, N
15
• Continuation of the dry branch
• Thermal conductivity - L II model
• Intracatalyst interface location-LIII
model
System: Cyclohexene hydrogenation
54
CREL
Three Types of Catalyst for Highly
Exothermic Reactions
55
Nonvolatile Liquid-Limiting Reactant
Completely Wetted Catalyst ( ce = F i =1 )
Reaction : A (gas) + B (liquid) = P (liquid)
• Kinetic rate
: kVBS
( mol / m3 catalyst - s )
( per unit catalyst volume )
• Rate in catalyst
: kvPBS ( 1- B ) ( mol / m3 reactor - s )
( per unit reactor volume )
• Transport rate
: kLS ap BL - BS ) ( mol / m3 reactor - s )
( per unit reactor volume )
56
Overall or Apparent Reaction Rate
Liquid-Limiting Reactant ( mol / m3 reactor - s )
P kV (1 - B ) BL = k app BL =
BL
1
k LS aP
+
1
P kV (1 - B )
57
Plug-Flow Model for Scale - Up
Nonvolatile liquid, 1st order reaction
XB
 3, 600 (1 - B ) k app 

= 1 - exp 


LHSV
3,600 uL
LR
where:
LHSV =
Using :
• Same catalyst activity
• Same size particles
• Same packing procedure ( B )
• Same feed
• Same Temperature
58
Gaseous-Limiting Reactant
Completely Wetted Catalyst ( ce = F i =1 )
Reaction : A (gas) + B (liquid) = P (liquid)
• Kinetic rate
: kVAS
( mol / m3 cat - s )
( per unit catalyst volume )
• Rate in catalyst
: kv ( 1- B )PAS ( mol / m3 reactor - s )
( per unit reactor volume )
• Transport rate
:
( mol / m3 reactor - s )
( per unit reactor volume )
1. Gas - liquid KLaB ( AG /HA - AL)
2. Liquid-solid kLS aP AL - AS )
59
Overall or Apparent Reaction Rate
Gas Limiting Reactant (mol / m3 reactor - s )
A 
A 
P kV (1 - B )  G  = k app  G  =
H A 
H A 
AG 
 
H A 
1
KL aB
+
1
k LS aP
+
1
P kV (1 - B )
60
Reactor Performance for a Gas-Limiting
Reaction with First-order Reaction
A (gas) +  B (liquid)
XB =
P (liquid)
 A * (1 - B ) 3600 k app
BLO LHSV
where:
k app =
CE
2
BiWG
+

tanh 
(1 - CE ) tanh 
+

An increase in CE may decrease kapp so that equal LHSV for
scale-up may not work, i.e., if kapp decreases as uL increases.
61
Scale-up Methodology for a
Gas-Limiting Reaction
• Keep same liquid hourly space velocity (LHSV)
• Keep same ratio of liquid to gas mass velocities (L / G )
• Keep same packed-bed length (i.e., same L (uL) )
These criteria are often impractical to implement.
Hence, a fundamental reactor model that captures the
key phenomena is needed for scale-up or scale-down.
62
TBR Scale - Up for Aldehyde Hydrogenation
Scale - up done based on equal LHSV with disastrous
results
Data
Plant
Laboratory
Height (m)
19.4
0.235
Diameter (m)
0.455
0.0341
LHSV (h-1)
1.3
1.3
UL (LHSV) (mh-1)
26
0.26
H2 flow (STD) (m3h-1)
1000
-
GHSV
-
312
Pressure (bar)
65 - 80
70
Temperature (oC)
110
110
Bed porosity
0.425
0.425
Catalyst tablets
3 / 16 “ x 1 /8 “
(Vp / SP = 0.31 cm )
Conversion (XB)
0.40
0.90
63
Scale-up & Scale-down from Pilot Plant to Commercial
Reactor
• Catalyst orientation (flat surface preferred)
• Addition of fines in pilot plant to simulate good
liquid distribution and absence of wall effects
•
• Reactor internals
- Inlet distribution
- Quench zones with redistribution
- Outlet collector geometry
64