education

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Chemical Reaction Engineering
An Introduction to Industrial
Catalytic Reactors
Tarek Moustafa, Ph.D.
November 2011

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Module objectives (TPO)
• To differentiate between various types of
catalytic reactors
• To apply the design equations: material,
energy and momentum balance equations
on ideal and industrial catalytic reactors

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Introduction
• In most of chemical engineering job venues,
a good understanding of industrial reactors is
essential and important
• The reactors are the heart of most chemical
processes and all technologies starts from the
reaction part and accordingly the reactor
• Many types of industrial reactors are
available depending on the reaction and the
process involved

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General Classifications
• Catalytic vs. non-catalytic Reactions
- Catalytic reactions are more dominant in
chemical industry (especially organic)
- Catalytic reactions are more difficult to handle
• Homogeneous vs. Heterogeneous Catalysts
- Homogeneous catalysts are generally more
active but a separation & recycle steps for the
catalyst are essential
- Heterogeneous catalysts are most widely used

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Introduction
• Ultimate Objective:
Commercial Reactor
– Design and Operate:
Successfully
• Typical Unfortunate News
– Catalyst does not perform
well when scaled-up to
commercial reactor
– Hot spot, temperature
runaway, explosion

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Phenomena in Commercial
Reactors
• Transport Phenomena
– Momentum Transfer
– Heat Transfer
– Mass Transfer
• Chemical Reactions
– On Heterogeneous Catalyst
Surface
All Happens Simultaneously !

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Types/Configurations of
catalytic reactors
• Fixed Bed Catalytic Reactors
- Adiabatic single packed bed
- Adiabatic beds in series with intermediate cooling or
heating
- Multi-tubular fixed bed
- Radial flow bed
- Reverse flow bed
- Auto-thermal reactors
• Fluidized Bed Reactors
• Moving Bed Reactors
• CSTR with jacket or coil (usually for liquid phase)

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Reactors’ Schematic
Single
Adiabatic
bed
Adiabatic beds in
series or staged
beds with
intermediate
heating or cooling
Multitubular
fixed bed

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Reactors’ Schematic
Radial
flow bed
Reverse flow
reactors
Auto-thermal
reactors
T
T0

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Important Phenomena & Considerations
• Adiabatic Packed Bed Catalytic Reactors
- Simplest design
- Used when reaction is associated with moderate heat
generation / consumption
• Multi-tubular fixed bed
- Reaction is associated with high heat generation /
consumption
• Radial flow bed
- Pressure drop is critical
• Reverse flow bed
- Used for endothermic reactions, to produce product and
exothermic catalyst regeneration

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Ideal reactors
• CSTR (continuous stirred tank reactor)
- Composition and temperature everywhere is the
same and equals that of the outlet
- Infinite diffusion and sometimes called one point
reactor
• PFR (Plug flow reactor)
- Composition and temperature changing from one
point to another along the length of the reactor
- No diffusion and flow is only due to bulk flow
inside the reactor

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Non-isothermal continuous-flow
stirred catalytic reactor
Process Feed
Cooling/Heating
fluid inlet

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Non-isothermal continuous-flow stirred
catalytic reactor – Design Equations
Q = Fout Cp (T – Tr) - FAo Cpo (To – Tr ) + FAo x  HR
• Material Balance
W rA = FAo x
• Rate Law (in case of first order reaction)
rA = ko e-E/RT CA
• Energy Balance
Q = U A (T – Tc)

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Example 101
An isomerization reaction is taking place in a
continuous stirred catalytic reactor: A  B
The reaction is first order with respect to A and the
rate can be expressed as: k = 16.96*1014 e-19400/T
m3/kg cat h. It is desired to feed 800 kgmole per hour
of pure liquid A to the reactor. If the reactor is
operated adiabatically and the inlet temperature and
concentration are 140°C and 10 gmol/l respectively.
What is the volume required of the catalyst to
achieve 20% conversion if the catalyst bulk density
is 2 g/cm3. (Hr = 21 kcal/gmole,
Cp A = 32 cal/gmole K and Cp B = 36 cal/gmole K)

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Solution
Q = Fout Cp (T – Tr) - FAo Cpo (To – Tr ) + FAo x  HR
• Material Balance
W rA = FAo x  W rA = 800 * 0.2
• Energy Balance
• Rate Law
0 = 800*32.8*(T – 298) – 800*32*(413 – 298 ) - 800*0.2*21000
rA = ko e-E/RT CA = 16.96 1014 e-19400/538.2 *10(1-0.2)
= 0.377 kgmol/kgcat h
T = 538.2 K
W = 424.6 kg and V = 0.2123 m3

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Isothermal plug-flow catalytic reactor
• Compositions and possibly pressure are
changing along the length of the reactor
• Rate is not constant inside the reactor, and
is varying form one location to another
Fs 2
T, P2
Fs 1
T, P1

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Isothermal plug-flow catalytic reactor
– Design Equations
• Material Balance
rA dW = FAo dx
• Rate Law
Could be power form or Langmuir-Hinshelwood
kinetics
rA = ko e-E/RT CA /(1+KACA+KBCB)

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Non-isothermal plug-flow catalytic
reactor
• Compositions, temperature and possibly
pressure are changing along the length of the
reactor
• Rate is not constant inside the reactor, and is
varying form one location to another
Fs 2
T2, P2
Fs 1
T1, P1

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Non-isothermal plug-flow catalytic
reactor – Design equations
F Cp dT + rA dW  HR
o - U A (T – Tc) = 0
• Material Balance
rA dW = FAo dx
• Rate Law (Langmuir-Hinshelwood kinetics)
rA = ko e-E/RT CA /(1+KACA+KBCB)
• Energy Balance
• Momentum Balance
dP/dL = - G (1-) [150(1- ) + 1.75 G]
Dp 3 Dp

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References
• Missen, R., Mims, C. and Saville, B., Introduction
to chemical reaction engineering and kinetics,
Wiley (1999).
• Fogler, S., Elements of chemical reaction
engineering, 4th ed., Prentice-Hall (2004).
• Froment, G.F. and K.B. Bishoff, “Chemical
reactor analysis and design”, 2nd ed., Wiley
(1990).