This document discusses the classification and selection of chemical reactors. It outlines the basic types of reactors including batch, continuous stirred-tank (CSTR), and plug flow reactors (PFR). Selection of reactors depends on factors such as the process type (batch, continuous, catalytic), phase (gas, liquid, solid), and required mass and heat transfer rates. For example, batch reactors are used for small batch production while CSTRs are common for liquid reactions requiring mixing. PFRs provide higher efficiency and are used when significant heat transfer is needed. Selection also considers whether the reaction involves single or multiple steps.

1. CLASSIFICATION & SELECTION OF CHEMICAL REACTORS
BASIC CLASSIFICATION
Sr.
Type of
No.
Reactor
1. Batch
Reactor
2
Continuous
Stirred
Tank
Reactor
(CSTR)
3
1
Plug Flow
Reactor
(PFR)
Principle of Working
Advantages
Limitations
All reactants are added
at the commencement
• Suitable for small scale • Not suitable for large batch
and the product
production
sizes
withdrawn at the
• Suitable for processes
• It is a closed system in
completion of the
where a range of different which once the reactants are
reaction.
products or grades is to added in the reactor, they will
They are conducted in
be produced in the same
come out as products only
tanks attached with
equipment
after the completion of the
impellers, gas bubbles or • Suitable for reactions
reaction
pumps.
requiring long reaction
times
• Suitable for reactions
with superior selectivity
One or more fluid
reagents are introduced
into a tank reactor
equipped with an
impeller while the
reactor effluent is
recovered.
A stepped up
concentration gradient
exists.
One or more fluid
reagents are pumped
through a pipe or tube.
These are characterized
by continuous gradients
of concentration in the
direction of flow.
• Highly flexible
device
• By products may be
removed in between the
reaction
• It is economically
beneficial to operate
several CSTRs in series
or in parallel.
• Reaction can be carried
out in horizontal as well
as vertical reactors
• More
complex and expensive than
tubular units
• All calculations performed
with CSTRs assume perfect
mixing
• At steady state, the flow rate
in must equal the flow rate
out, otherwise the tank will
overflow or go empty
• Higher efficiency than a
CSTR of the same
volume
• PFRs may have several
pipes or tubes in parallel
• Both horizontal and
vertical operations are
common
• They can be jacketed
• Reagents may be
introduced at locations
even other then inlet
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• Not economical for small
batches
Area of
Applications
Batch processes
are used in
chemical (inks,
dyes, polymers)
and food industry
Chemical industry
especially
involving
liquid/gas
reactions.
The tubular
reactor is specially
suited to cases
needing
considerable heat
transfer, where
high pressures and
very high or very
low temperatures
occur.

2. SELECTION OF REACTORS
Reactors can be selected depending upon following factors;
 Process Based Selection
 Phase Based Selection
 Transfer Based Selection
PROCESS BASED SELECTION
1) Batch process
Batch reactors are used. (i.e. batch processes are suitable for small production and for processes where a
range of different products or grades is to be produced in the same equipment for example, pigments, dye
stuff and polymers)
2) Continuous process
Continuous stirred tank reactors are used. (i.e. For example, Haber Process for the manufacture of
Ammonia)
3) Semi–batch process
Semi-batch reactors are used. (i.e. chlorination of a liquid.)
4) Catalytic process
Mostly followings are used;
Packed bed reactors where solid acts as catalyst.
Batch reactors are used where enzymes are involved.
5) Biological processes
Bioreactors are used depending upon mode of operation.
Bioreactor may be classified as;
 Batch Reactor
 Fed Batch Reactor
 Continuous Reactor
 moving media, also known as Moving Bed Biofilm Reactor (MBBR)
 Packed Bed Reactor
 Fibrous Bed Reactor
 Membrane Reactor
 Photo Bioreactor (PBR)
PHASE BASED SELECTION
1) Homogeneous phase reactions
 For gaseous phase
Tubular reactors are used. (i.e. in the thermal cracking of petroleum, crude oil fractions to ethylene,
and the thermal decomposition of dichloroethane to vinyl chloride.)
 For liquid phase
Batch or CSTR is used.
2) Heterogeneous phase reactions
 For Solid-liquid Gas phase we can use;
1) Trickle bed reactors
2) Flooded reactors
3) Slurry reactors
4) Fluidized bed reactors
 For liquid-liquid and Liquid-Gas phase we often use;

CSTR
 For Gas and Gas-liquid phase we use;

Packed bed reactors
3) Isolated elementary reaction or multi-step reaction mechanism

Laminar flow reactors (LFR) are often used to study them.
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3. TRANSFER BASED SELECTION
 Agitated CSTR’s are used for good Mass and Heat transfer based reactions depending upon the
Phase and Process-type match with the given prerequisites of CSTR.
 Fluidized bed reactors are used for excellent Mass and Heat transfer purposes if reaction conditions
fulfill the requirements to go for FBR. Thus FBRs are well suited to exothermic reactions.
 Tubular reactors are often used for high Heat transfer rates if the reaction conditions are given.
 Packed bed reactors often with large diameter are used where poor heat transfer is required.
 Laminar flow reactors (LFR) are operated at constant temperature systems. (i.e. LFR is generally a
long tube with constant diameter that is kept at constant temperature. conversion from methane to
higher hydrocarbons have been studied in a laminar flow reactor.)
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