1 Gulfam Raza Haidery

CLASSIFICATION & SELECTION OF CHEMICAL REACTORS

BASIC CLASSIFICATION

Sr.

No.

Type of

Reactor

Principle of Working Advantages Limitations Area of

Applications

1. Batch

Reactor

All reactants are added

at the commencement

and the product

withdrawn at the

completion of the

reaction.

They are conducted in

tanks attached with

impellers, gas bubbles or

pumps.

• Suitable for small scale

production

• Suitable for processes

where a range of different

products or grades is to

be produced in the same

equipment

• Suitable for reactions

requiring long reaction

times

• Suitable for reactions

with superior selectivity

• Not suitable for large batch

sizes

• It is a closed system in

which once the reactants are

added in the reactor, they will

come out as products only

after the completion of the

reaction

Batch processes

are used in

chemical (inks,

dyes, polymers)

and food industry

2 Continuous

Stirred

Tank

Reactor

(CSTR)

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.

• 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

Chemical industry

especially

involving

liquid/gas

reactions.

3 Plug Flow

Reactor

(PFR)

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.

• 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

• Not economical for small

batches

The tubular

reactor is specially

suited to cases

needing

considerable heat

transfer, where

high pressures and

very high or very

low temperatures

occur.

2 Gulfam Raza Haidery

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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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.)