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Chemical/Polymer ReactorDesign

Muhammad Zafar Iqbal


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What to do today.. Introduction to Reactor Design

Reactor Classification

Modes of Operation of Reactors

Choice of Operating Conditions: A practical

approach

Design of an ideal batch Reactor


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Fundamentals Chemical reactor is the heart of the plant

Basic aim is to produce a specified product at a given rate fromunknown reactants.

How to proceed:

1- The type of reactor and its method of operation

2- The physical condition of reactants at inletWhat is desired:

1- Reactor Size: Volume and important dimensions

2-Composition and physical conditions of product

3- Temperature inside the reactor and H.T methodology4- Operating pressure and any pressure drop occurring at

inlet or outlet of reaction mixture

The existence of any by product must be known


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Reactor Classification and type selection

Homogenous Reactors:

Only one phase is involved: gas or liquidWhen more phases are involved the mixing is very important

Heterogeneous Reactors:

Two or more phases are involved.

Normally solids if present then are in catalyst form.

A heterogeneous reactor may involve a heterogeneous reaction

or a homogeneous reaction.

Heterogeneous reactors show greater variety of configuration

and contacting patterns than homogenous reactors.


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Types of Reactors

Batch Reactor (BR, STR)

The reactants are initially charged into the vessel and are wellmixed and left to react for a certain period of time. The

resultant mixture is then discharged. This is an unsteady

operation where the composition changes with time but is

uniform throughout the reactor at a specific time.


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Continuous ReactorsContinuous stirred tank reactor (CSTR, MFR, BMFR)

An agitator is introduced to disperse the reactants thoroughly into

the reaction mixture immediately they enter the reactor.

Product is continuously drawn out and thats why known for perfect

mixing.

Compositions at outlet and inside reactor are same.

Best suitable for liquid phase reactions


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Plug Flow Reactor: (PFR)

These are tubular reactors generally but not necessarily. Often called piston flow, slug flow, ideal tubular flow or unmixed flow

reactors.

The residence time for all the elements is same: Must be

Sometimes used for liquid phase reactions but best suited for gas

phase reactions.


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Semi-Batch Reactors

Aim of their invention is to get benefit of any thing by changing the

contacting pattern.

One of the reactants may not be charged at once but slowly.

When required:

To react a gas with a liquid

To control a highly exothermic reaction

To improve the product yield in suitable circumstances


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Heat of Reaction and Reactor Type

When heat of Reaction is too small then can be neglected

But if it is high then this is major influencing factor The temperature of the system can rise or fall depending

upon the reaction type: Exothermic or Endothermic

A relation must be there among enthalpy, heat transferred,

and temperature change of the system (Energy balance)

Before designing, check for:

1- What is the heat of reaction?

2- Acceptable range of temperature?


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Different reactor configurations based on

Temperature(Modes of Operation)

Adiabatic Reactors

Very easy to design

Temperature drop or rise remains within acceptable range The properties of the product are not affected by such rise or

fall in temperature


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Reactors with Heat Transfer

This arrangement is used when isothermal operation isdesired

The temperature can be controlled through internal coils,

external jackets or external heat exchanger

The factors which influence the H.T. are:

1-H.T. coefficient

2- Jacket Pressure

3- Jacket Pressure drop

4- Reactor pressure

5- Cleanliness

6- Cost


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Reactor with Internal Coils


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Jacketed Reactor and its types


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Reactor with heat exchanger


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Auto thermal Reactors

These are the self supporting systems in which heat of one

stream is used to heat feed stream in order to raise the

reaction rate and save the time and the cost.

These show integrated reactor system with feed back systems

An external source of heat is required to start the reaction

once and then reaction proceeds on itself.

This is valid for Highly Exothermic Reaction Systems


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Choice of Process Conditions

Two main principles are involved:

1- Chemical Equilibrium2- Chemical Kinetics

If equilibrium contact is very large, then reaction is said to be

irreversible. But there lies a max. extent of that reaction upto

which it can proceed (Chem. Equil.).How to proceed: Find the applicable temperature range

of reaction and then investigate Kc under that temperature

range.

From recommended literature it is found that:


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Example (Coulson)

Statement:

A process for the manufacture of styrene by thedehydrogenation of ethylbenzene

C6H5-CH2-CH3 = C6H5-CH=CH2 + H2

At T= 560 degree C

Tasks:

1- Determine max. conversion of Et at P=1 bar

2- Determine max. conversion at Et: Steam = 1 : 15

Solve Yourself


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Ideal Batch ReactorDesigning: Calculation of Reaction Time: basic Design Equation

1-

2-

3-

4- Time to reach a specificconversion


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For Constant Density systems

For gas-phase reactions

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