Polymer/Chemical Reactor Design

Muhammad Zafar Iqbal

Today

• Recycle Reactors and some important considerations• Autocatalytic Reactors and their important considerations• Optimum temperature Progression • Reactor Operating Line• Basics of Non-linear flow: Fundamental Concept

Recycle ReactorsA reactor for which product stream is split and a part of that split

stream is sent back to reactor to enhance the reactor performance is called a Recycle Reactor.

Recycle Stream is defined as:

Recycle stream is introduced to enhance the degree of mixing.Therefore it is conventionally said that for R=0, the behavior is

totally plug and for R=very large, the behavior is mixed flow reactor.

Types of recycle reactor

Ref:Chemical Process design andIntegration by Smith, Ch-13,14

Performance Equation

For this plug flow reactor, the performance equation is given as:

The actual conversion at inlet is given by:

The concentration at inlet to the reactor is given by

So finally we get the following results:

The final equation for any expansion factor value is:

Also in terms of concentration,

Graphical representation

Autocatalytic Reactors• In general, when conc. Of reactants is high (at start) the rate

of reaction is also high. When conc. Is lowered, the reaction proceeds slowly.

• In autocatalytic reactions, the rate of reaction at the start is slow but as the product is formed more and more, the speed of reaction increases up to a certain level then drops.

• Therefore there is always a need for optimization of reactors for autocatalytic reactions.

• A general representation of autocatalytic reaction is given as:

Mixed flow Vs Plug flow Reactor

Temperature and Pressure Effects in Single Reaction based Reactors

• There is a great influence of operating conditions on the reactor set up and optimization.

Normally the following three step procedure is adopted:1- T and P effects on equilibrium composition, rate of reaction and product distribution2- The Heat effects and their impact on operating Temp.3- Economic optimization of process

Single Reactions:Two factors are considerable:1- Conversion Level no product distribution2- Reactor stability

Optimum Temperature Progression

Reactor Operating LineThe size of a reactor for a given duty and for a given

temperature progression is found from following procedure:

• Draw XA Vs T (Reactor Operating Line)

• Find Reaction rates at different XA along this path

• Plot 1/-rA Vs XA for this path

• Find the area under the curve or area of the rectangle depending upon the type of reactor used.

Ref:Chemical Reaction Engineering by LevenspielChapter 9.

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Non-Ideal Flow: Fundamental Concepts

Three main factors which can describe the flow are:

• RTD• State of Aggregation• Earliness and Lateness of Mixing

Residence Time Distribution

States of Aggregation of the flowing stream

Mixing

Ref:Chemical Reaction Engineering by LevenspielChapter 11.