Kingdom of Saudi Arabia
University of Hail
Faculty of Engineering
Department of Chemical Engineering
Chemical Reaction Engineering
Course code: CHE 402
Text Book:
Chemical Reaction Engineering, 3rd Edition ,
Author :Octave Levenspiel
Editor: John Wiley &Sons ,Copyright 1999.
References:
1-Elements of Chemical Reaction Engineering (4th Edition) by H. Scott Fogler , Publisher:
Prentice Hall , ISBN-10: 0130473944
2- Davis, Mark E. and Davis , Robert J. (2003) Fundamentals of Chemical Reaction
Engineering.
McGraw-Hill Higher Education , New York, NY. ISBN 0-07-245007-X
Introduction:
Chemical reaction engineering is simply defined as that engineering activity which is concerned
with the exploitation of chemical reactions on commercial scale.
Its main aim is the successful design and operation of chemical reactors . this activity
is unique for chemical engineers and this activity sets apart as a distinct branch of the
engineering profession.
Chemical engineers are faced by many questions as:
What kind of information is needed to face the problem? How best to obtain it? And how to
select a reasonable design from the many available alternatives?
The scope of this area of chemical engineering is to teach chemical engineers how to answer
these questions reliably and wisely ?
Any industrial chemical process is designed to produce a desired product economically from a
variety of starting materials through a various treatments as it can be illustrated in the following
figure 1-1:
The required raw materials have to undergo a number of physical treatment steps to put them in the
form in which they can react chemically. These treated materials are to pass through the reactor .
The products of the reactor are to be treated physically again – separation ,purification, etc. for the final
desired product to be obtained.
Design of equipments for physical treatment steps is discussed in the unit operation courses .
In this course we are to learn how to make calculations related to chemical treatments while our
concern will be concentrated on the heart of the process ,the reactor . The reactor is the thing which
makes or breaks the process economically.
It must be mentioned that the design of the reactor is no routine matter ,and many alternatives are
probable for each process . In searching for the optimum it is not just the cost of the reactor that
determines our decision about the reactor ,since one design may have the lowest reactor cost , but
The materials leaving the unit may be such that there treatment requires a much higher cost than
alternative designs. Hence the economics of the overall process must be considered.
Reactor design uses information ,knowledge and experience from a variety of chemical engineering
areas – thermodynamics ,chemical kinetics ,fluid mechanics ,heat transfer ,mass transfer and finely
the economics.
Chemical reaction engineering is the synthesis of all these factors with the aim of properly designing a
perfect chemical reactor.
To find what a reactor can do for us ,we need to know :
1- kinetics 2-the contacting pattern 3-the performance equation .These three parameters are
interrelated and illustrated in fig. 1.2
Much of our work will deal with how to find the expression for the relation between output and input
of the reactor which we will call the Performance equation , which states that:
Output=f{input , kinetics , contacting pattern} .The physical meaning of this statement is that the stream
which is to leave the reactor will have a composition which is independent on :
1- The composition of the reacting mixture at the inlet of the reactor.
2- The rate of the reaction which depends on the intrinsic reaction rate .the intrinsic reaction rate
Tells us information about the speed of the reaction ,if the rate is high ,then the chemical
equilibrium will tell us about what will leave the reactor, if the rate is not high(slow
reaction)then the mass and heat transfer phenomena in addition to the chemical step will tell us
about what will leave the reactor.
3- The effect of mass and heat transfer limitations on the intrinsic reaction rate ,this is illustrated
through the contacting pattern on how materials contact each other in the reactor .
Classification of reactions :
1- Homogeneous reactions are met in cases where the reaction mixture is composed of
gases only or liquids only, i.e one phase .
2- Heterogeneous reactions are met in cases where more than one phase are present in the
reactor , i.e liquid +solid ,gas +solid, liquid +gas or solid + gas + liquid simultaneously.
3- There is another class of reactions in which the classification is not clear as it is seen in
the biological reactions and the enzyme –substrate reactions .in these cases we can not
make distinction between homo- and heterogeneous reactions.
These two classes of reactions are illustrated with specified cases in the following table:
4- Catalytic or non catalytic reactions ,depending on whether catalyst is present or not. In a
homo. Or a heterogeneous reactions .
Variables affecting the rate of reaction :
These factors are : temperature ,pressure and composition in
homogeneous reacting systems .
But in heterogeneous systems , the effect of inter-particle and
intra-particle mass and heat transfer limitations are to be
considered .
In these cases when the rate is very high then the limitations are
controlling , but when the rate is too low ,the chemical reaction
rate itself is the controlling step.
Definition of the reaction rate :
Usually the rate is expressed as the amount produced or consumed
per unit time and per unit volume of (reactor ,catalyst)or per unit
mass of catalyst or per unit area of the interfacial surface area
between two phases , as it is seen from the following paragraphs.
ri=(1/v)*dNi/dt ,where ri: is the rate of generation or production of
The product i in moles /(second*unit volume of the reacting
mixture),v is the volume of the reacting mixture, t is the time in
seconds and Ni is the number of moles of I produced.
The speed of chemical reactions :the speed may vary from very
low as the case of chemical reactions in water treatment plants to
very high values met in fuel burning or bimolecular rxs. The
spectrum of reaction rates is illustrated in the following fig.1.3
overall plan :
Reactors may have any color , size and shape and can be used for all types
of reactions.
We may have giant cat. Crackers for oil refining , blast furnaces for iron
making , sludge bonds for sewage treatment ,amazing polymerization
tanks For plastics ,paints and fibers and the critically important
pharmaceutical vats for producing Penicillin ,aspirin and birth controlling
drugs .
These reactions are so different in rates and types and must not be treated
In the same way.
Each type requires the development of the appropriate set of performance
equation.
