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The term chemical species refers to any chemical p ycomponent or element with a given identity.

The identity of a chemical species is determined by the kind, number and configuration of that by e i d, u be a d co figu atio ospecies' atoms

Even though two chemical compounds have exactly the same number of atoms of each element, they could still be different species because of different pconfigurations

A chemical reaction has taken place when a pdetectable number of molecules of one or more species have lost their identity and assumed a newspecies have lost their identity and assumed a new form by a change in the kind or number of atoms in the compound and/or by a change in structurein the compound and/or by a change in structure or configuration of these atoms.

There are three basic ways a species may lose its chemical identity:chemical identity:• Decomposition

C bi i3 3 2 2 2CH CH H CH CH

• Combination

• Isomerization2 2N O 2NO

• Isomerization

Systems in which chemical yreactions take place are called reactorsreactors

Chemical Reaction EngineeringChemical Reaction Engineeringis the engineering activity concerned with exploitation of chemical reactions on achemical reactions on a commercial scale

Design of reactors involves:

Choosing the best type of reactor for a given reaction

Choosing the optimum operating conditionsoperating conditions

D t i i th Si f thDetermining the Size of the reactor

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Physical t t t t

Chemical treatment  Physical treatment steps steps treatment steps

CRE deals with Chemical treatment stepsp

Choice of the reactor dictates:• Pre and post treatment steps

Chemical reactor is the place in the process where themost value is added: lower-value feeds are converted

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most value is added: lower value feeds are convertedinto higher-value products.

Information needed to predict what a reactor can do

Performance equationrelates input to outputp p

Input OutputReactor

Contacting pattern Kinetics

Output = f [input, kinetics, contacting]

This is called the performance equation.

Homogeneous Heterogeneousg g

Elementary Non-elementary

Single Multiple

Chemical Bio-chemicalClassification of Reactions

Reversible Irreversibleof Reactions

Exothermic Endothermic

Constant density Variable densityConstant density Variable density

Catalytic Non-catalyticCatalytic Non catalytic

Reactor design require(almost all core areas of chemical engineering)

ThermodynamicsThermodynamics

Chemical KineticsChemical Kinetics

Fluid Mechanics

Heat & Mass transfer

Mathematics

Economics

Thermodynamics• Feasibility of a reactionFeasibility of a reaction• Heat of reaction, effect of temperature

Eq ilibri m ields constant composition• Equilibrium yields, constant, composition

Chemical KineticsChemical Kinetics• Quantitative studies of the rates at which

chemical processes occurchemical processes occur• Factors on which these rates depend• Reaction mechanism

A description of a reaction in terms of itsA description of a reaction in terms of itsconstituent molecular acts is known as themechanism of the reactionmechanism of the reaction.

Chemical Kinetics & Thermodynamics• Time is a variable in kinetics but not in

thermodynamics; TD does not deal with respect totime; equilibrium is a time-independent state.

• Information about the mechanism of chemical changeInformation about the mechanism of chemical changecan be obtained from kinetics but not fromthermodynamics.thermodynamics.

• The rate of chemical change is dependent on the pathf ti th d i i d ithof reaction; thermodynamics is concerned with

“state” and change of state of a system.

• Chemical kinetics is concerned with the rate ofreaction and factors affecting the rate, and chemicalthermodynamics is concerned with the position ofequilibrium and factors affecting equilibrium.

•Chemical kinetics is the study of chemical yreaction rates and reaction mechanisms.

•The study of chemical reaction engineering y g g(CRE) combines the study of chemical kinetics with the reactors in which thekinetics with the reactors in which the reactions occur.

•Chemical kinetics and reactor design are atChemical kinetics and reactor design are at the heart of producing almost all industrial chemicals

Th Ch i l R ti E i i (CRE)The Chemical Reaction Engineering (CRE) principles learned here can also he applied in areas such as:

• Waste treatment• MicroelectronicsMicroelectronics• Nanoparticles

Li i t• Living systems•Traditional areas of the manufacture of chemicals and phamaceutica1s.

The Chemical Reaction Engineering (CRE)The Chemical Reaction Engineering (CRE) principles learned here can also he applied in areas such as:areas such as:

• Waste treatmentMi l t i• Microelectronics

• Nanoparticles• Living systems• Traditional areas of the manufacture of d o e s o e u c u e ochemicals and phamaceutica1s.

Some of the examples that illustrate the wideSome of the examples that illustrate the wide application of CRE principles are shown in Fi 1 2Figure 1-2

Batch/ContinuousBatch/Continuous

Isothermal/Nonisothermal

Classification of reactorsof reactors

Ideal/Non-ideal

Homogenous/Heterogeneous

Types of reactors

Homogeneous Heterogeneousg g

Batch Packed bedBatch

Plug flow Moving bedg

CSTR Fluidized bed

Laminar flow

Recycle

The rate of reaction tells usThe rate of reaction tells us how fast a number of moles ofhow fast a number of moles of one chemical species are being o e c e ca spec es a e be g

consumed to form another chemical speciesp

How can reaction rate be expressed?How can reaction rate be expressed?

• Select one reaction component for consideration and define the rate in terms of this component, i.

• If the rate of change in number of moles of this component due to reaction is dNi/dt, then the rate of reaction in itsdNi/dt, then the rate of reaction in its various forms is defined as follows:

Definition of reaction rateBased on unit volume of reacting fluid

dN1 moles i formedii

dN1 moles i formedrV dt (mass of solid)(time)

Ni : moles of iV : volume of fluid

Based on unit mass of solid in fluid-solid systems

ii

dN1 moles i formedrW dt (mass of solid)(time)

W = Mass of solid( )( )

Based on unit interfacial surface area in two-fluid system orbased on per unit surface area of solids in gas-solid systemsbased on per unit surface area of solids in gas-solid systems

dN1 molesi formedii

dN1 molesi formedrS dt (surface)(time)

S = interfacial area

Based on unit volume of solid in gas-solid systems

ii

s

dN1 moles i formedrV dt (volume of solid )( time)

Vs : volume of solid

Based on unit volume of reactor

dN1 moles i formedii

r

dN1 moles i formedrV dt (volume of reactor)(time)

Vr = reactor volume

i i i s i r iVr Wr Sr V r V r i i i s i r i

EXAMPLE 1.1 THE ROCKET ENGINEA rocket engine, Fig. El.l, burns a stoichiometric mixture of fuel (liquid hydrogen)in oxidant (liquid oxygen). The combustion chamber is cylindrical, 75 cm long and60 cm in diameter, and the combustion process produces 108 kg/s of exhaustgases. If combustion is complete, find the rate of reaction of hydrogen and ofoxygen.

We want to evaluate:

Next, let us look at the reaction occurring

EXAMPLE 1.2 THE LIVING PERSONA human being (75 kg) consumes about 6000 kJ of food per day. Assume that thefood is all glucose and that the overall reaction is all glucose and that the overallfood is all glucose and that the overall reaction is all glucose and that the overallreaction is:

Find man's metabolic rate (the rate of living, loving, and laughing) in terms ofmoles of oxygen used per m3 of person per second.

We want to find:

Let us evaluate the two terms in this equation. First of all, from our life experience we estimate the density of man to be:

Therefore, for the person in question

Next, noting that each mole of glucose consumed uses 6 moles of oxygen and releases 2816 kJ of energy, we see that we need