overview of chemical reaction engineering

7/28/2019 Overview of Chemical Reaction Engineering

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The termchemical s eciesrefers to an chemical

component or element with a given identity.

The identity of a chemical species is determined

b thekind number and confi uration of that

species' atoms


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Even though two chemical compounds have exactly

the same number of atoms of each element, theycould still be different s ecies because of differentconfigurations


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A chemical reaction has taken lace when a

detectable number of molecules of one or more

form by a change in the kind or number of atoms

or configuration of these atoms.

There are three basic ways a species may lose its

Decomposition 3 3 2 2 2CH CH H CH CH

om nat on2 2N O 2NO


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S stems in which chemical

reactions take place are called

is the engineering activity

concerned with exploitation of

commercial scale


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Design of reactors involves:

Choosing the best type ofreactor for a given reaction

Choosing the optimum

e ermnng e ze o e

reactor

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Physical Chemicaltreatment Physicalrea men s eps steps treatmentsteps

CRE deals with Chemical treatment ste s

Choice of the reactor dictates: Pre and post treatment steps

Chemical reactor is the place in the process where the-

7into higher-value products.


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Information needed to predict what a reactor can do

Performance equationrelates in ut to out ut

Input OutputReactor

Contacting pattern Kinetics

Output = f [input, kinetics, contacting]

This is called the performance equation.


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Homo eneous Hetero eneous

Elementary Non-elementary

Single Multiple

Chemical Bio-chemicalClassification

Reversible Irreversible

Exothermic Endothermic

-


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Reactor design require

(almost all core areas of chemical engineering)

Fluid Mechanics

Heat & Mass transfer

Mathematics

Economics


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Thermodynamics

Heat of reaction, effect of temperature

u u y , ,

Quantitative studies of the rates at which

Factors on which these rates depend

Reaction mechanism

constituent molecular acts is known as the

.


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Chemical Kinetics & Thermodynamics

Time is a variable in kinetics but not inthermodynamics; TD does not deal with respect to

time; equilibrium is a time-independent state.

can be obtained from kinetics but not from

thermod namics.

The rate of chemical change is dependent on the patho reac on; ermo ynam cs s concerne w

state and change of state of a system.

Chemical kinetics is concerned with the rate of reaction and factors affecting the rate, and chemical

thermodynamics is concerned with the position of equilibrium and factors affecting equilibrium.


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Chemical kinetics is the stud of chemicalreaction rates and reaction mechanisms.

The study of chemical reaction engineering(CRE) combines the study of chemical

reactions occur.

the heart of producing almost all industrial

chemicals


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e emca eac on ngneer ngprinciples learned here can also he applied inareas such as:

Waste treatmentNanoparticles v n s s ems

Traditional areas of the manufacture ofchemicals and phamaceutica1s.


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principles learned here can also he applied in

Waste treatment croeec ron csNanoparticles

Living systemsTraditional areas of the manufacture ofchemicals and phamaceutica1s.

application of CRE principles are shown ingure -


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Isothermal/NonisothermalClassification

Ideal/Non-ideal

Homogenous/Heterogeneous


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Types of reactors

Homo eneous Hetero eneous

Packed bed

Plug flow Moving bed

CSTR Fluidized bed

Laminar flow

Recycle


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one chemical s ecies are beinconsumed to form another

chemical s ecies


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Select one reaction component for

consideration and define the rate in termsof this component, i.

If the rate of change in number of molesof this component due to reaction is

various forms is defined as follows:


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Definition of reaction rate

Based on unit volume of reacting fluid

iir

V dt (massof solid)(time)

Ni : molesof iV : volumeof fluid

Based on unit mass of solid in fluid-solid systems

ii

dN1 molesi formedrW dt massof solid time

W = Mass of solid

Based on unit interfacial surface area in two-fluid system or

-

i

ir S dt (surface)(time)

S = interfacial area


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Based on unit volume of solid in gas-solid systems

ii

s

dN1 molesi formedrV dt (volumeof solid)(time)

Vs : volumeof solid

Based on unit volume of reactor

i

ir

r V dt (volumeof reactor)(time)

Vr = reactor volume

Vr Wr Sr V r V r


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EXAMPLE1.1THEROCKETENGINEA rocket engine, Fig. El.l, burns a stoichiometric mixture of fuel (liquid hydrogen)

in oxidant (l iquid oxygen). The combustion chamber is cyl indrical, 75 cm long and60 cm in diameter, and the combustion process produces 108 kg/s of exhaust

gases. If combustion is complete, find the rate of reaction of hydrogen and of

oxygen.

We want to evaluate:


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Next, let us look at the reaction occurr ing

EXAMPLE 1 2 THE LIVING PERSON


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EXAMPLE 1.2 THE LIVING PERSONA human being (75 kg) consumes about 6000 kJ of food per day. Assume that the

reaction is:

Find man's metabolic rate (the rate of living, loving, and laughing) in terms of moles 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:


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Therefore, for the person in question

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

overview of chemical reaction engineering

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