chemical reaction engineering i chapter 1 mole balance and

Mole Balance and Kinetics by Sureena

Chemical Reaction Engineering I

Chapter 1

Mole Balance and Kinetics

by

Sureena AbdullahFaculty of Chemical and Natural Resources

Engineeringsureena@ump.edu.my

Mole Balance and Kinetics by Sureena

Chapter Description

Aims

Expected Outcomes

References & other information

• Describe on the concepts of rate of reactions • Explain about the chemical kinetics, emphasizing definitions and able to relate on

how the reaction rate depends on the concentrations of the reacting chemicals.

• Formulate the rate of reactions for elementary reactions • Define the Rate Law

• Elements of Chemical Reaction Engineering’, by H. Scott Fogler

Mole Balance and Kinetics by Sureena

Subtopics

Reaction Kinetics and Data Analysis

General mole balance equations

Introduction to conceptual design

1.1

1.2

1.3

Mole Balance and Kinetics by Sureena

Reaction Kinetics and Data Analysis

o Rate of reaction

o rA → the no. of moles reacting (A) per unit time per

unit volume (mol/dm3 . s)

o rA’ → the no. of moles A per unit time per unit

catalyst mass (mol/ s . g catalyst)

o Unit : mol/dm3/s

o Can be expressed in terms of (sign convention):

i. The rate of disappearance of a substance, -rA

ii. The rate of formation of the substance, rA

Mole Balance and Kinetics by Sureena

• The reaction kinetics are formulated based on experimentally proven mechanism, not an arbitrary phenomenon

• Rate law is the simplest model, for instance:

A → Products

The rate of transformation of A can be:-

1. Linear function of concentration; or

-rA = kCA

2. Quadratic function of concentration; or -rA = kCA2

• Other function of concentration, such as -rA = k1CA/(1+k2CA) etc

Reaction Kinetics and Data Analysis

Mole Balance and Kinetics by Sureena

Relation of Rate in Reaction

• For a reaction given below:

aA + bB → cC + dD

• Example:

2NO + O2 →2NO2

Mole Balance and Kinetics by Sureena

Rate Law

• Consider the following reaction:

aA + bB → cC + dD

The rate law may be written as :

e.g;

where k = specific reaction rate

α = order with respect to A

β = order with respect to B

α+β = overall order

• What happen if

1. α = a and β = b

2. α ≠ a and β ≠ b

Elementary Rate Law

• Stoichiometry coefficients = individual reaction order of each species.

• H2 +I2 → 2HI

(rHI) = k CH2 CI2

Non-elementary Rate Law

• CO+CI2→COCI2

• This rxn is 1st order with respect to CO,

3/2 order with respect to CI2 and 5/2

order overall.

Mole Balance and Kinetics by Sureena

General Moles balance Equation

FjoFj

Gj and

dNj/dt

System

Volume

Mole Balance and Kinetics by Sureena

Design Equation for Batch Reactor

j

AO

N

N A

A

)V(r

dNt

−𝑁𝐴0𝑑𝑋

𝑑𝑡= 𝑟𝐴 V

X=𝑁𝐴0−𝑁𝐴

𝑁𝐴0

Limiting reactant

𝑡 = න0

𝑋𝑁𝐴0𝑉

𝑑𝑋

−𝑟𝐴

BatchVrA

A dt

dN

Mole Balance and Kinetics by Sureena

Design Equation for Continuous Reactors

10

)(r

FFV

A

AA0

AA r

dV

dF

A

AO

F

F A

A

)(r

dFV

'A

Ar

dW

dF

A

AO

F

F

'

A

)(r

dFW

A

X=𝐹𝐴0−𝐹𝐴

𝐹𝐴0

Limiting reactant

𝑉 =𝐹𝐴0𝑋

−𝑟𝐴

𝑑𝑋

𝑑𝑉=−𝑟𝐴𝐹𝐴0

𝑉 = න0

𝑋

𝐹𝐴0𝑑𝑋

−𝑟𝐴𝑑𝑋

𝑑𝑊= −

𝑟𝐴′

𝐹𝐴0

𝑊 = න0

𝑋

𝐹𝐴0𝑑𝑋

−𝑟𝐴′

CSTR

PFR

PBR

Mole Balance and Kinetics by Sureena

Mole Balance for Reactive Unit

• GENERAL

• Stirred Tank Reactor (STR)

• Tubular Reactor

0

j

j j j

dNF F r V

dt

0A

A A A

dNF F r V

dt

AA V A V V A

dNF F r V

dt

Batch?

Continuous (CSTR)?

Plug Flow?

Packed-Bed?

Mole Balance and Kinetics by Sureena

Authors Information

Credit to the authors:

Dr Mohd Sabri Mahmud, Assoc Prof Dr

Maksudur Rahman Khan, Dr Hamidah

Abdullah