Chemical Reaction Engineering - PowerPoint Presentation

Slide1

Chemical Reaction Engineering (CRE) is the field that studies the rates and mechanisms of chemical reactions and the design of the reactors in which they take place.

Lecture

4

Slide2

Lecture 4

2

Block 1

Mole Balances

Size CSTRs and PFRs given –rA=f(X)Block 2Rate LawsReaction OrdersArrhenius EquationBlock 3StoichiometryStoichiometric TableDefinitions of ConcentrationCalculate the Equilibrium Conversion, Xe

Chapter 4

Slide3

Reactor

Differential

Algebraic

Integral

CSTR

PFR

Batch

X

t

PBR

X

W

3

Reactor

Mole Balances

Summary

in terms of conversion, X

Review Lecture 2

Slide4

Levenspiel Plots

4

Review Lecture 2

Slide5

5

PFR

Review Lecture 2

Slide6

6

Reactors in Series

Only valid if there are no side streams

Review Lecture 2

Slide7

7

Reactors in Series

Review Lecture 2

Slide8

8

Step 1:

Rate Law

Step 2:

Stoichiometry

Step 3: Combine to get

Two steps to get                    Review Lecture 2

Slide9

Building Block 2: Rate Laws

9

Power Law Model:

A reactor follows an elementary rate law if the reaction orders just happens to agree with the stoichiometric coefficients for the reaction as written.

e.g. If the above reaction follows an elementary rate law

2nd order in A, 1st order in B, overall third order

Review Lecture 3

Slide10

Arrhenius Equation

10

E = Activation energy (cal/mol)

R = Gas constant (cal/mol*K)

T = Temperature (K)A = Frequency factor (same units as rate constant k)(units of A, and k, depend on overall reaction order)

T

kReview Lecture 3

Slide11

Reaction Engineering

11

These topics build upon one another

Mole Balance

Rate LawsStoichiometryReview Lecture 3

Slide12

Algorithm

12

Step 1:

Rate Law

Step 2:

Stoichiometry

Step 3: Combine to get How to findReview Lecture 3

Slide13

Building Block 3: Stoichiometry

13

We shall set up

Stoichiometry Tables

using species A as our basis of calculation in the following reaction. We will use the stoichiometric tables to express the concentration as a function of conversion. We will combine Ci = f(X) with the appropriate rate law to obtain -rA = f(X).

A is the limiting reactant.

Chapter 4

Slide14

Stoichiometry

14

For every mole of A that reacts,

b/a

moles of B react. Therefore moles

of B

remaining

:Let ΘB = NB0/NA0Then:Chapter 4

Slide15

Batch System - Stoichiometry

Table

15

Species

SymbolInitialChangeRemainingBBNB0=NA0Θ

B

-b/aN

A0XNB=NA0(ΘB-b/aX)AANA0-NA0XNA=NA0(1-X)InertINI0=NA0ΘI----------NI=NA0ΘI

F

T0

N

T

=NT0+δNA0X

Where

:

and

C

C

N

C0

=N

A0

Θ

C

+c/aN

A0X

N

C=NA0(ΘC

+c/aX)

DDND0=NA0ΘD

+d/aNA0X

ND

=NA0

(ΘD+d/aX)

δ

= change in total number of mol per mol A reactedChapter 4

Slide16

Stoichiometry Constant Volume

Batch

16

Note:

If the reaction occurs in the liquid phaseorif a gas phase reaction occurs in a rigid (e.g. steel) batch reactor

Then

etc.

Chapter 4

Slide17

Stoichiometry Constant Volume

Batch

17

Suppose

Batch:

Equimolar

feed:Stoichiometric feed:

Chapter 4

Slide18

Stoichiometry Constant Volume

Batch

18

and

we have If

, then

Constant

Volume Batch

Chapter 4

Slide19

Batch Reactor - Example

19

Consider the following elementary reaction with

K

C=20 dm3/mol and CA0=0.2 mol/dm3. Find Xe for both a batch reactor and a flow reactor.Calculate the equilibrium conversion for gas phase reaction, Xe

.

Chapter 4

Slide20

Batch Reactor - Example

20

Step 1:

Step 2: rate law:

Calculate

X

e

Chapter 4

Slide21

Batch Reactor - Example

21

Symbol

Initial

ChangeRemainingB0½

N

A0

XNA0 X/2ANA0-NA0XNA0(1-X)Totals:NT0=NA0NT

=NA0

-N

A0 X/2

@ equilibrium: -r

A=0

Chapter 4

Slide22

Batch Reactor - Example

22

Species

Initial

ChangeRemainingANA0-NA0XNA=N

A0

(1-X)

B0+NA0X/2NB=NA0X/2NT0=NA0NT=NA0-NA0X/2Solution:

At

equilibrium

Stoichiometry:

Constant Volume:

Batch

Chapter 4

Slide23

Batch Reactor - Example

23

Chapter 4

Slide24

Flow System – Stoichiometry Table

24

A

A

FA0-FA0XFA=FA0(1-X)SpeciesSymbol

Reactor

FeedChangeReactor EffluentBBFB0=FA0ΘB-b/aFA0XFB=FA0(ΘB-b/aX)Where:

Chapter 4

Slide25

Flow System – Stoichiometry Table

25

Species

Symbol

Reactor FeedChangeReactor Effluent

Where

:

InertIFI0=A0ΘI----------FI=FA0ΘIF

T0

F

T

=FT0

+δFA0X

C

C

F

C0

=FA0ΘC

+c/aFA0X

F

C

=

FA0(ΘC+c/aX)

D

D

FD0=FA0

Θ

D

+d/aFA0

XFD=FA0

(ΘD+d/aX)

and

Concentration

– Flow System

Chapter 4

Slide26

26

Species

Symbol

Reactor

FeedChangeReactor EffluentAAFA0

-F

A0

XFA=FA0(1-X)BBFB0=FA0ΘB-b/aFA0XFB=FA0(ΘB-b/aX)C

C

F

C0

=FA0ΘC

+c/aFA0

X

F

C=FA0(ΘC

+c/aX)

DD

FD0=F

A0

Θ

D

+d/aFA0X

FD=

FA0(ΘD+d/aX)

InertI

F

I0

=FA0

ΘI----------F

I=FA0

ΘI

F

T0

F

T

=

FT0+δFA0X

Where

:

and

Concentration

– Flow System

Flow System –

Stoichiometry

Table

Chapter 4

Slide27

27

Stoichiometry

Concentration

Flow System:

Liquid

Phase

Flow System:Flow Liquid Phaseetc.We will consider CA and CB for gas phase reactions in the next lectureChapter 4

Slide28

Mole Balance

Rate Laws

Stoichiometry

Isothermal Design

Heat Effects28Algorithm

Slide29

End of Lecture 4

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