reaction engineering lectures_part2

8/11/2019 Reaction Engineering Lectures_Part2

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Batch Stoichiometric Table

Species Symbol Initial Change Remaining

D D

________ ____________

C C

B B

A A

Inert I -------

where and

B =

N B 0

N A0


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Concentration: Batch Systems

Constant Volume Batch:

Note: if the reaction occurs in the liquid phaseor

if a gas phase reaction occurs in a rigid (e.g., steel) batch reactor

Then

etc.

If then

And we have rA=f(X)


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Flow System Stoichiometric Table

Species Symbol Initial Change Remaining

________ ____________

A

B B

A

C C

D D

Inert I

where and

B =

FB 0

FA0


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Concentration: Liquid Flow System

Flow Stystem:

Liquid Phase Flow System:

etc.

If the rate of reaction were

then we would have

This gives us -rA = f(X). Consequently, we can use the methods discussed in

Chapter 2 to size a large number of reactors, either alone or in series.


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Concentration: Gas Flow System

= 0F T

F T 0

P 0

P

T

T 0

FTF

T 0

=F T 0 + FA 0 X

FT 0

= 1+ y A 0 X = 1 + X( )

FT = C T and FT 0 = C T 00 =

C T 0C

T 0

C T =P

RTand C T 0 =

P0RT

0

with

C A =F

A 01 X( )

THEN

Note that the reaction is: A + (b/a)B - (c/a)C + (d/a)D

THEN

IF the reaction rate is given by -rA = k CA2

CB


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Multiple ReactionsUse molar flow rates and concentrations; DO NOT use conversion!

Types of Multiple Reactions

1. Series Reactions

2. Parallel Reactions

3. Complex Reactions: Series and Parallel

4. Independent


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Selectivity and Yield

Instantaneous Overall

Selectivity

Yield:

Example: (1) desired product , rD=k1CA2

CB

(2) undesired product , rU=k2CACBA + B 2 U1


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Another example about Selectivity and Yield

(1) desired product , rD=k1CA2CB

(2) undesired product , rU=k2CACB

(3)

A + Bk

2 U1

A + Bk

3 U2

rU 2 = k 3C BC A3

SD/U1/U 2

=k

1C

A2 C

B

k2C

AC

B+ k

3C

BC

A3then =

k1CAk

2+ k

3C

A2

CA

SD/U1/U2


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Algorithm for Multiple Reactions


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Mole Balances


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Net Rate of Reaction for Species A


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Series Reactions

, t=0 CA

=CA0


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Series Reactions

dCC

dt= k 2CB , t = 0 C C = 0


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Elementary Multiple Reactions1( ) A + 2B C2( ) 3C+2A D

r1A

=1A

CA

CB2

r2C

= k2C

CA2 C

C3

rA = r1A + r2 A

rA

= k1A

CA

CB2 2

3k

2CC

A2 C

C3

r1A = k1A CA CB2

r2A

2 =r

2C

3

r2A

= 23

r2 C

= 23

k2C

CA2 C

C3

rD = 0 + r2D = r2C

3

rD

= 1

3

k2C

CC3 C

A2

rB = r1B + 0 = 2r1A

rB = 2k1ACACB2

r1B

2=

r1A

1r1B = 2r1Ar2B

= 0

rC

= r1C

+ r2C

= r1A

+ r2C

rC

= k1A

CA

CB

2 k2 C

CA

2 CC

3

r1A

1=

r1C

1r1C = r1Ar2C

= k 2 CC A2 CC3

r1D

= 0r2C

3=

r2 D

1


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Case 1:Liquid Phase Reaction in a CSTR


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Polymath Solution


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Polymath Solution


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Polymath Solution


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Elementary Multiple Reactions1( ) A + 2B C2( ) 3C+2A D

r1A

=1A

CA

CB2

r2C

= k2C

CA2 C

C3

rA

= r1A

+ r2 A

rA = k1ACACB

2 23

k2C

CA2 C

C3

r1A = k1A CA CB2

r2A

2 =r

2C

3

r2A

= 23

r2 C

= 23

k2C

CA2 C

C3

rD = 0 + r2D = r2C

3

rD

= 1

3

k2C

CC3 C

A2

rB = r1B + 0 = 2r1A

rB

= 2k1A

CA

CB

2

r1B

2=

r1A

1r1B = 2r1Ar2B

= 0

rC

= r1C

+ r2C

= r1A

+ r2C

rC

= k1A

CA

CB2 k

2 CC

A2 C

C3

r1A

1=

r1C

1r1C = r1Ar2C

= k 2 CC A2 CC3

r1D

= 0r2C

3=

r2 D

1


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Example: Liquid Phase Reaction


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Multiple Reactions Gas Phase

Use Molar Flow Rates!!!


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The Algorithm


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The Algorithm

(given)


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The Algorithm


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Heterogeneous Catalytic Reaction

1-External diffusion of reactants towards the external surface of the catalyst pellet

2-Internal diffusion of reactants into the pores of the catalyst pellet

3- Adsorption of reactants on the active sites

4- Surface reaction

5- Desorption of products from active sites into the pore volume of the catalyst

pellet

6- Internal diffusion of products through the pores of the catalyst pellet towards

the external surface of the catalyst pellet

7- External diffusion of products to the bulk of the fluid


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Molecular Adsorption


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Molecular Adsorption

CAS =

KA

PA

1+ KAPA


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Steps of Catalytic Reaction

B B


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Steps of Catalytic Reaction

B B

B DA

A B

C

C D

AB

C+ D

C

D

+ C

+ D


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Example: Catalytic Reaction to Improve

the Octane Number of Gasoline

Focusing on the second reaction:

E l C l i R i I


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the Octane Number of Gasoline

E l C l i R i I


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the Octane Number of Gasoline rN = rS = kS C N,S

CIS

KS

CV =CT

1+ KNP

N+ K

IP

I


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Different Surface Mechanisms

reaction engineering lectures_part2

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