Lecture 12

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 12

Lecture 12 – Tuesday 2/15/2011Multiple Reactions

Selectivity and Yield

Series Reactions

Complex Reactions

2

A DkD

A UkU

A B C

A + B C + D

A + C E

4 Types of Multiple ReactionsSeries: A → B → CParallel: A → D,

A → UIndependent: A → B,

C → DComplex: A + B →C + D,

A + C → EWith multiple reactors, either molar flow or number of moles must be used (no conversion!)

3

Instantaneous

Overall

There are two types of selectivity and yield: Instantaneous and Overall.

Selectivity and Yield

U

DDU r

rS U

DDU F

FS ~Selectivity

A

DD r

rY

AA

DD FF

FY

0

~Yield

4

ABA

BA

U

DUD C

kk

CCkCCk

rrS

2

1

2

21

To maximize the selectivity of D with respect to U run at high concentration of A and use PFR.

DBA 1k BAD CCkr 21Example: Desired Product:

UBA 2kBAU CCkr 2Undesired Product:

5

Selectivity and Yield

Gas Phase Multiple Reactions

6

Flow Batch

BB

AA

rdVdF

rdVdF

VrdtdN

VrdtdN

BB

AA

Multiple Reactions Chapter 8

7

A) Mole Balance of each and every Species

8

A) Rates:a) Rate law for each reaction

AAi

iAA rrrr 211

b) Net Rates

c) Relative Rates

ACAA

BAAA

CCkrCCkr

22

11

Multiple Reactions Chapter 8

TT

PP

FFCCA

ATA

0

000

Stoichiometry:

Gas

Example: A → B → C (1) A → B k1

(2) B → C k29

0AA FC

Multiple Reactions Chapter 8

Liquid

AC

AB

AA r

dtdC r

dtdC r

dtdC

V=V0 (constant batch)

10

1) Mole Balance:

Vrdt

dN

Vrdt

dN

Vrdt

dN

CC

BB

AA

Example: Batch Series Reactions

B2B1B

A1A

BB1B1

AA1A1

rrrrr

CkrCkr

Laws

Net rates

2) Rates:

111

r1

r1r

1r

C2B2

B1A1

Relative rates

Example: Batch Series Reactions

example: A → B → C(1) A →

B (2) B →

C

1) Mole Balance:

CC

BB

AA r

dtdC r

dtdC r

dtdC

ttop

t

Ci

A BC

12

sVV

Example: Batch Series Reactions

1r

1r

1r

1r C2B2B1A1

Relative:

B2B2

A1A1

CkrCkr

Laws:

13

2) Rates:

Example: Batch Series Reactions

BB r

dtdC

Species B:

B2A1B2B1NET BB CkCkrrrr

tkexpCkCkdt

dC10A1B2

B 14

Species A: A1AA Ckr

dtdC

tkexpCC 10AA

3) Combine:

Example: Batch Series Reactions

Using the integrating factor, tkexpdtkexp.F.I 22 tkkexpCk

dttkexpCd 120A1

2B

at t = 0, CB=0

BA0AC CCCC

15

tk1

tk2

12

0AC

21 e1ke1kkk

CC

Example: Batch Series Reactions

what is the optimal ?

00 AAA rCC

000 0

BB

BB

rCVrCv

00

000

0

VrvCvC

VrFF

AAA

AAA1) Mole Balance:

Example: CSTR Series ReactionsABC

16

2) Rates:

B2B2

A1A1

CkrCkr

Laws:

B2A1B2B1B

A1A1A

CkCkrrrCk0rr

Net:

1r

1r

1r

1r C2B2B1A1

Relative:

17

Example: CSTR Series ReactionsABC

3) Combine:

18

Example: CSTR Series ReactionsABC

dCBd

0

max 1k1k2

19

Find that gives maximum concentration of B

12

01

11 kkCkC A

B

Example: CSTR Series ReactionsABC

20

End of Lecture 12

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Supplementary Slides

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Supplementary Material - Blood Coagulation

23

24

Notations

25

Notations

26

Mole Balance

27

Mole Balance

28

Mole Balance

29

Result

30

Blood CoagulationMany metabolic reactions involve a large number of sequential reactions, such as those that occur in the coagulation of blood.

Cut → Blood → Clotting

Figure A. Normal Clot Coagulation of blood(picture courtesy of: Mebs, Venomous and Poisonous Animals, Medpharm, Stugart

2002, Page 305)31

Schematic of Blood Coagulation

32

Cut

A + B

C

D

E

F

Clot33