Download - 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 2/19/2013Multiple Reactions
Selectivity and Yield
Series Reactions
Complex Reactions
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A DkD
A UkU
A B C
A + B C + D
A + C E
Series: A → B → CParallel: A → D
A → UIndependent: A → B
C → DComplex: A + B →C + D
A + C → E
With multiple reactors, either molar flow or number of moles must be used (no conversion!)
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4 Types of Multiple Reactions
Instantaneous Overall
Selectivity
Yield
There are two types of selectivity and yield: Instantaneous and Overall.
U
DDU r
rS U
DDU F
FS ~
A
DD r
rY
AA
DD FF
FY
0
~
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Selectivity and Yield
ABA
BA
U
DUD C
kk
CCkCCk
rrS
2
1
2
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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:
Selectivity and Yield
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Gas PhaseMultiple Reactions
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Multiple Reactions
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Flow Batch
BB
AA
rdVdF
rdVdF
VrdtdN
VrdtdN
BB
AA
A) Mole Balance of each and every species
Multiple Reactions
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B) Rates
a) Rate Law for each reaction:
b) Net Rates:
c) Relative Rates:
ACAA
BAAA
CCkrCCkr
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11
AAi
iAA rrrr 211
Multiple Reactions
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C) Stoichiometry
Gas:
Liquid:
TT
PP
FFCCA
ATA
0
000
0AA FC
Example: A → B → C
(1) A → B k1
(2) B → C k2
Batch Series Reactions
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1) Mole Balances
Vrdt
dN
Vrdt
dN
Vrdt
dN
CC
BB
AA
AC
AB
AA r
dtdC r
dtdC r
dtdC
V=V0 (constant batch)
Batch Series Reactions
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2) Rate Laws
B2B1B
A1A
BB1B1
AA1A1
rrrrr
CkrCkr
Laws
Net rates
1r
1r
1r
1r
C2B2
B1A1
Relative rates
Example: Batch Series Reactions
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A → B → C
(1) A → B
(2) B → C
1) Mole Balances
CC
BB
AA r
dtdC r
dtdC r
dtdC
ttopt
Ci
A B C
OVV
Example: Batch Series Reactions
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2) Rate Laws
1r
1r
1r
1r C2B2B1A1
Relative:
B2B2
A1A1
CkrCkr
Laws:
Example: Batch Series Reactions
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3) Combine
Species A:
Species B:
A1AA Ckr
dtdC
tkexpCC 10AA
BB r
dtdC
B2A1B2B1NET BB CkCkrrrr
tkexpCkCkdt
dC10A1B2
B
Example: Batch Series Reactions
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Using the integrating factor, tkdtkFI 22 expexp.. tkkCk
dttkCd A
B1201
2 expexp
at t = 0, CB=0
BAAC CCCC 0
tktkAC ekek
kkCC 21 11 12
12
0
Example: CSTR Series Reactions
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ABCWhat is the optimal ?
00 AAA rCC
000 0
BB
BB
rCVrCv
00
000
0
VrvCvC
VrFF
AAA
AAA
1) Mole BalancesA:
B:
Example: CSTR Series Reactions
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ABC
2) Rate Laws
B2B2
A1A1
CkrCkr
Laws:
1 1
1 2 1 2
0A A A
B A B A B
r r k Cr r r k C k C
Net:
1r
1r
1r
1r C2B2B1A1
Relative:
Example: CSTR Series Reactions
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ABC
3) Combine
Example: CSTR Series Reactions
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ABC
dCBd
0
max 1k1k2
Find that gives maximum concentration of B
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01
11 kkCkC A
B
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End of Lecture 12
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Supplementary Slides
Blood Coagulation
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Notations
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Notations
Mole Balances
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Mole Balances
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Mole Balances
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Results
Many 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
Blood Coagulation
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Schematic of Blood Coagulation
Cut
A + B
C
D
E
F
Clot33