Lecture 12
description
Transcript of Lecture 12
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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
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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
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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
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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
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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:
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
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Multiple Reactions
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B) Rates
a) Rate Law for each reaction:
b) Net Rates:
c) Relative Rates:
ACAA
BAAA
CCkrCCkr
22
11
AAi
iAA rrrr 211
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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
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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)
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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
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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
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Example: Batch Series Reactions
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2) Rate Laws
1r
1r
1r
1r C2B2B1A1
Relative:
B2B2
A1A1
CkrCkr
Laws:
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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
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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
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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:
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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:
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Example: CSTR Series Reactions
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ABC
3) Combine
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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
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Blood Coagulation
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Notations
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Notations
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Mole Balances
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Mole Balances
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Mole Balances
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Results
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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
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Cut
A + B
C
D
E
F
Clot33