chemical reaction engineering (cre) is the field that studies the rates and mechanisms of chemical...
TRANSCRIPT
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
2
A DkD
A UkU
A B C
A + B C + D
A + C E
Series: A → B → C
Parallel: A → D
A → U
Independent: A → B
C → D
Complex: A + B →C + D
A + C → E
With multiple reactors, either molar flow or number of moles must be used (no conversion!)
3
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
~
4
Selectivity and Yield
ABA
BA
U
DUD C
k
k
CCk
CCk
r
rS
2
1
2
21
To maximize the selectivity of D with respect to U run at high concentration of A and use PFR.
DBA 1kBAD CCkr 2
1Example: Desired Product:UBA 2k
BAU CCkr 2Undesired Product:
Selectivity and Yield
5
Gas PhaseMultiple Reactions
6
Multiple Reactions
7
Flow Batch
BB
AA
rdV
dF
rdV
dF
Vrdt
dN
Vrdt
dN
BB
AA
A) Mole Balance of each and every species
Multiple Reactions
8
B) Rates
a) Rate Law for each reaction:
b) Net Rates:
c) Relative Rates:
ACAA
BAAA
CCkr
CCkr
22
11
AAi
iAA rrrr 211
Multiple Reactions
9
C) Stoichiometry
Gas:
Liquid:
T
T
P
P
F
FCC
A
ATA
0
000
0AA FC
Example: A → B → C
(1) A → B k1
(2) B → C k2
Batch Series Reactions
10
1) Mole Balances
Vrdt
dN
Vrdt
dN
Vrdt
dN
CC
BB
AA
AC
AB
AA r
dt
dC r
dt
dC r
dt
dC
V=V0 (constant batch)
Batch Series Reactions
11
2) Rate Laws
B2B1B
A1A
BB1B1
AA1A1
rrr
rr
Ckr
Ckr
Laws
Net rates
1
r
1
r1
r
1
r
C2B2
B1A1
Relative rates
Example: Batch Series Reactions
12
A → B → C
(1) A → B
(2) B → C
1) Mole Balances
CC
BB
AA r
dt
dC r
dt
dC r
dt
dC
ttopt
Ci
AB C
OVV
Example: Batch Series Reactions
13
2) Rate Laws
1
r
1
r
1
r
1
r C2B2B1A1
Relative:
B2B2
A1A1
Ckr
Ckr
Laws:
Example: Batch Series Reactions
14
3) Combine
Species A:
Species B:
A1AA Ckr
dt
dC
tkexpCC 10AA
BB r
dt
dC
B2A1B2B1NET BB CkCkrrrr
tkexpCkCkdt
dC10A1B2
B
Example: Batch Series Reactions
15
Using the integrating factor, tkdtkFI 22 expexp.. tkkCk
dt
tkCd A
B1201
2 expexp
at t = 0, CB=0
BAAC CCCC 0
tktkAC ekek
kk
CC 21 11 12
12
0
Example: CSTR Series Reactions
16
ABCWhat is the optimal ?
00 AAA rCC
0
00 0
BB
BB
rC
VrCv
0
0
000
0
VrvCvC
VrFF
AAA
AAA
1) Mole BalancesA:
B:
Example: CSTR Series Reactions
17
ABC
2) Rate Laws
B2B2
A1A1
Ckr
Ckr
Laws:
1 1
1 2 1 2
0A A A
B A B A B
r r k C
r r r k C k C
Net:
1
r
1
r
1
r
1
r C2B2B1A1
Relative:
Example: CSTR Series Reactions
18
ABC
3) Combine
Example: CSTR Series Reactions
19
ABC
dCBd
0
max 1
k1k2
Find that gives maximum concentration of B
12
01
11 kk
CkC AB
20
End of Lecture 12
21
22
Supplementary Slides
Blood Coagulation
23
24
25
Notations
26
Notations
Mole Balances
27
28
Mole Balances
29
Mole Balances
30
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
32
Schematic of Blood Coagulation
Cut
A + B
C
D
E
F
Clot33