Reaction Engineering Lectures_Part2
Transcript of 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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Case 1:Liquid Phase Reaction in a CSTR
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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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Example: Liquid Phase Reaction
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Example: Liquid Phase Reaction
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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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Example: Catalytic Reaction to Improve
the Octane Number of Gasoline
E l C l i R i I
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Example: Catalytic Reaction to Improve
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