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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 18
Web Lecture 18
Class Lecture 23–Tuesday 4/16/2013
Catalytic Mechanisms
Data Analysis
Chemical Vapor Deposition (CVD)
2
2A
cat
BC
Catalytic Mechanisms
3
(a) The initial rate of reaction is shown below
(A) (B)
(C)
A BC
(A) (B)
rA kPA
1KAPA KBPB
rA kPA
1 KAPA KCPC
(A) (B)
AS AS AS
AS
AS BSC AS BCS
BS BS CS
CS
4
Catalytic Mechanisms
2A B C
(C) (D)
rA kPA
2
1KAPA KCPC 2
rA kPA
2
1KAPA KCPC 2
(C) (D)
AS AS AS
AS
AS A g BCS AS AS BSCS
CS CS CS
CS
5
Catalytic Mechanisms
6
2A B C
AS AS
AS AS B CS
CS C S
r A kPA
2
1 KAPA KCPC 2
Catalytic Mechanisms
7
r A0 4PA
2
1 4PA0 KCPC0
For PC0 2 atm and PA0 1 atm, then r A0 0.0138mol
kgcat s
r A0 4
1 4 2KC 2 0.0138
One equation and one unknown
KC 6 atm1
r A0 4PA
2
1 4PA 6PC 2
Catalytic Mechanisms
2A BC
AS AS r A rA0 kA PACV
CAS
KA
CAS KAPACV
AS AS BSCS r A rS kSCAS
2
CS CS rA rDC kDC CCS PCCVKC CCS KCPCCV
8
Where KA = 4 atm–1 and KC = 6 atm–1
1) At what is the ratio of sites with A adsorbed to those sites with C
adsorbed when the conversion is 50%?
2) What is the conversion when the sites with A adsorbed are equal
to those with C adsorbed?
Catalytic Mechanisms
9
2A B C
AB
2
C
2KA 4 and KC 6
Ratio of site concentrations
CAS
CCS
KA PA CV
KC PC CV
KA PA
KC PC
PA PA0 1 X 1 X
PC PA0
X
2 1 X
CAS
CCS
KA PA0
1X
1 X
P
P0
KC PA0
X 2
1 X
P
P0
2KA 1X
KC X
Catalytic Mechanisms
10
1) At X = 0.5
2) At an equal concentrations of A and C sites, the conversion will be
CAS
CCS
~2 4 1 0.5
6 0.5 1.33
CAS
CCS
12KA 1X
KC X , then X
2KA
KC 2KA
2 4
6 2 4
8
14
X 0.57
Catalytic Mechanisms
11
2CH3OH CH3 – O CH3 H2O
2ME DMEW
Initially water does not exit the reactor the same as DME because
Which of the following best describes the data
A There is more DME than water.
B Steady state has been reached.
C Water reacts with ME.
D Water is adsorbed on the surface.
Dimethyl Either
Chemical Reaction Engineering in the Electronics Industry
ChE 342
Czochralski Crystal Growth – Heat Transfer
Doping of n/p junction – Diffusion
ChE 344
Chemical Vapor Deposition (Catalysis Analogy)
Photo Resist Formation
Photo Resist Dissolution
Etching
The 5 steps
1. Postulate Mechanism
(sometimes first includes a gas phase reaction (then
adsorption, surface reaction and desorption)
2. Postulate Rate Limiting Step
3. Evaluate Parameters in Terms of Measured Variables
4. Surface Area Balance
5. Evaluate Rate Law Parameters
Chemical Reaction Engineering in the Electronics Industry
14
Chemical Reaction Engineering in the Electronics Industry
Chemical Vapor Deposition
15
16
Chemical Vapor Deposition
17
1) Mechanism
Gas Phase
Homogeneous
Heterogeneous
SiH 2 ˜ S SiH 2
˜ S rAD kA PSiH2f V
fSiH2
KSiH2
SiH 2 ˜ S ˜ S H2 rDep rS kSfSiH2
f V = fraction of surface that is vacant
SiH 4 SiH 2 H2 rSiH4
kSiH4PSiH4
PH2
PSiH2
KP
Chemical Vapor Deposition
18
2) Rate Limiting Step
3) Express fi in terms of Pi
4) Area Balance
rDep rS kSfSiH2
rAD
kA
0
fSiH2KSiH2
f VPSiH2
1 fV fSiH2 fV KSiH2
PSiH2fV
Chemical Vapor Deposition
19
4) Area Balance
5) Combine
1 fV fSiH2 fV KSiH2
PSiH2f V
fV 1
1KSiH2PSiH2
rDep kSKSiH2
PSiH2
1KSiH2PSiH2
Chemical Vapor Deposition
Homogeneous Reaction
20
rSiH4
kSiH4
0 PSiH2
KPPSiH2
PH2
rDep kSKPKSiH2
PSiH4
PH2KSiH2
KPPSiH4
k1PSiH4
PH2K1PSiH4
SiH 4 SiH 2 H2 rSiH4
kSiH4PSiH4
PH2
PSiH2
KP
End of Web Lecture 18
End of Class Lecture 23
21
