Lecture 9
description
Transcript of Lecture 9
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 9
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Lecture 9 – Thursday 2/3/2011Membrane Reactors:
Used for Thermodynamically Limited Reactions
Balances in Terms of Molar Flow RatesBlock 1: Mole Balances
Balance Equation on Every Species Block 2: Rate Laws
Relative RatesTransport Laws
Block 3: Stoichiometry Block 4: Combine
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Reactor Mole Balance Summary
Reactor
Differential Algebraic Integral
The GMBE applied to the four major reactor types (and the general reaction AB)
A
AA
r
FFV
0CSTR
Review Lecture 1
Vrdt
dNA
A 0
A
A
N
N A
A
Vr
dNtBatch
NA
t
AA r
dV
dF
A
A
F
F A
A
dr
dFV
0
PFRFA
V
AA r
dW
dF
A
A
F
F A
A
r
dFW
0
PBRFA
W3
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Membrane ReactorsMembrane reactors can be used to achieve conversions greater than the original equilibrium value. These higher conversions are the result of Le Chatelier’s principle; you can remove the reaction products and drive the reaction to the right. To accomplish this, a membrane that is permeable to that reaction product, but impermeable to all other species, is placed around the reacting mixture.
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C3H8 ↔ H2 + C3H6 A ↔ B + C
Dehydrogenation Reaction:
Thermodynamically Limited:
XC
T
exothermic
endothermicXC
T6
Membrane Reactors
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Cross section of IMRCF Membrane Reactors
Cross section of CRM Schematic of IMRCF for mole balance
Membrane Reactors
W = ρbV
ρb = (1-ϕ)ρC
A,B,C
sweep
FA0
B
B
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A,C stay behind since they are too big
H2 H2 CBS
CB
Membrane Reactors
AA r
dV
dFA:
Mole Balance:
0
VrFF AVVAVA
Species A: In – out + generation = 0
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Membrane Reactors
RB moles of B through sides
volume of reactor
Species B: In – out – out membrane + generation = 0
0
VrVRFF BBVVBVB
)( BBB Rr
dV
dFB:
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Membrane Reactors
sm
molCCkW BSBCB 2
)('
3
2
4
2
4
lumereactor vo
areasurface membrane
m
m
DL
DLa
D
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BSBCBB CCakaWR '
sm
molCCkR BSBCB 3
Neglected most of the time
akk CC'
Membrane Reactors
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C
CBAA K
CCCkr
1 AA r
dV
dF
2 BBB Rr
dV
dF
3 CC r
dV
dF
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Mole Balance:
Rate Laws:
Membrane Reactors
Parameters: CTO = 0.2, FA0= 5, k = 4, KC
= 0.0004, kC = 8
111CBA rrr
Relative Rates:
,5 CABA rrrr
6 BCB CkR
7 0T
ATA F
FCC (isothermal, isobaric)
8 0T
BTB F
FCC
9 0T
CTC F
FCC
10 CBAT FFFF
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Net Rates:
Transport Law:
Stoichiometry:
Membrane Reactors
Example: The following reaction is to be carried out isothermally in a membrane reactor with no pressure drop. The membrane is permeable to product C, but impermeable to all other species.
C6H12 C6H6 3H2
A B 3C
For membrane reactors, we cannot use conversion. We have to work in terms of the molar flow rates FA, FB, FC.
Inert Sweep Gas
C6H6 (B)
Inert Sweep Gas
C6H12 (A)H2 (C)
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Membrane Reactors
AA r
dW
dF
BB r
dW
dF
CCCC Ckr
dW
dF
Mole Balances:
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Inert Sweep Gas
C6H6 (B)
Inert Sweep Gas
C6H12 (A)H2 (C)
Membrane Reactors
C
CBAAA K
CCCkr
3
Rate Law:
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Rates:
Relative Rates:
Net Rate:
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CBA rrr
AC
AB
rr
rr
3
Membrane Reactors
Stoichiometry:Isothermal, no pressure drop
0
00 RT
PCT
T
ATA F
FCC 0
T
BTB F
FCC 0
CBAT FFFF T
CTC F
FCC 0
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Membrane Reactors
Combine: – Use Polymath
Parameters:30 2.0
dm
molCT
s
molFA 100
scatkg
dmkC
5.03
scatkg
dmkA
103
6
2
200dm
molKC
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Membrane Reactors
Membrane Reactors
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Ci
W
C6H12 (A)
H2 (C)
C6H6 (B)
End of Lecture 9
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