lecture 10 - university of michigan · 2019-08-07 · lecture 10 – tuesday 2/12/2013 2 block 1:...
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 10
Lecture 10 – Tuesday 2/12/2013
2
Block 1: Mole Balances
Block 2: Rate Laws
Block 3: Stoichiometry
Block 4: Combine
Definition of Selectivity
Semibatch Reactors
Selectivity in Multiple Reactions
3
)(Undesired
(Desired)
2
2
BAUU
k
BADD
k
CCkrUBA
CCkrDBA
U
D
Selectivity Yield
Instantaneous SD/U = rD/rU
Overall ŜD/U = FD/FU
BU
AD
BAu
BAD
U
DUD
Ck
Ck
CCk
CCk
r
rS
2
2
/
)/(ˆ0 AADD FFFY
ADD rrY /
Keep CA high and CB low.
Semibatch Reactors
Semibatch reactors can be very effective in
maximizing selectivity in liquid phase reactions.
The reactant that starts in the reactor is always
the limiting reactant.
4
Semibatch reactors
A + B → C + D
5
A
B, v0
Initial V
m
Liquid level and volume increase
Semibatch Reactors
7
1) Mole Balance on Species A:
dt
dNVr AA 00
V
Cr
dt
dC AA
A 0
0dt
dV
Semibatch Reactors
[in] – [out] + [gen] = [acc]
dt
dVC
dt
dCV
dt
VCd
dt
dNA
AAA ][
8
1) Mole Balance on Species B:
Semibatch Reactors
V
CCr
dt
dC BBB
B 00
000 BB CF
dt
dNVrF BBB 00
[ ]B B BB
dN d C V dC dVV C
dt dt dt dt
0dt
dV
tVV
V
Cr
dt
dC
V
Cr
dt
dC
V
CCr
dt
dC
V
Cr
dt
dC
DD
D
CC
C
BBB
B
AA
A
00
0
0
00
0
5
4
3
)( 2
1
9
Semibatch Reactors
1) Mass and Mole Balance Summary
2) Rate Laws BAA CkCr 6
3) Stoichiometry 1111
DCBA rrrr
AB rr 7
AC rr 8
AD rr 9
0
0 10A
AA
N
NNX
000 11 VCN AA
VCN AA 12
4) Parameters 0000 , , , , BA CkVC
10
Semibatch Reactors
C
DCBAAA
K
CCCCkr
Everything is the same as for the irreversible case,
except for the rate law:
Consider the following reaction:
13
AB CD
Equilibrium Conversion in Semibatch
Reactors with Reversible Reactions
14
Equilibrium Conversion in Semibatch
Reactors with Reversible Reactions
Where:
V
XNtFC ABB
00
V
XNCC ADC
0
V
XNC AA
10
At equilibrium, then 0rA
eABe
eA
BeAe
DeCe
BeAe
DeCeC
XNtFX
XN
NN
NN
CC
CCK
00
2
0
1
Xe changes with time.
15
P6-6B - Semibatch Reactors
Sodium Bicarbonate + Ethylene Chlorohydrin Ethylene Glycol + NaCl + CO2
NaCHO3 + CH2OHCH2Cl (CH2OH)2 + NaCl + CO2
A + B C + D + CO2
16
P6-6B - Semibatch Reactors
Semibatch Reactors in terms of Moles
A + B C + D + CO2
2
22
22
)5(
0
)4(
)3(
)2(
)1(
2
0
CODCBA
COCO
COCO
CD
Cc
BBb
Aa
rrrrr
VrF
VrFCO
NND
Vrdt
dNC
VrFdt
dNB
Vrdt
dNA
Stoichiometry
Mole Balances
17
000
0
0
2
0
)14(
)13(
)12(
)11(
)10(
1000)9(
44)8(
)7(
)6(
2
2
2
aa
a
aa
BAA
BB
Aa
CO
CO
CO
CVN
N
NNX
CkCr
VNC
VNC
RHO
MWRHO
MWCOFdt
dV
Rest of the Polymath Statements
Similar to Concentration Program
Rate Laws
Three Forms of the Mole Balances applied to Semibatch Reactors:
Vrdt
dNA
A
VrFdt
dNBB
B 0
1. Molar Basis
VCr
dt
dCAA
A 0
V
CCrdt
dCBBB
B 00
Vrdt
dNA
A
VrFdt
dNBB
B 0
2. Concentration
Basis
0A
A
N
Vr
dt
dX 3. Conversion
25
Semibatch Reactors
Consider the following elementary reaction:
A+B C+D
-rA=kCACB
The combined Mole Balance, Rate Law, and
Stoichiometry may be written in terms of number
of moles, conversion, and/or concentration:
Conversion Concentration No. of Moles
tV
XNtFNXk
dt
dX ABBi
00
001
VCr
dt
dCAA
A 0
V
CCrdt
dCBBA
B 00
Vrdt
dNA
A
VrFdt
dNBA
B 0
26
Semibatch Reactors