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Chemical Reaction Engineering
Chapter 6Chapter 6
Mutiple Reactions
Define different types of selectivity and yield
Choose a reaction system
that would maximize the selectivity of the desired product
given the rate laws for all the reactions occurring in the system.
Describe the algorithm used to design reactors
with multiple reactions.
Size reactors to maximize the selectivity
and to determine the species concentrations in a batch reactor,
semi-batch reactor, CSTR, PFR, and PBR, systems.
Objectives
Parallel rxns (competing rxns)Parallel rxns (competing rxns) B
AC
Series rxns (consecutive rxns)Series rxns (consecutive rxns)
A B C
Complex rxns (Parallel + Series rxns)Complex rxns (Parallel + Series rxns)
A + B C + DA + C E
Independent rxnsIndependent rxns
A B + CD E + F
k1
k2
k1 k2
k1
k2
k1
k2
Definition of Multiple Reaction
Parallel rxns Parallel rxns (competing rxns)
2CO2 + 2H2OCH2=CH2 +O2
CH2-CH2
Series rxns Series rxns (consecutive rxns) O O CH2-CH2 + NH3 HOCH2CH2NH2 EO EO
(HOCH2CH2)2NH2 (HOCH2CH2)3NH2
Complex Rxns (Combination of parallel & series rxns)Complex Rxns (Combination of parallel & series rxns)
C2H5OH C2H4 + H2O C2H5OH CH3CHO + H2
C2H4 + CH3CHO C4H6 + H2O
Independent rxns Independent rxns ((The cracking of crude oil to form gasoline)
C15H32 C12H26 + C3H6
C8H18 C6H14 + C2H4
k1
k2
Examples of Multiple Reaction
Monoethanolamine
Dinoethanolamine Trinoethanolamine
Parallel ReactionsParallel Reactions
D (Desired Product)A
U (Undesired Product)
kD
kU
Competing or side rxn
A
D
A, U
reaction
separation
Total cost
Reaction cost
Separation costcost
Low High
The economic incentiveThe economic incentive
Maximize the formation of DMaximize the formation of D
Minimize the formation of U Minimize the formation of U
Rxn-separation system producing both D & U Efficiency of a reactor system
Desired and Undesired Reaction
Rate selectivity parameter, SRate selectivity parameter, S
D (Desired Product)A
U (Undesired Product)
The rate laws are
Rate selectivity parameter = Instantaneous selectivity
kD
kU
21
2
1
21
AU
D
U
DDU
AUU
ADD
AUADA
Ck
k
r
rS
Ckr
Ckr
CkCkr
We want to maximize
SDU
Rate selectivity parameter, SDU
=Rate of formation of U
Rate of formation of D
Overall Selectivity, SDU
~
Overall Selectivity
SDU =~
FU
FD =Exit molar flow rate of undesired product
Exit molar flow rate of desired product
For Batch Reactor
SDU =~
NU
ND
Example 6-1: Comparison between SDU and SDU in a CSTR~
Mission: Develop a relationship between SDU and SDU in a CSTR~
Solution
SDU = rU
rDand SDU =
~
FU
FD
By the way, FD=rDV and FU=rUV
SDU =~
FU
FD =rDVrUV
=rD
rU
= SDU
Instantaneous Yield and Overall Yield
Instantaneous Yield (Basis: Reaction Rate)
YD = -rA
rD
Overall Yield (Basis: Molar Flow Rate)
For a batch system: YD = NAo-NA
ND
For a flow system: YD = FAo-FA
FD
= Number of moles of key reactant consumed
Mole of desired productformed at the end of reaction
~
~
Overall SelectivityOverall Selectivity
Uof rate flowmolar exit
D of rate flowmolar exitsystem flow DU,
~
U
D
F
FS
rxn time theof end at the Uof moles ofnumber the
rxn time theof end at the D of moles ofnumber thesystembatch DU,
~
U
D
N
NS
Overall YieldOverall Yield
consumedbeen have that A, reactant,key theof moles ofnumber the
rxn time theof end at the D of moles ofnumber the
0
systembatch D,
~
AA
D
NN
NY
consumedbeen haveA that of moles ofnumber the
exit at the D of moles ofnumber the
0
system flow D,
~
AA
D
FF
FY
From an economic standpoint, overall selectivities and yieldsoverall selectivities and yields are important
in determining profitsprofits
Different definitions for selectivity and yield
Check carefully to ascertain the definition intended by the author
NoteNote
The instantaneous selectivitiesinstantaneous selectivities give insightsin choosing reactors and reaction schemeschoosing reactors and reaction schemes
that will help maximize the profit
Case 1: Case 1: 1 1 > > 2 2 , a = , a = 11- - 2 2
aA
U
D
U
DDU C
k
k
r
rS
maximize Smaximize SDUDU
- keeping the concentration of reactant A as high as possible during the rxn
- in gas phase rxn, we should run it without inerts and at high pressures to keep CA high
- in liquid phase rxn, the use of diluents should be keep to a minimum
- use a batch or plug-flow reactor
Maximizing SDU in Parallel Reactions
Case 2: Case 2: 2 2 > > 1 1 , a = , a = 22- - 1 1
aAU
D
U
DDU Ck
k
r
rS
1
maximize Smaximize SDUDU
- keeping the concentration of reactant A as low as possible during the rxn
- in gas phase rxn, we should run it with inerts and at low pressures to keep CA low
- in liquid phase rxn, the use of diluents should be keep to a maximum
- use a CSTR or recycle reactor (product stream act as a diluent)
Maximizing SDU for one reactant
Case 3: ECase 3: ED D > E> EU U
- kD (rD) increases more rapidly with increasing temperature than does the kU.
- keeping the temperature as high as possible to maximize SDU.
RT
EE
U
D
U
DUD
eA
A
k
k
Case 4: ECase 4: EU U > E> ED D
- keeping the temperature as low as possible to maximize SDU
- not so low that the desired rxn does not proceed to any significant extent.
Maximizing SDU for one reactantWhether the reaction should be run at high or low T
- Pre-exponential factors are comparable- the activation energies of (1) & (2) are much greater than that of (3).- at high temperature rQ << rD, rU
(4)(4)
(5)(5)
- From (5), SDU is minimized at low concentration of A
Example: Minimizing unwanted products (U & Q) for a single reactantExample: Minimizing unwanted products (U & Q) for a single reactant
DD (1)(1)
AA U U (2)(2)
QQ (3)(3)
AT
D Cer
1
300
1000,36
0002.0
5.11
300
1000,25
0018.0 AT
U Cer
5.01
300
1000,5
00452.0 AT
Q Cer
5.0
1
300
1000,11
11.0
largevery
A
T
U
DDU
Q
DDQ
C
e
r
rS
r
rS
1. High Temperatures (to minimize the formation of Q)1. High Temperatures (to minimize the formation of Q)2. Low concentration of A (to minimize the formation of U)2. Low concentration of A (to minimize the formation of U)
- Adding inerts, using low pressures, using CSTR or recycled reactor- Adding inerts, using low pressures, using CSTR or recycled reactor
YX
DYXD rr
rS
)/(
Textbook Example 6-2: 수업 후 집에서 꼭 풀어 보세요
Rate selectivity parameter, SRate selectivity parameter, S
D (Desired Product) A + B
U (Undesired Product)
The rate laws are
Rate selectivity parameter=Instantaneous selectivity
k1
k2
2121
22
11
2211
2
1
2
1
21
BAU
DDU
BAU
BAD
BABAA
CCk
k
r
rS
CCkr
CCkr
CCkCCkr
Reactor Selection and Operating Conditions
Different reactors and schemes for maximizing the desired productDifferent reactors and schemes for maximizing the desired product
AB
AB A
B
B
A
A
B
(a) CSTR (b) tubular reactor (c ) batch (d) semi-batch 1 (e) semi-batch 2
AB
AB
(f) Tubular reactor with side streams (g) Tubular reactor with side streams
AB
(i) Tubular reactor with recycle (h) Series of small CSTRs
BA
Figure 6-3Figure 6-3
Figure 6-3Figure 6-3Different reactors and schemes for maximizing the desired productDifferent reactors and schemes for maximizing the desired product
Example 6-3: Minimizing unwanted products for two reactantsExample 6-3: Minimizing unwanted products for two reactants
for the parallel reaction
D (Desired Product) A + B
U (Undesired Product)
Case I : 1 > 2, 1 > 2, a = 1-2 > 0, b = 1-2 > 0
the rate selectivity parameter
k1
k2
bB
aA
U
DDU CC
k
k
r
rS
2
1
To maximize the SDU, maintain the concentration of both A and B as high as possible
a tubular reactor (Figure 6.3 (b))a tubular reactor (Figure 6.3 (b))
a batch reactor (Figure 6.3 (c))a batch reactor (Figure 6.3 (c))
high pressures (if gas phase), reduce inerthigh pressures (if gas phase), reduce inert
Example 6-3: Minimizing unwanted products for two reactantsExample 6-3: Minimizing unwanted products for two reactants
for the parallel reaction
D (Desired Product) A + B
U (Undesired Product)
Case II : 1 > 2, 1 < 2, a = 1-2 > 0, b = 2-1 > 0
the rate selectivity parameter
k1
k2
bB
aA
U
DDU Ck
Ck
r
rS
2
1
To maximize the SDU, maintain CA high and CB low.
a semibatch reactor in which B is fed slowly into A. (Figure 6.3(d))a semibatch reactor in which B is fed slowly into A. (Figure 6.3(d))
a tubular reactor with side stream of B continually (Figure 6.3(f))a tubular reactor with side stream of B continually (Figure 6.3(f))
a series of small CSTRs with A fed only to the first reactor (Figure 6.3(h))a series of small CSTRs with A fed only to the first reactor (Figure 6.3(h))
Example 6-3: Minimizing unwanted products for two reactantsExample 6-3: Minimizing unwanted products for two reactants
for the parallel reaction
D (Desired Product) A + B
U (Undesired Product)
Case III : 1 < 2, 1 < 2, a = 2-1 > 0, b = 2-1 > 0
the rate selectivity parameter
k1
k2
bB
aAU
DDU CCk
k
r
rS
2
1
To maximize the SDU, maintain the concentration of both A and B as low as possible
a CSTR (Figure 6.3(a))a CSTR (Figure 6.3(a))
a tubular reactor in which there is a large recycle ratio (Figure 6.3(i))a tubular reactor in which there is a large recycle ratio (Figure 6.3(i))
a feed diluted with inert materiala feed diluted with inert material
low pressures (if gas phase)low pressures (if gas phase)
Example 6-3: Minimizing unwanted products for two reactantsExample 6-3: Minimizing unwanted products for two reactants
for the parallel reaction
D (Desired Product) A + B
U (Undesired Product)
Case IV : 1 < 2, 1 > 2, a = 2-1 > 0, b = 1-2 > 0
the rate selectivity parameter
k1
k2
aA
bB
U
DDU Ck
Ck
r
rS
2
1
To maximize the SDU, maintain the concentration of both A and B as high as possible
a semibatch reactor in which A is slowly fed to B (Figure 6.3(e))a semibatch reactor in which A is slowly fed to B (Figure 6.3(e))
a tubular reactor with side stream of A (Figure 6.3(g))a tubular reactor with side stream of A (Figure 6.3(g))
a series of small CSTRs with fresh B fed to each reactor (Figure 6.3(h))a series of small CSTRs with fresh B fed to each reactor (Figure 6.3(h))
In parallel rxns, maximize the desired product
by adjusting the reaction conditions
by choosing the proper reactor
In series rxns, maximize the desired product
by adjusting the space-time for a flow reactor
by choosing real-time for a batch reactor
Maximizing the desired product in series reaction
k1 k2A B C
If the first reaction is slow and second reaction is fast, it will be extremely difficult to produce species B.
If the first reaction (formation of B) is fast and the reaction to form C is slow, a large yield of B can be achieved.
However, if the reaction is allowed to proceed for a long time in a batch reactor or if the tubular flow reactor is too long, the desired product B will be converted to C.
In no other type reaction is exactness in the calculation of the time needed to carry out the reaction more important than in series reactions.
Maximizing the desired product in series reaction
k1 k2A B CDesired Product
Example 6-4: Maximizing the yield of the intermediate productExample 6-4: Maximizing the yield of the intermediate product
k1 k2CH3CH2OH(g) CH3CHO 2CO2
OHO 222
1 OHO 22 2
2
5
The oxidation of ethanol to form acetaldehyde is carried out on a catalyst of 4 wt% Cu-2wt% Cr on Al2O3. Unfortunately, acetaldehyde is also oxidized on this catalyst to form carbon dioxide. The reaction is carried out in a dilute concentrations (ca. 0.1% ethanol, 1% O2, and 98.9% N2). Consequently, the volume change with the reaction can be neglected. Determine the concentration of acetaldehyde as a function of space time.
The rxns are irreversible and first-order in ethanol and acetaldehyde, respectively.
Solution
Reaction paths for different ks in series reaction Reaction paths for different ks in series reaction
A B Ck1 k2
1
1~
1
2
1
2
1
2
1
k
k
k
k
k
k
A C
B
'1
'2
For k1/k2>1, aLarge quantity of BCan be obtained
For k1/k2<1, aLittle quantity of BCan be obtained 1st rxn is slow
2nd rxn is fast
'3
Long rxn time in batch or long tubular reactor-> B will be converted to C
Algorithm for solution to complex reactionsAlgorithm for solution to complex reactions
Steps in in Analyzing Multiple ReactionSteps in in Analyzing Multiple Reaction
1. Number each reaction. 2. Mole balance for each species. 3. Determine rij
4. Relate to rate of reaction of each species to the species for which the rate law is given. 5. Determine the net rate of formation of each species 6. Express rate laws as a function of Cj when X<<1. 7. Express rate laws as a function of mole when X>>1. 8. Combine all the above and solve the resulting set of equations
1. Mole balances for multiple reactions1. Mole balances for multiple reactionsIt is better to solve problems using moles (Nj) or molar flow rates (Fj) rather than conversion
V
CCr
dt
dCFVr
dt
dN
V
Cr
dt
dCVr
dt
dN
rdV
dCr
dV
dF
r
CCV
r
FFV
rdt
dCVr
dt
dN
BBB
BBB
B
AA
AA
A
AA
AA
A
AA
A
AA
AA
AA
][ 000
0
0
00
0
Reactor Gas Liquid
Batch
CSTR
PFR/PBR
Semibatch
2. Net Rates of Reaction2. Net Rates of Reaction
Reaction 1: A + B 3C + D
Reaction 2: A + 2C 3E
Reaction 3: 2B + 3E 4F
Reaction q: A + ½C G
...
k1A
k2A
K3B
kqA
Key point: to write the net rate of each species (e.g. A, B, …)
q
iiBqBBBBB
q
iiAqAAAAA
rrrrrr
rrrrrr
1321
1321
Net rates of reaction of A and B:
0
00
Total rate of formation of each species from all reactionTotal rate of formation of each species from all reaction
5533
4243232121
1212111
2
1
AAAq
AAAi
AAAA
AAA
qqjqj
pipkikjij
jj
jj
Reaction Number Reaction Stoichiometry
q
iijj rr
1
The net rate of rxn for A:
q rxns taking place
species
reaction number
3. Rate laws3. Rate laws
Reaction 1: A + B 3C + D
Reaction 2: A + 2C 3E
Reaction 3: 2B + 3E 4F...
k1A
k2A
k3B
We need to determine the rate law for at least one species in each rxn.
222 CAAA CCkr
222 CAAA CCkr 1 1 B
rA=r1A+r2A= -k1ACACB-k2ACACC2
4. Stoichiometry: Relative Rates of Reaction4. Stoichiometry: Relative Rates of ReactionGeneric reaction:
aA + bB cC + dD
Relative rate of reactions
Multiple rxns:
For example,
Relative rates of Rxn in reaction i
d
r
c
r
b
r
a
r DCBA
i
iD
i
iC
i
iB
i
iA
d
r
c
r
b
r
a
r
2222 33 CAAAE CCkrr
ik
ik
ij
ij rr
5. Combining individual rate laws to find net law5. Combining individual rate laws to find net law
6. Stoichiometry:6. Stoichiometry: Concentrations as a function of molar flow rate Concentrations as a function of molar flow rate
T
T
P
P
F
FC
T
T
P
P
F
FFFC
T
jT
T
jTjj
0
00
0
00
0
0
0
00 RT
PCT
n
jjT FF
1
Ideal Gas:
Isothermal gas phase without P:
0j
j
FC Liquid phase:
T
jTj F
FCC 0
T
jT
TT
TT
T
jT
TT
TT
F
FC
F
FC
F
FCfnr
F
FC
F
FC
F
FCfnr
02
01
022
02
01
011
,,,
,,,
Net rate of formation
Multiple Reactions in a PFR/PBRMultiple Reactions in a PFR/PBR(combining mole balance, rate law, and stoichiometry)(combining mole balance, rate law, and stoichiometry)
T
jT
TT
TTj
q
iijj
j
T
jT
TT
TT
n
ii
T
jT
TT
TT
m
ii
F
FC
F
FC
F
FCfnrr
dV
dF
F
FC
F
FC
F
FCfnrr
dV
dF
F
FC
F
FC
F
FCfnrr
dV
dF
02
01
01
02
01
021
222
02
01
011
111
,,,
,,,
,,,
.
.
.
Rate lawMole balance
j Coupled ODEsIsothermal gas phase without P:
Example 6-5: Write the rate law for each species in each reaction and then Example 6-5: Write the rate law for each species in each reaction and then
write the net rates of formation of NO, Owrite the net rates of formation of NO, O2, and N, and N22..
233
222
5.111
2222
22
3
ONOO
NONN
NONHNONO
CCkr
Ckr
CCkr
Solution
Reaction 1: 4NH3 + 6NO 5N2 + 6H2O
Reaction 2: 2NO N2 + O2
Reaction 3: N2 + 2O2 2NO2
Example 6-6: Write mole balance on a PFR in terms of molar flow rates for each speciesExample 6-6: Write mole balance on a PFR in terms of molar flow rates for each species Reaction 1: 4NH3 + 6NO 5N2 + 6H2O
Reaction 2: 2NO N2 + O2
Reaction 3: N2 + 2O2 2NO2
233
222
5.111
2222
22
3
ONOO
NONN
NONHNONO
CCkr
Ckr
CCkr
Solution
Example 6-7: Hydrodealkylation of Mesitylene in a PFRExample 6-7: Hydrodealkylation of Mesitylene in a PFR
The hydrodealkylation of mesitylene is to be carried out isothermally at 1500 R and 35 atm in a packed-bed reactor in which the feed is 66.7 mol% hydrogen and 33.3 mol% mesitylene. The volumetric feed rate is 476 ft3/h and the reactor volume (i.e. V=W/b) is 238 ft3.
CH3
CH3CH3
CH3
CH3
CH3
+ H2 + CH4
CH3
CH3
+ H2 + CH4
k1
k2
@1500R/hmol) /lb(ft20.30
@1500R/hmol) /lb(ft20.550.53
25.0
22
0.531
5.011
kCCkr
kCCkr
HXT
HMM
M=mesitylene, X=xylene, T=toluene, Me=methane, H=hydrogen
The bulk density of the catalyst has been included in the specific reaction rate (i.e., k1=k1’ b) Plot the concentrations of hydrogen, mesitylene, and xylene as a function of space-time.Calculate the space-time where the production of xylene is a maximum (i.e., opt) .
Reaction 1:Reaction 1: M + H M + H X + Me X + Me
Reaction 2:Reaction 2: X + H X + H T + Me T + Me
1.1. Mole balances:Mole balances:
Hydrogen
Mesitylene
Xylene
Toluene
Methane
2. 2. Rate laws:Rate laws:
MeMeMe
TT
XXX
MM
HHH
rrdV
dF
rdV
dF
rrdV
dF
rdV
dF
rrdV
dF
21
2
21
1
21
XHT
MHH
CCkr
CCkr5.0
22
5.011
3. 3. Stoichiometry:Stoichiometry: (no volume change with reaction, v=v0)
a. Reaction rates:
Reaction 1: -r1H = -r1M = r1X = r1Me
Reaction 2: -r2H = -r2X = r2T = r2Me
b. Flow rates:
4.4. Combining Combining and substituting in terms of the space-time ( )
If we know CM, CH, and CX, then CMe and CT can be calculated from the reaction stoichiometry. Consequently, we need only to solve the following three equations:
)(
)(
000
0000
0
0
0
XMMXMMT
HHHHMeMe
XX
MM
HH
CCCFFFF
CCFFCF
CF
CF
CF
0 V
XHMHX
MHM
XHMHH
CCkCCkd
dC
CCkd
dC
CCkCCkd
dC
5.02
5.01
5.01
5.02
5.01
5.5. Parameter evaluation:Parameter evaluation:
We now solve these three equations simultaneously using POLYMATH.
h 0.5h/ ft 476
ft 238
0C
mol/ft lb 0105.02
1
mol/ft lb 021.0R) R)(1500 mol atm/lbft (0.73
atm) (0.667)(35
3
3
0
X0
300
33
000
V
CC
RT
PyC
HM
HH
0.0 0.1 0.2 0.3 0.4 0.5
2.0
1.5
1.0
0.5
0.0 (hr)
Ci opt
CH
CMCX
Multiple reactions in a CSTRMultiple reactions in a CSTRFor a CSTR, a coupled set of algebraic eqns analogous to PFR differential eqns must be solved.
Rearranging yields where
After writing a mole balance on each species in the reaction set, we substitute for concentrations in the respective rate laws.
If there is no volume change with reaction, we use concentrations, C j, as variables.
If the reactions are gas-phase and there is volume change, we use molar flow rates, F j as variables.
q reactions in gas-phase with N different species to be solved
j
jj
r
FFV
0
VrFF jjj 0 ),...,,( 21
1 N
q
ijijj CCCfrr
001
0
001
0
100
1111110
,,
,,
,,
TT
NT
TNNNN
TT
NT
Tjjjj
q
iT
T
NT
Ti
CF
FC
F
FfVVrFF
CF
FC
F
FfVVrFF
CF
FC
F
FfVrVVrFF
Example 6-8: Hydrodealkylation of Mesitylene in a CSTRExample 6-8: Hydrodealkylation of Mesitylene in a CSTRCalculate the conversion of hydrogen and mesitylene along with the exiting concentrations of mesitylene, hydrogen, and xylene in a CSTR.
VrrF
VrF
VrrF
VrFF
VrrFF
MeMeMe
TT
XXX
MMM
HHHH
)(
)(
)(
21
2
21
10
210
1. Mole Balances:
2. Rate laws:
XHMeTXH
MHMeXMH
CCkrrrr
CCkrrrr2/1
22222
2/111111
3. Stoichiometry:
)(
)(
000
00
0
0
0
0
HHMeMe
XMMTT
XX
MM
HH
CCCF
FFFCF
CF
CF
CF
4. Combining and letting yields:0/ V
)(
)(
)(
2/12
2/11
2/110
2/12
2/110
XHMHX
MHMM
XHMHHH
CCkCCkC
CCkCC
CCkCCkCC
Example 6-8: Hydrodealkylation of Mesitylene in a CSTRExample 6-8: Hydrodealkylation of Mesitylene in a CSTRWe put these equations in a form such that they can be readily solved using POLYMATH.
XXHMHX
MHMMM
XHMHHHH
CCCkCCkCf
CCkCCCf
CCkCCkCCCf
)(0)(
)(0)(
)(0)(
2/12
2/11
2/110
2/12
2/110
For =0.5, the exiting concentrations are CH=0.0089, CM=0.0029 and CX=0.0033.The overall conversion is
72.00105.0
0029.00105.0 :Mesitylene
58.0021.0
0089.0021.0 :Hydrogen
0
0
0
0
0
0
0
0
M
MM
M
MMM
H
HH
H
HHH
C
CC
F
FFX
C
CC
F
FFX
2.0
1.5
1.0
0.5
0.0
Ci
CSTR
0.0 1.0 2.0
CH
CX
CM
The moles of hydrogen consumed in reaction 1 are equal to the moles of mesitylene consumed. Therefore, the conversion of hydrogen in reaction 1 is
The conversion of hydrogen in reaction 2 is
22.036.058.0
36.0021.0
0029.00105.0
12
0
01
HHH
H
MMH
XXX
C
CCX
The yield of xylene from mesitylene based on molar flow rates exiting the CSTR for =0.5 is
produced toluenemole
produced xylenemole7.0
00313.00029.00105.0
00313.0~
reacted mesitylene mole
produced xylenemole41.0
0029.00105.0
00313.0~
0
00
XMM
X
T
X
T
XXT
MM
X
MM
XMX
CCC
C
C
C
F
FS
CC
C
FF
FY
The overall selectivity of xylene relative to toluene is
Example 6-8: Hydrodealkylation of Mesitylene in a CSTRExample 6-8: Hydrodealkylation of Mesitylene in a CSTR
Selectivity and overall selectivity in a CSTRSelectivity and overall selectivity in a CSTR
For a CSTR the instantaneous selectivity and the overall selectivity are the same. For example, the instantaneous selectivity of xylene w.r.t. toluene is
Mole balances of xylene and toluene yields
Substituting in the instantaneous selectivity equation for rX and rT
T
XXT
T
XXT
F
FS
r
rS
~
The instantaneous selectivity
The overall selectivity
VrF
VrF
TT
XX
XTT
X
T
X
T
XXT S
F
F
VF
VF
r
rS
~
/
/
XTXT SS~
For all ideal CSTR
Homework
P6-9C (a)-(g)
P6-12A (a)-(h)P6-14B
Due Date: Next Week