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Lecture 22. 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. Today’s lecture. Blowout Velocity CSTR Explosion Batch Reactor Explosion. Last Lecture. - PowerPoint PPT Presentation
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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 22
Today’s lectureBlowout VelocityCSTR ExplosionBatch Reactor Explosion
2
CSTRs with Heat EffectsLast Lecture
3
dt
EdHFHFWQ sys
n
1iii
n
1i0i0iS
Energy balance for CSTRs
Pii
ARx0iPi0iS
CN
VrTHTTCFWQ
dt
dT
4
dT
dt
FA 0
N iCPi
G T R T
G T rAV HRx R T CPS
1 T TC
Energy balance for CSTRs
UA
FA 0CP 0
TC T0 Ta
15
0TTUATTCFXFH
XFVr
0dt
dN
dt
dT
a0Pi0A0ARx
0AA
A
i
0TRTG
At Steady State
Steady State Energy Balance for CSTRs
6
Solving for X
EB
Rx
a0A
0Pi
XH
TTFUA
TTC
Xi
Energy balance for CSTRs
Solving for T
i
i
Pi0A
0Pi0AaRx0A
CFUA
TCFUATHXFT
7
R(T)
T
Variation of heat removal line with inlet temperature.
Increasing T0
Energy balance for CSTRs
R T CPS1 T TC
8
R(T)
T0Ta T
κ=∞
κ=0
Increase κ
Variation of heat removal line with κ (κ=UA/CP0FA0)
Energy balance for CSTRs
R T CPS1 T TC
9
T,Xr
XFV
A
0A
BA
1) Mole Balance: A
0A
r
XFV
2) Rate Law:
AA kCr
10
4) Combine:
X1
Xk
X1kC
XC
X1kC
XFV
0A
00A
0A
0A
3) Stoichiometry: X1CC 0AA
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RxRTE
RTE
Rx
RTE
RTE
0A
00A
0A
0A
HAe1
AeHXTG
Ae1
Ae
k1
kX
X1
Xk
X1kC
XC
X1kC
XFV
12
Variation of heat generation curve with space-time.
13
Finding Multiple Steady States with T0 varied
14
Finding Multiple Steady States with T0 varied
15
Temperature ignition-extinction curve
16
Mole Balance
Rate Laws
Stoichiometry
Isothermal Design
Heat Effects
17
Mole Balance
Rate Laws
Stoichiometry
Isothermal Design
Heat Effects
18
Example B: Liquid Phase CSTRSame reactions, rate laws, and rate constants as example A
)1( CB2A
r1A k1ACACB2
NOTE: The specific reaction rate k1A is defined with respect to species A.
NOTE: The specific reaction rate k2C is defined with respect to species C.
)2( DA2C3
r2C k2CCC3CA
2
19
Example B: Liquid Phase CSTRThe complex liquid phase reactions take place in a 2,500 dm3 CSTR. The feed is equal molar in A and B with FA0=200 mol/min, the volumetric flow rate is 100 dm3/min and the reation volume is 50 dm3.
Find the concentrations of A, B, C and D existing in the reactor along with the existing selectivity.
Plot FA, FB, FC, FD and SC/D as a function of V
20
Example B: Liquid Phase CSTRSolution
Liquid CSTRMole Balances:
f CA 0CA 0 0CA rAV(1)
f CB 0CB 0 0CB rBV(2)
f CC 0CC rCV(3)
f CD 0CD rDV(4)
Net Rates:
rA r1A r2A(5)21
SelectivityIf one were to write SC/D=FC/FD in the Polymath program, Polymath would not execute because at V=0, FC=0 resulting in an undefined volume (infinity) at V=0. To get around this problem we start the calculation 10-4 dm3 from the reactor entrance where FD will not be zero and use the following IF statement. (15)
˜ S C D if V 0.001 then FC
FD
else 0
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SelectivityStoichiome
try:0AA FC (16)
0BB FC (17)
0CC FC (18)
0DD FC (19)
mindm100 30 (20)
minmoldm10k23
A1 (21)
minmoldm15k43
C2 (22)
Parameters:
23
H2O
N2O
Gas
200°F
510°F
Liquid
X
Ta0
NH4NO3 N2O 2H 2O
Ta
T0 200FmA0 310lb h
17%H2O
83%NH4NO3
NH4NO3
M 500 lb
P
Example 1: Safety in Chemical Reactors
24
FA0
FI0 A
dNA
tFA 0 FA rAV
dNB
tFB 0 FB rBV
dNC
tFC 0 FC rCV
CB2A
ON0H2NONH 2234
Example 1: Safety in Chemical Reactors
25
)TT(UA)HH()TT(CFQ
)H)(Vr(Q
a0BBB0PA0Ar
rxAAg
If the flow rate shut off, the temperature will rise (possibly to point of explosion!)
CN
QQgases) are CB, in vat,A (only
CN
t
T
PAA
rg
Pii
rg
Example 1: Safety in Chemical Reactors
26
Rearranging:
i
i
rg
Pi
rg
Pi
Q
a0iii0A
Q
RxA
CN
CN
TTUAHHFHVr
dt
dT
Additional information (approximate but close to the real case):
)ttancons( F500 at nitrate ammonium lb/Btu 336H Rx
F nitrate ammonium lb/Btu 38.0CP
F nitrate ofsteam lb/Btu 47.0CP
)h/lb( kMVV
MkVkCVr AA 27
Complete conversion FA = 0
dt
dTCNTTUAHFHgHTTCFHVr
dt
dTCNHFHVrHgHFTTCFQ
AA
AA
PA
2rQ
aVapA
1rQ
0BBB0P0A
gQ
RxA
PAAvapARxA0BBB0A0P0A
dt
dTCNQQQ
APA2r1rg
Batch Reactors with Heat Effects
Single Reactions
Multiple Reactions
Risk Rupture
a1r
Pi
rg
TTUAQ
CN
dt
dT
i
Qg rAV HRx
Qg r ijHRxijV
Qr2 Ý m vapHvap28
Keeping MBAs Away From Chemical ReactorsThe process worked for 19 years before
they showed up!Why did they come?What did they want?
29
Nitroaniline Synthesis Reaction
NO2
NH2
NO2
Cl
+ 2NH3 + NH4Cl
ONCB + Ammonia Nitroanaline + Ammonium
Chloride
30
Nitroaniline Synthesis Process
Autoclave175 oC
~550 psi
NH3 Separation
FilterPress
NH3 in H2O
ONCB
O-Nitroaniline
Product Stream
“fast” Orange
To Crystallizing Tanks
31
Nitroaniline Synthesis Reactor
Old3 kmol ONCB
43 kmol Ammonia100 kmol
WaterV = 3.25 m3
32
Nitroaniline Synthesis Reaction
NO2
NH2
NO2
Cl
+ 2NH3 + NH4Cl
ONCB + Ammonia Nitroanaline + Ammonium
ChlorideBatch Reactor, 24 hour reaction time
Management said: TRIPLE PRODUCTION33
MBA Style Nitroaniline Synthesis Reactor
New9 kmol ONCB
33 kmol Ammonia
100 kmol WaterV = 5 m3
34
Temperature-time trajectory
9:55t = 0
10:40 10:50
midnight 12:18
Isothermal
Operation
Cooling Restored20
0175
400
Tem
pera
ture
oC
fuse
35
Temperature-time trajectory
pWWpB0BpA0A
rxA0
CNCNCN
)DH)(Vr()TT(UA
dt
dT
p
rg
NC
dt
dT
36
End of Lecture 22
37
