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 lecture

Blowout Velocity

CSTR Explosion

Batch Reactor Explosion

2

CSTRs with Heat Effects

Last Lecture

3

dt

EdHFHFWQ

sysn

1i

ii

n

1i

0i0iS

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 CPS1 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

a

0A

0Pi

XH

TTF

UATTC

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)

T0 Ta 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

11

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 CSTR

Same reactions, rate laws, and rate constants as example A

)1( CB2A

r1A k1ACACB

2

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 k2CCC

3CA

2

19

Example B: Liquid Phase CSTR

The 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 CSTR Solution

Liquid CSTR

Mole 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

Selectivity

If 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

22

Selectivity

Stoichiometry:

0AA FC (16)

0BB FC (17)

0CC FC (18)

0DD FC (19)

mindm100 3

0 (20)

minmoldm10k23

A1 (21)

minmoldm15k43

C2 (22)

Parameters:

23

H2O

N2O

Gas

200°F

510°F

Liquid

X

Ta0

NH4NO3 N 2O 2H2O

Ta

T0 200F

mA0 310lb h

17%H2O

83%NH4NO3

NH4NO3

M 500 lb

P

Example 1: Safety in Chemical Reactors

24

FA0

FI0

A

0

0

0

AA A A

BB B B

CC C C

dNF F r V

dt

dNF F r V

dt

dNF F r V

dt

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!)

(only A in vat, B,C are gases) g r g r

i Pi A PA

Q Q Q QdT

dt N C N C

Example 1: Safety in Chemical Reactors

26

Rearranging:

i

i

rg

Pi

rg

Pi

Q

a0iii0A

Q

RxA

CN

QQ

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

QQ

dt

dT

i

Qg rAV HRx

Qg r ijHRxijV

Qr2 Ý m vapHvap28

Keeping MBAs Away From Chemical

Reactors

The 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

Autoclave

175 oC

~550 psi

NH3

Separation

Filter

Press

NH3 in H2O

ONCB

O-Nitroaniline

Product Stream

“fast” Orange

To Crystallizing Tanks

31

Nitroaniline Synthesis Reactor

Old

3 kmol ONCB

43 kmol Ammonia

100 kmol Water

V = 3.25 m3

32

Nitroaniline Synthesis Reaction

NO2

NH2

NO2

Cl

+ 2NH3 + NH4Cl

ONCB + Ammonia Nitroanaline + Ammonium

Chloride

Batch Reactor, 24 hour reaction time

Management said: TRIPLE PRODUCTION 33

MBA Style Nitroaniline Synthesis Reactor

New

9 kmol ONCB

33 kmol Ammonia

100 kmol Water

V = 5 m3 34

Temperature-time trajectory

9:55

t = 0

10:40 10:50 midnight 12:18

Isothermal

Operation

Cooling Restored

175

400

Tem

pera

ture

o C

fuse

35

Temperature-time trajectory

pWWpB0BpA0A

rxA0

CNCNCN

)DH)(Vr()TT(UA

dt

dT

p

rg

NC

QQ

dt

dT

36

End of Lecture 22

37