kinetic reactor design chapter 3 lecture 4

8/12/2019 Kinetic Reactor Design Chapter 3 Lecture 4

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CHAPTER 3Rate Laws and Stoichiometry

Lecture 4

Tell me and I'll forget; show me and I may remember;

involve me and I'll understand.Chinese Proverb


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CCB 3043 Kinetics and Reactor Design

Topics

Lecture 1: Basic definitions - Part 1

Types of reaction and relative rate of reaction

Lecture 2: Basic definitions - Part 2

Rate constant and activation energy

Lecture 3: Stoichiometric tables

Batch system

Consideration for constant volume system

Lecture 4: Stoichiometric tables

Flow systems

Consideration for changing volume systems


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Flow systems

Da

dC

a

cB

a

bA

FA0FB0FC0

FD0FI0

FAFBFC

FDFI

*PFR or CSTR

FA0

FB0FC0FD0FI0

FAFBFCFD

FI

Da

dC

a

cB

a

bA


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Batch systems

at t = 0

NA0NB0NC0

ND0NI0

at t = t

NANBNCND

NI


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Species Sym Initial Change Remaining

A A FA0 - FA0X FA= FA0(1-X)

B B FB0= FA0B -(b/a) FA0X FB= FA0[B-(b/a)X]

C C FC0= FA0C (c/a)FA0X FC= FA0[C+(c/a)X]

D D FD0= FA0D (d/a)FA0X FD= FA0[D+(d/a)X]

Inert I FI0= FA0

I - FI0= FA0

I

Total FT0 FT= FT0+ [d/a + c/ab/a a]FA0X

FT= F

T0+ F

A0X

Flow systems


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Where:

Flow systems

v

FC

1a

b

a

c

a

d

y

y

C

C

F

F

ii

0A

0i

A0

i0

A0

i0i

Valid for constant

volume system


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Flow system

Note that:

For liquid phase system (no phase change,constant volume);

For gas phase system, the above is not true;need to account for volume expansion

XCCvv

AA

10

0


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Volume change with reaction (gas

phase): Batch Reactors

Occur when a system does not have an equal no of productand reactant, (usually involve gas phase system) e.g.;

N2+ 3H22NH3

Combustion reaction

Need to take into account the expansion factor,

XN

NN

T

TT

0

0

X;conversionanyator

reactorthetofedmolesofnumbertotal

conversioncompleteformolesofnumberin totalchange

00

01

AT

A

yN

Na

b

a

c

a

d


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CONSTANT VOLUME

BATCH FLOW

v

FC

1a

b

a

c

a

d

y

y

C

C

F

F

ii

0A

0i

A0

i0

A0

i0

i

V

NC

1a

b

a

c

a

d

y

y

C

C

N

N

ii

0A

0i

A0

i0

A0

i0

i

ReactorVolume

Volumetricflowrate


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Gas system; (Equation of state):

RTZNPV T

P = Total pressure, 1 atm

V = Volume, dm3

Z = Compressibility factor

NT= Total number of moles

R = Gas constant,

0.08206 dm3.atm/mol.K

T = Temperature, K


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At t = 0:

00000 RTNZVP T



RTZNPV T

000

00

00000

T

T

T

T

NN

ZZ

TT

PPVV

RTNZVP

RTZNPV

:rearrangeDivide

(1)/(2):

Remember? =(NT-NT0)/NT0X

And for gas phase system, Z0Z

XT

T

P

PVV

1

0

00

Volume of gas for variablevolume batch reaction


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At any conversion;

0

0

0

0

0

1

A

T

A

T

TT

yN

Nab

ac

ad

XN

NN

XNa

b

a

c

a

dNN

From

ATT 00 1

:TabletricStoichiome

FT= FT0+ [d/a + c/a

b/a

a]FA0X

OR

NT= NT0+ [d/a + c/a b/a a]NA0X


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Volume change with reaction: BATCH

For batch system:

00

0 T

T

X1P

P

VV

0

0

01

A

T

A

y

N

Na

b

a

c

a

d


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Volume change with reaction:

FLOW SYSTEM

T

T

P

P

F

FCC

T

j

Tj0

0

0

Da

dC

a

cB

a

bA

0

0

0

0T

T

P

P

F

F

T

T

T

T

P

P

X

XvCC

jA

j0

0

0

1

Can be used for membrane reactorsand multiple reactions

FT= sum of molarflowratefrom each

speciesCT= sum ofconcentration fromeach specied

vj= stoichiometric

coefficient

vA= -1, vB= -b/a, vC= c/a, vD= d/a

Refer topg 113

0

00 1T

T

P

P

X


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VOLUME CHANGE

XT

T

P

PVV

1

0

00

0

00 1

T

T

P

PX

BATCH FLOW

P constant, T constant (isothermal):

XVV 10 X 10 BATCH FLOW


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Volume change with reaction:

FLOW SYSTEM

Try to der ive

those equations! !

(H int: Use the

I deal gas law)Refer to page

111(Fogler)

Read page 111 to115, to make youunderstand better

Where do we get those equations from???


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Important notes for Rate Law and

Stoichiometry

IMPORTANT TABLES:

Table 3-3(p101, Fogler): Stoichiometric

table for a BATCHsystemTable 3-4(p107, Fogler): Stoichiometric

table for a FLOWsystem

Table 3-5(p114, Fogler): Concentrations ina varible-volumegasFLOWsystem


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Example 3.5: Determining the concentration of

species involved in a gas phase reaction

Consider the oxidation of SO2below. A mixture of 28%

SO2and 72% air is charged to a flow reactor in which

SO2is oxidized. Given that the total pressure of the

system is 1485 kPa and the temperature is constant at227oC. Set up the stoichiometric tablefor the system and

evaluate the concentration of species presents in terms of

conversion. Plot the concentration profile of the species

with respect to conversion

2SO2+ O22SO3


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Example 3.6: Calculating the equilibrium conversionThe reversible gas-phasedecomposition of nitrogen tetroxide, N2O4,,

is carried out at constant temperature. The feed consists of pure N2O4at 340 K and 202.6 kPa (2 atm). The concentration equilibriumconstant Kc, at 340 K is 0.1 mol/dm

3.

a) Express the equilibrium conversion of N2O4in a constant-

volume batch reactor, in term of CA0and KC.

b) Express the equilibrium conversion of N2O4in a flow reactor,interm of CA0and KC

c) Assuming the reaction is elementary, express the rate of reactionsolely as a function of conversion for a constant-volumebatchand a flow system.

d) If kAis 0.5min-1and feed rate is 3 mol/min, determine the CSTR

volume necessary to achieve 80% of the equilibrium conversion

N2O4

2NO2


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Checklist..

Mole balance

Rate Law

Stoichiometry

Do you have all these building blocks?

CC 30 3 d


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kinetic reactor design chapter 3 lecture 4

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