Chemical Rxn Engg

7/30/2019 Chemical Rxn Engg

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Chemical Reaction Engineering

Asynchronous Video Series

Chapter 2:

Conversion and Reactors in Series

H. Scott Fogler, Ph.D.



Reactor Mole Balance Summary



Conversion



Conversion

X moles reactedmoles fed



Conversion

X moles reactedmoles fed



Batch Reactor Conversion

• For example, let’s examine a batch reactor with the following design equation:

dNA

dt r AV





• Consider the reaction:

dNA

dt r AV

moles remaining = moles fed - moles fed • moles reactedmoles fed






dNA

dt r AV







dNA

dt r AV

Differential Form:

Integral Form:




CSTR Conversion

Algebraic Form:

There is no differential or integral form for a CSTR.



PFR Conversion

PFR dF

A

dV r

A

FA

FA0

1 X



PFR Conversion

PFR dF

A

dV r

A

FA

FA0

1 X



PFR Conversion

PFR dF

A

dV r

A

FA

FA0

1 X

Differential Form:

Integral Form:



Design Equations



Design Equations



Design Equations



Design Equations

V



Design Equations

V



Example



Example

V FA0

1 r

A

dX

0

X

00.01



Example

0V FA0

1 r

A

dX

0

X

00.01



Example

0V FA0

1 r

A

dX

0

X

X 0.2 0.4 0.6 0.8

1020304050

1

r A

00.01



Reactor Sizing

• Given -r A as a function of conversion, -r A=f(X), one can size any type of reactor.



Reactor Sizing


• We do this by constructing a Levenspiel plot.





Reactor Sizing



• Here we plot either as a function of X.

• For vs. X, the volume of a CSTR is:FA0

r A

FA0

r A

or 1

r A

V F

A0X 0

r A EXIT Equivalent to area of rectangle

on a Levenspiel Plot

XEXIT

0.2 0.4 0.6 0.8

1020304050

1

r A



Reactor Sizing



• Here we plot either as a function of X.

• For vs. X, the volume of a CSTR is:

• For vs. X, the volume of a PFR is:FA0

r A

FA0

r A

or 1

r A

FA0

r A

Equivalent to area of rectangle

on a Levenspiel Plot

XEXIT

VPFR FA 0

r A0

X

dX

V F

A0X 0

r A EXIT

= area under the curve=area

0.2 0.4 0.6 0.8

1020304050

1

r A



Numerical Evaluation of Integrals

• The integral to calculate the PFR volume can be evaluated using Simpson’s

One-Third Rule:



Numerical Evaluation of Integrals

• The integral to calculate the PFR volume can be evaluated using Simpson’s

One-Third Rule (see Appendix A.4 on p. 924):



Reactors In Series



Reactors In Series



Reactors In Series



Reactors in Series

• Also consider a number of CSTRs in series:



Reactors in Series

• Finally consider a number of CSTRs in series:

• We see that we approach the PFR reactor volume for a large number of CSTRsin series:

FA0

r A

X



Summary



Summary



Summary



Summary



Summary

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Chemical Rxn Engg