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Lecture 2. 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 2 – Tuesday 1/15/2013. Review of Lecture 1 Definition of Conversion, X

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Lecture 2

Lecture 2

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 2 tuesday 1 15 2013
Lecture 2 – Tuesday 1/15/2013

  • Review of Lecture 1

  • Definition of Conversion, X

  • Develop the Design Equations in terms of X

  • Size CSTRs and PFRs given –rA= f(X)

  • Conversion for Reactors in Series

  • Review the Fall of the Tower of CRE


Reactor mole balances summary

Review Lecture 1

ReactorMole Balances Summary

NA

FA

FA

The GMBE applied to the four major reactortypes

(and the general reaction AB)

t

W

V

Batch

CSTR

PFR

PBR


Cstr example problem

Review Lecture 1

CSTR – Example Problem

Given the following information, Find V

Liquidphase


Cstr example problem1

Review Lecture 1

CSTR – Example Problem

(1) Mole Balance:

(2) Rate Law:

(3) Stoichiometry:


Cstr example problem2

Review Lecture 1

CSTR – Example Problem

(4) Combine:

(5) Evaluate:


Define conversion x
Define conversion, X

Consider the generic reaction:

Chose limiting reactant A as basis of calculation:

Define conversion, X



Batch1
Batch

Integrating,

The necessary t to achieve conversion X.


CSTR

Consider the generic reaction:

Chose limiting reactant A as basis of calculation:

Define conversion, X


CSTR

Well Mixed

Steady State


CSTR

CSTR volumenecessary to achieveconversion X.


PFR

Steady State


PFR

Integrating,

PFR volume necessary to achieve conversion X.


Reactor mole balances summary1
ReactorMole Balances Summary

in terms of conversion, X

X

Batch

t

CSTR

X

W

PFR

PBR


Levenspiel plots
Levenspiel Plots

ReactorSizing

Given –rA as a function of conversion, -rA= f(X), one can size any type of reactor. Wedo this by constructing a Levenspielplot. Here we ploteither (FA0/-rA) or (1/-rA) as a function of X. For (FA0/-rA) vs. X, the volume of a CSTR and the volume of a PFR can be represented as the shaded areas in the Levenspiel Plots shown as:


Levenspiel plots1
Levenspiel Plots


Area = Volume of CSTR

F

0

A

-

r

A

X

1

CSTR




Numerical evaluations of integrals
Numerical Evaluations of Integrals

  • The integral to calculate the PFR volume can be evaluated using method as Simpson’s One-Third Rule: (See Appendix A.4)

Other numerical methods are:

  • Trapezoidal Rule (uses two data points)

  • Simpson’s Three-Eight’s Rule (uses four data points)

  • Five-Point Quadrature Formula


Reactors in series
Reactors in Series

Given: rA as a function of conversion, one can also design any sequence of reactors in series by defining X:

Only valid ifthere are no sidestreams.

Molar Flow rate of species A at point i:



Reactors in series2
Reactors in Series

Reactor 1:

V1


Reactors in series3
Reactors in Series

Reactor 2:

V2


Reactors in series4
Reactors in Series

Reactor 3:

V3



Reactors in series6
Reactors in Series

Space time τ is the time necessary to process 1 reactor volume of fluid at entrance conditions.


Keeping up
KEEPING UP

  • The tower of CRE, is it stable?


Reaction engineering
Reaction Engineering

Mole Balance

Rate Laws

Stoichiometry

These topics build upon one another.


Heat Effects

Isothermal Design

Stoichiometry

Rate Laws

Mole Balance

CRE Algorithm


Rate Laws

Mole Balance

Be careful not to cut corners on any of the

CRE building blocks while learning this material!


Isothermal Design

Heat Effects

Rate Laws

Stoichiometry

Mole Balance

Otherwise, your Algorithm becomes unstable.


End of lecture 2
End of Lecture 2


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