lecture 10 - university of michiganessen/html/powerpoints/lecture_notes/lec10/cd/lec1… · lecture...

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 10

Today’s lecture   Definition of Selectivety

  Instantaneous SD/U = rD/rU

 Overall = FD/FU

  Semibatch Reactors

2

Selectivity in Multiple Reactions

Selectivity Yield

Instantaneous SD/U = rD/rU

Overall ŜD/U = FD/FU

3 Keep CA high and CB low.

Semibatch reactors   Semi Batch reactors can be very effective in maximizing

selectivity in liquid phase reactions.   The reactant that starts in the reactor is always the limiting

reactant.

4

Semibatch reactors

A + B → C + D

Semibatch reactors

5

A

B, v0  

Initial V

Liquid level and volume increase

Semibatch reactors

6

Mass Balance:

Semibatch

7

1)  Mole balances: Species A:

in – out + gen = acc

Semibatch

8

1)  Mole balances:

Species B:

Semibatch

9

Semibatch 2) Rate Law:

3) Stoichiometry:

4) Parameters: 10

example: A + B → C + D + CO2

A

B, v0 CO2

Semibatch Example

1a) Mole balances:

11

1 b) Mass balances:

Semibatch Example

2) Rate Law:

12

3) Stoich:

Semibatch Example

4) Parameters: 13

Polymath Screenshots:

14

Semi Batch Reactors Three Forms of the Mole Balance applied to Semi Batch Reactors:

1. Molar Basis

2. Concentration Basis

3. Conversion 15

Consider the following elementary reaction: A+B C+D

-rA=kCACB

The combined Mole Balance, Rate Law, and Stoichiometry may be written in terms of number of moles, conversion, and/or concentration:

Conversion Concentration No. of Moles

16

Polymath Equations:

17

Equilibrium Conversion in Semibatch Reactors with Reversible Reactions

Everything is the same as for the irreversible case, except for the rate law:

Consider the following reaction: A+BC+D

18

Equilibrium Conversion in Semibatch Reactors with Reversible Reactions Where:

At equilibrium, then

19 Xe changes with time.

End of Lecture 10

20