Page 68 - Modeling of Chemical Kinetics and Reactor Design

38 Modeling of Chemical Kinetics and Reactor Design

For example, for the decomposition of acetaldehyde:

 k  05 .
1
k 2  k   C 32 3
CH CHO
Chain length =  2 4
kC CH CHO
1
3
(1-157)
05 .
 k 2 
=  2  C 05 .
CH CHO
 2 kk  3
14
In this case, the chain length increases with the reactant concentration.

Example 1-1
The Hydrogenation of ethylene can be written as C H + H = C H .
4
6
2
2
2
It is suggested that the reaction sequence is:
Initiation

CH + H  → C H + H * (1-158)
*
k 1
2
5
4
2
2
Closed sequence
H + C H  → C H * (1-159)

*
k 2
2 4 2 5

CH + H  → C H + H * (1-160)
*
k 3
2 5 2 2 6
Termination

CH + H  → C H 6 (1-161)
*
*
k 4
2
2
5
Derive a rate expression for the overall reaction listing any assump-
tions made.
Solution
*
The overall rate of reaction of C H is
2
5