Page 48 - Modeling of Chemical Kinetics and Reactor Design

18 Modeling of Chemical Kinetics and Reactor Design
Br + Br → Br (1-70)
*
*
2
The Rice-Herzfeld mechanisms of reaction are:

1. Initiation
• Free radicals are formed by scission of the weakest bond in
the molecule.
2. Propagation
• One or both of the radicals formed in the initiation step abstracts
a hydrogen atom from the parent compound to form a small
saturated molecule and a new free radical.
• The new free radical stabilizes itself by splitting out a simple
molecule such as olefin or CO:

RCH − CH → R + CH = CH 2
*
*
2
2
2
3. Termination
• The chain is broken by a combination or disproportionation
reaction between the two radicals.
Employing mechanistic equations based on the Rice-Herzfeld postu-
lation yields:

1. Initiation

M → R + R * 1 (1-71)
*
k 1
2. Propagation

R + M  → R + R H (1-72)
*
*
k 2
2

R → R + P 1 (1-73)
*
k 3
2
3. Termination

R + R  → P 2 (1-74)
*
*
k 4
R + R  → P (1-75)

*
k 5
2 3

R + R  → P 4 (1-76)
k 6
2
2