Page 437 - Elements of Chemical Reaction Engineering Ebook

408 Nonelementary Reaction Kinetics Chap. 7

dent of reactor size. Guidelines for scaling from a pilot-plant bioreactor to a
commercial plant reactor are given on the CD-ROM. One key to a scale-up is
to have the speed of the end (tip) of the impeller equal to the velocity in both
the laboratory pilot reactor and the full-scale plant reactor. If the impeller
speed is too rapid, it can lyse the bacteria; if the speed is too slow, the reactor
contents will not be well mixed. Typica! tip speeds range from 5 to 7 m/s.

SUMMARY

1. The azomethane (AZO) decomposition mechanism is

k
2AZ0 e +AZO*
AZO
kz (S7-1)
AZO* " > N,+ethane
The rate expression for the mechanism of this decomposition,
- k(AZO), (S7-2)
-
IN2 1 + k'(AZ0)'
exhibits first-order dependence with respect to AZO at high AZO con-
centrations and second-order dependence with respect to AZO at low
AZO concentrations.
2. In the PSSH, we set the rate of formation of the active intermediates
equal to zero. If the active intermediate A* is involved in m different
reactions, we set it to
m
(S7-3)

This approximation is justified when the active intermediate is highly
reactive and present in low concentrations.
3. Polymerization: (step reactions and chain reactions)
(a) Steps: initiation, propagation, transfer, termination.
(b) The fraction of functional groups that have reacted is
M,-M
P=-
Mo
(c) The degree of polymerization is

(S7-4)

(d) The Flory distribution for the mole fraction is

Y, = (1 -PIP'-' .(S7-5)