Page 66 - Modeling of Chemical Kinetics and Reactor Design

36 Modeling of Chemical Kinetics and Reactor Design

Using the steady state approximation,
( +r CH CO * ) net = 0 and ( +r CH 3 * ) net = 0

3

The overall rate equation is:

3
− ( r ) =− dC CH CHO
CH CHO net dt
3
(1-150)
= kC + k C C
1 CH CHO 2 CH 3 * CH CHO
3
3
From Equations 1-148 and 1-149, 2kC 2 = k C and
4 CH * 3 1 CH 3 CHO
 k  05 .
C * =  1 C CH CHO (1-151)
CH 3  2 k 4 3 

Substituting Equation 1-151 into Equation 1-150 gives

dC CH CHO
− ( r CH CHO ) = – 3
3
dt
 k 1  05 . (1-152)
= kC CH CHO + k 2  2 4 • C CH CHO   C CH CHO
1
3
3
 k
3
 k  05 .
If k 2 1 C CH CHO >> k C CH CHO , then Equation 1-152 becomes
1
 2 k 4 3  3

dC CH CHO
− ( r ) =− 3
CH CHO dt
3
and

2
dC dC  kk  05 .
− CH CHO = CH 4 =  2 1  C 32 (1-153)
3
CH CHO
dt dt  2 k 4  3