Page 78 - Elements of Chemical Reaction Engineering 3rd Edition

50 Conversion and Reactor Sizing Chap. 2

Example 2-5 Comparing Volumes for CSTRs in Series

For the two CSTRs in series, 40% conversion is achieved in the first reactor. What
is the total volume of the two reactors necessary for 80% overall conversion of the
species A entering reactor l? (If FA2 is the molar flow rate of A exiting from the last
reactor in the sequence, FA2 = 0.2FA0.)

Solution
FAo = 0.867 mol/s

800

CSTR 1

BCSTR 2
I
200

0 0.2 0.4 0.6 0.8 1.0
Conversion, X
Figure E2-5.1 Levenspiel plot for two CSTRs in series.

For reactor we observe from either Table 2-2 or Figure E2-5.1 that when X = 0.4,
then

-
I
- - 250 dm3. s/mol
- rAl
VI = FA0 (&I X 0.867 [&) (0.4) = (0.867)(250)(0.4)
Then

V, = 86.7 dm3 (liters)
For reactor 2, when X, = 0.8, then (l/--rA) = 800 dm3-s/mol, and

= (0.867 $1 (800 '$1 (0.8 - 0.4)

= 277.4 dm3 (liters)