Sustainability and Stability - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 793

From Fig. 16.8 , we observe that the CSTR operating conditions show a hysteresis when the
dilution rate is increased and then decreased, or decreased and then increased. The cause of
the hysteresis is due to the fact that the middle steady-state branch is not stable and cannot be
operated on. Therefore, the path for increasing the dilution rate does not follow the reverse of
decreasing the dilution rate. From Fig. 16.8 , we also learned that how to operate the CSTR to
achieve high conversions.

Example 16-1. Multiple steady states. The oxidation of carbon monoxide is carried out in
a “fluidized” CSTR containing catalyst particles impregnated with platinum:

k S K A K 1=2 C A C 1=2

1
2

Pt

B
ð1þK A C A þK 1=2

B

CO þ O 2 ! CO 2 ; r ¼

C 1= B Þ

2

B

where C A is the concentration of carbon monoxide and C B is the concentration of oxygen.
When the oxygen is in excess, the rate law can be reduced to

kC A
ð1þKC A Þ

r ¼ (E16-1.2)

2

) where MSS exits.
Solution. A schematic of the fluidized bed reactor is shown in Fig. E16-1.1 .
Since oxygen is in excess, the concentration change of oxygen is negligible. Mole balance

Determine the region (values of feed concentration C A0 and space time

s

Exhaust gas

CO 2 , CO, O 2

Catalyst
particles

C A0 , Q 0

Feed

CO, O 2

FIGURE E16-1.1 A schematic of fluidized bed CO converter.