
145Homogeneous Reactors
the outlet. Thus, the concentration level of A, C
A
, is always higher in a PFR than
in a CSTR. So, the net rate of reaction is always higher in a PFR than in a CSTR.
Hence, a PFR compared to a CSTR requires smaller space time to achieve a speci-
ed level of conversion X
Af
.
PROBLEM 3.3
A continuous-ow reactor is to be designed to carry out a second-order reversible reaction
1
and achieve 90% equilibrium conversion. The rate equation is
()−= −rk
C
AAB1
2
2
2
The feed contains 5 kmol/m
3
of A. The reaction rate constant k
1
= 0.1 (m
3
/kmol) (1/min)
and the equilibrium constant K = 9. What is the space time required to ...