Question

The liquid-phase reaction

    A---> B + C

takes place in a series of two CSTRs with an overall conversion of 0.75. Two newly purchased CSTRs are added to the series. The volumetric flow rate is then increased in order to keep the overall conversion at 0.75.

(a) List all your assumptions.
(b) If the original flow rate was 150 L/min, determine the new flow rate (L/min).

Answer 1

Assuming reaction is elementary and hence the order of the reaction is 1.

For a CSTR, performance equation is given by

Case 1: 2 CSTR in series

Assuming CSTRs are of equal volume V (generally, the volume of CSTRs are same because it's economically feasible)

For 1st CSTR

For 1st order reaction

(-r_A ) = kC_A

For 2nd CSTR:

On solving, we get

For X_A = 0.75

V*k = v₀ = 150 L/min

Now, 2 CSTRs are added

V*k = 0.414 v₀^'

but V*k = 150 L/min

.: v₀^' = 150 / 0.414

.: v₀^' = 362.3188 L/min