Consider the reaction of species A to form product B in a constant-density isoth
ID: 702081 • Letter: C
Question
Consider the reaction of species A to form product B in a constant-density isothermal system. The rate of disappearance of A is given by a second-order rate, that is, ( ) = r kC A A 2 . A process plant carries out the reaction using a single PFR with 95% conversion of A. To increase production, a second reactor is to be added. The second reactor is to have the same volume as the first one, and the overall conversion from the system of two reactors is to remain at 95%. Four scenarios are imagined, as given in the following. For each case, determine by what factor the plant can increase production of B. Justify your answer using the appropriate mathematics or impeccable logic.
a. The second reactor is also a PFR and is operated in parallel.
b. The second reactor is a PFR and is operated in series.
c. The second reactor is a CSTR in series placed before the PFR.
d. The second reactor is a CSTR in series placed after the PFR.
Explanation / Answer
B) The second reactor is a PFR and is operated in series.
Explanation: It is given that the volume of both the reactors are same. So if we add the other PFR of the same volume the conversion will be constant as,
The volume for a PFR where PFRs are in series V = ˆ Xf Xi FA0 dX rA – PFRs in series have the same total volume for the same conversion as one PFR:
Vtotal = ˆ X2 0 FA0 dX rA = ˆ X1 0 FA0 dX rA + ˆ X2 X1 FA0 dX rA