A first-order reaction is carried out in an isothermal plug flow reactor (PFR) with recycle. The fresh feed concentration (
) and volumetric flow rate
are known. Use sliders to change the recycle ratio and the PFR volume. The correct reactant exit concentration
is obtained iteratively: the reactor feed concentration
is guessed with the slider, the PFR mass balance is then solved to determine
, and a mass balance around the mixing point before the PFR yields the calculated
value. Next, change the "
guess" using the slider until the calculated
(the black arrow on the left) equals 0.2 mol/L (the center of the green circle). The graph on the right plots the reactant concentration down the PFR using the guessed
value. For larger values of the recycle ratio, the PFR with recycle behaves like a continuous stirred-tank reactor (CSTR).