Isothermal Plug Flow Reactor with Recycle

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).
  • Contributed by: Rachael L. Baumann
  • Additional contributions by: John L. Falconer and Nick Bongiardina
  • (University of Colorado Boulder, Department of Chemical and Biological Engineering)


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Mole balance:
where is the rate of reaction (mol/[L s]), is the rate constant (1/s), is the concentration of the reactant (mol/L), is molar flow rate of reactant (mol/s), is the volumetric flow rate entering the PFR (L/s), and is reactor volume (L).
Initial conditions:
where is the concentration of the fresh feed (mol/L), is pressure (bar), is the ideal gas constant ([L bar]/[mol K]), is temperature (K), is the calculated fresh feed concentration from (mol/L), is the concentration of PFR inlet, guessed using the slider (mol/L), is recycle ratio, is the concentration at the exit of the PFR (mol/L), and is the volumetric flow rate of fresh feed (L/s).
The screencast video at [1] shows how to use this Demonstration.
[1] Isothermal Plug Flow Reactor with Recycle. www.colorado.edu/learncheme/kinetics/IsothermalPFRRecycle.html.
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