When designing ideal reactors it is possible to use experimental rate data to calculate the volume required. Based on conversion the reactor volume can be given by,
CSTR | PFR |
V=FA,0−rAX | V=∫X0FA,0−rAdX |
This means that if FA,0/−rA is plotted against the conversion X then the volume of a CSTR is given by the rectangle from the exit conversion to the inlet conversion, whereas the volume of a PFR is given by the area under the curve.
The graph below shows the volume of 2 reactors in series. For a PFR the total volume is always the same, but sensible selection of the intermediate conversion for the CSTRs can reduce the total reactor volume.