Residence Time Distribution: Summary
Key points from this module:
- For most reactors, not all molecules spend the same time in a reactor.
- Tracer experiments can be used to determine the residence time distribution (RTD) for a reactor to determine how close the reactor is to an ideal reactor.
- For a PFR (plug flow reactor), all molecules spend the same time in the reactor.
- For a CSTR, molecules have a large range of residence times, and the largest fraction leave at very short times.
- As the number of CSTRs in series increases while keeping the total volume constant, the residence time distribution (RTD) starts to approach the RTD for a PFR.
- Different residence times means different reaction times, and this can affect the product distribution. Thus, the RTD affects the product distribution for polymerization reactors.
- For a pulse injection of a tracer into a reactor or series of reactors, the concentration of tracer at the outlet is proportional to the RTD.
From studying this module, you should now be able to:
- Calculate the average residence time from a tracer measurement on a reactor.
- Explain the shape of residence time distribution (RTD) for a plug flow reactor and a continuous stirred tank reactor.
- Explain the shape of the RTD for multiple CSTRs in series.
- Set up and solve material balances for a tracer pulse injection into CSTRs in series.
Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder