Isothermal Semibatch Reactors Summary

The answers to the ConcepTests are given below and will open in a separate window. 
Key points from this module:
  • Semibatch reactors are usually for reactions that take place in the liquid phase. A liquid or gas can then be added as reaction proceeds or a vapor can be removed.
  • A solid reacting with a gas can be modeled as a semibatch reactor.
  • Semibatch reactors are used:
    • to increase selectivity
    • to control the rate for fast reactions or highly exothermic reactions
    • because a gas reactant has limited solubility
  • The mass balances for a semibatch reactor are best solved numerically, with one mass balance for each component in the system. For real systems where multiple reactions occur and the reactor is non-isothermal, the ordinary differential equations must be solved numerically.
  • The mass balance equations for a non-isothermal semibatch reactor are identical to those for an isothermal semibatch reactor except the rate constant k is a function of temperature so it changes with time, and mass balances must be solved simultaneously with an energy balance.
From studying this module, you should now be able to:
  • Determine the number of moles of reactants and products in a semibatch reactor as a function of time, given the rate constant, order of reaction, initial moles in the reactor, and feed and/or effluent flow rates.
  • Determine when a semibatch reactor should be used and how it should be run.
Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder