Multi-Stage Batch Distillation: Summary
The answers to the ConcepTests are given below and will open in a separate window.
Key points from this module:
- Batch distillation is a transient process in which the compositions in the still and the distillate change with time.
- For multi-stage batch distillation, the system is usually started up with total reflux until equilibrium is reached.
- High purity distillates can be obtained using a multi-stage batch distillation if the number of stages, the reflux ratio, and/or the relative volatility is high enough.
- The reflux ratio is usually not changed during a batch distillation run.
For batch distillation of a binary mixture
- Temperature increases with time during distillation.
- The distillate concentration of the more-volatile component decreases with time.
- Multi-stage distillation can dramatically increase the concentration of the more volatile component in the distillate.
- For multi-stage distillation, increasing the number of stages in the column and/or increasing the reflux ratio increases the concentration of the more volatile component in the distillate.
- For a minimum boiling point azeotrope, the distillate composition will move away from the azeotrope composition as more distillate is collected.
- For a maximum boiling point azeotrope, the distillate composition will approach the azeotrope composition as more distillate is collected.
From studying this module, you should now be able to:
- Explain how the number of stages and the reflux ratio affect separations in multi-stage batch distillation.
- Represent batch distillation of a binary mixture on an x-y diagram.
- Solve the Rayleigh equation for batch distillation.
Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder