Batch Distillation Hints Updated 3/1/2005

1. There is always a little holdup in the line from the previous experiment, so don’t look at the first liquid coming out.
2. Do not turn the valve that says, “Do not turn.”
3. It the reflux valve is set too low, trays dry out. If the reflux valve is set too fast, you get sloppy response.
4. The readings on the refractometer are sensitive to temperature. Try to always measure at the same temperature.
5. Don’t fill the bottom too full.
6. Monitor the temperature in the reboiler.
7. The equations work.
8. There is a Mathcad version of the batch column on the web page. Assume constant molal overflow (L and V are the same on each stage).
9. Monitor purity versus time.
10. Rayleigh equation ignores any holdup in the column.
11. Statistics will be mainly on the calibration curve.
12. The batch distillation column in the UO Lab has 39 stages, but they are not equilibrium stages. You need to get an efficiency to match your data. The Mathcad sheet assumes equilibrium stages. The efficiency can be used to decrease the number of equilibrium stages. For example, if you guess an eficiency of 60%, the number of equilibrium stages becomes 24.