The easiest way for finding the right conditions is by applying the “delta 20 rule”:
- Heating bath temperature should be 20 degrees higher than the boiling point of the solvent to be evaporated at the vacuum chosen
- Cooling temperature should be at least 20 degrees lower than the boiling temperature of the solvent
A bath temperature of 50 °C is recommended for many applications.
Example:
- 50 °C heating bath temperature
- 30 °C boiling temperature (by adjusting the vacuum)
- < 10 °C cooling temperature
There are many advantages of heating the bath to a maximum of 50 °C:
- No risk of scalding when handling the evaporation flask
- Lower evaporation of heating liquid (e.g. water)
- Higher energy efficiency compared to other heating bath temperatures