6.2 Selecting the distillation conditions
To achieve optimal distillation conditions, the distillation energy supplied by the heating bath must be
removed by the condenser.
To ensure this, operate the instrument according to the following rule of thumb:
Cooling water: max. 20 °C Vapor: 40 °C Bath: 60 °C
How are these conditions achieved?:
• Set the bath temperature to 60 °C.
• Set the cooling water temperature not higher than 20 °C.
• Allow cooling water to flow through the condenser: >1.2 l/min (continuous not pulsed).
• Define the operating vacuum in such a way, that the boiling point of the solvent is 40 °C. The corre-
sponding pressure can be seen from the Solvent Table in chapter 3.
Advantages associated with bath temperatures of 60 °C:
• The evaporating flask can be replaced without risk of burns.
• The evaporation rate of the water from the heating bath is low (low energy loss).
• The heating bath energy is used at a good degree of efficiency.
This rule can also be applied to lower bath temperatures, e.g.:
Cooling water: 0 °C Vapor: 20 °C Bath: 40 °C
Δ T
2
(min. 20 °C)
Δ T
1
(min. 20 °C)
Fig. 6.1: 20-40-60 ° rule
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