36
BÜCHI
Vacuum Controller
V-800/V-805
9
Information on choosing
distillation conditions
45: “20-40-60”
Condensation range
9 Distillation conditions
To achieve optimum distillation conditions when rotary
evaporators are used, the energy, supplied for distillation from
the heating bath, must be removed via the condenser. To
guarantee this, operations should be performed according to
this rule of thumb.
Cooling water
Vapour
Bath
max. 20°C
40°C
60°C
How can you achieve these conditions?
•
Set the bath temperature to 60 °C
•
Set cooling water, temperature no higher than 20°C
•
Allow cooling water to flow through the condenser at
approximately 40 – 50 l/h
•
The working vacuum is to be chosen, so that the boiling
point of the solvent is 40 °C. You can get the corresponding
pressure from the Solvent Table (next page).
Advantages associated with 60 °C bath temperature:
•
The evaporating flask can be replaced without risk of
scalding.
•
The evaporation rate of the water from the heating bath is
not very high (energy loss).
•
The heating bath energy is employed at a good degree of
efficiency.
This rule can also be applied to lower bath temperatures, for
example:
Cooling water
Vapour
Bath
max. 0°C
20°C
40°C
Optimising distillation:
Depending on distilled solvent, distillation may have to be
optimised again. However, before you optimise distillation again,
the heating bath must have reached 60 °C.
The following applies: condensation of solvent should be 2/3
to 3/4 of the existing condenser coil.
There are basically two possibilities for optimising distillation:
1. Slowly reduce pressure again
Bath must have reached 60 °C (Boiling point is reduced,
increase of
∆
T1, resulting in increase of distillation capacity) or
2. increasing bath temperature
(Increase of
∆
T1, resulting in increase of distillation capacity).
By increasing the bath temperature, not all of the additional
energy is supplied to distillation, but more is also discharged
into the environment. This is due to the increase temperature
difference between bath and environmental temperature.
∆
T
2
(min. 20°C)
∆∆∆∆∆
T
1
(min. 20°C)
2
/
3
2
/
3
