How to determine the best distillation conditions – VACUUBRAND PC 620 User Manual
Page 37
Documents are only to be used and distributed completely and unchanged. It is strictly the users´ responsibility to check
carefully the validity of this document with respect to his product. Manual-no.: 999029 / 01/10/2009
page 37 of 48
How to determine the best distillation conditions
Determine the temperature of the available coolant.
☞ In most cases the coolant temperature is given (e. g. tap water, in house cooling water circuit). For
maximum solvent recovery, carefully choose the boiling point of the product (by choosing the vacuum
level) and the bath temperature accordingly.
☞ Determine the lowest boiling point of the product (solvent).
☞ The temperature difference between boiling point of the product and the coolant should be more than
20°C, otherwise low vacuum level will lead to significant loss of solvent.
☞ Select a water bath temperature of 20-30°C above the boiling point of the product to provide sufficient
heat transfer.
Determine the bath temperature
☞ If there is no limitation from the product side, a water bath temperature of 60-70°C is usually recom-
mended (efficient heating with minimum generation of water vapour from the bath).
Example:
☞ Cooling temperature assumed to be 15-20°C.
☞ Water bath temperature between 60-70°C. Wait until temperature is reached.
☞ Determine the vacuum level for a boiling point (use published data of solvents). Reduce pressure until
a sufficient level of evaporation is attained.
☞ If hysteresis is set manually, avoid frequent operation of the in-line valve (approx. not more than two
operations per minute).
List of solvents
Appropriate selection of
ΔΔΔΔΔp
-
Choose
Δp in a range from 5 mbar (high boiling solvents, e. g. water, toluene) to 150 mbar (low boiling
solvents, e. g. methanol, dichloromethane).
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7
Note: Changing set point p while process control is stopped leads at the same time to automatic preselection
of
Δp. During process control hysteresis is adapted only in case of great set point changes. Hysteresis Δp
can be changed manually at any time.