Heidolph LABOROTA 20 compact and safety - Manual (Page 66)

66
E
Select pressure p as to locate boiling point of the substance to be distilled between bath
temperature and coolant temperature, make reference to General Notes. For more information
refer to table and chart on page 68.
 
p (hysteresis) value defines max. pressure rise in mbar to open the vacuum valve.
Extended open valve times results in high rates of solvent loss due to extensive gas
transfer.
Low-boiling substances require a higher

p-value (5
– 10 mbar), high-boiling substances a lower
value (1 – 5 mbar)
2.2. T
auto
vacuum control mode
The T
auto
mode includes the following features:

Needs optional temperature sensor, vacuum valve and vacuum pressure sensor

Selective distillation of substances does not need manual pressure setting

Easy to reproduce

Easy setting

No need to know about thermodynamic substance data

first choice for low-pollution / zero-loss distillation.

 Due to its location, the temperature sensor detects coolant temperature as an approximate
only. Set

T auto values of 2 – 8°C above coolant temperature for optimum reproducibility.
Increasing this temperature span results in a higher rate of distillation with a decrease in
reproducibility.
3. Solvent data

Examples for using table and chart:

The table displays essential substance data, the chart makes reference to the relationship
between pressure and boiling point of some solvents. In this case, 1/T is plotted as a function
of log p in accordance with the Clausius-Clapeyron equation.
a) Distillation of a solvent contained in the table:

on the LABOROTA 20 c ontrol set the value from column “vacuum for set point at 40°C“ as
reference value for Set Vacuum.
b) Distillation of a solvent contained in the chart, with a boiling point other
than 40°C:

Mark the boiling point desired on the temperature axis of the chart

Draw a line to the right to get an intersection with the solvent

Vacuum pressure required for this one situation is found by drawing a vertical line from this
intersection down to the horizontal axis.
c) Distillation of a solvent not contained in the table or chart:

The following notes may be helpful to determine the appropriate vacuum pressure: