Rotary Speed Of Evaporator Flask; 11. Temperature Difference Between Hot Bath And Vapor; 12. Temperature Difference Between Vapor Temperature And Coolant; 13. Solvent Data - Heidolph VV Micro Instruction Manual

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10. Rotary speed of evaporation flask
Raise distillation speed by raising rotational speed. This methods cuts distillation time and
protects the substances handled.

11. Temperature difference between hot bath and vapor

This temperature difference should at least be 20 K to reach adequate distillation speed. If
acceptable by thermal stability of the substances handled, you even may raise the
temperature difference.
Rule of thumb: double temperature to double distillation speed.

12. Temperature difference between vapor temperature and coolant

This temperature difference should be no less than 20 K to guarantee adequate
condensation. Low temperature difference, effectiveness of solvent recovery drops.
Choose an as high as possible temperature difference in particular for high-boiling
substances.

13. Solvent data

Examples for using reference table and nomogram:
This reference table details substance data needed for distillation, whereas the nomogram
reflects relationship between pressure and boil temperature of some solvents. Go by the
Clausius-Clapeyron equation and plot 1/T against log p.
13.1. At boiling temperature of 40°C
Vacuumcontroller: in column "vacuum for boil temperature" use the "Set Vac" nominal
value as depicted for 40°C.
13.2. At boiling temperatures deviating from 40°C
1. On temperature axis of the nomogram mark boil temperature needed.
2. Draw a line to the right and determine intersection with the solvent line.
3. From this intersetion draw a straight line down to determine the vacuum pressure
neeed for this particular application.
13.3. Solvents not depicted
- The following items might help in determining the right vacuum pressure:
1. Raise of the straight line is a function of evaporation enthalpy. It is similar for similar
chemical substances with similar boil temperature. Hence, straight lines depicted may
be used for rough reference to a lightly deviating boil point.
2. A water jet pump or diaphragm-type pump may lower boil temperature by about 100°C.
3. Rule of thumb: decrease pressure to ½ will decrease boil point by about 15°C.
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