Question

1. In micro-scale distillation, should you be more aggressive with the heat as you were in macro-scale distillation (or less or about the same)? Justify your answer.

Answer 1

A distillation is one of the most commonly used techniques to purify liquids (in some cases also solids if their boiling points are not too high i.e., phenol, antimony(III) chloride). For instance, it is used to refine alcohol from the fermentation process or to purify water (=distilled water) or separate different hydrocarbons in raw oil (i.e., kerosine, gasolines, naphtha, etc.). In general, there are two important processes involved in this technique.

Microscale distillation:

The conical vial should be securely attached to the Hickman head and the air condenser using the compression cap and the O-ring (shown on the right). All pieces should have a ground-glass joint (=a rough surface on the inside on the top) and fit together well (=no major leaks). The spin vane should be placed in the conical vial, point down (▼). The flat septum and the small compression cap are used to close the side port of the Hickman head. The entire setup is placed in the appropriate hole in the Al-block and centered on the hotplate before starting to stir (otherwise the spin vane will flip over and rotate improperly). The Hickman head and the air condenser have to be cooled with the wet paper towel (an intimate contact between the wet paper towel and the glassware is very important here!). The setting for the heat source should be at a level that the compound of interest distills over slowly. This way, it condenses at the walls of the air condenser and the Hickman head, and collects in the dwell of the Hickman head. If the dwell is full, the compound has to be removed using a Pasteur pipette. If the dwell is very deep, a pipette with a bent tip might have to be used in order to reach the liquid from the top.

If there is more than one volatile compound in the vial, it will be necessary to start with low heat to distill the lower boiling compound first. This way, compounds with a difference of boiling point of at least 50 ºC can be separated relatively cleanly if the distillation is performed properly.