HISTORY
Early forms of distillation were known in Mesopotamia (nowadays Iraq).
In the eighth century, alchemists in the Middle East carried out distillation processes to
purify chemical substances for industrial purposes such as isolating natural perfumes or
producing pure alcohol.
APPLICATIONS
Distillation is a laboratory technique used for liquid separation and purification.
Commercially, distillation has several usages. It is used to separate crude oil in its
different fractions for specific uses such as transport, power generation and heating.
Water is distilled to remove impurities such as salt from sea water. Distillation of
fermented solutions has been done since ancient times to produce distilled beverages
with higher alcohol content.
CAUSE AND EFFECT
Distillation usually forms part of a larger chemical process. It is the most frequent and
important method for liquid purification. It is used to separate the non-volatile solutes
from a liquid or, when possible, to separate two or more liquids.
When you heat a liquid mixture of two different substances, they boil at a different
temperature due to their different boiling points so we can separate them.
DESCRIPTION
In the distillation process, a liquid L1 is heated until it passes to gas phase, G. After that,
this gas is condensed by cooling becoming a liquid again, in this case L2, which is free
from other components that could be present in L1.
Assuming we have two liquids, the more volatile one (the one with the lower boiling
point) will evaporate first and the vapour will pass to a condensing column, where it
will be reverted into a liquid (condensed). It will trickle on a cool glass into a receiving
flask. Further heating will cause the less volatile liquids to evaporate and distil.
A simple distillation apparatus consists of a distillation flask (a rounded bottom flask)
joined to a distillation head (three way adapter) holding a thermometer (to determine the
boiling temperature of the liquid). The adapter connects to a condenser into which cold
water is constantly passed through. All the hot vapours produced are channeled into this
condenser which cools and condenses them.
During distillation, the thermometer head must be at exactly the same height of the
lower part of the distillation head in such a way that all the thermometer head is covered
by the ascending vapor. Distillation must be done slowly but constantly, with no
interruptions, so the appropriate temperature for the heat source must be controlled.
To avoid liquid overheating and bubble formation, before starting the distillation a
magnetic follower, anti-bumping granules or mechanical stirrer should be added to the
liquid. This stirrer will eventually capture in its pores any bubble formed and allowing
the liquid to boil normally when its boiling temperature is reached.
The previously described simple distillation is usually used to separate mixtures of two
components with boiling points separated at least by 25 ºC. For a lower difference,
repeated distillations should be done collecting each time a richer mixture (richer in the
sense of more relative abundances of one of the components of the mixture).
PIECES OF EQUIPMENT
Laboratory distillation set-up from left to right:
1: Heat source. 2: Distillation flask. 3: Distillation head 4: Thermometer. 5: Condenser.
6: Adapter. 7: Receiving flask.
How to do a simple distillation step by step?
1. Equipment.
2. Begin with a round bottom flask.
3. The three way adapter or Y-adaptor sits on top of the distillation flask. Simply place
it on top.
4. Connect the condenser to the Y-adaptor.
5. The next item you need is an adaptor that should be connected to the condenser. Add
a couple boiling chips to the round bottom flask by dropping them down the distillation
head.
6. Place a stemmed funnel into the top of the distillation head and pour the liquid to be
distilled through it so that it goes into the distillation flask. The flask should be from 1/2
to 2/3 full, no more, no less. When done, remove the funnel.
7. A flask is placed under the adaptor. This is the receiving flask. A beaker or graduated
cylinder could also be used.
8. The next items to be added are the thermometer and the thermometer adaptor. They
are connected on top of the distillation head. The thermometer is always the last piece
added because it is large and susceptible to break.
9. Adjust the height of the apparatus as necessary.
10. Connect two pieces of rubber hose to the condenser. The one on the lower
connection goes to the water source; the one on the upper connection goes to the drain.
Make sure all of the glass and hose joints are tight before turning on the cooling water.
You have done it!