Miscellaneous: Ethanol purification (method 1)

The distillation of concentrated ethanol, mixed with calcium oxide, can result in almost pure ethanol. Calcium oxide reacts with the present water and forms calcium hydroxide which is not soluble in ethanol. Because of that, ethanol can easily be separated from calcium hydroxide via distillation. For this experiment, one needs to prepare a basic distillation apparatus, a graduated cylinder, ethanol solution, calcium oxide, an electrical hot plate and a fairly accurate scale.

The first part is relatively simple. One needs to add calcium oxide to the ethanol. The following reaction takes place:

CaO + H₂O -> Ca(OH)₂

One can see that per one mole of water, we need one mole of calcium oxide. First, 500 mL of ethanol (96%) were measured out. Since there is 4% of water in the mentioned solution, that would mean that there is around 20 mL of water present, which is a little over one mole ( M(H₂O) = 18.015 g/mol ). Because of that, one needs at least 1.11 moles of calcium oxide. Since a surplus of calcium oxide can't really hurt the reaction, and since the calcium oxide that I used was home made, I added even more CaO (about 110 grams).

This solution was left for about 24 hours in a cold and dark place, and after that time, the distillation apparatus was prepared. The solution was poured in a round bottom flask. By playing with friction and mass centers, the apparatus on the image was made very stable, although it may not seem so. The flask and the condenser were connected with a simple improvisation made of polyamide, which is resistant to solvents (and thereby, ethanol as well), and is stable up to temperatures of 100 to 110 °C.

Then the heat source was activated and the temperature started to increase. After some time, from the outlet of the Liebig condenser, concentrated ethanol started to drip gradually.

When the end of the process was approached, the dripping slowed down considerably. After more than 412 mL of distilled ethanol was obtained, the distillation was discontinued since the content of the round bottom flask started to dry up. Further heating would result in an overheated distillation apparatus, which is not desired.

On the image above, one can see the result - about 412 mL of distilled ethanol (99+%).