The Process of Ethanol Purification by Distillation

There are many ways to create ethanol. However, most of these methods, such as ethylene hydration and brewing, create a mixture that contains both ethanol and water. Unfortunately, this mixture does not meet the requirements of most industrial and fuel uses. For ethanol to be used, it usually has to be purified.

The Ethanol Purification Process

The purification process of ethanol is normally done through a method called fractional distillation, which can lead up to a concentration of 95.6 percent by weight.

The fractional distillation of ethanol refers to the process of separating a mixture into its different components or fractions by heating them up to a certain temperature that will cause some of the fractions to evaporate.

After distillation, the resulting mixture will be composed of 95.6 percent ethanol and 4.4 percent water. At 95.6% ethanol and 4.4% water, the ethanol mixture is considered as an azeotrope with a 78.2 degrees Celsius boiling point. This is why this method is also called the azeotrope distillation of ethanol. However, this is the most purified form that ethanol can take when it is purified through distillation; ethanol cannot be further purified through this method. The reason is that the ethanol and water mixture is more volatile than pure ethanol. Thus, the 95% ethanol and 5% water mixture is already a very common solvent. If, however, a 100% concentration is necessary, other ethanol purification methods should be used.

During fractional distillation of a solution consisting of ethanol and water, the most volatile component of the said mixture will concentrate and vaporize, thus separating from the liquid.

How is Fractional Distillation Done?

The purification distillation of ethanol is conducted in a laboratory and makes use of common apparatuses including a Bunsen burner, a round-bottom flask, a condenser, and a fractionating column. The ethanol purification by distillation is mainly done by exposing ethanol to heat coming from a hot plate, preferably one with a magnetic stirrer. Here are the steps involved.

Step 1: The ethanol is placed in a round-bottom flask that will ensure even heating, preferably with boiling chips. A magnetic stirrer bar, preferably one coated with Teflon, can also be used.

Step 2: The round-bottom flask should be connected to a fractionating column, which is attached to a thermometer. The Bunsen burner, which is the heat source, should be placed at the bottom of the pot.

Step 3: As the distance from the stillpot of the fractionating column increases, you will observe a heat gradient forming. The top part will be coolest, while the bottom part will be hottest. The mixed vapor will then ascend along this gradient, with some of them condensing and re-vaporizing along the way. Every time the vapor condenses and vaporizes, the more volatile liquid in the vapor increases in composition, causing distillation.

Step 4: Eventually, the vapor will consist only of the more volatile liquid before it finally condenses on the glass platform or tray inside the column.

Step 5: The vapor at the bottom of the column will then pass into the condenser, which cools it down and liquefies it. A Liebig condenser, a Graham condenser, or an Allihn condenser may be used. The liquid form of ethanol will then be led to the receiving flask.

Step 6: The process should be continued until all the ethanol has been boiled out of the mixture. You will be able to tell when this has occurred by checking for sharp increases in temperature, as shown on the thermometer attached to the fractionating column.

Fractional distillation is a special type of distillation and is generally used when the parts of the compound boil at temperatures with a difference of less than 25 degrees Celsius.

However, if the difference in the boiling points of the components is greater than 25 degrees Celsius, simple distillation methods can be used. Since ethanol has a boiling point of 78.4 degrees Celsius and water has a boiling point of 100 degrees Celsius, the difference between the two is 21.6 degrees Celsius. This is why fractional distillation is the method used in ethanol purification by distillation.