Obtaining Gases from Air
We know that air is a homogeneous mixture of gases. It constitutes of gases like nitrogen, oxygen, carbon dioxide, argon, etc. in different proportion. Since it is a homogeneous mixture, we need special separation techniques. Fractional distillation is the technique that is used for obtaining different components from the air.
Fractional distillation is a separation method where the difference in boiling points of components is used to separate the liquid mixture into fractions through distillation. The process begins with the liquefaction of air. Let’s try to understand the process with the help of an illustration of separation of nitrogen from the air.
In order to obtain nitrogen gas from air, we need to remove rest of the constituents of air. Before we start, air is filtered to remove the dust particles and then liquefied
Step 1:Conversion of air into liquid air
The air which is in gaseous form is converted into liquid air. This is done under high pressure. Under high pressure, the air is compressed and then cooled by reducing the temperature. This results in liquid air.
Step 2:Fractional Distillation
The liquid air is then passed through the fractional distillation column. Here, the liquid air is allowed to warm-up. The bottom of the fractionating column is warmer than the top. Each gas starts to separate at different temperatures according to its boiling point.
Nitrogen has a boiling point of -196°C while oxygen has -183°C. The nitrogen gas will start to escape through the outlet and it is collected. The liquid oxygen will be collected in the fractionating column.