Question

Draw a diagram of bubble plate type fractionating column. When do we require such type of a column for separating two liquids. Explain the principle involved in the separation of components of a mixture of liquids by using fractionating column. What industrial applications does this process have?

Answer 1

Diagram of bubble plate type fractionating column and their requirement:

• Fractionating column is required to separate two liquids whose boiling point difference is not too much.
• Liquids having different boiling points vapourise at different temperatures. The vapours are cooled, and the liquids so formed are collected separately.
• The vapours of a substance formed are condensed and the liquid is collected in a conical flask.

Principle involved in fractionating column:

• The principle involved in the separation of components of a mixture of liquids by using fractionating column is that different liquids boil and evaporate at different temperatures.
• The vapours rising up in the fractionating column become richer in more volatile components and pass through the condenser and the pure liquid is collected in a receiver.

A fractionating column provides many surfaces for heat exchange between the ascending vapours and the descending condensed liquid. Some of the condensing liquid in the fractionating column obtains heat from the ascending vapours and revaporises. The vapours thus become richer in low boiling component. The vapours of low boiling component ascend to the top of the column. On reaching the top, the vapours become pure in low boiling component and pass through the condenser and the pure liquid is collected in a receiver .
After a series of successive distillations, the remaining liquid in the distillation flask gets enriched in high boiling component .

Industrial applications of fractionating column:

Fractional distillation is one of the popular separation techniques used in several industries:

1. Fractional distillation is used in the petroleum industry for the fractional distillation of Crude oil. Crude oil normally contains substances such as paraffin wax, gasoline, diesel, naphtha, lubricating oil and kerosene. The fractional distillation process helps in separating these components effectively.
2. Fractional distillation is used in several industries like oil refineries and chemical plants mainly for purification and separation of many organic compounds.
3. Fractional distillation is used for the purification of water as well as separating acetone and water.
4. Fractional distillation is also used for the separation of (liquefied) air. Components like liquid nitrogen and oxygen as well as concentrated argon are obtained through this.