What Does Fractional Distillation Mean?

Fractional distillation is the name given to the refinement procedure carried out to purify petroleum. The question which arises is how does this take place? The petroleum is first vaporized and then introduced near the base of the tall air-cooled fractionating column. The column is divided into a number of sections, each containing trays fitted with bubble caps. This set up liquid vapor equilibria in each section and the different fractions are collected in trays from where they are led out. The main fractions collected in this process of fractional distillation are as follows:

-Refinery Gas- this mainly consists of hydrocarbon and is mostly gases at room temperature. It is used mainly as gaseous fuel and also as feedstock for petrochemicals.

-The second main fraction separated is gasoline. It also is made up of hydro carbons. Its major use is as fuel for internal combustion engines.

-Kerosene separated is used mainly as jet engine fuel. Small amounts are also used for domestic heating. It may also be cracked to yield hydrocarbons in the petrol range.

-Gas oil and diesel oil separated is used as diesel engine fuel and furnace heating. Gas oil is further cracked to produce gasoline.

Other extracts include lubricating oil and some residue containing bitumen.

This technique is used to separate two liquids that dissolve in one another. They are said to be miscible liquids are the dissolve completely to form one liquid. The separation relies on the difference in the boiling points of the two liquids. For example, water and alcohol mix completely. There boiling points are 100 degrees and 78 degrees Celsius respectively.

The fractionating column is packed with glass beads of some other un-reactive substance. This provides a larger surface area for the heated vapor to cool. As the flask containing the mixture of water and ethanol is heated, vapors are produced.

Initially, this vapor would contain both water and ethanol but it would be rich in ethanol because the boiling point of ethanol is lower. As the vapor travels up the fractionating column it cools and falls back into the heating flask. When the temperature of the apparatus reaches 78 degrees Celsius, the ethanol begins to boil. Ethanol vapors are able to escape from the fractionating column to the Liebig condenser. The vapor cools back to liquid in the condenser and can be collected in a beaker.

When the temperature reaches 100 degrees Celsius, water vapor travels through the fractionating column to the Liebig condenser. The water can be collected in a separate beaker.