Fraction by Distillation of Crude Petroleum

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Fractional Distillation

Fractional distillation of crude petroleum

Fig (1) Fractional distillation of crude petroleum

In this process lighter and heavier portions are separated out. If the temperature of the crude oil rises above 400°C , cracking takes place. Hence, crude oil is heated up to 400°C . It is then flashed into the fractional column made up of steel. The vapours of the oil rises up in the fractionating column. They get cooler and then condenses on the shelves having opening at various heights.

The lowest boiling fractions (like gasoline, kerosene oil, diesel oi etc.) condenses at the top.

The highest boiling fractions (like lubricating oil, residual oil etc.) condense at the bottom.

The various fractions are removed continuously. The uncondensed volatile gases escapes at the head of the column (Fig1). Gasoline obtained by the fractional distillation of petroleum is known as straight run gasoline.

Table(1) Fraction by distillation of crude petroleum

S. No Name of the fraction Hydrocarbons interms of carbon atom Boiling point°C Uses
1. Uncondensed gas C1-C4 <30° As domestic fuel under the name of L.P.G.
2. Petroleum ether C5 -C7 30-70° As solvent for varnish
3. Gasoline or petrol C5 – C9 70-120° As fuel in ICE of automobiles and aeroplanes.
4. Naphtha or solvent spirit C9 – C10 120-180° As solvent in dry cleaning, used as fuel.
5. Kerosene oil C10 – C16 180-250° As an illuminant, jet engine fuel and for preparing laboratory gas.
6. Diesel oil or fuel oil or gas oil C15 – C18 250 -320° Diesel engine fuel.
7. Heavy oil C17 – C30 320-400° For getting gasoline by cracking process.
8. Residue: asphalt C30 and above >400° Water – proofing of roofs and road making.
9. Petroleum coke As a fuel and in light rods.

Fractionation of heavy petroleum oils

S. No Name of the fraction Uses
1. Lubricating oil It is used as lubricants
2. Petroleum jelly or vaseline It is used in medicines and cosmetics.
3. Grease It is used as lubricant.
4. Paraffin wax It is used in candles, boot polishes etc.
5. Pitch at above 4000°C Used for making roads, water proof roofing etc.
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