Petroleum, Fractional Distillation & Octane Number | Chemistry for JAMB PDF Download

Petroleum Composition

Petroleum is a complex mixture of hydrocarbons that is naturally formed from the remains of ancient marine organisms. It consists mainly of carbon and hydrogen atoms, with smaller amounts of sulfur, nitrogen, oxygen, and trace elements. The hydrocarbons in petroleum can be categorized into three main groups: alkanes (saturated hydrocarbons), alkenes (unsaturated hydrocarbons with double bonds), and aromatic hydrocarbons (containing a ring structure).

Fractional Distillation

To separate the different components of petroleum, a process called fractional distillation is used. Crude oil is heated in a fractionating column, and the vapors rise through the column, cooling as they go higher. As the temperature decreases, different fractions condense at different heights, based on their boiling points. The column is divided into several trays or stages, each collecting a specific fraction.

Major Products from Fractional Distillation

The fractional distillation of petroleum yields various fractions, each with its own unique properties and uses:

• Refinery gases: These are the lightest fractions and include propane and butane, which are used as fuel.
• Gasoline: This fraction is volatile and used as a fuel for internal combustion engines.
• Kerosene: It is used as jet fuel and for heating and lighting.
• Diesel oil: This fraction is used as fuel for diesel engines.
• Lubricating oil: It has higher viscosity and is used for lubrication purposes.
• Fuel oil: This fraction is used in industrial burners and ships.
• Bitumen: It is a thick, heavy fraction used for road construction and roofing.

Cracking and Reforming

Cracking is a process used to break down heavier hydrocarbon molecules into lighter ones. It involves the application of heat and pressure, or the use of catalysts, to break the carbon-carbon bonds. Cracking helps to increase the yield of gasoline and other lighter fractions from crude oil.
Reforming is another process used to convert low-octane hydrocarbons into high-octane compounds. It involves rearranging the carbon and hydrogen atoms within the molecules to produce compounds with improved fuel qualities.

Petrochemicals - Starting Materials of Organic Syntheses

Petrochemicals are chemical compounds derived from petroleum. They serve as crucial starting materials for the production of various organic compounds. Petrochemicals include ethylene, propylene, benzene, toluene, and xylene, among others. These compounds are used in the production of plastics, synthetic fibers, rubber, dyes, detergents, pharmaceuticals, and many other products.

Quality of Petrol and Octane Number

The quality of petrol is determined by several factors, including its composition and performance characteristics. One important parameter is the octane number, which indicates the anti-knock properties of the fuel. The octane number represents the fuel's ability to resist knocking or premature combustion in internal combustion engines. Higher octane numbers indicate better resistance to knocking, allowing engines to operate smoothly and efficiently.

In summary, petroleum is a complex mixture of hydrocarbons, and fractional distillation is used to separate its components. The major products obtained through fractional distillation have specific properties and uses. Cracking and reforming processes are employed to improve the quality and yield of desired fractions. Petrochemicals derived from petroleum serve as essential starting materials for various organic syntheses. The quality of petrol is evaluated based on factors such as its composition and octane number, which indicates its anti-knock properties.