Crude Oil and Petrochemicals – JSS2 Basic Science Lesson Note (Third Term)

Crude oil is a dark brown or greenish flammable liquid mixture of hydrocarbons found naturally underground, and petrochemicals are useful chemical compounds made from it.

Behavioural objectives

1. Define hydrocarbons, crude oil and petrochemicals.
2. Give examples of petrochemicals.
3. Describe how crude oil is refined by fractional distillation.
4. List the products obtained from crude oil.
5. State the uses of petrochemicals and the importance of crude oil.

What is crude oil?

Crude oil is the liquid form of unrefined petroleum, a flammable mixture of hydrocarbons found underground.

• Hydrocarbons: compounds containing carbon and hydrogen only.
• Petroleum: a mixture of liquid, gaseous and solid hydrocarbons found naturally underground.
• Colour: dark brown or greenish.
• Composition: a complex mixture of hydrocarbons that differ in appearance, composition and purity.
• Impurities: small amounts of materials such as sulphur and metals.

What are the other forms of petroleum?

• Natural gas: the gaseous form of petroleum, used as fuel. Cooking gas in cylinders is liquefied petroleum gas.
• Bitumen: the thick, solid or semi-solid form, used for tarring roads.

What are petrochemicals?

Petrochemicals are chemical compounds derived from the refining of petroleum.

• Methane: a refinery product used to make carbon black.
• Ethane and propane: gases used as raw materials for making other chemicals.
• Plastics: such as polyethylene.
• Synthetic fibres and rubber: such as nylon.
• Detergents: used for washing and cleaning.
• Industrial chemicals: used to make paints, medicines, insecticides, herbicides, nematicides, rodenticides and avicides.

How are petrochemicals produced?

1. Crude oil is refined into fractions.
2. The fractions are treated.
3. Organic compounds are produced, which form the base of other industrial products.

How is crude oil refined?

Crude oil is refined by fractional distillation, a physical method that separates a mixture by the different boiling points of its parts.

• Fraction: a group of hydrocarbons with similar boiling points, collected together.
• Volatile: turns to vapour easily, so it has a low boiling point.
• Viscous: thick and slow flowing.
• Refining: fractional distillation, purification and conversion of the fractions into more useful products.

How does crude oil get to the refinery?

1. Crude oil from the rock is piped straight into oil storage tanks.
2. It is transported from the storage tanks to the refinery.
3. At the refinery, it is separated into its components. Crude oil is a mixture, so a physical method is used.

What are the steps in fractional distillation?

1. The crude oil is heated in a furnace by passing it through heating pipes. It turns into vapour.
2. The vapour passes into a tall fractionation tower. The tower is hottest at the bottom and cooler towards the top.
3. Fractions are collected from different levels in the trays of the tower.
4. Each tray has many bubble caps. Vapours with similar boiling points pass through them and condense.
5. The most volatile components are collected at the top of the tower.

What are the products of fractional distillation?

There are seven main products from crude oil, listed here from the top of the tower to the bottom.

How can the fractions be told apart?

• Texture: from thin and runny to thick and sticky.
• Colour: lighter fractions are paler, heavier ones darker.
• Odour: each fraction has its own smell.
• Volatility: how easily it turns to vapour.
• Ease of ignition and burning: light fractions catch fire easily.

What are the uses of petrochemicals?

Petrochemicals are raw materials for the industrial production of many essential materials.

• Polymers (plastics): buckets, bottles, bags and pipes.
• Paints: for decorating and protecting surfaces.
• Synthetic rubber and textiles: tyres and nylon clothing.
• Food additives: substances added to food.
• Cosmetics: such as creams and lotions.
• Pesticides: chemicals that kill farm pests.
• Fertilizers: substances that add nutrients to the soil.

Why are crude oil and petrochemicals important?

Crude oil and petrochemicals are important because they give income, energy, jobs and raw materials.

• Source of income: a major source of income in Nigeria and other oil-exporting countries.
• Source of energy: fuel for heating and motor vehicles.
• Employment opportunities: oil production, refining, distribution, marketing and exportation create jobs.
• Raw materials for industries: products supply raw materials that keep industries working.

Evaluation

1. What are hydrocarbons?
2. Name the method used to separate crude oil into its components.
3. Where in the fractionation tower are the most volatile components collected?
4. List four products obtained from the refining of crude oil.
5. State three examples of petrochemicals.

Assignment

Describe how crude oil is separated by fractional distillation, then name four of its products and one use of each.