Fuels & Separation of Petroleum | Chemistry for Grade 11 (IGCSE) PDF Download

Common Fossil Fuels

• A fuel is a substance that, upon combustion, releases heat energy.
• This released heat energy can be converted into electricity, which is extensively used in our daily lives.
• The most prevalent fossil fuels comprise coal, natural gas, and hydrocarbons like methane and propane, derived from crude oil. 
• Hydrocarbons exclusively consist of hydrogen and carbon atoms.
• Methane, represented as CH₄, stands as the primary component of natural gas.

Petroleum & Fractional Distillation

• Petroleum, also known as crude oil, is a complex mixture of hydrocarbons along with natural gas. 
• It is a thick, sticky, black liquid found under porous rock formations, whether underground or under the sea.
• Diagram showing crude oil under the sea:
  
• Petroleum, as a mixture, is not directly useful, but its components, known as fractions, have various applications. These fractions are separated through a process called fractional distillation.
• During fractional distillation, fractions in petroleum are separated based on their similar properties and boiling points, which are influenced by the number of carbon atoms in their molecular chains.
• The boiling point and viscosity of each fraction increase as the length of the carbon chain grows.

Fractional Distillation

Diagram showing the process of fractional distillation:

• Fractional distillation takes place in a fractionating column.
• The fractionating column is hot at the bottom and cools at the top.
• When crude oil is introduced into the column, it is heated, causing vapors to rise.
• Vapors of hydrocarbons with high boiling points condense into liquids and are collected at the bottom.
• Vapors of hydrocarbons with low boiling points rise to the top of the column and are collected there.
• Various fractions condense at different heights based on their boiling points and are collected as liquids.
• Fractions with smaller hydrocarbons are gathered at the top as gases.
• Fractions with larger hydrocarbons are collected in the lower sections of the column.

Properties of Fractions

Fractions obtained through fractional distillation exhibit distinct properties:

• Volatility: Refers to how easily a substance vaporizes. For instance, lighter fractions have higher volatility compared to heavier ones.
• Boiling Points: Different fractions have varying boiling points, leading to their separation during distillation. For instance, gasoline has a lower boiling point than diesel.
• Viscosity: This property determines the fluidity of a fraction. Lighter fractions are less viscous than heavier ones. For example, kerosene is more viscous than gasoline.
• Flammability: Some fractions are more flammable than others due to their chemical composition. For example, lighter fractions like gasoline are highly flammable compared to heavier fractions like lubricating oil.

Key Concepts in Hydrocarbon Properties

Viscosity

• Viscosity pertains to how easily a liquid flows. 
• Liquids with high viscosity are thick and flow less readily. 
• When the number of carbon atoms in a hydrocarbon chain increases, the attraction between the molecules intensifies, leading to a higher viscosity as the chain lengthens. 
• Consequently, liquids become more viscous with increasing molecular mass, causing them to flow less easily.

Colour

• The color of a liquid darkens as the carbon chain lengthens, signifying increased thickness and viscosity.

Melting Point/Boiling Point

• Larger molecules exhibit greater intermolecular attraction, requiring more heat to separate them. 
• Consequently, as molecular size increases, so does the boiling point.

Volatility

• Volatility denotes a substance's tendency to vaporize. 
• As molecular size grows, hydrocarbon liquids become less volatile due to heightened intermolecular attraction with increasing molecular size.

Uses of Various Fractions

• Refinery gas: used for heating and cooking purposes
• Gasoline: serves as fuel for automobiles (petrol)
• Naphtha: utilized as a raw material for chemical production
• Kerosene: essential for jet fuel production (paraffin)
• Diesel: functions as fuel for diesel engines (gas oil)
• Fuel oil: used for powering ships and home heating
• Lubricating oil: necessary for lubricants, polishes, and waxes
• Bitumen: employed in road surfacing applications

Trends in Chemical Properties