Chemistry Notes on Fuels and Atmosphere

Hydrocarbons and Crude Oil

Hydrocarbons are compounds containing only hydrogen and carbon, which can be chain or ring-shaped.

Crude oil is a dark, thick liquid, a mixture of different hydrocarbons (mostly alkanes) found in underground deposits. It serves as fuel and feedstock (basic chemicals supply) for the chemical industry.

Crude oil is a finite resource, meaning there's a limited amount that will eventually run out, making it a non-renewable resource.

Uses of Crude Oil Fractions Based on Molecule Size

Small Molecules:

  • Light in color.

  • Easy to ignite.

  • Runny.

  • Low boiling point.

Large Molecules:

  • Dark in color.

  • Hard to ignite.

  • Thick.

  • High boiling point.

Different Fractions:

  • Refinery Gas (Bottled Gas): 20°C

  • Petrol (Gasoline): 70°C (Petrol for Vehicles)

  • Naphtha: 120°C (Chemicals)

  • Kerosene: 170°C (Jet fuel, Paraffin for lighting and heating)

  • Diesel: 270°C (Diesel fuels)

  • Lubricating Oil: (Lubricating Oils, Waxes, Polishes)

  • Fuel Oil: (Fuel for Ships, Factories, and Central Heating)

  • Bitumen: 340°C (Roads and Roofing)

Viscosity refers to how easily a fluid flows; a higher viscosity means a thicker fluid.

Ease of ignition is how easily a substance catches fire.

Fractional Distillation of Crude Oil

Fractional distillation separates a mixture of compounds according to their boiling points.

Crude oil is heated, turning nearly everything into a gas. Hot gases rise up a fractionating column until they cool and condense. The separated liquids and gases are collected at different temperatures.

Alkanes

A homologous series is a family of closely related compounds with similar properties (e.g., Alkanes).

A general formula describes the number of each atom in any member of a homologous series.

Alkanes are hydrocarbons containing only single bonds. Their names end with '-ane'. The general formula for alkanes is CnH{2n+2}.

Examples:

  • Methane: CH_4

  • Ethane: C2H6

  • Propane: C3H8

  • Butane: C4H{10}

Complete and Incomplete Combustion

Complete combustion produces only water and carbon dioxide and releases the most possible energy.

The complete combustion equation:

Fuel + oxygen → carbon dioxide + water

Example:

Ethane + oxygen → carbon dioxide + water

2C2H6 + 7O2 \rightarrow 4CO2 + 6H_2O

Incomplete combustion occurs in limited oxygen, producing a mixture of carbon dioxide, carbon monoxide, carbon, and water, while releasing less energy.

Combustible Fuels and Pollution

Sulfur is an impurity naturally present in small amounts in oil and coal.

Sulfur dioxide (SO_2)is a gas formed from the sulfur in oil and coal when it is burned.

Sulfur dioxide dissolves in water in clouds to form sulfurous acid (H2SO3), which oxidizes to become sulfuric acid (H2SO4), a component of acid rain.

Carbon monoxide (CO) is a colorless, odorless, and highly toxic gas.

CO sticks to hemoglobin in the blood, preventing it from carrying oxygen.

Soot consists of small particles of carbon.

Problems with soot:

  • Causes lung problems when breathed in.

  • Blackens and dirties buildings.

Effects of acid rain:

  • Soil becomes too acidic for crops and plants to grow well.

  • Acid in rivers and lakes kills fish and some insects.

  • Corrosion of limestone damages buildings and statues.

Nitrogen oxides (NO_x) are various gases formed at high temperatures inside internal combustion engines.

Problems of nitrogen oxides:

  • Can dissolve in clouds to form acid rain.

  • NO_2 causes lung damage.

  • NO_x can cause smog formation.

Cracking

Cracking is the breaking down of longer, less useful hydrocarbons into shorter, more useful ones (to meet higher demand, e.g., petrol).

Hydrogen Fuel

Hydrogen combusts easily and produces no greenhouse gases.

However, it is difficult to store (as a gas) and use in an engine.