Fractional Distillation & Properties of Hydrocarbons

Fractional distillation of crude oil

• Crude oil is separated into fractions: groups of hydrocarbons with a similar number of carbon atoms and so similar boiling points
• How it works:
  • The crude oil is heated until it evaporates (most of it becomes vapour)
  • The vapour enters a fractionating column that is hot at the bottom and cooler at the top: a temperature gradient
  • As the vapours rise they cool. Each hydrocarbon condenses when it reaches the height where the temperature equals its boiling point
  • Large molecules with high boiling points condense low down; small molecules with low boiling points rise to the top and leave as gases
• The fractions are then processed into fuels (petrol, diesel, kerosene, heavy fuel oil, liquefied petroleum gas) and feedstock for the petrochemical industry, which makes solvents, lubricants, polymers and detergents
• So many carbon compounds exist because carbon atoms can form chains and rings, giving families of similar compounds