Crude Oil and Fractional Distillation
Crude oil is the untouched oil, as it comes out of the ground, in order to make it useful for a wide range of purposes, it undergoes fractional distilation where the different lengths of alkanes are separated.
Fractional Distilation
At different levels are bubble caps. The crude oil is heated and the longer chain alkanes that have a high boiling point will rise out of the bubble cap. But when it reaches its fraction level higher up that is cooler the vapour condenses and runs out of the distiller.
Fractions
The groups of oil that are removed at different levels that have similar boiling points are called fractions.
| Fraction | Uses |
|---|---|
| Gases | A mixture of small hydrocarbons (ethane, propane etc..). Liquified as LPG (liquified petroleum gas). This is a chemical feedstock (see below). |
| Petrol | Used as fuel for cars. |
| Kerosene | A fuel for jet engines and oil powered domestic heating. This fraction is used in cracking. |
| Diesel | To power combustion engines in cars and ships. |
| Lubricating Oil | Waxes, greases (like Vaseline) and polishes. Mostly used in cracking. |
| Bitumen | Semi solid tar substance left over from distilation. Used for road surfaces and waterproofing roofs. |
Chemical feedstocks are fractions used to produce various chemicals. Naptha is the chief feedstock and used in paints, cosmetics, drugs, glues and pesticides. This is why oil is so important to us today - it isn't just used in cars - and the rapid depletion (loss) of oil reserves is such a critical issue.