When crude oil
is put through the process of fractional distillation
, various hydrocarbons are pumped out. A few hydrocarbons, the temperature at which they condense, the number of carbon atoms in their chain and their uses are as follows -
- Bottled gas - 3 carbon atoms. No set temperature for condensing, just rolls out of the top of the fractioning tower.
- Petrol - 8 carbon atoms, comes off at 40 degrees. Used for automobile fuel.
- Naphtha - 10 carbon atoms, comes off at 110 degrees. Used for high-temperature cracking in chemical production.
- Kerosine - 15 carbon atoms, comes off at 180 degrees. Used as jet fuel.
- Diesel - 20 carbon atoms, comes off at 250 degrees. Used as automobile fuel.
- Oil - 35 carbon atoms, comes off at 340 degrees. Used as lubrication.
- Bitumen - 40 carbon atoms, used for tarmac.
As the size of the hydrocarbon chain increases -
- The boiling point increases.
- It gets less flammable.
- It gets more viscous.
- It gets less volatile. The vapours of the more volatile hydrocarbons are very flammable, which is why smoking in petrol stations is a bad idea.
Complete combustion of hydrocarbons - safe
When a hydrcocarbon combusts safely, it burns with a blue flame. The equation for complete combustion is -
hydrocarbon + oxygen -> carbon dioxide + water (+ energy)
The two waste products here are perfectly safe.
Incomplete combustion of hydrocarbons - unsafe
If there isn't enough oxygen available, incomplete combustion
takes place. The equation here is -
hydrocarbon + oxygen -> carbon dioxide + water + carbon monoxide + carbon (+ energy)
This leaves a tell-tale, sooty deposit of carbon. This is a clue the fuel is not burning fully. Carbon monoxide is a deadly gas which is colourless and odourless.