Chemistry [[Module Three]] Petroleum: Fractional Distilation

[[Petroleum]]

Complex micture of hydrocarbens (mainly alkanes)
Derived from remains of sea creatures and plants which died and sank to the sea floor millions of years ago.
Susequent deposits compressed the material
High pressures, high temperatures and lack of air converted it to oil and gass.

[[Alkanes]]

Homologous series of saturdated hydrocarbens with the general forumula CnH2n+2
Boiling points increase with length of carbons as van der waals forces between the molecules increase
Increase of boiling points allows for seperation of crude oil by fractional distilation

[[Fractional Distilation]]

Seperation of the mixture of alkanes in crude oil into less complicated mixtures (or fractions)

1) Crude Oil Heated
2) Vapour/Mixture passed into a tower
3) Temperature gradient in tower means that it is cooler at the top than it is at the bottom
4) The temperature gradient seperates the mixture into fractions depending on the boiling points of the compounds present

The hydrocarbens with low boiling points reach the top
The other condense in trays at different levels along the tube and are drawn off

The residue still contains useful materials, sich as lubricting oils and waxes
These boil at above 350 degrees at atmospheric pressure
To avoid such high temps (At which other useful products would decompose) the residue is distilled under reduced pressure duing vacuum distillation.
In vacuum distilation, the remaining hydrocarbens can be distilled at lower temperatures without decomposing.

The amount of products produced from fractional distilation does not meet the demand, so to solve this, longer chain alkanes are broken up in a process called Cracking.