how does crude oil form?
the slow decay of marine animals and plants over millions of years under heat and pressure
composition of crude oil?
Mixture of hydrocarbons - mostly alkanes
why and how is crude oil separated?
no use in raw form
differences in physical properties (boiling points) allow it to be separated by fractional distillation
how does fractional distillation work?
- crude oil vaporised in a furnace
- vaporised crude oil passes into fractionating column (cooler at top than at bottom)
- vapours pass up and cools
- fractions condense at diff temperatures (larger lower down column) - drawn off at different levels in column
- shorter chain hydrocarbons condense nearer to the top as have lower boiling points
- largest don’t vaporise and run to bottom - the thick residue collected at the bottom is called tar- can be used to resurface roads or is further processed to give more valuable products
- molecules with lowest boiling points don’t condense and are drawn off as gases at the top
what is a fraction
mixture of hydrocarbons with similar boiling points
as carbon chains get longer, what happens the properties of hydrocarbons?
- more viscous
- harder to ignite
- less volatile (the tendency of a substance to vaporise)
- higher boiling points
what happens to the residue from primary distillation? why?
separated by further distillation at lower pressure (vacuum distillation) - contain useful substances but would decompose if heated above 350 degrees at atmospheric pressure
where does fractional distillation take place?
fractionating tower
what type of bonds are broken and reformed in fractional distillation?
van der waals - physical process
