Fractional distillation + uses and cracking of crude oil

What is crude oil?

A fossil fuel

How is crude oil formed?

From the remains of plants and animals, mainly plankton, that died millions of years ago. Over millions of years, with high temperature and pressure, the remains turn to crude oil, which can be drilled from the rocks where it is found.

Why are fossil fuels finite?

They take so long to make that they’re being used up faster than they are formed

What is crude oil a mix of?

Different hydrocarbons, most of which are alkanes.

How are the compounds in crude oil separated?

Fractional distillation

What properties do shorter carbon chains have vs longer carbon chains?

• the shorter chains are more runny - that is the less viscous it is

• The shorter the carbon chain the more flammable

• Shorter carbon chains have have lower boiling points

What happens to longer hydrocarbons during fractional distillation?

With high melting points. They condense into liquids and drain out of the column early on when they’re near the bottom

What happens to shorter hydrocarbons during fractional distillation?

They have lower melting points. They condense and drain our much later on, near the top of the column where it is cooler

What is the temperature gradient like in a fractionating column?

It’s hot at the bottom and cooler as you go up

What happens to crude oil as it heated during fractional distillation?

Turns to gas which enter a fractionating column

What does it mean to say than a resource is ‘finite’?

That ir js being used up quicker than it is being replenished

Why type of substance does crude oil mainly contain?

Alkanes

What property of the molecules in crude oil is used to separate them into different fractions?

Boiling point

How does the fractioning column separate molecules in crude oil into different fractions

• the fractioning column has a temperature gradient (hot at the bottom and cool at the top)

• The longer hydrocarbons gave a higher boiling point so condense at the bottom

• The shorter hydrocarbons have lower boiling points so condense at the top

Fractions boil over a range of temperatures much narrower than the original crude oil. What does this suggest about the structures of the hydrocarbons in a fraction?

They have a similar chain length

What is cracking?

The process of splitting up of long-chain hydrocarbons into smaller, more useful ones

Why are short chain hydrocarbons good for fuels?

Because they are flammable

What does cracking produce?

Alkanes and alkenes

What are alkenes used as?

Starting material when making other compounds and also making polymers

What kind of reaction is cracking?

Thermal decomposition

What is thermal decomposition?

Breaking molecules down by heating them

What are the steps of cracking?

• heat the long hydrocarbon chains to vaporise them (turn them into gas)

• The vapour is then passed over a hot powered aluminium oxide catalyst

• The long-chain molecules split apart on the surface of the specks of catalyst - this is catalytic cracking

What types of useful material are produced from crude oil fractions?

• solvents

• Lubricants

• Detergent

• Polymers

Why do we break up long hydrocarbons into shorter chain hydrocarbons?

Because they are more useful and can be used in more applications