Noadswood Science, 2011

Crude Oil

To understand what crude oil is and how it can be used

Wednesday, April 19, 2023

Crude Oil

How is oil formed and how is it found in its ‘natural’ state?

Fossil fuels formed millions of years ago from the remains of living things (coal from plants and natural gas and oil from sea creatures) - they were gradually buried by layers of rock which stopped them rotting…

Crude Oil

• The buried remains were put under pressure and chemical reactions heated them up, gradually changing into fossil fuels

Crude Oil

• Some oil and natural gas was covered by cap rock which is impermeable (not letting them through)

• They can be removed from the ground by drilling through the rock

Fossil Fuels

Coal

Oil & Gas

Crude Oil

Crude oil is a mixture of compounds called hydrocarbons – they only contain hydrogen and carbon atoms, joined together by chemical bonds

There are different types of hydrocarbon, but most of the ones in crude oil are alkanes…

Alkanes

The alkanes are a family of hydrocarbons that share the same general formula: -

CnH2n+2

The general formula means that the number of hydrogen atoms in an alkane is double the number of carbon atoms, plus two

E.g. methane is CH4 and ethane is C2H6

Alkane molecules can be represented by displayed formulae in which each atom is shown as its symbol (C or H) and the chemical bonds between them by a straight line…

Alkanes

*The bonds are not really at 90o – as shown by the ball and stick model

Alkane Formula Chemical structureBall-and-stick

model

Methane CH4

Ethane C2H6

Propane C3H8

Butane C4H10

Alkanes

As the alkane chain increases in length the properties change…

Longer chains mean: -

Less ability to flow (more viscous)

Less flammable

Less volatile

Increased boiling points

Increasing chain length

Alkanes

Alkanes are saturated hydrocarbons – this means that their carbon atoms are joined to each other by single bonds

This makes them relatively un-reactive, apart from their reaction with oxygen in the air during combustion (they do burn well)!

Alkanes

Hydrocarbons have different boiling points, and can be either solid, liquid or gas at room temperature: -

Small hydrocarbons with only a few carbon atoms have low boiling points and are gases

Hydrocarbons with between 5 and 12 carbon atoms have medium boiling points and are usually liquids

Large hydrocarbons with many carbon atoms have high boiling points and are solids

Crude Oil

Why is crude oil so important?

Some of the 21st century’s most important chemistry involves chemicals that are made from crude oil – they are used for fuels in cars; warming of homes; making electricity etc…

When oil prices rise it affects us all – countries that produce crude oil can have an affect on the world economy by the price charged for oil

Crude oil originates as a dark, smelly liquid which is a mixture of lots of different chemical compounds – it is not much use straight out of the ground (there are too many substances in it, all with different boiling points). As such it needs to be refined…

Parts

Although we can get useful substances from oil, crude oil itself has no uses

In order to make crude oil into useful substances we first have to separate the mixture into molecules of similar size – this is done in an oil refinery…

Parts

Crude Crude oil is a mixture of different sized hydrocarbons – the exact composition depends upon where the oil comes from but typically it contains a lot of big molecules

Distillation

Distillation is a process that can be used to separate a pure liquid from a mixture of liquids – it works when the liquids have different boiling points

Fractional Distillation

Fractional distillation differs from distillation only in that it separates a mixture into a number of different parts, called fractions

A tall column is fitted above the mixture, with several condensers coming off at different heights

The column is hot at the bottom and cool at the top – substances with high boiling points condense at the bottom and substances with low boiling points condense at the top

Like distillation, fractional distillation works because the different substances in the mixture have different boiling points

Fractional Distillation

Watch the demo of fractional distillation of crude oil…

Fractional Distillation

Because they have different boiling points, the substances in crude oil can be separated using fractional distillation

The crude oil is evaporated and its vapours allowed to condense at different temperatures in the fractionating column – each fraction contains hydrocarbon molecules with a similar number of carbon atoms

Fractional Distillation

Oil fractions – the gases condense at the top of the column, the liquids in the middle and the solids stay at the bottom…

The main fractions include refinery gases, gasoline (petrol), naphtha, kerosene, diesel oil, fuel oil, and a residue that contains bitumen

These fractions are mainly used as fuels, although they do have other uses too

Hydrocarbons with small molecules make better fuels than hydrocarbons with large molecules because they are volatile, flow easily and are easily ignited

Fraction Differences

Observe the differences in the fractions between their viscosity, flammability and volatility…

Natural Gas BitumenPetrol

Fractional Distillation