C1a - Making Crude Oil Useful

Notes on everything you need to know for C1 - making crude oil useful.

This is for the new specification for OCR Gateway B

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  • Created on: 23-01-13 18:36
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Carbon Chemistry
C1a) Making crude oil useful
Hydrocarbons are a compound with hydrogen and carbon atoms only.
Crude oil, Natural gas and coal are fossil fuels. Non-renewable/finite
Info about Crude oil: Crude oil is thought to have been made from the remains of marine plants and animals that died
millions of years ago. Crude oil is used to make fuels for transport, heating and generating electricity. Plastic too.
Most hydrocarbons in crude oil are compounds called alkanes with single covalent bonds. Saturated (a solution that won't
dissolve any more solute at that temperature) compounds only contain single covalent bonds. Alkenes are a hydrocarbon
with double covalent bonds between carbons. Unsaturated.
Alkanes formula: CnH2n+2 and Alkenes formula: CnH2n
Problems with crude oil: Burning the products of crude oil as fuel produces gases and particles that contribute to global
warming and air pollution such as Carbon dioxide and water vapour. CO2 is trapped in the stratosphere. It absorbs energy
from the Sun. That energy is radiated from the CO2 as heat which raises temperatures. The more CO2 you have to translate
the energy from the Sun into heat the more heat you have available. Removing oil from the ground, as well as oil spillages
and slicks, can be very damaging to wildlife and the environment. The high value of oil means it is sometimes the cause of
military conflict.
Catalytic Cracking: Fuels made from oil mixtures containing large hydrocarbon molecules are not efficient. They do not flow
easily and are difficult to ignite. Crude oil often contains too many large hydrocarbon molecules, and not enough small
hydrocarbon molecules, to meet demand. This is where cracking comes in. Cracking allows large hydrocarbon molecules to be
broken down into smaller alkanes and alkene molecules, smaller hydrocarbons are more useful as fuels, such as petrol and
alkenes are useful, because they are used to make polymers. Fractions containing large hydrocarbon molecules are vaporised
and passed over a hot catalyst. This breaks chemical
bonds in the molecules and forms smaller
hydrocarbon molecules.
Fractions: LGP (liquid petroleum gas), petrol, paraffin, light
gas oil, diesel, heating oil, fuel oil, residue (bitumen)
Fractional distillation is a process used to separate a mixture
of liquids that have different boiling points. The forces
between molecules are called intermolecular forces. These forces are broken during boiling.
Large molecules = long chains = strong force of attraction = high boiling points (and vice versa)
Process: Crude oil must be refined first because it has no uses. This is done in the oil refinery. The first step is to separate compounds
in the oil into groups called fractions. Each fraction contains a mix of compounds with a similar number of carbon atoms.
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. When crude oil is heated, substances with high boiling points condense at the
bottom and substances with lower boiling points condense on the way to the top.
The crude oil is evaporated and its vapours condense at different temperatures in the fractionating column. Each fraction contains
hydrocarbon molecules with a similar number of carbon atoms.
The oils are separated by fractional distillation.
1. Crude oil is heated at the bottom of a tower
2. Fractions with a high boiling point `exit' at the bottom of
the tower
3. Other fractions boil and their gases rise up the tower
4. The tower gets colder the higher up it is. The column has a
temperature gradient.
Fractions with lower boiling points such as LGP `exit' or
condense at the top of the tower, where it's colder.
Oil that does not boil sinks to the bottom. This fraction is called
bitumen (used to make tar for roads/high boiling point).


lisa linsdell

Good revision notes for this unit, although the small font does make it a little difficult to read.

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