Slides in this set
FUELS FROM CRUDE OIL Boiling point and
Crude oil is a mixture of state at room
compounds called temperature
hydrocarbons. Many useful Hydrocarbons
materials can be produced have different
from crude oil. It can be boiling points, and
separated into different can be either solid,
fractions using fractional liquid or gas at
distillation, and some of room
these can be used as fuels. temperature:
Unfortunately, there are Small
environmental hydrocarbons with
consequences when fossil only a few carbon
fuels such as crude oil and atoms have low
its products are used. boiling points and
Most of the compounds in
between five and
crude oil are hydrocarbons.
12 carbon atoms
This means that they only
are usually liquids.
contain hydrogen and
carbon atoms, joined
together by chemical bonds.
There are different types of
atoms have high
hydrocarbon, but most of Fractional distillation
boiling points and
the ones in crude oil are Fractional distillation differs from distillation only in that it separates a mixture into a
alkanes. 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
The main fractions include
and cool at the top. Substances with high boiling points condense at the bottom and
refinery gases, gasoline (petrol),
substances with low boiling points condense at the top. Like distillation, fractional
naphtha, kerosene, diesel oil,
distillation works because the different substances in the mixture have different boiling
fuel oil, and a residue that
contains bitumen. These
Fractional distillation of crude oil
fractions are mainly used as
Because they have different boiling points, the substances in crude oil can be separated
fuels, although they do have
using fractional distillation. The crude oil is evaporated and its vapours allowed to
other uses too.
condense at different temperatures in the fractionating column. Each fraction contains
Hydrocarbons with small
hydrocarbon molecules with a similar number of carbon atoms.
molecules make better fuels
than hydrocarbons with large
The diagram below summarises the main fractions from crude oil and their uses, and the
molecules because they are
trends in properties. Note that the gases condense at the top of the column, the liquids
volatile, flow easily and are easily
in the middle and the solids stay at the bottom.
Incomplete combustion Sulfur
COMBUSTION OF FUELS
If there is insufficient air for complete combustion, we get Most hydrocarbon fuels naturally contain some sulfur compounds.
incomplete combustion instead. The hydrogen is still When the fuel burns, the sulfur it contains is oxidised to sulfur
oxidised to water, but instead of carbon dioxide we get dioxide.
Fuels burn when they react
with oxygen in the air. The carbon monoxide. Particles of carbon, seen as soot or
smoke, are also released. Sulfur dioxide
hydrogen in hydrocarbons Sulfur dioxide is produced when fuels that contain sulfur
is oxidised to water compounds burn. It is a gas with a sharp, choking smell. When
(remember that water, Clouds of smoke and other combustion products are emitted
from chimneys sulfur dioxide dissolves in water droplets in clouds, it makes the
H2O, is an oxide of rain more acidic than normal. This is called acid rain.
hydrogen). If there is The combustion of a fuel may release several gases into the
atmosphere, including: Effects of acid rain
plenty of air, we get Acid rain reacts with metals and rocks such as limestone. Buildings
complete combustion and ·water vapour
·carbon dioxide and statues are damaged as a result. Acid rain damages the waxy
the carbon in hydrocarbons layer on the leaves of trees and makes it more difficult for trees to
is oxidised to carbon ·carbon monoxide
·particles absorb the minerals they need for healthy growth. They may die as
dioxide: a result. Acid rain also makes rivers and lakes too acidic for some
hydrocarbon + ·sulfur dioxide
These products may be harmful to the environment. aquatic life to survive.
oxygen water + Reducing acid rain
carbon dioxide Sulfur dioxide can be removed from waste gases after combustion
of the fuel. This happens in power stations. The sulfur dioxide is
treated with powdered limestone to form calcium sulfate. This can
be used to make plasterboard for lining interior walls, so turning a
harmful product into a useful one. Sulfur can be removed from
fuels at the oil refinery. This makes the fuel more expensive to
produce, but it prevents sulfur dioxide being produced. You may
have noticed 'low sulfur' petrol and diesel on sale at filling stations.
Tiny particles that are released when fuels are burned cause global
As you can see from the graphs, the amount of carbon dioxide in the atmosphere has dimming. Like global warming, this process may change rainfall
increased steadily over the past 150 years, and so has the average global temperature. patterns around the world.
Carbon dioxide is a greenhouse gas. It absorbs heat energy and prevents it escaping from The amount of sunlight reaching the Earth's surface has decreased
the Earth's surface into space. The greater the amount of carbon dioxide in the atmosphere, by about 2 per cent every ten years, because more sunlight is being
the more heat energy is absorbed and the hotter the Earth becomes. reflected back into space. The particles from burning fuels reflect
Sun's rays enter the Earth's atmosphere, Heat is reflected back from the Earth's surface, sunlight, and they also cause more water droplets to form in the
Heat is absorbed by carbon dioxide (greenhouse gas) and as a result becomes trapped in the clouds. This makes the clouds better at reflecting sunlight back into
Earth's atmosphere,The Earth becomes hotter as a result space.
Results of global warming It is likely that global dimming has hidden some of the effects of
A rise of just a few degrees in world temperatures will have a dramatic impact on the global warming, by stopping some of the Sun's energy reaching the
climate: Global weather patterns will change, causing drought in some places and flooding Earth's surface in the first place. Governments around the world
in others. Melting of polar ice caps will raise sea levels, causing increased coastal erosion are introducing controls on pollution. There is the possibility that as
and flooding of low-lying land including land where major cities lie the air becomes less polluted by smoke and soot, global dimming
will decrease, causing the effects of global…read more