Chapter 23Fossil Fuels

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Chapter 23 Fossil Fuels
23.1 Fossil fuels as a major energy source
23.2 Coal
23.3 Petroleum and natural gas
23.4 Refining petroleum
CONTENTS OF CHAPTER 23
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23.1 FOSSIL FUELS AS A MAJOR ENERGY
SOURCE ENERGY AND FUEL An important way of
obtaining energy is to burn fuels.
23.1 FOSSIL FUELS AS A MAJOR ENERGY
SOURCE
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Figure 23.1 Burning fuels to provide energy.
23.1 FOSSIL FUELS AS A MAJOR ENERGY
SOURCE
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A FUEL is a substance which is burnt to
produce heat.
At present, the commonest fuels are fossil
fuels. WHAT FOSSIL FUELS ARE Coal, petroleum
and natural gas are collectively called fossil
fuels. They are so called because they were
formed from the remains of plants and animals
that lived hundreds of million years
ago. Different fossil fuels have different
properties. Yet they have one thing in common
they all contain hydrocarbons. (Hydrocarbons are
compounds containing hydrogen and carbon only.)
23.1 FOSSIL FUELS AS A MAJOR ENERGY
SOURCE
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23.2 COAL The most abundant fossil fuel is coal.
Coal is a black solid, usually quite hard. It
consists of 65 95 carbon, together with
hydrocarbons and some other compounds.
Figure 23.3 Coal is a black solid consisting
mainly of carbon. Its composition varies with the
type of coal.
23.2 COAL
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ORIGIN OF COAL Coal was formed from the remains
of plants that grew in swamps 250 million years
ago. Due to movements of the Earths crust, the
plant remains were deeply buried under layers of
mud and sand. Under high pressure and
temperature, the decaying plants gradually turned
into coal.
23.2 COAL
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Figure 23.4 Plants that lived 250 million years
ago were buried and turned into coal that we burn
today.
23.2 COAL
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Figure 23.5 The formation of coal.
23.2 COAL
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USING COAL About two-thirds of the coal mined
today is burnt in power stations to generate
electricity. Coal can be changed to a number of
useful substances by a special process.
23.2 COAL
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Figure 23.8 The Lamma power station in Hong Kong
burns coal to generate electricity. The picture
shows coal being unloaded from a ship.
23.2 COAL
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23.3 PETROLEUM AND NATURAL GAS Petroleum is
a smelly oily liquid, usually quite thick its
colour ranges from greenish brown to black,
depending on where it is obtained. Petroleum is
a complex mixture consisting mainly of
hydrocarbons. Natural gas is also a mixture
mainly of hydrocarbons. It consists chiefly of
methane CH4, with small amounts of ethane C2H6,
propane C3H8 and butane C4H10.
23.3 PETROLEUM AND NATURAL GAS
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Figure 23.9 A sample of crude oil.
23.3 PETROLEUM AND NATURAL GAS
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ORIGIN OF PETROLEUM AND NATURAL
GAS Petroleum and natural gas were formed from
very small sea animals and plants (e.g.
planktons) that lived hundreds of million years
ago.
23.3 PETROLEUM AND NATURAL GAS
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Figure 23.10 Planktons are very small sea
organisms.
23.3 PETROLEUM AND NATURAL GAS
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Figure 23.11 The oil story.
23.3 PETROLEUM AND NATURAL GAS
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A23.1
This is due to the movements of the Earths crust.
USING PETROLEUM AND NATURAL GAS Petroleum is
not burnt directly to supply energy. In fact,
petroleum must be treated or refined first. The
process of separating hydrocarbons in petroleum
into several parts (fractions) is called the
refining of petroleum. Unlike petroleum, most
natural gas is burnt directly as a fuel. It burns
with a clean blue flame, causing little pollution.
23.3 PETROLEUM AND NATURAL GAS
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Figure 23.16 Natural gas burns with a clean
blue flame.
23.3 PETROLEUM AND NATURAL GAS
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Uses of petroleum At present, petroleum
supplies about 40 of the worlds energy needs.
Figure 23.17 Contribution of various energy
sources to the worlds energy needs.
23.3 PETROLEUM AND NATURAL GAS
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23.3 PETROLEUM AND NATURAL GAS
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Figure 23.18 Uses of petroleum.
23.3 PETROLEUM AND NATURAL GAS
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A23.2
Drugs (e.g. Panadol), soapless detergents,
plastic items (e.g. electrical socket),
insecticides etc. (Many answers are possible.)
Petroleum resource is running out Petroleum
resource is limited and non-renewable.
23.3 PETROLEUM AND NATURAL GAS
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23.4 REFINING PETROLEUM WHAT IS OIL
REFINING? In oil refining, the complex mixture of
hydrocarbons is separated (by fractional
distillation) into less complex mixtures which
are useful. Fractional distillation can be used
because the hydrocarbons have different boiling
points. In general, a hydrocarbon with larger
molecules has a higher boiling point. This is
because van der Waals forces are greater between
larger molecules. These parts (simpler mixtures)
are called fractions.
23.4 REFINING PETROLEUM
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Figure 23.19 Before and after refining of
petroleum (a) Petroleum is a complex mixture,
consisting of hundreds of hydrocarbons. (b) A
petroleum fraction is still a mixture, but it is
a mixture simpler than petroleum.
23.4 REFINING PETROLEUM
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An OIL FRACTION is a mixture of hydrocarbons of
similar boiling points and other properties.
THE REFINING PROCESS In an oil refinery,
petroleum is first heated in a furnace to about
400oC. The hot oil, now partly liquid and partly
vapour, is pumped into the bottom of a tall tower
called fractionating tower.
23.4 REFINING PETROLEUM
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Figure 23.20 Fractionating towers in an oil
refinery. (Each tower is about 30 meters high.)
23.4 REFINING PETROLEUM
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A typical fractional distillation of petroleum.
23.4 REFINING PETROLEUM
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The heavy fractions (with high boiling point
ranges) condense in the lower (hotter)
compartments. The lighter fractions (with lower
boiling point ranges) condense in the higher
(cooler) compartments. RELATIONSHIP BETWEEN
BOILING POINT RANGE AND NUMBER OF CARBON
ATOMS IN HYDROCARBONS
23.4 REFINING PETROLEUM
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Figure 23.23 The petrol fraction consists of
C5 C10 hydrocarbon molecules.
An oil fraction consisting of hydrocarbon
molecules with more carbon atoms has a higher
boiling point range.
FRACTIONAL DISTILLATION OF CRUDE OIL IN THE
LABORATORY
23.4 REFINING PETROLEUM
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Figure 23.24 Fractional distillation of crude oil
in the laboratory.
23.4 REFINING PETROLEUM
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Fractional distillation of crude oil in the
laboratory.
23.4 REFINING PETROLEUM
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23.4 REFINING PETROLEUM
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An oil fraction with a higher boiling point range
has a darker colour and is more viscous it is
less volatile, less flammable and burns less
completely.
A23.3
There is physical separation but no chemical
decomposition.
A23.4
Industrial refining, different, same, fractions,
laboratory, different, in turn
23.4 REFINING PETROLEUM
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Activity 4
Some examples are (1) Plastics There are many
useful plastics. The commonest plastic is
polythene, made from ethene. Ethene is obtained
by cracking naphtha or gas oil. (2)
Alcohol Ethanol can be manufactured from
ethene. (3) Detergents Synthetic detergents are
made from petroleum products. (4) Medicines and
insecticides Many of these are made from
substances obtained from petroleum.
23.4 REFINING PETROLEUM
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SUMMARY
1. Coal, petroleum and natural gas are fossil
fuels. 2. Coal was formed from the remains of
plants that lived 250 million years
ago. Petroleum and natural gas were formed from
the remains of very small sea animals and plants
that lived hundreds of million years ago.
SUMMARY
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3. Petroleum has great economic importance.
Petroleum-based fuels are burnt to provide heat
and electricity for homes and industries.
Petroleum also provides the starting chemical
materials for the manufacture of a variety of
important products. However, petroleum resource
is limited and non-renewable. 4. Petroleum is a
complex mixture mainly of hydrocarbons.
Hydrocarbons are compounds containing hydrogen
and carbon only. 5. In refining, petroleum is
separated into several useful parts (fractions)
by fractional distillation. This works because
different hydrocarbons have different boiling
points.
SUMMARY
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6. Each petroleum fraction has its particular
uses. Refer to Figure 23.21 for the major uses of
the various fractions. 7. A small-scale refining
of crude oil can also be performed in the
laboratory by fractional distillation. 8. As the
number of carbon atoms in the molecules of an oil
fraction increases, the properties of the
fraction change as follows ? Boiling point
range increases ? Volatility decreases ?
Colour darkens ? Viscosity increases ?
Flammability decreases ? Flame (on burning)
becomes darker and sootier
SUMMARY