1 chapter 23fossil fuels 23.1fossil fuels as a major energy source 23.2coal 23.3petroleum and...
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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
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 hydroc
arbons and some other compounds.
Figure 23.3
Coal is a black solid consisting mainly of
carbon. Its composition varies with the
type of 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 Earth’s 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
23.3 PETROLEUM AND NATURAL GAS
Petroleum is a smelly oily liquid, usually quite thick; its colour rang
es from greenish brown to black, depending on where it is obtaine
d.
Petroleum is a complex mixture consisting mainly of hydrocar
bons.
Natural gas is also a mixture mainly of hydrocarbons. It consis
ts chiefly of methane CH4, with small amounts of ethane C2H6, pro
pane C3H8 and butane C4H10.
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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 Earth’s 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 world’s energy
needs.
natural gas25% petroleum
38%
others 16%coal 21%
Figure 23.17
Contribution of various
energy sources to the
world’s 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
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 use
ful. Fractional distillation can be used because the hydrocarbons h
ave different boiling points. In general, a hydrocarbon with larger
molecules has a higher boiling point. This is because van der Wa
als’ forces are greater between larger molecules.
These parts (simpler mixtures) are called fractions.
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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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23.4 REFINING PETROLEUM
A typical fractional distillation of 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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0 – 360oC thermometer
clamp
short rubber connecting tubing
bent delivery tube
small test tube
water oil fraction
heat
rocksil soaked with crude oil
Figure 23.24
Fractional distillation of crude
oil in the laboratory.
23.4 REFINING PETROLEUM
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23.4 REFINING PETROLEUM
Fractional distillation of crude oil in the laboratory.
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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 mil
lion years ago.
Petroleum and natural gas were formed from the remains of v
ery small sea animals and plants that lived hundreds of millio
n years ago.
SUMMARY
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SUMMARY
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.
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SUMMARY
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