1. 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

2. 23.1 FOSSIL FUELS AS A MAJOR ENERGY SOURCE
ENERGY AND FUEL
An important way of obtaining energy is to burn fuels.
FOSSIL FUELS AS A MAJOR ENERGY SOURCE

3. Figure 23.1 Burning fuels to provide energy.
FOSSIL FUELS AS A MAJOR ENERGY SOURCE

4. 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.)
FOSSIL FUELS AS A MAJOR ENERGY SOURCE

5. 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.
COAL

6. 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.
COAL

7. Figure 23.4
Plants that lived 250 million years ago were buried and turned into coal that we burn today.
COAL

8. Figure 23.5 The formation of coal.

9. 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.
COAL

10. Figure 23.8
The Lamma power station in Hong Kong burns coal to generate electricity. The picture shows coal being unloaded from a ship.
COAL

11. 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.
PETROLEUM AND NATURAL GAS

12. Figure 23.9 A sample of crude oil.
PETROLEUM AND NATURAL GAS

13. 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.
PETROLEUM AND NATURAL GAS

14. Figure 23.10 Planktons are very small sea organisms.
PETROLEUM AND NATURAL GAS

15. Figure The oil story.
PETROLEUM AND NATURAL GAS

16. USING PETROLEUM AND NATURAL GAS
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.
PETROLEUM AND NATURAL GAS

17. Figure 23.16 Natural gas burns with a clean blue flame.
PETROLEUM AND NATURAL GAS

18. Uses of petroleum
At present, petroleum supplies about 40% of the world’s energy needs.
natural gas
25%
petroleum 38%
others 16%
coal 21%
Figure 23.17
Contribution of various energy sources to the world’s energy needs.
PETROLEUM AND NATURAL GAS

19. 23.3 PETROLEUM AND NATURAL GAS

20. Figure 23.18 Uses of petroleum.
PETROLEUM AND NATURAL GAS

21. Petroleum resource is running out
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.
PETROLEUM AND NATURAL GAS

22. 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.
REFINING PETROLEUM

23. Before and after refining of petroleum:
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.
REFINING PETROLEUM

24. 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.
REFINING PETROLEUM

25. Figure 23.20
Fractionating towers in an oil refinery. (Each tower is about 30 meters high.)
REFINING PETROLEUM

26. A typical fractional distillation of petroleum.
REFINING PETROLEUM

27. 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
REFINING PETROLEUM

28. FRACTIONAL DISTILLATION OF CRUDE OIL IN THE LABORATORY
Figure 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
REFINING PETROLEUM

29. short rubber connecting tubing
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.
REFINING PETROLEUM

30. Fractional distillation of crude oil in the laboratory.
REFINING PETROLEUM

31. REFINING PETROLEUM

32. There is physical separation but no chemical decomposition.
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
REFINING PETROLEUM

33. Ethanol can be manufactured from ethene. (3) Detergents
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.
REFINING PETROLEUM

34. 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

35. 3. Petroleum has great economic importance
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

36.  Boiling point range increases  Volatility decreases
6. Each petroleum fraction has its particular uses. Refer to Figure 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