Presentation on theme: "1 Chapter 23Fossil Fuels 23.1Fossil fuels as a major energy source 23.2Coal 23.3Petroleum and natural gas 23.4Refining petroleum CONTENTS OF CHAPTER 23."— Presentation transcript:
1 Chapter 23Fossil Fuels 23.1Fossil fuels as a major energy source 23.2Coal 23.3Petroleum and natural gas 23.4Refining petroleum CONTENTS OF CHAPTER 23
2 23.1FOSSIL 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.) 23.1 FOSSIL FUELS AS A MAJOR ENERGY SOURCE
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.
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 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 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 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
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 CH 4, with small amounts of ethane C 2 H 6, propane C 3 H 8 and butane C 4 H 10.
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 Planktons are very small sea organisms PETROLEUM AND NATURAL GAS
15 Figure The oil story PETROLEUM AND NATURAL GAS
16 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 PETROLEUM AND NATURAL GAS
17 Figure Natural gas burns with a clean blue flame PETROLEUM AND NATURAL GAS
18 Uses of petroleum At present, petroleum supplies about 40% of the worlds energy needs. natural gas 25% petroleum 38% others 16% coal 21% Figure Contribution of various energy sources to the worlds energy needs PETROLEUM AND NATURAL GAS
PETROLEUM AND NATURAL GAS
20 Figure Uses of petroleum PETROLEUM AND NATURAL GAS
21 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
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 Figure 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 400 o C. 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 Fractionating towers in an oil refinery. (Each tower is about 30 meters high.) 23.4 REFINING PETROLEUM
REFINING PETROLEUM A typical fractional distillation of 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 23.4 REFINING PETROLEUM
28 Figure The petrol fraction consists of C 5 – C 10 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
29 0 – 360 o C thermometer clamp short rubber connecting tubing bent delivery tube small test tube water oil fraction heat rocksil soaked with crude oil Figure Fractional distillation of crude oil in the laboratory REFINING PETROLEUM
REFINING PETROLEUM Fractional distillation of crude oil in the laboratory.
32 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
33 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 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.
36 SUMMARY 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