coal and petroleum(chapter)

In our everyday life, we use a large number of materials for our basic needs. Some of these materials are found in nature whereas others are man-made. Air, water, soil, sunlight, coal, petroleum, natural gas and minerals are obtained from nature, so they are called natural resources. On the other hand, plastics, synthetic fibres, paints, drugs, explosives, etc., are all man-made materials. Inexhaustible and Exhaustible Natural Resources Anything in the environment ‘which can be used’ is called a ‘resource’. All the natural resources can be classified into two main groups : (i) Inexhaustible natural resources, and (ii) Exhaustible natural resources. The term ‘inexhaustible’ means something ‘which cannot be used up completely’. Those natural resources which are present in unlimited quantity in nature and are not likely to be exhausted by human activities are called inexhaustible natural resources. The examples of inexhaustible natural resources are : Sunlight, Air and Water. There is a never ending supply of inexhaustible resources in nature. The inexhaustible resources can be used again and again. They last forever. The term ‘exhaustible’ means ‘something which can be used up completely’ (so that nothing is left behind). Those resources which are present in a limited quantity in nature and can be exhausted by human activities, are called exhaustible natural resources. The examples of exhaustible natural resources are : Coal, Petroleum, Natural gas, Minerals, Forests and Wildlife, etc. The exhaustible natural resources do not last forever. In this Chapter we will study some exhaustible sources of energy like coal, petroleum and natural gas. Coal, petroleum and natural gas are also called non-renewable sources of energy. This is because when all the coal, petroleum and natural gas present under the earth will get used up (or exhausted), no more supply of these fuels will be available in the near future. Before we go further, we should know the meaning of the term ‘fossil’. Fossils are the remains of the pre-historic plants or animals, buried under the earth millions of years ago. 81 © S Chand and Company Pvt Ltd Lakhmir Singh’s Science Class 8 FOSSIL FUELS 82 The natural fuels formed from the remains of living organisms buried under the earth long, long ago, are called fossil fuels. Coal, petroleum and natural gas are fossil fuels. Coal, petroleum and natural gas are called fossil fuels because they were formed by the decomposition of the remains of pre-historic plants and animals (fossils) buried under the earth long, long ago. Fossil fuels are exhaustible natural resources because once all the fossil fuels are used up, they will be gone forever. How Fossil Fuels were Formed Fossil fuels were formed from the dead remains of living organisms (plants and animals) buried under the earth millions of years ago. This happened as follows : The plants and animals which died millions of years ago, were gradually buried deep in the earth and got covered with sediments like mud and sand, away from the reach of air. In the absence of air, the chemical effects of heat, pressure and bacteria, converted the buried remains of plants and animals into fossil fuels like coal, petroleum and natural gas. Please note that the buried remains of large land plants were converted into coal whereas those of tiny marine plants and animals were converted into petroleum and natural gas. COAL Coal is a hard, black combustible mineral that consists mainly of carbon (see Figure 1). Coal is found in deep coal mines under the surface of the earth. In India, coal is found mainly in Bihar, West Bengal, Orissa and Madhya Pradesh. Coal is found in abundance in our country and it is the most important source of energy in our country. How Coal was Formed Coal was formed by the decomposition of large land plants and trees buried under the earth about 300 million years ago. This happened as follows : About 300 million years ago, the earth had dense forests in low lying wet land areas. Due to natural processes like earthquakes, volcanoes and floods, etc., these forests were buried under the surface of earth. As Figure 1. Coal. more soil deposited over them, they were compressed. The temperature also rose as they sank deeper and deeper. Due to high pressure and high temperature inside the earth, and in the absence of air, the wood of buried forest plants and trees was slowly converted into coal. The slow process by which the dead plants buried deep under the earth have become coal is called carbonisation. Since coal was formed from the remains of plants, therefore, coal is called a fossil fuel. Coal is a Source of Energy Coal is mainly carbon. When heated in air, coal burns and produces mainly carbon dioxide gas. A lot of heat energy is also produced during the burning of coal. This can be written as : Carbon + (Coal) Oxygen (From air) ⎯→ ⎯ Carbon dioxide + Heat Coal is important because it can be used as a source of heat energy as such (just by burning it), or it can be converted into other forms of energy such as coal gas, coke or electricity. The real source of energy of coal is the solar energy (or sun’s energy). This is because the plants and trees which decomposed to form coal grew on the earth by absorbing sunlight energy during the process of photosynthesis. Uses of Coal (i) Coal is used as a fuel in homes and industry. (ii) Coal is used as a fuel at Thermal Power Plants for generating electricity. (iii) Coal is used to make coal gas which is an important industrial fuel. © S Chand and Company Pvt Ltd Lakhmir Singh’s Science Class 8 83 (iv) Coal is used to make coke. (v) Earlier, coal was used as a fuel to make ‘steam’ to run steam engines of trains. (vi) Coal was also used as a source of organic chemicals. Products of Coal When coal is heated strongly in closed retorts in the absence of air, a number of useful products are obtained. The various useful products obtained by processing the coal by heating in the absence of air are : (i) Coal gas, (ii) Coal tar, and (iii) Coke. Coal gas, coal tar and coke are called products of coal. Please note that these products are obtained when coal is heated in the absence of air. This is because if coal is heated in the presence of air, then coal burns to produce mainly carbon dioxide gas and no other useful products are obtained. The strong heating of coal in the absence of air is called destructive distillation of coal. We will now describe the various products of coal in somewhat detail. Coal Gas Coal gas is a gaseous fuel which is obtained by the strong heating of coal in the absence of air during the processing of coal to get coke. Coal gas is mainly a mixture of methane and hydrogen, with some carbon monoxide. All the gases present in coal gas can burn to produce heat, due to which coal gas is an excellent fuel (having high calorific value). Coal gas is used as a fuel in industries (which are situated near the coal processing plants). When coal gas burns, it also produces a good amount of light. So, in the past, coal gas has also been used for lighting purposes (or illumination purposes). Coal gas was used for street lighting for the first time in London in the year 1810. It was used for street lighting in New York around 1820. These days, however, coal gas is used as a source of heat rather than light. Coal Tar Coal tar is a thick, black liquid having an unpleasant smell which is obtained by heating coal in the absence of air (see Figure 2). Coal tar is not a single compound. Coal tar is a mixture of about 200 carbon compounds (or organic compounds). The useful carbon compounds (or organic compounds) present in coal tar include benzene, toluene, naphthalene, anthracene, phenol and aniline. Thus, the naphthalene balls used to repel moths and other insects (in stored clothes, etc.) are obtained from coal tar. The various compounds present in coal tar are separated by the process of fractional distillation. The compounds (or products) obtained from coal tar are used as starting materials for manufacturing a large number of substances used in everyday life and industry. For example, the products of coal tar are used to make synthetic fibres, drugs (medicines), plastics, synthetic dyes, perfumes, paints, varnishes, pesticides, photographic materials, roofing materials and explosives, etc. Coal tar has been traditionally used for metalling the roads. These days, however, bitumen (a petroleum product) is being used increasingly for metalling the road surfaces (in place of coal tar). Coke Coke is a tough and porous black solid substance (see Figure 3). Coke is prepared by heating coal in the absence of air. When coal is heated in the absence of air, then coal gas and coal tar are eliminated, and coke is left behind as a black residue. Thus, coal minus volatile constituents is coke. Coke is an almost pure form of carbon. It is 98 per cent carbon. Figure 2. Coal tar. Figure 3. Coke. © S Chand and Company Pvt Ltd Lakhmir Singh’s Science Class 8 84 Coke is mainly used as a reducing agent in the extraction of metals (like iron, zinc, etc.) Coke is used in the manufacture of steel. Coke is also used as a fuel. Coke is a better fuel than coal because it produces more heat on burning than an equal amount of coal. Moreover, coke burns without producing any smoke whereas coal produces a lot of smoke on burning. PETROLEUM Petroleum is a dark coloured, thick crude oil found deep below the ground in certain areas. It has an unpleasant odour. The name ‘petroleum’ means ‘rock oil’ (petra = rock ; oleum = oil). It is called petroleum because it is found under the crust of earth trapped in rocks. Petroleum is not a single chemical compound. Petroleum is a complex mixture of compounds known as hydrocarbons (Hydrocarbons are compounds which are made up of only two elements : carbon and hydrogen). Petroleum is insoluble in water. Petroleum is a natural resource obtained from deep oil wells which are dug in certain areas of the earth. Just like coal, petroleum is also a fossil fuel. Please note that petroleum is also called ‘crude oil’ or ‘mineral oil’. How Petroleum was Formed Petroleum (oil) was formed by the decomposition of the remains of tiny plants and animals buried under the sea millions of years ago. It is believed that millions of years ago, the tiny plants and animals which lived in the sea, died. Their dead bodies sank to the bottom of sea and were soon covered with mud and sand. Due to high pressure, heat, action of bacteria, and in the absence of air, the dead remains of tiny plants and animals were slowly converted into petroleum. The petroleum thus formed got trapped between two layers of impervious rocks (non-porous rocks), forming an oil deposit. Figure 4. Petroleum (Crude oil). Occurrence and Extraction of Petroleum Petroleum occurs deep under the surface of earth between two layers of impervious rocks (see Figure 5). Petroleum is lighter than water, so it floats over water. Petroleum oil deposits are usually found mixed with water, salt and earth particles (sand, etc.). Petroleum does not occur in all the places of earth. It is found in only certain areas of the earth. Natural gas occurs above the petroleum oil trapped under the rocks (see Figure 5). Petroleum is extracted by drilling holes (called oil wells) in the earth’s crust, where the presence of oil has been predicted by survey. The oil wells are drilled by using ‘drilling rigs’(A drilling rig is a large structure with equipment for drilling an oil well). When an oil well is drilled through the rocks, natural gas comes out first with a great pressure and for a time, the crude petroleum oil comes out by itself due to gas pressure. After the gas pressure has subsided, petroleum is pumped out of the oil Figure 5. Petroleum and natural gas deposits under the surface of earth. well. Some wells dug into the earth yield both petroleum and natural gas but some wells yield only natural gas but no oil. Early drilling of oil wells for getting petroleum was done only on land. Later on, oil wells were also drilled under the sea-bed by using new techniques. Thus, some of the oil wells are now drilled under the sea for the extraction of petroleum. © S Chand and Company Pvt Ltd Lakhmir Singh’s Science Class 8 85 The world’s first oil well was drilled in Pennsylvania (USA) in 1859. Eight years later in 1867, oil was struck at Makum in Assam. In India, petroleum (oil) is found in Assam, Gujarat, Mumbai High (off-shore area), and near the basins of Godavari and Krishna rivers. The off-shore oil bearing area called Mumbai High is located in high seas at a distance of about 150 kilometres west of Mumbai city. The oil deposits of Mumbai High are buried at a depth of about 1000 metres below the sea-bed. A special platform of steel has been erected in the Mumbai High sea to pump out petroleum from under the sea-bed. Refining of Petroleum The crude petroleum oil is a complex mixture of solid, liquid and gaseous hydrocarbons. It is not very useful to us as such. So, before petroleum can be used for specific purposes, it has to be refined (or purified). The process of separating crude petroleum oil into more useful fractions is called refining. The refining of petroleum (or separation of petroleum) into different fractions is based on the fact that the different fractions of petroleum have different boiling point ranges. The refining of petroleum is carried out in an oil refinery (see Figure 6). The crude petroleum oil extracted from oil wells is taken to the ‘oil refinery’ through pipes. In the oil refinery, crude petroleum oil is refined (or separated) into different useful fractions. The separation of petroleum into different fractions is done by the process of ‘fractional distillation’. Fractional distillation is a process in which fractions of petroleum having different boiling point ranges are collected separately. The various useful fractions obtained by the refining of petroleum are : Petroleum gas, Petrol, Kerosene, Diesel, Lubricating oil, Paraffin wax and Bitumen. The Various Fractions of Petroleum and Their Uses Figure 6. An oil refinery. The refining of petroleum gives the fractions (or products) such as petroleum gas, petrol, kerosene, diesel, lubricating oil, paraffin wax and bitumen. The important uses of the various fractions of petroleum are given below. (i) PETROLEUM GAS. Petroleum gas is used as a fuel in homes and industry. Petroleum gas is used as a fuel as such or in the form of Liquefied Petroleum Gas (LPG). (ii) PETROL. Petrol is used as a fuel in light motor vehicles (such as cars, motorcycles, and scooters, etc.). Petrol is also used as a solvent for drycleaning. (iii) KEROSENE. Kerosene is used as a fuel in wick stoves and pressure stoves to cook food. Kerosene is also used in lanterns for lighting purposes (see Figure 7). A special grade of kerosene oil is used as aviation fuel in jet aeroplanes. (iv) DIESEL. Diesel is used as a fuel in heavy motor vehicles (such as buses, trucks, tractors, and diesel train engines). Diesel is also used to run pump sets for irrigation in agriculture and in electric generators (to produce electricity on a small scale). (v)LUBRICATING OIL. Lubricating oil is used for lubrication in machines and engines (like car engines). Figure 7. Kerosene is used as a fuel in lanterns. © S Chand and Company Pvt Ltd Lakhmir Singh’s Science Class 8 86 (vi) PARAFFIN WAX. Paraffin wax is used for making candles, vaseline, ointments, wax paper, and grease. (vii) BITUMEN. Bitumen is used for road surfacing. It is also used for water-proofing the roofs of buildings. Bitumen is used in making black paints. Please note that the fuels such as petroleum gas, petrol, kerosene, and diesel are also fossil fuels (because they are obtained from a major fossil fuel called petroleum). The most common fuel used in homes is liquefied petroleum gas (or LPG). The petroleum gas which has been liquefied under pressure is called liquefied petroleum gas. The liquefied petroleum gas (or LPG) consists mainly of butane (C4 H10 ) (which has been liquefied by applying pressure). Thus, the domestic gas cylinders like ‘Indane’ contain mainly ‘butane’ (see Figure 8). The gas used for domestic cooking is called liquefied petroleum gas because it is obtained from petroleum and it is liquefied by compression before filling into the gas cylinders. When we turn on the knob of the gas cylinder, the pressure is released, due to which the highly volatile LPG is converted into gas. This gas goes into the burner of LPG stove. When a lighted matchstick is applied to the burner, the gas burns with a blue flame producing a lot of heat. This heat is used for cooking food. Liquefied petroleum gas (LPG) is a good fuel because of its following advantages : (i) LPG burns easily. Figure 8. These gas cylinders contain LPG. (ii) LPG has a high calorific value. Due to this, a given amount of LPG produces a lot of heat. (iii) LPG burns with a smokeless flame and hence does not cause air pollution. (iv) LPG does not produce any poisonous gases on burning. (v) LPG does not leave behind any solid residue on burning. We will now discuss natural gas. NATURAL GAS Natural gas consists mainly of methane with small quantities of ethane and propane. In fact, natural gas contains about 95% methane, the remaining being ethane and propane. Natural gas occurs deep under the crust of earth either alone or alongwith oil above the petroleum deposits. Thus, some wells dug into the earth produce only natural gas whereas others produce natural gas as well as petroleum oil. Natural gas is formed under the earth by the decomposition of vegetable matter lying under water. This decomposition is carried out by anaerobic bacteria in the absence of air. Just like coal and petroleum, natural gas is also a fossil fuel. India has vast reserves of natural gas. In India, natural gas has been found in Tripura, Rajasthan, Maharashtra, and in Krishna-Godavari delta. When natural gas is compressed by applying pressure, it is called Compressed Natural Gas (which is written in short form as CNG). In fact, natural gas is stored under high pressure as compressed natural gas (or CNG). It becomes easier to store, transport and use natural gas in the form of CNG. Natural gas is called a clean fuel because it burns without producing any smoke and does not cause air pollution. Advantages of Using Natural Gas (or Compressed Natural Gas, CNG) 1. Natural gas (or CNG) is a good fuel because it burns easily and produces a lot of heat. Moreover, natural gas burns with a smokeless flame and causes no air pollution. It also does not produce any poisonous gases on burning. Natural gas does not leave behind any solid residue on burning. Natural gas is, therefore, a clean fuel (as compared to other fossil fuels). 2. Natural gas (or CNG) is a complete fuel in itself and can be used directly for heating purposes in homes and industry. There is no need to add anything else to it. © S Chand and Company Pvt Ltd Lakhmir Singh’s Science Class 8 87 3. A great advantage of natural gas is that it can be supplied to homes and factories through a network of underground pipes and this eliminates the need for additional storage and transport. Such a network of pipelines for the supply of natural gas exists in Vadodara (in Gujarat), in some parts of Delhi and a few other places. Uses of Natural Gas (or CNG) 1. Natural gas is used as a domestic and industrial fuel. 2. Natural gas is used as a fuel in Thermal Power Stations for generating electricity. 3. Compressed natural gas (CNG) is being used increasingly as a fuel in transport vehicles (like cars, buses, etc.) in place of petrol and diesel. CNG is a good alternative to petrol and diesel in vehicles because it is a cleaner fuel and does not cause much air pollution. In fact, CNG is being used in many vehicles these days to reduce air pollution in cities. CNG which is used in vehicles is filled in cylinders. These cylinders can be refilled at CNG Filling Stations (see Figure 9). 4. Natural gas is used as a source of hydrogen gas needed to manufacture fertilisers. When natural gas is heated strongly, the methane present in it decomposes to form carbon and hydrogen. This hydrogen is then used to manufacture fertilisers. Figure 9. CNG being filled in a car at a Filling Station. 5. Natural gas is used as a starting material for the manufacture of a number of chemicals (which are called petrochemicals). PETROCHEMICALS Many useful chemicals (or substances) are obtained from petroleum and natural gas. Those chemicals which are obtained from petroleum and natural gas are called petrochemicals. Some examples of petrochemicals are : methyl alcohol, ethyl alcohol, formaldehyde, acetone, acetic acid, ethylene, benzene, toluene, vinyl chloride and hydrogen. Petrochemicals are very important because they are used to manufacture a wide range of useful materials such as : Detergents, Synthetic fibres (like Polyester, Nylon, Acrylic, etc.), Plastics (such as Polythene, Polyvinyl chloride, Bakelite, etc.), Synthetic rubber, Drugs, Dyes, Perfumes, Fertilisers, Insecticides and Explosives, etc. Hydrogen gas is obtained as a petrochemical from natural gas. Hydrogen gas obtained from natural gas is used in the manufacture of fertilisers (such as ammonium nitrate and urea). Thus, petroleum is not only a source of fuels but also provides raw materials (in the form of petrochemicals) to manufacture a large number of useful substances. Due to its great commercial importance, petroleum is also called “black gold”. Energy Resources of Earth are Limited Most of the energy that we use today comes mainly from the three exhaustible resources of the earth : coal, petroleum and natural gas The amount of coal, petroleum and natural gas present in the earth is limited. The known reserves of coal, petroleum and natural gas will last only for about 100 years. Once the present stock of coal, petroleum and natural gas present in the earth gets exhausted, no new supplies of these fossil fuels will be available to us in the near future (because it takes millions of years to convert the dead organisms into fossil fuels in nature). So, fossil fuels should be used with care and caution, and not wasted at all so that the existing reserves of fossil fuels can be used over as long a period as possible. Moreover, the burning of fossil fuels is a major source of air pollution. The use of fossil fuels is also linked to global warming (because they produce a lot of greenhouse gas ‘carbon dioxide’ on burning). So, the use of lesser fossil fuels will lead to cleaner environment and smaller risk of global warming. From the above discussion we conclude that we should use fossil fuels only when absolutely necessary because : © S Chand and Company Pvt Ltd Lakhmir Singh’s Science Class 8 88 88 (i) it will ensure the availability of fossil fuels for a longer period of time. (ii) it will reduce air pollution and lead to a cleaner environment. (iii) it will reduce the risk of global warming. Please note that the fossil fuels such as coal, petroleum and natural gas cannot be prepared in the laboratory from dead organisms (dead plants and animals). This is because the formation of fossil fuels is a very, very slow process and the conditions for their formation cannot be created in the laboratory. How to Save Petrol and Diesel Petrol and diesel are the two main fuels which are used for driving vehicles. We should make every effort to avoid the wastage of these precious fuels. In India, the Petroleum Conservation Research Association (PCRA) advises people on how to save petrol (or diesel) while driving vehicles. The various tips for minimising the wastage of petrol and diesel while driving vehicles are as follows : (i)Drive the vehicle at a constant and moderate speed as far as possible. (ii)Switch off the vehicle’s engine at traffic lights or at a place where a person has to wait. (iii)Ensure correct air pressure in the tyres of the vehicle. Low tyre pressure consumes more fuel. (iv)Ensure regular maintenance of the vehicle (including engine tuning).