The concept of thermodynamics is a key aspect of Chemistry Topics as it deals with the study of energy transformations in chemical systems and the relationships between energy, heat, and work.
Describe Why Petroleum and Natural Gas are Referred to as Fossil Fuels and Its Uses
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.
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).
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 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.
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).
The crude petroleum oil extracted from oil wells is taken to the ‘oil refinery’ through pipes. In the oil refinery, Figure. An 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
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.
- 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).
- 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 dry cleaning.
- 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).
A special grade of kerosene oil is used as aviation fuel in jet aeroplanes. - 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).
- LUBRICATING OIL. Lubricating oil is used for lubrication in machines and engines (like car engines).
- PARAFFIN WAX. Paraffin wax is used for making candles, vaseline, ointments, wax paper, and grease.
- 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 (C4H10) (which has been liquefied by applying pressure). Thus, the domestic gas cylinders like Tndane’ contain mainly ‘butane’ (see Figure).
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:
- LPG burns easily.
- LPG has a high calorific value. Due to this, a given amount of LPG produces a lot of heat.
- LPG burns with a smokeless flame and hence does not cause air pollution.
- LPG does not produce any poisonous gases on burning.
- 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.
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).
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.
5. Natural gas is used as a starting material for the manufacture of a number of chemicals (which are called petrochemicals).