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Products of Coal: Coke, Coal Tar and Coal Gas

  • Difficulty Level : Medium
  • Last Updated : 17 Aug, 2021

We use various materials for our basic needs. Some of them are found in nature and some have been made by human efforts. In the light of the availability of various resources in nature, natural resources can be broadly classified into two kinds:

  1. Inexhaustible Natural Resources: These resources are present in unlimited quantity in nature and are not likely to be exhausted by human activities. Examples are sunlight, air.
  2. Exhaustible Natural Resources: The amount of these resources in nature is limited. They can be exhausted by human activities. Examples of these resources are forests, wildlife, minerals, coal, petroleum, natural gas, etc.

Here, we will learn about some exhaustible natural resources like coal, petroleum, and natural gas. These were formed from the dead remains of living organisms. So, these are all known as fossil fuels.

What is Coal?

Coal is one of the most useful fossil fuels. It is used in variety of things like production of heat for various purposes, domestic or commercial, firing of industrial generators, manufacturing of cast iron and many more. It is used in industries to get products like coke, tar and coal gas which benefits us in many ways.

Origination of Coal

About 300 million years ago the earth had dense forests in low-lying wetland areas. Due to natural processes, like flooding, these forests got buried under the soil. As more soil was deposited over them, they were compressed. The temperature also rose as they sank deeper and deeper. Under high pressure and temperature, dead plants got slowly converted to coal. As coal contains mainly carbon, the slow process of conversion of dead vegetation into coal is called carbonization

Since it was formed from the remains of vegetation, coal is also called a fossil fuel.  When heated in the air, coal burns and produces mainly carbon dioxide gas. Coal is processed in the industry to get some useful products such as coke, coal tar, and coal gas.

Properties of Coal

  • It is a black-colored hard substance.
  • It is composed of carbon, hydrogen, nitrogen, oxygen, a minor amount of sulphur.
  • Anthracite, bituminous, lignite are the major types of coal.
    • Anthracite: Hardest coal with higher carbon concentration and energy.
    • Lignite: Softest coal with low carbon concentration but high oxygen and hydrogen.
    • Bituminous: Coal is in a moderate state.

Uses of Coal

Coal is used for a variety of purposes like:

  1. Electricity generation: Power generation is the primary use for coal. Thermal coal is burnt to create steam that drives turbines and generators for the production of electricity.
  2. Metal production: Metallurgical coal is a key ingredient in steelmaking. Coal converted to coke is used to produce around 70% of the world’s steel.
  3. Cement Production: Coal is used as a key energy source in cement production. By-products of coal combustion such as fly ash also play an important role in cement manufacture and the wider construction industry.
  4. Gasification and Liquification: Coal is heated and pressurized with steam to produce town gas for domestic lighting, heating, and cooking. It is liquefied to make synthetic fuels similar to petroleum or diesel.
  5. Chemical and other industries: Syngas can be further processed to produce chemical building blocks such as methanol, ammonia, and urea. Other major users of coal include the paper, textile, and glass industries. Coal is also used in the manufacture of carbon fiber and specialist ingredients such as silicon metals.

Products of Coal

The following are the many valuable products generated by processing coal by heating in the absence of air:

  1. Coke, 
  2. Coal Tar, and
  3. Coal Gas.

The process of rapidly heating coal in the absence of air is known as a destructive distillation of coal. When coal is burned in the presence of air, it burns primarily to create carbon dioxide gas, with no other valuable products produced.

Coke

The high-carbon product is obtained by the destructive distillation of coal. Carbon content in coke is very high thus it is called to be an almost pure form of carbon. It is greyish-black in color and is a hard, porous solid. It is used as a reducing agent in the extraction of minerals, manufacturing of steel and is also used as a fuel.

Characteristics of Coke:

  1. The almost pure form of carbon,
  2. Tough Porous and black, and 
  3. Burns without producing any smoke.

Uses of Coke:

  1. Used as the reducing agent in the extraction of metal,
  2. Used in manufacturing of steel, and
  3. Also used as a fuel.

Coal Tar

Coal Tar is obtained as a by-product in the process of making coke. Its color is similar to coke but it is a highly viscous liquid accompanied by an unpleasant smell. It is used to make synthetic dyes, drugs, perfumes, plastic, paints, etc. Naphthalene balls are also obtained from it. It contains 42% carbon, 48% hydrocarbons, and the rest of the percentage is occupied by water and possesses a characteristic smell.

Uses of Coal Tar:

  1. Earlier coal tar was extensively used for metalling roads. But nowadays Bitumen has replaced coal tar to serve this purpose.
  2. Naphthalene balls used as moth repellent in the storage areas are the derivatives of coal tar.
  3. It is extensively used as a starting material in the industries for manufacturing synthetic dyes, explosives, drugs, paints, perfumes, photographic materials, and many more.

Coal Gas

Just like coal tar, it is also obtained as a by-product while producing coke. It has an unpleasant smell. It is a highly flammable gas so it can easily catch fire and its main component is methane. Thus, it should be carefully regulated as it can combine with air that can result in explosions. It is used as fuel in many industries and is an important source of heat and light.

The production process is distinct, both physically and chemically, from that used to create a range of gaseous fuels known variously as manufactured gas, syngas, hygas, Dowson gas, and producer gas. 

Can Natural Gas replace Coal Gas?

In most places, natural gas is replacing coal if it is available. In the USA, gas is cheaper than coal, and it costs less to build a new gas-fired power plant compared to a coal plant. The presence of pollution laws also makes gas a better choice. However, still, the global usage of coal is increasing because gas is not available everywhere and it is costly too.

What is Petroleum?

Petroleum is a mineral oil that is found under the ground or sea and is used to make petrol, plastic and other types of chemical substances. Various by-products of petroleum are kerosene, Liquified Petroleum Gas (LPG), petrol, bitumen, lubricating oil, wax and diesel.

Origination of Petroleum: Petroleum was formed from organisms living in the sea. As these organisms died, their bodies settled at the bottom of the sea and got covered with layers of sand and clay. Over millions of years, the absence of air, high temperature, and high pressure transformed the dead organisms into petroleum and natural gas.

Natural Gas: Natural gas is easy to transport through pipes and is stored under high pressure as compressed natural gas (CNG). CNG is used for power generation. It is now used as a fuel for transport vehicles because it is less polluting. It is also a clean fuel.

Sample Problems

Problem 1: Define fossil fuels. Give examples.

Solution:

Fossil fuels are those natural fuels that are made up by burial of living organisms deep down the earth for long period of time. For example, coal, petroleum, natural gas.

Problem 2: Describe how coal is formed from dead vegetations?

Solution:

Coal is obtained by natural process about 300 million years ago. The earth had dense forests in low lying wetland areas. Due to natural processes like flooding, these forests got buried under the soil. As soil deposited over them, they were compressed. Temperature rose as they sank deeper. Under high pressure and temperature, dead plants got slowly converted to coal.

Problem 3: What are the various properties of coal tar?

Solution:

Coal tar is used as starting materials for manufacturing substances used in everyday life like synthetic dyes, drugs, explosives, perfumes, plastics, paints etc. It is used to make synthetic dyes, drugs, perfumes, plastic, paints etc. Naphthalene balls is also obtained from it. 

Problem 4: Is Coke a smokeless fuel?

Solution:

Smokeless fuels do not produce smoke when burned and this term is generally used for solid fuels like anthracite, coke, and charcoal. Thus, coke is a smokeless fuel. 

Problem 5: Discuss different varieties of coal.

Solution:

Depending upon the amount of carbon content, coal may be of four types:

  1. Peat: Most inferior and softest form of coal with low carbon content. It has a large amount of moisture and is not much suitable to be used as fuel.
  2. Lignite: Comparatively harder than peat, but still very soft. Its carbon content is more than that of peat.
  3. Bituminous: Its carbon content is higher, as it is free from moisture and other impurities.
  4. Anthracite: Highest grade coal. This is also known as hard coal. It has maximum amount of carbon. It produces a very little smoke.

Problem 6: What constituents the mixture of coal gas? Where is it used?

Solution:

It is a mixture of methane, hydrogen and carbon monoxide. It is used in variety of things like production of heat for various purposes, domestic or commercial, firing of industrial generators, manufacturing of cast iron and many more.

Problem 7: The burning of fossil fuels causes air pollution. Explain.

Solution:

The burning of fossil fuels causes a lot of air pollution and produces gases like carbon dioxide, carbon monoxide, sulphur dioxide which can lead to undesirable changes in climate due to increase greenhouse effect. The major air pollutants produced by the burning of petrol in automobiles are carbon monoxide, sulphur dioxide, unburnt hydrocarbons, etc. 

Problem 8: How is energy useful to us?

Solution:

Some of the uses of energy are:

  1. To generate electricity and to run vehicles.
  2. To run our electrical appliances like refrigerator, TV, radio, computer, etc.
  3. We need energy at construction sites to construct houses, buildings, etc.
  4. To cook our food and other domestic use.


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