COAL

CONTENT
⦁ Definition of Coal
⦁ Types of Coal
⦁ Destructive Distillation of Coal
⦁ Uses of Products of Destructive Distillation of Coal

Definition of Coal
Coal is one the two most principal sources of fuel and energy, the other being petroleum. Coal was found as a result of complex chemical and physical changes when the remains of forest were buried under the earth millions of years ago under great pressure in the absence of air.
Coal is found in great abundance in very many parts of the world including Nigeria. Coal is a complex mixture of hydrocarbons (compounds of carbon and hydrogen) and other organic and inorganic compounds containing small amounts of nitrogen, sulphur and phosphorus as impurities.
Types of Coal
Coal is derived from wood; it naturally contains a lot of carbon.  There are four main types of coal, arising from the progressive variation in their carbon content. They are:
⦁ Peat-like coal: contains about 60 of carbon.
⦁ Lignite coal: contains about 70 of carbon.
⦁ Bituminous coal: contains about 85  of carbon: This is the type that is mostly used for our everyday domestic application.
⦁ Anthracite coal: contains about 94 of carbon.
The carbon content of each type of coal reflects its rank or degree of classification. Based on carbon content, the different types of coals are put into ranks as follows: Peak   →    Lignite     →      Bituminous     →      Anthracite
Coal is used mainly as a fuel to generate power for station engines, factories and electric parts. It is also used for making various chemicals.
EVALUATION
⦁ Carbon occurs most abundantly both naturally as …………… and ……………
⦁ With two equations only, describe the combustion of carbon allotropes.
⦁ Mention four types of coal

Destructive Distillation of Coal
Destructive distillation of coal involves heating of coal to a very high temperature (600 – 1200o C ) in the absence of air. During the process, coal decomposes to give coal gas, coal tar, ammoniacal liquor and coke as the main products.
Coal   +   heat   →  coal gas + coal tar  +  ammoniacal liquor   +  coke
The process is also known as industrial distillation of coal. The destructive distillation of coal can be carried in the laboratory using the set up below.

Uses of Products of Destructive Distillation of Coal
(i) Coal gas:
Coal gas is a gaseous mixture of hydrogen, methane, carbon (ii) oxide and small amount of ethane, hydrogen sulphide and sulphur (iv) oxide. The main use of coal gas is as fuel. It is cleaner and more efficient than coal and solid or liquid fuel.
(ii) Coal tar:
Coal tar, a thick brownish-black liquid, is a mixture of many organic chemicals including benzene, toluene, phenol, naphthalene and anthracene. The components can be separated by fractional distillation and are used for the manufacture of commercial products including drugs, dye, paints, insecticides, explosives, etc.
(iii) Ammoniacal liquor:
This an aqueous solution containing mainly ammonia and is used in the manufacture of ammonium tetraoxosulphate (iv), (NH4)2SO4 .
(iv) Coke:
Coke is non-volatile residue which contains about 90% of amorphous carbon and is chemically similar to hard coal. Coke is used in the manufacture of carbide, as a fuel and as a reducing agent in the extracting of metals. Coke is used to make producer gas and water gas through a process called gasification.
Uses of Coke
⦁ It is used as fuel both industrially and domestically
⦁ It is used to manufacture carbide used in production of ethyne.
⦁ It is a reducing agent in the extraction of metals from their ores.
⦁ It is used in the production of graphite.
Gasification of Coke
Gasification of gas is the conversion of coke to combustible gases by incomplete oxidation with steam and air at 1000oC. Partial oxidation of coke with air and steam gives producer gas and water gas respectively.

Gasification of Coke
Producer Gas
This is a mixture of one-third of carbon(II)oxide and two-thirds nitrogen by volume. It is obtained by heating coke in a furnace in a limited. This is achieved by passing air through red hot coke. During the process, coke is oxidized to carbon (IV) oxide which is subsequently reduced by the hot coke to carbon (II) oxide, a combustible gas. The process can be represented by the following equations.
O2   + 4N2   +   2C         →       4N2(s)   +   2CO(s) +   heat
Uses of Producer Gas
⦁ Producer gas is used as fuel in furnaces, retorts and limekilns.
⦁ It is used as a source of nitrogen for the manufacture of ammonia.
Water Gas
Water gas is produced by passing steam through hot coke at 1000oC. This results in reduction of the steam; carbon (II) oxide and hydrogen are formed. Water gas is mixture containing hydrogen and carbon (II) oxide in equal volume.
C(s)       +   H2O(l)      →       CO(s)   +   H2
Water gas has a high calorific value because both carbon (II) 0xide and hydrogen are combustible, whereas the calorific value of producer gas is low because nitrogen which is one of its constituents is not combustible
Uses of Water Gas
⦁ Water gas is used as a fuel.
⦁ It is used as a source of hydrogen and other organic compounds.

EVALUATION
⦁ Differentiate between water gas and producer gas.
⦁ What is gasification of coke?
⦁ Highlight 4 main products of destructive distillation of coal. State their uses.
⦁ Explain briefly, how destructive distillation of coal is obtained.