We have previously discussed the origin of coal in details. See http://coalgeology.com/coal-formation-and-coal-rank-the-buried-sunshine/18610/
In this article, let’s focus on some chemistry of coal formation.
Cellulose – The framework component
- Carbon, oxygen and hydrogen are the main components of vegetal matter.
- Cellulose, C6H10O5, is the principal substance forming the framework of vegetal matters.
- Cellulose can be used to derive the chemical equation for the formation of “peat”.
- In presence of free oxygen: Organic matter / Cellulose + oxygen = Carbon di oxide + water (oxidation of organic matter).
- In environments where oxygen is limited, the cellulose does not completely decompose. Incomplete oxidation removes some of the carbon and all of hydrogen and oxygen from the cellulose. This process produces pure charcoal (carbon only).
Incomplete oxidation occurs under water. We can write some simplified reaction for peat formation –
- 5(C6H5O10) = C20H22O4 (lignite) + 3CH4 + 8H2O + 6CO2 + CO
- 6(C6H5O10) =C22H20O3 (bituminous coal) + 5CH4 + 10H2O + 8CO2 + CO
Note that during the reactions, carbon is getting enriched in the products. They are not the exact reaction that goes on during the formation of coal, but are fairly representative to show the chemical change.