Definition:
Pyrolysis is the heating of an organic material, such as biomass, in the absence of oxygen. Materials do not undergo combustion in absence of oxygen however chemical compounds such as (i.e. cellulose, hemicellulose and lignin) that make up the material thermally decompose into combustible gases and charcoal.
It is the decomposition of a compound by heat, by the absence of air.
Therefore it is a process of chemically decomposing organic materials at elevated temperatures in the absence of oxygen. Unlike other high-temperature processes like hydrolysis and combustion, they does not involve reaction with water, oxygen or other reagents.
In other words, when pyrolysis takes place in alkanes, the process is termed as cracking.
For instance: Alkanes on heating in the absence of air and under high temperature or in the presence of a catalyst .The alkanes are broken down into lower alkanes, and alkenes and also hydrogen.
There are three types of pyrolysis:
1) Conventional/slow pyrolysis,
2) Fast pyrolysis, and
3) Ultra-fast/flash pyrolysis.
Pyrolysis is also the initial step in gasification and combustion and occurs in the absence or near absence of oxygen, therefore it is distinct from combustion, as it takes place sufficient presence of oxygen. Above all the rate of the process increases with temperature.
The process is often carried out at 430 °C and (about 800 °F) or higher in industries, whereas in smaller-scale operations the temperature may be much lower. Two well-known products created by them are a form of charcoal called biochar, created by heating wood, and coke (and used as an industrial fuel and a heat shield), created by heating coal. It also produces condensable liquids (or tar) and non condensable gases.
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