Pyrolysis

Its the heating of an organic material, such as biomass, in the absence of oxygen, the process typically occurs at temperatures above 430 °C and under pressure.
At high temperatures and in the absence of oxygen, the organic material gets decomposed and its larger size molecules break down to smaller size molecules resulting into phase change, e.g., solid to liquid and gaseous form.

When complex organic material is heated up in the absence of oxygen, it gets decomposed and its larger size molecules or long chain hydrocarbons get broken into smaller size and simpler molecules such as light hydrocarbons.

If there is presence of oxygen in the process, the organic material gets burnt instead of getting decomposed.
The pyrolysis process results into change of phase of the organic material/ bio-mass e.g. change from solid state to liquid and gaseous state.

The process is widely used in the production of charcoal, activated carbon and methanol.
It is also used to decompose scrap and waste tires.