Pyrolysis is a process of thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. The word pyrolysis is derived from the Greek words pyro, meaning fire, heat, or fever, and lysis, meaning separating. Pyrolysis is one of the various types of chemical degradation processes that occur at higher temperatures (above the boiling point of water or other solvents) . It differs from other processes like combustion and hydrolysis in that it usually does not involve the addition of other reagents such as oxygen (O2, in combustion) or water (in hydrolysis) .

Pyrolysis produces solids (char), condensable liquids (light and heavy oils and tar), and non-condensable gases. Pyrolysis is different from gasification, which refers to a partial thermal degradation of carbonaceous materials that takes place in an inert (oxygen-free) atmosphere and produces mainly gaseous output.

Pyrolysis is used in various industries, including biomass conversion to biofuels, thermal cleaning, and waste management. During biomass pyrolysis, organic materials such as biomass are heated in the absence of oxygen, usually at or above 500°C, to produce bio-oil, bio-char, and syngas. Pyrolysis is also used for thermal cleaning, an industrial process that removes contaminants from surfaces by heating them to high temperatures in the absence of oxygen.

Pyrolysis products always produce solid (charcoal, biochar), liquid, and non-condensable gases (H2, CH4, CnHm, CO, CO2, and N) . The liquid phase is extracted from pyrolysis gas only during its cooling down, and in some applications, these two streams can be used together when providing hot syngas directly to the burner or oxidation chamber.

In summary, pyrolysis is a thermal decomposition process that occurs at elevated temperatures in an inert atmosphere, producing solids, condensable liquids, and non-condensable gases. It is used in various industries, including biomass conversion to biofuels, thermal cleaning, and waste management.