pyrolysis - Anhydrous pyrolysis, Pyrolysis and waste management, Hydrous pyrolysis, Vacuum pyrolysis

The decomposition of a substance by heating in the absence of oxygen, usually resulting in simpler compounds being formed. The most important example is the pyrolysis or ‘cracking’ of petroleum, by which alkanes are converted into alkenes and shorter alkanes, eg propane may be converted to ethene and methane: CH₃CH₂CH₃?CH₂=CH₂+CH₄.

Pyrolysis is the chemical decomposition of organic materials by heating in the absence of oxygen or any other reagents, except possibly steam.

Extreme pyrolysis, that leaves only carbon as the residue, is called carbonization.

Pyrolysis is a means of reusing the scrap tires. Pyrolysis in this context is the degradation of the rubber of the tire using heat in the absence of oxygen.

Anhydrous pyrolysis

Pyrolysis is usually understood to be anhydrous (without water). In fact, the flames of a wood fire are due to combustion of gases released by pyrolysis, not combustion of the wood itself. Thus, the pyrolysis of common materials like wood, plastic and clothing is extremely important for fire safety and fire fighting.

An ancient industrial use of anhydrous pyrolysis is the production of charcoal through the pyrolysis of wood.

Anhydrous pyrolysis has been assumed to take place during catagenesis, the conversion of kerogen to fossil fuels. Anhydrous pyrolysis can also be used to produce liquid fuel similar to diesel from solid biomass or plastics .

Pyrolysis and waste management

The application of pyrolysis to waste management has been gaining acceptance along with other advanced waste treatment technologies. Pyrolysis also can be used as a form of thermal treatment to reduce waste volumes and produce fuels as a byproduct. Low temperature pyrolysis can also be used to produce a synthetic diesel fuel from waste film plastic, through systems such as Thermofuel.

Hydrous pyrolysis

The term pyrolysis is sometimes used to encompass also thermolysis in the presence of water, such as steam cracking of oil, or more generally hydrous pyrolysis.

Vacuum pyrolysis

In vacuum pyrolysis organic material is heated in a vacuum in order to decrease boiling point and avoid adverse chemical reactions.