Pyrolysis is a form of decomposition which takes place in an environment with little to no oxygen which is very hot, and may also be at high pressure. This form of decomposition can occur in nature, and it can also be used in controlled environments for various purposes. Some industrial products are produced with the assistance of pyrolysis, and it is also used to produce experimental fuels and in various other applications, both experimental and commercial.
With pyrolysis, thermal decomposition occurs, with the material breaking down under the heat to produce gases, some water, and solid byproducts which can take the form of ash or char. Sometimes thick tar is produced during pyrolysis as well, depending on what is being broken down. In an example of this phenomenon in nature, lava causes thermal decomposition when it flows over vegetation. In labs and manufacturing settings, pyrolysis is often accomplished in a reactor.
The more oxygen present during thermal decomposition, the more oxidation will occur during the reaction. Thus, people may take steps to try and minimize oxygen in the environment where they are creating a pyrolysis reaction, and may even conduct the reaction in a vacuum in some cases. In other cases, the reactor will simply be solidly built with seals which are designed to keep as much oxygen out as possible, because oxidation can interfere with the process.
Pyrolysis can be used specifically to process various materials to access useful byproducts of thermal decomposition, such as pyrolysis oil, a type of synthetic fuel, and various gases which are used in industrial processes. A wide variety of materials can be broken down with this process, including products like rubber tires, which can be broken down and turned into useful byproducts with thermal decomposition instead of simply being landfilled. Thermal decomposition of other materials may also help to reduce the strain on the world's landfills.
Pyrolysis of biomass is a process of particular interest to people who are interested in developing alternative fuels. Gasification, as it is sometimes called, can be used to fuel engines without relying on petroleum-based fuels. In fact, gasification has been used historically during periods of fuel shortages. Working gasification vehicles have been built to demonstrate the potential applications of this process, with their drivers sometimes even using them as primary vehicles for transport. These drivers also like to use their vehicles for public relations, demonstrating that pyrolysis is possible and has potential by modeling it on the streets.