How Pyrolysis Works

The word pyrolysis contains the Greek roots for ‘fire’ and ‘loosening, unbinding’ which already tells us about the process: pyrolysis is a thermal treatment that decomposes organic material into its component parts. Industrial pyrolysis is done in an oxygen-free atmosphere, so that different kinds of decomposition reaction take place rather than simple burning. Pyrolysis is chosen when combustion reactions are not desired.

Pyrolysis Process

In practice, forms of pyrolysis have been traditionally used for thousands of years, for example to make charcoal, or to obtain tar and pitch to be used as sealants and adhesives.

Pyrolysis involves the breaking of organic bonds. Depending on the material, this usually occurs at temperatures up to 900 °C, but below the melting point of the material. These are the conditions under which bonds can be broken in large organic molecules in the absence of oxygen or other oxidizing gases. To make the process more effective, sometimes dehydrating or dehydrogenating agents are added.

In this way pyrolysis transforms the chemical state of the material and also, partly, the phase. The end products include gases, solids and liquids; their composition depends on the raw material, the pyrolysis temperature, the other reactants that are added and the duration of the treatment.

Allothermic and Autothermic Pyrolysis

In principle, we divide pyrolysis methods into two types according to the heat source. The heat can come from the material itself, if a certain degree of combustion is allowed; this is called autothermic pyrolysis. Alternatively, the heat can be applied from outside the closed reaction chamber: this is called allothermic pyrolysis.

Many products can be made either by autothermic or allothermic pyrolysis, for example activated charcoal. Nowadays, in industrial production, allothermic pyrolysis is most often used, because it allows for precise control of the reaction conditions.

Pyrolysis at IBU-tec

At IBU-tec we can perform both types of pyrolysis. Indirectly fired rotary kilns are predestined for pyrolysis because the heat source is isolated from the material and we can easily regulate the gas atmosphere. In principle, it is also possible to perform pyrolysis in directly fired rotary kilns by running the flame deliberately with sub-stoichiometric oxygen levels.

Using pyrolysis processes, we have already produced catalysts, battery materials and zeolites. Another area of growing interest is the conversion of biomass to useful organic products – this subject is currently the focus of much research.

Another interesting application is pyrolysis of motor vehicle tires. Used tires are often simply burnt in waste incineration plants. Pyrolysis offers the alternative of converting them to useful materials such as carbon black and oil – and in a process that even has a negative CO2 balance.

Working with customers, we have developed a process which is now being used successfully to introduce circular economics to carbon black market.

If you need help with any pyrolysis-related projects, we will be happy to advise you.