End-of-life tyres are bulky, and they are built to last, which makes them awkward waste. For pyrolysis, though, they are one of the best feedstocks available: they break down into oil, carbon, gas and steel cord, and each of these has an established use. This article sets out what tyres become, in what proportions, and where each output goes.
Why tyres suit pyrolysis
A tyre is made mainly of rubber, carbon black and steel cord. Rubber is a polymer, which is exactly the kind of material that cracks into shorter hydrocarbons at 400–600 °C when no oxygen is present. Our explainer What pyrolysis is and how it differs from incineration walks through the process step by step.
Tyres are also predictable. Compared with mixed waste, their composition is fairly uniform and they are usually collected separately, so the process can be tuned more precisely than for a varied mix of materials.
There are other routes for tyres, such as grinding them into rubber crumb or burning them as fuel, for instance in a cement kiln. Pyrolysis takes a third path: rather than grinding or burning the rubber, it breaks it back down into oil, gas and carbon black.
Shredding to about 55 × 55 mm
Whole tyres do not go into the reactor. They are first shredded into pieces of about 55 × 55 mm, which heat evenly and can be fed in continuously. The steel cord stays in the shred and is separated from the solid residue after pyrolysis.
A continuous industrial line processes 700–1,000 kg an hour: up to 17 t a day, or 5,600–8,000 t a year over 8,000 operating hours. For smaller volumes, a compact batch module handles 1–3 t a day in three independent reactors. It accepts tyres under waste code 16 01 03 and runs cycles of 8 or 12 hours.
The tyre mass balance
Tyres give a different split of outputs from plastics. Because they contain carbon black and steel, more of their mass ends up as solid carbon and less as oil. The table compares the two.
| Output | Tyres | Plastics |
|---|---|---|
| Oil | 36% | 63% |
| Gas | 23% | 34% |
| Carbon | 34% | 3% |
| Steel | 7% | – |
Steel accounts for about 70 kg in every tonne of tyres. Solid carbon makes up almost as large a share as oil, so its quality and its market deserve attention from the start of a project.
Who buys the outputs
Oil
Pyrolysis oil has a lower heating value of around 39 MJ/kg, against roughly 43 MJ/kg for diesel. Petrochemical plants use it as a feedstock and crack it back into monomers for new plastics, while boiler and CHP operators burn it as fuel. A compact module can split it into light and heavy fuel oil; our article on what pyrolysis oil is used for goes into more detail.
Recovered carbon black and carbon
Much of the solid residue is the carbon black that was mixed into the rubber when the tyre was made. As recovered carbon black (rCB), it goes back into rubber products and pigments. The carbon can also serve as a filter sorbent, a concrete additive or an industrial raw material, and from a compact module it is more than 92% carbon with low sulphur.
Steel and gas
Once separated, the steel cord is sold to steelworks as secondary raw material. The gas, with a heating value of around 31.8 MJ/m³ (natural gas: about 34 MJ/m³), fuels the plant's CHP unit. That unit produces electricity and heat, covers the line's own demand of about 380 kW, and leaves any surplus for the site or the grid.
What to check before a project
The technology is only one part of a project. Before deciding, it pays to check three things.
- Tyre supply. How much material is available, how steadily and on what terms.
- Offtake. Who will take the oil and carbon, and what quality specifications they require.
- Permits. In the Czech Republic, EIA screening, the air-protection permit, the waste-facility operating permit and the building permit are usually the longest part of the whole project.
Products registered under REACH can be sold as products rather than waste. If you would rather not handle offtake yourself, we offer an operation-and-offtake model: we buy the oil, gas and carbon at a price fixed in the contract, collection included.
To see how turnkey delivery, operation or offtake could work for your site, visit our page on ways to work together.