Master’s thesis rates circular economy methods for recycling end-of-life tyres

In addition to the flurry of research relating to tyre pyrolysis published at the end of 2020 and the start of this year, in February it emerged that another related study has been released. In his master’s thesis for Tampere University, Mikko Sirén explored the best technologies for turning scrap tyres into secondary raw material and value-added products. The research project started in May 2020 as an initiative of Black Donuts, the turn-key tyre industry consultants, who desired up-to-date research relating to the recycling of discarded tyres as part of their circular economy initiatives.

“The ideas of circular economy are inherent in our business philosophy, as we consider every stage and aspect of tire production and consumption. End-of-life tyres and their re-use possibilities are a key topic at the moment for both our customers and us, Technical Director Martti Päivinen said.

Studying circular economy as his minor, Sirén was eager to dive deeper into the suggested research topic. Black Donuts gave him a free rein to do his research. In terms of the research context, some additional detective work was needed.

“The world of tyres was totally new to me, so it was both challenging and interesting to learn more about tire industry,” Sirén said.

“And valuable for us, thanks to Mikko’s fresh and new ideas,” Päivinen added.

Sirén’s research concentrates on comparing two circular economy tyre recycling methods: devulcanization and pyrolysis. Although both methods offer an environmentally attractive way to transform waste into something useful, there was no consensus about their economic and environmental feasibility for tyre industry.

“Next, we are going to explore the quality of the pyrolytic carbon black more deeply in order to evaluate its most efficient usage in tyre construction and production”

Devulcanization means reprocessing the vulcanized rubber back to its original formulation. The process causes a breakup of certain chemical bonds so that the rubber can be mixed again. From here, devulcanized rubber can replace natural and synthetic rubber, so it has good potential to increase productivity due to savings in raw material purchases.

Pyrolysis, on the other hand, is an endothermal process where organic material is degraded in the absence of oxidizing material. In practice, when tires are pyrolyzed, they break down into carbon black, gas, oil, and metal residue.
Pyrolysis means a 100 per cent recycling of tyres. After separating the materials, it is practically possible to recycle everything to make new products.

As valuable by-products, the process generates gas and oil which can be used to support the energy production of the factory. For Mikko and the BD team, the most interesting subject for future research is carbon black.

“Next, we are going to explore the quality of the pyrolytic carbon black more deeply in order to evaluate its most efficient usage in tyre construction and production,” Martti Päivinen revealed.

Mikko Sirén’s concluded that the characteristics of the recycling technologies vary and so feasibility should be evaluated on a case-by-case basis: “The analysis identified that devulcanization technology can replace larger quantities of raw material and at the same time has a higher potential in reducing the carbon footprint. Pyrolysis was also identified to be profitable but had a smaller carbon footprint reduction potential.”

However, pyrolysis was seen as a more feasible option than devulcanization for two reasons: firstly, it can process all the rubber waste generated during tyre manufacturing; and secondly, pyrolysis is a more flexible, less risky and less expensive method optimal for the particular needs of a tyre factory. Therefore, “embedding a recycling facility in the tyre plant is reasonable” Sirén concluded.

Mikko Sirén’s complete research paper is available to download free-of-charge here: https://trepo.tuni.fi/handle/10024/124452

And you can keep up to date with the latest tyre industry research (including research specifically related to recycling and tyre pyrolysis) here: https://www.tyrepress.com/tag/research/