Developments in the End-of-Life Tire Recycling Process

Dear Colleagues,

End-of-life tires are discarded on a daily basis, but even at present, limited action has been taken toward boosting their recyclability as most of the tires are either incinerated or landfilled/stockpiled. The complexity of tires has also been drastically increased, with little attention paid to designing them specifically for recycling. The retreading process is currently under intense development, and end-of-life tires have the ability to be retread several times. Furthermore, powdering (pulverization and grinding) the tires and separating the steel and textiles from this stream is a promising route that has found expanding applications. The particle size and surface area of the produced powder, purity, rubber degradation, and cost of equipment and production are the determining factors. In terms of processability, devulcanization has received a lot of attention from the tire recycling industry, and numerous physical, chemical, and microbial processes and combinations are being developed to be industrialized in the near future. Nevertheless, none of these processes are currently at a high enough technological readiness level to be operated at a large scale. In the dissolution extraction process, such as as in physical recycling, the solvent extraction devulcanizes and separates rubber from other tire components at low temperatures in addition to breaking sulfur bonds. In this way, the purity of the extracted products, e.g., rubber, carbon black (CB), and minerals, is much higher than that from other recycling methods.

Since applications of the mentioned recycled products (powder and devulcanized tire) are limited, tire pyrolysis has become extremely important. Process parameters and reactor design play a significant role in the degradation mechanisms and pyrolysis products, e.g., light olefins and dienes, naphthenes, mono-aromatics, tar, polar aromatics, and coke. Catalytic pyrolysis with promoted zeolites leads to larger yields of valuable products at the expense of the formation of tar and polar aromatics, i.e., N/S/O-containing aromatics. In addition, upgrading processes, e.g., hydro-treating, can reduce polar aromatics in the pyrolysis products by up to 90%. Furthermore, the demineralization of pyrolytic carbon black and activated carbon production are promising processes that result in increased tire recovery rates.

Dr. Mehrdad Seifali Abbas-Abadi
Dr. Gartzen Lopez
Guest Editors

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• end-of-life tire
• pyrolysis
• oil treatment
• retreading
• devulcanization
• powdering
• tire dissolution