Pyrolysis of different types and sections of end-of-life tyres: Kinetics and experiments to improve product quality

Abstract

Pyrolysis contributes to the transition of the tyre industry towards a circular economy model. Tyre rubber is a complex blend of polymers, inorganic additives and grades of carbon black, depending on the tyre type and section. The products of the end-of-life tyres (ELTs) pyrolysis are heavily influenced by the original composition, so separation prior to pyrolysis could be an important step in optimising the recycling process. However, recyclers often ignore the composition of ELTs. This study aims to develop a simple methodology for evaluating the potential resource recovery of ETLs samples from a set of thermogravimetric experiments applying a Distributed Activation Energy Model (DAEM). Pyrolysis experiments were also carried out in a fixed-bed reactor to analyse the composition of the products. Direct linear relations were identified between specific values of the initial mass fraction parameter of the DAEM and the natural and synthetic rubber content, and notably with the limonene content in the pyrolysis oils. A high 12 wt% limonene in the oil product was obtained from the sample with the 83 wt% natural rubber content at 450 ºC. In addition, significant differences in the ash content were observed in the raw recovered carbon black from the tread sections (31 wt%-55 wt%) to the non-tread sections of the ELTs (7 wt%-16 wt%), which had a positive effect on its quality. This work demonstrates that the application of a straightforward methodology on separated types and sections of ELTs can greatly enhance the economic and environmental sustainability of their recycling processes.