Impact of Temperature and Residence Time on the Recovery of Isoprene through Pyrolysis of Polyisoprene Rubber

Pyrolysis is increasingly garnering attention as a viable process for recovering valuable resources from used tires. In this study, we examined the recovery of isoprene through pyrolysis of used tires and assessed the influence of the pyrolysis conditions on product yields. Polyisoprene-based tire rubber containing carbon black (CB) was subjected to pyrolysis in a tubular reactor at different temperatures and residence times to recover the isoprene monomer. The highest isoprene monomer yield (13.9 wt %) was achieved at 800 °C and a residence time of 2.7 s, whereas upon increasing temperature and residence time the yield decreased. At 500 °C, the predominant oligomers comprised components with isoprene skeletons, whereas at 800 °C, a more pronounced thermal decomposition occurred, leading to the generation of higher molecular weight polycyclic aromatic compounds. The molecular weight distribution of the products collected from the reactor tube and oil trap exhibited a marked decrease as the pyrolysis temperatures increased, shifting from Mw = 1000 at 500 °C to Mw = 600 at 700 °C. Our results highlight the importance of exploring the pyrolysis conditions that afford low molecular weight compounds, facilitating the degradation of the isoprene skeleton in the oligomer and thus increasing the isoprene yield.