Pyrolysis behaviors of different parts in waste tire and catalytic enhancement mechanism of high-value aromatics via upgrading over char-based catalyst

Pyrolysis is an effective approach to achieve clean and efficient utilization of massive waste tires. However, the differences of rubber compositions in different parts of tire result in significant variation on pyrolysis products distribution. Therefore, exploring pyrolysis characteristics of different parts in waste tire is crucial for efficient utilization. Herein, the effects of process parameters on products distribution and tar compositions from pyrolysis of tire tread, sidewall and bead were investigated. Meanwhile, pyrolysis char of tire bead was modified by acid leaching or activation by slight O2 and used as catalyst to upgrade tread pyrolysis volatiles to further enrich highvalue aromatics. Results indicate that the highest tar yield of 68.38 wt% is obtained from tread pyrolysis due to its high volatile content. Pyrolysis tar from tire sidewall is mainly cycloolefins with D-limonene content up to 35.40%, while aromatics dominate tread pyrolysis tar due to its higher content of styrene butadiene rubber, primarily enriching high-value D-limonene and aromatics. Besides, WTC-Acid catalyst effectively improves mesoporous structure and acidic sites, which is beneficial to the diffusion of pyrolysis volatiles, resulting in increase of aromatics content and yield in tar up to 82.34% and 46.75 wt%. Meanwhile, the yields of toluene, ethylbenzene and xylene are increased by 71.5%, 34.6% and 134.2%, respectively, over WTC-Acid than blank experiment and catalytic mechanism of tread pyrolysis volatiles was proposed. Tar yield remains stable within 54.97 wt% - 56.78 wt% after three loops of WTC-Acid. This study provides a guidance for optimizing clean and high-value pyrolysis of waste tire via individual pyrolysis of different parts and upgrading of pyrolysis volatiles over char from tire pyrolysis.