Regulation of volatile reactions through thermal/catalytic cracking during scrap tires pyrolysis for high-valued chemicals production

Pyrolysis has emerged as a compelling thermochemical method for effectively managing scrap tires, recovering high-value chemicals to bolster circularity within the tire industry. This study focuses on comparing slow and fast pyrolysis for obtaining pyrolysis oil and further explores the integration of Ga species and mesoporous to enhance the aromatics selectivity. Slow pyrolysis yields more oil products with D-limonene (relative content >13.0%), reflecting the original monomer structure of tires. Conversely, fast pyrolysis, due to a larger temperature gradient, mainly promotes cracking reaction of volatiles, leading to more gaseous products with a high C2–C4 olefins content. Loading Ga onto HZSM-5 for fast pyrolysis facilitates de-heteroatom, dehydrogenation, and aromatization, resulting in a 3.5% increase in polycyclic aromatic hydrocarbon (PAHs) and a 2.8% decrease in heteroatomic compounds. The creation of mesopores in Ga/ZSM-5 optimizes volatiles' diffusion and catalyst's acidity, resulting in the highest content of aromatics (88.0%) and the lowest value of heteroatomic compounds (11.6%). Significantly, the relative content of high-valued benzene, toluene, ethylbenzene and xylene (BTEX) increases sharply from 3.3% for fast pyrolysis alone to 47.8% over Ga/ZSM-5-meso. In short, chemicals recovered from the pyrolysis process can be repurposed to manufacture new tires, thus closing the loop for the tire industry.