Catalytic upgrading of waste tire pyrolysis volatiles over Ga/ZSM-5 catalysts

To improve the product distribution of waste tire pyrolysis through catalytic upgrading of pyrolysis volatiles, Ga/ZSM-5 catalysts of various particle sizes (150 nm and 5 μm) and Si/Al ratios (70 and 19) were synthesized and evaluated in a two-stage fixed bed reactor. Insights into the morphological, structural, and compositional features of Ga/ZSM-5 catalysts were obtained using SEM-EDS, XRD, XPS, physisorption, and NH₃-TPD. As compared to non-catalytic pyrolysis, Ga/ZSM-5 catalysts increased the yield of pyrolysis oil from 33.48 % to 39.64 % while boosting the total fraction of aromatics in oil from 62.4 % to > 92 %, exhibiting strong capabilities of converting alkenes to aromatics. In addition, with Ga/ZSM-5 catalysts, the pyrolysis oil contained a significant fraction of benzene and toluene (>19 %), while the fraction of heteroatomic compounds decreased. Specifically, the loading of 3 wt% Ga, the use of nano-sized ZSM-5, and a lower Si/Al ratio enhanced the overall catalytic performance. Moreover, the occurrence of sulfur in pyrolysis products was explored. This work demonstrated Ga/ZSM-5 as effective catalyst for ex-situ catalytic pyrolysis of waste tire.