Catalytic pyrolysis of polypropylene over acid-modified coal gangue: product distribution and catalyst performance.

To address the dual challenges of coal gangue solid waste and waste plastic pollution, this work develops a series of coal gangue-based catalysts via hydrochloric acid modification of coal gangue samples with different iron contents, and applies them to the catalytic pyrolysis of polypropylene (PP). The results showed that, compared with unmodified coal gangue, the acid-modified catalyst increased the PP pyrolysis gas yield by up to 20.06 wt%, and the gas product exhibited potential as an alternative to natural gas. The initial decomposition temperature of PP was reduced by up to 78 °C. The quality of the liquid oil was significantly improved, with hydrocarbon content increasing by up to 33.26 area %, while the proportion of oxygenated compounds decreased by up to 42.97 area %. Characterization by XRF, XRD, and BET indicated that acid treatment enlarged the specific surface area and pore volume of coal gangue, promoted the formation and enrichment of active iron-based oxides, and generated acidic sites, thereby enhancing catalytic activity. This work offers a reference for the co-processing and high-value utilization of coal gangue and waste plastics.