CO2-induced co-pyrolysis of Pennisetum hydridum and waste tires: Multi-objective optimization of its synergies and pyrolytic oil, char and gas outputs

This study quantified the CO2-induced co-pyrolysis of Pennisetum hydridum (PHY) and waste tires (WT), as well as optimizing synergies and yields of pyrolytic char, oil, and gas to promote sustainable waste co-circularity. High-temperature (>700 °C) CO2-driven co-pyrolysis proved to be a viable waste reduction strategy, reducing residuals by 3.14–16.39 % compared with N2 pyrolysis. The complexity of the co-pyrolysis process was evident in the increased activation energy and reaction order. Synergistic interactions between the feedstocks enhanced the quality of resulting oil and char products. Co-pyrolytic oils exhibited lower oxygenation levels (92.44 %, 75.09 %, and 55.78 %) than PHY oil (92.54 %), with reductions in furans, ketones, and phenols, but with increased hydrocarbon contents (3.66 %, 14.23 %, and 33.31 % for PW31, PW11, and PW13, respectively). The co-pyrolytic chars showed improved pore structure and thermal stability. CO2 facilitated the consumption of furans, decarbonylation of ketones, and aromatization, while promoting the emissions of S- and C-containing gases and HCN, and inhibiting NH3 release. The multi-objective optimization showed that the CO2-induced co-pyrolysis minimized S- and N-containing emissions between 750 and 950 °C. These findings offer insights into achieving harmonious and sustainable co-pyrolysis for energy and product generation.