Experimental Investigation of Carbon Black and Hydrogen-Enriched Gas Production from Polypropylene and Polystyrene by a Two-Stage Slow Pyrolysis–Plasma-Assisted Pyrolysis Approach

This study investigated the influence of hydrocarbon feedstock composition evolved from slow pyrolysis of polypropylene (PP) and polystyrene (PS) and plasma gas flow rate on the carbon black and hydrogen production yields and quality. The temperature distribution and feedstock flow within the carbon black formation zone with plasma were supplementarily modeled using computational fluid dynamics. TG-FTIR-GC/MS was employed to analyze thermal degradation patterns of plastics and to estimate the composition of volatile intermediates of plastics’ slow pyrolysis. Produced CB was characterized, encompassing physical, structural, and compositional properties using thermogravimetric analysis, CHNS analysis, scanning electron microscopy–energy dispersive spectroscopy, transmission electron microscopy, Brunauer-Emmett-Teller, and Raman spectroscopy. The results revealed that both feedstocks yield CB with comparable structural characteristics; however, PS-derived (aromatic-rich) volatiles produce significantly higher CB yields, whereas PP-derived (aliphatic) volatiles favor hydrogen formation. Differences in carbon structure were also observed, with PP-derived CB exhibiting a higher degree of graphitic ordering compared to the more disordered CB obtained from PS. The optimal flow rate of plasma gas was identified as 6.1 L/min. Increasing the flow rate to 7.2 L/min led to reduced conversion efficiency for PP-derived long-chain hydrocarbons. Overall, the findings demonstrate the potential of this approach for the co-production of high-quality carbon black and hydrogen from plastic waste.