Tuning Feedstock-to-Catalyst Ratio for Efficient Coproduction of Hydrogen and Nanocarbon from Polyolefin Waste Pyrolysis

A sustainable approach to valorizing plastic waste involves using catalytic pyrolysis to simultaneously generate hydrogen and nanocarbon from polyolefins, contributing to a circular material flow. This study investigates the impact of varying the ratio of feedstock (HDPE and PP) to the Ni/Al2O3 catalyst (F/C) on the yield, composition, and quality of the gaseous and solid products generated during pyrolysis. Experiments were conducted in a two-stage reactor system, where the feed in the first stage was maintained at 500 °C for pyrolysis and the catalyst in the second stage was kept at 800 °C. The F/C ratio was maintained at 1, 1.5, 2, and 2.5 to elucidate an optimal balance between hydrogen generation and nanocarbon formation. The results obtained indicated an enhanced catalytic activity at a lower F/C ratio, producing approximately 65–70 vol % hydrogen, promoted by the efficient cracking and dehydrogenation of hydrocarbons. As a result, higher hydrogen and nanocarbon depositions were observed on the active Ni sites. Increasing the feed amount led to pore blockage, thereby reducing the catalytic activity. The study overall provides critical insights into feedstock–catalyst interactions for process intensification in waste-to-resource conversion, thus paving the way for the development of scalable systems for simultaneous hydrogen and nanocarbon generation from plastic waste pyrolysis.