High-yield hydrogen production from plastic pyrolysis oil by microwave-induced plasma steam reforming

Plasma-assisted gasification represents a promising resource-recovery strategy for converting plastics into hydrogen (H 2 ). However, this technology still suffers from substantial energy consumption due to the melting-induced adhesion of plastics coupled with the restricted interaction zone of high-energy plasma species. To improve the energy efficiency of the plasma-based processes, we herein propose a tandem plastic valorization process that integrates pyrolysis with microwave-induced plasma reforming. The feasibility of this tandem process was evaluated, and results demonstrated that the hydrogen-rich syngas constitute more than 95% of the gaseous products, with an H 2 /CO molar ratio of approximately 2.5. The microwave-induced plasma reforming process attains an H 2 yield of 75% and an energy efficiency of 2.1 g H 2 ∙kWh −1 using polypropylene (PP) pyrolysis oil. Under the optimal operating conditions, the steam reforming of representative model compounds (1-Octene) achieves an H 2 yield exceeding 90% and an energy efficiency of approximately 2.5 g H 2 ∙kWh −1 . A comparison of the decomposition and steam reforming processes reveals that the introduction of steam effectively enhances the absolute H 2 yield by over 20%. According to product composition and optical emission spectroscopy analysis, the possible reaction pathway is that plastic pyrolysis oil is fragmented into various hydrocarbon radicals through collisions with high-energy plasma species (e.g., N 2 , N+ 2, e). Most of these radicals subsequently undergo C C and C H bond cleavage, yielding C 1 and C 2 intermediates. Upon steam introduction, OH radicals react with C 1 and C 2 intermediates to produce hydrogen molecules, effectively suppressing the dehydrogenation pathway. This study confirmed the practicability of the proposed tandem process and achieved a remarkable efficient hydrogen production performance for the first time. It could establish a baseline performance reference for the conversion of plastic pyrolysis oil to H 2 and to contribute to the development of scalable plastic-to-H 2 technologies.