A novel slurry co-pyrolysis process for hydrogen production from polypropylene and waste motor oil based on a...

Efficient conversion of urban organic solid waste into hydrogen-rich gas constitutes a pivotal pathway toward achieving carbon neutrality goals. In this work, a slurry-assisted, sorption-enhanced co-pyrolysis/reforming strategy was employed to optimize the blending ratio and operating parameters for waste polypropylene (PP) and waste motor oil (WMO). Experimental screening identified a polypropylene-to- waste motor oil mass ratio of 7:3 as optimal, yielding 4.91 mmol/g H₂ yield and 32.32 % H₂ at 800 °C without catalyst. Implementation of the slurry-assisted process improved heat and mass transfer, increasing the H₂ concentration to 35.79 % and the H₂ yield to 7.24 mmol/g. Introducing Ni/ZSM-5 markedly enhanced hydrogen generation, producing 60.43 % H₂ and 35.31 mmol/g H₂ at 800 °C; further coupling with CaO increased the H₂ fraction to 62.74 % and reduced CO₂ content to 3.81 %. The optimal reforming temperature was 750 °C, where the Ni/ZSM-5 + CaO system achieved 31.38 mmol/g H₂, 39.16 mmol/g syngas yield, and 3.44 % CO₂. SEM/TEM characterization revealed extensive carbon nanotube formation and severe coking on Ni/ZSM-5, mitigated by CaO addition. ReaxFF molecular dynamics simulations with hydrogen-atom tracking confirmed that PP acted as a hydrogen donor during co-pyrolysis, elucidating the mechanistic basis of the observed synergy. This slurry-assisted and sorption-enhanced co-pyrolysis/reforming strategy significantly enhances hydrogen yield and purity from waste PP and WMO co-conversion, offering a novel approach and theoretical insight for high-value valorization of polymers and waste oils toward targeted H₂ production.