The increasing accumulation of polypropylene (PP) waste presents a significant environmental challenge. To address this issue, a three-stage reactor using molten metals (MMs) was developed for PP pyrolysis, enabling high-efficiency clean hydrogen production. The first stage reactor models PP decomposition into hydrogen, gas-phase hydrocarbons (C1-C6), and solid carbon using an empirical equation. The evolved hydrocarbons are subsequently processed in the second and third stages, each modeled as a one-dimensional (1D) plug-flow reactor (PFR) within molten-metal bubble column reactors (MMBCRs), where non-catalytic reactions occur inside the gas bubbles and catalytic reactions at the bubble surface, alongside with heat transfer. The model was validated against experimental data measured over a wide temperature range. Sensitivity analyses revealed the influence of temperature, pressure, gas holdup, and reactor dimensions on hydrogen yield and product distribution. The maximum hydrogen yield of 95 % was achieved at 1000oC in the three-stage reactor. This study provides a guideline for designing multi-stage MMBCRs and optimizing hydrogen production processes from PP pyrolysis.
