Title : Transforming waste plastic into renewable hydrogen: A review of progress, challenges, and future directions through pyrolysis, distillation, and hydrotreatment process
Abstract:
The rapid growth of the global plastic waste burden and the concurrent demand for low-carbon hydrogen have driven research into thermochemical routes that convert post-consumer plastics into hydrogen. This review synthesises recent advances in a three-step processing chain—pyrolysis to depolymerise mixed plastics into oils and light gases, distillation/fractionation to upgrade and separate pyrolysis condensates, and hydrotreatment (hydrogenation/steam reforming) to produce high-purity hydrogen—highlighting process mechanisms, catalyst and reactor design, integration strategies, and environmental and economic considerations. This study summarises progress in feedstock pretreatment and reactor concepts that improve oil yield and gas composition, innovations in distillation and solvent-assisted fractionation that stabilise pyrolysis condensates for downstream upgrading, and hydrotreatment pathways (including catalytic steam reforming, autothermal reforming, and hydrocracking followed by reforming) that maximise hydrogen selectivity while minimising coke and tar formation. Remaining challenges are discussed: wide feedstock variability, catalyst deactivation and sulphur/nitrogen poisoning, thermal and material inefficiencies, process emissions, hydrogen inventory requirements for hydrotreatment, and techno-economic barriers to industrial scale-up. The study identifies priority research directions—tailored catalyst development and regeneration strategies, heat- and hydrogen-integration across unit operations, modular and decentralised process concepts, life cycle and techno-economic assessments, and policy frameworks to valorise plastic waste as a feedstock within a circular economy. The review concludes that while plastic-to-hydrogen routes are technically promising, coordinated advances in materials, systems integration, and policy are essential to realise economically and environmentally sustainable deployment.
