Hydrogen Production from Pyrolysis-Based Thermochemical Processes of Plastic and Composite Wastes: A Review

Hydrogen production from plastic waste via pyrolysis-based thermochemical processes is gaining attention as a promising approach to managing plastic waste while generating multiple energy sources. Pyrolysis and catalytic pyrolysis, often combined with catalytic reforming and, in some cases, hydrogen enhancement methods, are considered effective ways to increase the hydrogen yield from plastic-derived gases. This review focuses on hydrogen production from plastic- and polymer-based composite waste through thermochemical processes, especially pyrolysis coupled with catalytic reforming. Thermal degradation of conventional plastics, including thermoplastics and thermosets, is first detailed to describe the main reaction pathways, the different products formed and the resulting gas yields under distinct operating conditions. Polymer-based composites are then analyzed to highlight how the presence of fibers, fillers, and additives influences the pyrolysis behavior, gas composition, and hydrogen production when followed by catalytic reforming. Hydrogen production from pyrolysis coupled with catalytic reforming, including dry and steam reforming, is compared across studies for thermoplastics, thermosets, and composites, with detailed analyses of the effects of the feedstock type, catalyst type, and process conditions (temperature and pressure) on hydrogen yields. Reported hydrogen yields range from 1.2 to 37 wt % depending on the feedstock and the process configuration. The highest hydrogen production is generally achieved with pyrolysis coupled to steam reforming operated at pyrolysis temperatures between 400 and 650 °C and reforming temperatures ranging from 650 to 900 °C, over Ni-based catalysts. In addition, a techno-economic analysis is realized, and some existing industrial plants for the process are reviewed to evaluate the practical potential and scalability of these processes. Finally, the review identifies the current challenges, limitations, and research gaps in hydrogen production from plastic and composite wastes, advising future studies on more efficient solutions.