Pyrolysis as the gateway thermochemical route for plastic-to-hydrogen-rich gas valorization

The rapid growth in plastic production has intensified environmental challenges, while conventional management routes such as recycling or incineration remain limited by costs, pollution, and low circularity. Against this background, pyrolysis stands out as an essential first stage within multi-step thermochemical routes for plastic conversion. This review critically evaluates the role of pyrolysis as the primary platform for hydrogen-oriented valorization schemes, emphasizing its capacity to transform diverse polymeric feedstocks into intermediate gas and liquid fractions. The influence of operating parameters such as temperature, residence time, heating rate, and particle size on product distribution and quality is systematically analyzed. Beyond pyrolysis, the review explores complementary downstream processes, including gasification, catalytic and thermal reforming, water–gas shift reactions, and plasma-assisted upgrading, highlighting their synergetic role in boosting hydrogen yield and purity. A comparative discussion of thermal versus catalytic pathways is provided, together with an overview of emerging integrated configurations. Furthermore, recent techno-economic analyses and life-cycle assessments are assessed to examine the scalability, energy efficiency, and environmental footprint of these multi-stage systems. Overall, this review positions pyrolysis not as a standalone solution but as a pivotal enabling step in advanced thermochemical strategies for sustainable hydrogen production from plastics, contributing to the development of circular economy models.