Integrated In situ catalytic steam gasification of mixed plastic waste for hydrogen-rich syngas production

Steam gasification offers a promising route for converting plastic waste into hydrogen-rich syngas; however, challenges remain in processing mixed plastic feedstock and optimising operating conditions to enhance hydrogen production and minimize tar formation. This study systematically investigated the steam gasification of waste polyethylene (PE), focusing on the effects of steam to plastic (S/P) ratio, feedstock heterogeneity, and a Ni/Al 2 O 3 catalyst addition, on product distribution, syngas quality, and process efficiency. Moderate steam (S/P ∼ 1–2) enhanced gasification performance by promoting steam reforming reactions and increasing hydrogen production. Ni/Al 2 O 3 significantly improved gasification performance, achieving ∼ 90 wt% gas yield and ∼ 65 vol% H 2 , with a hydrogen productivity of 221 g H 2 kg⁻ 1 plastic and a carbon conversion efficiency of 82.8%, while substantially reducing tar and char formation. Feedstock mixtures comprising waste PE, PP, and PC were subsequently evaluated. PP addition promoted gas formation and CO production, whereas PC slightly increased tar formation, which may be associated with the formation of aromatic intermediates. Despite these differences, the mixed feedstocks maintained high gasification performance and hydrogen-rich syngas. Preliminary catalyst stability tests showed no observable deactivation over four consecutive reaction experiments, while XRD and BET indicated reversible Ni ↔ NiO redox behaviour and limited sintering under the conditions tested. These results demonstrate the potential of in situ Ni/Al 2 O 3 catalysed steam gasification as an effective route for producing hydrogen-rich quality syngas from mixed plastic waste.