Plastic waste gasification to synthetic natural gas: experimental catalytic steam gasification and methanation process modelling in aspen plus

Population growth and economic development significantly increased plastic consumption, leading to a rise in plastic waste (PW) generation. Only a small fraction of this waste is currently recycled, with the majority being landfilled or released into the environment. Among emerging waste management strategies, chemical recycling through gasification stands out for its flexibility and potential to valorise non-recyclable plastic fractions. This study investigates the steam gasification of a representative PW mixture in a bench-scale fluidized bed reactor operated at 850 °C, equipped with a ceramic filter candle in the freeboard for in-situ hot-gas cleaning. At a steam-to-plastic ratio of 1.5, the process produced 2.4 Nm 3 /kg PW of nitrogen-free gas containing over 50 vol% hydrogen. The introduction of a commercial Ni-based catalyst reduced tar content by 70%, increased gas yield above 3 Nm 3 kg⁻ 1 PW, and raised hydrogen concentration to about 56 vol%. Building upon these results, an Aspen Plus model was developed to evaluate system integration of steam gasification for synthetic natural gas (SNG) production. The simulation confirmed the feasibility of converting plastic-derived syngas into high-purity SNG with a yield of approximately 0.9 kg SNG /kg PW , and an overall thermal efficiency of 93.5% after process optimization and heat recovery. The combined experimental and modelling results demonstrate that catalytic steam gasification represents a technically viable and sustainable waste-to-fuel pathway, enabling the conversion of mixed PW into recycled carbon syngas and SNG within future circular and low-carbon energy systems.