Efficient syngas generation from heterogeneous waste for low-carbon methanol synthesis

Plastic solid waste (PSW) represents a critical environmental challenge that requires valorization pathways capable of meeting both technical and regulatory requirements for renewable fuels. While biomass-to-methanol routes are widely investigated, achieving the greenhouse gas (GHG) savings required under current legislation remains challenging when PSW are processed alone. In this context, this work proposes and demonstrates an integrated process route combining co-pyrolysis of PSW and residual lignocellulosic biomass (RLB) in a 1:1 ratio with in-line steam reforming to produce syngas tailored for methanol synthesis. The innovation of the proposed approach lies in the strategic co-processing of waste plastics and biomass to enhance syngas quality while enabling compliance with the Renewable Energy Directive (RED III) criteria for Recycled Carbon Fuels. An experimental campaign was carried out in a batch configuration to evaluate pyrolysis–steam reforming performance and catalyst effects on product distribution. Two Ni-based catalysts (Ni/Al2O3 and Ni/ZSM-5) were assessed against a non-catalytic setup using PSW, residual lignocellulosic biomass (RLB), and their blend. Ni/ZSM-5 exhibited the best performance due to its acidity and high surface area, achieving for the blend 68 wt% gas yield with 61 vol% H2. These experimental data were used to develop a detailed process simulation, predicting a methanol production of 732 kg/h from 1000 kg/h of blended feedstock. The environmental assessment performed according to RED III showed total emissions of 18.0 GCO2,eq/MJfuel and GHG savings of 81% when char is valorized, exceeding the 70% threshold required for renewable classification. The results demonstrate that biomass blending plays a decisive role in increasing the renewable fraction of the fuel and enabling regulatory compliance also for plastic wastes. Overall, the proposed integrated co-pyrolysis-reforming route represents a technically feasible and regulation-oriented strategy for converting mixed waste-biomass streams into advanced renewable methanol, providing an alternative to conventional PSW disposal pathways.