Hydrodeoxygenation of Mixed Plastic Wastes Towards Aviation Fuels over Ni−Re Alloy Catalyst

Abstract

To address the challenge of mixed plastic waste management, we present a one-pot hydrodeoxygenation (HDO) process that selectively converts mixed oxygenated aromatic plastics including polyethylene terephthalate (PET), polycarbonate (PC), polyphenyl ether (PPO), and bisphenol-A-based epoxy resin (E20) into high-value cycloalkanes suitable as blendstocks for aviation fuel. Employing a cost-effective Ni−Re/SiO2 bimetallic catalyst with metal loadings of 15.0 wt % Ni and 11.9 wt % Re, we achieve near-quantitative conversion (up to ca. 94% carbon yield) under mild reaction conditions (240 °C, 4 MPa H2) and at a high substrate loading of 11.4 wt %. The HDO reaction proceeds through the initial depolymerization of the polymers via acyl and alkyl C−O hydrogenolysis, followed by hydrogenation and deoxygenation. Mechanistic studies including systematic characterizations, control experiments with model compounds, in situ spectroscopy, and DFT calculations indicate that Ni−Re alloy serves as the active site for HDO, with electron-deficient metallic Ni facilitating hydrogen activation and aromatic ring hydrogenation, while oxophilic Re species promote the adsorption and cleavage of diverse C−O bonds. Furthermore, the upscaling potential of this catalytic process was evaluated by integrating laboratory-scale batch experiments with steady-state process simulation (Aspen Plus). Techno-economic analysis (TEA) and life cycle assessment (LCA) reveal that increasing the plastic feedstock concentrations from 4.5 wt % to 11.4 wt % significantly optimizes both economic and environmental performance: the minimum selling price (MSP) is reduced by 6.89% (from 1349 $/t to 1256 $/t), and the global warming potential (GWP) is lowered by 20.7% (from 3.05 to 2.42 kg CO2 eq). This work provides a practical and non-noble-metal approach for chemically upcycling high concentrated mixed plastic waste, effectively bridging plastic waste valorization with aviation fuel production.