Upcycling of real-world HDPE plastic wastes into high-purity methane and hierarchical porous carbon materials: Influence of plastics additives

The massive use and discarding of plastics have brought serious environmental problems. Upcycling of plastic waste into fuels and value-added materials is a promising approach for mitigating environmental pressure and the energy crisis. However, pure plastic resins were used in most current research, and the influence of plastics additives is seldom studied. In this study, real-world high-density polyethylene (HDPE) plastic wastes (PWs) with additives of CaCO3 and carbon black were investigated. PWs were converted into high-purity methane (>93 %) and hierarchical porous carbon materials (HPCs) with high specific surface area (2785-2913 m2 g- 1) through autogenic pressure pyrolysis-KOH activation. Applied in supercapacitors, HPCs exhibited outstanding specific capacitance (301 F g- 1 at 1 A g-1), rate performance (89.1 % at 20 A g-1), and cyclic stability (82 % after cycling for 5000 times). The additives showed little influence on the product distribution and methane content, but changed the morphology and properties of HPCs. With additives, the meso-and macro-pore proportion and surface functional groups increased, but the graphitization degree decreased, which further altered the capacitive performances of HPCs. HPC from PWs with additives exhibited higher specific capacitance, and better rate performance, but lower cyclic stability. This work paved an efficient and sustainable way for the high-value utilization of PWs.