A value-added and carbon-reduction approach to upcycle mixed plastic waste into methane and carbon microspheres

The mass production, consumption, and disposal of plastics pose a considerable threat to the environment and human life; however, the recycling of plastic waste remains challenging. This study converted mixed plastic waste into gas and solid without generating a liquid product. The pyrolysis gas had a high CH₄ content and a high heat value. The solid product comprised 2–8 μm carbon spheres with a semicrystalline graphitic structure. The techno-economic and carbon footprint analyses revealed that the upcycling of mixed plastic waste into carbon black and natural gas substitutes produced a high internal rate of return (56.9%), a short payout period (3.46 years), and negative carbon emissions (−449 kg CO2-eq per t plastic waste). The product price and plant capacity are the main factors influencing the profitability of the project. Compared with autogenic pressure pyrolysis for the production of liquid fuels, this method showed considerably higher economic and environmental benefits.