An LCA answer to the mixed plastics waste dilemma: Energy recovery or chemical recycling?

Abstract

The study focuses on mixed plastics waste (MPW), whose complex and unpredictable composition (due to high polymer heterogeneity, additives, and contaminants) makes its valorisation a true technical, environmental, economic, and regulatory challenge. Chemical recycling by means of advanced thermochemical treatments (ATT) could be a successful strategy, able to support the transition from a carbon intensive to a carbon negative sector, and alternative to the current treatments of energy recovery or mechanical downcycling. Some of these ATTs provide an efficient recovery of valuable resources, such as fuels and chemicals, but their role is mainly limited by time necessary to complete the process optimization and implement the required infrastructures. A reliable identification of the best alternatives is thus crucial. A specific LCA approach quantifies the environmental performances of a selected set of ATT technologies for resource recovery from MPW. It includes plastics-to-energy, by combustion or gasification; plastics-to-methane and plastics-to-hydrogen, by gasification; and plastics-to-oil, by thermal pyrolysis. The results highlight the crucial role of carbon capture and storage (CCS) units, which partially reduces that of the specific thermochemical treatment. The best performances, particularly for Climate Change category, are those of the MPW-to-hydrogen by gasification, followed by those of MPW-to-energy by combustion or gasification, all equipped with CCS. The sensitivity analysis considers the evolution of the European energy mix, characterised by a larger utilisation of renewable energy sources, and highlights the corresponding increased sustainability of chemical recycling by ATTs. This suggests that the MPW dilemma should be definitively solved in a close future.

Keywords: Life Cycle Assessment; Mixed Plastics Waste; Technological Readiness Level; Waste-to-Chemicals; Waste-to-Energy; Waste-to-Fuel.