Developments in the life cycle assessment of chemical recycling of plastic waste – A review

Research into chemical recycling of plastic has increased over the last decade. At the same time, Life Cycle Assessment (LCA) methodology and application has developed and LCA continues to be an important tool for understanding the environmental impacts of materials and processes. LCA of chemical recycling processes is a growing area and this review gives a critical summary of the current research status. It is highlighted that there is confusion with nomenclature, with chemical recycling and feedstock recycling being used interchangeably to mean the processes of pyrolysis, gasification, hydrocracking or depolymerization of plastic waste. However, the two terms are rarely mentioned together. This causes inconsistency and a lack of visibility in the literature, confusion over term definitions and which term to use. Consequently, terminology use needs to be tightened. A critical analysis of nine chemical recycling LCA papers found that there are two approaches to modelling: a comparison of chemical recycling methods to other plastic waste management techniques, for example mechanical recycling, or the modelling of chemical recycling methods in combination with other plastic waste management methods, to treat mixed plastic waste. The direct comparison of chemical recycling methods and mechanical recycling is no longer valuable. Chemical recycling supports mechanical recycling by recycling plastic waste, which is not mechanically recycled, therefore there is no need to determine which method is best. Pyrolysis is the most researched chemical recycling method, as well as being the most common method modelled using LCA. Pyrolysis is often highlighted as the best chemical recycling method. It was concluded that there may be unintentional bias in these results due to more and higher quality data availability for pyrolysis. Therefore, further research on gasification, depolymerization and hydrocracking of plastic waste is needed to increase data availability and quality and enable better LCA modelling comparisons.