The lack of holistic recycling technologies for discarded plastics and associated waste mismanagement issues have resulted in substantial accumulation of plastics in landfills and the environment. Among chemical recycling technologies being considered, pyrolysis and gasification are some of the methods reported to date that can potentially deconstruct mixed plastics with a high degree of contamination and across a broader slate of polymers than those eligible for mechanical recycling. To examine the potential of these approaches, here we conduct techno-economic analysis and life-cycle assessment of two conceptual process designs based on catalytic fast pyrolysis and steam gasification of mixed plastic waste.<br/><br/>For pyrolysis, the modded case converts 240 tonnes/day of mixed waste plastics into aromatics, olefins, and naphtha-range products. Assuming aromatics (BTX) as the primary product and the sale of olefins contributing to co-products revenue, we predicted that the BTX product derived from pyrolysis of mixed plastics can be cost-competitive with fossil-derived BTX, particularly if the mixed waste plastics feedstock is available for less or if crude oil prices are high. Additionally, the pyrolysis of waste plastics can reduce total supply chain energy (SCE) use by 75-85% and greenhouse gas (GHG) emissions by 21-58% per kg of BTX, relative to the virgin manufacturing of BTX. Further, we investigate additional scenarios wherein different products such as naphtha and olefins are produced. In all these cases, we observed that feedstock, co-products, downstream capital, and operating costs are some of the key factors that have a substantial economic and environmental impact. Similarly for gasification, two separate pathways that convert mixed plastic waste to methanol and hydrogen are studied. For reference, the same products were also assumed to be produced by a more contaminated municipal solid waste. Again, we observed that a very low waste plastic feedstock price can help the mixed plastic waste-based processes to achieve cost-parity with existing fossil-fuel-derived pathways. Methanol and hydrogen produced from mixed plastic waste gasification can reduce the total SCE use by 59-64%, but the GHG emissions increased by more than 67%. Overall, this work identifies the critical variables and their relative impact on the cost and GHG emissions by pyrolysis and gasification pathways, which can guide future research in these domains.

Techno-economic and life-cycle analysis of mixed plastic waste via pyrolysis and gasification

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