Life cycle greenhouse gas emission assessment of pyrolysis-based chemical recycling of post-consumer waste: focus on feedstock composition, oil processing and balancing consistency

Pyrolysis-based chemical recycling (P-CR) of non-recyclable plastic containing waste to generate chemical feedstock is a developing alternative to conventional treatment options. Currently, polyolefin-rich waste fractions (MPO) are primarily targeted, which represent only a fraction of plastics in post-consumer waste and possibly compete with direct mechanical recycling. In this investigation, treatment options of residual fractions from mechanical sorting of lightweight packaging waste (LWP) in mixed polyolefins, mixed plastics and sorting residues are assessed in terms of greenhouse gas (GHG) emissions. The focus is placed on the varying composition depending on sorting plant configuration and the subsequent impact on the pyrolysis and oil processing steps, while maintaining consistency in mass, element and enthalpy balances. Applied methods include the component-specific material flow balancing of the mechanical recycling process using EASETECH and thermodynamic modelling of pyrolysis oil treatment using Aspen Plus. Results show that the application of P-CR instead of incineration with energy recovery of sorting residual fractions can potentially enable GHG reductions up to 435 kg CO2eq ton-1 LWP processed. The specific GHG reduction potential by CR application of different fractions varies between 0.74 and 1.33 kg CO2eq kg-1 fraction, while the respective sorting yield determines the total reduction potential. Mechanical recycling is shown to be superior to chemical recycling under all circumstances if applicable, including for recovered MPO fractions. Sensitivity analysis reveals critical process balancing parameters, including the electricity mix, substitution factors for mechanical recycling, energy efficiency of waste incineration and oil treatment hydrogen demand.