Balancing cost and quality: Multi-level modelling of sorting and pretreatment pathways for mixed plastic waste towards pyrolysis feedstock

Sorted post-household mixed plastic packaging waste requires additional treatment steps to ensure that its pyrolysis products satisfy hydrotreatment specifications. Cost and contaminant minimisation should be considered when designing a feedstock upgrading process. A Superstructure–Decision-Making (SS–DM) framework was developed to address this challenge by evaluating more than 3,000 sorting and washing sequences from a multi-level perspective. The results reveal that optimal performance is achieved with (i) a 4-step NIR-sorting cascade including NIR-cleaner(s) (high % polyolefin (PO) recovery and purity, low cost), and (ii) either cold washing with density separation or dry washing. Increasing the PET/MPO/film content while decreasing the PO content in the input decreases %PO purity, %PO recovery, and contaminant removal efficiency. In varying decision-making priorities, balancing cost and quality allows fulfilment of all constraints. Beyond decision support, SS–DM functions as a fast-track tool that generates high-resolution outputs across all units, serving as valuable inputs for pyrolysis modelling.