Storage Stability of Plastics Pyrolysis Oils from Post-Consumer Polyolefin Waste

This study investigates the influence of storage temperature and heteroatom content on the physicochemical stability and property variations of pyrolysis oils. Virgin polyolefins and commercially available pre-treated mixed polyolefin waste were pyrolyzed in a pilot-scale screw reactor. The resulting oils were stored at ambient temperature and 60 °C for up to eight weeks. Changes in their chemical composition and physical properties were monitored using GC-FID, GCxGC-MS/FID-NCD, NMR, and viscosimetry, across multiple time scales. Within the first days of storage, small amounts of a highly viscous, bitumen-like phase formed in the samples with elevated levels of heteroatoms stored at ambient temperature. No viscous phase formation was observed in the oil from virgin polymers. Pyrolysis oils showed no changes in hydrocarbon composition throughout the evaluated storage period, neither at room temperature nor at 60 °C. We therefore argue that storage stability of plastics-derived pyrolysis oils is a multifaceted phenomenon. This systematic study highlights the crucial role of heteroatom contamination in the degradation processes. These insights into the processes during storage can inform mitigation strategies against degradation. Improving the storage stability of plastics-derived pyrolysis oils represents a significant step towards the implementation of chemical recycling at industrial scale.