Pyrolysis of mixed contaminated plastic wastes: Assessing the influence of polymers composition, temperature and residence time

The European Union’s recycling objectives of 50 % for packaging by 2025 and 55 % by 2030 are still far from the current recycling rate of 37.8 %. Thermochemical recycling via pyrolysis might improve recovery rates, especially for challenging post-consumer dirty and contaminated plastics. Many studies focus on the pyrolysis of virgin plastics and artificial mixtures of these plastics to simulate real-world mixed plastic waste scenarios. This study examines a sample of pre-sorting waste from an Italian composting plant to represent real plastic mixtures within the collection chain. This waste contains plastics, organics, paper, and others, with plastics making up 72.18 % of the sample, primarily identified as LDPE, PP, and HDPE. The plastics were tested individually and as a mixture, mirroring the concentrations observed within the original sample, in a bench-scale semi-batch reactor at varying temperatures (420 °C, 470 °C, and 520 °C) and residence times. The analysis indicated that temperature and residence time considerably influence product yields and composition, although temperature has a more dominant effect. Wax analysis showed paraffins and olefins as the primary components, with a peak carbon number distribution in the C₁₄-C₁₉ range at elevated temperatures. Contaminant analysis of wax identified substantial levels of halogens and metals, posing challenges for downstream processes. Results from the mixture tests revealed that the product yields of individual polymers could be predicted as a linear combination of their behaviors, with an accuracy within a 10 % margin of error across the examined temperature range and lower residence times.