Characterization of the residue of a commingled post-consumer plastic waste treatment plant: a thermal, spectroscopic and pyrolysis kinetic study

A plastic packaging residue provided by a central Italy recycling facility was the subject of study of the present paper. The aim is to propose the valorization of plastic film residue (PFR) through a pyrolysis process. The PFR was thermo-chemically characterized through heating value, proximate and ultimate analysis. Fourier transformed infrared measurements have shown that PFR is constituted by 92–95 mass% of polyethylene (PE) film, around 5 mass% of PP, polystyrene (PS) < 1 mass%, PET < 1 mass% and traces of foreign materials. The extremely high percentage (98.7 mass%) of volatile matter and the low content of ash (2.1 mass%), humidity (0.6 mass%) and chlorine (0.1 mass%) make PFR an optimum candidate as load of a pyrolytic reactor. Thermogravimetry (TG) experiments were carried out at five different heating rates (2, 5, 7, 10, 12 K min−1) to determine the kinetic parameters of pyrolysis (activation energy E, pre-exponential factor A and the reaction model). No significant variation of activation energy, calculated by an integral isoconversional method proposed by Vyazovkin, is observed with increasing the degree of conversion. An average value of 264 ± 5 kJ mol−1 was estimated. Then, the Coats–Redfern method and the compensation effect were used to determine the lnA versus α data (being 41.9 the average value within the 0.25 < α < 0.85 range) and the reaction mechanism (R2 contracting cylinder model). Furthermore, the minimum energy required to pyrolyze 1 kg of PFR, about 2.27 MJ, was estimated by differential scanning calorimetry. It corresponds to about 5.5% of the exploitable energy of the input material.