Thermo-Kinetics of Chemical Recycling of Real-World Waste Plastics

An enormous amount of plastic waste is engendered diurnal, and its severe environmental impacts prompted the development of an apt recycling methodology. In this view, an environmentally friendly and commercially feasible way of utilizing waste plastics for producing useful products requires a comprehensive understanding of their thermal splintering. Therefore, we evaluate the kinetics and thermodynamics of the thermal breakdown (pyrolysis) of real-world waste plastics (majorly composed of polyolefins) like mixed waste plastics, packaging plastic bag waste, personal protective equipment kit waste, and milk pouch waste obtained from the local dumping sites. For this, these waste plastics are cracked at multiple heating rates of 5, 10, and 20 °C min–1 in an inert atmosphere. Besides, the thermogravimetric analyses and iso-conversional models are employed to evaluate the essential thermo-kinetics. The average activation energy of the concerned waste plastics samples ranges between 112.97 and 170.16 kJ mol–1. Besides, the thermodynamic parameters like Gibbs free energy, enthalpy, and entropy lie in the ranges of 226.4 to 229.6, 113.3 to 163.7, and −0.085 to −0.14 kJ mol–1, respectively, for the concerned waste plastic samples. The cracking kinetic analysis confirmed that the mixed waste plastics consume significantly higher energy than the other types of waste plastics to initiate the thermal breakdown reaction. Besides, the model of Flynn–Wall–Ozawa has closely predicted the experimental data than the models of Kissinger–Akahira–Sunose and Starink, due to its rigorousness. This thermo-kinetic investigation can contribute towards comprehensive understanding and utilization of waste plastics collected from actual dumping sites for optimizing the real-time reaction devices and producing useful petrochemical products like diesel, gasoline, benzene, toluene, and xylene in an eco-friendly and sustainable way.