Isoconversional analysis of kinetic pyrolysis of virgin polystyrene and its two real-world packaging wastes

Abstract

In present work, two polystyrene packaging wastes of expanded polystyrene (EPS) foam and Yakult polystyrene milk bottle (YPS) along with pure polystyrene (PS) have been subjected to high-temperature nitrogen pyrolysis experiments under four heating rates of 5, 10, 15 and 20 K min−1. A comparison among these samples in terms of pyrolysis features and specific decomposition temperatures has been made, and EPS tends to be the most readily to undergo pyrolysis while YPS appears to be the most thermally stable. Based on thermogravimetric data, kinetic analysis has been systematically performed using various isoconversional methods. The calculations show that the activation energies calculated over the whole pyrolysis range are slightly different among the six temperature-integral methods, but the temperature-differential Friedman method has given rather distinct activation energies. The activation energies over the whole pyrolysis process are mass conversion-dependent for three samples and the activation energy averaged is the highest for YPS, followed by pure EPS and then EPS. A method combining master-plots method and differential composite method has been attempted to search the most suitable reaction models and chemical reaction order-based F0.58, F0.61 and F1.14 are found to be the most suitable reaction models for describing pyrolysis of PS, EPS and YPS, respectively. With the Coats–Redfern method, the mass-conversion curves along with its differential curves have been simulated, yielding very satisfactory performances for three polystyrene samples. In addition, thermodynamic functions such as the changes of entropy, enthalpy and Gibbs free energy during waste pyrolysis processes are also considered.