Kinetic studies on the pyrolysis of plastic waste using a combination of model-fitting and model-free methods

In this work, the pyrolysis behavior of plastic waste-TV plastic shell-was investigated, based on thermogravimetric analysis and using a combination of model-fitting and model-free methods. The possible reaction mechanism and kinetic compensation effects were also examined. Thermogravimetric analysis indicated that the decomposition of plastic waste in a helium atmosphere can be divided into three stages: the minor loss stage (20-300°C), the major loss stage (300-500°C) and the stable loss stage (500-1000°C). The corresponding weight loss at three different heating rates of 15, 25 and 35 K/min were determined to be 2.80-3.02%, 94.45-95.11% and 0.04-0.16%, respectively. The activation energy (E_a) and correlation coefficient (R²) profiles revealed that the kinetic parameters calculated using the Friedman and Kissinger-Akahira-Sunose method displayed a similar trend. The values from the Flynn-Wall-Ozawa and Starink methods were comparable, although the former gave higher R² values. The E_α values gradually decreased from 269.75 kJ/mol to 184.18 kJ/mol as the degree of conversion (α) increased from 0.1 to 0.8. Beyond this range, the E_α slightly increased to 211.31 kJ/mol. The model-fitting method of Coats-Redfern was used to predict the possible reaction mechanism, for which the first-order model resulted in higher R² values than and comparable E_α values to those obtained from the Flynn-Wall-Ozawa method. The pre-exponential factors (lnA) were calculated based on the F1 reaction model and the Flynn-Wall-Ozawa method, and fell in the range 59.34-48.05. The study of the kinetic compensation effect confirmed that a compensation effect existed between E_a and lnA during the plastic waste pyrolysis.