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

Abstract

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 ( Ea) 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 Eα 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 Eα 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 Eα values to those obtained from the Flynn–Wall–Ozawa method. The pre-exponential factors (ln A) 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 Ea and ln A during the plastic waste pyrolysis.

Pyrolysis kinetic modelling of abundant plastic waste (PET) and in-situ emission monitoring

“…3b. The results herein are lower than those reported by Yao et al [36], who reported 184-269 kJ mol −1 . This is maybe due to the fact that they did not specify the plastic waste that they used along with the high heating rates used (15,25, and 35 °C min −1 ).…”

Pyrolysis kinetic modelling of abundant plastic waste (PET) and in-situ emissions monitoring

“…While the Flynn-Wall and Ozawa (FWO) method (Equation 4) showed a variation of E a during the reaction progress in the range of 166-180 kJ.mol -1 as shown in Figure 3 (b). The results herein are lower than that reported by Yao et al [36], who reported 184-269 kJ.mol -1 . This is maybe due to the fact that they did not specify the plastic waste that they used along with the high heating rates used (15, 25 and 35 °C.min -1 ).…”

Pyrolysis kinetic modelling of abundant plastic waste (PET) and in-situ emissions monitoring

“…This in agreement with the Ea value reported by Saha and Ghoshal which was 162.15 kJ.mol -1 using the ASTM-E698 method[38].While the Flynn-Wall and Ozawa (FWO) method (Equation 4) showed a variation of Ea during the reaction progress in the range of 166-180 kJ.mol -1 as shown inFigure 4 (b). The results herein are lower than that reported by Yao et al[39], who reported 184-269 kJ.mol -1 . This is maybe due to the fact that they did not specify the plastic waste that they used along with the high heating rates used (15, 25 and 35 °C.min-1 ).…”