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 (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 Ea and lnA during the plastic waste pyrolysis.
Highlights
Once touted as a 'material of a thousand uses', plastic meets our demand across various sectors and has become an essential part of daily life (Rahimi and García, 2017)
The kinetic parameters calculated using the KAS method displayed a similar trend to those from the Friedman method, they were smaller than the latter (Figure 4)
Based on the TG analysis, the activation energy and linear correlation coefficient were determined at different conversion rates using four model-free methods
Summary
Once touted as a 'material of a thousand uses', plastic meets our demand across various sectors and has become an essential part of daily life (Rahimi and García, 2017). Concomitant with usage, the worldwide generation of plastic waste is rapidly increasing and the amount produced since 2015 is estimated to be 6300 Mt. only 9% of this waste has been recycled and 79% has accumulated in landfill sites or has been dumped in the natural environment (Geyer et al, 2017). It is well known that traditional plastics are difficult to decompose and the disposal of plastic waste poses a long-term threat to the natural environment. In order to tackle the plastic disposal problem, the development of alternative recycling or treatment technologies for them is mandatory. Traditional landfilling offers an inexpensive solution for the solid waste, but it will take up land resources and waste the energy intrinsic in plastics (Li et al., 2014). There are drawbacks to recent recycling methods, such as mechanical separation, pelleting and regeneration, attributed to their high labor cost and water contamination (Datta and Kopczyńska, 2016; Deng et al, 2017; Hamad et al, 2013)
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