Determination of the Thermodynamic Parameters of the Pyrolysis Process of Post-Consumption Thermoplastics by Non-Isothermal Thermogravimetric Analysis

Abstract

Currently, the pyrolysis process is an important technology for the final treatment of plastic waste worldwide. For this reason, knowing in detail the chemical process and the thermodynamics that accompany cracking reactions is of utmost importance. The present study aims to determine the thermodynamic parameters of the degradation process of conventional thermoplastics (polystyrene (PS), polyethylene terephthalate (PET), high-density polyethylene (HDPE), polypropylene (PP) and polyvinyl chloride (PVC)) from the study of their chemical kinetics by thermogravimetric analysis (TG). Non-isothermal thermogravimetry was performed at three heating rates from room temperature to 550 °C with an inert nitrogen atmosphere with a flow of 20 mL min−1. Once the TG data is obtained, an analysis is carried out with the isoconversional models of Friedman (FR), Kissinger-Akahira-Sunose (KAS), and Flynn-Wall-Ozawa (FWO) in order to determine the one that best fits the experimental data, and with this, the calculation of the activation energy and the pre-exponential factor is performed. The validation of the model was carried out using the correlation factor, determining that the KAS model is the one that best adjusts for the post-consumer thermoplastic degradation process at the three heating rates. With the use of the kinetic parameters, the variation of the Gibbs free energy is determined in each of the cases, where it is necessary that for structures containing aromatic groups a lower energy is presented, which implies a relative ease of degradation compared to the linear structures.

Synthesis and Application of ZSM-5 Catalyst Supported with Zinc and/or Nickel in the Conversion of Pyrolytic Gases from Recycled Polypropylene and Polystyrene Mixtures under Hydrogen Atmosphere

“…The PS spectrum ( Figure 2 b) presents three groups of absorption bands, which shows the multiple tension movements of the C-H bonds at 2700–3000 cm −1 , C-C at 1400–1600 cm −1 , of the aromatic ring and a bending movement of -CH 2 and tensions of aromatic rings between 700–800 cm −1 . In addition, both spectra obtained coincide with the results obtained in other works reported in the literature [ 6 ].…”

“…Pyrolysis involves the high-temperature anaerobic decomposition of plastic waste with or without the presence of a catalyst to obtain biofuels with high calorific values comparable to commercial fuels, generating the development of a circular economy [ 5 ]. Moreover, this process has the potential to reduce the carbon footprint of plastic products by reducing carbon dioxide and carbon monoxide emissions [ 6 ]. Previous works investigating thermal [ 7 , 8 ] and catalytic [ 9 ] pyrolysis have shown its potential, as well as the optimal operating conditions for the recovery of cleaner energy from plastic waste [ 6 , 10 ] or specific mixtures [ 7 ].…”

“…Moreover, this process has the potential to reduce the carbon footprint of plastic products by reducing carbon dioxide and carbon monoxide emissions [ 6 ]. Previous works investigating thermal [ 7 , 8 ] and catalytic [ 9 ] pyrolysis have shown its potential, as well as the optimal operating conditions for the recovery of cleaner energy from plastic waste [ 6 , 10 ] or specific mixtures [ 7 ]. However, there is currently great interest, especially in catalytic pyrolysis, due to its great advantages, which include the following: (i) it accelerates the reaction rate of the process, allowing a greater depolymerization of the raw material; (ii) it reduces the energy necessary for the degradation of plastic waste; and (iii) it provides greater selectivity to obtain higher-quality pyrolytic products [ 11 ].…”

Thermal degradation of virgin and waste plastics: Estimation of kinetic and thermodynamic parameters using model‐free iso‐conversional methods

“…Negative average values of entropy change, ΔS * , were observed for all virgin, waste and mixed plastics (Table 7), indicating that the activated complex formed through bond dissociation was more ordered (lower entropy) than the initial reactant 60 . Similar negative values of ΔS were reported by other researchers for plastic waste mixtures, 62 PP and PVC 63 and PET 64 …”

“…11,28,[58][59][60][61] Negative average values of entropy change, ΔS*, were observed for all virgin, waste and mixed plastics (Table 7), indicating that the activated complex formed through bond dissociation was more ordered (lower entropy) than the initial reactant. 60 Similar negative values of ΔS were reported by other researchers for plastic waste mixtures, 62 PP and PVC 63 and PET. 64 The effect of conversion on the thermodynamic properties, estimated by Vyazovkin method at the heating rate of 10 • C min −1 , was investigated for all seven samples (Table 9).…”