Kinetic Study of Plastic Waste Pyrolysis Reactions

Camila Geirinhas Cameira

Key information

Authors:

Camila Geirinhas Cameira (Camila Geirinhas Cameira)

Supervisors:

Kevin Van Geem; Maria Amélia Nortadas Duarte de Almeida Lemos (Maria Amélia Nortadas Duarte de Almeida Lemos)

Published in

09/21/2021

Abstract

The study of plastic waste degradation is more than a trending topic, it is necessary to advance the knowledge and technologies to allow for proper treatment and handling of this type of waste in a more efficient way, leading to its valorization in a circular economy approach. Chemical recycling shows a promising route, through pyrolysis and gasification processes. The difficulty in accurately identifying feed composition constitutes a major problem, as it is complicated to predict the outcome of these processes, hence a better way of dealing with this is needed. This work investigated one of the most recently developed/improved detailed kinetic modeling for four hydrocarbons with different chain lengths. The results were validated against experimental data obtained in the literature and the effect of chain length was assessed. Moreover, a thorough analysis of the product and radical distributions was performed clarifying the effect of each reaction family considered. By creating an elemental virtual framework, gas-phase pyrolysis was simulated in a discontinuous reactor, with a fixed volume and adiabatic conditions. All reactants showed a marked preponderance to form light chain molecules, mainly ethylene and methane, primarily produced through beta scission and homolytic scission reactions. Isomerization reactions are responsible for a more uniform production of radicals while many are also formed by H-abstraction which subsequently suffer beta scission. The mechanism, modeled as a 40-carbon atom hydrocarbon, tetracontane, can correctly describe the experimental results for HDPE thermal decomposition, despite substantial improvements needed regarding its complex chemistry and kinetics parameters in future developments.