Kinetics and Thermodynamics of the Pyrolysis of Waste Polystyrene over Natural Clay

Abstract

Due to the massive increase in polymer manufacture, there has been a remarkable increase in plastic waste. With fewer landfills being used to dump plastic waste each year, it is becoming increasingly important to use effective recycling methods for plastic waste decomposition. In the present work, waste polystyrene was degraded in the presence of natural clay (K_0.02, Ca_0.15 [Mg_0.25, Al_0.69, Fe_0.06], [Si_2.0, Al_0.6] O_6.8 (O₁₀) nH₂O). The waste polymer was pyrolyzed at different heating rates i.e., 5, 10, 15 and 20°C min^-1 in an inert environment using nitrogen within the temperature range of 40 to 600°C. Thermogravimetric data were interpreted using various models, including fitting kinetic methods i.e., Coats-Redfern and model-free methods i.e., Ozawa-Flynn-Wall, Kissinger-Akahira-Sunose and Friedman method. The activation energy determined by Coats-Redfern, Ozawa-Flynn-Wall, Kissinger-Akahira-Sunose and Friedman models were in the range of 83.22-150.37, 74.52-133.71, 73.16-131.23, and 78.40-140.67 kJmol^-1, respectively. Among them, the lowest activation energy for polystyrene degradation was observed using Kissinger-Akahira-Sunose method. The calculated kinetic parameters would be useful in determining the reaction mechanism of the solid-state reactions in a real system.