Development of a microwave thermogravimetric analyzer and its application on polystyrene microwave pyrolysis kinetics

Abstract

To study pyrolysis kinetics inside a microwave environment, a microwave thermogravimetric analyzer was developed. A sample mass as low as 0.3 g can be studied along with silicon carbide as the microwave receptor. The temperature is measured with a custom-made infrared thermopile equipped with different optical filters specific to this application. Validation of the microwave thermogravimetric analyzer features showed that the measured data can be used as is for kinetic development. Different heating profiles can be achieved by modulating the microwave power. The microwave thermogravimetric analyzer was then used for the kinetic development of polystyrene microwave pyrolysis. Polystyrene was chosen because of its low recycling rate and its great potential to produce high-valued products, like styrene. Three heating rates (24.5, 38.5 and 49.5 °C min−1) were used to estimate the kinetic parameters. By comparing several reaction models, a random scission model was found to best explain the experimental data. The choice of the reaction model was made based on two statistical tests: the coefficient of determination R2 and the residual sum of squares RSS. With this reaction model, an activation energy of E = 45 kJ mol−1 and a pre-exponential constant of ln(A) = 3.6 were found for polystyrene microwave pyrolysis.