In this article, the results of the application of several catalysts, including zeolites (i.e., ZSM-5, HY, USY and Hβ), an equilibrium fluid cracking catalyst (FCC E-cat) and other acid aluminosilicates such as MCM-41 or natural clay, in the pyrolysis and in the thermal oxidation of different polymers and copolymers (PE, PP and EVA) is studied. The relation between the structural characteristics of the catalysts and their activity is illustrated, and the good behaviour of the materials with higher pore sizes, higher external surfaces and with higher number and stronger acid sites is showed. The obtained results reveal the importance of  the accessibility of the polymer molecules to the active sites in the behaviour of a given polymer + catalyst system.

 

Pyrolysis experiments with and without catalyst performed in a TG equipment at several heating rates under inert (N₂) or oxidizing (air) atmospheres showed the classical shift to higher temperatures for all processes involved when increasing the heating rate. The presence of catalyst produces a remarkable decrease of the temperature of decomposition of the studied polymers and in some cases, a saturating effect has been observed, and the addition of more catalyst does not provide any further benefit.

 

Quantitative mechanistic kinetic models which are able to predict the weight loss behaviour of the several polymer-catalyst systems studied are also suggested, and the corresponding kinetic parameters, obtained from the fit of the experimental thermogravimetric data, are presented and discussed, showing the reduction in the activation energy of the catalytic decomposition as compared to the thermal process.

 

Some aspects related to the deactivation-regeneration behaviour of the catalysts are also discussed.