Thermal decomposition of polyolefins under different oxygen content. Kinetic parameters evaluation

In the study, new kinetic models of pyrolysis and gasification of polyethylene and polypropylene in gaseous nitrogen with oxygen content of 0, 1, 2, 4, 10, and 21%vol were analyzed. It has been shown that the optimal way to describe the decomposition process of polyolefins is to use a model of two simultaneous chemical reactions, homolytic and heterolytic dissociations, characterized by noticeably different activation energies. A fit of the model to experimental data expressed as R2 was greater than 0.99999, which is better than values known from the literature. The validity of the proposed two-reaction model was demonstrated by analyzing the composition of released gases using a gas chromatograph equipped with a highly sensitive helium discharge detector for hydrogen and CxHy. In particular, it is clear that the release of certain gaseous products, such as H2 and unsaturated hydrocarbons, corresponds to the mechanism of heterolytic dissociation, while the release of saturated hydrocarbons is consistent with the mechanism of homolytic dissociation of covalent bonds in polymer molecules. It is noticeable that different groups of gas components are released in different temperature ranges, in accordance with the dynamics of the reactions used in the two-reaction kinetic model.