Study of the catalytic decomposition of polyethylene terephthalate (PET) using zeolitic catalysts with hierarchical pore structures

Abstract

The increasing production of plastic waste, especially polyethylene terephthalate (PET), has become a problem, since almost all plastics are produced from petroleum-derived chemicals and are difficult to degrade. In order to minimize this problem, the thermocatalytic degradation of PET was studied using HZSM-12 zeolite catalysts with hierarchical pore structures. The hierarchization of the HZSM-12 zeolite into two levels, HZSM-12(H1) and HZSM-12(H2), was performed by means of an alkaline treatment. The catalysts were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and nitrogen adsorption/desorption at 77 K. The study of the catalytic decomposition of PET was carried out via thermogravimetry with heating rates of 5, 10 and 20 ºC.min^-1, using mixtures of a pulverized commercial plastic container (PET bottle) and the zeolites HZSM-12, HZSM-12(H1) and HZSM-12(H2), in a mass proportion of 30% zeolite and 70% PET. The results indicate that the presence of zeolite catalysts in the PET pyrolysis reactions caused a significant reduction in the initial temperatures of polymer degradation. The activation energy for PET pyrolysis was determined by the Vyazovkin and Goryachko method. The presence of zeolites in general caused a decrease in the activation energy for PET decomposition in relation to pure PET, with the HZSM-12(H1) sample presenting better results with the reduction of the energy required for the PET degradation process.