Catalytic Pyrolysis of Polyethylene Terephthalate and Its Copyrolysis with Polyethylene

Polyethylene terephthalate (PET) is one of the most abundant municipal polymer waste due to its widespread use in plastic industry. Therefore, its catalytic recycling into valuable products is of great interest. This study aims to achieve catalytic pyrolysis of PET into useful hydrocarbons. The pyrolysis of PET was carried out in the presence of aluminum in the temperature range of 450-650 degrees C using a batch steel reactor, which resulted in wax, pyro-gases, and coke. The amount of wax was maximum at 500 degrees C, whereas higher temperature favored formation of pyro-gases; however, pyrolysis oil formation was not observed. The gas chromatography mass spectrometric (GC-MS) analysis revealed that PET was degraded mainly into benzene derivatives through random scission of ester linkages. Knowing this fact, PET was copyrolized with polyethylene (which is readily convertible to pyrolysis oil) so as to increase aromatic hydrocarbons in pyrolysis oil by the interaction of degradation fragments of both polymers. The copyrolysis resulted in aromatics in the pyrolysis oil, which were further increased by the application of aluminum catalyst. Long chain paraffins were predominant in thermal pyrolysis oil with relatively higher amounts of carboxylic acids, alcohols, and ketones, which rendered the fuel heavier and acidic. In contrast, the catalytic pyrolysis oil contained lighter hydrocarbons with lower amount of acidic and oxygenated compounds, which could be attributed to enhanced scission and deoxygenation reactions by aluminum catalyst. The catalytic process also increased isoparaffins, olefins, and naphthenes in pyrolysis oil. These functionalities could further improve the fuel quality and combustion properties of pyrolysis oil. These findings have broader implications in terms of producing better fuel from waste plastics with the desirable fuel properties, as well as their mitigation from the environment.