Catalytic pyrolysis of polyethylene terephthalate over zeolite catalyst: Characteristics of coke and the products

Polyethylene terephthalate (PET) is highly used in the packaging industry, which triggered the pile-up of a huge amount of waste in the environment. Catalytic pyrolysis can convert PET waste into fuel in solid, liquid, and gaseous products. In this study, the catalytic pyrolysis of PET granules in the presence of zeolite (A4 type) was studied. The results indicated that zeolite could remarkably influence the yields, properties, and compositions of the products by affecting the secondary and primary reactions. The yields of H2 and light hydrocarbons increased in the gaseous product due to the higher rate of dehydrogenation and cracking reactions catalyzed by the zeolite catalyst. In addition, the zeolite catalyst could crack down wax and char, increasing the yields of gas and tar while simultaneously reducing the yield of acids and aromatics inside the tar. The obtained char from the catalytic pyrolysis was more aliphatic and less aromatic, but the formation of the graphite-type structure was enhanced. The coke, containing oxygen-rich aliphatic species and aromatics, deposited on the catalyst, blocked pores, and significantly reduced the activity of the catalyst. In addition, the contents of metals increased on the surface of the zeolite catalyst due to the migration of inorganics from PET.