Petrochemical feedstock from pyrolysis of waste polyethylene and polypropylene using different catalysts

In this work, thermal and catalytic pyrolysis of urban plastic waste composed of a mixture of polyethylene (PE) and polypropylene (PP) was studied. The catalysts investigated were HZSM-5, USY, NH4ZSM-5 (ZSM-5 in ammonium form), and their corresponding alkaline-treated (BHZSM-5, BUSY, and BNH4ZSM-5) or acid-leached (LHZSM-5, LUSY, and LNH4ZSM-5) forms. The catalytic pyrolysis using BHZSM-5 (ZSM-5 in alkaline form), USY, BUSY, and NH4ZSM-5 resulted in higher amounts of liquid fraction, which was composed of alkylbenzenes, naphthalenes, and olefins. Acid leaching of zeolite NH4ZSM-5 increased both the specific area and the mesopore volume, allowing an increase in the liquid and gas fractions, and a reduction in the solid fraction. BHZSM-5 zeolite showed the best catalytic performance for the production of a high amount of liquid fraction, which was virtually composed of olefinic hydrocarbons without the formation of solid products. Moreover, BNH4ZSM-5 zeolite (alkaline-treated NH4ZSM-5) was a good pyrolysis catalyst also due to its high specific area and pore volume, resulting in higher gas formation in comparison with the liquid fraction (composed mostly of alkylbenzenes), and almost no solid fraction.