Recycling waste polyethylene into fuels over Fe/USY catalyst: Evaluation on the catalytic activities of varied iron states

Abstract

Iron-modified zeolite catalyst has a good application prospect on recycling the waste plastics into value-added fuels via catalytic pyrolysis. Distinguishing the catalytic activities of varied iron states on catalyst is crucial to catalyst designation and plastic-to-fuel process. In this work, we prepared three Fe/USY catalysts, termed Fe(O-550)/USY, Fe(R-300)/USY and Fe(R-450)/USY, that contain different iron states – Fe2O3, Fe3O4 + Fe (dominantly) and Fe respectively, and investigated their catalytic activities in polyethylene pyrolysis for fuel oils. The results show that loading of the iron species on USY zeolite decreases the catalyst acidity. H2 reduction treatment in catalyst preparation has no significant influence on the total acidity but slightly changes the concentration of Brønsted and Lewis acid sites. The oil yield after catalysis with different catalysts follows the order: Fe(O-550)/USY (72.5 %) > Fe(R-300)/USY (69.9 %) > Fe(R-450)/USY (66.7 %) > USY (56.5 %). The oil includes a mixture of C6-C34 compounds especially abundant in C6-C10. It is mainly in gasoline and diesel range and consists of alkanes as majority. Generally, loading of the iron species on USY zeolite increases the oil yield and produces lighter oil and more aromatics and alkenes, while the Fe(R-450)/USY shows higher catalytic cracking activity than Fe(O-550)/USY, Fe(R-300)/USY and USY catalysts. Among the varied iron states, the metallic iron is more active than the other iron oxides to promote the catalytic cracking of PE to produce fuel oil, especially the light oil and aromatic fractions.