Temperature and Positioning Effects of Spent Fluid Catalytic Cracking Catalyst in the Reactor on Pyrolysis of Polyethylene Terephthalate

Abstract Results are presented on the influence of positioning of spent Fluid Catalytic Cracking (FCC) catalyst and reactor temperature in pyrolyzing of waste polyethylene terephthalate (PET). The catalyst bed was modified to be directly mixed with the feedstock bed (in-situ) for a solid-solid contact or separated but kept at the same temperature so that the catalyst encountered only the volatiles released from PET (quasi in-situ). The synthesis gas (syngas) evolved from the pyrolysis of PET was analyzed and compared. For in-situ position of the catalyst at 900 °C, the syngas yield and energy yield increased by 40% and 35%, respectively, as compared to non-catalytic case at 800 °C. In contrast, they were only 20% and 13.3% for the quasi in-situ case. This suggests that PET in-situ catalytic pyrolysis is more efficient and effective than quasi in-situ pyrolysis for increased syngas yield. PET yields had low fixed carbon as shown from proximate analysis and thus its devolatilization provided only a trace amounts of char from pyrolysis. The lack of significant char formation and its possible inhibitive behavior over the catalyst surface allowed for the catalyst’s direct contact to be beneficial, unlike the inhibitive behavior observed during in-situ catalytic pyrolysis for other feedstocks that had substantial fixed carbon. The carbon conversion rates at 800 °C also increased from 44% via non-catalytic pyrolysis to 60% with in-situ catalysis, suggesting the effectiveness of the catalyst. Increase in temperature resulted in increased syngas and energy produced. Catalytic conversion resulted in ∼1 wt.% of the feedstock to thermally stable coke that resulted in plateau of overall pyrolysis gas yields with increase in temperature.