Impact of Nitrogen and Other Heteroatoms on Catalytic Cracking of Crude Waste Plastic Pyrolysis Oil for Light-Olefin Production

Waste plastic pyrolysis oil (WPPO), a feasible alternative to crude oil, is an important enabler of circular plastic economy. However, the types and levels of impurities in WPPO are distinct from those in crude oil and pose significant challenges for the direct utilization of WPPO in refining and petrochemical processes. A systematic investigation of the impact of these impurities on the catalytic cracking of WPPO over a microspherical phosphorus-modified steamed ZSM5 catalyst, with an emphasis on the production of light olefins, is reported. Under the tested conditions, sulfur-, chlorine-, and oxygen-containing compounds minimally affect the yield of C 2 –C 4 olefins. In contrast, nitrogen-containing compounds cause severe catalytic deactivation in the following order: 2-methylpyridine > pyridine > quinoline > pyrrole > benzonitrile. Notably, the introduction of 2200 ppm 2-methylpyridine into WPPO significantly lowers the total yield of C 2 –C 4 olefins and BTXs from 68.7 to 55.7 wt %. Although the poisoning effect is generally correlated with the proton affinity (PA) of the nitrogen-containing compounds, the PA alone cannot sufficiently explain the observed deactivation trend. Machine-learning potential calculations identified site-dependent steric hindrance as another factor that affects the adsorption energy of these compounds. Furthermore, nitrogen poisoning proves to be both concentration- and temperature-dependent. Higher nitrogen concentrations intensify deactivation, whereas elevated temperatures mitigate this effect. Coke deposition causes a gradual decline in the light-olefin yield; however, the catalytic activity is fully restored after regeneration. These findings highlight the feasibility of employing a circulating fluidized bed reactor with continuous regeneration for the industrially viable large-scale catalytic cracking of WPPO, even in the presence of high levels of diverse impurities.