Maximizing light olefins and aromatics as high value base chemicals via single step catalytic conversion of plastic waste

• Testing of steam-treated FCC catalysts and HZSM-5 additives, and a commercial E-Cat. • Steaming reduced activity and required high catalyst/feed ratios. • In-line cracking of LDPE and mixed polyolefins pyrolysis vapors. • 60–70% C 2 –C 4 olefins, 10–20% aromatics, and 10–20% C 5 –C 11 aliphatics produced. • Reduced coking propensity of steamed catalyst decreased deactivation rate. Chemical recycling of plastic waste via thermochemical processes is essential to move to a carbo-circular economy, reducing our dependence of fossil resources. However, recovering monomers from polyolefins in one or multiple steps is challenging due to their chemical inertness. In the present work, a tandem micro-pyrolyzer coupled to comprehensive two-dimensional gas chromatography and FID/ToF-MS detectors was utilized to study the performance of industrial formulations of steam-treated FCC catalysts and HZSM-5 additives for the in-line catalytic upgrading of polyolefin pyrolysis products towards light olefins and aromatics in two steps. When upgrading pyrolysis vapors from LDPE over the steam-treated catalysts at 600 °C, CH 4 yields did not exceed 0.5 wt% due to their low acidity. The FCC catalyst formulations obtained higher yields of C 5 -C 11 aliphatics (up to 42 wt%) and were more active in converting C 12 + products than the HZSM-5-containing additives. The highest C 2 -C 4 olefin selectivity of 53 wt% was obtained using a bare steam-treated HZSM-5 additive. With this catalyst, at higher catalyst loading and temperature (700 °C), the light olefin yield reached 69 wt% (19% ethylene, 22% propylene, 10% 1,3-butadiene, and 18% other C 4 olefins). Importantly, similar yields of light olefins with even higher propylene yields of 31 wt% were obtained when processing real post-consumer mixed polyolefin waste. An adjusted loading of unsteamed catalyst (to obtain a similar level of initial conversion of C 12 + products) showed higher coking propensity and deactivated more rapidly than its steam-treated version. The research results show great potential for the pyrolysis of mixed polyolefin waste followed by the direct in-line upgrading of the pyrolysis vapors to produce high value base chemicals such as C 2 -C 4 olefins, aromatics, and naphtha-range aliphatics at high selectivity while limiting formation of coke, CH 4 , and H 2 .