Impact of inorganic plastic additives on zeolite-catalyzed chemical recycling of polyolefin

Abstract: Chemical recycling of waste plastics into naphtha-range hydrocarbons is a promising route toward a circular carbon economy. Zeolite-catalyzed degradation enables selective formation of light hydrocarbons suitable for existing naphtha crackers; however, post-consumer plastics contain inorganic additives that may deactivate catalysts. The effects of such additives under realistic recycling conditions remain poorly understood. Here, we investigate the impact of inorganic additives in real polyolefin wastes on zeolite-catalyzed degradation in a hydrocarbon solvent, focusing on calcium carbonate and talc. Catalytic degradation experiments were carried out in a batch reactor using a hydrocarbon solvent to ensure sufficient fluidity of molten plastics and effective contact with the catalyst. Typically, 5 g of plastic sample and 20 g of solvent were charged into the reactor together with 0.25 g of an acid-type Beta zeolite catalyst. For comparison, thermal degradation experiments were conducted under identical conditions without the catalyst. After purging the reactor with nitrogen, the system was heated at a rate of 10 oC min-1 to 400 oC and maintained at this temperature for 60 min. Upon completion of the reaction, the reactor was cooled to room temperature. Gaseous products were collected, and the liquid and solid phases were separated by filtration. Polymer conversion was determined gravimetrically from the remaining solid residue. Additives were identified by XRD and ICP-OES, product distributions were analyzed by GC-FID, and catalyst acidity was evaluated by NH3-TPD. Calcium carbonate–containing plastics wastes showed a strong suppression of naphtha-range (C3–C9) oning via Ca2+ leaching and ion exchange with zeolite acid sites. In contrast, talc-containing plastics exhibited only minor reductions in light hydrocarbon yields, and the zeolite retained its acidity, suggesting that Mg species in talc remain structurally stable and do not participate in ion exchange. These results demonstrate that inorganic additives exert highly additive-specific effects on zeolite-catalyzed chemical recycling. Avoiding catalyst-poisoning fillers such as calcium carbonate, or replacing them with benign mineral additives like talc, is crucial for efficient and selective plastic chemical recycling from a green chemistry perspective.