Selective Production of Diesel-Range Hydrocarbons from Catalytic Pyrolysis of Polypropylene Waste Using Modified Natural Zeolites: Interplay of Acidity, Temperature, and Reaction Parameters.

In the context of this study, it is investigated whether catalytic pyrolysis of post-consumer polypropylene might prove an interesting route to the generation of liquid hydrocarbon materials from plastic waste. The optimum product selectivity can be achieved using the appropriate catalyst. To address this problem, we tested three altered natural zeolites as follows: H-ZN, AT-ZN, and AA-ZN, according to a factorial design which accounts for temperature (400-500 °C), heating rate (10-20 °C per minute), and catalyst loading (5-10 percent by weight). Initially, we verified by thermogravimetric and micro-Raman analyses the thermal behavior of the catalytic systems and the consistency of the polypropylene feedstock. This work confirms that the catalyst assists in initiating the chain-scission process, as changes to the zeolites are responsible for the breakdown of polypropylene at a lower temperature. H-ZN showed high liquid recovery (75.4 wt%), particularly under moderate conditions, as confirmed by product-yield analysis. On the other hand, AT-ZN was more conducive to gas formation and light-fraction production at higher temperatures. H-ZN kept the diesel-range fraction (C12-C20) stable nearly to 51%, according to GC-MS; AT-ZN shifted selectivity to gasoline-range hydrocarbons (C6-C11), up to 57% under severe conditions. AA-ZN showed intermediate behavior. The overall conversion and molecular profile of the liquid products were influenced not only by catalyst acidity, temperature, and their interactions but also by Pearson correlation and ANOVA. The results described above indicate that H-ZN is the most promising catalyst for selective polypropylene-to-diesel conversion and prove that modified natural zeolites are an inexpensive and scalable method for valorizing plastic waste in a circular economy.