Physicochemical Properties of Mechanochemical Activated HZSM-5 Zeolite for Thermocatalytic Pyrolysis of Polypropylene

In this work, we explore a mechanochemical approach using ball milling to synthesize hierarchical HZSM-5 zeolites, eliminating the need for hydrothermal processing. The synthesis was conducted using dual organic templates, cetyltrimethylammonium bromide (CTMABr), and tetrapropylammonium bromide (TPABr), under varying conditions of milling time, rotational speed, and solvent presence. The aim was to investigate the structural evolution of ZSM-5 under mechanical activation while avoiding amorphization. Characterization techniques including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and nitrogen physisorption revealed that even five minute of milling induced significant modifications in the chemical structure and morphology. These changes involved recrystallization processes and the formation of new Si-O and - Al-O- bonds, resulting in restructured pore environments that may influence catalytic behavior. The best HZSM-5 sample mechanochemically activated was evaluated in the thermocatalytic pyrolysis of polypropylene at 475 °C in a fixed-bed reactor, under nitrogen as a gas carrier. After 30 min of reaction, the products were collected and analyzed by coupled gas chromatography and mass spectrometry. The catalyst demonstrated high selectivity toward monoaromatic hydrocarbons in the C₇-C₉ range, particularly alkylbenzene, toluene, xylene, and ethylbenzene. These results suggest a synergistic effect between the enhanced porosity and retained acidity of the modified zeolite, offering a promising route for the valorization of plastic waste into valuable hydrocarbons.