Tuning carbon-number selectivity in catalytic pyrolysis of polypropylene face masks via Ni- and Ni-W-modified ZSM-5

Disposable polypropylene (PP) face masks constitute a persistent waste stream that is poorly suited to mechanical recycling. Catalytic pyrolysis over ZSM-5 is a widely studied route for converting PP-derived vapors into fuel- and chemical-range hydrocarbons, yet the effects of bifunctional metal/acid zeolite modification on condensed-oil composition remain less explored for mask-derived feedstocks. In this study, ZSM-5 (SiO 2 /Al 2 O 3 = 38) was modified with Ni and Ni W by wet impregnation and evaluated for catalytic pyrolysis of three-ply PP masks in a semi-batch fixed-bed reactor at 475 °C. Condensed oils were characterized by GC–MS/FID, density, and viscosity at 20 °C. Relative to parent ZSM-5, Ni/ZSM-5 shifted the recovered liquid product toward a C 8 maximum and increased the relative abundance of C 7 –C 9 monoaromatics, yielding an oil with lower density (0.809 g mL −1 ) and the lowest kinematic viscosity (0.778 mm 2 /s). In contrast, Ni-W/ZSM-5 produced a less aromatic condensed oil with a pronounced C 9 maximum, reduced heavy fractions, and the lowest density (0.782 g mL −1 ). These results show that Ni and Ni W modification of ZSM-5 can induce modest shifts in condensed-oil composition under the tested conditions.