Catalytic pyrolysis of saturated hydrocarbon plastics over fluorinated gamma-alumina towards the production of liquid fuels

Plastic pollution has escalated into a dire threat to the environment, prompting an urgent need for improved plastic waste management. Pyrolysis is among the fastest-developing technologies for converting certain waste plastics into fuels and chemicals. In this work, we studied fluorinated γ-alumina as a catalyst for the two plastics with the highest global production volumes: high-density polyethylene (HDPE) and polypropylene (PP). Catalysts with varying fluorine loadings (0, 2, 4, 8, and 20 wt%) were readily prepared by partial fluorination of γ-alumina with aqueous NH₄F. Pyrolysis experiments were conducted in a stainless-steel batch reactor at 420 °C for HDPE and 370 °C for PP. The resulting crude pyrolysis oils were separated by distillation into two distillate fractions (bp. RT–200 °C and 200–300 °C), and the bottom product. Compared to thermal pyrolysis, catalytic pyrolysis promoted more extensive fragmentation and significantly increased volatile yields (gases and distillates), reaching 84% for HDPE and over 90% for PP. It also reduced the minimum temperatures required to obtain fully liquid crude pyrolysis oils, from 420 °C to 380 °C for HDPE and from 370 °C to 340 °C for PP. • F-doped γ-alumina (0–20% F) was tested for HDPE and PP pyrolysis. • 20% F-doped γ-alumina increased volatile yields to 84% (HDPE) and > 90% (PP). • All pyrolysis processes required low catalyst loadings (2.4 w /w%). • NMR and GC–MS confirm enhanced polymer chain fragmentation in catalytic pyrolysis. • F-doped γ-alumina lowers the minimum temperature required for fully liquid oil.