Catalytic hydrothermal conversion of polypropylene at sub-critical conditions with Ni-supported zeolites

Hydrothermal plastic processing is a developing technology that can provide a clean pathway for plastic waste disposal. In this work, the use of catalyzed hydrothermal conversion in subrcritical conditions was evaluated with nickel impregnated zeolite catalysts. Previously, catalysis of hydrothermal conversion had scarcely been reported on polypropylene (PP) feedstock. Here we screened the activity of various nickel-based catalysts supported on zeolite, titanium oxide and magnesium oxide at 350 °C and 20.7 MPa for 1 h. At these conditions, up to 20 % gas yield was obtained, producing 215 g of C₃H₈ per kg of PP feedstock using the nickel impregnated zeolite catalyst I. Analysis of oil products showed the presence of aromatic compounds, notably p-tert-butylphenol, as well as the presence of fatty acids such as n-hexadecanoic acid in select samples. This process offers a basis for the catalytic conversion of polypropylene feedstock into gas and oil products below supercritical water conditions.