Green energy production: hydroprocessing of waste plastic to diesel fuel using bimetal of Mn/Zn supported on activated carbon†

This research introduces a Mn/Zn-activated carbon (AC) bimetallic catalyst for hydroprocessing polypropylene pyrolysis oil (PPO) into hydroprocessed polypropylene pyrolysis oil blend (HPPO-B), which closely mimics commercial diesel. Under optimized conditions (70 bar, 350 °C), the catalyst efficiently converts PPO into iso-alkanes, n-alkanes, and aromatics, achieving a 95% compositional match with diesel. HPPO-B meets European EN590 diesel standards, with viscosity (3.9 mm² s⁻¹), density (855 kg m⁻³), and cetane index (64), ensuring compatibility with diesel engines. Combustion tests show HPPO-B exhibits peak pressure and heat release rates within 96% and 95% of diesel values, respectively. Emission analysis reveals slightly higher CO (4–9 ppm) and CO₂ (2.4–8.7%) emissions but lower unburned hydrocarbon (UHC) emissions (up to 9.5% reduction). The catalyst supports hydroisomerization, hydrogenation, aromatization, and hydrocracking, producing a fuel with a balanced iso-alkane to n-alkane ratio (2.8 : 1), similar to diesel (2.2 : 1). HPPO-B also contains 7% more aromatics, improving fuel stability. The study confirms HPPO-B can be blended with diesel up to 40% without major performance or emission compromises. This research presents a sustainable solution for plastic waste management, converting polypropylene into transport fuel and promoting hydroprocessing as an environmentally friendly approach to mitigating plastic pollution.