An experimental analysis of diesel fuel produced from HDPE (high-density polyethylene) waste using thermal and catalytic pyrolysis with passive heat pipe cooling system

Diesel produced from plastic waste is an attractive alternative energy source as it offers the dual benefits of satisfying the increasing global energy demand and reducing plastic waste. Pyrolysis is considered to be one of the most reliable oil conversion methods from high-density polyethylene (HDPE) waste into diesel fuel, but it requires a large amount of energy. Therefore, we propose thermal and catalytic pyrolysis methods that require a minimal amount of cooling energy to produce diesel fuel from HDPE using a passive cooling system with heat-pipes. The specific energy consumption of 44.35 Wh/g, a heating rate of 14497.85 KJ/h, and a reactor feedstock size of 2–20 mm. The oil produced through thermal pyrolysis was 61.1 wt% liquid, 1.29 wt% wax, and 37.61 wt% gas, and its density, kinematic viscosity, high heating value, and cetane index were 0.83 g/ml, 2.045 mm²/s, 0.185 MJ/kg, and 32.6, respectively. The oil produced through catalytic pyrolysis was 85 wt% liquid and 15 wt% gas, with no wax phase. Its density, kinematic viscosity, high heating value, and cetane index were 0.827 g/ml, 1.038 mm²/s, 59.57 MJ/kg, and 90, respectively. The optimal pyrolysis operating conditions were a reactor temperature of 500 °C, and liquid collection system (LCS) cooling water temperature of 20 °C. The cetane index of the catalytic pyrolysis oil was significantly higher than the corresponding standard specification for diesel. Owing to its high cetane index, the catalytic pyrolysis diesel can be combined with conventional diesel to increase its cetane index and combustion performance.