Pilot-scale production and characterization of liquid fuel from mixed non-recyclable plastics for potential...

Post-sorting non-recyclable plastic residues pose significant management challenges due to the limitations of mechanical recycling. This study demonstrates a novel, direct vacuum-assisted pilot-scale batch pyrolysis of mixed plastic rejects dominated by polypropylene (PP, ≥45 wt%), low-density polyethylene (LDPE, ≥45 wt%), polystyrene (PS, ≤5 wt%), and high-density polyethylene (HDPE, ≤5 wt%) in an insulated 1,000 L reactor without continuous inert-gas purging. Under optimized operating conditions (30 min air pre-evacuation at 15-20 kPa, 20 kg feed loading, LPG heat input at ∼25% maximum flow, and 1 h reaction at ∼450 ^°C), a high condensable liquid yield of ∼80 wt% was achieved. Comprehensive structural and compositional characterization via FTIR confirmed the pyrolytic liquid's aliphatic-rich nature, featuring strong C-H stretching vibrations (2956-2850 cm^-1), C-H bending (1455 cm^-1 and 1375 cm^-1), and unsaturated alkene C[double bond, length as m-dash]C bonds (1640 cm^-1 and 990-890 cm^-1). GC-MS analysis further revealed a carbon number distribution highly compatible with commercial heavy fuel oil, dominated by heavy (>C₁₃, 63.02% area) and middle-distillate (C₁₀-C₁₃, 23.28% area) fractions, with low total aromaticity (11.57% area in >C₁₃). Fuel-property benchmarking demonstrated a high heating value (43 115-43 500 cal g^-1) and kinematic viscosity at 50 °C (∼12 cSt) closely matching commercial furnace oil (43 619 cal g^-1 and 12 cSt), alongside environmentally advantageous ultra-low sulfur (0.0038-0.0057 wt%) and ash contents (<0.001 wt%). Washing pretreatment offered no improvement in liquid recovery while significantly increasing water and sediment content (20 vol% vs. 0.9 vol% for unwashed feed) due to trapped residual moisture. Distance-resolved air-quality monitoring confirmed rapid dispersion of particulate matter (PM_2.5: 293 → 165 → 22 µg m^-3; PM₁₀: 384 → 134 → 28 µg m^-3 at 0/5/10 m), establishing a safe operational buffer distance of ≥10 m. Overall, this single-step, direct vacuum-assisted process offers an energy-efficient, low-cost solution for converting municipal plastic waste into high-quality commercial fuel oil substitutes without requiring catalytic upgrading or post-pyrolysis distillation.