Catalytic Vapor Upgrading of Waste-Plastic Pyrolysis Products: Fuel Quality Enhancement, Engine Performance Testing, Exergy Performance, and Emission Implications

Abstract

A pilot-scale pyrolysis process was designed to produce gasoline and diesel-range fuels from waste plastic bags through pyrolysis reaction, ex-situ catalytic cracking, and staged condensation. The catalytic upgrading unit was operated at 400–440 °C and consisted of different catalysts such as ZSM-5, dolomite, or kaolin catalysts. The surface properties of the catalysts were analyzed using Brunauer–Emmett–Teller (BET) and scanning electron microscopy (SEM) techniques. The products were highly temperature-dependent, with a maximum liquid yield at 420 °C, above which secondary cracking led to increased gas yield. ZSM-5 catalysts facilitated extensive aromatization, yielding gasoline-range plastic pyrolysis oil (G-PPO) with a high heating value of 44.5 MJ kg–1 and high benzene and toluene content, while dolomite catalysts facilitated the production of stable diesel-range hydrocarbons with high cycloalkane content, whereas kaolin catalysts inhibited heavy wax production with high liquid yield. Gas chromatography mass spectrometer (GC–MS) analysis validated that radical cracking, β-scission, cyclization, and dehydrogenation were the dominant product evolution pathways, which were highly dependent on catalyst acidity and structure. Engine testing with a 20% G-PPO blend showed a predictable rise in the brake thermal efficiency with increasing load, with exhaust gas temperature and emissions correlating with the aromatic composition of the fuel. Exergy analysis showed that ZSM-5-derived G-PPO had the lowest exhaust exergy and irreversibility losses, suggesting a more efficient conversion of chemical energy to useful work. Although pyrolysis can help with waste disposal of plastic bag, but emission data from blend fuel (20% G-PPO) revealed higher NOx and particulate emissions compared to commercial gasoline.