Catalytic ring-expansion and hydrogenation of coal tar derivatives for high-density fuel: Modifier evaluation and kinetic elucidation

To address the bottleneck of insufficient fuel density in Coal Tar (CT), this study proposes a molecular group-oriented ring expansion modification strategy to enhance the content of condensed polycyclic aromatic hydrocarbons (PAHs) and optimize hydrogenation processes for high-density fuel production. Three modifiers—furan (FA), maleic anhydride (MA), and NA anhydride (NA)—combined with Lewis acid catalysts (AlCl₃, FeCl₃, etc.) were employed to modify low- and medium-temperature CT. The modified products were characterized using GC–MS, FT-IR, Raman spectroscopy, and ¹³C NMR. Fuel performance was evaluated via density, viscosity, calorific value, and hydrogenation experiments under optimized conditions with a Ni-Mo/γ-Al₂O₃ catalyst. Post-modification, the tricyclic aromatic hydrocarbon content increased by 20 %, the condensed aromatic peak area rose by 450 %, and the graphitization degree improved by up to 120 %. MA demonstrated the best modification effect, yielding a hydrogenated product with a density of 0.9547 g/mL and a calorific value of 42.2 MJ/kg. Kinetic analysis identified AlCl₃-catalyzed reactions at 100 °C for 24 h as optimal, involving synergistic Diels-Alder and Friedel-Crafts alkylation mechanisms. This work pioneers a molecular group-oriented ring expansion strategy for CT, overcoming the limitations of traditional hydrogenation in enhancing ring numbers and offering a novel pathway for coal-based high-density fuel development.