Technical study on upgrading coal-derived diesel to rubber extender oil

Coal-derived diesel is a clean synthetic hydrocarbon stream, but its low cyclic and aromatic content limits its direct use as rubber extender oil. This study developed a controllable upgrading route to increase molecular weight, ring content, and solvency through tandem Friedel–Crafts alkylation and Diels–Alder cycloaddition. Coal-derived hydrotreated diesel and tetralin model systems were modified using α-olefins as alkylation modifiers, 2,5-dimethylfuran as the cycloaddition modifier, and AlCl3 as the Lewis-acid catalyst. Reaction sequence, catalyst type, olefin chain length, modifier type, temperature, and time were evaluated by density, feedstock conversion, simulated distillation, GC–MS, FT-IR, Raman, aniline point, and viscosity analyses. The Friedel–Crafts-first sequence showed the strongest synergy, and AlCl3, 1-tetradecene, and 2,5-dimethylfuran gave the most effective densification and heavy-end enrichment. Under optimized conditions, the product density reached 0.966 g cm-³, with enrichment in the 240–280 °C and >280 °C fractions. Structural analyses confirmed long-chain alkylation, olefinic-bond consumption, oxygen-containing Diels–Alder-related products, and enhanced aromatic-framework contribution, providing a reaction-sequence-based strategy for high-value utilization of coal-derived liquid products.