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<p>This study investigates the molecular modification effects of stepwise Friedel–Crafts (FC) alkylation and Diels–Alder (DA) cycloaddition using the light fraction of low-temperature coal tar as feedstock. It is postulated that the Lewis acid catalyst AlCl<sub>3</sub> may stabilize the carbocation intermediate and the furan diene transition state via potential π-cation interactions. Experiments using 1-methylnaphthalene as a model compound revealed a synergistic effect when the FC reaction preceded the DA reaction. Following this order, the conversion rates of 1-methylnaphthalene and 2,5-dimethylfuran were 45.18 and 98.05%, respectively, whereas the reverse order inhibited FC activity due to steric hindrance. The optimal conditions were determined as AlCl<sub>3</sub> (5% addition), a temperature of 100&#xa0;°C, a molar ratio of 1:1:1, and a sequence of 3&#xa0;h for the FC reaction followed by 14&#xa0;h for the DA reaction, yielding a product density of 0.966&#xa0;g/cm<sup>3</sup>. Upon actual modification of coal tar, the dominant carbon number shifted from C8 to C16. The proportion of monocyclic aromatic hydrocarbons decreased from 70 to 40 wt%, while bicyclic aromatic hydrocarbons increased to 50 wt%, and those with three or more rings reached 15 wt%. Additionally, the unsaturated hydrocarbon content rose from 68 to 77%. This study provides a theoretical basis and process parameters for the conversion of coal tar into high-density fuels.</p>

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Sequential Friedel–Crafts/Diels–Alder modification of coal tar: exploration of ring expansion and side-chain elongation pathways

  • 期刊论文

  • 发表日期：

    2026年7月23日

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  • Menglong Niu,
  • Xueyao Lin,
  • Yihang Geng,
  • Lihang Liu,
  • Xiaohua Chai,
  • Ben Niu,
  • Baoqi Ma

摘要

This study investigates the molecular modification effects of stepwise Friedel–Crafts (FC) alkylation and Diels–Alder (DA) cycloaddition using the light fraction of low-temperature coal tar as feedstock. It is postulated that the Lewis acid catalyst AlCl3 may stabilize the carbocation intermediate and the furan diene transition state via potential π-cation interactions. Experiments using 1-methylnaphthalene as a model compound revealed a synergistic effect when the FC reaction preceded the DA reaction. Following this order, the conversion rates of 1-methylnaphthalene and 2,5-dimethylfuran were 45.18 and 98.05%, respectively, whereas the reverse order inhibited FC activity due to steric hindrance. The optimal conditions were determined as AlCl3 (5% addition), a temperature of 100 °C, a molar ratio of 1:1:1, and a sequence of 3 h for the FC reaction followed by 14 h for the DA reaction, yielding a product density of 0.966 g/cm3. Upon actual modification of coal tar, the dominant carbon number shifted from C8 to C16. The proportion of monocyclic aromatic hydrocarbons decreased from 70 to 40 wt%, while bicyclic aromatic hydrocarbons increased to 50 wt%, and those with three or more rings reached 15 wt%. Additionally, the unsaturated hydrocarbon content rose from 68 to 77%. This study provides a theoretical basis and process parameters for the conversion of coal tar into high-density fuels.