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<p>The conventional hydrothermal upgrading (HT) of lignite exhibits high dehydration efficiency, but high reaction pressure and temperature, coupled with substantial wastewater generation, constrain its widespread adoption. Mild heat-pressure upgrading (MHU) conducted under reduced reaction conditions, despite not relying on liquid water, has constrained dehydration capabilities, thus falling short of delivering the anticipated enhancement in lignite quality. This study proposes a waterless mild heat-pressure upgrading (DES-MHU) strategy based on a deep eutectic solvent that efficiently dehydrates and deoxygenates lignite by restructuring the hydrogen bond network, thereby enhancing lignite rank. Compared to HT, DMT significantly reduced the reaction pressure from 8.6&#xa0;MPa to 3.2&#xa0;MPa at 300&#xa0;°C, achieving dehydration efficiency of 77.11% and an oxygen removal rate of 14.49% at 280&#xa0;°C. Compared to MHU, DES-MHU enhanced the removal of hydroxyl and carboxyl groups, especially in the 250–280&#xa0;°C range, increasing them by 15.34% and 39.00%, respectively, and improved the removal of bound water by 15.24%. Density functional theory calculations revealed that the deep eutectic solvent effectively weakens the hydrogen bond strength between water molecules and oxygen-containing functional groups, with reductions of 12.66% for hydroxyl groups and 44.68% for ester groups, while reducing the Mayer and Laplace bond orders of the C–O and O–H bonds. This study presents a promising, environmentally benign strategy for lignite upgrading, contributing to the development of more efficient, lower-energy industrial processes.</p>

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Deep eutectic solvent mild thermal upgrading of lignite: enhancing dehydration and deoxygenation via hydrogen bond network reconstruction

  • 期刊论文

  • 发表日期：

    2026年1月23日

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  • Xin Zhao,
  • Ping Wu,
  • Jianzhong Liu,
  • Rui Huang,
  • Jianyong Yin,
  • Shijie Zhang,
  • Yujie Yu

摘要

The conventional hydrothermal upgrading (HT) of lignite exhibits high dehydration efficiency, but high reaction pressure and temperature, coupled with substantial wastewater generation, constrain its widespread adoption. Mild heat-pressure upgrading (MHU) conducted under reduced reaction conditions, despite not relying on liquid water, has constrained dehydration capabilities, thus falling short of delivering the anticipated enhancement in lignite quality. This study proposes a waterless mild heat-pressure upgrading (DES-MHU) strategy based on a deep eutectic solvent that efficiently dehydrates and deoxygenates lignite by restructuring the hydrogen bond network, thereby enhancing lignite rank. Compared to HT, DMT significantly reduced the reaction pressure from 8.6 MPa to 3.2 MPa at 300 °C, achieving dehydration efficiency of 77.11% and an oxygen removal rate of 14.49% at 280 °C. Compared to MHU, DES-MHU enhanced the removal of hydroxyl and carboxyl groups, especially in the 250–280 °C range, increasing them by 15.34% and 39.00%, respectively, and improved the removal of bound water by 15.24%. Density functional theory calculations revealed that the deep eutectic solvent effectively weakens the hydrogen bond strength between water molecules and oxygen-containing functional groups, with reductions of 12.66% for hydroxyl groups and 44.68% for ester groups, while reducing the Mayer and Laplace bond orders of the C–O and O–H bonds. This study presents a promising, environmentally benign strategy for lignite upgrading, contributing to the development of more efficient, lower-energy industrial processes.