Understanding the structural properties of lignite during hydrothermal treatment would aid in predicting the subsequent behavior of coal during the pyrolysis, liquefaction, and gasification processes. Here, hydrothermal treatment of Inner Mongolia lignite (IM) was carried out in a lab autoclave. The distribution of carbon in the lignite was monitored via solid ¹³C nuclear magnetic resonance spectroscopy, and the functional groups of oxygen in lignite were determined by Fourier transform infrared spectroscopy. The curve-fitting method was used to calculate the content of the functional groups quantitatively. The results show that hydrothermal treatment is an effective method for upgrading the lignite. The side chains of the aromatic ring in lignite are altered, while the main macromolecular structure remains nearly the same. The hydrothermal treatment of IM could be divided into three temperature-dependent stages. The first stage (< 493 K) is the decomposition reaction of oxygen functional groups, where the O/C ratio decreases from 0.203 in raw IM to 0.185 for the IM treated at 493 K. In the second stage (493–533 K), hydrolysis of functional groups and hydrogen transfer between water and lignite occur. Here, the ratio of methylene to methyl increases from 0.871 in IM-493 to 1.241 for IM-533, and the content of quinone generates from the condensation of free phenol increased. The third stage (> 533 K) involves breakage of the covalent bond, and the content of CH₄ and CO in the emission gas clearly increase.

了解褐煤在水热处理过程中的结构特性将有助于预测煤在热解，液化和气化过程中的后续行为。在此，在实验室高压釜中对内蒙古褐煤（IM）进行了水热处理。通过固体¹³监测褐煤中碳的分布用傅立叶变换红外光谱法测定C核磁共振波谱，并测定褐煤中氧的官能团。曲线拟合法用于定量计算官能团的含量。结果表明，水热处理是褐煤提质的有效方法。褐煤中芳环的侧链发生了变化，而主要的大分子结构几乎保持不变。IM的水热处理可以分为三个温度依赖性阶段。第一阶段（<493 K）是氧官能团的分解反应，其中O / C比从原始IM的0.203降低到在493 K处理的IM的0.185。在第二阶段（493-533 K），发生官能团水解以及氢在水和褐煤之间的转移。在此，亚甲基与甲基的比例从IM-493中的0.871增加到IM-533中的1.241，并且由游离酚的缩合产生的醌含量增加。第三阶段（> 533 K）涉及共价键的断裂和CH的含量₄，废气中的CO明显增加。