School of Earth Science and Engineering, Hebei University of Engineering
Key Laboratory of Resource Exploration Research of Hebei Province
School of Resources and Geosciences, China University of Mining and Technology

傅里叶变换红外光谱技术（FTIR）作为一种非破坏性的手段被广泛用于化合物的鉴定及分子结构的表征。为了查明不同燃烧温度下木炭的化学结构变化特征，进而对煤中丝质体的成因提供理论基础，选取现代野火中的不同燃烧程度的植物样品（木炭），运用FTIR对它们的化学结构进行了定量表征。结果表明：样品的反射率和燃烧温度呈正比，测得燃烧程度最高的1号样品的最大燃烧温度达到了518 ℃。除1号样品外，其余样品中芳香结构均以苯环三取代为主，但随着燃烧温度的升高，发生了脱氢缩合反应，致使苯环三取代含量降低至20.5%，由于环烷结构的脱氢芳构化，四取代含量升高，五取代含量的变化则与脂肪链的环化和苯环的脱羧反应有关。随着燃烧温度的升高，由于环烷烃等脱氢后形成芳烃或是分子侧链脱落，导致C=C含量逐渐升高，在1号样品中达到32%。C－O的含量先降低再升高，在1号样品中烷基醚和芳基醚的含量最低，酚羟基的含量最高，可能是高温燃烧下醚键受热断裂生成酚类物质。C=O含量升高再降低，在1号样品中含量低至5.6%，这是由于该键的稳定性较差。由于燃烧温度的影响，脂肪类物质的含量变化较大，整体上亚甲基含量逐渐升高，甲基减少，支链化程度增大。样品中存在5种氢键类型，受低温影响的样品中主要以醚氧氢键为主（>55%）。在1号样品中，出现了环状氢键和羟基－N氢键，同时醚氧氢键含量显著降低至13.2%，这是由于温度升高引起的含氧官能团的减少。对比煤中丝质体的反射率和FTIR特征发现，煤中丝质体（半丝质体）与木炭的特征十分相近，可能主要由野火产生。这些变化表明了燃烧温度对木炭中化学结构的影响，反映了木炭中有机分子结构随温度的变化过程，为探索煤中有机质演化和丝质体的成因提供了理论依据。

Fourier transform infrared spectroscopy (FTIR), as a non-destructive method, is widely used for the identification of compounds and the characterization of molecular structures. In order to characterize the changes in the chemical structure of charcoal under different combustion temperatures, and thus to provide a theoretical basis for the formation of fusinite in coal, plant samples (charcoal) from modern wildfires with different degrees of combustion were selected to quantify their chemical structures using FTIR. The results shown that the sample reflectance was positively proportional to the combustion temperature. The sample No. 1 with maximum combustion temperature had the highest degree of combustion, which was measured to reach 518 ℃. The aromatic structure was dominated by tri-substituted benzene rings in all samples except the highest combustion sample No. 1, but dehydrocondensation occurred with increasing combustion temperature, resulting in a reduction of tri-substituted content of benzene rings to 20.5%. The tetra-substituted content was elevated due to dehydroaromatization of the naphthenic structure, while the change in the penta-substituted content was related to the cyclization of aliphatic chain and the decarboxylation of benzene ring. With the increase of combustion temperature, the CC content gradually increased due to the formation of aromatic hydrocarbons or the shedding of molecular side chains after dehydrogenation of cycloalkanes, reached 32% in the sample No. 1. The content of C－O first decreased and then increased. In the sample No. 1, the content of alkyl ether and aryl ether was the lowest, and the content of phenolic hydroxyl group was the highest, which may be the generation of phenolic substances by thermal breakage of ether bond under high temperature combustion. The CO content increased and then decreased to as low as 5.6% in the sample No. 1, which was due to the poor stability of the bond. Due to the influence of combustion temperature, the content of fatty substances varied greatly, with an overall gradual increase in methylene content, a decrease in methyl group, and an increase in branching degree. There were five types of hydrogen bonds in the samples, with ether-oxygen hydrogen bonds predominating in samples affected by low temperature (>55%). Cyclic hydrogen bonds and hydroxyl-N hydrogen bonds appeared in sample No. 1, while the content of ether-oxygen hydrogen bonds decreased significantly to 13.2%, which was attributed to the reduction of oxygen-containing functional groups caused by the increasing temperature. Comparison of reflectance and FTIR characteristics of fusinite in coal revealed that the characteristics of fusinite (semifusinite) in coal were very similar to those of charcoal, which might be produced mainly by wildfires. These changes indicated the effect of combustion temperature on the chemical structure in charcoal, reflecting the process of organic molecular structure changed with temperature in charcoal, and providing a theoretical basis for the evolution of organic matter and the formation of fusinite in coal.

国家自然科学基金资助项目（42102215）；河北省自然科学基金杰出青年基金资助项目（D2021402017）；河北省高等学校科学技术研究资助项目（ZD2020184）

郭　旭，姚建国，李鸿豆，等. 不同燃烧程度木炭的FTIR特征对煤中丝质体成因的指示意义[J]. 煤炭科学技术，2023，51（9）：292−301

GUO Xu，YAO Jianguo，LI Hongdou，et al. FTIR characteristics of charcoal with different combustion degrees as an indication of the genesis by and their significances for formation of fusinite in coal[J]. Coal Science and Technology，2023，51（9）：292−301