不同变质程度煤样化学结构特征FTIR表征

FTIR Characterization of Chemical Structures Characteristics of Coal Samples With Different Metamorphic Degrees

为研究煤样的化学结构特征随煤样变质程度加深的演化规律,采用傅里叶变换红外光谱与分峰拟合技术研究了5种不同变质程度煤样的官能团分布特征,并依据其结果计算了结构参数。结果表明:不同变质程度煤样的化学结构特征存在明显差异,但随煤样变质程度加深,其演化规律整体趋势相似,即相对具有较高活性的官能团逐渐减少,较为稳定的官能团逐渐增加,煤样的化学结构整体向稳定、有序发育。在羟基官能团方面,游离羟基逐渐减少,而羟基与芳环中π电子云间形成的羟基-π氢键逐渐增加,羟基自缔合氢键是煤中羟基氢键的主要类型,其相对含量在40%~55%内波动,羟基醚氧氢键与环状缔合氢键整体呈减少趋势。在脂肪烃结构方面,实验煤样中亚甲基的相对含量均高于甲基与次甲基,说明煤中脂环结构与脂链结构较为发达;而结构参数A(CH2)/A(CH3)先增后减,说明由甲基、亚甲基与次甲基构成的脂肪链在低变质程度煤样中有发育趋势,在中、高变质程度煤样中开始断裂,脂肪链总体长度呈先增长后缩短趋势,但支链数量整体上却呈先减后增趋势。在含氧官能团方面,芳香酯减少,活性较高的羧基逐渐减少,羰基在低、中变质程度煤样中相对含量的变化较小,而在高变质程度煤样中的相对含量明显减少;酚中C—O的相对含量呈先增后减趋势,芳基醚与烷基醚的相对含量逐渐增加,并成为无烟煤中的主要含氧官能团。在芳香烃结构方面,苯环取代以三取代为主,结构参数farC与DOC逐渐变大,说明煤中芳香体系增大,芳香结构缩合程度逐渐增强,无烟煤中芳香结构的缩合程度远强于其他煤样。

In order to study the evolution of the chemical structural characteristics of coal samples with the increase of the degree of metamorphism, the distribution of functional groups of five coal samples with different degrees of metamorphism was studied by Fourier transform infrared spectroscopy and split-peak fitting technique, and the structural parameters were calculated based on the results. The results showed that the chemical structure of the coal samples with different degrees of metamorphism differed significantly, but the overall trend of the evolution of the samples was similar as the degree of metamorphism increased, i. e., the relatively more active functional groups gradually decreased, the more stable functional groups gradually increased, and the chemical structure of the coal samples as a whole developed towards stability and order. With the deepening of coal sample metamorphism, in terms of hydroxyl functional groups, the free hydroxyl group gradually decreased. At the same time, the hydroxyl-π hydrogen bond gradually increased, and the relative content of hydroxyl self-conjugated hydrogen bond fluctuated within 40% to 55%, which was the main type of hydroxyl hydrogen bond in coal. The overall trend of hydroxyl ether-oxygen bond and ring-conjugated hydrogen bond decreased. In terms of aliphatic hydrocarbon structure, the relative content of methylene in the experimental coal samples was higher than that of methyl and hypomethyl, indicating that the lipid ring structure and lipid chain structure were more developed in coal. At the same time, the structural parameter A(CH2)/A(CH3) increased and then decreased, indicating that the fatty chains composed of methyl, methylene and hypomethyl tended to develop in the coal samples with low degree of metamorphism, and started to break in the coal samples with medium and high degree of metamorphism. The overall length of fatty chains tended to increase and then shorten, but the number of branched chains as a whole tended to decrease and then increase. The relative content of C—O in phenols tended to increase and then decrease, and the relative content of aryl ethers and alkyl ethers gradually increased and became the main oxygen-containing groups in anthracite coals. Functional groups in anthracite. In the aromatic hydrocarbon structure, the benzene ring substitution is mainly trisubstituted, and the structural parameters f■ and DOC gradually become larger, which indicates that the aromatic system in coal increases and the degree of aromatic structure condensation gradually increases, and the degree of aromatic structure condensation in anthracite coal is much stronger than other coal samples.