Abstract In order to characterize the effect of ionic liquid concentration on the molecular structure of lignite, the X-ray diffraction (XRD) and Fourier transform infrared (FTIR) experiments were performed on lignite coal samples treated with different concentrations of ionic liquids. The results show that with the increase of IL concentrations, the apparent aromaticity fa increases gradually. The chemical bonds on both sides of the alkyl groups are destroyed, the alkyl chains become shorter, and the molecular structure become more compact. The C-O groups such as alcohol, phenol and ether groups are converted to C O groups such as carbonyl, aldehyde and carboxy groups. The inter-layer spacing (d002) ranges from 0.374 to 0.379, which is slightly higher than that in pure graphite. It indicates that the crystalline order in coal samples is in a lower degree. The La ranges from 3.05 to 4.05 nm and Lc ranges from 0.98 to 1.11 nm, which indicates the crystallite size increases further and the order degree of coal samples gradually approaches graphitization. The results of this paper can provide some reference for studying the characteristics of molecular structure change of coal.

中文翻译：

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离子液体处理褐煤的FTIR和XRD光谱表征

摘要 为了表征离子液体浓度对褐煤分子结构的影响，对不同浓度离子液体处理的褐煤样品进行了X射线衍射（XRD）和傅里叶变换红外（FTIR）实验。结果表明，随着IL浓度的增加，表观芳香度fa逐渐增加。烷基两侧的化学键被破坏，烷基链变短，分子结构更致密。醇基、酚基、醚基等CO基团转化为羰基、醛基、羧基等CO基团。层间距（d002）范围为0.374～0.379，略高于纯石墨。表明煤样的结晶有序度较低。La范围为3.05～4.05 nm，Lc范围为0.98～1.11 nm，表明微晶尺寸进一步增大，煤样有序度逐渐接近石墨化。本文的研究结果可为研究煤的分子结构变化特征提供一定的参考。