Industrial applications of coal rely on understanding its macromolecular structure, which is primarily controlled by coal type and rank. The present study assessed five (5) samples from different collieries extracting coal from the No. 4 Seam of the Highveld Coalfield and their float products, produced at relative densities (RD) of 1.7 and 1.9 g/cm. The aim was to assess changes in maceral composition and coal quality following the density fractionation, and to use Raman Spectroscopy to compare differences in macromolecular structures between the parent samples and the float products. Raman parameters were also determined for specific macerals, i.e., semifusinite and collotelinite. Mean random vitrinite reflectance (%RoV) values for the studied coals range between 0.57 and 0.60% (medium rank D/C bituminous) and the parent coals are inertinite-rich (70.3 to 88.7 vol% mmf), enriched in semifusinite and inertodetrinite. Following density fractionation, reactive macerals (a combination of liptinite, vitrinite, and reactive semifusinite) are enriched in the float products (designated by “F”), specifically in the products obtained at the 1.7 RD. In comparison, the proportion of inert macerals is higher in the F1.9 samples. These differences in maceral composition are reflected in the Raman spectra and parameters. Although the G and D1 bands for the parent coals and F1.9 samples are similar, these bands are narrower than for the F1.7 samples, indicative of greater aromaticity. The G FWHM values for the F1.9 samples are comparable to those for the parent coal samples, and lower than for the F1.7 samples. This reflects larger differences in maceral composition between the parent coals and the F1.7 samples. In contrast, the D1 FWHM values for the float products, particularly the F1.7 samples, are slightly higher than the parent coals, reflecting a disordered aromatic character mainly related to the presence of aliphatic chains. The Raman spectra for the F1.7 samples are more like that for collotelinite. In contrast, the Raman spectra and parameters (G and D1 FWHM) for the F1.9 samples are more comparable to semifusinite. Thus, the increased aliphaticity for the F1.7 samples is attributed to the relative enrichment of reactive macerals, whereas higher aromaticity for the F1.9 samples reflects a larger proportion of inert macerals Raman spectroscopy expanded on the petrographic data by interrogating the macromolecular structure of the isorank Highveld coals and their float products. This may assist in predicting the behaviour of the coals during industrial applications (i.e., liquefaction, gasification, combustion, and carbon fibre production).

中文翻译：

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用于表征 Highveld 煤大分子结构的拉曼光谱（南非）


煤炭的工业应用依赖于对其大分子结构的了解，而大分子结构主要受煤炭类型和等级控制。本研究评估了来自不同煤矿的五 (5) 个样品，这些煤矿从 Highveld 煤田 4 号煤层中提取煤炭及其浮选产品，这些产品的相对密度 (RD) 为 1.7 和 1.9 g/cm3。目的是评估密度分馏后显微组分和煤炭质量的变化，并使用拉曼光谱比较母体样品和浮选产品之间大分子结构的差异。还确定了特定显微组分（即半熔铁矿和胶锰矿）的拉曼参数。研究煤的平均随机镜质体反射率 (%RoV) 值范围在 0.57 至 0.60%（中级 D/C 烟煤）之间，母煤富含惰性质体（70.3 至 88.7 vol% mmf），富含半熔质体和惰性质质体。密度分级后，反应性显微组分（脂铁矿、镜质体和反应性半熔岩的组合）在浮选产品（用“F”表示）中富集，特别是在 1.7 RD 获得的产品中。相比之下，F1.9 样品中惰性显微组分的比例较高。这些显微成分的差异反映在拉曼光谱和参数中。尽管母煤和 F1.9 样品的 G 和 D1 谱带相似，但这些谱带比 F1.7 样品更窄，表明芳香度更高。 F1.9 样品的 G FWHM 值与母煤样品的 G FWHM 值相当，但低于 F1.7 样品。这反映了母煤和 F1.7 样品之间显微组分成分存在较大差异。 相比之下，浮选产品（特别是 F1.7 样品）的 D1 FWHM 值略高于母煤，反映了主要与脂肪链的存在有关的无序芳香特征。 F1.7 样品的拉曼光谱与硅锰矿的拉曼光谱更相似。相比之下，F1.9 样品的拉曼光谱和参数（G 和 D1 FWHM）与半熔岩更具可比性。因此，F1.7 样品的脂肪族度增加归因于反应性显微组分的相对富集，而 F1.9 样品较高的芳香性反映了惰性显微组分的比例较大，通过询问岩石学数据的大分子结构扩展了拉曼光谱。等等级高地煤及其浮选产品。这可能有助于预测工业应用（即液化、气化、燃烧和碳纤维生产）期间煤炭的行为。