Abstract

The functional-group composition and structure of hexane-insoluble asphaltenes from coal pitch are studied. The methods employed are chemical (elemental) analysis, nuclear magnetic resonance (NMR), IR spectroscopy, scanning electron microscopy, X-ray phase analysis, and differential thermal analysis in combination with chromatography and mass spectrometry. Analysis of the results shows that the hydrocarbon skeleton of the mean hypothetical macromolecule of the asphaltenes may be regarded as a set of condensed aromatic cores of pericondensed type, with seven rings. Alkyl substituents are present; the mean length of the connecting bridges is two carbon atoms. On average, there is one sulfur atom for each 500 carbon atoms; one nitrogen atom for each 50 carbon atoms, and one oxygen atom for each 167 carbon atoms. The ratio of structural units in asphaltene powder is as follows: for one S-bearing structure, there will be 4–5 N-bearing structures and 1.3–1.7 O-bearing structures. Sulfur atoms are present in thermally stable thiophene-like structural fragments. They enter the coke residue without decomposition. Oxygen is present in thermally unstable carboxyl and phenol groups, which break down to form CO₂. It is also present in aromatic esters, which pass to the coke residue. Crystallographic analysis of the ordered structures formed by asphaltene macromolecules confirms that such macromolecules tend to undergo self-organization. The mean diameter L_a of such ordered structures (packets) is around 0.66 nm, while their thickness is L_c ≈ 1.30 nm. The distance between individual layers d₀₀₂ ≈ 0.34 nm; the mean number of layers in the packets is n ≈ 5–7. Asphaltene powder has no more than 30% crystal structure. The data obtained by different methods are in good agreement and more completely characterize the structure of the asphaltene macromolecules in coal pitch.

中文翻译：

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煤沥青中己烷不溶性沥青的组成和结构

摘要

研究了煤沥青中己烷不溶性沥青质的官能团组成和结构。所采用的方法是化学（元素）分析，核磁共振（NMR），红外光谱，扫描电子显微镜，X射线相分析以及与色谱和质谱联用的差热分析。结果分析表明，沥青质的平均假设大分子的烃骨架可以看作是一组具有七个环的过缩型稠合芳烃核。存在烷基取代基；连接桥的平均长度是两个碳原子。平均而言，每500个碳原子有一个硫原子；每50个碳原子一个氮原子，每167个碳原子一个氧原子。沥青质粉末中结构单元的比例如下：对于一种含硫结构，将有4-5个含氮结构和1.3-1.7个含O结构。硫原子存在于热稳定的噻吩样结构片段中。它们进入焦炭残渣而不分解。氧存在于热不稳定的羧基和酚基团中，它们分解形成一氧化碳₂。它也存在于芳族酯中，并传递到焦炭残渣中。由沥青质大分子形成的有序结构的晶体学分析证实，这种大分子倾向于经历自组织。平均直径大号_一个这样的有序结构（数据包）的大约是0.66纳米，而它们的厚度是大号_Ç ≈1.30纳米。各层之间的距离ð ₀₀₂ ≈0.34纳米; 在分组层的平均数目为Ñ ≈5-7。沥青质粉末具有不超过30％的晶体结构。通过不同方法获得的数据吻合良好，并更完整地表征了煤沥青中沥青质大分子的结构。