Key Takeaways & Executive Findings
- •• Comprehensive structural characterization of Shendong subbituminous coal using FTIR, XRD, XPS, and 13C SSNMR. • Determination of key structural parameters: normalized formula C100H68.5O35.7N1.2S0.2, average aromatic rings 1.98, and microcrystalline parameters (d002=0.1832 nm, Lc=1.4688 nm, La=2.0852 nm, Nc=9.017). • Construction of a molecular model with atom composition C214H214O49N2S, validated against experimental 13C SSNMR spectra. • Insights into the chemical structure of subbituminous coal, providing a basis for its efficient transformation and utilization.
Abstract
Coal has a highly complex chemical structure, similar to polymers, coal is a macromolecular structure composed of a large number of “similar compounds”, which is called the basic structural unit. Understanding coal structure is the basis of its transformation and utilization. Shendong (SD) coal was analyzed by FTIR, XRD, XPS, and NMR. The results show that SD coal normalized structure formula is C100H68.5O35.7N1.2S0.2 and the average number of aromatic rings is 1.98. eCH2d content accounts for about 82% in aliphatic CeH region, and the ratio of ether bond CeO, aromatic ether CeO and C]O is about 2:1:11 in oxygen-containing functional group region. The d002, LC, La and NC of SD coal micro-crystalline structure parameters are 0.1832 nm, 1.4688 nm, 2.0852 nm and 9.017, respectively. Aromatic carbon and aliphatic carbon ratios of SD coal are 55.67% and 29.97%, aromatic cluster size and average methylene chain length are 0.224 and 1.817. Based on these structural parameters, molecular model of SD coal was constructed with 13C SSNMR experimental spectra as a reference. The model was constructed with an atom composition of C214H214O49N2S.
1. Introduction
China is relatively rich in coal resources and subbituminous coal accounts for about 40% of the total coal [1]. Shendong coalfield (SD), a kind of subbituminous coal, is one of the eight largest coalfields in the world, with the advantages of convenient mining and excellent quality [2]. Understanding SD coal structure is the basis of its transformation and utilization.
It is well-known that coal has a highly complex chemical structure, similar to polymers, coal is a macromolecular structure composed of a large number of “similar compounds” known as basic structural unit [3,4]. Due to the complexity and diversity of coal, its molecular structure has not been fully understood [5]. The methods to study coal structure are mainly chemical and physical methods. The chemical method is complicated, time-consuming and low sensitivity, which is gradually replaced by physical method [6]. The earliest structural models were based on conventional analyses such as proximate analysis and ultimate analysis [7]. With the development of a series of advanced analytical techniques such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and solid-state nuclear magnetic resonance spectroscopy (SSNMR), more than 125 coal molecular models have been proposed [8,9]. Wang et al. [10] investigated the Inner Mongolia lignite structure by using XRD, 13C NMR, TEM and XPS techniques and constructed its molecular model, the molecule formula is C166H130O49. Lin et al. [11] investigated Indonesian brown structure by using 13C NMR, FTIR, XPS and XRD, the results indicated that the ratio of bridge carbon/surrounding carbon is 0.0696 and the molecule formula for Indonesian brown coal is C190H170O50N2. Baysal et al. [12] investigated Turkish lignites by using XRD, 13C NMR, FTIR and XPS, the results shown that the XRD aromaticity of the coals ranged between 0.642 and 0.777. Okolo et al. [13] investigated South African bituminous coal by using XRD, FTIR, 13C NMR and TEM, the results shown that the aromaticity of the samples determined by 13C NMR ranged from 0.74 to 0.87. Zhang et al. [14] investigated Xishan bituminous coal by using ultimate analysis, TEM, LD-TOF M
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Xiaoping Su, Ning Li, Longjian Li, Reyila Tuerhong, Yongchong Yu, Ping Zhang, Qiong Su, Tao Shen, Ming Sun, Xiaoxun Ma (2024). Structural parameters and molecular model of Shendong subbituminous coal. Chinese Journal of Chemical Engineering. https://doi.org/10.1016/j_cjche_1448
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Frequently Asked Questions
What is the molecular formula of Shendong subbituminous coal?
The normalized structure formula is C100H68.5O35.7N1.2S0.2, and the constructed molecular model has an atom composition of C214H214O49N2S.
Which analytical techniques were used to characterize Shendong coal?
The coal was analyzed using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and solid-state nuclear magnetic resonance spectroscopy (SSNMR).
What are the key structural parameters of Shendong coal?
Key parameters include an average aromatic ring number of 1.98, microcrystalline parameters (d002=0.1832 nm, Lc=1.4688 nm, La=2.0852 nm, Nc=9.017), and aromatic carbon ratio of 55.67%.
How was the molecular model of Shendong coal constructed?
The molecular model was constructed based on structural parameters derived from experimental analyses, with 13C SSNMR spectra as a reference, resulting in a model with formula C214H214O49N2S.
Why is understanding coal structure important?
Understanding coal structure is fundamental for its efficient transformation and utilization, as it provides insights into its chemical composition and reactivity.
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