Application of Raman Spectroscopy in the Characterization of Coal Macromolecular Structure

Tian Wang

doi:10.62051/ijnres.v5n3.04

Authors

Tian Wang

DOI:

https://doi.org/10.62051/ijnres.v5n3.04

Keywords:

Raman spectroscopy; Coal macromolecular structure; Peak fitting; Structural order; Coalification degree

Abstract

Raman spectroscopy is a rapidly developing rapid and non-destructive characterization technique for carbon materials in recent years, which has been widely applied to the characterization research of coal macromolecular structures. Through a systematic investigation, analysis, and summary of the research progress of Raman spectroscopy technology in the characterization of coal macromolecules at home and abroad, the following conclusions are obtained: (1) For the Raman spectroscopy testing of coal, processes such as boiling glue, polishing the sample, choosing different laser light sources, laser energies, and signal collection times will all have an impact on the Raman spectrum. Moreover, when performing peak fitting on the Raman spectrum, the coal rank of the sample and the structural information contained in the spectral peaks should be fully considered. (2) The influence of temperature on the structural evolution of organic matter in coal can be divided into two stages. Before graphitization, the Raman spectrum of coal shows irregular changes, while during the high-temperature graphitization process, the Raman disorder parameter gradually decreases. Under normal temperature and pressure conditions, the characteristic peaks of the Raman spectrum will shift linearly to a higher peak position, which is consistent with the response variation law of the Raman spectrum to stress. Additionally, the structural defects caused by tectonic stress will reduce the structural order of coal-measure graphite. (3) There is no strict corresponding relationship between the Raman spectrum disorder parameter and the coalification degree. Based on previous research results, it is believed that this may be closely related to factors such as the fact that the evolution of the order of coal macromolecular structures and the evolution of chemical structures are not completely synchronous, and that tectonic stress increases structural disorder by introducing structural defects. (4) Other applications of Raman spectroscopy in the characterization of coal structures include calculating the size of aromatic lamellae, the indicative significance of special peaks, and using the second-order Raman spectrum to characterize coal structure information. However, caution is still required during practical use.

References

[1]Liu X, Song D, He X, Nie B, Wang Q, Sun R, et al. Coal macromolecular structural characteristic and its influence on coalbed methane adsorption. Fuel. 2018; 222:687-94.

[2]Karayigit AI, Atalay M, Oskay RG, Cordoba P, Querol X, Bulut Y. Variations in elemental and mineralogical compositions of Late Oligocene, Early and Middle Miocene coal seams in the Kale-Tavas Molasse sub-basin, SW Turkey. Int J Coal Geol. 2020; 218:103366.

[3]Mathews JP, Chaffee AL. The molecular representations of coal - A review. Fuel. 2012;96(1):1-14.

[4]Zhang K, Zou A, Wang L, Cheng Y, Liu C, Li W. Morphological characterization of the microcrystalline structure of tectonic coal and its Intrinsic connection with ultra-micropore evolution. Energ Fuel. 2022; 36(3):1482-94.

[5]Jia J, Song H, Jia P. Selective adsorption mechanism of CO2/CH4/N2 multi-component gas mixtures by N/S atoms and functional groups in coal. Process Saf Environ. 2024; 182:210-21.

[6]Zhang Q, Zhu H. Macromolecular insights into the influence of bituminous coal matrix deformation on CH4-N2 competitive adsorption and diffusion. Colloid Surface A. 2024; 694:213198.

[7]Zhou D, Liu Z, Feng Z, Shen Y. Accessibility of methane at micro-pore passage and its effect on the methane desorption in coal. Journal of China Coal Society. 2019; 44(09):2797-802.

[8]Chen L, Wang L, Yang T, Yang H. Deformation and swelling of coal induced from competitive adsorption of CH4 /CO2 /N2. Fuel. 2021; 286:119356.

[9]Wang K, Pan J, Wang E, Hou Q, Yang Y, Wang X. Potential impact of CO2 injection into coal matrix in molecular terms. Chem Eng J. 2020; 401:119356.

[10]Li J, Pan J, Wang X, Wang K, Nie S, Gao D. Potential effect of carbon dioxide injection on the functional groups of medium volatile bituminous coals analysed using in-situ diffuse reflectance Fourier-transform infrared spectroscopy. Int J Coal Geol. 2023; 265:104169.

[11]Boyd AD. Risk perceptions of an alleged CO2 leak at a carbon sequestration site. Int J Greenh Gas Con. 2016; 50:231-9.

[12]Goodman AL, Favors RN, Hill MM, Larsen JW. Structure changes in Pittsburgh No.8 coal caused by sorption of CO2 gas. Energ Fuel. 2005; 19(4):1759-60.

[13]Pan J, Lv M, Hou Q, Han Y, Wang K. Coal microcrystalline structural changes related to methane adsorption/desorption. Fuel. 2019; 239:13-23.

[14]Cheng N, Pan J, Shi M, Hou Q, Han Y. The impacts of stress on the macromolecular structure of anthracites: Implications for the mechanochemical effects. Int J Coal Geol. 2022; 264:104151.

[15]Gao F, Jia Z, Cui Z, Li Y, Jiang H. Evolution of macromolecular structure during coal oxidation via FTIR, XRD and Raman. Fuel Process Technol. 2024; 262:108114.

[16]Wang S, Tang Y, Chen H, Liu P, Sha Y. Chemical structural transformations of different coal components at the similar coal rank by HRTEM in situ heating. Fuel. 2018; 218:140-7.

[17]Mastalerz M, Hampton L, Drobniak A, Loope H. Significance of analytical particle size in low-pressure N2 and CO2 adsorption of coal and shale. Int J Coal Geol. 2017; 178:122-31.

[18]Zhang L, Li T, Quyn D, Dong L, Qiu P, Li C. Structural transformation of nascent char during the fast pyrolysis of mallee wood and low-rank coals. Fuel Process Technol. 2015; 138:390-6.

[19]Song Y, Feng W, Li N, Li Y, Zhi K, Teng Y, et al. Effects of demineralization on the structure and combustion properties of Shengli lignite. Fuel. 2016; 183:659-67.

[20]Xu Y, Chen X, Wang L, Bei K, Wang J, Chou I, et al. Progress of Raman spectroscopic investigations on the structure and properties of coal. J Raman Spectrosc. 2020; 51(9):1874-84.

[21]Li HT, Cao DY, Zhang WG, Wang L. XRD and Raman spectroscopy characterization of graphitization trajectories of high -rank coal. Spectrosc Spect Anal. 2021; 41(8):2491-8.

[22]Xu J, Tang H, Su S, Liu J, Xu K, Qian K, et al. A study of the relationships between coal structures and combustion characteristics: The insights from micro-Raman spectroscopy based on 32 kinds of Chinese coals. Appl Energ. 2018; 212:46-56.

[23]Zhu W, Li X, Sun R, Yan Y, Liu J, Wang Z, et al. Microstructural evolution of coal to char after pyrolysis using laser-induced breakdown spectroscopy and Raman spectroscopy. Energy. 2023; 267:126558.

[24]Li X, Zeng Q. Development and progress of spectral analysis in coal structure research. Spectrosc Spect Anal. 2022; 42(2):350-7.

[25]Li J, Qin Y, Chen Y, Shen J, Song Y, Wang Z. Structural characteristics and evolution of meta - anthracite to coaly graphite: A quantitative investigation using X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy. Fuel. 2023; 333:126334.

[26]Ulyanova EV, Molchanov AN, Prokhorov IY, Grinyov VG. Fine structure of Raman spectra in coals of different rank. Int J Coal Geol. 2014; 121:37-43.

[27]Henry DG, Jarvis I, Gillmore G, Stephenson M, Emmings JF. Assessing low-maturity organic matter in shales using Raman spectroscopy: Effects of sample preparation and operating procedure. Int J Coal Geol. 2018; 191:135-51.

[28]Han Y, Wang J, Dong Y, Hou Q, Pan J. The role of structure defects in the deformation of anthracite and their influence on the macromolecular structure. Fuel. 2017; 206:1-9.

[29]Xu J, Xiang X, Xu K, He L, Han H, Su S, et al. Developing micro-Raman spectroscopy for char structure characterization in the scale of micro- and bulk: A case study of Zhundong coal pyrolysis. Fuel. 2021; 291:120168.

[30]Xu C, Li H, Lu J, Lu Y, Shi S, Ye Q, et al. An investigation into the modification of microwave-assisted oxidation in the macromolecular structure of coal via XRD and Raman spectroscopy. Fuel. 2023; 338:127192.

[31]Yuan X, Mayanovic RA. An empirical study on Raman peak fitting and its application to Raman quantitative research. Appl Spectrosc. 2017; 71(10):2325-38.

[32]Li G, Li J, Pan J, Liu L, Zhang M, Zhang L, et al. Adsorption of CO2 /CH4 on the aromatic rings and oxygen groups of coal based on in-situ diffuse reflectance FTIR. Gas Science and Engineering. 2024; 130:205440.

[33]Yu J, Guo Q, Ding L, Gong Y, Yu G. Studying effects of solid structure evolution on gasification reactivity of coal chars by in-situ Raman spectroscopy. Fuel. 2020; 270:117603.

[34]Cheng N, Pan J, Shi M, Hou Q, Han Y. Using Raman spectroscopy to evaluate coal maturity: The problem. Fuel. 2022; 312:122811.

[35]Chen C, Tang Y, Guo X. Comparison of structural characteristics of high-organic-sulfur and low-organic-sulfur coal of various ranks based on FTIR and Raman spectroscopy. Fuel. 2022; 310:122362.