Abstract
Four coal samples from Jharia basin, India are treated with nitric acid in glacial acetic acid and aqueous media to find out the chemical, petrographic and spatial structure of the organic mass by X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) techniques. X-ray parameters of coal like interlayer spacing (d002), crystallite size (Lc), aroamticity (fa), average number of aromatic layers (Nc), and coal rank (I26/I20) have been determined using profile-fitting software. Considerable variation is observed in treated coals in comparison to the demineralized coals. The d002 values of treated coals have increased in both the media showing increase in disordering of organic moieties. A linear relationship has been observed between d002 values with the volatile matter of the coals. Similarly, the d002 values show linear relationship with Cdmf contents for demineralized as well as for the treated coals in both the media. The Lc and Nc values have decreased in treated coals corresponding to demineralized coals. The present study shows that nitration in both the media is capable of removing the aliphatic side chains from the coals and aromaticity (fa) increases with increase in rank and shows a linear relationship with the vitrinite reflectance. The corresponding I26/I20 values are least for treated coals in glacial acetic acid medium followed by raw and then to treated coals in aqueous medium. FTIR studies show that coal arenes of the raw coals are converted into nitro-arenes in structurally modified coals (SMCs) in both the media, the corresponding bands at 1550–1490 and 1355–1315 cm−1 respectively. FTIR study confirms that nitration is the predominant phenomenon, though, oxidation and nitration phenomena takes place simultaneously during treatment with nitric acid to form SMCs. In comparison to raw coals, the SMCs show higher aromaticity and may be easily converted to coal derived products like activated carbon and specialty carbon materials.
Highlights
Coal has manifold uses, as for instance, solid fuel, gives coke for metallurgical use, coal chemicals and many more
Significant observation in the present study is that nitration in both the media is capable of removing the aliphatic side chains for the coals and aromaticity increases with increase in rank of coal
In the case of low rank coals, glacial acetic acid medium being milder medium might have resulted in the formation of covalent nitro groups (Ar–O–NO2) in the range 1300–1255 cm-1 which is absent in relatively stronger aqueous medium where oxidation is active phenomenon
Summary
As for instance, solid fuel, gives coke for metallurgical use, coal chemicals and many more. Nitration of Jharia basin coals, India: a study of structural modifications by XRD and FTIR (Domazetis and James 2006; Mathews and Chaffee 2012; Li et al 2015; Yan et al 2020). Hirsch (1954) carried out X-ray diffraction studies of low rank coals and anthracite He found that the low rank coals up to carbon content 85% have ‘‘open structure’’. FTIR spectroscopy exploits the fact that molecules absorb or transmit specific frequencies that are characteristic of their structure It is generally studied in mid-infrared zone, approximately 4000–400 cm-1 wave number range. Jharia Basin coal is very important as it is the only caking/coking coal producing horizon of India. Twelve numbers of samples have been prepared in total for the present study
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