Nitration of Jharia basin coals, India: a study of structural modifications by XRD and FTIR techniques

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 (d(002)), crystallite size (L-c), aroamticity (f(a)), average number of aromatic layers (N-c), and coal rank (I-26/I-20) have been determined using profile-fitting software. Considerable variation is observed in treated coals in comparison to the demineralized coals. The d(002) values of treated coals have increased in both the media showing increase in disordering of organic moieties. A linear relationship has been observed between d(002) values with the volatile matter of the coals. Similarly, the d(002) values show linear relationship with C-dmf contents for demineralized as well as for the treated coals in both the media. The L-c and N-c 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 (f(a)) increases with increase in rank and shows a linear relationship with the vitrinite reflectance. The corresponding I-26/I-20 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.