Maturity Parameter of Carbonaceous and Coaly Matter Revealed through Raman Spectroscopy

Abstract

Abstract This article presents the results of ten coal samples of sub- bituminous rank collected from working mines in Chhattisgarh, India, and subjected to proximate and ultimate analysis, organic petrology and Raman spectroscopic study to reveal their maturity parameters and structural characteristics of carbonaceous materials. Vitrinite reflectance measurement was also performed to understand the maturity parameter, with values ranging from 0.35% to 0.57%. The research is unique as it combines petrological, geochemical and spectroscopic technique on coals of Hasdeo basin. Conventional parametei; volatile matter ranges from 21.83 and 33.68% suggesting low maturity. The ash yield values range from 12.04 and 26.61%. Petrographically, the coals are vitrinite rich ranging from 53.95 to 63.47% while the inertinite group range from 17.9 to 29.2%. The liptinite concentration the samples remain below 10%. The maceral constitution of the coals indicates carbonaceous materials undergoing early diagenetic phase. The Raman results showed the presence of the D and G bands, two prominent spectral signatures, which are typical of natural materials rich in carbon. The Raman shift recorded for the D band ranges from 1348 to 1385 cm-1 and for the G band, the Raman shift was recorded between 1607 to 1616 cm-1. The ratio of the various parameters derived from the two bands aid to understand the material response to the changing physical and chemical variables in the geological setup. The intensity ratio of the ID/IG band ranged from 0.15 to 0.79 (average 0.50), while the (G-D1) parameter ranges from 225 to 260 indicating heterogeneity in the samples. However; the ratio of AD1/AG did not show any regularity, with values ranging from 0.07 to 1.85. The investigation elucidates that by integrating Raman spectroscopy analysis with vitrinite reflectance (VRo), we can discern distinctive structural attributes characteristic of immature kerogen. Furthermore, the petrological, proximate, and ultimate data collectively corroborate the carbonaceous, coaly material in its early stages of coalification.