A multi-analytical study on the sulphur components in some high sulphur Indian Tertiary coals

Abstract

The main source of industrial energy in the world is coal. To better understand the distribution of sulphur containing components in high sulphur Tertiary coals, a multi-analytical analysis was carried out on four industrially important high sulphur northeast region (NER) Indian coals. Some of the relevant information on the distribution and speciation of sulphur functionalities in these Tertiary coals were obtained by using chemical analysis, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and Mössbauer spectroscopy techniques. The study revealed the presence of various sulphur compounds such as pyrite (FeS2), disulphides (S–S), sulphone (−SO2–) and aryl thioether (R1–S–R2) in the coals, which are essential to be removed before the coal could be utilised. Sulphur is present in high amounts in MEG (4.54 %) and NG (4.56 %) coal samples. The lowest amount of sulphur was found in TP coal. In the present study, it is shown that the NER Tertiary coals contain higher amounts (>50 %) of organic sulphur, which may be difficult to remove by conventional methods. X-ray photoelectron spectroscopy (XPS) analysis of these Tertiary coals revealed that sulphur is present in two forms namely inorganic and organic. TPR also provide information on sulphur association in coals as iron pyrite, sulphides, thiophene, thiols, etc. Fe components in NER coals contain typically pyrite and Mössbauer spectroscopy where pyrite, illite, marcasite and hematite were observed, which is in agreement with the results obtained with other techniques