Pore Characteristics and Gas Adsorption Properties of Permian Coals in Sohagpur Coalfield, India: A Comprehensive Multi-Analytical Study

The Sohagpur Coalfield, located in central India, is a prominent coal and coal bed methane (CBM) producing region in India and is also a potential site for carbon dioxide (CO2) sequestration. For the estimation of the storage and movement of both CBM and CO2, comprehensive pore characterization is essential. However, studies on this topic have so far been limited in this area, as evidenced by the small number of research articles. This study aims to understand the pore characteristics and gas adsorption behavior of coal samples from the Sohagpur Coalfield. It presents both quantitative and qualitative analyses of pore attributes and gas adsorption behavior using a multi-analytical approach, combining low-pressure gas adsorption (LPGA) analysis, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The gas adsorption behavior of these coals was investigated through adsorption isotherm studies using nitrogen as the adsorbate. The adsorption isotherms exhibited Type IIb characteristics of meso- and macropores. The specific surface area ranges from 4.679 to 21.974 m2/g, and the total pore volume of coal samples ranges from 0.027 to 0.054 cm3/g. The average pore diameter ranges from 9.834 to 26.145 nm based on the BET (Brunauer–Emmett–Teller) model, while the BJH (Barrett–Joyner–Halenda) model, which considers cylindrical pores, yields values ranging from 6.402 to 15.964 nm, indicating a significant gas adsorption potential. SEM imaging provided insights into the microstructure, pore, and morphology of coal pores and fractures, contributing to gas migration and adsorption. FTIR spectra exhibited characteristic peaks corresponding to various functional groups (such as CH2–CH3, C═O, and C–O) that contribute to the surface reactivity of the coals and enhance their gas adsorption capacity. This detailed characterization of isotherms and functional groups contributes to a deeper understanding of how functional groups and pore characteristics influence gas adsorption behavior in coal samples. The results suggest that the Sohagpur coals have sufficient capacity to store gas and a pore network favorable for gas transfer, which is crucial for CBM production as well as CO2 sequestration.