Physical and structural effects of carbon dioxide storage on vitrinite-rich coal particles under subcritical and supercritical conditions

The effects of CO₂ sequestration on the chemical and physical properties of coal have been shown to be influenced by the coal's maceral composition. Whilst inertinite-rich coal particles have insignificant changes upon exposure to subcritical CO₂ conditions for extended time periods (6months), vitrinite-rich coal particles had changes in the structure and physical properties. In the present paper, changes in the structural and physical characteristics of a South African vitrinite-rich dry coal were studied after exposure to subcritical (42bar, 25°C), and supercritical (125bar, 35°C) CO₂ conditions for 6months. The samples were characterised pre- and post-CO₂ exposure. The characterisation techniques used were: CO₂ adsorption capacity (using a custom built high pressure volumetric system), surface area and pore size distribution analysis using both N₂ and CO₂ gas and the Brunauer-Emmett-Teller method (BET) and Fourier-Transform Infrared Spectroscopy (FTIR). Structural and physical changes in the coal were observed; these changes differed for subcritical and supercritical conditions. It was found that the surface area and number of micro-pores decreased sharply for the supercritical treated coal sample when compared to the untreated and subcritical treated coal sample. The adsorption capacity of the supercritical treated coal was also reported to be lower than the subcritical treated coal over the same period.