Adsorption and desorption of CO₂ on Korean coal under subcritical to supercritical conditions

Coal seams have been reported as possible storage sites for CO₂ to help mediate the global greenhouse gas problem. The adsorption and desorption characteristics of CO₂ on dry and wet (3.64 wt %) Korean coal (Kyungdong, anthracite coal) were studied using a static volumetric method at 298 and 318 K, and up to 150 atm. The adsorption of CO₂ was favorable at low temperatures and dry coal conditions. The hysteresis of coal swelling through adsorption, desorption, and readsorption of CO₂ was observed at subcritical condition. Hysteresis between adsorption and desorption isotherms occurred in both dry and wet coals. The crossover between adsorption and desorption isotherms in dry coal was observed near the critical region, while the excess amount of adsorbed CO₂ on wet coal was lower during desorption than during adsorption. Structural variations of the coal after the wet experiment were significant compared to those in the dry coal. In wet coal, the dissolution of H₂O in the CO₂ phase, absorption of CO₂ in the aqueous phase, and coal structure changes affected the estimation of adsorption amount, especially under supercritical condition.