Competitive adsorption equilibria of CO2 and CH4 on a dry coal

Gases like CO(2) and CH(4) are able to adsorb on the coal surface, but also to dissolve into its structure causing the coal to swell. In this work, the binary adsorption of CO(2) and CH(4) on a dry coal (Sulcis Coal Province, Italy) and its swelling behavior are investigated. The competitive adsorption measurements are performed at 45 degrees C and up to 190 bar for pure CO(2), CH(4) and four mixtures of molar feed compositions of 20.0, 40.0, 60.0 and 80.0% CO(2) using a gravimetric-chromatographic technique. The results show that carbon dioxide adsorbs more favorably than methane leading to an enrichment of the fluid phase in CH(4). Coal swelling is determined using a high-pressure view cell, by exposing a coal disc to CO(2), CH(4) and He at 45 and 60 degrees C and up to 140 bar. For CO(2) and CH(4) a maximum swelling of about 4 and 2% is found, whereas He shows negligible swelling. The presented adsorption and swelling data are then discussed in terms of fundamental, thermodynamic aspects of adsorption and properties which are crucial for an ECBM operation, i.e. the CO(2) storage capacity and the dynamics of the replacement of CH(4) by CO(2).