Measuring and modeling the competitive adsorption of CO2, CH4, and N2 on a dry coal

Data on the adsorption behavior of CO2, CH4, and N-2 on coal are needed to develop enhanced coalbed methane (ECBM) recovery processes, a technology where the recovery of CH4 is enhanced by injection of a gas stream consisting of either pure CO2, pure N-2, or a mixture of both. The pure, binary, and ternary adsorption of these gases on a dry coal from the Sulcis Coal Province in Italy has been measured at pressures up to 180 bar and temperatures of 45 and 70 degrees C for the pure gases and of 45 degrees C for the mixtures. The experiments were performed in a system consisting of a magnetic suspension balance using a gravimetric-chromatographic technique. The excess adsorption isotherms are successfully described using a lattice density functional theory model based on the Ono-Kondo equations exploiting information about the structure of the coal, the adsorbed gases, and the interaction between them. The results clearly show preferential adsorption of CO2 over CH4 and N-2, which therefore indicate that ECBM may be a viable option for the permanent storage of CO2.