Assessment of energetic heterogeneity of coals for gas adsorption and its effect on mixture predictions for coalbed methane studies

This study explains the single-component and binary mixture adsorption studies on two different coals from the Zonguldak Basin (Northwestern Turkey). Assessment of energetic heterogeneity of coal surface and its effect on the equilibrium binary gas adsorption are discussed. Single component adsorption tests were performed using methane and carbon dioxide at 30°C. Binary mixtures prepared with 10, 15 and 20% carbon dioxide were also tested at the same temperature. Various single-component adsorption isotherms were fitted to the experimental data of single gases. The data obtained from these models were interpreted to determine the energetic heterogeneity of the coals towards adsorption of methane and carbon dioxide. Ideal adsorbed solution (IAS) theory was used to predict the data and discrepancies between experimental data, and the model predictions were interpreted. Results showed that coals exhibit a heterogeneous behavior in gas adsorption. This heterogeneity can be different for each coal–gas pair and the extent of the heterogeneity makes the binary gas predictions differ from the experimental data. The deviations between IAS and experimental data increase as the amount of gas, to which the coal shows high heterogeneity, increases in the mixture.