Adsorption of Pure Carbon Dioxide on Wet Argonne Coals at 328.2 K and Pressures up to 13.8 MPa

Carbon dioxide (CO2) adsorption isotherms were measured on five different rank coals at 328.2 K and pressures up to 13.8 MPa using a volumetric method. Specifically, Beulah Zap, Illinois #6, Pocahontas #3, Upper Freeport, and Wyodak coals from the Argonne premium coal sample program were used for these isotherm measurements. These newly acquired data are compared to our previous data on dry coals. As expected, the adsorption on the wet coals is lower than that on the dry coals, At 7 MPa, Pocahontas, Upper Freeport, Illinois #6, Wyodak, and Beulah Zap coals exhibited, respectively, about 19, 17, 48, 76, and 79% reduction in the amount adsorbed on the wet coal when compared to the adsorption on the dry coal. These reductions in CO2 adsorption correlate positively with the amount of moisture present on the coal. The isotherms on wet coals were measured at their equilibrium moisture content. The adsorption isotherm for each of the wet coals exhibited a Gibbs adsorption maximum between 8 and 12 MPa and occurred at a higher pressure than that of the dry coal. The simplified local-density/Peng-Robinson model was used to correlate the adsorption data. The model was found capable of representing precisely the CO2 adsorption on both dry and wet coals. Specifically, the overall weighed average absolute deviation (WAAD) for the five dry and wet coals was 0.99 and 0.42, respectively. Nevertheless, more rigorous accounting for the water interactions with the coal matrix and the competitive adsorption between water and CO2 would provide an even more realistic description of coal-bed gas adsorption phenomenon on wet coals.