A detailed experimental study has been made of the adsorption of pure methane, nitrogen, carbon dioxide, and their binary mixtures on dry activated carbon (Filtrasorb 400, 12 × 40 mesh, Calgon Carbon) at 318.2 K and pressures up to 13.6 MPa. The mixture measurements were made at nominal feed-gas compositions of 20, 40, 60, and 80 mol %. The mixture data clearly elucidate the competitive nature of the individual-component adsorption from the mixtures. Measurements were made using a volumetric technique, coupled with gas chromatographic analysis of the equilibrium gas-phase compositions. Error propagation analysis reveals the expected average experimental uncertainties in the amount adsorbed of 2% for pure methane and nitrogen and 6% for CO2. For the mixture measurements, the uncertainties are estimated to be about 3% for the total adsorption, while the individual-component uncertainties vary from 0.02 to 0.2 mmol/g activated carbon, depending on the mixture composition. The data were correlated using the two-dimensional Zhou−Gasem−Robinson equation of state model. The model fits the pure-component adsorption data within their experimental uncertainties, whereas the total and individual-component adsorptions in the binary systems are represented within one to two times the expected experimental uncertainties. As an additional benefit, the good agreement between the present data and those of Humayun and Tomasko for pure carbon dioxide (using two very different experimental techniques) suggests that these data provide a useful reference for benchmarking new experimental apparatus/techniques intended for the high-pressure adsorption measurements of supercritical gases.

Adsorption isotherms, which describe the coal's gas storage capacity, are important for estimating the carbon sequestration potential of coal seams. This study investigated the interlaboratory reproducibility of carbon dioxide isotherm measurements on dry Argonne Premium Coal Samples (Pocahontas No. 3, Upper Freeport, Illinois No. 6, and Beulah Zap). Four independent laboratories provided isotherm data for the five coal samples at temperatures of either 22 °C or 55 °C and pressures up to 7 MPa. The differences among the data sets in this study appeared to be rank-dependent in that the data among the laboratories agreed better for high-rank coal samples than for low-rank coal samples. A number of parameters such as sample size, equilibration time, and apparatus dimensions were examined to explain the rank effect, but no trend could be found that explained the differences. The variations among the data are attributed to different procedures for removing moisture to obtain the "dried" coal.

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