Modeling of gas adsorption using two-dimensional equations of state

Scope and method of study. New temperature relations were developed for the two-dimensional (2-D) equation of state (EOS) parameters to facilitate precise representations and accurate predictions of high-pressure, supercritical pure-gas adsorption encountered in coalbed methane (CBM) recovery and carbon dioxide (CO2) sequestration. One-fluid mixing rules and the Wong-Sandler excess Gibbs free energy mixing rules were applied to extend the 2-D EOS to mixture adsorption modeling. In addition, an iteration function method (IFM) for mixture adsorption equilibrium calculations was developed for 2-D EOSs, and the robustness of the IFM algorithm was evaluated for CBM-type systems.; Systematically-selected adsorption measurements were conducted to supplement existing data on carbon matrices. The measurements were conducted for pure methane, nitrogen, CO2, and their mixtures on an activated carbon and on selected coals at temperatures of 319 K and 328 K and pressures to 13.8 MPa. These data were used to support the model development efforts.; Findings and conclusions. The new temperature relations for the 2-D EOS parameters appear effective in modeling pure-gas adsorption on carbon matrices at supercritical and near-critical regions. The 2-D Peng-Robinson (PR) EOS with the new temperature relations can represent adsorption on activated carbon and coals within their expected experimental uncertainties. Further, the new temperature relations, which are generalized in terms of adsorbate properties and accessible adsorbent characterizations, can predict the adsorption isotherms of activated carbons with an average absolute deviation (AAD) of 9% or within three times the expected experimental uncertainties.; Both the Zhou-Gasem-Robinson (ZGR) EOS and the 2-D PR EOS are capable of predicting binary and ternary gas adsorption within twice the experimental uncertainties, on average. Further, the total and individual component adsorption can be represented within the expected experimental uncertainties with the use of binary interaction parameters. Results of the mixture modeling using the Wong-Sandler mixing suggest the possibility of nonrandom mixing in the adsorbed phase.; The present results involving many CBM adsorption systems indicate that the new IFM algorithm for the 2-D EOS is effective in performing equilibrium mixture adsorption calculations based on feed compositions.