Adsorption/desorption characteristics for methane, nitrogen and carbon dioxide of coal samples from Southeast Qinshui Basin, China

This paper presents an experimental and modelling study of the adsorption/desorption of pure gases CH4, CO2 and N-2 and their binary and ternary mixtures on coal samples obtained from southeast Qinshui Basin, China. Results show that the adsorbed amounts of N-2, CH4 and CO2 have approximate ratios of 1.0:1.3:2.4, respectively. No significant hysteresis from adsorption to desorption is observed for pure N-2 and CH4 whereas significant hysteresis is measured for CO2 in CO2-CH4 and CO2-CH4-N-2 mixtures and CH4 in the N-2-CH4 mixture. The experimental observations are modelled using three different models, namely the extended Langmuir (EL), the Langmuir-based ideal adsorbed solution (L-IAS) and the Dubinlin-Radushkevich-based ideal adsorbed solution (D-R-IAS). The models predict well the experimental observations for desorption tests. But the measurements for the low adsorbate capacity in binary and ternary mixtures are overestimated by the prediction models. It is found that the EL model predicts the CO2-CH4 desorption test better while the D-R-IAS model is the best model for the CO2-CH4-N-2 adsorption.