Sorption of Methane, Carbon Dioxide, and Their Mixtures on Shales from Sichuan Basin, China

High pressure sorption isotherms of pure CH4 and CO2 at 80 degrees C and CH4/CO2 mixtures at 30 and 80 degrees C on shale samples from Sichuan Basin, China, were measured by a modified volumetric method. The multicomponent sorption measurements were conducted on the mixtures with feed gas compositions of 79.50% and 48.62% CH4. The sorption isotherms of pure CH4 and CO2 were fitted by a modified Langmuir equation, and the sorption isotherms of the total and individual component of CH4/CO2 mixtures were fitted by an extended Langmuir (EL) equation. Qualitative and quantitative characterizations of selective sorption of CH4 and CO2 were discussed at different temperatures and gas compositions. The results indicate that the sorption capacity of pure CO2 is larger than that of pure CH, with the Langmuir sorption capacity of pure CO2 being approximately 2.5 times of pure CH4. However, a higher sorption amount of CH4 than CO2 is obtained in competitive sorption of mixed gas with a feed gas composition of 79.50% CH, suggesting that sorption behavior of individual component under competitive condition depends not only on the sorption affinity of the component, but also on the partial pressure of the component in the mixture. The separation factors calculated from multicomponent sorption data are in a range of 1.0-2.5, which are far less than that calculated from single gas sorption data, indicating that the presence of CH4 greatly weakens the preferential sorption of CO2. On the contrary, increasing temperature and CO2 content in the mixture will promote preferential sorption of CO2.