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

Qi, Rongrong, Ning, Zhengfu, Wang, Qing, Zeng, Yan, Huang, Liang, Zhang, Shuang, Du, Huaming
Energy & fuels 2018 v.32 no.3 pp. 2926-2940
basins, carbon dioxide, equations, fuels, methane, shale, sorption, sorption isotherms, temperature, China
High pressure sorption isotherms of pure CH₄ and CO₂ at 80 °C and CH₄/CO₂ mixtures at 30 and 80 °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 CH₄, 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% CH₄, 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.