Models of pure CO₂ and pure CH₄ adsorption on the late paleozoic coals from the Kailuan Coalfield, Hebei, China

Isothermal adsorption experiments of pure CO₂ and CH₄ on different coals in rank (the No. 11 Coal from the Linnancang Mine and the No. 9 Coal from the Majiagou Mine) from the Kailuan Coalfield of Hebei Province, China, have been studied. Four different models (Langmuir, BET, D-R, and D-A) were used to fit the experimental data of CO₂ and CH₄ adsorption and their fitting degree were investigated. The results showed that the adsorption capacity of the Majiagou coal(R_{o, ran} = 1. 21%) is higher than that of the Linnancang coal (R_{o, ran} = 0. 58%). The adsorption capacity of CO₂ is higher than that of CH₄ on the same coal under the same pressure. The adsorption isotherms of pure CO ₂ and pure CH₄ on the Majiagou coal can be classified as Type I and their fitting errors of curves are very weak; thus the experimental data can be presented using the Langmuir isotherm. However, the adsorption of Linnancang coal is more complicated, and can be presented using D-A model because of its minimum error. Monolayer adsorption occurs during the adsorption of pure CO₂ and pure CH₄ on the No. 11 Coal and that of pure CH₄ on the No. 9 Coal.