Study on adsorption equilibrium and diffusion model of CH₄ and N₂ on a carbon molecular sieve

Adsorption isotherms and kinetic curves of pure CH₄ and N₂ gases absorbing onto a carbon molecular sieve were measured by an intelligent gravimetric analyzer apparatus (IGA-100, HIDEN) at 298, 313 and 328 K, respectively. Thermodynamics and diffusion behaviors of CH₄ and N₂ on the carbon molecular sieve were also investigated. The Double Langmuir (DL) model and the Fick model were introduced to fit the adsorption isotherm and adsorption kinetic data, respectively. The fitting correction coefficients of the DL model for CH₄ and N₂ are close to 1 and the adsorption capacity of N₂ is higher than that of CH₄ on the carbon molecular sieve. The results of the Fick model indicate that the diffusion rate of N₂ is much faster than that of CH₄ on the carbon molecular sieve. Therefore, it is possible to enrich CH₄ through a fixed bed using the carbon molecular sieve studied.