Determination of Binary CO ₂ /CH ₄ Adsorption Isotherms and Kinetics over Hierarchical Activated Carbons via the Zero-Length Column Technique

Current adsorption processes generally rely on unary adsorption isotherms to assess the efficacy of adsorbent materials suitable for a particular separation. While unary adsorption isotherms provide important information about the adsorbent's affinities toward adsorbates of interest, they fail to accurately determine the real response of adsorbents in multicomponent systems. This is mainly due to cooperative and competitive adsorption phenomena that often take place in complex environments. As such, it is essential to obtain binary/multicomponent equilibrium data to have a realistic assessment of adsorption materials. In this work, we utilized the zero-length column (ZLC) technique to obtain binary adsorption isotherms of CO₂ and CH₄ over two hierarchical microporous-mesoporous carbons, namely, Br-318 and Nuchar. The ZLC generated low-pressure equilibrium isotherms of pure CO₂ and CH₄ closely resembled the volumetric isotherms, and the trend revealed by the experimental data of binary adsorption isotherms was qualitatively consistent with that obtained from the theoretical model, confirming the alignment between the two equilibrium data acquisition methods, as well as the theoretical and experimental approaches. The kinetic analysis of the ZLC profiles in the binary mixture indicated 55 and 66% reductions in diffusion of CO₂ through Br-318 and Nuchar, respectively, in the presence of CH₄ relative to the pure system. The findings of this investigation highlight the efficacy of the ZLC method in accurately determining the binary adsorption data.