Unprecedented performance of N-doped activated hydrothermal carbon towards C2H6/CH4, CO2/CH4, and CO2/H2 separation

Abstract

A series of N-doped porous carbons with different textural properties and N contents was prepared from a mixture of algae and glucose and their capability for the separation of CO₂/CH₄, C₂H₆/CH₄, and CO₂/H₂ binary mixtures under different conditions (bulk pressure, mixture composition, and temperature) were subsequently assessed in great detail. It was observed that the gas (C₂H₆, CO₂, CH₄, and H₂) adsorption capacity at different pressure regions was primarily governed by different adsorbent parameters (N level, narrow micropore volume, and BET specific surface area). More interestingly, it was found that N-doping can selectively enhance the heats of adsorption of C₂H₆ and CO₂, while it had a negligible effect on those of CH₄ and H₂. The adsorption equilibrium selectivities for separating C₂H₆/CH₄, CO₂/CH₄, and CO₂/H₂ gas mixture pairs on the porous carbons were predicted using the ideal adsorbed solution theory (IAST) based on pure-component adsorption isotherms. In particular, sample NAHA-1 exhibited by far the best performance (in terms of gas adsorption capacity and selectivity) reported for porous carbons for the separation of these three binary mixtures. More significantly, NAHA-1 carbon outperforms many of its counterparts (e.g. MOFs and zeolites), emphasizing the important role of carbonaceous adsorbents in gas purification and separation.