Adsorptive separation of CO₂ in sulfur-doped nanoporous carbons: Selectivity and breakthrough simulation

Sulfur-doped nanoporous carbons were synthesized by post-synthesis modifications with a sulfur-bearing compound that simultaneously enhanced the surface area and introduced sulfur functionalities on carbon. The BET surface areas of these materials were within 837–2865 m²/g with total sulfur contents of 8.2–12.9%. The heat of adsorption of CO₂in low uptake was 60–65 kJ/mol, which is the highest for CO₂adsorption in porous carbons. In order to investigate the adsorptive separation of CO₂, nitrogen (N₂) and methane (CH₄) adsorption isotherms were also measured at 298 K and 760 torr. The selectivity of separation for CO₂/N₂and CO₂/CH₄was calculated based on the Ideal Adsorbed Solution Theory (IAST) and all the results demonstrated the high CO₂selectivity for the carbon with higher sulfur content. The adsorption isotherms were combined with mass balances to calculate the breakthrough behavior of the binary mixtures of CO₂/N₂and CO₂/CH₄. The simulation results demonstrated that the dimensionless breakthrough time is a decreasing function of the mole fraction of CO₂in the feed stream. In a comparative study with a commercial activated carbon (Maxsorb: BET∼3300 m²/g), both selectivity and breakthrough time were higher for sulfur-doped carbons. The overall results suggest that these sulfur-doped carbons can be employed as potential adsorbents for CO₂separation, natural gas sweetening and biogas upgrading purposes.