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

Abstract

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 CO2 in low uptake was 60–65 kJ/mol, which is the highest for CO2 adsorption 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/N2 and CO2/CH4 was calculated based on the Ideal Adsorbed Solution Theory (IAST) and all the results demonstrated the high CO2 selectivity 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/N2 and CO2/CH4. The simulation results demonstrated that the dimensionless breakthrough time is a decreasing function of the mole fraction of CO2 in 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 CO2 separation, natural gas sweetening and biogas upgrading purposes.