Adsorption of CO2, CH4, and N2 in Micro-Mesoporous Nanographene: A Comparative Study

In this work, we have measured the adsorption isotherms and calculated the equilibrium selectivity for CO2, CH4, and N-2 on micro-mesoporous nanographene at three temperatures of 298 K, 278 K, and 263 K and pressures up to 760 Torr. The nanographene sample possesses a particle size range of 50 rim to 250 nm along with a Brunauer-Emmett-Teller (BET) specific surface area of 514 m(2)/g and total pore volume of 3 cm(3)/g. The pore widths varied from 3.5 angstrom to 8 angstrom in the microporous region and very large distributed widths within 45 A to 250 A in the region of mesoporosity. The calculated equilibrium selectivity of gas separation at 298 K by pressure swing adsorption for CO2/N-2, CO2/CH4, and CH4/N-2 are 55, 8.2, and 6.5, respectively, whereas the adsorption selection parameters for same pair of gases are 540, 101, and 117, respectively. To compare the equilibrium selectivity values with other adsorbents, we have measured the gas adsorption isotherms for CO2, CH4, and N-2 on Maxsorb (a commercial activated carbon with BET surface area 3200 m(2)/g) and calculated the selectivity values for several adsorbents based on their adsorption isotherms reported in the literature. We have found that equilibrium selectivity for all the gas pairs are higher for graphene compared to Maxsorb. We also found that the equilibrium selectivity for CO2/N-2 for graphene is higher than all the carbon-based materials reported so far. The equilibrium selectivity for CO2/CH4 and CH4/N-2 in graphene is also higher than the majority of the adsorbents reported in the literature. Our findings suggest that graphene can serve as a potential adsorbent for gas separation purposes.