CO2-Filling Capacity and Selectivity of Carbon Nanopores: Synthesis, Texture, and Pore-Size Distribution from Quenched-Solid Density Functional Theory (QSDFT)

Abstract

Porous carbons synthesized by KOH activation of petroleum coke can have high surface areas, over 3000 m²/g, and high CO₂ sorption capacity, over 15 wt % at 1 bar. This makes them attractive sorbents for carbon capture from combustion flue gas. Quenched solid density functional theory (QSDFT) analysis of high-resolution nitrogen-sorption data for such materials leads to the conclusion that it is the pores smaller than 1 nm in diameter that fill with high-density CO₂ at atmospheric pressure. Upon increasing pressure, larger and larger pores are filled, up to about 4 nm at 10 bar. An ideal CO₂/N₂ selectivity of such carbon materials tends to decrease substantially upon increasing pressure, for example, from about 8–10 at 1 bar to about 4–5 at 10 bar. All in all, this work confirms the robust CO₂-filling properties of porous carbon sorbents, their low-pressure selectivity advantages, and points to the critical role of <1 nm pores that can be controlled with activation conditions.