Increased CO₂ selectivity of asphalt-derived porous carbon through introduction of water into pore space

The development of inexpensive porous solid sorbents, such as porous carbons, that can selectively capture carbon dioxide (CO₂) from natural gas wells is essential to reduce emission of CO₂ to the atmosphere. However, at higher pressures, the selectivity for CO₂ over that for methane (CH₄) remains poor. Here we show that H₂O can be imbibed within asphalt-derived porous carbon, with a surface area of 4,200 m² g^-1, to generate a hydrated powder material. While maintaining a high CO₂ uptake capacity of 48 mmol g^-1 (211 wt%), the molar selectivity for CO₂ over CH₄ increases to >200:1 and the H₂O remains within the pores on repeated cycling. To mimic realistic natural gas wells, we used a 90% CH₄ and 10% CO₂ gas mixture and showed selective CO₂ separation at 20 bar. Furthermore, in situ vibrational spectroscopy reveals the formation of an ordered matrix within the pores consisting of gas hydrates.