Facile preparation of N and O-rich porous carbon from palm sheath for highly selective separation of CO₂/CH₄/N₂ gas-mixture

Novel N- and O-rich porous carbons were facilely prepared by one step NaNH₂ activation of palm sheath at 350–550 °C for the highly selective separation of CO₂/N₂, CO₂/CH₄, and CH₄/N₂. The biomass of palm sheath was used as the precursor. The BET surface area, pore size distribution, and polar functional groups (O&N) ratio could be easily tailored by changing the activation temperature or NaNH₂/biomass ratio. The co-effect of O&N and the effect of microporous structure on gas adsorption and separation were investigated, indicating the ultra-micropore (<0.9 nm) dominated the CO₂ and CH₄ adsorption at the pressure of 1.0 bar, while both ultra-micropores and heteroatoms (O&N) affected CO₂ and CH₄ adsorption capacities at the low-pressure range (<0.15 bar) as well as the gas separation performance. The obtained porous carbon adsorbents exhibited a large BET surface area (up to 2181 m²/g), narrow pore size distribution, and abundant polar groups (O&N). Due to the high surface area and ultra-micropores, as well as moderate polar group ratio, the as-prepared porous carbon exhibited excellent CO₂/N₂, CO₂/CH₄, and CH₄/N₂ selectivities of 107, 10.7, and 7.6 at 298 K and 1.0 bar, respectively. The carbons also showed outstanding CO₂ and CH₄ uptakes. Furthermore, the breakthrough and regeneration experiments further confirmed their feasibility as promising adsorbents for CO₂/N₂, CO₂/CH₄, and CH₄/N₂ separation.