Tuning N-doping thermal-process enables biomass-carbon surface modification for potential separation effect of CO2/CH4/N2

Gas-adsorption-Sieving especially for CO2/CH4/N2 became attractive in flue-gas separation, natural-gas energy upgrading, and gas-layer-methane recovery. Herein, a detailed study on the potential adsorption separation effect of CO2/CH4/N2 using two kinds of synthesized temperature-tuning N-doping biomass activated carbon (BCx and GCx) derived from banana peel and grapefruit peel was explored. A comprehensive comparison of the structural properties and surface character of N-doping carbon was conducted through various characterizations, revealing that two N-doping AC both afford a better doping effect and higher post-implanted surface skeleton N species at 600 °C. Impressively, CO2 adsorption capacity of optimal GC600 and BC600 at 0 °C/25 °C and 1 bar reaches 5.09/3.05 mmol g−1 and 3.04/3.57 mmol g−1, respectively, which have exceeded most reported AC adsorbents. Especially, BC600 affords appreciable N and O component proportion, which renders better surface affinity for CO2 adsorption at 25 °C. While GC600 endows better CO2 adsorption at 0 °C by right of the highest occupation fraction of pore-volume-selected corresponding to specific pore-size of 1.2 nm and post-implanted beneficial surface N species. The tentative linear fitting among CO2 adsorption performance with surface N species state and structural properties validates their comprehensive influence on CO2 adsorption. Through the rational correlation of the adsorption of pure components, the adsorption selectivity to the binary mixture of CO2/N2(15/85), CO2/CH4(10/90), and CH4/N2(30/70) is predicted for optimized GC600 and BC600 through Ideal Adsorbed Solution Theory(IAST), which reaches 22.84/3.46/5.84 and 17.45/3.66/3.98, respectively and reveals obvious improvements compared to original biomass-carbon and traditional AC adsorbents. Most importantly, the optimal adsorbent afford extremely low-level adsorption heat for CO2, thereby rendering the good reversibility and reusability during 7 cycles at room temperature without any extra thermal process.