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

Abstract

• The optimal N-doping temperature of 600 ℃ for biomass activated carbon was validated. • The detailed comparative studies of two types of activated carbon were conducted. • The thermal stability of N-doping activated carbon was improved from 403 ℃ to 541 ℃. • The adsorption ability of the optimized sample for CO 2 was drastically enhanced. • The N-doping activated carbon afford great potential for separation of CO 2 /CH 4 /N 2 . Gas-adsorption-Sieving especially for CO 2 /CH 4 /N 2 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 CO 2 /CH 4 /N 2 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, CO 2 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 CO 2 adsorption at 25 °C. While GC600 endows better CO 2 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 CO 2 adsorption performance with surface N species state and structural properties validates their comprehensive influence on CO 2 adsorption. Through the rational correlation of the adsorption of pure components, the adsorption selectivity to the binary mixture of CO 2 /N 2 (15/85), CO 2 /CH 4 (10/90), and CH 4 /N 2 (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 CO 2 , thereby rendering the good reversibility and reusability during 7 cycles at room temperature without any extra thermal process.